Concrete has inherent fire resistance and is a material ideally suited for providing fire safe construction. However, fires in tunnels and the collapse of the World Trade Centre towers on September 11th 2001 focused attention on the robustness of all construction materials in a fire. Also, the concrete design Eurocode (EN 1992: 1-2) includes design methodology which can lead to more efficient design in concrete but is still unfamiliar to UK designers.
From the early 1990’s it has been evident that the possibility of a rare form of sulfate attack, the thaumasite form of sulfate attack, or TSA, on concrete in particular soil conditions should be considered for safe durable design. Consideration is particularly important as the TSA deterioration will not be visible in the above-ground parts of the affected structures.
DEF has caused cracking in some heat cured precast concrete components many years after the concrete was produced. There is a concern that cracking has also occurred in larger insitu concrete structures as a result of the build up of heat of hydration in the early life of the structure.
During 1975-1990 some expansion and cracking occurred in a number of buildings and structures due to a reaction between certain types of aggregate and alkalis in the concrete pore fluid. This alkali silica reaction (ASR) can often continue for more than five years before any damage becomes apparent. This form of concrete deterioration received widespread press coverage, often being dubbed ‘concrete cancer’. Reassurance is still needed that recently constructed buildings will not suffer from ASR in the future.
Self-compacting concrete (SCC) was developed in Japan in the late 1980’s and allows concrete to be placed fully compacted without segregation and with no additional compactive effort such as internal or external vibration. It currently makes up about 5% of the Japanese concrete market and around 15% of the Danish and Swedish markets. SCC has economic, social and environmental benefits over conventionally vibrated concrete offering faster construction times, increased workability and ease of flow around heavy reinforcement.
There is a public will to reduce the use of primary aggregates in construction, including concrete. Inert, construction and demolition waste (and especially crushed concrete) forms a possible source for recycled aggregates when produced in accordance with a WRAP Quality Protocol. Over 60% of this type of material is used as aggregate, general fill or for land reclamation. British Standards permit the use of recycled aggregates in some forms of new construction. Around 17% of UK aggregate needs are already met from recycled material.
A major priority for cement makers is the safe manufacture of high quality cement. The UK cement industry is committed to achieving this in a sustainable way: environmentally, socially and economically. To achieve greater sustainability of its manufacturing process it is essential that all available resources are used efficiently and effectively. Many wastes from within the industry or from external sources have potential for use within cement manufacture, either as fuels or replacement raw materials, and the industry is actively pursuing their beneficial use within its processes.
Low carbon, factory-made Portland-limestone cements (PLC) have been produced commercially by MPA Cement’s Member Companies since the mid-1990s and are available packed and in bulk (see also MPA Fact Sheets 14a and 14b - Modern cements). Parts of the concrete sector may still be unfamiliar with this type of cement and its properties and there has been some confusion about the nature and composition of Portland-limestone cements. This Fact Sheet has been prepared to describe the properties and performance of these cements and to differentiate them from CEM I cement which can also have a limestone minor additional constituent (mac) of up to 5% by mass.
In the UK, MPA Cement's Members have been CE marking their common cements conforming to European standard BS EN 197-1 since its implementation in April 2001, noting that the standard was revised in 2011. Some twelve years on, and CE marking of a wide range of cements, and related products, has, under the former Construction Products Directive (CPD), become established throughout the European Economic Area (EEA). On 1 July 2013, however, the Construction Products Regulation (CPR) came fully into force and its CE marking provisions, and requirement for declarations of performance (DoPs), replaced those of the CPD. The CE marking of cements, and provision of related information, is now facilitated via the procedures outlined below.
When the REACH Regulation [Registration, Evaluation, Authorisation (and Restriction) of Chemicals] came into force on 1 June 2007, clause 47 of its Annex XVII replaced/superseded the cement-related chromium (VI) provision in former EU Directive 2003/53/EC. The legislative provision, however, remains unchanged and continues to restrict the marketing and use of cement and cement-based preparations, where they contain when hydrated more than 0.0002 % (2 ppm) chromium (VI) of the dry weight of cement.
Why does cement contain chromium? The chromium in cement comes primarily from some of the naturally occurring raw materials used in the manufacture of cement. What does chromium do? When cement is mixed with water some of the chromium dissolves (like salt in water) and can cause allergic dermatitis if in contact with skin for prolonged periods of time.
Clause 47 of Annex XVII of the REACH Regulation regulates cement and cement-containing preparations for their water-soluble chromium (VI) content. It has the objective of minimising the occurrence of chromium (VI)-related allergic dermatitis which can arise from contact with wet cement during use.
In order to be able to quantitatively determine the chromium (VI) content of cement, the European Commission has officially acknowledged a test method – EN 196-10 - developed by CEN, the European Committee for Standardisation.
In order to demonstrate compliance, MPA Cement's Member Companies are all participants in a Kitemark Verification Scheme developed by BSI Assessment and Certification. This Scheme is based on the provisions in normative Annex A of BS EN 196-10 'Evaluation of the compliance of cement with the regulatory limit in Directive 2003/53/EC [now REACH] on water-soluble hexavalent chromium content'. The test method used is described in the same European Standard.
The introduction of legislation (now Clause 47 of Annex XVII of the REACH Regulation) which regulates cement and cement-containing preparations for their water-soluble chromium (VI) content, and the advent of the 'shelf-life' concept for cement, has made it more likely than before that cement may be discarded as waste. At expiry of the 'chromium (VI)-related shelf-life' (declared storage period), or earlier if a reduced cement has not been stored as recommended by the manufacturer, the cement may become a waste because the 'holder' will be unaware of, or be unable to apply, the several alternatives available. This Fact Sheet describes the options under the chromium (VI) legislation.
Traditional Portland cement-based concrete provides the foundation for the built environment. Buildings constructed appropriately and imaginatively from this material can and do exhibit an impressive array of properties especially those that have been designed to optimise the thermal mass of concrete. This type of concrete building is expected to adapt best to the UK's changing climate.
'Cement' is the basic ‘glue’ that binds together all the components of concrete which, in turn, is the most widely used construction material on earth. But what is cement? And what are ‘modern cements’?
What are modern cements? 'Cement' is the basic ‘glue’ that binds together all the components of concrete which, in turn, is the most widely used construction material on earth. But what is cement? And what are ‘modern cements’?
The Weights and Measures (Packaged Goods) Regulations 2006 mean that bags of cement will be marked with a nominal quantity, and it is the cement packers' responsibility to ensure that: a) the actual contents of the bags shall not be less, on average, than the nominal quantity; b) the proportion of the bags short of the stated quantity by a defined amount (the “tolerable negative error” or TNE) should be less than a specified level; and c) no bag shall be short by more than twice the TNE.
The REACH regulation came into force on 1 June 2007. 'REACH' stands for – Registration, Evaluation, Authorisation (and Restriction) of Chemicals - and it implements a uniform legal system, effective for all chemicals inside the European Community (EEA). This system is intended to enhance the safe use of chemicals in all types of application by providing appropriate health, safety and environmental information and communicating it to relevant stakeholders.
The information in this fact sheet is aimed at providing lifecycle1 data to inform ‘carbon footprinting’ in the concrete supply chain. This fact sheet replaces a previous version which was based on 2010 data and reflects greenhouse gas reductions achieved by the sector. It includes all greenhouse gases converted to a CO2 equivalent basis (CO2e).
This Fact Sheet describes the position of cement and cementitious products under the current (2014) legislative/regulatory framework established in the UK. This limits water suppliers (public supply) and contractors/other stakeholders (premises of all types receiving water) to use only products and substances which meet the requirements of the relevant regulations, including official approval, or authorization, where required by the relevant authority.
Note: MPA Cement Fact Sheet 11, ‘The classification and characterisation of cement where discarded as waste’, has been withdrawn. Subsequent Environment Agency advice concludes that because the cement product is classified as an irritant when handled and in use, that when discarded, cement should therefore be classified as hazardous waste for the purposes of disposal. This is contrary to an expert opinion sought by MPA Cement (formerly BCA), however users should adopt a precautionary approach and follow the Environment Agency's recommendations.