Title : ADMIXTURES FOR GEOPOLYMER CONCRETE: THE PERFORMANCE OF ACCELERATING ADMIXTURES
Authors : Roar Myrdal and Ryan Griffith
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Price : 250
Abstract : Alkali-activated low-calcium fly ash geopolymers are considered eco-friendly and durable binders, however they require thermal curing to gain acceptable strength. Geopolymers therefore, have found some niche areas of application, particularly in the precast industry. In order to expand the application of geopolymers, it is important to develop accelerating admixtures which allow acceptable setting and curing at ambient temperatures. Today’s common accelerators for OPC concrete were tested, but they did not show any accelerating effect on alkali-activated low- calcium fly ash binders, except calcium chloride and an organic accelerator which had a minor effect on 1 day strength. Actually, in this study most of the OPC accelerators retarded strength development. This lack of accelerating effect is most likely due to the absence of calcium in these mixes. Calcium plays a key role in the chemistry behind OPC/accelerator interactions. Two organic admixtures greatly affected the setting and hardening of alkali-activated low-calcium fly ash at 20°C. One organic admixture (ORG2), when dosed at 10% by weight of fly ash, resulted in flash set after approximately 30 seconds. Compressive strength value as high as 2 MPa after 1 hour were obtained. This accelerator might be a potential candidate if sprayed geopolymer concrete is to be developed for tunneling applications, partly due to the fire resistant properties of geopolymers.