Effects of Elevated Temperature on the Strength Development and Microstructure of High-Performance Concrete with Fly Ash

Abstract

The objective of this paper is to study the effects of the elevated internal temperature on the strength development and microstructure of high performance concrete with 40% fly ash in mass structures. The concrete walls were designed using three different depths, being 1.5 m, 0.8 m, and 0.3 m. Temperature histories at different locations in the walls were recorded and the strength development of concrete at those locations were measured. In addition, the change of the degree of hydration, hydration products, and microstructure development of concrete at the different locations were investigated. Test results indicated that high elevated temperatures in mass concrete structures with fly ash significantly accelerate the strength development of concrete at the early ages, while the long-term strength development is decreased. The long-term strength loss is caused by the reduction of the degree of hydration and increased the total porosity and amount of smaller pores. The use of fly ash in mass concrete structure reduces the detrimental effect of high curing temperature on the strength development of concrete.