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Concrete In Australia : September 2013
Concrete in Australia Vol 39 No 3 29 for geopolymer concrete. e Concrete Institute of Australia (CIA) has produced a recommended practice for geopolymer concrete (CIA, 3). is document provides background information on geopolymer chemistry and materials and properties of geopolymer concrete. Recommendations on modification to current standards are given in the document. RILEM Technical Committee 224-AAM on Alkali-Activated Materials has an objective of developing performance-based specifications and recommendations for development of standards for these materials. e scope includes alkali- activated slags and fly ashes, geopolymer and other emerging technologies. e committee aims to deliver recommendations on performance-based requirements for alkali-activated materials which can be used by national standards bodies. It is expected that the committee will finalise a document in 2013. e RILEM committee also plans to conduct a durability testing program. ASTM committees C01 (Cement) and C09 (Concrete and Concrete Aggregates) are considering standards for non- Portland cement binders such as geopolymers and related alkali- activated aluminosilicates. Such standards should increase user confidence with these materials. 4.0 BARRIERS TO IMPLEMENTATION OF GEOPOLYMER CONCRETE Implementation of low CO2 concrete materials on a large scale requires identification of barriers to use. Adoption of new or different materials in the construction and other industries also face barriers typically associated with regulatory or institutional issues, risk-averse decision makers or lack of flexibility in standards and specifications rather than technical barriers. 4.1 Prior assessments Several authors have highlighted technical, regulatory, economic and supply chain barriers specific to widespread use of geopolymer concrete. For example, van Deventer et al (4) identified the following barriers compared with concrete based on ordinary Portland cement: • variability in source materials • development of suitable admixtures • required operator skill at batch plants • capital intensive set up of processing facilities • existing prescriptive standard framework based on Portland cement binder rather than performance • lack of long-term durability data, particularly field performance • development of appropriate tests methods • risk of supply chain issues such as reduced availability of suitable fly ash and blast furnace slag. Duxson and Provis (5) stated that: " e main impediment facing the uptake of new construction materials is the existing standards regime, where prescriptive standards specify particular mix designs for concrete rather than allowing any material which meets given performance standards to be utilised". Acceptance of geopolymer concrete was also considered by Aldred and Day (6). It was noted that the term "geopolymer" covers a wide range of binder materials and, hence, wide variation in properties and performance. is can be confusing to designers and specifiers. e use of prescriptive standards and codes and exclusion of non-Portland cement binders in these regulations were identified as an impediment to acceptance of geopolymers (Aldred and Day, 6). RILEM Technical Committee 224-AAM has listed the major obstacle hindering the widespread uptake of alkali-activation technology in the construction industry as the lack of uniformly accepted standards. e Federal Highway Administration (FHWA) produced a TechBrief on geopolymer concrete as part of the Concrete Pavement Technology Program (FHWA, 7). is document considered current limitations for geopolymers as follows: • difficulty and care required in working with available systems • safety risk associated with alkalinity of activating solution • processing of high alkalinity solutions and associated energy consumption and greenhouse gas generation • temperature sensitivity • elevated temperature curing under strict control required. It was suggested by the FHWA that geopolymer concrete in the transportation industry is best suited to precast applications until the above limitations are overcome. While geopolymer concrete offers potential benefits in terms of greenhouse gas reduction compared with Portland cement concrete, sustainability and reduced emissions could be viewed as intangible. Improvement in tangible properties such as cost, strength or durability is likely to be more readily understood by end users than associated greenhouse gas emissions. ere is also variability in published greenhouse gas data depending on the raw materials, transportation and calculation methodology as discussed by McLellan et al (8) and Turner and Collins (9). Conflicting emission data is regarded as detrimental to the adoption of geopolymer concrete. 4.2 Industry survey on barriers A survey consisting of six questions was undertaken to obtain input from representatives of the concrete and affiliated industries. Participants were asked to identify barriers to the implementation of geopolymer concrete and provide opinion on potential pathways for overcoming these barriers. ere were 42 total respondents to the survey and 40-42 responses to each question. e results for the first section of the survey are presented in the figures below. Full details of the survey, including the additional written comments, will be presented in a final report for the CRC. As shown in Figure 1, the majority of survey respondents were material suppliers, government, academic/researchers or engineering consultants. A significant proportion of respondents were in the "other" category. e roles of these people were retired/author, asset manager, coal power generators and construction materials consultant. Figure 2 indicates that most respondents were knowledgeable on geopolymer concrete to some degree and that the majority had a moderate level of knowledge.