Due to the high viscosity of geopolymer concrete, the workability of fresh geopolymer
concrete was tested in term of slump flow according to ASTM C1611 (2010). The results as shown in Fig. 3 indicated that fresh geopolymer concrete had the slump flow between 550-660 mm. These slump flow values suggested that the geopolymer concretes in this study was class SF1 self-compacting concrete in accordance with EFNARC (2005). The use of saturated surface dry RCA tended to give a higher workability than that with LS. Because of the RCA particles contain a larger volume of pore and water at saturated surface dry condition than that of LS particles. The water inside RCA particles was available and improved the workability of the mixes (Poon et al., 2004). The report of Mefteh et al. (2013) showed that the use of RCA in pre-wetting and saturated surface dry conditions improved the concrete workability. In addition, at the same liquid to ash ratio, the use of high NH concentration gave geopolymer concrete with low slump flow. This was due to the increase in NH concentration resulted in leaching of more silica and alumina and thus increase the geopolymerization and the stiffness of the system