Shrinkage characteristics of high-strength concrete for large underground space structures

This study forms part of a research project that was carried out on the development and application of high-strength concrete for large underground spaces. In order to develop 50 MPa high-strength concrete, eight optimal mixtures with different portions of fly ash and ground granulated blast furnace slag, which make the pozzolanic reaction, were selected. For assessments of shrinkage characteristics, free shrinkage tests with prismatic specimens and shrinkage crack tests were performed. The compressive strength was more than 30 MPa at 7 days, and stable design strength was acquired at 28 days. High-strength concrete containing blast furnace slag shows large autogenous shrinkage, while large shrinkage deformations and cracks will occur when mixtures are replaced with large volumes of cementitious materials. Hence, for these high-strength concrete mixtures, the curing conditions of initial ages that affect the reaction of hydration and drying effects need to be checked.