THE MAGAZINE OF THE CONCRETE SOCIETY Volume 54 October 2020 Issue 08

concreteVisit: www.concrete.org.uk

Dust to dust Consigning poor H&S to history

Car parks Corrosion testing

Research/development 3D-printable AACCs

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COVERS OctoberCONCRETE2020.indd 3 29/09/2020 11:49:55 Contents 3 From the Editor 4 World News 6 Letter to the Editor/Obituary

Slipform Construction 8 Straight to the top Eric Vere

Car Parks 12 Green Street multi-storey car park, Jersey Martyn Lewis 16 Car park corrosion testing Warren Thomas 19 Concrete companies come together for charity project Concrete report

Sawing and Drilling 21 Consigning poor health and safety to dust Walid Hussain

Research and Development 24 3D-printable cementitious composites Seyed Hamidreza Ghaffar and Mehdi Chougn 28 Towards a low-carbon future Mike McCarthy, Moray Newlands and Rod Jones

Durability/Aggressive Environments 30 Silica fume concrete – high-performance concrete perfect for hostile environments Lee Baldwin 32 Multi-faceted approach to ensure the durability of concrete in aggressive environments Kai Yang, Susan Bernal and Muhammed Basheer

Formwork and Falsework 36 BIM and temporary works Billy McCormick and Paul McLaughlin 38 On the move in one of London Underground’s busiest stations Concrete report

40 Features List/Ad Index/Subscriptions

concrete magazine is produced in-house by The Concrete Society, The October 2020 cover a not-for-profit, independent membership organisation dedicated to Dust is one of the biggest supporting the use of concrete, the most widely used building material in health and safety concerns the the world. construction industry is facing. It poses a significant risk to Established in 1966, and with members from around operatives wellbeing and employers’ the world, The Society has built on its technical base operations. However, there is still to become a leading provider of information, serving a lack of understanding around the needs of clients, architects, engineers, specifiers, these detrimental impacts, and the suppliers, contractors and users of concrete. solutions that exist to address the associated problems. Visit: www.concrete.org.uk See page 21

(Photo: Hilti.) Follow concrete on Pinterest Go to pinterest.com/concretemag/boards, click on a board to view images from projects featured in current and past issues. Share images with Follow: @ukConcrete Find us on: others within the concrete community.

1-7OctoberCONCRETE2020.indd 1 29/09/2020 11:50:18 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.

The Society receives special support from the following:

SPECIAL CATEGORY MEMBERS

www.breedongroup.com www.laingorourke.com www.tarmac.com

www.cemex.co.uk www.sir-robert-mcalpine.com www.hanson.co.uk

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

1-7OctoberCONCRETE2020.indd 2 29/09/2020 11:50:19 FROM THE EDITOR

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

EDITORIAL ASSISTANT: Helen Marney No room for Tel: +44 (0)1276 607159 [email protected]

TECHNICAL ADVISOR: Richard Day complacency DESIGN: Darryl Killoran To err is human – we all make mistakes. Both at home and in the workplace errors creep in. The trick is to learn from them and move on. SALES REPRESENTATIVE: Vicky Ashby Tel: +44 (0)20 3859 7097 [email protected] s any amateur DIYer knows, was described only as “engineering issues”, the best old adage to follow is to although news outlets were reporting errors James Pembroke Media Ltd is The Concrete Society’s appointed measure twice and cut once (then with reinforcement. advertising sales agency. A use the sander to make it fit). As In a similar vein, in Sheffield the concrete a nation with a passion for DIY, we regularly frame of a new university building faced SUBSCRIPTIONS MANAGER: put up shelves with a noticeable gradient, being pulled down after reportedly suffering Val Goddard splash paint over untouched skirting board from structural problems due to piling. Tel: +44 (0)1276 607149 and produce cupboards with doors that drop [email protected] six inches when opened. Semi-skilled but Costly mistakes concrete is published 10 times a year (2020) enthusiastic, our errors only matter at home. These two examples will be very costly and sent free to all Concrete Society members. Errors in the workplace though are rather mistakes to rectify and should also serve as a Annual prepaid subscriptions for 2020: more serious. And in construction the reminder that complacency has no place on UK £125, Europe £150, outside Europe £170 (prices inc. p&p). Single copies and back outcome can be catastrophic; from millions of the construction site or in design offices. issues: £15 (exc. p&p). pounds of damage to a worst-case scenario of Think about every different party involved fatalities. One only needs look at the annual in planning, designing, specifying and THE CONCRETE SOCIETY figures from the Health and Safety Executive constructing a project and its various phases. President: to see the effect that errors of judgement, Think about all the building regulations Deiniol Williams application or knowledge can have on lives. being followed, all the Standards invoked and Recent collapses of bridges in America and all the guidance adhered. And yet still, in the Managing Director: Europe, with resulting loss of life, further two examples shown, errors were made or Kathy Calverley mbe highlight the seriousness of human error. calculations mistaken. The Concrete Society, Of course, this is why so many rules, It’s always easy to believe, ‘it won’t happen Riverside House, 4, Meadows Business Park, regulations, legislation, Standards, best to my project’, or ‘these things rarely happen’. Station Approach, Blackwater, Camberley, Surrey GU17 9AB, UK practice guidance etc are devised to mitigate But the fact remains that they do occur. And Tel: +44 (0)1276 607140 such errors. so all the seemingly endless time checking Fax: +44 (0)1276 607141 And yet despite all these efforts, mistakes and double-checking designs or calculations, e-mail: [email protected] happen. Thankfully, major errors are very few regulations and rules, or updating or www.concrete.org.uk and far between. Which is why when they do refreshing skill sets etc is never time wasted. Printed by Bishops Printers come to light they are all the more surprising. Enjoy the issue! Portsmouth, Hampshire So the reporting of two stories over the © The Concrete Society, 2020 summer concerning major issues with ISSN 0010-5317 concrete-frame buildings should make everyone in industry sit up and take notice. Neither Concrete nor The Concrete Society are In Manchester, a new development responsible for the statements made or the opinions of high-rise flats made the news, when expressed in this journal by third parties and James Luckey, Editor structural problems meant that the recently organisations. Tel: 01276 607158 completed ten-storey concrete core had [email protected] to be partially demolished. The problem

www.concrete.org.uk October 2020 concrete 3

1-7OctoberCONCRETE2020.indd 3 29/09/2020 11:50:20 WORLD NEWS NEWS IN BRIEF Concrete targets „ UK • Appointment Simon Willis, CEO of Hanson UK, has been appointed Mineral Products Association (MPA) chair, succeeding carbon-neutral future Martin Riley, senior vice-president at FORTY of the world’s leading cement reuse and recycling of concrete and Tarmac. Nigel Jackson, CEO at MPA, said, and concrete companies recently buildings, and harnessing concrete’s “Simon’s wide industry knowledge and unveiled a joint industry ‘2050 ability to absorb and store carbon experience will be invaluable as we play Compact mixing Climate Ambition’. The ambition from the atmosphere. our part in the economic recovery, while LIEBHERR has responded to growing continuing to operate safely and securely statement demonstrates the The climate ambition sets out commitment of the industry across a global vision for the long-term demand for smaller, reliable mixing and tackle major issues.” plants by launching the LCM 1.0. The the globe to drive down the CO2 sustainability of concrete, the vital footprint of the world’s most used building material that has shaped the compact plant will allow contractors „ UK • Training man-made product, with an aspiration modern world. to produce their own concrete with The National Federation of Builders has to deliver society with carbon neutral Dinah McLeod, GCCA chief low procurement costs. The plant is launched a new online and face-to-face concrete by 2050. executive, said, “As we face the easy to install, transport and operate training service to deliver a full range of Launched by the Global Cement challenges for future generations with a control system operated via construction-specific training. Subjects and Concrete Association (GCCA) and begin global economic recovery, a lap-top computer. The plant has range from health and safety, and safe on behalf of its member companies, concrete will be even more critical an output of up to 60m³ of fresh operation of plant and equipment, concrete. Various aggregate silos through to business development and the ambition statement represents a to building the sustainable world of critical milestone for the industry. It tomorrow. That is why we are making with a storage volume of 40–100m³ online training, Visit: www.builders.org. are available and the plant can be uk/training. is the first time it has come together this commitment today, in order globally to state a collective ambition that our crucial industry aligns with equipped with up to three 100-tonne for a carbon neutral future. The global targets, including the Paris cement silos. „ Mexico • Infrastructure statement identifies the essential Agreement.” CEMEX has supplied more than levers that will be required to achieve Albert Manifold, GCCA president 70,000m3 of specialised concrete for Broken concrete carbon-neutral concrete, including: and chief executive of CRH, said, “The the construction of Park Garage, the reducing and eliminating energy 2050 Climate Ambition represents second largest vehicle storage building to replace sand in the world, which has the capacity to related emissions, reducing process commitment to further reducing emissions through new technologies emissions and ensuring that the vital ETH Zurich spin-off Neustark has store and transfer up to 10,000 vehicles developed concrete recycling plants destined for export from the Port of and deployment of carbon capture, product we provide can be delivered that can store CO over the long term. Veracruz in Mexico. more efficient use of concrete, on a carbon-neutral basis by 2050.” 2 Neustark’s pilot plant turns broken

concrete and CO2 into stone granulate „ UK • ICT that can serve as a replacement for The Institute of Concrete Technology sand and gravel in fresh concrete. (ICT) will publish the 25th edition of CMABREEDON’S purchase concern of CEMEX oversuppliers. The asset CMA is therefore sale Founders Johannes Tiefenthaler and the ICT Yearbook in January. Meanwhile, assets raises competition concerns concerned that the deal could Valentin Gutknecht say that what is Raman Mangabhai has been elected in the supply of building materials in result in a substantial lessening of particularly special about Neustark’s an honorary fellow for his contribution some parts of the UK, the Competition competition, leading to higher prices technology is that it binds CO2 in the to the Institute. Raman is a materials pores and on the surface of concrete technologist with broad experience and Markets Authority (CMA) has said. and lower-quality building materials granulate as limestone. This granulate in academia and industry. Under his Breedon announced in January that for UK construction projects. can then be mixed into fresh concrete presidency of the ICT, he was responsible it had agreed a £178 million deal to Colin Raftery, CMA senior director, as a replacement for sand and gravel. for launching the ICT Showcase, Annual buy approximately 100 CEMEX sites, said, “As many of these materials are Report, CPD app and other initiatives. including aggregates quarries, ready- sourced locally, it is vital to ensure The upgraded granulate means that mixed concrete facilities, asphalt that enough competition will remain less cement is required, while the properties remain the same. Germany • Sustainability plants and a cement terminal. at the local level so there is enough „ The CMA found that the deal choice and prices remain fair.” “I’m very excited by the fact that Interior finishing is currently being gives rise to competition concerns in The CMA has since said that this solution isn’t just coming in five carried out on world’s first Passive House or ten years – it’s available now,” hospital in Frankfurt, Germany, after an relation to the supply of ready-mixed undertakings offered by Breedon said Gutknecht. The granulate will extremely successful airtightness test concrete, non-specialist aggregates might be acceptable. This will require gradually be brought into operation for the 78,000m2 project. The Passive or asphalt in 15 local markets across the divestment of a small number at Neustark’s pilot plant at the Kästli House Institute in Darmstadt will provide the UK. In all these local markets, of ready-mixed concrete plants and certification for the project. the two businesses currently have a an asphalt plant in England, and two concrete facility near Bern. large presence and compete closely, quarries and a cement terminal in In a further project, supported by with limited competition from other Scotland. the Federal Office for the Environment „ UK • Infrastructure and the Swiss Climate Foundation, Balfour Beatty has been awarded a Neustark aims to demonstrate the £108m contract to design and build a value added along the whole value dual carriageway linking the M67 with SIKA has appointed Drummond Welsh as its national sales manager for creation chain: the plan is for the the A57 in Manchester. The company will concrete. With over 25 years’ experience in admixtures for ready-mixed CO to be sourced from a biogas design and construct dual-and single- concrete, coupled with spending 11 years in the Middle East, Welsh has a 2 separation plant at the Arabern lane carriageways, and an underpass wealth of experience with best-practice concrete technologies for extreme underneath the village of Mottram. conditions. He is a prominent figure within the concrete community, as a past wastewater treatment facilities in chair of both The Concrete Society Scotland Region and construction industry Herrenschwanden. Neustark will then charity, Lighthouse Club. treat the demolished concrete in its

pilot plant using this CO2.

4 concrete www.concrete.org.uk October 2020

1-7OctoberCONCRETE2020.indd 4 29/09/2020 11:50:20 THE POWER BEHIND THE PERFORMANCE

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1-7OctoberCONCRETE2020.indd 5 29/09/2020 11:50:20 LETTER TO THE EDITOR/OBITUARY Mitigating Risk

Dear Sir, harmony and rhythm of life within the city. Winogrand observed, it’s not the thing itself The concrete blocks have an aesthetic but how you make it look. I remind my e are all too familiar with quality blending into the landscape. Lunchtime students of this regularly. Many of the new cars and trucks being used by drinkers use them as additional seating for mitigation systems are metal and painted terrorists to cause carnage the busy market and seen from above the black. While they serve their purpose they are around the world. There have ones outside the British Museum resemble a not beautiful.▮ Wbeen numerous responses to limit the threat perforated line. and are often referred to collectively as ‘vehicle American street photographer Garry Nick Brewer mitigation’. They have morphed into the urban landscape becoming street furniture familiar to city dwellers like benches or bollards. As a photographer and educator, I capture their beauty to bring appreciation of these essential security measures. I love concrete. It is the texture and tone that makes it so fascinating. Borough Market and Westminster Bridge, the scenes of terror attacks in 2017–18, respectively feature in the latest pictures (www. nicholasbrewer.co.uk). The work shows a Street scenes and furniture feature in Mitigating Risk.

Peter G Fookes (1933–2020)

It is with great regret that we report the The huge expansion of the infrastructure death of Professor Peter George Fookes construction sector in the Gulf States in the on 7 September 2020, aged 87 years. 1970s unfortunately resulted in these often- fine new concrete structures showing signs of rof Peter George Fookes was first early and rapid deterioration. Dr Fookes was and foremost a geologist, but one employed by the (mainly British) consultants who specialised in its application and contractors to determine the cause of Professor Fookes (left) receives honorary to engineering – indeed he has this deterioration. He identified inadequacies fellowship from ICT president Tony Roeder. Pbeen referred to as the ‘father of engineering in the concreting materials used and, more author for The Concrete Society’s major work, geology’ – and specifically the effect of importantly, made it clear that the then current the two-volume Gulf Guide of 2002. He was geological properties on the materials used in standards were not adequate for the onerous writing right up to this past year, with The concrete construction. exposure conditions in the arid lands of the Engineering Geology of Concrete in Hot Dry Born in Romford on 31 May 1933, his Middle East. Without his work, it is difficult to Lands issued in 2019. education took him from a BSc in chemistry see how the extremely rapid development of His achievements were matched by awards. to a PhD and eventually a DSc(Eng) and by the the modern Gulf States, which rely so heavily By 1983, he was visiting professor at Queen mid 1960s he was identified with the career in on concrete structures, could have taken place. Mary College London and, in addition to his which he was to make his mark. By the mid- These developments are reflected in the academic qualifications, was also a chartered 1970s, he was living in Surrey and working literature, with over 180 papers published geologist and a fellow of the Royal Geological as a consultant in private practice, retained in such as the Proceedings of the ICE and the Society, Royal Academy of Engineering and part-time variously by Rendel Palmer & Tritton, Quarterly Journal of Engineering Geology. He IOM3. In 1992, he was elected an honorary Messrs Sandberg and Engineering Geology. He wrote numerous articles for Concrete, notably fellow of the Institute of Concrete Technology described himself as a ‘consulting engineering in the 1970s and early 1980s, and presented and delivered the fifth Sir Frederick Lea Memorial geologist’ and specialised in the performance of papers to the joint Concrete Society/Bahrain Lecture at that year’s ICT’s convention. construction materials as affected by different Society of Engineers conference in 1991 (CS ▮ terrains and climates. 108). Some years later, he was a contributing Ted Kay and Edwin Trout

6 concrete www.concrete.org.uk October 2020

1-7OctoberCONCRETE2020.indd 6 29/09/2020 11:50:21 Recover with Confidence

Improve and regain your output with efficient and safe products and services. Formwork Scaffolding Engineering Discover how we can help you recover Maintain Recover with confidence: www.peri.ltd.uk output confidently www.peri.ltd.uk

1-7OctoberCONCRETE2020.indd 7 29/09/2020 11:50:21 Straight to the top Slipform is by no means a new invention – it has been used in UK construction since the 1980s and for the past ten years it has been used regularly to create many structures around UK. Eric Vere of Stephenson reports.

Above: Placing boom here are several commonly held Formwork on top deck of rig. misconceptions with regard to The slipform rig is made of modular slipform: it is only suitable for very components: jacks, yokes and climbing tubes, T tall structures; it must be carried which can be arranged to form any required out on a 24-hour cycle; and it is prohibitively shape, from a circular core with acute internal expensive. None of these are necessarily true. wall angles to the simplest of boxes. Similar principles of design exist with all Limitations slipform rigs: the locations of the yokes, jacks Having used slipform on structures from and climbing tubes need to be placed to give under ten storeys to over 50, at Stephenson, an even lift across the entire rig and within it has also proved to be the preferred system their overall lifting capacity – generally at no for the construction of reinforced concrete more than 1800mm spacings, and 6 tonnes stair and lift cores. That said, the process is per jack. Where possible they should be not without its limitations; from the outset, positioned to ensure that climbing tubes are the core structure needs to be designed to be not within openings, which will reduce the free-standing – ideally without any additional amount of secondary bracing required within temporary works – and although adaptions the openings. can be undertaken, slipform is best suited to designs that do not require adaptions to An essential component to the the layout or thicknesses of walls within the “ sliding height. successful use of slipform is to ensure that Both the tolerances and the required the concrete setting times are controlled to finish for the final structure need to be taken match the required rate of climb. in to account. Slipform is generally only completed to a tolerance of ±25mm across ” the entire height of the structure with the The slipform rigs are constructed at use of laser plummets, with the finish classed ground level and the shutters always remain as an ordinary finish, as defined by section fixed during the sliding process. The rig 8.6.1.2 of the National Structural Concrete itself consists of multiple levels, which are (1) Specification 4th Edition . referred to as decks: top deck; working deck;

8 concrete www.concrete.org.uk October 2020

8-26OctoberCONCRETE2020.indd 8 29/09/2020 11:50:42 SLIPFORM CONSTRUCTION

and hanging decks, with stoppages required The concrete is placed evenly around the only to fix on the hanging decks as the slide rig in 200mm-high layers. The rig will start to proceeds, or to make any required adaptions. lift when the first layer has set and the second layer has started to stiffen. On a 12-hour slide, Setting times concrete remains in the formwork overnight, An essential component to the successful which will leave visible bands in the finished use of slipform is to ensure that the concrete concrete, whereas with a 24-hour slide, it is setting times are controlled to match the possible to use concrete buffing machines on required rate of climb. During the slide, a the hanging deck to improve finish, although range of mixes may be required to allow for this is not to the standard of an architecturally variations on-site; for example, a constant finished product. ambient temperature may need to be checked With reinforcement, some design with a trial mix before recommencing a elements are similar to those used in slide on a Monday morning after a weekend jumpform, namely ‘conti-bar’ to pick break. High-strength concretes may require up floor plates, although overall the specialist admixtures to ensure pumpability reinforcement detailing can be quite and consistence retention, while maintaining different to allow for the threading of the compressive strength. horizontal bars under the yoke channel, or

Slipform elevation.

www.concrete.org.uk October 2020 concrete 9

8-26OctoberCONCRETE2020.indd 9 29/09/2020 11:50:42 SLIPFORM CONSTRUCTION

AWARDSAWARDS20202020

Slipform plan. Wall finishes as they emerge from the slipform.

a horizontal ‘stagger’ of the laps on vertical It is often desirable to complete the lobby bars around the slipform rig as it progresses slabs ahead of the floor plates, whether that upwards – this is to prevent any undue be for stability reasons, or to provide access in Announcement - live online! urgency in fixing to the entire rig at once. advance of the following floor plates. Using a lightweight steel pan with preattached Positive hand rails, the stairs can be completed within There is a significant reduction in dependency the slipform from below without the need during the slide – not only on cranage, but to open up the rig, which in turn allows for The winners of The Concrete Society also on-site storage space, often two of the earlier commencement of following trades, scarcest resources on tight city projects. When such as the lift installation. the rig is also fixed with a placing boom Awards 2020 will be announced by the release on the top deck and connected to a static Has its place concrete pump, dependency on cranage is Although there can be financial implications further reduced and while the crane is still to slipform, such as the need for three-phase of a video on our website at 3pm on the required to feed items such as reinforcement power and the potential need to jump the throughout the day, it is generally free to be crane earlier in order to prevent following working on floorplates as the slipform out- floorplate works from becoming jib bound, 9th November. accelerates the rest of the structure and moves slipform certainly has its place in UK off the project's critical path. construction – and not only for the tallest building projects. ▮ Reference: 1. CONCRETE CENTRE, National Structural Concrete Specification for Building Construction. Edition 4, Camberley, 2010. Available at: https://bit.ly/2R7rchv. www.concrete.org.uk

We thank our sponsors for their continued support of the 2020 Awards and CRASH, as our nominated charity for this year.

Premier sponsor For further information about The Society Awards email: [email protected] or call: 01276 607140 Above: A busy slipform to deck, placing boom and toilet. Left: The working deck showing a door opening being cast in, with a jack and yoke visible behind.

Supporting sponsors

10 concrete

8-26OctoberCONCRETE2020.indd 10 29/09/2020 11:50:44 AWARDSAWARDS20202020

Announcement - live online! The winners of The Concrete Society Awards 2020 will be announced by the release of a video on our website at 3pm on the 9th November. www.concrete.org.uk

We thank our sponsors for their continued support of the 2020 Awards and CRASH, as our nominated charity for this year.

Premier sponsor For further information about The Society Awards email: [email protected] or call: 01276 607140

Supporting sponsors

8-26OctoberCONCRETE2020.indd 11 29/09/2020 11:50:44 Green Street multi-storey car park, Jersey Located in St Helier, Jersey, Green Street multi-storey car park spans five levels, with 670 parking spaces. The in-situ concrete car park was refurbished for the Government of Jersey as part of a £2.3 million contract. Martyn Lewis of Concrete Repairs Limited (CRL) reports.

he refurbishment of Green charging bays and additional disabled parking Above: Split-level Street multi-storey car park was bays. ramps. undertaken as part of an ongoing Repaired Above left: T maintenance programme carried Typical level out for the Government of Jersey and Green Street multi-storey car park had complete. was funded by revenue generated from previously been repaired and protected by user parking charges. CRL had already CRL in 1999–2000 when extensive structural refurbished two other car parks for the States repairs were carried out, coatings applied and of Jersey – Pier Road and Sand Street. Green an impressed current cathodic protection Street was the third and most challenging (ICCP) system installed. As a testament to structure to be renovated. The repair work the high standard of the works carried out in was carried out over a 34-week period, 1999–2000, minimal maintenance had been completing in October 2019. required since that refurbishment and this Green Street multi-storey car park phase of works was only needed to bring the provides parking spaces for shoppers, tourists car park up to current-day standards. and commuters in St Helier, Jersey’s capital. The overhaul was mainly required as the The structure is attached to the States existing deck and wall coatings had exceeded of Jersey Police HQ and throughout the their life expectancy and to maintain refurbishment it was crucial that there was protection of the concrete structure, now minimal disruption and that the car park needed to be overcoated, or stripped off and remained operational 24/7. To comply with renewed where necessary. Other typical these criteria, during the course of the project, problems were parking spaces being lost due it was only allowed to close one level of the to water ingress through the soffit dripping car park at a time. The overall objective onto and marking vehicles parked below, of the refurbishment was to transform the perimeter metal fencing corroding (due structure into a safe, vibrant parking facility, to the location of the car park in a marine while improving the look and feel of the car environment), and the existing lighting and park and providing improved electric vehicle lightning systems being dated and failing.

12 concrete www.concrete.org.uk October 2020

8-26OctoberCONCRETE2020.indd 12 29/09/2020 11:50:48 CAR PARKS

The project involved a complex, fast- • upgrading of the lighting system to LED moving programme with vehicle circulation • replacement of the existing lightning routes and pedestrian areas refurbished system with a modern wireless system during off-peak times. This necessitated the • drainage survey, repairs and additional use of high-quality, rapid-curing materials. installation to prevent ponding water. There were three segments to the works: internal car parking deck areas, communal Due to the use of sea-dredged aggregates staircases and external façade elevations. in the initial construction of the car park and the marine environment of Jersey, Noise the concrete structure had a high chloride As with all construction works, noise was an content. This had been controlled by the issue. Due to the proximity of the car park installation of an ICCP system 20 years to offices it was still necessary to encapsulate ago. However, with the need to remove the the working areas with acoustic hoarding and existing decking that was integral to the protective sheeting to keep the noise levels cathodic protection system, protecting the to a minimum. To ensure noise never went deck meant that a new strategy needed to be above an acceptable level, regular assessments introduced. were carried out. The main activities carried out on this project were as follows: All the concrete decks were prepared by • concrete delamination surveys planing“ and enclosed captive shot-blasting • water suppressed media shot blasting and surface preparation to remove existing pressure washing (to remove existing coatings) coatings and prepare the decks for the • extensive concrete repairs to decks, new anti-slip waterproof coatings. soffits, columns and walls ” • application of an anti-carbonation coating to all concrete surfaces After extensive testing and research, • mechanical movement joint installation a hydrogel treatment was specified. The • deck joint sealant replacement hydrogel works by penetrating into the • application of anti-slip waterproof deck concrete elements (the defective coatings coatings had to be removed first) and transforming • application of lines markings and all moisture within the substrate into a information symbols semi-solid hydrogel throughout the porosity • replacement of the existing cathodic network. This process physically binds protection system with a new innovative any free chlorides within the hydrogel impregnation waterproof solution to prevent corrosion inducement. The • back propping and new bearing pad Aquaron materials incorporated the hydrogel installation treatment with a migrating corrosion

Above: Final cleaning of decking. Right: Preparation work for application of deck coating.

www.concrete.org.uk October 2020

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inhibitor (MCI) to add to the natural installed to the deck of level five, between the passivation of the reinforcing steel. Following old and new decks, including a waterproofing the surface preparation process to decks and interface. In addition, two pedestrian the water blasting of perimeter parapets and staircases and the external façade areas walls, the hydrogel treatment and the MCIs concrete and metal balustrading areas were were applied to all concrete decks, internal carefully cleaned, repaired and coated. Each and external parapets, and walls. level of the car park was colour coded for ease All the concrete decks were prepared by of identification by using different colours on planing and enclosed captive shot-blasting the columns and the staircases. surface preparation to remove existing coatings and prepare the decks for the new Spirit of co-operation anti-slip waterproof coatings. This was Ross Fearnley, Government of Jersey project followed by the application of a partially manager, says, “This project was tendered reinforced heavy-duty, rapid-curing Triflex using an NEC3 Option A contract. This PMMA waterproofing decking system form of contract requires all parties to act incorporating a quartz anti-slip finish. This ‘in a spirit of mutual trust and co-operation’, layer of material protects the decks and ramps to provide the highest level of quality and from water ingress, chlorides, chemical attack finish to the end user. By working closely and heavy traffic, as well as the extremes with CRL with open communication and of weather on the top exposed deck. The an equal ambition to deliver a great project, Government of Jersey has been able to we were able to overcome issues in a timely brand its car parks using a colour-coded and cost-effective manner. This enabled the scheme within the Triflex surfacing, with project to finish on programme, despite much clearly defined parking bays and walkways larger areas of repair being required, as well as leading pedestrians to the newly refurbished additional structural works to replace bearing staircases. pads on an upper floor. In order to keep costs down, as well as “The waterproof colour scheme deck reduce waste, excess quartz was swept up and coatings have been adopted throughout recycled for future use, providing a saving Jersey car park refurbishments and provide of 25 tonnes of quartz. The use of a rapid- clear areas of traffic, parking and pedestrian curing PMMA, coupled with the use of fast- segregation, while providing future protection curing line markings and symbols, enabled to the structure. Carrying out these types all high traffic areas to be handed over within of operations safely, while keeping the car just hours of application, helping to reduce park open to the public, required close the time parking spaces were out of use. co-operation between the site management team and the client. CRL accomplished this Structural works and, where inconvenience to the public was Structural works were also carried out to a unavoidable, dealt with it in a professional previous new extension on level five, where and courteous manner.” poor detailing around the movement joint CRL was able to use innovative was leading to cracking of the structure. engineering solutions to deliver cost savings A number of beams were propped back to for the delivery of this scheme and any future the ground floor to allow the release and ongoing maintenance. The internal and separation of sections of the structure, and external concrete frame has been extensively new bearings were introduced to newly repaired and treated to enhance its durability, formed corbels to allow the structure at the improve aesthetics, increase personal safety, movement joint to move freely. and meet the client’s objectives of upgrading A new mechanical expansion joint was and increasing the life of its structure. ▮

Examination of original deck. Preparing for handover of another level.

8-26OctoberCONCRETE2020.indd 14 29/09/2020 11:50:53 Ancon lsotec

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8-26OctoberCONCRETE2020.indd 15 29/09/2020 11:50:53 Car park corrosion testing Aged reinforced concrete structures requiring assessment are common; however, when a car park only five years old displayed deterioration that is often only associated with older assets, it was obvious something was seriously wrong. Warren Thomas of Henderson Thomas Associates outlines how the company discovered the root of the problem.

mbedded post-tensioning with put forward. Shortly after, a very large piece cementitious grout is the most of concrete failed, falling from the car park common form of construction roof, prompting investigations to take place. E within the UK; it involves the The post-tensioned special inspection casting of extruded aluminium sheaths within (PTSI) at the car park consisted of initially the concrete element during the build, which inspecting the tendons and ducts in the areas allows the passing of strands to be stressed, of spalled concrete at the mid-span of the providing the structure with sufficient downstand beams, which had already been strength. On stressing the strands, the sheath identified during a cursory visual inspection. or duct is then filled with grout to remove In many of these areas, the metal sheath air pockets, protect the strands from outside surrounding the tendons was found to elements and ultimately bonding them to the have completely deteriorated, exposing the sheath. tendons themselves, which had subsequently undergone severe corrosion and loss in Inspection section. In multiple areas, the strands Initial works were carried out by a roped- themselves were broken and it was clear access company, which only involved that no grout had ever been present in some investigating the parapet anchorages, which locations. appeared to be in a satisfactory condition. This failure is a prime example of why it is However, signs of leakage at the anchorages paramount that grouting during construction were noted. HTA was asked to comment on is carried out professionally to eradicate air the findings and a testing specification was pockets within the sheath because areas with

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All figures: Exposed tendons in void. In many of these areas, the metal sheath surrounding “ the tendons was found to have completely deteriorated, exposing the tendons themselves, which had subsequently “undergone severe corrosion and loss in section.

no grout can lead to structural failure. ungrouted areas detected via non-destructive Due to the severe condition of the strands testing, then confirmed via localised noted in the initial inspection of the marked breakouts, clearly demonstrated the extent of locations, HTA was requested to carry out the defects within the car park that were set further post-tensioned inspections to areas in motion on construction. where there were no visible signs of defects. Ground-penetrating radar (GPR) was employed to locate the tendons and their depth to prevent damage to the sheaths and tendons during localised break outs. In the locations where voidage was detected via GPR, the post-tension ducts were found to be ungrouted and the associated strands suffering varying degrees of corrosion. In one location, water was found to be running out from one of the exposed post- tension ducts and it was clear that the strands themselves had been submerged in water for a significant amount of time. Also, the water appeared to refill the exposed tendon after rain fall during the site works. As it was with the other areas investigated, there was no grout present within this sheath to provide protection to the post-tensioning system. The risk posed by the presence of standing water within the post-tension duct cannot be understated; this, alongside many poor and

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It was latterly surmised that there had been a joint defect between the parapet and deck unit, and it was this that allowed the tendon to fill with water. It was believed that the water had been present since construction and had frozen during the winter months when stressing took place. This meant that due to the presence of ice, the grouting operation did not prove successful because of the presence of the ice within the duct. The anchor pockets were also exposed and inspected to check for corrosion and slippage of the strands from the anchor blocks. In this instance, the blocks only displayed surface corrosion and thus were not of concern for the durability of the structure. Works programme From the data collected from the PTSI concerning the condition of the post-tension strands and the lack of grout present within the ducts, a full remedial works programme was undertaken, in which the strands and sheaths were given sufficient protection to ensure the post-tension system was fully grouted. The effectiveness of the grouting process was confirmed by further, limited intrusive works. During construction of this post-tensioned structure, the presence of water within the ducts in the form of ice resulted in voidage within the sheath/duct. Better workmanship and on-site quality control would have eliminated such a scenario occurring. With this relatively new car park, the lack of initial quality control has often resulted in the exposure of the strands to moisture and oxygen, leading to aggressively rapid corrosion and loss of section. Ultimately, left untreated, this could reduce the structural integrity of the structure and its required Water leaking from load-carrying capacity far more quickly than PTSI duct. anticipated. ▮

Read concrete? Why not write for concrete? New contributors to the magazine are always welcome. Articles, case studies, papers and comments for submission can be sent to the Editor.

There is NO charge for article contributions; material is published on merit. Contact: James Luckey, Editor, Tel: 01276 607158 E-mail: [email protected]

8-26OctoberCONCRETE2020.indd 18 29/09/2020 11:50:57 Completed new car park Above and below: Construction of retaining wall, kerbs, paving and drainage. Concrete companies come together for charity project The car park at Grove House in St Albans, the site of Rennie Grove Hospice Care, was remodelled following a decision by the hospital trust to reclaim parking space. The project involved extending the car park into part of the garden and was generously supported by CRASH, the construction industry charity that supports hospice and homelessness projects. Concrete report.

ennie Grove Hospice Care is a considering taking back the parking for its and Beyond Awards to acknowledge this charity that provides specialist own use. If this happened, Rennie Grove commitment. In 2018 A J Morrisroe + Sons care and support for adults and would only have half the number of spaces, was recognised as the patron who provided R children with life-limiting illnesses which would have a serious impact on the the greatest value of professional expertise in Buckinghamshire and Hertfordshire. The accessibility of the hospice and the number of to CRASH during that year and in 2019 organisation’s main building, Grove House, people who could benefit from its services. Hanson received the charity’s Above and is located in St Albans and is the home of its Initially, CRASH agreed to help Rennie Beyond Award in recognition of 20 years of day hospice as well as the headquarters for its Grove with the internal refurbishment patronage. Hospice at Home services. project and secured through its patrons an Over the course of their patronage Rennie Grove initially applied to CRASH architect, project manager, quantity surveyor, both firms’ support has included donating for support with the internal refurbishment interior designer, engineering team and fire materials to deliver improvements to hospice of Grove House. As part of the application safety adviser. But when it became apparent car parks, providing expertise to save the process, the charity visited the property that the car park was a pressing issue, charity money on building projects and alongside two construction professionals from CRASH adapted quickly and secured from fundraising. its patron companies. During this visit, it was patrons (and Concrete Society members), AJ Together, Arcadis, Hanson and Morrisroe noted that as well as the need for an internal Morrisroe & Sons and Hanson, along with generously provided professional expertise refurbishment there was also a potential issue a third patron, Arcadis, design consultancy saving Rennie Grove Hospice Care £62,172 with the car parking arrangements. services. and delivering the new car park. CRASH CRASH has been the UK construction With the support of the companies, the added a grant of £40,000 bringing the total industry’s social impact partner for 25 years. car park belonging to the hospice, plus some value of support to £102,172. It unites the power of the industry to do good of its garden area, were redeveloped to create Trisha Pickersgill, director of finance and by channelling patrons’ professional expertise, the urgently needed parking facilities with facilities at the Hospice, says, “Rennie Grove construction products and fundraising. The associated paths, lighting etc. would not have had the skills required or charity helps homelessness and hospice Morrisroe provided construction the resource to have ensured the project ran organisations with their construction projects, engineering and management services for as smoothly as it did, completing within transforming hostels and day centres for the six-week project. This involved enabling timescales and with minimal unforeseen people who have been homeless. It also helps works and hard and soft landscaping. Due to problems. It has been an excellent well-led children and adults who need end-of-life care water saturation of the ground surface, gullies project and we are hugely grateful. in a hospice, by creating caring environments and soakaways were incorporated to facilitate “Without refurbishing and creating where families can spend precious time drainage. replacement parking spaces, local patients together. Concrete products included precast kerbs, with life-limiting illness and their families edging and cast-stone paving, which were would not have been able to access the range Parking site supplied by Direct Site Supplies. For bedding of therapies, treatments and holistic care As it stood, a small area for parking at the St and base foundations, Hanson supplied provided by Rennie Grove Hospice Care at Albans site belonged to the hospice but the 86.5m3 of differing strength-class concretes its Grove House building.” other half of the car parking available was (dependent on use) for the project. CRASH is the chosen charity for the actually loaned from the neighbouring St A J Morrisroe + Sons and Hanson have 2020 Concrete Society Awards. To make a Albans City Hospital. During discussions, been long term patron partners of CRASH donation, visit: www.crash.org.uk/how-you- it became clear that the hospital was and both have received CRASH Above can-help/make-a-donation. ▮

www.concrete.org.uk October 2020 concrete 19

8-26OctoberCONCRETE2020.indd 19 29/09/2020 11:50:57 AWARDSAWARDS20202020

The Society wishes to thank all its sponsors for their continued support of the Awards and draws readers’ attention to their details below:

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Premier sponsor http://sikaconcrete.co.uk www.mass-concrete.com www.ihsmarkit.com

For further information about The Society Awards email: [email protected] or call: 01276 607140 www.concrete.org.uk

8-26OctoberCONCRETE2020.indd 20 29/09/2020 11:50:57 AWARDSAWARDS Figure 1: Dust exposure can cause a number of serious health problems, from Figure 2 (above): Generated by the abrasive treatment skin and eye irritation to fatal diseases such as silicosis and lung cancer. of concrete and other materials, dust disperses into the 20202020 air harming operatives and surrounding environments. Consigning poor health and safety to dust Dust is one of the biggest health and safety concerns the construction industry is facing. It poses a significant risk to operatives’ wellbeing and employers’ operations. However, The Society wishes to thank all its there is still a lack of understanding around these detrimental impacts, and the solutions that exist to address the associated problems. Walid Hussain of Hilti reports. sponsors for their continued support arlier this year, the Health & Safety pulmonary disease, and silicosis. As particles Executive (HSE) reclassified are so small, they build up in the lungs over of the Awards and draws readers’ respirable crystalline silica dust time and the more severe effects are not E (RCS) as a carcinogen in a watershed always immediate. By the time symptoms moment for the industry. With growing present themselves, the damage is often momentum, the All-Party Parliamentary already irreversible. attention to their details below: Group (APPG) for Respiratory Health Due to regular interaction with processes is now urging the UK Government to that produce dust, construction operatives take further legislative action with ten have a higher risk of developing these recommendations in their report, Silica – the diseases. According to HSE statistics for next asbestos(1). The growing evidence and Great Britain, occupational lung diseases research into the effects of dust show it’s time account for approximately 12,000 deaths for construction businesses to act now. estimated to be linked to past exposures There are multiple touch points in the at work. HSE further estimates that dust www.socotec.co.uk www.peri.ltd.uk www.ancon.co.uk construction process that generate dust has been the cause of death for over 500 and it’s found on almost all jobsites. Very construction operatives per annum. fine RCS dust is generated by the abrasive treatment of concrete (and other materials, like mortar or tile). Drilling, sawing, breaking, Premier sponsor and grinding of these silica-containing http://sikaconcrete.co.uk www.mass-concrete.com www.ihsmarkit.com materials disperses fine dust particles into the air. It’s important to note here that dust isn’t just a risk while carrying out these tasks and is also released into the air after carrying out tasks from clothing, disturbance through cleaning, or via the transportation of materials (such as moving or emptying bags of cement). This poses a great risk for operatives and the surrounding environment. Breathing in dust makes for uncomfortable working conditions, irritating the eyes, nose and For further information about The Society Awards throat. Regular inhalation of RCS particles can lead to serious long-term health problems email: [email protected] or call: 01276 607140 like asthma, lung cancer, chronic obstructive Figure 3: The HSE report showed a huge disparity into the www.concrete.org.uk effectiveness of three manufacturers’ dust removal systems.

www.concrete.org.uk October 2020 concrete 21

8-26OctoberCONCRETE2020.indd 21 29/09/2020 11:50:58 SAWING AND DRILLING

Wake-up call Table 1 – Comparison of dust extraction systems The damning figures from the HSE are Dust Concentration (mg.m–3) a wake-up call to the industry and focus System 1 Respirable 0.85 is now on how to tackle the issue. Dust suppression is one of the key focuses in the Inhalable 2.45 construction industry currently, along with System 2 Respirable 7.65 Covid-19 working restrictions. Contractors Inhalable 16.55 must ensure jobsites adhere to physical distancing, tool maintenance and hygiene System 3 Respirable 15.65 practices, while bearing in mind the current Inhalable 38.90 lack of PPE available, and the added focus on the detrimental effects of respiratory illness. The good news is that solutions Standard will help guide manufacturers to exist that can reduce operatives' exposure design tools with safety at the fore. to dust and, in certain instances, assist with A report carried out by the HSE entitled, workplace management during the Covid-19 Assessment of dust extraction system solutions restrictions. on hand-held electric diamond cutters to BS EN On-tool extraction and dust removal 50632(3), calls into question the effectiveness systems (DRS) maximises the amount of dust of three tool manufacturers’ dust extraction removed at source, so less time is needed to systems in relation to the European Standard. set up and clean down working areas before The report examines the exposure levels to and after carrying out a job. Using DRS RCS, comprising the tool, insert and vacuum also supports Covid-19 working restrictions, unit. It shows a clear distinction between the eliminating the numbers of people needed to systems and found that not all dust extraction carry out tasks with single-person operation systems are created equal. Out of the three solutions. tools tested, the mean respirable dust As well as improved health and safety, concentrations for System 1 (Hilti) measured using dust extraction systems also increases 0.85mg/m3, followed by System 2 at productivity. Dust affects operatives' comfort, 7.65mg/m3 and System 3 at 16.65mg/m3, impairs their ability to see exactly what differences of circa 100 and 200% (see Figure they’re doing, and can cause damage to 3 and Table 1). surrounding fixtures and fittings. With the The severe effects of construction dust on right preventative measures in place and the operatives’ health and safety is a conversation correct tools for the job, such as on-tool dust that needs to keep taking place in order to extraction systems, you can protect operatives, spark change. Permanent lung damage and increase productivity, lengthen product fatal disease shouldn’t have to be by-products life spans and protect the surrounding of working in construction, and protecting environment. operatives should be considered a top priority Getting projects back up and running for businesses going forward. Construction post Covid-19 is vital. Dust clogs up tools dust can be tackled through sharing best and can cause unnecessary downtime. Using practice, education and tool innovation. the right DRS can help reduce the need for The research and work taking place now is repairs and replacements that can impact forging the construction site of the future, project deadlines. The longevity of the tool’s where virtually dust-free working will be the life is increased with less dust building up and standard. ▮ affecting it so work can be carried out with References: fewer interruptions and less downtime. 1. ALL-PARTY PARLIAMENTARY GROUP FOR Choosing the correct tools to support RESPIRATORY HEALTH AND B&CE. Silica – the next dust suppression will help minimise the asbestos? B&CE Holdings, Crawley, 2020. amount of respirable dust on-site. The 2. BRITISH STANDARDS INSTITUTION, BS EN 50632. (2) Electric motor-operated tools. Dust measurement European Standard BS EN 50632 is a key procedure. BSI, London, 2015. piece of legislation created specifically for 3. POCOCK, D., CLARKE, A. and SAUNDERS, J. Assessment measuring dust created by power tools in ‘real’ of dust extraction system solutions on hand-held electric environments and the effect of their on-tool diamond cutters to BS EN 50632. HSE, Derbyshire. 2019. dust extraction, where appropriate. This Visit: www.hsl.gov.uk.

Figure 4: Image shows how dust begins to spread after just one Figure 5: The effects of how dust permeates the second into working without dust removal systems. environment after six seconds of work.

8-26OctoberCONCRETE2020.indd 22 29/09/2020 11:51:00 EURO II II ----:::J ACCESSORIES

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8-26OctoberCONCRETE2020.indd 23 29/09/2020 11:51:00 RESEARCH AND DEVELOPMENT 3D-printable cementitious composites Seyed Hamidreza Ghaffar and Mehdi Chougn of the Department of Civil and Environmental Engineering at Brunel University London discuss research on the use of advanced materials for mechanical properties improvements.

esearchers at Brunel University London have developed a novel 3D-printable alkali-activated R cementitious composite (AACC), which has been optimised and selected from six mix designs, based on fresh and hardened properties evaluated for both printed and traditionally cast samples. Subsequently, the two mix designs with adequate printing properties (ie, fresh properties) and minimum mechanical performance gap between printed and cast specimens were identified. Further tests, ie, buildability, were executed to identify the best concrete out of the two options. The best mix was reinforced by 0.1%, 0.3%, 0.5% and 1% of nano-graphite Figure 1: (a) Flowability, and (b) setting time of AACCs. platelets (NGPs) (see Table 1). Several tests (shape retention, shape stability, structural build-up and micro-structural analysis) were printable feedstock need to be formulated compared with conventionally cast-in-situ performed to evaluate the performance of the and developed to make this technology cementitious composite structures. NGP-reinforced AACC concretes. useful for the making of structural load- Recent studies showed that the use of (1,2) Additive manufacturing (AM) bearing elements (see Ghaffar et al ). AACCs followed by the incorporation of technology has the potential to transform The weak mechanical properties of the different additives, including nano-particles the construction industry into a responsive 3D-printed parts, which is attributed to and fibres, could improve the printability and and technically advanced sector, although, the weak interlayer bonding, can also limit mechanical properties of printed structures. different grades of advanced and eco-friendly the competence of this technology when Mix formulation Table 1 – Mix design formulations The fresh properties, including the flowability and setting time, are the most important Mixture Binder Additive Aggregate Na SiO : NaOH 2 3 aspect for successful 3D printing (Figure name NGPs ratio Fly Ash GGBS Silica 0–0.5mm 0.5–1mm 1a-b). The characteristics of aggregates such wt% wt% wt% Fume wt% wt% as size, shape, gradation and surface textures, wt% as well as its volume fraction, can significantly Mix 1 60 35 5 – 40 60 2:1 influence the fresh properties (see Bhowmick and Ghosh(3)). The results revealed that by Mix 2 60 30 10 – 40 60 2:1 decreasing the GGBS content (from 35 wt Mix 3 60 25 15 – 40 60 2:1 to 15 wt %) and replacing it with the other Mix 4 60 25 15 – 60 40 2:1 binder components (fly ash and silica fume), the flowability of the concrete increases Mix 5 65 20 15 – 40 60 2:1 considerably. Moreover, the aggregate Mix 6 70 15 15 – 40 60 2:1 size reduction, from Mix 3 to Mix 4, led M4-nG-0.1 60 25 15 0.1 60 40 2:1 to increased cohesiveness and reduced flowability, while maintaining good shape M4-nG-0.3 60 25 15 0.3 60 40 2:1 stability. It can be seen that the setting time M4-nG-0.5 60 25 15 0.5 60 40 2:1 of the mixtures has considerably increased M4-nG-1 60 25 15 1 60 40 2:1 from 12 to 47 minutes, for Mix 1 to Mix 6, respectively (Figure 1b).

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Figure 2: Mechanical properties of printed (PM) and cast (CM) AACCs.

Figure 2a–b presents the mechanical samples. The flexural strength of 3D-printed Based on the previous results obtained performance of AACCs for both printed and Mix 3 (PM3), unlike the other compositions, from fresh and hardened property conventionally cast samples. The difference was 12% higher than that of the cast Mix 3 assessments, Mix 3 and Mix 4 demonstrated between the cast and printed specimens has (CM3). It is evident that all the cast better printing performance and mechanical been compared by means of compressive and samples demonstrate greater compressive properties. Therefore, buildability tests by flexural strength measurements (according strength compared with their 3D-printed printing 25 layers (300mm) were carried to BS EN 196-1(4)). For all of the samples, counterparts. The density of all the out to select the superior mixture for the except Mix 3, the flexural strength of compositions, both printed and cast samples, incorporation of NGPs and to evaluate their 3D-printed samples is lower than the cast was registered between 2000 and 2300kg/m3. reinforcing effect. As demonstrated in Figure 3a, for Mix 3, after ten layers of printing, the geometry experienced a considerable distortion and collapse, while for Mix 4 (Figure 3b) the geometry was printed successfully with an adequate shape without any apparent distortion. In order to investigate shape stability of Mix 4 further, the dynamic shape retention of this mix during the deposition of layers was carried out. In this examination, the height reduction of the first layer after the deposition of each upper layer was measured and plotted in Figure 3c. The results indicate that after 15 layers, maximum height reduction for the first layer was observed, after which the first layer was set and its height reduction stopped. The superior shape retention of the first deposited layer can serve as a base to hold the weight of the upper layers and therefore, lead to better performance of this mixture for large-scale structure 3D printing. At this stage of the study, Mix 4 – as an appropriate mix design that satisfied the necessary requirements for 3D printing – was nominated to be used as a suitable feedstock for the incorporation of NGPs to assess its reinforcing effect. Nano-additive incorporation The printing properties of AACCs in fresh state, including rheology and shape retention, are sensitive to the addition of NGPs. The fresh property results of the mixtures revealed that the presence of nano-graphite particles in AACCs can consume the moisture of the Figure 3: Buildability test of (a) Mix 3 and (b) Mix 4, and (c) dynamic shape retention test of Mix 4 for 25 layers of printing.

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Figure 4: Mechanical performance of Mix 4 with different NGP ratios.

mixture, while, the lubrication effect of NGPs addition of NGPs was measured in the range the stress concentration increase. Thus, in certain dosages (see Meng and Khayat(5)) of 2800–3200kg/m3. The results also revealed as soon as the micro-cracks meet the is observed. In this study, the addition of that the addition of NGPs progressively NGPs with higher elastic modulus, more maximum dosages of NGPs (1%) improves increases the flexural strength from 10.5MPa energy is needed to overcome the high- the printing property parameters. The for the cast sample to 10.7, 11.2, 15 and energy absorbance of NGPs, subsequently, observation can be explained by the presence 15.3MPa for M4-nG-0.1, M4-nG-0.3, increasing flexural strength (see Ranjbar et of Van Der Waals forces between the NGPs M4-nG-0.5 and M4-nG-1, respectively al(7)). Contrary to the flexural strength, the and their super-sorbent characteristics, which (Figure 4a). The highest percentage increase compressive strength of 3D-printed samples leads to AACCs' main components to be was 46% (with respect to the cast Mix 4) modified by NGPs (Figure 4b), increased closely packed together and hence obtain as observed in the case of M4-nG-1. The from 50MPa (for cast samples of Mix 4) to a better shape retention (see Meng and superior improvement in flexural strength is 59 and 57MPa only for 0.1 wt % and 1 wt % Khayat(5), and Yang et al(6)). The presence potentially attributed to the crack bridging of NGPs addition, respectively. Therefore, of NGPs has simply made the paste more and crack blocking caused by the presence it can be concluded that the incorporation cohesive and, therefore encouraged a denser of NGPs in AACCs' micro-structure. As of 1% NGPs will exhibit better results on packing, which contributes to better shape can be seen in Figure 5, after micro-crack flexural and compressive strength. ▮ retention. initiation caused by the imposed load in a The mechanical properties of NGP- three-point bending test, the micro-cracks reinforced AACC are shown in Figure 4a-b. tended to grow and propagate through References: The density for all compositions after the the micro-structure of the AACC due to 1. GHAFFAR, S. and MULLETT, P. Commentary: 3D printing set to transform the construction industry. ICE Proceedings, Structures and Buildings, Vol.171, No.10, October 2018, pp.737–738. 2. GHAFFAR, S., CORKER, J. and FAN, M. Additive manufacturing technology and its implementation in construction as an eco-innovative solution. Automation in Construction, Vol.93, September 2018, pp.1–11. 3. BHOWMICK, A. and GHOSH, S. Effect of synthesizing parameters on workability and compressive strength of Fly ash based Geopolymer mortar. International Journal Of Civil And Structural Engineering, Vol.3, No.1, 2012, pp.168–177. 4. BRITISH STANDARDS INSTITUTION, BS EN 196-1. Methods of testing cement. Determination of strength. BSI, London, 2016. 5. MENG, W. and KHAYAT, K.H. Effect of graphite nanoplatelets and carbon nanofibers on rheology , hydration , shrinkage , mechanical properties , and micro-structure of UHPC. Cement and Concrete Research, Vol.105, March 2018, pp.64–71. 6. YANG, H., CUI, H., TANG, W., LI, Z., HAN, N. and XING, F. A critical review on research progress of graphene/ cement based composites. Composites Part A: Applied Science and Manufacturing, Vol.102, November 2017, pp.273–296. 7. RANJBAR, N., MEHRALI, M., MEHRALI, M., ALENGARAM, U.J. and ZAMIN, M. Graphene nanoplatelet-fly ash based geopolymer composites. Cement and Concrete Research, Vol.76, October 2015, pp.222–231. Figure 5: The micro-structural analysis of the failure zone of Mix 4 with 1% of NGPs addition.

26 concrete www.concrete.org.uk October 2020

8-26OctoberCONCRETE2020.indd 26 29/09/2020 11:51:01 BANAGHER PRECAST CONCRETE

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Towards a low-carbon future Research at the Concrete Technology Unit, University of Dundee, continues to examine challenges associated with the specification and use of low-carbon concretes. Two projects, in collaboration with the Mineral Products Association, UK Quality Ash Association and the Scottish Research Partnership in Engineering (SRPe), are focusing on how wet-stored fly ash can be recovered and used in concrete, and how developments in testing can help with identifying the materials’ performance. Mike McCarthy, Moray Newlands and Rod Jones report.

he use of fly ash in concrete construction can mainly be traced to the latter half of the 20th Century, T with the technical benefits the material offers increasingly recognised and exploited since. Other attributes associated with fly ash mean it also has an important role in sustainable construction, including use in ternary blends and the manufacture of low-carbon concretes (see Taylor(1)). Recent developments in electricity generation, with the gradual withdrawal of coal-fired power stations and increasing use of alternative fuels and technologies, however, mean that sourcing of fly ash is changing. Figure 1: Processing techniques used during the pilot-scale trial. Options for fly ash supply in future are likely to include importing of material, potentially supplemented with that from wet with various other processing techniques, The benefits could be generally related to (2) storage areas (see BEIS research paper ); for before use. These include coarse screening the degree of fly ash particle size reduction example, stockpiles and landfills near power or de-agglomeration, which improved dry following processing. It was also possible to stations. In the UK, variations in supply and handling properties and reduced variability. meet requirements of the fly ash Standard, demand over time, mean that significant Thereafter, sieving, air classifying, grinding EN 450-1(5), but some properties needed reserves of accessible material, of the order and carbon removal were considered, to give greater processing than others to achieve of 100 million tonnes, are believed to be finer material and remove unburnt particles, this; for example, water requirement. The available for recovery. with this being carried out at both laboratory outcomes of the research were encouraging, Research in this area suggests that low- and pilot scales. with technical papers currently in preparation lime fly ash, of the type produced in the The processes used during the pilot-scale and a follow-up project initiated to address UK, held under wet-storage conditions trial are shown in Figure 1 and involved some of the outstanding issues. can undergo some physical and chemical initial drying and de-agglomeration, The overall aim of the additional studies changes – for example, agglomeration followed by the application of one or more referred to, is to further the understanding and weathering – compared with recently techniques. An indication of the effects of the factors influencing fly ash properties produced material and may also be prone to of these on selective fly ash and concrete and recovery/processing, which can be variability (McCarthy et al (3,4)). As a result, properties is given in Table 1 (fly ash feed affected by the materials’ characteristics and evaluation of this material and development material fineness > 40% retained on a 45µm storage conditions, and to examine wider of recovery strategies, involving processing, sieve; loss-on-ignition = 6.3%). As shown, performance. The research will consider or beneficiation to homogenise fly ash, prior processing by the various means enabled both dry- and wet-stored processed fly ash to use in concrete are likely to be necessary. increases in fineness and reductions in loss- in binary and ternary blend concretes, with These represent areas that have recently on-ignition (reflecting carbon content), aspects of interest including, engineering been studied at the University of Dundee, in with improvements in water requirement and durability properties (chloride ingress, collaboration with industry. and reactivity achievable. Reductions in carbonation, sulfate attack, alkali–aggregate This research has investigated fly ash from superplasticiser dose requirement (for a reaction and freeze–thaw scaling). The a range of different storage areas, examining target slump) and enhancements in concrete practical outcomes of the work will be its physical and chemical properties, and strength (28 days, water cured) were also explored and consideration given to how this mainly considering drying, combined obtained. material could be included in Standards.

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Low-carbon concrete methods, the EN 12390-10(6) chamber Acknowledgements: durability assessment test and the EN 12390-12(7) accelerated Thanks are given to the Engineering and Physical (8) Sciences Research Council, the Scottish Research In response to climate change issues, a carbonation test (see Harrison ). These Partnership in Engineering and the Mineral Products low-carbon ‘route map to 2050’ for new procedures do not reflect the performance Association, the UK Quality Ash Association and its low-carbon concrete has been established of slowly reacting cements, eg, concretes members, and partners LKAB and BASF, for supporting the research described. Thanks are also given to Dr globally and this will require replacing of with higher clinker replacements, in the real Thomas Hope, Mr Josh Norrie and Mr Maciej Jozwik for up to 60% Portland cement clinker with environment. undertaking the work. combinations of limestone, fly ash and/or Work has started to address these issues slag (see GCCA 2050 Climate Ambition with test procedures at the University of References: https://gccassociation.org/climate-ambition). Dundee. The project is examining the 1. TAYLOR, M.G. Modern cements (Bulk). Fact Sheet 14b, In the UK alone, this has the potential to development of concrete micro-structure MPA Cement, 2015, 8pp. 2. DEPARTMENT FOR BUSINESS, ENERGY AND reduce CO2 emissions by up to 4 million through increasing the rate of hydration and INDUSTRIAL STRATEGY. Fly ash and blast furnace slag tonnes/year. However, the take-up of new reaction by modifying temperature to achieve for cement manufacturing. BEIS research paper No.19, generations of low-carbon concretes will maturities equal to those used in current BS 2017, 33pp. not be straightforward, as there are key EN test methods. 3. McCARTHY, M.J., JONES, M.R., ZHENG, L., ROBL, T.L. and GROPPO, J.G. Characterizing long-term wet- issues that need to be resolved to provide Initial data suggests that providing stored fly ash following carbon and particle size confidence for industry, particularly with standard curing is used for approximately separation. Fuel Journal, Vol.111, 2013, pp.430–441. respect to durability, such as carbonation- three days prior to high-temperature curing, 4. McCARTHY, M.J., ROBL, T.L. and CSETENYI L.J. Chapter induced corrosion. the resulting pore micro-structure does not 14: Recovery, processing and usage of wet-stored fly ash. Coal Combustion Products. Characteristics, Assessing the durability of such concretes deviate significantly from standard curing to Utilization and Beneficiation. Ed. T.L. Robl, A. Oberlink containing ‘slower’ reacting cements requires 28 days. and M.R. Jones, Woodhead Publishing, Cambridge, the ability to carry out rapid and fair tests to Working in collaboration with the UK, 2017, pp.343–367. identify optimal combinations of materials. University of Aberdeen, the project is also 5. BRITISH STANDARDS INSTITUTION, BS EN 450-1. Fly ash for concrete. Definition, specifications and However, current test periods are too long examining the influence of modifying the conformity criteria. BSI, London, 2012. (typically four to 12 months) for practical cement chemistry system as a means of 6. BRITISH STANDARDS INSTITUTION, BS EN 12390. applications, and there is the need for a rapid altering the rate of hydration to reduce the Testing hardened concrete. Part 10 – Determination of method that compares and selects different time of testing. Furthermore, changes in the carbonation resistance of concrete at atmospheric levels of carbon dioxide. BSI, London, 2018. combinations of materials for their effect hydrate chemistry and micro-structure, due 7. BRITISH STANDARDS INSTITUTION, BS EN 12390. on the required mechanical and durability to the use of cement combinations may Testing hardened concrete. Part 12 – Determination of properties pertaining to particular projects. At produce different fire performance. To the carbonation resistance of concrete — Accelerated this stage, it is not expected that the result of date, this has not been quantified and, in a carbonation method. BSI, London, 2020. 8. HARRISON T.A. Specifying resistance against these types of accelerated test would be used post-Grenfell era, there is an urgent need to carbonation-induced corrosion by performance. for long-term modelling. establish behaviour in fire conditions. The Magazine of Concrete Research, Vol.71, No.7, April Ongoing European developments for project will examine the effect that changes in 2019, pp.341–348. a durability testing approach with respect these properties of low-carbon concretes have to carbonation-induced corrosion of on their fire behaviour with colleagues at the ▮ reinforcement have issues with the likely University of Edinburgh.

Table 1 – Indication of processing (pilot-scale) effects on selective fly ash and concrete properties Processing method Property Dry/de-agglomeratedx Air classified+ Micronised+ Carbon removed+

Fly ash

Fineness (45µm sieve retention) Large increase Large increase Large increase Small increase

Loss-on-ignition No change No change Small increase Decrease

Water requirement Small decrease Small decrease Small decrease Decrease

Activity index No change Increase Large increase Increase

Concrete*

Superplasticiser requirement Decrease Decrease Decrease –

Cube strength (28 days) No change No change Increase –

x Effect compared with feed material + Effect compared with dry/de-agglomerated material * Equal w/c mix (30% fly ash in cement)

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27-35OctoberCONCRETE2020.indd 29 29/09/2020 12:01:07 Silica fume concrete – high- performance concrete perfect for hostile environments Incorporating silica fume in concrete is one method of meeting the variety of construction requirements that call for the use of technologically advanced concrete. Lee Baldwin of Sika explains how its properties make it an ideal choice for harsh environments requiring strength and durability.

ilica fume is composed of very within the gel increases the compressive and used in conjunction with superplasticisers fine solid glassy spheres of silicon therefore flexural strength of the concrete. is used to produce very high compressive dioxide. It is a by-product of Second, there is the void reduction. Silica strength concrete. It can also aid S the industrial manufacture of fume particles have a diameter of less than pumping concrete up high-rise buildings ferrosilicon and metallic silicon in high- 1μm; approximately 100 times smaller than during construction, when used at temperature arc furnaces. When used as the average cement particle. These fine appropriate dosages in concrete. an addition in concrete, typically based particles fill the tiny voids and capillary pores • Chemical resistance – the reduced on a percentage of cement, it dramatically within the cement matrix, and significantly permeability of silica fume provides improves the strength, durability and the reduce porosity to produce an extremely protection against intrusion of chloride impermeability of the concrete, making it dense and impermeable concrete. ions, thereby making it ideal for a perfect choice for environments where applications where concrete will be performance demands are high. Property advantages required to be resistant to chemical Thanks to the pozzolanic and micro-filler attack. Silica fume is more resistant to How does it work? effects, silica fume particles improve many chemical attack due to its dense pore There are two key actions that occur when properties of concrete helping with its structure, thereby it is considered to be silica fume is added to concrete that drives its durability, including: more resistant to, for instance, chloride performance. • Abrasion resistance – the abrasion ingress, sulfate and acid attack. First, there is the pozzolanic action. This resistance is much higher than normal. • Freeze–thaw resistance – decreased is the chemical reaction that takes place When used in floor and pavement permeability reduces water saturation,

between the free lime Ca(OH)2 in the construction, its increased durability aids giving the concrete excellent freeze–thaw Portland cement paste and the silica fume resistance to wear and abrasion from resistance because less water is trapped particles. This results in the formation of an vehicles. This additional durability can inside the cement paste. additional calcium silicate hydrate (C-S-H) extend the service life of a slab, thus gel, which acts as the glue that binds the reducing the frequency of repair and Immingham Dock, Grimsby concrete constituents together. reinstatement and associated costs. After the existing concrete slab failed in the The formation of this extra binding force • High strength – silica fume concrete shed bagging area, a fertiliser storage facility

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27-35OctoberCONCRETE2020.indd 30 29/09/2020 12:01:11 Pouring, placing, finishing and completed slab for fertiliser storage facility at Immingham Dock, Grimsby.

at Immingham Dock, Grimsby, needed a new the nature of the fertilisers being housed and, aggressive chemical nature of the fertiliser, solid floorplate constructing quickly. in addition, to resist the scuffing action from which can include nitrogen and sulfur. Located at a major east-coast port, the the wheels of loading vehicles. As the facility SikaFume-50 S is a concrete additive in facility has been used for bulk storage for the is in operation for more than ten hours a liquid form, based on silica fume technology. past 50 years, handling thousands of bags of day, the solution needed to provide minimal When added to concrete, it changes the fertiliser each year. disruption. In order to mitigate the impact rheology and reacts with the cement hydration With nine different ranges, the storerooms on day-to-day operations, specialist BCJ products to improve its strength and durability house a large amount of liquid nitrogen and Construction was appointed. dramatically, making it ideal to meet the sulfur fertilisers available to purchase by durability specification for the project. customers across the globe. Highly reactive Some 10,000 litres of the product were Following the failure of the existing Thanks to its highly reactive pozzolanic delivered directly to Breedon’s concrete plant floorplate, approximately 900m² needed materials and stabilisers, SikaFume-50 S was in Grimsby, minimising any disturbance covering with the new internal slab. The slab specified for the project to ensure the concrete to the client’s site. The concrete, totalling was required to be chemically resistant due to would withstand both the weight and 170m³, was delivered in a single pour. ▮

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27-35OctoberCONCRETE2020.indd 31 29/09/2020 12:01:14 DURABILITY/AGGRESSIVE ENVIRONMENTS Multi-faceted approach to ensure the durability of concrete in aggressive environments Unlike other properties, eg, mechanical characteristics, durability reflects the long-term interaction between materials and service environments, and cannot be defined by a single parameter. The development of performance-based specifications, advances in in-situ performance tests and structural health monitoring techniques enable the estimation of both the durability and the service life of structures at multiple stages. A combination of materials science, digital technologies and service life prediction models provides a route to form a ‘closed-loop’ control. Kai Yang, Susan Bernal and Muhammed Basheer of the School of Civil Engineering, University of Leeds report.

epair and rehabilitation of structures accounts for approximately 50% of the construction budget in R most developed countries. As a result, attention is given to new materials, optimising concretes, improving construction practices and maintenance of structures to enhance their durability performance and ultimately extend their service life. Although durability is not a property of concrete to specify, unlike strength, it is widely accepted that if concrete structures are designed without due consideration of their potential durability, they would deteriorate prematurely, which could lead to catastrophic failures. Numerous cases of collapse of concrete structures could be related to deficient durability, eg, collapse of the Montreal bridge in 2007 and Polcevera viaduct in Genoa in Figure 1: A conceptual model relating concretes, micro- 2018. Concrete durability reflects the long- structure, transport properties and durability(1). term interaction between materials and servicing environments, which cannot be described by a single parameter. However, the permeation properties are known to reflect Current approaches environments and choosing concretes based closely the durability, and when combined The durability of concrete structures on prescriptive specifications, the more with environmental exposure characteristics is ensured by classifying the exposure comprehensive BS 8500(3) provides a flexible and mechanical properties, it is possible to environments (23 different types are trade-off between cover depth and concrete predict durability (and service life) in the classified in BS EN 206(2)) and specifying quality. service environment. concretes that would withstand these However, it has been recognised that the Basheer et al (1) illustrated these interactions exposures (BS 8500(3)). These Standards durability of concrete structures depends also between materials, micro-structure, transport specify prescriptive-based parameters, on construction-related issues. The quality properties, environmental penetrations such as minimum strength grade, cover of concrete in structures could greatly be leading to different mechanisms of to reinforcement and cement content, different from that of standard concretes and deterioration resulting in cracking and how and maximum water:binder ratio for when exposed to the service environments, one mechanism could lead to another, as in different exposure classes. While EN 206 the variations in quality could compromise Figure 1. gives guidance for classifying exposure their durability and service life. One approach

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to address this variability is to resort to probability-based durability design. This could be combined with performance-based specifications for durability and service life. Although Annex J of EN 206 gives some details of the approach and principles for performance-related design methods with respect to durability, the lack of reliable, consistent and standardised test procedures for evaluating concrete performance has methodology for ensuring the intended durability and service life. Further, numerous models are available for predicting the performance and service life of reinforced concrete structures, some of which enable numerical prediction of the service life based on both the material characteristics and the exposure parameters, whereas some depend on data from either non-destructive testing or structural health monitoring (SHM), combined with input of exposure parameters and material characteristics. It is largely recognised that these models need Figure 2: Different durability scenarios considered by a to be validated based on field data before they can form part of the performance designer, depending on the importance of the structure specifications for durable structures. and the planned maintenance and repair. Challenges and proposed changes Despite great progress in specifying and ensuring the durability of concrete structures, mechanical properties are very similar. a concrete structure is in good service lack of durability of modern concrete Likewise, even a given structural element condition for the pre-specified life span. structures is still an issue. This could be due could present two different performances This requires systems thinking, linking to a combination of reasons: at two different micro-environmental various elements dynamically, eg, service • When it is a critical structure (case 1, exposures in a structure. These variations conditions, loading conditions, structural Figure 2), design for durability is are not reflected normally in performance and materials characteristics, extremely conservative, but for most performance specifications and service whose synergy will provide the expected structures (cases 3 and 4, Figure 2), it is life models used to predict the service performance and durability. Unlike expected that structures would performance. mechanical properties, durability can only be deteriorate with time, which could be • Durability assessment of concrete defined under the specific service condition, restored by routine maintenance and structures in aggressive environments and this performance should directly link to repair, though there could be an ongoing based only on ‘simulated’ conditions loads on the structure and both micro- and cost associated with this approach. If within a relatively short period using macro-environments. As such, the general consideration to durability design is not current specifications is not reliable due ‘linearity concept’ used in classical structural given, structures could fail suddenly (case to the combined effects of micro- engineering design approach is not suitable. 2, Figure 2), with catastrophic environments, different behaviour of new Essential aspects that require attentions are consequences. materials, heterogeneous nature of highlighted next without listing any specific • Unlike impact, fire and earthquake concrete and temporal loads. The use of approach so as to leave this to the discretion effects, deterioration of concrete classical ‘open-loop’ design methodology of readers to select available local materials structures occurs over a long period – is unable to address these issues. and techniques. decades rather than a few years. So the • A recent Google search on ‘durability of urgency to deal with durability is not felt concrete structures’ has returned more Reconcile material science by owners and manufacturers at all times, than 29 million results, reflecting that and engineering practice quite often resulting in leaving the countless time and resources have been Understanding the current durability design structure with inadequate maintenance spent addressing the issue, but the methods is a good starting point. These and repair. methodology for specifying concrete approaches clearly define typical (aggressive) • It is possible that similar structural structures for durability and the environment conditions and list requirements elements manufactured by a particular prediction of their service life in different for each corresponding situation. These manufacturer, using the same raw micro- and macro-exposure prescriptive parameters work well for the materials, exhibit entirely different environments are not sufficiently robust purpose of general durability control, are performances in service due to the and reliable at present. easy to understand and apply, and are widely variations in their micro-structural accepted by public. However, due to the characteristics, even though the bulk Durability studies aim to ensure that rapidly growing demands on infrastructure

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both in terms of volume and speed of are made to consider the influence of loads and evaluate both the service conditions and construction, these standards are not often and material heterogeneity. performance of concrete structures. followed. Although BS 8500 permits the use of proprietary concrete containing new Use of performance-based designs Service-life models materials, there are limitations in applying The successful use of performance-based Beyond real-time performance assessment, traditional knowledge of the behaviour of design requires techniques that can determine data collected from non-invasive techniques designated, designed or prescribed concretes targeted parameters. and SHM, in principle, can be fed into the when using these proprietary concretes. As most durability problems occur service-life prediction models to give an “If you can measure it, you can control from chemical and physical interactions early warning to users, so that pre-treatments it” – this is true only for data that can reflect between concrete and micro-environment, can be carried out to lower future risks. the real situation. It is costly and dangerous and the near-surface concrete provides the It would also address the issue of ‘time- to design and build structures on misleading first line of defence against the ingress of lagged’ durability-related maintenance and information. aggressive substances from the environment repairs. However, with respect to service- Naturally, the next task is to ensure into the concrete, transport properties of life prediction from such data, numerous that durability test methodologies are cover concrete could be used to assess the issues need to be solved before reaching representative, simple and fast. Selection durability of the material. Among many reliable conclusions. One main barrier of suitable methods to assess the durability methods available for this purpose, field non- is the limitation of current models for is never easy, particularly for proprietary invasive permeation test methods and SHM describing coupled deterioration dynamics concrete, as time and cost are normally techniques have the greatest potential. under unsteady states, as most currently restricted to get reliable data for service-life Non-invasive techniques can provide used service-life models are generally modelling. relevant data intermittently at the time of built on ‘static’ conditions. Some of the It is known now that durability defined testing, while SHM can record variations current models include improvement in under accelerated conditions may not of performance of concrete at fixed points performance due to continuous hydration represent that in actual conditions. Simulated continuously. of cementitious materials when concrete environmental conditions are streamlined as The emergence of new techniques is free from micro-defects, whereas they opposed to compounded, which is normally – eg, IoT (Internet of Things) enabled could mislead if micro-cracks occur due to found in service and too aggressive for a devices, data visualisation and data mining chemical–physical interactions in concrete, particular type of deterioration. techniques, artificial intelligence, etc – make corrosion of reinforcement or the load acting Further, specimens tested in laboratories both the remote access of data from structures on structures. The future of organically are too small to represent uniformity of and the assessment much easier, and allow linking site results with service-life models concrete in structures, and almost no efforts unlimited possibilities of choices to describe is encouraging, but substantial progress

Figure 3: Proposed ‘specify, evaluate, predict, optimise and feedback' (SEPOF) strategy for ensuring the durability and expected service life of concrete structures.

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needs to be made on both experimental and foundation for performance optimisation. allows a ‘closed control loop’ to enhance theoretical aspects in order to reliably predict With rapid advances in material science, durability and achieve the expected service early warning of durability issues using many techniques and methods can be used life of concrete structures. This could be service-life models. for any performance requirement, provided simplified as ‘SEPOF’ – specify, evaluate, the target performance is clearly defined predict, optimise and feedback – as illustrated Continuous improvement and can be assessed. A clear understanding in Figure 3. Selection of these techniques is The assessment of performance of structural of strengths, weaknesses and interactions of flexible and there would be more than one concrete can provide valuable information, different types of performance improvement option to achieve the specified durability and but cannot give a longer service life. To form techniques could assist in identifying practical service life, as long as the service condition is a ‘closed control loop’ for controlling the improvements that can be achieved in clearly defined.▮ durability, material optimisation techniques practice. That is, a ‘closed control loop’ for the are needed. Fortunately, fundamental ideas durability enhancement can be established. Acknowledgement: to improve the durability have not changed The authors gratefully acknowledge input by Dr Sreejith A paradigm strategy shift Nanukuttan, School of Natural and Built Environment, significantly for decades; concrete with less Queen’s University Belfast, Northern Ireland and Prof connected pores in a homogeneous structure The knowledge in concrete technology grows John McCarter, School of Built Environment, Heriot-Watt generally provides longer service in practice. exponentially, but the philosophy behind the University, Edinburgh, Scotland for developing the Prior to selecting which performance- durability design is still based on a 100-year- principles outlined in this paper. enhancement techniques to adopt, it is old empirical strength design approach important to understand deterioration and, as a typical ‘open loop’, no prediction References: mechanisms for specific micro-environments. and rapid feedback strategy (see the central 1. BASHEER, P.A.M., NANUKUTTAN, S., MCCARTER, J. and The progress in knowledge of the nature grey box in Figure 3). This is inadequate LONG, A.E., Performance based specifications for of hydration products, eg, calcium silicate to satisfy durability and service-life design durability of concrete structures – Opportunities and Challenges. Proceedings of the 1st International hydrate (C-S-H), and secondary hydration requirements today and in future, as service Conference on Cement and Concrete Technology: products, and their response in aggressive conditions of concrete structures, raw Concrete for the Modern Age – Developments in agents, has enabled the development of materials and construction techniques have Materials and Process, Whittles Publishing, Dunbeath, deterioration thermodynamic models to changed significantly. November 2017, pp.253–274. 2. BRITISH STANDARDS INSTITUTION, BS EN 206. estimate potential material performance Effectively combining a performance- Concrete – Specification, performance, production and decay, vulnerable phases and relevant based design approach, dynamic deterioration conformity. BSI, London, 2013. deterioration rates at nano- and micro- modelling, non-invasive tests and SHM, 3. BRITISH STANDARDS INSTITUTION, BS 8500. Concrete level as a function of mix design/degree numerical service-life simulation, and – Complementary British Standard to BS EN 206. BSI, of hydration. This could then serve as the performance-optimisation techniques London, 2019. Archived concrete

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27-35OctoberCONCRETE2020.indd 35 29/09/2020 12:01:16 BIM and temporary works Thanks to digital engineering, concrete contractors are now able to work with temporary works specialists to efficiently design, plan and visualise a formwork scheme in a 3D digital environment, before they get on-site. Here, Billy McCormick and Paul McLaughlin from Mabey Hire discuss how both building a relationship with a temporary works specialist and the use of BIM can ensure successful project delivery, improve efficiency levels and offer enhanced visibility.

hile both formwork panels more informed and detailed bid to the client, and falsework props are with an initial, engineered formwork design wholly temporary in nature, already created, one would also be able to W they can have a very real offer more accurate time and cost estimates. and permanent impact, with the success of Cost, as always, is a very important factor, the concrete pour – and the overall project with the potential for a concrete job to go delivery – often depending heavily on the considerably over budget if formwork is not initial formwork scheme design. given ample consideration at this initial stage. It is for this reason that temporary works would perhaps be better labelled as enabling On-time delivery works, something to be considered at the Put simply, a successful and efficient initial design and strategy stage of a project, as formwork project relies on more than just the permanent works are. Despite this, there the kit itself. Instead, it needs a detailed and is still the potential for a project’s temporary engineered temporary works design behind works to not be given the attention needed, it, with a focus on planning and optimisation as well as underestimating the level of cost right from the start. and labour that formwork can require. While Formwork projects often have a strict smaller projects may only need a standard deadline, especially if the concrete has formwork solution, this is not the case for all, already been ordered for the site. So, any with some sites requiring a bespoke and more issue with the formwork design could result complex design. in long – and costly – delays. Even small mistakes could create big issues, such as a Early engagement simple case of human error when counting As with all temporary works, early the number of kit components needed. engagement is important. Liaising with a This is one area of formwork that the use of temporary works specialist as early as the building information modelling (BIM), in tender stage of a concrete project could particular, has helped to transform in recent provide real benefits for you as a contractor. years. It enables temporary works specialists As well as enabling the submission of a to automatically generate kit lists from the

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completed model and provide contractors project teams to progress from a 3D way of with the assurance that the correct equipment working to a 4D project planning process. will be delivered to site ready for installation. With the increased levels of visibility that BIM offers, concrete contractors are able BIM to better plan the whole scheme and in In many ways, BIM can be central to ensuring higher levels of detail, right down to the a successful formwork delivery. While it is phasing of concrete pours and the reuse of perhaps more commonly associated with formwork panels and props, where applicable. permanent works, designing and visualising Particularly beneficial on larger commercial a project’s temporary works in this 3D digital and industrial projects, where there may be environment can provide similar rewards. any great number of separate concrete pours, When working with a temporary works this enhanced visibility and information-rich specialist with BIM capabilities, one can data can be used to create a project timeline, either provide 2D drawings for the temporary helping to better plan the most efficient works engineers to first model in a 3D installation and pouring sequence. environment, followed by the formwork scheme, or – if a company also has BIM Digital rehearsal processes and workflows – a 3D model of the It can be said that BIM offers a digital permanent concrete structure can be provided rehearsal of the temporary and the permanent for the formwork and falsework to then be works, before you get on-site. designed around. Effectively, BIM allows you to ‘build it Using intelligent BIM software, such as before you build it’. Being able to see the Revit, to model and visualise the formwork whole formwork scheme and phased concrete scheme – as opposed to 2D drawings – can pours in the context of the overall project or reduce the likelihood of design issues or construction sequence will not only aid better rework being required on-site, with features delivery of the works but can also improve such as clash detection helping to ensure co-ordination and communication between that the proposed formwork is both correct project parties. Once a 3D model has been and constructible. Not only this, but moving created of the temporary formwork scheme, from 2D to 3D can also enable more complex this visual tool can be shared between all geometry – such as curved concrete walls parties and disciplines, from the installer and – to be created, with the temporary works concrete contractor to the site manager and specialist and contractors able to more client. effectively visualise and plan the formwork Liaising with a temporary works specialist scheme required to bring the end vision to with virtual reality capabilities, as well as BIM reality. processes, takes this one step further, offering teams a virtual walkthrough of the formwork Optimisation scheme and construction site. As well as improving design accuracy and While only temporary in nature, formwork helping to facilitate more complex projects, and falsework schemes have an integral role BIM can also help to enhance the overall to play in the success of a project’s permanent formwork scheme’s efficiency by reducing concrete works, with any mistakes, clashes the amount of steel props, frames or supports or delays at this stage potentially having needed. a significant impact further down the Through the use of a 3D digital construction sequence. With this in mind, environment, temporary works specialists are liaising with a temporary works specialist able to model, analyse and consider multiple with BIM capabilities can provide you and formwork design iterations with a level of your client with numerous benefits and certainty that simply would not be possible in assurances, from the initial tender stage traditional 2D. This allows engineers to select through to on-site delivery. As BIM becomes the design that strikes the optimum balance firmly embedded in construction’s permanent between performance and steel weight. Put works, designing and visualising a project’s simply, the fewer components used, the lower temporary works, such as formwork, in this the cost. Not only this, but fewer components same 3D digital environment is surely a ▮ Temporary works can also result in time savings, with the natural next step. design using BIM. formwork and falsework being quicker to assemble and disassemble on-site. What’s more, this concept of using BIM to see the ‘bigger picture’ when designing a formwork scheme has many practical applications, enabling contractors and

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On the move in one of London Underground’s busiest stations

London Underground is going through significant changes across some of its most populated stations, with Bank Station being one of them. With it being the third busiest interchange, the current station is undergoing an expansion of its Northern line platform, complete with the installation of several escalators and a new public entrance. A highly manoeuvrable traveller system allowed for sprayed concrete and waterproofing operations to proceed smoothly on the tunnelling. Concrete report.

he main contractor, Dragados, shelf components. This user-friendly concept won the project in 2013 and has was first introduced during tunnelling work been working directly with London at Farringdon Station where it fulfilled a T Underground ever since to ensure it similar requirement. is complete by 2022. However, on this project, designers took Once the tunnels had been excavated by the traveller a step further so that it could Dragados, the surface was ready to be spray- accommodate changes in the tunnel’s concrete lined and waterproofed. To enable diameter across three of its sections. these two processes, mobile access to the tunnel’s surface was crucial. Ideally, the same Well-thought-out design access solution had to be capable of moving Designing in 3D allowed all parties to see on flat as well as sloped ground conditions how the traveller would accommodate the in the escalator shafts. The point of entry changes in geometry. By using standard into the tunnel also had to be taken into components, scaffolders could make consideration during the design process. All adjustments independently, saving the equipment was brought down to the working customer time when moving the system area via one tunnel shaft, making it a very between sections. congested area to begin with. The system provided a safe and secure With this in mind, PERI developed the working platform that could be adjusted UP Traveller, made with standard off-the- in order to move from a larger section to a

38 concrete www.concrete.org.uk October 2020

36-40Concrete2020.indd 38 29/09/2020 12:02:16 FORMWORK AND FALSEWORK

smaller section with ease and then finally incorporated in key locations to enable the back into a larger section without dismantling decking to support 3.0kN/m2. This allowed the whole unit. the decking to fully support the live load on Regardless of the changes in geometry, the platforms, in addition to the load of the 360° access to the tunnel's surface was feasible waterproofing membrane. at all times. Any changes in the height and A huge benefit of the system was reuse. width of the tunnel were overcome by using The length of the traveller was ideal in that an identical layout of horizontal ledgers it did not occupy the entire tunnel like a 500mm below the platform horizontals. The stationary solution might have. Instead, handrails and standards were designed so the customer was able to reuse the system a that the top layer could be easily removed, section at a time, ensuring enabling works and the decking was lowered by 500mm stayed ahead of the in-situ concrete. to reduce the height of the traveller. Both sides of the platform were simply stripped Manoeuvrability back, making the whole traveller smaller For the escalator shafts, the system was and narrow enough to move into the smaller modified so that it could move on an incline. section with ease. Mounting the system onto Castors were replaced with RCS rails and a large castors made it easy to reposition and hydraulic winch to enable manoeuvrability increased productivity on a time-sensitive and keep material to a minimum. The winch project, as major dismantling operations pulled the entire scaffolding unit in one lift, were not necessary. With less dismantling making movement up and down the tunnel and assembly required, the customer also quick and easy for the customer. experienced a reduction in working at height Again, the size of the traveller enabled the and fewer operatives were needed for the job. team to work on a section at a time, freeing up The access staircase trailing behind the other areas of the tunnel for concurrent tasks. unit enabled operatives to enter different The integration between the scaffolding and levels of the traveller, without losing any formwork components was well received due platform space. This also created additional to the time it saved the customer and the working platforms for waterproofing and flexibility it offered on this part of the project. made it easier to push the traveller from one “These solutions have helped us to keep side. erection time and site disturbance to a Typically, platforms for access scaffolding minimum,” says Diarmaid Long of Dragados. would be designed to support 1.5kN/m2. “What makes each of the solutions work for Due to the live load and unknown weight us in the tunnel is that they can be moved as of the waterproofing membrane, loadings and when required, providing the site team were calculated according to load class four. with access to any wall of the tunnel at any Heavy-duty ledgers (UVH ledgers) were time, giving us greater flexibility.”▮

The PERI UP Traveller, capable of being used on sloped as well as flat ground.

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