Ready-Mixed Concrete – Practical guide for site personnel brmca british ready-mixed concrete association Mineral Products Association into contact with fresh concrete, skin irritations Health are likely to occur owing to the alkaline nature of cement. The abrasive effects of sand and aggregate in the concrete can aggravate the and Safety condition. Potential effects range from dry skin, irritant contact dermatitis, to – in cases of Health and safety prolonged exposure – severe burns. All construction sites include potential hazards where appropriate precautions are required, Take precautions to avoid dry cement entering and where the legal responsibility for health the eyes, mouth and nose when mixing mortar or and safety is likely to be the project manager concrete by wearing suitable protective clothing. or those responsible for the construction work. Take care to prevent fresh concrete from entering However, everyone working on a construction boots and use working methods that do not site, including those delivering goods and require personnel to kneel in fresh concrete. services, is responsible for their safety and the Unlike heat burns, cement burns might not safety of those around them. The Health and be felt for some time after contact with fresh Safety Executive provides a wide range of useful concrete, so there might be no warning of guidance, downloadable at no cost from damage occurring. www.hse.gov.uk, and include: If cement or concrete enters the eye, immediately ¡ Managing health and safety in construction. wash it out thoroughly with clean water and Construction (Design and Management) seek medical treatment without delay. Wash wet Regulations 2015. Guidance on regulations. concrete off the skin immediately. Barrier creams Health and Safety Executive, L153, April 2015. may be used to supplement protective clothing ¡ Health and safety in construction. Health and but are not an alternative means of protection. Safety Executive, HSG150, Third edition. 2006. ¡ Personal protective equipment (PPE) at work. Health and Safety Executive, INDG174(rev2), August 2013. ¡ HSE information sheet – Cement. CIS26(rev2). 2002. ¡ HSE information sheet – Construction dust. CIS36(rev2). 2013 Cement burns Personal Protective Equipment (PPE) for working There are particular concerns where skin comes with concrete. This booklet is available for download from www.brmca.org Sampling and testing procedures are included as appendices in this document. A - Sampling concrete B - Consistence tests C - Air content tests D - Strength test specimens For hard copies please refer to the contact page of the BRMCA website: www.brmca.org.uk 2 Contents Health and safety 6. Finishing concrete ..................................................16 1 Introduction .............................................................. 4 6.1 General 2 Specifying concrete ................................................ 5 6.2 Formed surface finishes 2.1 General 6.3 Unformed surface finishes 2.2 Consistence 7. Curing concrete ......................................................18 2.3 Designated concretes 7.1 General 2.4 Ordering 7.2 Polythene sheeting 3 Delivery ....................................................................... 8 7.3 Sprayed membrane 3.1 Site preparation Appendices 3.2 Receiving A Sampling concrete ..............................................22 3.3 Sampling and testing A.1 General 4 Placing concrete ....................................................10 A.2 Composite sample 4.1 General A.3 Spot sample from initial discharge 4.2 Time limits B Consistence tests ..................................................24 4.3 Hot weather B.1 Slump test 4.4 Cold weather B.2 Flow test 4.5 Formwork B.3 Slump-flow test 4.6 Placing concrete B.4 Consistence retention testing 4.7 Deep beams and columns C Air content tests ....................................................31 4.8 Slab formwork C.1 General 4.9 Cold joints in mass concrete C.2 Water column method 5. Compacting concrete ...........................................13 C.3 Pressure gauge method 5.1 Entrapped air D Strength test specimens ....................................34 5.2 Poker vibrators D.1 General 5.3 External vibrators D.2 Cubes – normal consistence concrete 5.4 Vibrating beams D.3 Cube specimens, cement bound concrete 5.5 Plastic settlement and voids or granular mixes D.4 Stripping and storing Standards ......................................................................39 3 Practical guide for site personnel Where Designated concrete is not specified and 1. Introduction where the ready-mixed concrete supplier has no product conformity certification then it may be This guide is for construction site personnel to appropriate for identity testing to be specified, help them specify, order, receive, place, compact, where this is carried out by site personnel. finish and cure ready-mixed concrete. Most requirements of a concrete specification are The standard procedures for sampling concrete, derived off-site by a designer, or the designer consistence tests, air content tests and making specifies a Designated concrete where most of specimens for strength tests are included in the the requirements are pre-specified. Designated appendices. Any identity testing will be part of concretes can only be supplied by ready-mixed the receiving concrete procedures that should concrete companies who have a suitably high also include site preparation. Thereafter guidance level of product conformity certification and so for placing, compacting, finishing and curing there is verification of the concrete delivered is concrete are also outlined to ensure that the consistent with that ordered. hardened concrete performs as anticipated by the designer. Where a Designed, Prescribed, Standardized Prescribed or Proprietary concrete is specified then any requirement for the producer to have product conformity certification is an additional requirement that should be included in the specification. This requirement may be specified by the designer or the contractor. The contractor also has to specify the required consistence, that is the workability, of the concrete to be delivered and these aspects are covered in Chapter 2. 4 Specifying concrete 2.2 Consistence 2. Specifying Consistence is the European and British Standard word for workability. For the most common concrete applications consistence is specified by slump class, where consistence is measured using the 2.1 General slump test as described in Appendix B.1. For more workable concrete consistence should be The concrete specification given to the ready- specified by slump-flow class, where the test is mixed concrete producer should include all described in Appendix B.3. the required properties. Although the designer specifies those properties of concrete required Specifying and ordering the highest consistence to ensure it remains serviceable during its class concrete possible will minimise the time working life it is up to the contractor to complete required to place and compact concrete. the specification. Where the designer has not In general this will minimise the cost of included a requirement for the ready-mixed construction as the cost of extra manpower to concrete producer to have product conformity place low workability concrete generally exceeds certification then the contractor should take this the extra cost of higher workability concrete. option to ensure the concrete delivered is of the required performance. Table 1 shows consistence slump classes as requirements for tests on spot samples taken Product conformity certification. from initial discharge. QSRMC and BSI Kitemark Scheme for ready- mixed concrete set the required product Table 1. Consistence specified as a slump class conformity certification level standards Specified Spot samples taken from initial discharge for producers to supply Designated slump class Not less than, mm Not more than, mm concretes. Companies awarded QSRMC or BSI Kitemark certification are licensed to S1 0 60 use the Certification Mark on literature and S2 30 110 documentation, including quotations and S3 80 170 delivery dockets. S4 140 230 S5A) 200 — The contractor also adds the additional properties required for transportation after A) The slump test should only be used for slump ≥ 10 mm and ≤ 210 mm. For higher workability concrete it is delivery, placing, compaction and any preferable to specify by slump-flow class. requirement for early age strength. In most cases the contractor only needs to specify the As shown in Table 1 where very workable required consistence where this is added to the concrete is required, at a slump in excess of designer’s specified requirements to complete 200 mm, then the slump test is not a suitable test the specification that goes to the ready-mixed and it is preferable to specify by slump-flow class concrete producer. or by flow class. 5 Practical guide for site personnel Designated Concrete, where these concretes are Ordering the correct consistence class The correct way to order consistence class S3 largely defined by their designation, as shown is to order consistence class S3. As measured in Table 2. Designated concretes are normally by slump tests on spot samples from initial supplied by default at S3 consistence. The discharge the range of slump from 80 mm exceptions are PAV1 concrete which is supplied to 170 mm appears quite wide, but it should at a default slump class of S2 and Cement-bound be remembered that fresh concrete losses (CB) concrete which is supplied earth-dry.