THE MAGAZINE OF THE CONCRETE SOCIETY Volume 54 April 2020 Issue 03

concreteVisit: www.concrete.org.uk

Core matters Assessment of in-situ concrete strength

Frame Preventing the risk of shear failure

Fibres Ultrasonic pulse technology

coversConcreteApril20.indd 2 24/03/2020 15:26 Vertua~ Low carbon by design

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coversConcreteApril20.indd 3 24/03/2020 15:26 Photo of the month The wet docks at Bassins à Flot are a key aspect of the harbour city of Bordeaux. As part of the redevelopment of this district in the north of the city, the wet docks have become a major area of public space. One of the regeneration projects has recently been completed after 18 months’ work – the construction of the G7 and G8 mixed-use buildings carried out by Eiffage Construction Sud-Ouest. The 4300m² G8 plot, designed by Martin Duplantier , is set between the last piece of boulevard and the docks; it houses a business school as well as retail. Its striking aspects are the four as-struck concrete façades. Largely open along its ground floor, the building recalls the industrial past of the site, all the while conferring an abstract, timeless aesthetic. Two large patios on the first floor, covered with concrete pergolas (shown above), create spaces that favour interaction between visitors. (Photo: Schnepp Renou.)

1-14ConcreteApril2020.indd 1 26/03/2020 09:50 Contents

1 Photo of the Month 5 From the Editor 6 World News 10 Obituary 12 Society News 14 Book Review

Frame Construction 16 Preventing the risk of punching shear Mike Revans 20 Clayton Hotel, Charlemont, Dublin Neil Flanagan 25 Concrete frame is at the heart of luxurious city centre development Erol Erturan 28 It never rains but it pours: statutory adjudication and the supply of concrete Kieran Fano

Fibres 30 Time to call in reinforcements Andy Taurah 32 Fibres in ultra-high-performance concrete Peter Buitelaar and Stephan Müller 35 Ultrasonic pulse technology Warren Thomas 38 Hybrid reinforcement is gaining in popularity Ben Vanheuverzwijn

Standards 40 Assessment of in-situ concrete strength – revised BS EN 13791 and BS EN 12504-1 Neil Crook

Construction Chemicals 46 Crystalline admixtures – more support and research needed Ben Hickman 48 Protection of urban spaces – sustainable mineralisation of concrete and other construction substrates Chris Sugden and Olivier Debas

Roads Railways Tunnels 51 Linear drainage on M6 smart motorway scheme Jeanette Edwards

Concrete On-Site 54 On-site concrete solution to London piling project Chris Smith

56 Features List/Ad Index/Subscriptions

2 concrete www.concrete.org.uk APRIL 2020

1-14ConcreteApril2020.indd 2 26/03/2020 09:50 William Mitchell (1925–2020)10 Fibres in UHP concrete 32 Crystalline admixtures 46

concrete magazine is produced in-house by The Concrete Society, a not-for- profit, independent membership organisation dedicated to supporting the use of concrete, the most widely used in the world.

Established in 1966, and with members from around the world, The Society has built on its technical base to become a leading provider of information, serving the needs of clients, architects, engineers, specifiers, suppliers, contractors and users of concrete.

Visit: www.concrete.org.uk

The April 2020 cover In January, BSI published a revised BS EN 13791 Assessment of compressive strength in structures and precast concrete component. This uses the revised BS EN 12504-1 Testing concrete in structures. Part 1 – Cored specimens – taking, examining and testing in compression. What are the changes? See page 40.

(Photo: Socotec.)

Follow concrete on Pinterest Cover Story Go to pinterest.com/concretemag/boards, click on a board to view images from projects featured in current and past issues. Share images with others within the concrete community. Follow: @ukConcrete Find us on: 40 www.concrete.org.uk April 2020 concrete 3

1-14ConcreteApril2020.indd 3 26/03/2020 11:25 THE CONCRETE SOCIETY is an independent membership organisation dedicated to supporting the use of concrete – the most widely used building material in the world.

Established in 1966, The Society encourages innovation and the exchange of knowledge and experience across all disciplines. The Society works through the co-operation of our members, who come from all sectors of the industry to exchange information and experience, and to enhance the performance, productivity and quality of concrete as a construction medium. Supported by the technical and administrative staff of The Society, our members collaborate to produce and disseminate state-of-the-art reports, recommendations and practical guidance.

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The Society is supported by a global community of 250+ Corporate and 500 individual members. www.concrete.org.uk

1-14ConcreteApril2020.indd 4 26/03/2020 09:50 FROM THE EDITOR

EDITOR: James Luckey Tel: +44 (0)1276 607158 [email protected]

EDITORIAL ASSISTANT: Helen Marney Tel: +44 (0)1276 607159 [email protected]

TECHNICAL ADVISOR: Richard Barnes Ploughing on DESIGN: Darryl Killoran Strange times. One minute, industry matters are looking promising; the next

SALES REPRESENTATIVE: minute, life – and indeed the world – is put on hold. There’s no precedent in Fred Combe modern times for the sheer disruption and stranglehold that coronavirus has Tel: +44 (0)20 3859 7097 placed on ordinary activities. But perhaps rather than wallow in a present situation [email protected] beyond much control, we should keep that upper lip stiff and focus on more James Pembroke Media Ltd is optimistic issues. The Concrete Society’s appointed advertising sales agency. herever you are reading this profile and boost their marketing/PR SUBSCRIPTIONS MANAGER: Val Goddard copy of Concrete, here’s hoping outreach. you are safe and well, and that If it’s bespoke technical information Tel: +44 (0)1276 607149 [email protected] W the pages inside can provide you are after, then The Society’s renowned an informative distraction (especially if you’re advisory service is still on hand to answer concrete is published 10 times a year (2020) working from home) from current affairs. queries. Our library team is also here to field and sent free to all Concrete Society members. Annual prepaid subscriptions for 2020: If you’re away from the office for day- research enquiries and those looking for UK £125, Europe £150, outside Europe £170 to-day work now, remember that Concrete general information. (prices inc. p&p). Single copies and back Society members have access to a wealth So despite the present difficulties issues: £15 (exc. p&p). of information via our website and the providing a reality check and maybe a Members’ Area in particular. So much of change in perspective and priorities, with THE CONCRETE SOCIETY our material is available at your fingertips the hyperconnectivity of the modern world President: (including, coincidentally, ‘@ Your Fingertips’, people can adapt to new circumstances. Deiniol Williams the nuggets of free information), from advice Clearly, we all look to future days Managing Director: sheets and ‘Concrete on site’ booklets, to the (whenever they are) when life can return Kathy Calverley MBE Concrete Vault and magazine archive. to ‘normal’. But to focus on the positives, Although a number of the Regional circumstances have reset the nation’s focus on The Concrete Society, Riverside House, 4, Meadows Business Park, Network events over the coming weeks have where its true priorities lie, in looking out for Station Approach, Blackwater, faced uncertainty, a visit to the Events page each other, and we have a Government that Camberley, Surrey GU17 9AB, UK on-line will keep you updated as to the latest seems willing to throw money, everything and Tel: +44 (0)1276 607140 news. the ‘kitchen sink’ at the current situation. Fax: +44 (0)1276 607141 e-mail: [email protected] One event that ploughs on is the 2020 In reading our news section this month, www.concrete.org.uk Concrete Society Awards. The deadline maybe reflect that life was indeed ‘normal’; for entries is fast approaching (22 April) we’ve kept it focused on pre-virus updates. Printed by Bishops Printers and the competition is open to structures Stay well and wash your hands (again). Portsmouth, Hampshire substantially completed between October Enjoy the issue! © The Concrete Society, 2020 2018 and April 2020. As in recent years, ISSN 0010-5317 there are no formal categories; we are looking for projects with concrete as the majority Neither Concrete nor The Concrete Society are structural component. responsible for the statements made or the opinions expressed in this journal by third parties and If your company has been involved with organisations. such a project that has a certain je ne sais quoi, then entry to the awards is highly James Luckey, Editor recommended. Success at the awards has Tel: 01276 607158 helped innumerable companies raise their [email protected]

www.concrete.org.uk APRIL 2020 concrete 5

1-14ConcreteApril2020.indd 5 26/03/2020 09:50 WORLD NEWS

NEWS IN BRIEF Bendable concrete Construction contract made from waste „USA • Nuclear Power Workers at Georgia Power’s Vogtle A NEW type of concrete that is made plant have completed the final from waste materials that can bend awards increased under load has been developed and concrete placement inside the Unit 3 containment vessel, which houses the ACCORDING to the latest edition of contract award was the £2bn Dogger patented by Swinburne University of unit’s reactor. Georgia Power is leading the Economic & Construction Market Bank Creyke Beck 1.4GW offshore Technology researchers Dr Behzad work on the US$25 billion (£21bn) Review from industry analyst Barbour windfarm. The second largest contract Nematollahi and Professor Jay effort to expand Vogtle with two new ABI, the value of all construction award was the £1bn Silvertown Tunnel Sanjayan. The material incorporates reactor units. Completing this milestone contracts awarded in January 2020 project for Transport for London to industrial waste products such is an important step that allows for the was £5.5 billion, based on a three- provide a new car crossing between as fly ash. It is especially suited installation of machinery that will be month rolling average. This is an Thamesmead and Beckton. to construction in earthquake used to load fuel into the unit. increase of 18.5% on December 2019 Regional analysis indicates that zones where the brittle nature of and is also 2.1% ahead of January 2019. London maintained its leading conventional concrete often leads to „UK • Flooring In the three-month period ending position, accounting for 32.5% of disastrous building collapses. Manufacturer and supplier of precast January 2020, total construction all contract awards. With a share Traditional concrete is not only concrete products, Milbank has contract awards were valued at of 26.6%, Yorkshire & Humber was prone to shatter when being stretched designed WarmFloor, an insulated £15.6bn, which is 7.1% higher than the second largest region in January. or bent, but also has a significant concrete flooring system that combines the previous quarter and is also 5.1% The remaining regions all attracted carbon footprint due to cement rigid insulation blocks manufactured higher than the comparable quarter significantly smaller individual share, production. “Production of this novel from lightweight, closed-cell, expanded ending January 2019. with Scotland and the East of England concrete requires about 36% less polystyrene (EPS) sandwiched In January, the number of vying for third place with respective energy and emits up to 76% less CO2 between prestressed concrete beams construction contract awards was shares of 6.5% and 6.4%. as compared to conventional bendable and finished with an EPS top sheet, 893, which is an increase of 95.4% on Commenting on the figures, Tom concrete made of cement,” said Dr membrane and concrete screed. It can December 2019. Hall, chief economist at Barbour ABI Nematollahi. achieve U values as low as 0.07W/m²K. The largest sector was and AMA Research, said, “January’s Furthermore, the inclusion of short infrastructure, with attributable strong contracts awards data suggests polymeric fibres in this novel concrete „UK • Infrastructure share of 42.7% of awards and with construction industry activity may allows it to sustain multiple hair-sized Kier Highways has signed the contract the residential sector in second be starting to respond after a clear cracks when put under tension or to build the £150 million A585 Windy place – attracting share of 25.5%. The general election result and the UK’s bending and not break into pieces. Harbour to Skippool improvement infrastructure sector accounted for exit from the EU finally occurring, In fact, it is able to bend when force scheme with Highways England. The the two largest contract awards, with even if it is largely symbolic at this is applied to it, meaning that buildings scheme will see the construction of combined value of £3bn. The largest early stage.” made from it will be much more likely a new three-mile dual-carriageway to remain intact during earthquakes, bypass to alleviate the congested A585 hurricanes, projectile impacts, and between Windy Harbour and Skippool, blasts. Dr Nematollahi added, “Our near Poulton-le-Fylde. Construction MPA launches new voice laboratory test results showed that work will start in spring 2020 and this novel concrete is about 400 times completion is expected in summer for the concrete industry more bendable than normal concrete, 2023. yet has similar strength.” THE Mineral Products Association has all depend on concrete and create „UK • Infrastructure launched UK Concrete, a new public the demand for it. It is time for the Balfour Beatty has secured a £63m and political advocacy vehicle for the features and benefits of concrete to Scottish Government A19 highways improvement contract UK’s concrete industry. UK Concrete’s be recognised and valued together enhances rail capabilities on behalf of Highways England to principle aim is to proactively engage with the commitments the industry is THE Scottish Government has develop, design and deliver critical with political stakeholders and public making to support the transition to a allocated £1.49m to Tarmac’s dual-carriageway upgrades on the A19 bodies, and promote the advantages net zero-carbon society by 2050.” Dunbar cement plant in a Freight between Norton and Wynyard in the of building in concrete and the vital Over 95% of UK concrete Facilities Grant, which will support north of England. Forming a key part role it plays in our everyday lives. is produced domestically from the company’s drive to enhance its of the Government’s Road Investment Chris Leese, former vice-president approximately 1000 sites nationwide, rail capabilities to provide cement Strategy, works will include the at CEMEX UK, has been appointed with over 90 million tonnes consumed products for construction projects transformation of a 5km stretch of the as director of UK Concrete. He in a typical year. The concrete sector across Scotland and England. The fund, A19 to increase lane capacity. commented, “Concrete is essential is a key part of a combined mineral which is open to companies looking to for our economy and our way of life, products industry, which contributes move freight by the more sustainable UK • Infrastructure now and in the future. New homes, approximately £18bn to the UK’s GDP „ modes of rail or water instead of road, Britpave has published a new guide schools, hospitals, workplaces, roads and directly employs 74,000 people, will be used towards expanding the addressing benefits of concrete and railways and infrastructure, supporting a further 3.5 million jobs. plant's rail operation. motorway barriers, which include superior vehicle containment to Michael Matheson, Cabinet Secretary for Transport, Infrastructure reduce the risk of crossover accidents, CEMEX has launched its Vertua low-carbon concrete range in the UK, which and Connectivity, said, “The recently a performance life of at least 50 includes the option to offset residual CO2. The range features a variety of bespoke years, minimal land take, the use of concrete mix designs and includes the Vertua ultra-zero option. This product published National Transport Strategy sets out the Government’s vision recycled aggregates and full end-of-life achieves a 70% reduction in eCO2 emissions, with the remaining unavoidable recyclability. Motorway barriers: the emissions offset through working with Natural Capital Partners, a carbon for a sustainable, inclusive, safe and concrete benefits is available as a free offset and carbon neutrality specialist. CEMEX is introducing a new innovative accessible transport system where our download from: www.britpave.org.uk. geopolymer cement solution, developed at its R&D centre in Switzerland. businesses make sustainable choices for the delivery of goods and services.”

6 concrete www.concrete.org.uk APRIL 2020

1-14ConcreteApril2020.indd 6 26/03/2020 09:50 WORLD NEWS

NEWS IN BRIEF „UK • Stadiums & Arenas „UK • Appointment „Global • Cement „UK • Standards Everton Football Club has appointed Ian Price has been appointed managing The World Cement Association has Aggregate Industries has achieved Laing O’Rourke as preferred director of Hanson UK’s national road welcomed Raysut Cement Company certification from BSI to ISO 50001 contractor for its 52,000 capacity surfacing and contracting infrastructure (RCC) as a new corporate member. Energy management systems, after stadium at Bramley-Moore Dock on business, Hanson Contracting. He Founded in 1981, RCC is the largest demonstrating its company-wide Liverpool’s waterfront. Dan Meis’s moves from his role as major projects producer of cement in Oman, with commitment to energy efficiency. This design takes its inspiration from the manager to replace Rick Green, who clinker and cement manufacturing follows the successful certification of historic maritime and warehouse is now managing director of Hanson’s assets in Oman, Yemen and UAE. It has its cement business, Lafarge Cement, in buildings nearby. A preconstruction asphalt and quarrying business, MQP. diversified into producing ready-mixed 2018. The latest version of the Standard services agreement for a design and Price is responsible for all commercial concrete and other cement products. offers guidance on how to manage build contract is to be signed and and operational aspects of Hanson With a total annual production capacity energy consumption and reduce usage. both parties will develop a design and Contracting, which has extensive of 7.1 million tpa, the company exports As part of the company’s commitment delivery programme for the £500m experience of working with Highways 1.5 million tpa of cement and clinker to this, it set up a dedicated energy project. Work will start later this year England, local authorities and private across the Middle East, Indian Ocean taskforce with specific monitoring and and take three years to complete. clients throughout the UK. Islands and East Africa. performance targets.

Benefits of off-site ‘Concrete Stories’ construction THE Global Cement and Concrete Association (GCCA) and its member CIRIA and the Laing O’Rourke Centre companies around the world have for and launched ‘Concrete Stories’, a Technology, University of Cambridge, major new global communications have launched a new guidance campaign, which aims to increase Methodology for quantifying the awareness of the vital role concrete benefits of off-site construction plays in everyday life. (C792). Off-site construction offers The campaign aims to engage the potential to deliver a number members of the public by telling the of benefits, including better quality ‘Story of Concrete’ through a number construction, improved health and of different themes, including how safety, and a faster construction concrete contributes to everyday life, programme as well as predictability concrete as an enabler of change, of cost and time on any given project. and creative uses of concrete around Despite this, uptake of off-site the world. Additional themes will construction is slow as there is no run throughout 2020 and will focus industry method for assessing the on the important role the cement benefits of off-site techniques. and concrete industry will play in This new CIRIA guide proposes addressing climate change. 3D printing at Bautec Berlin a framework for comparing Benjamin Sporton, GCCA chief construction approaches, making it executive, said, “Concrete is an DURING the recent international pumping equipment has meant that possible to keep consistent records unsung hero. This is a material that Bautec construction exhibition in the maximum speed so far has been across projects and identify all the is all around us and which we rarely Berlin, over 30,000 visitors from only 40cm per second. The BOD2 has possible benefits available. more than 40 countries watched a modular build and can be extended consider. Throughout 2020 and COBOD and PERI’s BOD2 3D with modules in width, length and starting with ‘Concrete Stories’, we construction printer live creating a height of up to 2.5m. Carbon capture want to show its versatility, its beauty small house. The BOD2 printer shown at Bautec COSTAIN has won technical as well as its numerous performance The BOD2 has a maximum speed is a model 2-2-2, which has a printing consultancy work for what could credentials. So many parts of our day- of 100cm per second, although area of approximately 5m width, be the UK’s first carbon capture and to-day lives are made possible by this limitations caused by materials and length and height. storage (CCS) project. amazing material. The firm has been selected by Pale “Cement and concrete are Blue Dot to accelerate the Acorn CCS fundamental to our daily lives – the BSI gives Brexit update on committees project. way we travel, our housing, our work SCOTT Steedman, BSI’s director CENELEC committees and avoids the Rob Phillips, Costain energy and many other aspects. ‘Concrete of Standards, has given a Brexit risk of challenge to our chairs and sector director, said, “Hydrogen Stories’ will bring the role that update now that the UK is in a secretaries. As we have now left the and CCS play a fundamental role in this ‘super’ material plays into the transition period where it is no EU, members of these organisations decarbonising gas for domestic and foreground. The campaign will also longer represented in the EU political have set a timeframe to update industrial heating, powering industry showcase the innovations that the institutions, but the rules and the statutes to reflect the UK’s EU and large-scale transport. Large-scale cement and concrete industry is obligations of EU membership are still departure. It is due to run until the and relatively cost-effective carbon developing and show how it can be in effect until 31 December 2020. end of December 2020 and the CEN capture at the source of production used in sometimes surprising and “BSI’s membership of CEN and and CENELEC boards have proposed is key to unlocking this potential and often beautiful ways,” added Sporton. CENELEC continues as normal, with to extend it until the end of 2021. is one of many low-carbon solutions The initial ‘Concrete Stories’ all its obligations and rights, said BSI’s membership of organisations ISO Costain is progressing as part of the campaign will run for six weeks and Steedman. “This ensures continuity and IEC is unaffected by the UK’s exit decarbonisation of the UK footprint will be featured primarily on GCCA’s for our stakeholders in CEN and from the EU.” and driving clean growth UK-wide.” social media channels.

www.concrete.org.uk APRIL 2020 concrete 7

1-14ConcreteApril2020.indd 7 26/03/2020 09:50 WORLD NEWS

NEWS IN BRIEF Skanska-led alliance to build new hospital COVID-19 A SKANSKA-LED alliance has signed the contract for a new hospital VIRUS building in Oulu, Finland. The overall project consists of two parts built by The Concrete Society can two alliance consortiums. Skanska is assure all members that the main contractor in the B alliance, we continue to provide which is worth €375m (£354m). full access to our resources Oulu University Hospital, Caverion, and to maintain all existing Siemens and Tierna Group, a joint member benefits, within the venture of architectural agencies, are restrictions of Government also part of the alliance. advice relating to COVID-19 Skanska’s share of the contract Visit: https://bit.ly/2xm0737 Specially designed roller-compacted is worth €190m (£175m). Caverion Unfortunately we have had will be responsible for the technical to cancel or postpone all concrete for dam construction systems, safety and communications technology, and design management. HQ and Regional events 3 CEMEX is supplying concrete specially 600,000m of roller-compacted Oulu University Hospital’s new scheduled for the near future. designed for the construction of the concrete (RCC), a concrete technology Please see our events listing ten-storey main building, which Bicentennial Dam located in the state designed specifically for the 2 on the website for up-to-date has a total area of about 59,000m , of Sonora, in north-west Mexico. construction of this type of dam,” said notices. will house emergency rooms, The dam has a storage capacity Ricardo Naya, president of CEMEX intensive care units, operating Visit: https://bit.ly/3behkKC 3 of 484 million m of water and aims Mexico. “During peak production, up rooms, delivery wards and support 3 to control the floods that affect the to 2000m of concrete were placed functions. Preparatory construction local community during the rainy in a single night, a challenge that works began in 2019. The project is „UK • Contractors season. It is estimated that the dam meant keeping not only operation and scheduled for completion in phases JRL Group topped the Contractors contributes to the protection of auxiliary equipment ready, but also and is due to be finished in its League Table for February, largely due approximately 11,000 homes in urban raw material logistics co-ordination entirety by the end of 2023. to its award to build Consort Place on areas, 6000 rural homes, 34,000 for timely delivery. the Isle of Dogs valued at £470m. The hectares of crops, and 48,615 hectares “The RCC system offers benefits large mixed development will provide of infrastructure – roads, agriculture, such as the reduction of displaced Major Canadian rail a full community lifestyle including health and education. areas and cost and quality control of apartments, a hotel, school, health “We supplied more than the finished elements.” projects begin tender centre and retail outlets. process UK • BIM Historic England publishes advice for tall buildings INFRASTRUCTURE Ontario and „ Metrolinx have issued requests for Trimble has introduced the latest HISTORIC England has published Policy Framework and recent good qualifications for the first phase of versions of its Tekla software solutions an updated draft Advice Note to practice. It offers useful guidance to for BIM, and guide the planning and design of those involved with the planning and work on the Scarborough Subway steel fabrication management. tall buildings, which is now out for design of tall buildings. Extension and the Eglinton Crosstown The update includes: geometry public consultation. The Advice Note, The organisation says well- West Extension. The decision to improvements to enable easier which was originally published in designed tall buildings can be positive award the tunnelling contracts first is modelling of complex shapes; better 2007, states that while tall buildings additions to towns and cities when intended to expedite work. Separate usability and control with concrete can make a positive contribution thought is given to their location, but contracts will then follow for the reinforcement detailing enhancements; to city life, by virtue of their size it sees many ill-considered proposals balance of the work on each project, quick and easy formwork modelling; and widespread visibility they can that would harm their surroundings. including building the stations, fitting- improved hollow-core concrete also seriously harm the historic With London and major towns and out the tunnels and installing and detailing; and enhanced drawing tools. character of places. It highlights the cities throughout the UK receiving commissioning the systems. importance of carefully considering large numbers of applications every The Scarborough project involves „Global • Formwork historic context and protecting the year, Historic England has updated its an approximately 8km extension Formwork, falsework and ground historic environment, and the need for advice on planning for tall buildings of Line 2 from Kennedy Station to shoring provider RMD Kwikform has high-quality design and sustainable so it reflects recent experience and McCowan Road/Sheppard Avenue. launched Tetrashor, a lightweight development. The Advice Note has restates the need for new buildings The second scheme involves a modular propping system that can been updated in response to recent to offer a meaningful response to the 9.2km extension of the Eglinton deliver a loading capacity of up to changes in the National Planning history and character of cities. Crosstown Light Rail Transit. 400kN. The system has been designed The extension will run mostly for the building refurbishment and underground, westward from the markets, finding ANCON’S balcony connectors have been re-engineered and now feature non- future Mount Dennis Station to applications in: dead shoring; façade combustible mineral wool insulation and improved fire-rated thermal pads to Renforth Drive. A future connection to retention; propping and needling; maintain their impressive thermal insulation properties and provide the required Toronto Pearson International Airport supporting precast concrete bridge A1/A2 reaction to fire rating. The Ancon connectors provide contractors with a is also being studied. beams and structural steelwork frames; fire-safe solution for all multi-occupancy buildings, regardless of height. They and restraining tall single- and double- are available in a range of types, including Ancon Isotec for concrete-to-concrete sided formwork. applications, Ancon STS for anchoring steel balconies to a structural steel frame, VISIT: and Ancon STC for steel-to-concrete fixing. www.concrete.org.uk

8 concrete www.concrete.org.uk APRIL 2020

1-14ConcreteApril2020.indd 8 26/03/2020 09:51 MASTER ® >>BUILDERS

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1-14ConcreteApril2020.indd 9 26/03/2020 09:51 Part of the Stations of the Cross at Clifton Cathedral. Corn King and Spring Queen sculpture at Wexham Springs.

William Mitchell (1925–2020) Known for his large-scale murals and other public works of art, many of them in concrete, William Mitchell’s reputation flourished in the 1960s and 70s. His work was characterised particularly by his transformation of the vertical plane to a three-dimensional sculptural surface, through moulding and texture and the incorporation of mixed, sometimes recycled, materials. With ten works listed Grade II and Grade II*, his citation by Heritage England refers to a “distinctive tactile concrete sculpture”.

illiam George Mitchell was by the C&CA to experiment with concrete in Concrete Quarterly – at The Three Tuns, born in Maida Vale, London on and then, in a series of commissions, to Coventry (1966), Hockley Circus (1968) and the 30 April 1925. Childhood illness demonstrate different techniques and effects. Kidderminster ring road retaining wall (1973– W severely limited his educational Most famous of his works at Wexham were 76). Minute Men (1967) at Salford University, opportunities and in 1938 he was apprenticed The Vortex and The Corn King and Spring Queen was unveiled by HRH Prince Philip, who at the as a decorator with Maples to learn the skills (1964). time had just been made an honorary fellow of of gilding, graining and marbling. Demobbed He established his own company in the The Concrete Society. from the Royal Navy, he obtained a job with early 1960s, setting up a workshop in Cumbria, Mitchell’s talks at the C&CA led to an the NAAFI, organising the refurbishment of its where he went on to employ a staff of 25. His invitation to lecture in San Francisco and to a facilities, and painting scenes and panoramas. London business was based first in Forest Hill succession of American commissions, including He enrolled at the Southern College of Art, and then in Victoria Way, Woolwich. There he the HiSAM Sculpture Garden in Honolulu supporting himself by working as an insurance continued with commissions from LCC (GLC (1972). He remained in the USA for six years. agent. A scholarship took him to the Royal from 1965) and British Rail, even working on The 1980s saw him working in the Middle College of Art, where success was rewarded the design of the Intercity 125. Eventually, East, notably at Doha Zoo, and by 1996 he with the Silver Medal and Abbey Award. This however, finding he was spending more time was working as artistic advisor for Mohammed enabled a post-graduate year with the British on management than sculpture, he sold off the al-Fayed, where projects included the Egyptian School at Rome, where he also spent time in workshops to his staff. Room and Escalator Hall at Harrods. the offices of Geo Ponti and Pier Luigi Nervi. The 1960s were perhaps the most prolific Mitchell was an excellent communicator, Returning to Britain, he was taken on as period of his career; all but two of his listed lecturing widely over many years. He even a consultant to the London County Council works date from 1960 to 1968. A reputation presented several episodes of BBC’s Tomorrow’s (LCC), preparing murals for public sector for reliability and timely delivery ensured World. Publication of his autobiography, buildings throughout the 1950s. An exhibition commercial success and the opportunity to Self-Portrait: The Eyes Within (Whittles, in London prompted further commissions from develop a recognised style. Concrete was a 2014) prompted a revival of interest in his the likes of Sir Basil Spence and Sir Ove Arup. staple medium, but so too was fibre glass. earlier work. Indeed, he won British Precast’s In later life, Mitchell recalled his introduction Recycled wood, glass, resin and polyurethane ‘Creativity in Concrete’ award at The Concrete to the Cement & Concrete Association (C&CA). all found their way into his work, which was Society Awards that year. He was working on furniture in a shop and treated with sand-blasting, colouring and The doyen of British muralists and a the window display of aggregate inlay work metallic effects. He pioneered the use of champion of creative concrete, he died on 30 attracted the attention of J Gilchrist Wilson, the Faircrete, a John Laing innovation that allowed January, in Cumbria, aged 94. He was, in the C&CA’s , who was passing by. Wilson the carving of concrete while still plastic and is words of his mentor at the C&CA, “An ebullient invited him to give a talk on this technique at most notably demonstrated in his Stations of design consultant who has perhaps done more the C&CA’s campus at Wexham Springs. It was the Cross (1973) at Clifton Cathedral. than anyone in this, or any other, country to a great success and led to regular talks there Other notable works in concrete include exploit the plasticity of concrete.” „ on Friday afternoons and later to speaking murals at the Lee Valley Water Works (1965) engagements further afield. He was invited – the largest single cast to date, featured Edwin Trout, The Concrete Society

10 concrete www.concrete.org.uk APRIL 2020

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1-14ConcreteApril2020.indd 11 26/03/2020 09:51 SOCIETY NEWS Members’ library at RECENTLY ADDED The Concrete Society Sarah Gerrard and Edwin Trout review the library’s latest additions and look into The Society’s extensive archive collection.

HIGHLIGHTS FROM THE COLLECTION

Concrete Plant International a simpler cover design of a single image on CPI-Concrete Plant International was added a white background. By February 2014, the to our collection in 1999 not long after Union flag had made its appearance on the Quality Concrete ceased publication. Both English edition. 24th ICT Yearbook (2019–2020) focused principally on the precast sector. By The many association logos that appeared In addition to the customary inclusion of papers chance, Quality Concrete had itself replaced on the cover (including British Precast), presented at the institute’s annual technical Concrete Works International, so while there indicated Ad-media’s close links with symposium, abstracts of reports and dissertations was no connection between the magazines, associations, conferences and exhibitions. submitted for the award of diploma or MSc in the subject matter was represented by the These remain key to the magazine’s close Advanced Concrete Technology and an interview appearance of continuity. connection with industry. (with Dr John Newman, past President of The The publishing house Ad-media Verlag of Published six times a year, each issue blends Concrete Society), this year’s edition includes additional articles of general interest. An account Cologne was established in 1992 by Gerhard event reports and academic articles with of the progress of low-carbon cements in China Klockner, who having covered other aspects commercial ‘advertorial’. Content is divided accompanies historical articles on early concrete of construction decided to publish a new into sections: News; Concrete Technology; construction in France and the testing of cement magazine that would serve the precast Concrete Products/Cast Stone; Concrete Pipes in the London main drainage scheme. There is concrete industry in particular. It was launched and Manholes; Precast Concrete Elements; an explanation of the institute’s coat of arms in 1998 as BWI BetonWerk International, but Reinforcement Technology; Readymix and the first of a new series on the work of the with a concurrent English language edition. Concrete; and Fairs & Events. institute’s committees. The launch of the fifth This was the first time in this sector that From February 2005, Klockner was joined as edition of Lea’s Chemistry of Cement & Concrete is reported on, as is the new certification scheme the same magazine would appear in two joint MD by editor-in-chief Holgar Karutz. Their for concrete field-testing technicians. Of the separate editions. Other languages followed: photographs appeared on the opening page three prize-winning papers included, one is by the Spanish in 2001, Italian in 2003, French and (wearing branded shirts and ties from 2008) first student to win the newly launched ICT Prize Russian a year later, and in 2007 CPI-North to stamp a close personal identity on the for Best MSc Dissertation in Advanced Concrete America addressed Canada and the USA. Polish magazine. Looking back, they noted that “since Technology. followed in 2008 and by 2018 the number of the 1-2005 edition, you have always been INSTITUTE OF CONCRETE TECHNOLOGY, 2019, languages had reached 13. greeted here by the duo of Klockner/Karutz and 109 PAGES Besides the multiplicity of languages, invited to read the current issue with its up-to- the story of CPI has been one of growth. Its date statement”. initial 15,000 copies had doubled to 30,000 When Klockner retired in November 2018, by 2008: “no other magazine has so many his place alongside Karutz as joint MD was subscribers that want to be supplied on a taken by Alexander Olbrich, Ad-media’s head of regular basis with technical formation from the marketing. The announcement was made under concrete and precast concrete industry”. The the heading, “27 years in the service of the trend has continued. concrete and precast concrete industry – and at “Not only has the editorial content always the same time prepared for the future”. „ been up to date – the layout of the magazine has consistently been modernised” was the management’s proud claim in 2008. And looking at the back issues that is apparent, CPI covers down the years. from the first title banner to a redesign in February 2001 that saw the letters CPI highlighted in red with the expansion in black, modified later that year. In 2006, a new type face and the use of grey for the date strip Contact The Concrete Society for more details: replaced red and from 2008 there has been Tel: 01276 607140 or e-mail: [email protected]

12 concrete www.concrete.org.uk APRIL 2020

1-14ConcreteApril2020.indd 12 26/03/2020 09:51 SOCIETY NEWS

Society takes on CBDG admin Concrete provides an update on the work of the Concrete Bridge Development Group and looks ahead to its annual conference.

he Concrete Bridge Development up the position of executive secretary, effective Group (CBDG) aims to promote from 1 January 2020. excellence in the design, construction The first major task is to organise the annual T and management of concrete road, conference. As it happens, this will be the 25th rail and footbridges. annual conference, the first being in March Membership includes all sectors involved in 1996. Prior to this, a series of update seminars the concrete bridge industry – bridge owners were given at various venues across the UK. and managers, contractors, designers and The 25th annual conference (date to be suppliers. confirmed) will be held in London at the The group provides an excellent vehicle Institution of Structural Engineers, for the for the industry to co-ordinate an effective fifth year running. Typically, ten papers are approach and to enhance the use of concrete. presented from a broad spectrum of the Through an active programme – including industry. An after-conference drinks reception is an annual conference, committees, study visits included, with the option to attend an evening and publications – the CBDG aims to: dinner at a local restaurant. • address the challenges to bridges and to The theme for 2020 is ‘Temporary Works maximise opportunities to develop the and Design for Construction’ and the subject wider and better use of concrete areas presented will encompass: • provide a focus for all those involved in • interaction between temporary and concrete bridge design, construction and permanent works management, temporary works, • stability of temporary and permanent maintenance, inspection and monitoring, works and materials • good detailing • promote an integrated approach and the • case studies use of best practice in design and • improving buildability construction • fabrication, transport and erection of • encourage the development of innovative beams ideas and concepts • safety management. • support and encourage education and training initiatives This theme links with the soon-to-be- • identify and support future research and published CBDG Technical Guidance TG16 development needs. Temporary Works for Concrete Bridges, expected in May 2020. Membership of the CBDG is open to those This guide presents the different temporary who have an interest in promoting and works used in concrete bridge construction, enhancing the concrete bridge industry. describing both their design and installation, The group’s inauguration was in March and their interaction with permanent works. 1992, with the first executive secretary being A key aim is to provide permanent works appointed in 1994. This position has been held designers with an understanding of temporary by Alan Tovey since 2007, until his retirement works and how these influence their design (along with his long-time administration work. „ assistant Carmen Shead) at the end of 2019. Further information: The CBDG is now being administered by The Concrete Society under a service-level For more information on the developing programme, venue sponsorship and booking, please agreement. In this respect, Richard Day, The e-mail: [email protected] or visit the conference Society’s head of technical services, has taken website: www.concrete.org.uk/cbdg.

www.concrete.org.uk APRIL 2020 concrete 13

1-14ConcreteApril2020.indd 13 26/03/2020 09:51 BOOK REVIEW

Lea’s Chemistry of Cement and Concrete (Fifth Edition)

First published in 1935, this publication has It would not be possible to provide an become acknowledged as a comprehensive in-depth review of such a hefty tome here, but reference work for the science and dipping into the text there are some areas that technology of cements and concrete. would benefit from improvement. There is a disappointing lack of clarity his fifth edition has two new chapters when referring to the strength of concrete. entitled ‘Geopolymers and other When a 40MPa concrete is referred to, does alkali-activated materials’ and ‘The this mean a characteristic cube strength of T influence of water:cement ratio 40MPa (strength class C32/40), a characteristic on the sustainability of concrete’ reflecting cylinder strength of 40MPa (strength class that in the 20 years since the fourth edition C40/50) or an average cube strength of 40MPa was published, greater emphasis has been (more like a C25/30 strength class)? That’s a placed on the importance of sustainability and 20MPa range of uncertainty. environmental considerations. In total there Chapter 11 refers to silica fume (the correct are 17 chapters by 32 authors, every chapter non-proprietary term, as used in the Standards) having been updated. The introduction of as ‘microsilica’ throughout. ‘Microsilica’ is in colour brings greater clarity to the figures, with fact an abbreviation of the registered trademark graphs, diagrams and photographs benefitting ‘Elkem Microsilica’, so it is comparable to from this improvement. referring to ‘hoovers’ rather than vacuum The first part of the book covers topics cleaners. Possibly not such a major issue, apart such as the history of calcareous cements, from the erroneous claim that silica fume is any manufacture of Portland cement, components powder coming from the smelting industry, of Portland cement clinker, specification while “microsilica (the Elkem product) is a of Portland cement and the hydration of material that has property and quality good Portland cement. Moving to concrete, the enough for use in concrete”. No surprise then next chapter examines durability but then we to learn that the chapter was written by Elkem are straight back to cement with a chapter on (note that the requirements of silica fume for physicochemical and mechanical properties concrete are specified in BS EN 13263(1)). of Portland cements. Other cementitious materials are covered, with chapters on Worthy successor low-energy cements, pozzolanas, blast- Notwithstanding these issues, this latest furnace slag cements, silica fume, calcium version is a worthy successor to previous aluminate cements, special cements and the editions and is likely to earn its place on the aforementioned chapter on geopolymers. (heavily reinforced) bookshelf of many concrete Aggregates and admixtures are also covered, technologists. „ with a chapter on each. Reference: 1. BRITISH STANDARDS INSTITUTION, BS EN 13263. Silica The final chapter fume for concrete. Part 1 – Definitions, requirements and The final chapter doesn’t seem to fit in with the conformity criteria. Part 2 – Conformity evaluation. BSI, rest of the book, as it is more of a discussion London, 2005+A1:2009. article than a source of reference. Perhaps Richard Barnes, The Concrete Society this is why it is missing from the listing on the Elsevier website or maybe it was a late addition. It might have been preferable to EDITORS PC HEWLETT AND M LISKA have included more reference information on PUBLISHER ELSEVIER sustainability issues, as there’s no mention of ISBN 9780081007730 subjects such as: china clay stent secondary YEAR 2019, 896PP (HARDBACK £200, aggregate, aggregate transportation issues or E-BOOK £240) the embodied CO2 of different concretes.

14 concrete www.concrete.org.uk APRIL 2020

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15-26ConcreteApril2020.indd 15 26/03/2020 09:55 FRAME CONSTRUCTION

Preventing the risk of punching shear

Flat slab construction carries with it the inevitable risk of punching failure. When loads in the stress areas are increased, careful thought has to be given to criteria such as the quality of the concrete, additional reinforcement content and even enlarging the column heads. These options are not time-efficient or cost-effective and rarely solve the problem to an acceptable performance level. To prevent any potential punching shear problems at the major new Anthology Hale Works Tower, the solution needed to be cost-effective, easy to install and dependable. Mike Revans for Schöck reports.

ale Village is a multi-award- homes and over 1115m2 of mixed commercial Above: General view winning, 11-phase, urban use. There is a selection of studios, one- of the western side redevelopment in Tottenham and two-bedroom homes with features of the tower. H Hale ‒ one of north London’s including a 24-hour concierge, residents’ sky most diverse communities. With lounge and garden, expansive landscaping sustainability and community at its heart, the and private balconies. The striking design new development is minutes from tube and of the tower will act as a landmark for national rail links, yet only a stone’s throw Tottenham Hale and Hale Village, while from the Lee Valley’s attractive waterways simultaneously achieving the highest design and Regional Park. and environmental standards. Hale Village already includes a mixture of private and affordable homes, student Challenges accommodation and a range of non- The logistics on residential uses including a gym, supermarket, the project were considerable, as it involved community centre and church. It has been working next to existing buildings on three voted one of the top 30 best regeneration sides, Tottenham Hale underground station projects in the UK and the most innovative on the Victoria line, live overground lines affordable housing scheme. and an existing viaduct. At basement level, This last piece of land to be developed, the construction at Anthology Hale Works Anthology Hale Works Tower, is an elegant Tower involved a single-storey basement 108m-high, 32-storey tower. It offers 279 box. Dewatering of the excavations during

16 concrete www.concrete.org.uk APRIL 2020

15-26ConcreteApril2020.indd 16 26/03/2020 09:55 FRAME CONSTRUCTION

Graphic of the product in a typical situation.

Close up of the tower under construction.

General view of the tower under construction.

construction of the basement was necessary too, as was the provision of a permanently waterproofed basement box on completion. The 32-storey building has a jumpformed core and concrete frame, and due to the adjacent London underground line, the first six levels had to be acoustically separated from the basement structure using anti-vibration bearings. The flat slab floor method used for the tower is first and foremost an economical form of construction but it offers other benefits as well, including: minimisation of formwork time; simplification of reinforcement work; ease of under-slab work, such as ducting; and the optimum use of space. Crucial With flat slab construction and the increasing trend for thinner slabs, there is the inevitable risk of punching failure around column heads. When loads in the stress areas are increased, consideration has to be given to issues such as the quality of the concrete, additional reinforcement content and enlarging the column heads. However, these are traditional solutions that rarely solve the problem to acceptable time- or cost-performance levels and the solution to resolving any potential problems of punching shear needs to be cost-effective, easy to install and dependable.

www.concrete.org.uk APRIL 2020

15-26ConcreteApril2020.indd 17 26/03/2020 09:56 FRAME CONSTRUCTION

Increased shear force resistance The reinforcement used to prevent punching failure at Anthology Hale Works Tower is Advantages in flat slabs the widely used Bole system, which consists Flat slabs are reinforced concrete slabs that of double-headed studs and anchors with are not supported by downstand beams or spacing bars to enable installation after the walls, only by columns. bottom reinforcement and before the top Special plus points are: layer. Two spacer bars are welded to the • minimisation of formwork time vertical studs to ensure the correct distance • simplification of reinforcement work between uprights; the forged stud heads • ease of under slab work (eg, air ducts) guarantee a perfect finishing bond with the • minimisation of storey heights. concrete. When compared with a typical stirrup reinforcement system, an increased Flat slabs are an economical form of floor The Bole type O. shear force resistance of approximately 70% is construction, at the same time offering achievable. It is a genuinely cost-effective and optimum use of space and unhindered time-saving solution. extension possibilities.

Variants Punching failure in flat slabs In addition to the standard Bole solution, The risk of punching failure is often a Schöck has developed three other punching determining factor when deciding the shear reinforcement variants: type U is a thickness of floors supported by columns. solution designed for installation before Other options to consider when increasing the lower mat; type O is for installation the loads in the stress area are concrete after the top reinforcement layer; and type quality, increasing the reinforcement content, F is designed for use in element slabs at enlarging columns head, etc. The options prefabricating plants. The entire range is detailed above are not time- nor cost-effective supplied ready for installation and provides a and often are not even capable of providing reliable solution to the problem of punching an improvement that justifies their use. shear in flat slabs. Downloadable, user-friendly design software is available to enable fast and simple dimensioning of the product to British Standards and the export of CAD drawings with DXF format. The calculation program The Bole type U. helps provide structural validation of the chosen products and creates drawings and sketches for correct installation. The software products are generally free of charge and run on all common Windows systems. „

The Bole system being installed. The solution The nature of the Bole system prevents punching failure. The two spacer rods, which are welded to the vertical studs, ensure the correct distance between uprights. The size of the stud heads also ensures a perfect finishing bond with the concrete, thus an increased shear force resistance of approximately 70 % can be achieved in comparison with the usual stirrup reinforcement system.

www.concrete.org.uk APRIL 2020

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15-26ConcreteApril2020.indd 19 26/03/2020 09:56 FRAME CONSTRUCTION Clayton Hotel, Charlemont, Dublin This 187-bedroom, five-storey plus basement city-centre four-star hotel is located on the corner of Charlemont Mall and Charlemont Street, and forms part of a vista that includes the Grand Canal. The scheme was originally designed by Henry J Lyons Architects. Delivery architect Urban Innovations redesigned the internal configuration of the buildings to address the hotel operator’s requirements and worked alongside McAleer & Rushe, which acted as the project’s main contractor. Neil Flanagan of MCR Consulting Engineers reports.

he building was designed to integrate into and reflect the environment of the surrounding T area. It responds sensitively to the historic context but is also a response to access routes, daylighting and views to and from the building. The scheme has two brick wings arranged to form an open central courtyard and an atrium space to the rear of the 18th Century protected structure. This atrium embraces 37 Charlemont Street and with its clerestory windows, integrates it into the wider complex. The building has been carefully composed to respond sensitively to the scale, rhythm, texture and variety of the surrounding context. As such it makes a positive contribution to restoring the urban grain of this part of the city. The new concrete-framed building ties in with two Georgian buildings that were refurbished and incorporated into the scheme. Secant-piled walling formed the basement box and upper floors were constructed with 275mm-thick flat slabs supported on a series of concrete columns and walls. The project is a city-centre five-storey four-star hotel with a single-storey basement. The site is in a busy district of Dublin with adjacent buildings on three boundaries and Charlemont Mall and Grand Canal to the southern boundary. The development also contained a three-storey listed building and two four-storey Georgian houses, with a basement requiring protection during the works. These buildings, containing bedrooms and conference facilities, were also sensitively upgraded as part of the project and are Front elevation along seamlessly linked to the main hotel. Charlemont Mall. The basement contains back-of-house facilities, a gym and parking spaces accessed via a car lift. The ground floor contains bar/restaurant areas and kitchen, as well

20 concrete www.concrete.org.uk APRIL 2020

15-26ConcreteApril2020.indd 20 26/03/2020 09:56

View from Charlemont Street, with refurbished The atrium creates a welcoming space enclosed by 18th Century properties in the foreground. both the modern and the historic. Design of the framing was carried out“ using 3D finite-element modelling, with the model linked to the BIM model, resulting in a streamlined design process.

as conference facilities. Floors one to five floor plates; a precast twin-walled frame contain bedrooms constructed in a ‘U’ shape solution for the upper floors, springing off around an external landscaped terraced a first-floor podium slab; and a reinforced area located at first-floor level. Although flat-slab solution with a consideration of the ground conditions indicated that post-tensioning the floor plates. Following impermeable Dublin black clay was present a number of iterations, an in-situ reinforced immediately below the building footprint, flat-slab solution was adopted. there were also shallow lenses of granular material that were fully saturated, allowing Superstructure groundwater to flow through the site. The superstructure frame was supported on The water table was approximately 1.5m a series of columns and shear walls. Lateral below existing ground level (approximately stability to the frame was provided by the 2.5m above excavation depth for the reinforced concrete shear walls located basement). It was therefore concluded that around the lift and stair cores. Through the a secant-piled wall was required to restrict use of BIM, the design team were able to water ingress during the construction phase co-ordinate designs and operate a system of the basement box. The secant-piled of clash detection. 3D walkthroughs were wall was designed for temporary lateral produced for presentation to the client, Below: Flat-slab loads during construction and also the reinforcement ready permanent vertical loads from the structure. for concrete pour. In the permanent condition, two levels of water protection were used through the introduction of an external tanking membrane and water-resistant concrete box. The tanking membrane also acted as the gas- proof membrane. Internally, the foundations were traditional pad foundations bearing on the stiff Dublin black clay. At an early stage in the project development, MCR Consulting considered alternative structural framing solutions in conjunction with the contractor, to ensure the most economically advantageous solution was adopted to suit the planning restrictions on-site, as well as the client’s programme and budget. These included: a steel frame with composite concrete floors and precast

www.concrete.org.uk APRIL 2020

15-26ConcreteApril2020.indd 21 26/03/2020 09:57 FRAME CONSTRUCTION

BIM modelling was instrumental Frame construction to the success of the project. nearing completion.

allowing for an improved collaborative and restoration of the historic structures – 35, process. Design of the framing was carried 36 and 37 Charlemont Street. The character out using 3D finite-element modelling, with and interest these buildings bring are key to the model linked to the BIM model, resulting the interest the project generates. in a streamlined design process. The 3D These conservation assets now contribute model was in turn used to predict long-term positively to the surrounding area. The frame deflections, which the curtain walling restoration of the façade of 37 Charlemont manufacturer was able to use in its detailing Street and the associated landscaping works and design. are particularly powerful. With the removal Within the concrete framing, bespoke of the various annexes and outbuildings, these concrete solutions were used to ease and buildings regain architectural prominence speed-up construction on-site. Examples of and their presence in the streetscape is these were punching shear rail systems in the restored. All of the buildings are now used flat slabs around column heads and insulated as sleeping accommodation for the hotel. As break pads between the concrete frame and such, the buildings are brought back to life projecting steelwork. Basement floor levels with the façades animated throughout the within two of the existing buildings needed day and night. to be reduced to form bedrooms. This Surviving significant original details have required temporary propping of the historic been carefully preserved and integrated into structure, to allow the existing foundation to the building. A good example of this is the be underpinned (which was located below staircase in 37 Charlemont Street. Externally, the water table) and then the installation of all modern cement roughcast renders were two levels of waterproofing ‒ including the removed and replaced with a traditional lime tanking membrane system ‒ in conjunction render, including the reinstatement of the with a water-resistant concrete to the floor decorative mouldings, parapet and quoin and walls. stones. A generous foyer surrounds and embraces Following its completion, the hotel was 37 Charlemont Street, which is lit by nominated in the 2019 Irish Building clerestory windows, for guests to mingle and & Design Awards in the categories of relax in seated areas. This space is the main ‘Architectural Project of the Year’ and focal point of the project. Key to the success ‘Tourism and Hospitality Project of the of the project was the careful preservation Year’. „

Clayton Hotel, Charlemont, Dublin Client Dalata Hotel Group Consultant engineer MCR Consulting Engineers Contractor McAleer & Rushe Architect Urban Innovations M&E engineer Caldwell Consulting Piling subcontractor FK Lowry

Construction of basement box nearing completion.

www.concrete.org.uk APRIL 2020

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15-26ConcreteApril2020.indd 23 26/03/2020 09:57 Nominations c lose 22n d Apri AAWARDSWARDS l AWARDS202022020020

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15-26ConcreteApril2020.indd 24 26/03/2020 09:57 Student accommodation. Study space.

Concrete frame is at the heart of luxurious city centre development Oasis Residence is a £16 million student accommodation scheme, just off Millennium Square, in Leeds city centre and the building’s concrete frame has been cited as a big part of its success. Erol Erturan of Adept Consulting Engineers, the civil and structural consultant for the project, explains.

he ethos at Oasis Residence was all in 1999 but closed in summer 2013. It then about creating a landmark building sat empty for several years before planning on Cookridge Street that would was approved in 2016 and work of T surpass anything else in the student the two-storey bar started in 2017. accommodation market in Leeds, with a luxurious feel throughout and this started Concrete in construction with the engineering process. Once the site was cleared, the first phase The development, which completed last of the construction programme involved year, was created by Leeds company YPP, extending the existing basements. A piled which develops and manages properties in solution was proposed toward the boundaries cities across the north. Oasis Residence now of the site, due to the proximity of the public offers 96 self-contained studio apartments highway and O2 Academy, with reinforced in a part-six and part-eight-storey building. concrete wall construction used to the rear The main part of the building features stone of the site. Due to the historic nature of the to match neighbouring buildings, with two O2 Academy, detailed analysis of predicted stepped storeys on top, constructed mainly of settlements of the piles was undertaken at glass. The ground floor of the development the design stage and vibration monitoring also offers a 1400ft2 (130m2) office unit and a used during construction to ensure there were 2300ft2 (214m2) retail space. no adverse effects in either the temporary condition or longer term. The site A concrete frame, with narrow blade Being in the heart of the city centre naturally columns built into the partition walls, helped made it a constrained site, but the modern Brewster Bye Architects’ internal layouts new building is specifically designed to for the scheme and this was favoured over respond to the tight urban nature of its the steel option, in which universal columns surroundings, between the beautiful and would have encroached into the rooms. A historic façade of the O2 Academy and a new flat-slab construction with transfer beams Oasis Residence, Leeds. hotel development. in limited locations also satisfied the clear The site was formerly home to Australian headroom heights, while allowing for the themed bar chain, Walkabout, which opened unrestricted routing of services.

www.concrete.org.uk APRIL 2020 concrete 25

15-26ConcreteApril2020.indd 25 26/03/2020 09:57 Above: Leeds Beckett students toured Oasis Residence with the development team. (Photo: Simon Dewhurst Photography Ltd.)

The concrete option was also preferred This meant the whole development by the client and architect due to its thermal was designed in a collaborative manner, mass and acoustic performance, providing an with regular information sharing and close economical solution. In addition, it will help communication, which saved time and with the energy efficiencies of the structure in money while minimising errors and ensuring the long-term. a quality result for the client. The development benefitted local The structural BIM was available students during construction, by offering throughout the development to assist with them a detailed insight into the engineering cost management, construction sequencing, processes, design and construction, sustainability, safety and in all areas of surrounding innovative, large-scale construction and facilities management. development projects. Students from Leeds Beckett University’s The result School of Built Environment & Engineering Oasis Residence is a modern development, course toured the development and met offering exceptional living accommodation representatives from all companies involved with on-site facilities including a lounge, with the project, which offered a real taste fitness suite, cinema room and study areas. of life on a live construction project. This It has become a landmark building where a also provided a great insight into both the derelict bar once stood, just a short walk from construction programme and the thought Leeds city centre’s main university campuses, process behind all the various aspects of the with a huge range of shops, restaurants and scheme. bars on its doorstep. In addition, it’s now one of the city centre’s The design most sought-after student developments, The structural frame was designed using which is currently fully occupied, even though 3D modelling software, which allowed for some of the studio apartments are priced at an accurate assessment of wind loading and more than £300 per week. „ vertical load paths to provide an efficiently designed structure. Transfer beams were used to accommodate step backs in the building 3D capture of façade at the upper levels and to provide a building frame column-free entrance area. (Cookridge St A lightweight steel framing system façade (front)). was incorporated into the design to keep the loads on the slab at the perimeter down and ensure an economical design. Drawings were also produced from a 3D structure model, allowing for greater co-ordination with architectural and service engineer drawings. As part of this process, the reinforcement design aspects of the project were undertaken using a range of advanced 3D modelling tools, as well as BIM design processes, which Oasis Residence, Leeds were shared between the entire design team. Developer YPP Shearail punching shear reinforcement was Engineering services Adept Consulting Engineers introduced to avoid the need for drop heads Architect Brewster Bye Architects to columns, which would have encroached Principal contractor The Broadley Group into the services zone. M&E design NOVO

26 concrete www.concrete.org.uk APRIL 2020

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27-44ConcreteApril2020.indd 27 26/03/2020 09:58 FRAME CONSTRUCTION

It never rains but it pours: statutory adjudication and the supply of concrete

Kieran Fano of London law firm Goodman Derrick examines the England and Wales High Court’s (EWHC) decision in Universal Sealants (UK) Ltd vs Sanders Plant and Waste Management Ltd [2019] EWHC 2360 (TCC) and considers what can be learnt for participants in the concrete supply industry.

ollowing the introduction of the which had not been specified and was not fit Housing Grants, Construction and for purpose. As a result, the concrete had to Regeneration Act 1996 (‘the Act’), be broken out and replaced. F statutory adjudication has become The dispute was referred to adjudication a prominent feature of the UK construction and SPW was found liable and ordered to pay industry and a body of jurisprudence damages to USL to the sum of £52,259. SPW has developed in the Technology and did not comply with the adjudicator and USL Construction Court. Despite this – and the applied to court to enforce the adjudicator’s prevalence of concrete as a building material decision. This application was resisted by – the High Court has only recently, for the SPW on the basis that the adjudicator did first time, been faced with the question of not have jurisdiction to determine the dispute whether a contract for the supply of concrete under the contract, as the delivery to site of falls within the Act. materials was excluded from the Act. Universal Sealants (UK) Ltd (USL) was engaged to carry out works on a project in Decision Gateshead, which involved the removal The adjudication provisions of the Act apply of existing bridge expansion joints and only to contracts for the carrying out of installation of replacement joints. In March “construction operations”. This definition 2017, USL entered into contract with includes the construction, alteration, repair, Sanders Plant and Waste Management Ltd maintenance, extension and demolition (SPW) for the supply of concrete as part or dismantling of any buildings, structures of its works. As USL’s works progressed, a or works forming, or to form, part of the dispute arose between the parties in relation land. However, section 105(2)(d) of the Act to the quality of concrete that was supplied excludes certain activities, including the by SPW. “manufacture or delivery to site of building In particular, USL contended that SPW or engineering … materials … except under was engaged to supply concrete designated a contract, which also provides for their M50 [note: this is not a classification in common installation”. As such, the question before the usage], but had instead supplied ST5 concrete, court was to establish whether the contract

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for the supply of concrete also provided for its The court therefore found that the act of installation. delivering concrete to site and pouring were In answering this, the court embarked synonymous, as the act of pouring constituted upon two exercises. First, an analysis of the part of the delivery and was not an additional contract wording and contract sum analysis act of installation involving some work on, or to determine properly the extent of SPW’s related to, the materials. contractual scope, followed by an analysis of In this regard, the court was cognisant of what in fact happened during the works. the fact that in order for the materials to be In relation to the first issue, the court noted delivered to site, the concrete is poured where that although the purchase order forming it is required, rather than with bricks or glass, the basis of the contract did not make express for example, which may be stored before reference to installing concrete or include a being installed. rate for doing so, this was indicative but not determinative of the nature of the contract. Comment On the second issue, the court noted: (i) While this case provides a useful illustration the concrete was delivered to the site by a of how the court will apply exclusions under mixer truck; (ii) the concrete was poured section 105(2) of the Act, the following directly into a channel for the expansion principles of general application to joints that were being installed; and (iii) there participants in the concrete supply industry was no evidence as to what was done to the can be discerned: concrete after it had been poured. • While contracts for the supply of concrete (cast-in-situ) are most likely to “The court therefore found that the act be excluded from the Act, the exclusion of delivering concrete to site and pouring is unlikely to apply if it can be shown that the concrete is worked following the were synonymous, as the act of pouring pour into where it is required. It is constituted part of the delivery. therefore likely that wetting and the ” application of heat, sheet or curing In considering the extent to which SPW membrane during the curing process are was involved in the installation of concrete, likely to amount to installation, as will the court accepted that while it was correct the use of a vibration poker or finishing that concrete was not installed, it nevertheless aids, such as superplasticisers. dismissed a narrow construction of the word • The Act’s exclusion is less likely to apply “installation” and confirmed that it was to the supply of precast concrete, as there intended to connote some work done to the is no pouring involved on-site and the materials after delivery. In addition, the court acts of delivery and installation will be went on to note that: “Concrete is an unusual more readily distinguishable. material in this respect because, once it is mixed, wet concrete starts to set. It would be As it is not possible to contract out of the highly unusual for it to be delivered to some Act, subcontractors who procure concrete on sort of holding facility before it was poured a supply-only basis may wish to ensure that where it was required and the act of delivery there is a contractual right to adjudication, and pouring are, therefore, commonly the while concrete suppliers involved in same thing, if, as in this scenario, the concrete installation are sensible to ensure that they is being supplied from off-site rather than have robust procedures in place so that they manufactured on-site”. are prepared for references to adjudication. „

25th Annual Conference Temporary Works and Design for Construction Due to the ongoing Covid-19 threat this With emphasis on Road, Rail and Footbridges – Temporary conference has been postponed. New date and Permanent Works Interactions and Stability • Detailing • to be confirmed, please visit: Safety Management • Case Studies • Improving Buildability • www.concrete.org.uk/cbdg Fabrication, Transport and Erection of Beams. For more information contact: [email protected]

27-44ConcreteApril2020.indd 29 26/03/2020 09:59 Time to call in reinforcements With developments in concrete technology progressing apace and health and safety remaining at the top of the industry agenda, how can manufacturers continue to deliver on ever-changing project requirements? Andy Taurah of Sika explains how fibre-reinforced concrete (FRC) is helping to bridge the gap of the age-old conundrum of cost versus value.

arpets of steel-welded fabric Harpur Hill Business Park reinforcement (mesh) have long A recent project that benefitted first-hand been a staple of building projects from FRC was the construction of a 4000m2 C across the UK. Forming the warehouse on the Harpur Hill Business Park physical and metaphorical foundations in Buxton, Derbyshire. of a building project, the trustworthy The new-build scheme for occupier Eagley reinforcement method has provided stable Plastics required the concrete slab to provide platforms on which to build. But we all know a strong, ultra-flat surface to support large that stability comes in different shapes and amounts of high-rise racking. forms, and modern methods of technology With the building shell already have encouraged the implementation of constructed, the main complexity of this fibre-reinforced concrete (FRC), where project was working within the constraints micro, macro or steel fibres help to transform of the building’s walls to deliver a slab that the mix into something more fit for purpose. would be fit for purpose. The ground was piled prior to the slab pour, each at 3.5m The right ingredients apart, making it logistically difficult for Whether it’s a non-structural fibre to vehicles to both get into and move around the reduce plastic shrinkage, a structural fibre building. to increase crack control or steel fibres to improve structural performance, fibres can help to meet specification requirements and reduce manual handling and placement time. But ultimately, they help to reduce overall construction cost when compared with steel reinforcement bar because they: • eliminate trip hazards • reduce the amount of plant equipment needed • are less labour intensive • eliminate the need for storing large volumes of steel on-site • support discharge at the point of installation. Above and top of page: Industrial laser screed levelling the steel-fibre concrete. Addition of dry-shake powder seen in the foreground.

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27-44ConcreteApril2020.indd 30 26/03/2020 09:59 Site support. Concrete delivery from RT Mycock.

An added complication was the impending trucks delivered a total of 1000m3 of material arrival of an expert team of installers from to provide a 250mm-deep slab. While the Belgium, who were due to begin installing project came with associated complexities the floor covering in eight weeks. Additional of its own, an additional hurdle to overcome pressure was added by the occupier, who was that ready-mixed concrete supplier imposed a strict occupation date that left no RT Mycock had never delivered an FRC room for manoeuvre in the build programme. installation before. Following a plant visit, the project team designed and constructed The job at hand a gantry to feed the fibres into the mixers Main contractor J Milner & Sons worked in order to deliver the requisite batching alongside ready-mixed concrete supplier RT sequence. Mycock to discuss the project requirements. This challenge was compounded by the RT Mycock called on specialist support from time in which the project needed to be Sika, which – following an engineer visit – completed. specified fibre technology to deliver on the project’s strength and finishing requirements. End result By using this specification, the timescale, The Belgian team of experts arrived on time budget and logistical needs of the scheme and swiftly delivered the flooring installation were met in the following ways: without a hitch. The slab provided the glass- • FRC was discharged directly from the like finish required by the occupier, bolstered wagon at the point of the pour, removing by the strength-providing fibres distributed the need for expensive pumping throughout the concrete. equipment Paul McGinnis of RT Mycock says, “We • FRC eliminated the need for traditional really had an extremely tight deadline in fabric reinforcement solutions, reducing which we couldn’t afford anything to go labour costs and risks to health and safety wrong with this project. The team did a • FRC provided the residual strength tremendous job in getting the task done required, even on a piled floor design within the timeframe and the product has • FRC reduced the risk of cracking, been faultless since its implementation. Both subsequently delivering a more robust the client and the contractor were very happy material. with the finishing result.” Aside from the tight timescale, restricted The concrete space and the lack of familiarity with FRC With a requirement to cover the whole schemes, this project is a great example floorplate inside the 4000m2 warehouse, of thinking outside the box – literally and Sika developed a mix design that included a figuratively – to get the job done in time dosage of steel fibres strong enough for the and within budget. Increasingly, the market task. Novocon HE1060 HT (high tensile) is coming around to the many benefits of dosed at 45kg/m3 was specified and swiftly FRC when compared with traditional fabric accepted by the engineering team in order to reinforcement jobs and examples like this are meet the timescale constraints. when modern methods of construction really Over the duration of a week, 125 mixer come into their own. „

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27-44ConcreteApril2020.indd 31 26/03/2020 10:00 FIBRES Fibres in ultra-high-performance concrete Peter Buitelaar of Peter Buitelaar Consultancy and Stephan Müller of KrampeHarex discuss the use of fibres in ultra-high-performance concrete (UHPC) and look at some European project examples.

fter the initial development of UHPC in 1978 (by Hans Henrik Bache), it soon became very clear A that the ultra-high-strength binder (cement plus ultra-fine fillers) was brittle like glass and more brittle than traditional cement paste. As with traditional cement paste, the ultra-high-strength cement paste needs Figure 1: Fine fibre embedded in cement paste (left) and UHPC paste (right). The mechanical to be combined with sand, aggregate and fixation of the short and thin fibre is greatly increased by incorporating the ultra-fine particles reinforcement. The effect of aggregates in the spaces between the cement particles (Hans Henrik Bache 1978). on the fracture energy is, compared with traditional concrete, reduced in UHPC unless very strong aggregates are used. the fresh and hardened UHPC. Fibre lengths produced for tyre cord. The quantity of steel In general, the greater the volume and for UHPC are in the range of 6–20mm, while fibres in the UHPC for short fibres and dimensions of strong aggregates used, the less fibre diameters are 0.009–0.5mm. micro-fibres is 81,000–675,000 per kg. brittle the UHPC. However, such a UHPC In the main, steel fibres are used in will only be useful for certain applications and UHPC since they are the best choice Cocktails and hybrids not for most precast and applications where economically and contribute most to the It is thus also possible to make a fibre blend/ a certain rheology is needed. The first tests properties of the fresh and final concrete cocktail. This can be a mix of different types on such UHPC showed that the mechanical product. Polypropylene fibres are used for of fibres, for example, steel and polypropylene fixation of very fine fibres was greatly non-structural applications to control plastic fibres to improve fire resistance, but also steel increased (four to five times higher than in shrinkage, such as in UHPC sprayed concrete fibres of different lengths and diameters. traditional concrete mortar) in the very dense and toppings, and in combination with Buitelaar et al carried out research in 1986(1) micro-structure of the ultra-high-strength steel fibres to obtain a certain degree of fire with UHPC and combinations of steel binder (Figure 1) and that high volumes resistance. PVA fibres are mainly used for fibre blends of short and long fibres. While could be added due to the properties of the smaller elements and when very high flexural short fibres are very efficient to bridge ultra-high-strength binder. The only way to strengths are demanded. micro-cracks, longer fibres are very efficient give the UHPC a high degree of ductility is Steel fibres for UHPC are straight and to bridge macro-cracks (Figure 2). This thus to incorporate high-energy-absorbing cold-drawn. The carbon steel fibres mostly positively influences the strain hardening but reinforcement (bars, fibres and combinations have a brass coating, which indicates that also impacts the strength and toughness of of both). the fibre is made from wire that was initially the UHPC. The addition of high-strength steel fibres will thus make a brittle material much more ductile. This is influenced by the following parameters: fibre content; fibre geometry (length, diameter in relation to maximum particle size UHPC); fibre orientation; bond between fibre and matrix; and stiffness of the fibres. Types of fibres used in UHPC The selection of fibres is very important for the design of the UHPC, as it has a strong influence on the composition, strength, ductility and price of the concrete and the final product. Although there are many types of fibres – including carbon, basalt and many Figure 2: The main principle of hybrid fibre concrete: a) The influence of short thin fibres on synthetic fibres – three types of fibres are the bridging of micro-cracks and the increase of tensile strength; b) the influence of long mainly used in UHPC: polyvinyl alcohol thick fibres on the bridging of macro-cracks and the increase of ductility (Markovic 2006). (PVA), polypropylene and steel. Different kinds of fibres result in different properties of

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27-44ConcreteApril2020.indd 32 26/03/2020 10:00 Figures 3 and 4: TGV station, Montpellier, France. (Photo: Ductal/Hisao Suzuki.)

Table 1 – Properties of three types of fibres used in UHPC The separate units are joined together by PVA Polypropylene Steel post-tensioning. The units are cast in a white Ductal UHPC with stainless steel fibres Tensile strength (MPa) 880–1600 600–1200 1200–3000 type KrampeHarex DG 14/0.2 E316 to Elongation at break (%) 6 25 3–4 avoid corrosion of exposed fibres during its Young’s modulus (GPa) 25–41 2–9 200 expected lifespan. Density (g/cm3) 1.30 0.91 7.80 University of Southern Denmark The façade of the new building for the Faculty of Engineering at the University In addition, combining traditional and aggregates. The typical percentages of of Southern Denmark (SDU) in Odense reinforcement and steel fibres in a UHPC steel fibres in UHPC are 1–3% (V/V); in is based on the idea of a glasshouse placed element or structure is a very interesting special applications higher dosages are used. within a shroud made up of prefabricated option. This hybrid reinforced UHPC as-struck UHPC elements. The perforated is mainly known as compact reinforced Typical applications façade is created from 292 elements, each composite (CRC) and was invented by Hans The use of different fibre types performing in sized 5 × 3m and with a thickness of 65mm. Henrik Bache in 1986. This combination various UHPCs with varying requirements is The façade around the building is reducing of UHPC, very short, thin and strong steel described below in a few applications. direct sunlight by up to 50%. Differently fibres, and reinforcement bars (steel, high- sized circular openings with a maximum strength steel, carbon, etc) results in an TGV station, Montpellier, France diameter of approximately 2m in the white extremely high compressive strength, flexural The Montpellier train station’s striking concrete façade provide the building with strength and ductility. 10,000m2 roof structure has drawn natural ventilation and glare protection, while inspiration from the Mediterranean lending it a feeling of airiness and elegance. Selection of fibres surroundings with its organic double-curved The façade’s prefabricated panels are made The selection and percentage of fibres is very UHPC shells and glass panes embedded of white CRC concrete reinforced with important, since the addition of fibres will directly into the UHPC and looking like 140kg/m³ KrampeHarex DG 12.5/0.3 E304 influence the rheology and final properties of super-sized palm tree leaves. Each unit (115 stainless steel fibres. Additional reinforcement the UHPC. When aesthetics are important in total) is 18m long, 2.7m wide and has a bars have been placed at critical locations – but also absolutely necessary in the case of 3m depth, with a wall thickness of 50mm. around the circular openings. exposure to high and very high temperatures such as in applications of special refractory UHPC – stainless steel fibres are a good but expensive alternative. Special fibre shapes – Figure 5: University of such as hooked, crimped, corrugated, paddled, Southern Denmark, Odense. etc – are not only difficult and thus expensive (Photo: Hi-Con.) to produce as short and thin micro-fibres but also will change the rheological properties of the UHPC. Special fibres will thus have much influence on the maximum dosage of steel fibres and on the composition and the packing model of cement, ultra-fine fillers

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27-44ConcreteApril2020.indd 33 26/03/2020 10:00 Figure 6: University of Southern Figure 7: A4 Küsstnacht–Brunnen, Switzerland. Figure 8: Grand Pont Bridge, Thouaré Denmark, Odense. (Photo: Hi-Con.) (Photo: ASTRA Federal Roads Office/KrampeHarex.) Sur Loire, France. (Photo: Vicat.)

loads and corrosion had damaged the existing concrete deck, masonry arches and steel girders, resulting in restricted traffic. Initially suggested renovation resulted in a too high dead weight, couldn’t cope with Eurocodes and would take longer than 12 months. A lightweight UHPC deck consisting of 218 prefabricated slabs of 624 × 158mm and 70mm thick at the edge and 120mm at the axis has been placed on additional girders with Nelson studs on top of the existing girders. Prefabricated panels and girders are joined together using the integrated transversal reinforcement bars and Nelson studs in a small wet joint with UHPC grout. A thin wearing course was applied on the UHPC. A new pedestrian and bicycle lane as overhanging structures will be realised later; the prefabricated UHPC panels here are only 40mm thick. Dead weight has been Figure 9: Lubina River footbridge, Czech Republic. reduced by 43%, with a shorter closure of (Photo: KŠ PREFA - Štětí, Marek Blank.) the bridge (total duration of six months) and the project has remained within budget. The prefabricated slabs were cast in Vicat’s A4 Küsstnacht–Brunnen, Switzerland Deteriorated concrete girders were repaired SMARTUP UHPC with 200kg/m³ This project saw the overhaul of a 5km and strengthened with an additional UHPC KrampeHarex DM 12.5/0.175 steel fibres. stretch of national road and sections of layer. A total area of 14,000m2 was resurfaced road with several large bridge structures, with UHPC, with the use of a slipform Lubina River bridge, Czech Republic renovation of two tunnels and expansion paver. A 45mm-thick layer was applied in This 36m-long footbridge has been built of two tunnel control centres. Several the field area and a 100mm-thick layer in the from five prefabricated elements (each deteriorated bridges needed strengthening support section of the bridges. The UHPC section 7.2 × 2.5 × 0.8m) made from UHPC. and rehabilitation to increase the maximum was mixed on-site in a mobile batching plant To create the support-free bridge with a loads and to extend their lifespan. The to reduce transport time. The UHPC was slenderness ratio of 1:44, the designer used construction period was significantly reinforced with 250kg/m³ KrampeHarex a post-tensioning concept with a unique shortened when the weather-dependent work DM 12.5/0.175 steel fibres, which were multiple system of cable protection. To – such as sealing and waterproofing with a automatically weighed and added in the achieve a lightweight structure, the bridge membrane – was replaced with the use of a batching plant. elements are recessed with polystyrene blocks, UHPC overlay. reducing the amount of UHPC. KS Prefa, In comparison with similar older projects Bridge, Thouaré Sur Loire, France a mid-size precast company, has developed in The Netherlands, where only a thin The 394m-long steel through-truss ‘Grand its own UHPC, achieving a compressive wearing course or porous asphalt has been Pont’ bridge crossing the Loire River was strength of ≥120MPa and the post-cracking applied, two additional layers of gussasphalt erected in 1882 and was damaged during strength of ≥7MPa. The concrete has a on the UHPC are used as a wearing course. World War II. Leaking rainwater, traffic binder content of more than 700kg/m3 and a water:cement ratio from 0.18. To achieve the necessary ductility, the UHPC is reinforced with 120kg/m3 KrampeHarex DG Figure 10: Lubina River 12.5/0.175 steel fibres. „ footbridge, Czech Republic. (Photo: KŠ PREFA - Štětí, Marek Blank.) Reference: 1. BUITELAAR, P., BAALBERGEN, J. and VAN DEN HEUVEL, E.A. Failure behavior of notched specimens made from Densit concrete reinforced with steel fibers. Ultra-High- Strength Concrete Task Force, Aannemingsbedrijf J.G. Nelis, 1986–1987, Haarlem, The Netherlands.

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Ultrasonic pulse technology

With steel-fibre-reinforced concrete becoming more prevalent in construction, problems can arise in determining potential defects, such as voidage due to clumping of the fibres. Warren Thomas of Henderson Thomas Associates outlines how ultrasonic pulse technology (tomography) overcame the issue of detecting the presence of such voids in a fibre-reinforced concrete slab.

he ground-bearing slab within layers) depth and thicknesses of elements, and Figure 1 (above): this particular warehouse under even the presence of post-tensioned ducts in A section of investigation was some 6500m² highly reinforced concrete. Voidage detection slab showing T in area and problems had been in slabs and beneath slabs has also been clumping of the detected while drilling holes into the slab for successfully undertaken. fibres, resulting in the insertion of a racking anchorage system. However, the physics behind the voidage. applications above mean virtually 100% Initial detection failure of the radio waves will be reflected from Initially, the contractor on-site extracted metal objects in concrete. With a steel- cores from the affected area and these clearly fibre-reinforced slab this technique is showed the presence of major voidage. A fraught with problems and at best only testing consultant was appointed initially, limited information can be obtained. The in an attempt to determine the extent and effectiveness of the technique is always site location of voids throughout the entire slab. specific. Figure 2 (below): 2 The investigation was carried out by using Surveying 6500m ground-penetrating radar (GPR), which warehouse slab. proved unsuccessful. Limitations of GPR GPR is a traditional, multi-faceted technique, allowing engineers to determine details of concrete elements, as well as other structural assets and other applications. GPR works by emitting a radio wave into the material/asset under investigation. Our experience with reinforced concrete structures has allowed – with precision – for the detection of reinforcement (multiple

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Figure 3: Undertaking GPR scan on a beam. Figure 4: Undertaking tomography scan on a suspended slab.

The detection of voidage beneath a highly can be seen in Figure 5. This is primarily due reinforced slab is therefore problematic and to the reflection of the pulses being of such an in this instance was found to be unsuccessful, obtuse angle that the multiple transducers to due to the presence of dense fibres in the the Pundit Live Array were not detecting the concrete slab (the latter the most likely reason responses. for the production of the observed voidage). Even though tomography can detect The GPR plots received by HTA were voids, currently the technology is such that found to be undecipherable due to the the actual volume or connectivity cannot be presence of densely packed steel fibres. accurately determined. Having completed the works, the technology was used as a quality Ultrasonic pulse technology assurance tool to check the integrity of the Using a wireless inspection solution with resin injection repairs made to the slab in multi-channel ultrasonic pulse echo question. technology was the direction decided upon. From comprehensive research and Judgement development over a number of years plus This project ultimately proved successful. extensive use of this technique on various However, it highlights the necessity to projects, there was confidence that this have years of experience and engineering approach would overcome the limitations of judgement to be able to use the latest the GPR. technology and innovation in non- Ultrasonic technology (tomography) works destructive evaluation. „ by emitting ultrasonic pulses into concrete, with only between 40 and 50% of the pulse being reflected/attenuated by metal objects. Figure 5: Tomography technique – This allows 50%+ of the ultrasonic pulse to three designations of concrete areas. penetrate deeper into the concrete element. These pulses, on encountering an air gap, will be totally reflected and produce a target on the B-scan (live time response from equipment, as seen in Figure 5). Site survey A one-day trial was undertaken and proved successful in locating the initial voids detected during drilling operations. A full survey was then commissioned to investigate the slab for any further voidage. This required 24-hour working by multiple teams to allow compliance with a tight contract time constraint. The survey detected three general conditions of the concrete present in the slab, namely: good-quality concrete; concrete with small/isolated voids; and significantly voided concrete (as shown in Figure 5). In the area designated significantly voided, the voids were of such a size as not to enable the technique to detect a back wall echo, as

36 concrete www.concrete.org.uk APRIL 2020

27-44ConcreteApril2020.indd 36 26/03/2020 10:01 ER FIBRES,

. ~

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27-44ConcreteApril2020.indd 37 26/03/2020 10:01 FIBRES Hybrid reinforcement is gaining in popularity

Engineers and contractors are increasingly opting for traditional reinforcement combined with steel fibres to better protect car parks, basements and offices against water pressure. This also achieves better crack control. Ben Vanheuverzwijn examines some notable evolutions that have been identified at Bekaert in recent years.

n the past, steel fibres were mainly used cultural centre in the country. That project for industrial floors and prefabricated is located right by the sea and, therefore, tunnel segments. The publication of also had to deal with a substrate with water I some local and international Standards pressure. Here, the classic reinforcement was and the development of new fibre types – converted into a hybrid reinforcement and with greatly improved performance – have steel fibres added. The deeper one builds, the broadened the scope for steel-fibre concrete more the water pressure increases and the in recent years. Steel fibres have mainly been more important it is to have crack control. If able to make their way into more structural the cracks grow too big, the water just goes applications, such as ground-supported right through it, with all the consequences. slabs, walls in underground car parks and basements. Crack control There is often water pressure against If crack control needs to be used and a certain the bottom of the ground-supported slabs limit on the cracking width has to be met, in basements, due to the depth of these contractors and designers could opt for and the level of the water table. hybrid reinforcement. The tensile strength These pressures can be quite high where and anchorage of the Dramix 4D fibres were building right by a canal, a river or the sea. specifically developed to control cracking Thanks to the addition of steel fibres, the and limit crack openings to between 0.1 amount of traditional reinforcement can and 0.3mm, so that durable and liquid-tight be reduced greatly and the cracks can be structures can be created. These fibres, which controlled more efficiently at the same time. have a Seco application certificate, offer the

A few years ago, Bekaert was also involved highest fR1 value of all of Bekaert fibres. They in the construction of new accommodation provide the highest flexural tensile strength at the National Museum of Norway, which, in the operating limit state (SLS) within with an area of 54,000m2, is the largest the Dramix steel-fibre range when tested

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according to BS EN 14651(1). The steel fibres are homogeneously distributed across the entire concrete mass. Hybrid reinforcement creates more cracks, but these cracks are much smaller and finer, so that no water can pass through. From the moment a small crack occurs in the concrete, it will be immediately bridged by another fibre. With traditional reinforcement, there are fewer cracks but they are often much larger, allowing water to flow through. Popular Engineers, designers and contractors are increasingly opting for hybrid reinforcement in combination with steel fibres. Traditional reinforcement is increasingly being converted into hybrid reinforcement, in combination with steel fibres. It has also been noted that many designers Page opposite, above and below: The construction site are struggling to deal with water pressure. of the Grotius’ project, which entailed the construction of Providing comprehensive technical support two large tower blocks in The Hague in The Netherlands. is important in helping clients choose the most suitable fibre type, the optimal dosage and the relevant concrete quality for a range of applications. Once contractors have used steel fibres, they see the many advantages in material costs, work, placement and time. Many designers also admit that with traditional reinforcement they do achieve the stability they want, but do not always achieve their desired crack width. In this case, engineers have to prescribe much more traditional reinforcement, which is more expensive, more labour intensive and harder to place. „ Reference: 1. BRITISH STANDARDS INSTITUTION, BS EN 14651. Test method for metallic fibre concrete. Measuring the flexural tensile strength (limit of proportionality (LOP), residual) . BSI, London, 2005. 2. PARMENTIER, B. Design and implementation of liquid- proof concrete structures. Technical Information 247, Scientific and Technical Center for Construction (WTCB), Brussels, 2012.

Left: The intended crack width depends mainly on the water pressure and the thickness of the slab itself. The relationship you can see here is often used by engineers to determine the design width of the crack. The higher the water pressure, the tighter the crack should be. The thicker the slab, the bigger the crack. In any case, 0.2mm is the upper limit(2).

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27-44ConcreteApril2020.indd 39 26/03/2020 10:02 STANDARDS

(Photo: Socotec.) Assessment of in-situ concrete strength – revised BS EN 13791 and BS EN 12504-1 On 14 January 2020, BSI published a revised BS EN 13791(1) Assessment of compressive strength in structures and precast concrete component (effective from February 2020). This uses the revised BS EN 12504-1(2) Testing concrete in structures. Part 1 – Cored specimens – taking, examining and testing in compression published on 9 December 2019. Neil Crook of The Concrete Society looks at the changes.

oth these Standards have been strength for design, a lower partial factor for subject to in-depth review. The concrete can be used (minimum 1.3), see revisions are significant and will BS 1992-1-1:2004 Clause A.2.3(5). B require changes to the taking and testing of cores and the method by which the Testing data is used to: a) estimate the characteristic The main changes to the taking and testing in-situ compressive strength of the concrete of core samples given in BS EN 12504-1, for existing (unknown/old) structures; and b) with its national annex, relate to the assess the compressive strength class where procedure for extracting the sample, its there is doubt over the strength of recently storage, preparation and any adjustment to

supplied concrete. the core strength fc,core. The revised BS EN 13791, which Samples should ideally be at least 75mm supersedes the withdrawn 2007 version, diameter but smaller cores are permitted (not includes a national foreword and annex that less than 50mm) if this is not possible. The covers all the relevant content of number of cores required is increased for BS 6089:2010(3), which is also withdrawn. small diameters. The diameter of the core A new publication PD CEN/TR 17086(4) should also be at least three times the upper is anticipated later in 2020 and will include aggregate size used in the concrete. further guidance and worked examples based The assessment of in-situ strength is based on BS EN 13791 using in-situ strengths from on the concrete as it exists in the structure direct and indirect test methods. without change to its moisture condition. It should be realised that the characteristic After extraction, the sample is to be retained

in-situ compressive strength fck,is is not in a sealed container until prepared for a direct substitute for the characteristic testing. The water used in the extraction

strength fck for specifying the strength. When of the core, density measurement and end using an estimated characteristic in-situ preparation is not considered to impart

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a material change in the overall moisture condition of the specimen. The samples are prepared by grinding (recommended) or capping to produce a core with a length:diameter ratio of 1:1 or 2:1. Generally, but not exclusively, 1:1 cores of 100mm diameter should be used in cases of doubt (as these reflect the aspect ratio of production and identity test cubes). Estimation of characteristic in-situ strength is based on a 2:1 core, as cylinder strength is used in structural design. A 1:1 core can be converted to an equivalent 2:1 core using the core length factor (CLF) of 0.82 (0.91 in the case of lightweight concrete). There are permitted limits on the length:diameter ratio:

• for a 1:1 specimen the length to diameter (Photo: RSK.) ratio is to be within 0.90:1 and 1.10:1 • for a 2:1 specimen the length to diameter ratio is to be within 1.95:1 and 2.05:1.

Undersized specimens should be rejected; obtained are considered unrepresentative of oversized cores trimmed to meet the limits. the true strength of the concrete and should Reinforcement reduces the strength of be excluded from the assessment. the core and its presence should be avoided Density and excess voidage may be if possible. If reinforcement is present, it recorded. While there is an accepted should be predominantly horizontal to the relationship between excess voidage and direction of testing and not more than 2% of strength, it is not used to adjust the recorded the volume of the specimen. In addition, with core strength in the assessment. However, 2:1 specimens the reinforcement should be high voidage and/or low density values may contained within 30mm of each end. indicate problems during the execution of the works that have adversely affected the strength obtained. Assessment of in-situ strength The structure of BS EN 13791 remains substantially the same as the previous version, with the primary focus to estimate the characteristic in-situ strength for structural design with BS EN 1990(6) and BS EN 1992-1-1(5). However, substantial changes in the methodology have been made to the procedures to estimate characteristic in-situ strength of an existing structure (Clause 8) based on a 2:1 core strength and for those cases where there is doubt over the compressive strength class of recently supplied concrete (Clause 9). Both (Photo: RSK.) applications have a number of common steps but the assessment methods differ and may lead to significantly different outcomes. Before embarking on a course of in-situ strength determination, the test region, Provided that the requirements for number of test locations, testing procedures moisture containment, length:diameter and how the results are to be analysed needs ratio limits and limits on the presence to be set out and agreed. The number of of reinforcement are met, there is no valid test results should be sufficient to adjustment to the core strength. If any of ensure there is confidence in the strengths these requirements are not met, the values obtained and they are representative of the

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against core data taken from the structure under consideration. For the purposes of structural assessments (Clause 8) of the in-situ strength of a small test region comprising one to three elements and not more than 10m3, at least three valid test results are required. For a test region not greater than 30m3, indirect testing in conjunction with at least three valid core test results can be used. For the assessment of compressive strength class of concrete in case of doubt (Clause 9), the main source of doubt normally arises from low strength of identity test samples, lack of samples or problems during execution of the works. In the previous Standard, a test region was defined as a region comprising many batches or a small region comprising (Photo: RSK.) one or a few batches of concrete. The volume associated with each region was undefined. This had been a matter of controversy and was recognised by the drafting committee. region tested. This is particularly important Consequently, in the revised Standard the where there is doubt over the strength of concrete under investigation is still split into recently supplied concrete (Clause 9), as test regions but each test region is limited there are many interested parties involved in to a total volume of approximately 180m³. the production, placement and design of the It is then broken down into volumes of concrete and structure. approximately 30m³, which might align with the lots (defined volumes) used for identity Strength results testing (BS EN 206 Annex B(7)). If less than The strength results, either directly from 30m³, it may be treated as a single volume, cores or indirect test methods, need to be provided the concrete was supplied on a visually assessed to determine if there is single day and there was no information to evidence that the test region contains two suggest that one of the loads is different to or more concretes. The data should also be the others. ‘Approximately’ is used to allow for checked for statistical outliers; more than a small increase in the volume of a part load. two outliers could indicate that the test The minimum number of valid test results region comprises more than one compressive for each test location and the criteria to strength class. The Grubb test is referenced confirm that the concrete has conformed in BS EN 13791 to determine whether a high to the compressive strength class based on or low test result is an outlier. The inclusion the specified characteristic strength f or exclusion of an outlier is a matter for ck,spec for the test region under investigation is engineering judgement. given in BS EN 13791 Table 8 (see Table The estimation of characteristic in-situ compressive strength of existing structures (Clause 8) is based on a minimum of eight (Photo: Socotec.) valid test results expressed as the strength of a 2:1 core (or from 12 test locations if based on single 50mm-diameter cores). To allow for possible outliers, the number of samples taken should be increased by at least two more than the minimum number of valid results required. The standard deviation is calculated and compared against a coefficient of variation with the greater value used. The characteristic in-situ strength of the test region is estimated as the lower value of two formulas, one based on the mean of the valid test results and the other based on the lowest valid test result. A procedure is also given for the estimation of characteristic in-situ strength based on indirect testing, calibrated

42 concrete www.concrete.org.uk APRIL 2020

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Table 1 – Criteria for assessment based on core test data only Number of approximate 30m3 Minimum number of Mean of 1:1 core test results for Lowest 1:1 core test volumes in test region valid test results the test region result(a) 1(b) 3– 24

36≥ 0.85 (fck,spec,cube + 1) ≥ 0.85 (f – M) 48 ck,spec,cube 510 ≥ 0.85 (f + 2) 612ck,spec,cube (a) where M = 4MPa for compressive strength class C20/25 or higher. For C16/20, C12/15 and C8/10 the margin M is reduced to 3, 2 and 1 respectively. (b) provided it is treated as a single volume.

1 above). Logically, to allow for possible doubt over the strength – and subsequent outliers, it is recommended that the number assessment to Clause 9 shows that conformity of specimens taken is at least one more than with the declared strength class cannot be the minimum indicated for a single volume of confirmed – this does not necessarily indicate approximately 30m³, increasing to two more that the concrete production was non- than the minimum number for total volumes conforming. The production process may be greater than approximately 30m³. conforming, albeit to a lower strength class Where practical, the core should be the and different design parameters would then same length:diameter ratio as the specimens be applicable. used for conformity by the producer. In the Concrete Advice 68(8) goes into greater UK, this would be a 100mm-diameter core detail and explanation of the changes to the having a length to diameter ratio of 1:1 (ie, a Standards. It provides examples on the use of length to diameter ratio in the range 0.90:1 core data in the determination of estimated to 1.10:1). characteristic in-situ strength of an existing If both criteria are satisfied, the concrete structure and the assessment of strength can be accepted as having conformed to the class in the case of doubt of recently supplied specified strength class for the test region concrete. A webinar to watch and guides under investigation. on the subject, produced by BRMCA, is Procedures are also given for the use available at: www.brmca.org.uk/downloads. „ of indirect testing in conjunction with References: selected core test data and the criteria to confirm that the concrete has conformed 1. BRITISH STANDARDS INSTITUTION, BS EN 13791. Assessment of compressive strength in structures and to the specified strength class for the test precast concrete component. BSI, London, 2019. region under investigation. This procedure 2. BRITISH STANDARDS INSTITUTION, BS EN 12504. will be described in a forthcoming article Testing concrete in structures. Part 1 – Cored specimens. entitled ‘Assessment of in-situ compressive Taking, examining and testing in compression. BSI, London, 2019. strength class using a minimum of cores’ by 3. BRITISH STANDARDS INSTITUTION, BS 6089. Chris Clear of MPA–British Ready-mixed Assessment of in-situ compressive strength in structures Concrete Association (BRMCA). and precast concrete components – complementary The UK national annex gives a procedure guidance to BS EN 13791. BSI, London, 2010, withdrawn. for comparative testing in the case of doubt, 4. BRITISH STANDARDS INSTITUTION, PD CEN/TR 17086. where recently supplied concrete under Further guidance on the application of EN 13791:2019 investigation used in one or more elements is and background to the provisions. BSI, London, (under compared against concrete in elements that preparation). 5. BRITISH STANDARDS INSTITUTION, BS EN 1992. have been accepted using indirect testing. Eurocode 2. Design of concrete structures. Part 1-1 – If a producer declares a non-conformity General rules and rules for buildings. BSI, London, 2004. in respect to strength, Clause 9.5 lists 6. BRITISH STANDARDS INSTITUTION, BS EN 1990. information the producer must supply to Eurocode – Basis of structural design. BSI, London, 2002 +A1:2005. the involved parties, which may necessitate 7. BRITISH STANDARDS INSTITUTION, BS EN 206. an estimation of characteristic in-situ Concrete. Specification, performance, production and compressive strength (Clause 8). This conformity. BSI, London, 2013+A1:2016. can then be used in structural design with 8. THE CONCRETE SOCIETY. Assessment of in-situ concrete strength using data obtained from core and an appropriate partial factor for concrete. other testing techniques. Concrete Advice 68, The However, if the purchaser expresses Concrete Society, Camberley, 2020.

44 concrete www.concrete.org.uk APRIL 2020

27-44ConcreteApril2020.indd 44 26/03/2020 10:05 Tunnelingapplications: Concretesegments reinforcement

sing steel fiber reinforcement for tunnel applications assures a and optimal crack control. Thrs results in:

• A safer, more durable concrete structure

• A reduced carbon footprint

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Crystalline admixtures – more support and research needed Crystalline water-resisting admixtures have been available on the market for quite some time, with many claims as to their positive impact on producing ‘watertight’ concrete. Yet, the industry remains sceptical – and Standards, silent – about their use. Ben Hickman of CSSW.LONDON discusses the limitations of current testing of crystallising admixtures and asks what more is needed to support their use.

rystallising admixtures are designed apparently forgetting that concrete is an Assessing the effectiveness to form crystals in cracks and effective self-healing material on its own, To try to shed some light on the issue, a capillaries in the concrete when without crystallising admixtures. recent research project reviewed the results of they come into contact with Within the industry as a whole, there is eight studies undertaken since 2010 into the C (4) water, blocking its passage. In doing so, they therefore significant debate and scepticism efficacy of crystallising . Overall, it found enhance the natural autogenous healing over the efficacy of water-resisting the results generally positive on the impact of capability of concrete to seal cracks, which admixtures. A 2015 design guide from crystallising admixtures in aiding autogenous occurs in a variety of ways. The Concrete Centre(1), for example, states healing, with a number of studies showing The work of crystallising admixtures is that “watertightness and durability can be concretes with crystallising admixtures therefore said to be dynamic, as it happens achieved using good-quality concrete alone”. achieving higher levels of crack healing than at the point a crack appears or when a crack The waters are further muddied by the that achieved by normal concrete. On this is exposed to water, even if this occurs a treatment of water-resisting admixtures in basis, it appears that the use of crystallising considerable time after the concrete has been the relevant Standards. admixtures to enhance autogenous crack cured. Although the current Eurocode 2 healing and ‘waterproof ’ concrete is (BS EN 1992-3(2)) includes an entire supported. Potential and confusion section of liquid-retaining and containment However, the study also identified several The potential of crystalline admixtures could structures (Part 3), water-resisting admixtures challenges and gaps in the research that will therefore be significant. However, there is are not mentioned at any point. Instead, need to be addressed in future research. much confusion about their use – not helped it seems implicitly to rely on autogenous Assessment of crystallising admixtures by the manufacturers of these admixtures. healing for waterproof protection by limiting is not the easiest of processes to begin with. As one (confusingly) remarks on its website, crack widths. As noted above, their work mimics that of its products “achieve waterproof concrete Similarly, BS 8102:2009(3) concludes that, autogenous crack healing and is dynamic, structures without the need for any physical because the mechanisms used by different reacting to water ingress as and when it barriers, by turning concrete itself into an admixtures “are quite diverse, it is not possible occurs. Almost all tests require a control effective self-healing waterproof barrier,” […] to give specific guidance on their use”. sample, as well as a test sample, with a

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comparison of the water permeability of both samples used to assess the efficacy of the admixtures. Although this sounds a simple matter, the samples must be controlled for water:cement (w/c) ratio, as the addition of a water-resisting admixtures by default changes this ratio. Failure to do so – as occurred in three of the eight studies – at the very least diminishes the value of the comparison and could invalidate it altogether. This complaint is picked up in an article by a former President of The Concrete Society for Newton Waterproofing(5). The review also found that none of the studies accounted for hydraulic gradient when assessing the efficacy of crystallising admixtures. This is despite evidence that autogenous crack healing is impacted by hydraulic gradient(6), findings that are reflected in BS EN 1992-3. Indeed, the most common permeability test used when examining crystallising admixtures, specified in BS 12390-1-2009(7), does not include consideration of hydraulic pressure, despite best practice guidance for the design of waterproofing concrete structures (BS EN 1992-3) demanding its consideration. Typically, tests on crystallising admixtures also fail to consider rehydration (for example, those used by the British Board of Agrément). Indeed, there appears to be no standard method to investigate how effective crystallising additives are under these conditions. Crack healing with varying MgO compounds. The left column shows a control The lack of research into the impact sample with autogenous crack healing (reproduced with permission(8)). of rehydration and hydraulic gradient on concrete containing crystallising admixtures References: poses a challenge to specifiers to quantify hydraulic gradients; and examines the the benefit of such admixtures. Specifiers contents of healed cracks in comparison with 1. CONCRETE CENTRE. Concrete Design Guide No.1, cracks that have healed autogenously. Guidance on the design of liquid retaining structures. are left to rely on experience to judge The , Vol.92, No.1, 2015, pp.44–49. whether crystallising admixtures will offer Open publication of the results of such 2. BRITISH STANDARDS INSTITUTION, BS EN 1992. better water-resistance performance than testing would go a long way in helping Eurocode 2. Design of concrete structures. Part 3 – liquid autogenous healing on its own. specifiers understand the impact of crystalline retaining and containment structures. BSI, London, admixtures in waterproofing concrete, laying 2006. A final weakness in much of the academic 3. BRITISH STANDARDS INSTITUTION, BS 8102. Code of research comes from a reluctance to identify to rest the confusion and debate that exists practice for protection of below ground structures which crystallising admixtures are being today. against water from the ground. Section 9 – Type B investigated. This limits the repeatability of Finally, much current academic research (Structural Integral) Protection. BSI, London, 2009. is focusing on self-healing concretes, 4. HICKMAN, B. and MACMILLAN, S. Efficacy of crystalline the studies, as well as making them all but waterproofing for basement concrete. Proceedings of valueless to specifiers. dealing with a range of subjects that may the Institution of Civil Engineers – Construction be of interest in waterproofing concrete, Materials, Vol.172, No. 5, October 2019, pp.256–262. Concluding remarks including bioremediation, expansive agents 5. CATHER, B. Waterproofing Concrete – Admixtures. and superabsorbent polymers, encapsulation Newton Waterproofing, Tonbridge, UK, available at: Although, from the evidence available, https://bit.ly/398EG3F, accessed 6 February 2020. crystallising admixtures appear to offer and fibre reinforcement, to name a few. Such 6. EDVARDSON, C. Water permeability and autogenous benefits to waterproofing concrete, much research must not fall into the same trap as healing of cracks in concrete. ACI Materials Journal, more could be done to aid specifiers and the research into crystallising admixtures but Vol.96, No.4, July 1999, pp.44–48. provide results that are easily applicable to 7. BRITISH STANDARDS INSTITUTION, BS 12390. Testing support the use of admixtures in commercial hardened concrete. Part 1 – Shape, dimension and other applications. As a start, manufacturers of real-world projects. „ requirements for specimens and moulds. BSI, London, crystallising admixtures should undertake Further information: 2012. testing of their products that: ensures the 8. QURESHI, T.S. and AL-TABBAA, A. Self-healing of CONCRETE SOCIETY, The Influence of Integral Water- drying shrinkage cracks in cement-based materials same w/c ratio in control and test samples; Resisting Admixtures on the Durability of Concrete. The incorporating reactive MgO. Smart Materials and considers the impact of rehydration and Concrete Society, Camberley, UK, 2013. Structures, Vol.25, No.8, July 2016.

www.concrete.org.uk APRIL 2020 concrete 47

45-56ConcreteApril2020.indd 47 26/03/2020 10:05 CONSTRUCTION CHEMICALS Protection of urban spaces – sustainable mineralisation of concrete and other construction substrates Concrete structures, slabs and paving stones are present in existing cities and their use is becoming ever-more widespread in new urban developments and many other challenging environments. Decorative concrete (cast- in-situ or precast) and, in the broadest sense, ‘mineral’ families of products have been present in the heart of cities for several decades. Existing concrete structures, plus new and future projects, are opportunities for sustainable mineral protection solutions. Chris Sugden and Olivier Debas of Hydro-Mineral International report.

rom an environmental perspective, specifiers and contractors within the built environment seek F effective and evermore sustainable surface protection solutions, decreasing or eliminating the use of oil-based products. Surface treatment by inorganic mineralisation – not derived from the oil industry – is an effective non-film-forming permanent treatment and is not sensitive to UV. Application is by brush or spray. In addition to the advantage of initial carbon footprint reduction, there are many longer- term benefits. Why protect substrates? Many mineral protection solutions are particularly aimed at local authorities – small, medium and large municipalities – as the maintenance costs are their responsibility. The advantages linked to ease of maintenance and cost savings generated by mineral protection will be ever-increasing focal points, as local authorities need evidence The effects of water on concrete slab in treated and untreated to facilitate decision making. areas: 300 bar/26 litres/minute (1560 litres per hour). There are also cost requirements to consider in terms of effective cleanliness, without excessive local nuisance, and the needs of retailers who wish to limit the Which protection? presence of cleaning machines in front of Surface treatment of concrete can be carried their stores. out by two types of treatments: organic Effective mineralisation surface treatment chemistry and mineral (inorganic) chemistry. projects have resulted in increased quality of life for local residents and business owners: Organic chemistry treatment water and detergent savings achieved; This is the chemistry of synthetic polymers increased cycle intervals of cleaning (petroleum-based) from which resins, schedules; and the reduction of noise varnishes, silicones and bitumen are derived. pollution. Consumption of water, energy This chemistry is not sustainable and and chemical products has been shown to be protection applications need to be reapplied reduced by approximately 30–40%. every two to five years depending on the

48 concrete www.concrete.org.uk APRIL 2020

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products, their exposure to UV rays and their Applications abrasion behaviour. All porous mineral substrates can be mineralised: stone, terracotta, common and Inorganic chemistry treatment aesthetic concretes, slates, granites, renders The mineralisation reaction is definitive; it’s a and screeds, paving, tile joints, etc. The kind of cold liquid glass, occurring once in the mineralisation consolidates the substrate to life of the material. The mineral constituents make it more resistant to frost, de-icing salt of the product will be integrated naturally in and high-pressure cleaning, while facilitating the porous structure of the material to form its maintenance. silica (glass – service life approximately 4000 Mineralisation reduces drying times and years). limits the impregnation of greasy substances The development of the unsustainable and the adherence of chewing gum. Non- organic oil-based chemical industry after film-forming, mineralisation leaves the World War II led to the disappearance of material in compliance with slip standards, early mineralisation techniques in favour of allows the material to breathe and retains its organic chemistry. natural appearance. Formulation differences The term ‘mineraliser’ has developed substantially over the past few years in France, but not all mineralisers give the same result. The development of in-house products and the problems encountered by some other manufacturers have shown that it is possible to obtain an effect contrary to the one sought.

“Surface treatment of concrete can be carried out by two types of treatments: organic chemistry and mineral (inorganic) chemistry.”

Some mineralisers can cause an alkali reaction, which modifies the pH of the concrete and as a consequence, accelerates Magnification of mineralised carbonation. This phenomenon leads to the substrate at 60x. oxidation of the steel reinforcement in the concrete and creates spalling. In other cases, the mineraliser causes an increase in flaking under the effect of freeze– Functions of hydro-mineralisers thaw. Some mineraliser formulations may In concrete and other cement-based cause excessive hardening of the substrate, materials, there is the presence of slaked lime causing it to spall for no apparent reason. and in this there is a tiny part of unslaked For technical proof of the advantages lime (known as free lime), which acts like of mineralisation, Hydro-Mineral has a blotting agent. At the same time, mineral over 30 test reports carried out in different materials are more or less porous depending independent laboratories. In 2018, as part on the capillary networks that compose them. of a continuous improvement process for Hydro-Mineral mineralisers penetrate these products, the company launched the the substrates by capillary action, where production of Environmental and Health they crystallise the lime and form silica in Declaration Sheets (FDES) for these flagship the pores. Sealing is achieved according to products. This approach provides a better the saturation rate of the silica pores and understanding of the impact of mineralising is invisible to the naked eye. In harmony products in the aqueous phase and enables with the environment and treated materials, the communication of this information to mineralisation is not sensitive to UV nor to specifiers and users. abrasion and the silica remains inert; it does FDES can be consulted on the INIES not generate any decomposition rejection. database (www.inies.fr/home). „

50 concrete www.concrete.org.uk APRIL 2020

45-56ConcreteApril2020.indd 50 26/03/2020 10:06 Linear drainage on M6 smart motorway scheme

Aqua-Slot lifter being used to help with line and level.

Installing an effective motorway drainage system can be a challenge due to strict installation schedules, limited work area space, safety concerns and the proven efficiency of a system to cope with demanding rainfall events. Jeanette Edwards of Stanton Bonna looks at an innovative precast solution installed on the M6.

he upgrade of many motorways to While reviewing options, Kier met with smart motorway schemes provides Stanton Bonna at the Highways UK event in an opportunity to improve drainage 2017 to discuss developing a precast product. T capacity and avoid standing water Initially, it found a product that was already issues caused by existing drainage systems available and supplied by the precaster, which being overwhelmed. was called Slot Drain. This was used as an Traditional methods of road level drainage, initial basis for the design. such as cast-in-situ and slipforming, can be a lengthy restrictive process as they rely on good weather, no congestion and on-time The completed drainage system. deliveries of materials. Traditional methods also require more labour, plant and equipment – plus cast-in-situ requires temporary formwork and bracing to avoid flotation and movement.

Product design During the early stages of the M6 J13–J15 Highways England smart motorway scheme, Kier’s engineering and efficiencies team looked at various on-site and off-site options. After reviewing the risks of quality and programme constraints with in-situ options, it was decided it required an off-site option for the linear drainage. This would help meet the objective of improving certainty of the programme, reducing congestion and improving vehicle throughput on-site.

www.concrete.org.uk APRIL 2020

45-56ConcreteApril2020.indd 51 26/03/2020 10:06 ROADS RAILWAYS TUNNELS

After some discussions and further Manufacture designing, drawings and defining between Once this off-site linear drainage solution the precaster and main contractor teams on was designed and approved, the next the required specifications, a new design was challenge was to ensure capacity could be created specifically to meet UK highways met. Working together with Kier’s area team, standards. This evolution is the precast a production programme was agreed to concrete Aqua-Slot Drain, which is made to schedule in 31km of product. BS EN 1433(1). With the investment of further moulds, The design is a rectangular shape with an the precast production capacity was increased effective length of 2500mm. The top surface to over 400m per week. Just-in-time delivery of each unit contains seven trapezoidal slots was planned to ensure continual installation. (size 40 × 130mm), which allow for rapid The installation process involves rainwater run-off while pulling detritus excavation, levelling and preparation of the through to help avoid blocking. Each unit has bedding (on Type 1 and regulating sand a socket one end and a spigot on the other to layer). A joint lubricant is then applied to the enable correct jointing and alignment, plus precast product seal and each unit is lifted an integrated gasket stops the egress of water. into place. A spigot unit is pushed into the The design allows a 1° deflection in all plains. socket of the previously laid unit. Backfill A smooth-bore centre ensures the efficient and compacting work is then carried out as flow of water away from the area. Grated required. A rodding access point is provided rodding points and catchpit sumps complete every 25m. the system, with a kerb option also available. After initially using a block grab to off- The incorporated ironwork and sump unit load and push together during installation, means that once the unit is installed there is the team developed the Aqua-Slot Lifter. virtually no other follow-up work required. This was used to help lift and position the Factory-made units are high quality to product in place for easier installation. tight tolerances and CE marked. It means Rapid installation achieved outputs in a reduced workforce around the operation, excess of 200m per day per three-operative minimising the people–plant interface and an team. Four lorries per day (50+ linear metres ability to change work fronts with minimal per lorry load) regularly provided the 200m. impact if blockers are identified or there This caused minimal site obstruction, with are unforeseen issues; this provides greater flexibility to work in multiple locations flexibility. simultaneously and quickly move from one string to another. Installation of such units is rapid in virtually all weather conditions, requiring minimal plant and manpower. There is also reduced waste compared with wet casting, as no cutting out is required to form outlets. The system also proved to be safer, with no need for saw cuts, minimising HAVS issues. For the M6 smart motorway, some 14km of Aqua-Slot was provided in the central reservation and 17km in the verges. Richard French, project director of M6 13–15, says, “In the first weeks of laying, outputs were better than expected and we are very pleased with the product. Any reduction in trades and numbers in what is a very constrained environment has to be seen as a positive.” „ Reference: 1. BRITISH STANDARDS INSTITUTION, BS EN 1433. Drainage channels for vehicular and pedestrian areas. Classification, design and testing requirements, marking and evaluation of conformity. BSI, London, 2002.

Precast units in place in the central reservation on the M6.

www.concrete.org.uk APRIL 2020

45-56ConcreteApril2020.indd 52 26/03/2020 10:06 TCS Photo.indd 1 17/08/2018 11:27:10 BNMBQDSD OGNSNFQ@OGX

BNMBQDSDmagazine prides itself on giving concrete a • It’s all about the angles • The people behind the bold, vibrant image. Our front covers are an important buildings aspect of that goal... • First light on-site • Sunset and evening. WE invite all budding amateur photographers among our readership The best photos will be used in to submit suitable images for use on the front cover of BNMBQDSD or future editions of the magazine and Concrete Engineering International magazine. the photographer provided with a framed high-quality print of the cover featuring their submitted image. Photos must be sized at a minimum To get you started here are some possible categories: of 185mm (width) × 235mm (height) at 300dpi resolution (or 2200 × • Breathtaking buildings 2800px). • Work in progress A list of full terms and conditions can be requested from the Editor. • From the ground up E-mail: [email protected]

TCS45-5 Photo.indd6Concrete A 1pril2020.indd 53 17/08/201826/03/2 0 11:27:1020 10:06 CONCRETE ON-SITE On-site concrete solution to London piling project

Mixamate recently teamed-up with Cannon Piling, to pump concrete directly into piles being drilled in the tightest of central London locations. The month-long job required daily pours and with other large-scale builds going on around the site in every direction, accessibility and flexibility were key. Chris Smith reports.

ncreasingly felt to provide a safer and sturdier alternative to traditional foundation methodology, concrete I piling has become more popular in recent years. This is particularly true in central London, where space can be severely limited and high-rise buildings are still very much the order of the day. On a recent job, which was wedged between Victoria Station and Parliament Square, building work could simply not have been undertaken without using this technique. “The job was very restrictive both in terms of the size of the site itself and all of the other builds going on around it,” says Tom Goodchild, contracts manager for Cannon Piling. “Due to the space restrictions, we had to use one of our smallest machines and that piece of equipment can’t have concrete being pumped into it non-stop, because it would overflow faster than it goes into the ground. We were provided with a kind of ‘concrete- on-demand’ service, where on-site pours could be switched on and off at will, and administered exactly when we needed them.” Once set, concrete piles are used to support more shallow building foundations and are topped by either a ground beam or a slab. In the case of the Victoria job, Cannon was preparing the site for the construction of a new block of flats and required a DC3 CEM II concrete, for which specialist cement had to be transported all the way from Scotland. The Mixamate Concrete Pumping Truck incorporates an on-board computer system that produces a printout ticket of the nature of the concrete it produces, making the tie-up The cramped space between the two companies a natural fit. on-site in London. A simple signalling system was set up between Cannon Piling’s rig operator and Constructing foundations in this way can the truck driver, with the two machines be a comparatively time-consuming process, connected via the latter’s on-board pumping and a month is an unusual timeframe over hose. When enough concrete had poured into which to conduct a single mix-on-site job. the piling machine, the pump was switched But it was this level of manual control and off until the next pour. attention to detail that allowed Cannon

54 concrete www.concrete.org.uk APRIL 2020

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Above and left: Pumping had to The presence of other construction be tightly controlled. projects around the site made the pumping job restrictive. Where mix-on-site jobs were previously carried “ out via barrow or mini-dumper, or required a “separate concrete pump to be on-site, delivery of the entire service is now from a single vehicle.

Piling to complete the work with maximum precision and zero waste. The All-in-One Concrete Pumping Truck has helped to advance the mix-on-site process significantly in recent years. Where mix-on-site jobs were previously carried out via barrow or mini-dumper, or required a separate concrete pump to be on-site, delivery of the entire service is now from a single vehicle. Customers like this because it means that a single driver can arrive on-site in a single truck, with no mess and no waste. In the case of a sensitive piling job such as this, the combined mixing pan-pump approach is particularly useful, as it allows us to meticulously control the flow of concrete throughout the days and weeks. This one-truck approach was essential, not only in the piling process itself but also to the environment in which it took place. A single road was being used to provide access to multiple construction sites, on All-in-One Concrete which the truck needed to park in order to Pumping Truck. run its pumping hose directly onto the site. But because all of the works were being process has evolved in recent years and the administered by a single mobile batching way in which more modern techniques such plant, it meant that this vehicle could be as pumping and piling are being used to moved at various points throughout the day advance the process. By combining the two, to allow different suppliers to access different Cannon and Mixamate were able to create sites, without disturbing the piling process. a streamlined system to administer concrete The job represents a good example of to a tight location, without disturbing any how the traditional mix-on-site concreting other nearby sites. „

www.concrete.org.uk APRIL 2020 concrete 55

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coversConcreteApril20.indd 4 24/03/2020 15:26 ~cordek

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