Title: High-Performance Concrete Incorporating Zeolite, Fly Ash and Silica Fume
Author(s): Sammy Y. N. Chan and Xihuang Ji
Publication: Symposium Paper
Appears on pages(s): 951-970
Keywords: Absorption; chlorides; diffusion; fly ash; high-performance concretes;
In this research, the effectiveness of zeolite, silica fume and fly ash in making high performance concrete with a strength range between 50 and 120 Mpa and a slump around 2OOmm is compared. In the first series of experiments, the results showed that zeolite could decrease bleeding, and increase marginally the viscosity of concrete without significantly compromising the slump. Although zeolite could not increase the strength of concrete as high as silica fume, it performed better than fly ash due to much finer and high content of soluble Si02. At 15% replacement of cement by zeolite, it could result in 14% increase of concrete strength at 28-day compared with the control concrete without any mineral admixture. The test results also showed that although the replacement percentages of cement from 5 up to 15% by zeolite, silica fume and fly ash could all raise the 7 and 28-day strength of concrete, there existed an optimum replacement percentage for the admixtures to effect a decrease in ISA, and in chloride diffusivity of concrete. In the second series of experiments, the test results confirmed that zeolite could perform better than fly ash but was inferior to silica fume in terms of increasing strength and improving permeation characteristics. It was further found that when w/(c+p) was greater than 0.45, the strength of the concretes incorporating zeolite or fly ash (by direct replacement) would decrease. The test results alsoshowed that zeolite could reduce the diffusion of chloride into concretes. The micro-structural study on concrete with zeolite revealed that the soluble SiO, and A1203 could react with Ca(OH), to produce C-S-H which could densify the concrete matrix. Furthermore, zeolite could have the refinement effect on the pore structure of hardened cement paste, decreasing the content of the harmful large pores, hence making concrete more impervious.