Comparative study of the initial surface absorption and chloride diffusion of high performance zeolite, silica fume and PFA concretes

Abstract Zeolite, a type of natural pozzolanic material, has been used in producing blended cement and concrete in China. The purpose of this study is to evaluate the effectiveness of zeolite in enhancing the performance of concrete in comparison with silica fume and pulverized fuel ash (PFA). In the first series of experiments, zeolite, silica fume, and PFA were all used to replace 5%, 10%, 15% and 30% of cement by weight in concrete with water to total cementitious material ratio (W/(C + P)) kept at 0.28. The results showed that zeolite decreased bleeding and increased marginally the viscosity of concrete without significantly compromising the slump. And at 15% replacement level, it resulted in 14% increase in concrete strength at 28-day compared with the control concrete. The test results also showed that there existed an optimum replacement level for zeolite to effect a decrease in initial surface absorption and in chloride diffusion of concrete. The test results of the second series of experiments where zeolite, silica fume and PFA were in turn used to replace 10% of cement in concretes with W/(C + P) in the range of 0.27 to 0.45 appeared that zeolite performed better than PFA but was inferior to silica fume in terms of increasing strength, decreasing initial surface absorption and chloride diffusion. It was further found that when W/(C + P) was greater than 0.45, the strength of the concretes incorporating zeolite or PFA (by direct replacement) was lower than that of the control concrete. The micro-structural study on concrete with zeolite revealed that the soluble SiO2 and Al2O3 could react with Ca(OH)2 to produce C–S–H which densified the concrete matrix. Pozzolanic effect of zeolite improved the microstructure of hardened cement paste and reduced the content of the harmful large pores, hence made concrete more impervious.