RESPONDING TO DEMAND FOR A LOWER CARBON FOOTPRINTREVISION OF THE AUSTRALIAN CEMENT STANDARD
Concrete and the environment • Concrete is ubiquitous • It is the largest volume man-made construction material used • Concrete uses a number of natural raw materials and their acquisition has some environmental impacts • Concrete delivers many environmental benefits, including: - buildings are low maintenance and long lasting - its thermal mass can increase the energy efficiency of buildings - buildings can be designed for reuse and then recycled at the end of their lives - it provide good indoor air quality - it is non-combustible and has good fire resistance - it is of high quality and affordable
Concrete and CO2 • The strength and resilience of concrete is due primarily to its binder, that is, Portland cement • Portland cement has a high “carbon intensity” and its manufacture is generally viewed as contributing about 5% of global carbon dioxide production • This “carbon intensity” derives from several process components: - the calcination of limestone (which is effectively 44% CO2) - the combustion of fossil fuels to provide the approximately 1400 degrees Centigrade temperatures required to effect the chemical conversion of the raw materials into the Portland cement minerals - the use of electricity to drive equipment used to process raw materials (raw mill, kiln, fans) and to grind cement clinker into cement powder • Historically it was viewed that 1 tonne of cement = 1 tonne CO2
Cement industry response to CO2 The Australian cement industry has responsibly worked to address concerns about CO2 for some years. Several approaches have been taken, including: • Modernisation of cement making technology • Use of alternative fuels • Use of supplementary cementitious materials (SCM’s) Ref: 2009 Australian Cement Industry Sustainability Report - CIF
Ongoing cement industry activity The cement industry, through its involvement with the Cement Industry Federation and Cement Concrete & Aggregates Australia, has a number of continuing and ongoing initiatives to reduce CO2 and reduce energy consumption, including: • Working collaboratively with Government in several areas • Pursuing emerging technology opportunities through the Asia-Pacific Partnership on Clean Development and Climate • Targeting higher usage levels for SCM’s • Increasing efficiency in the use of energy and resources • Maximising use of recycled materials (eg. alternative fuels) • Directly reducing the clinker content of cement products through use of higher levels of mineral addition
Mineral addition in cement • Mineral addition was introduced into the Australian Standard for cement in 1991, at a level of “up to 5%” for all cements. • Allowable mineral additions are fly ash, slag and limestone. • Mineral additions are also included in EN and ASTM Standards in all of the cements covered in those Standards. Over two years ago, CCAA began work on proving the use of a higher level of mineral addition, at “up to 10%”, for use in all cements included in the AS 3972 “Portland and blended cements” Standard. This meant that, if approved, Australia would be the first country where >5% mineral addition was allowed in all cement types. Trial work was to be carried out using 10% limestone mineral addition.
Use of limestone in cement Limestone was chosen for use in the test program as it should be the most difficult test of the 10% mineral addition proposition. Limestone is commonly used in “general purpose cements”, particularly in Europe. This also meant that there would be a plentiful supply of technical data, as these cements have been in use since the 1970’s. Note: EN 197 has a product called “Portland Cement” where the only allowable additions to cement clinker are gypsum and mineral addition at a level of “up to 5%”. The CCCA proposal was for all AS 3972 cement types to be allowed to have mineral addition levels of “up to 10%”
Limestone cement use in Europe • Limestone cements containing 6-20% limestone are now the typical “general purpose” cements used in many parts of Europe, particularly France and Switzerland • Their use is not confined to basic concrete • There are two levels of limestone use – from 6-20% (CEM II/A-L) and from 21-35% (CEM II/B-L) • CEM II / A-L used in paving for the Gotthard Tunnel, Switzerland
The CCAA proposal and trials The proposed amendment to the Australian Standard 3972 was in several parts: • To increase the allowable level of mineral addition to 10% for all cement types (Type GP, Type GB, Special Cements) • To allow part (up to 5%) of the mineral addition to be “minor additional constituents” – “selected inorganic mineral materials derived from the clinker production process – such as cement kiln dust” To assess the effects of these materials, trials were carried out at 8 cement plants, followed by extensive cement and concrete testing The trials were hampered by short runs, and the trial product was not able to be fully optimised
Trial results Cement testing showed that the trial products gave similar performance to Type GP containing 5% mineral addition – similar workability; slightly lower strength; slightly lower shrinkage Laboratory concrete testing results mirrored the cement test results, both with and without SCM’s. Field testing of concrete gave results that were at least as good as those from cement containing 5% mineral addition. Test results were provided to interested parties, and presented to a reconstituted Standards committee (BD 10), along with substantial literature reviews that compiled and assessed the international experience with limestone mineral addition levels >5%.
Standards deliberations The Standards committee was reasonably evenly weighted between the cement and concrete representatives and the specifier nominees representing APCC, Austroads, Engineers Australia and ATIC. The major area of contention was the lack of published information on the Australian experience with cement and concrete using higher levels of mineral addition. Despite a wealth of information on experiences with these products in Europe and Canada, and technical substantiation of the physical and chemical reaction mechanisms occurring with mineral addition, an effective stalemate was reached on the 10% addition level proposal. The opportunity to move forward came with the decision to compromise on a 7.5% mineral addition level, and agreement to enter into a 2 year research program to establish the optimum level of mineral addition.
AS 3972 - 2010 The new version of AS 3972 has been published, with the following changes from the previous addition: • The allowable level of mineral addition increased to 7.5% • The mineral addition may contain up to 5% “minor additional constituents” • Introduction of a new type of cement – general purpose limestone cement - Type GL – which contains 8-20% limestone • A limit of 0.10% by mass of chloride • Additional compliance requirements for sampling, testing and labelling • The option for data on the “Evaluation of uniformity of cement strength from a single source” to be requested by users
The new Standard This Standard provides rigour around the manufacture, testing and reporting of cement quality that is the equal of any in the world, and is in fact significantly stronger than most other Standards. It retains its fundamental “performance-based” approach The Standard moves us a little closer to our goals relating to reducing the carbon footprint of concrete, without any detriment to quality (If adopted fully, the nominal reduction in CO2 is about 200kt per annum) The Standard provides an opportunity to trial higher mineral addition levels while maintaining conformance with AS 3972 requirements, through the use of the Type GL product Deliberations about the Standard gave all industry groups the opportunity to elaborate on their particular expectations in relation to product performance and concrete durability
Next moves A Working Group of industry parties will now develop a testing program that will be undertaken (primarily) by the cement and concrete members of CCAA There will be the integral involvement of the various specifier groups in both developing the testing program and reviewing results The fundamental aim will be to achieve an optimised position where the carbon footprint of the industry is minimised and the effectiveness of our products is enhanced
The beginning ……………. Of the next round of work with our industry partners to improve the technical performance of our products, while even further reducing the carbon footprint of our industry!