Influence of Silica Fume Additive and Temperature History on the Volume Change of Ultra-High-Strength Cement Paste and Concrete

Abstract

Abstract In this article, the temperature dependency of the autogenous shrinkage and the thermal expansion coefficient (TEC) of ultra-high-strength concrete (UHSC) and cement paste is discussed. The concrete and cement paste binder is mixed with portland cement and silica fume (SF) with water-to-binder ratios ranging from 13 to 20 % and SF replacement rates ranging from 7.5 to 17.5 %. First, we confirm that the autogenous shrinkage of a concrete specimen can be estimated from that of cement paste by using the theory of composite materials. Second, the SF reaction ratio and portlandite consumption for each temperature history is examined simultaneously with measurements of the autogenous shrinkage and the TEC of ultra-high-strength cement paste. The results show that, for the same specimen, the apparent activation energy of autogenous shrinkage and TEC is larger than that of physical properties such as Young’s modulus. This is attributed to the amount of calcium hydroxide consumption per SF reaction being much larger at high temperatures than at 20°C and the rapid increase in the Brunauer-Emmett-Teller (BET)-specific surface area of hardened cement paste at high temperatures. From the previous results, it is inferred that the microstructure of UHSC containing SF is modified to exhibit increased sensitivity to volume. These results indicate that not only the thermal strain but also the thermos-active properties of autogenous shrinkage need to be considered when conducting numerical analysis for crack risk assessment.