THE EFFECT OF C-S-H AND PORE STRUCTURE ON COMPRESSIVE STRENGTH OF CEMENT HARDENED WITH VOLCANIC GLASS POWDER

Abstract

In this study, the hydration reaction between cement and volcanic glass powder （VG）and its hydrates were clarified, assuming the use of VG as a substitute for silica fume （SF）, which is often used in ultra-high-strength concrete. Furthermore, the relationship between the pore structure formed by the hydrates and the compressive strength development was also examined. As a result, the following findings were obtained. The total pore volume of the cement hardened body mixed with VG reached a minimum and the compressive strength peaked when the admixture ratio was 25％. On the other hand, in the case of SF, the total pore volume was at its minimum and the compressive strength peaked when the admixture ratio was 20％. As the admixture ratio of both VG and SF increased, the amount of C-S-H formation increased and the pore volume decreased due to the pozzolanic reaction, resulting in an increase in compressive strength. The peak admixture ratio of the pozzolanic reaction was 25％ and 20％, respectively. The C-S-H produced when the VG admixture ratio was below 30％ had a higher percentage of high-density C-S-H compared to SF, and the percentage of low-density C-S-H increased rapidly when the admixture ratio reached 30％. The amount of C-S-H produced when the VG admixture ratio was 30％ increased over that at the VG admixture ratio was 25％, but the amount of pores increased. However, the compressive strength when the VG admixture ratio was 30％ was similar to that at the VG admixture ratio was 25％. Based on the analysis of pore size distribution volume and C-S-H density, it was inferred that this was caused by an increase in the amount of pores in the gel porosity region due to the formation of more low-density C-S-H.