Effect of modified zeolite on the expansion of alkaline silica reaction

Effect of modified zeolite (MZ) on the ASR expansion was analyzed, and comparison between MZ and other mineral admixtures such as fly ash and ground blast furnace slag was made according to ASTM C441. It is shown that the modified zeolite derived from immersion of natural zeolite(NZ) in 2 N NH4Cl solution might decrease the concentration of soluble alkalis in pore solution more effectively, as the alkali ions could be exchanged by NH4+ existed in MZ with formation of NH3·H2O, as a result, the expansion due to alkali-silica reaction (ASR) was controlled consequently. In ASTM C441 test, the 14-day expansion of the specimen incorporating 5% of MZ was less than 0.1%, while the percentage of the fly ash and blast furnace slag with the same efficiency was about 25% and 40%, respectively. Physical properties of cement incorporating 5% of MZ, such as normal consistency, setting time, bending and compressive strength also met the requirement of the Chinese national standard.