Experimental study of macroscopic and microscopic properties of long-age hydraulic concrete based on high-temperature accelerated curing

Abstract

Determining the long-term mechanical properties of hydraulic concrete currently requires time-consuming and expensive tests, which has hampered investigations into the mechanical properties of long-age hydraulic concrete. In this study, the indoor macroscopic mechanical property tests of long-age hydraulic concrete with different curing ages (90, 180 days and 1, 2, 3 years) and different fly ash contents (0%, 15%, 35%) were designed and carried out on hydraulic concrete with 0.5 water-to-binder ratio by using a high-temperature accelerated-curing method based on equivalent age theory. Further tests were carried out using SEM, XRD, and MIP tests on long-age hydraulic concrete specimens with different fly ash contents to determine and analyze the long-term evolution of the macroscopic and microscopic properties of hydraulic concrete. The results showed that the fly ash content significantly affects the activation energy Ea of hydraulic concrete and that the curing time required to reach the designed hydration degree increases with increasing fly ash content. The long-age compressive strength and splitting tensile strength of hydraulic concrete with different fly ash contents increased logarithmically with curing age. After hydration for the curing age of 3 years, the overall microscopic structure of the mortar region of the long-age hydraulic concrete becomes dense, and the main XRD peak is due to quartz. The porosity decreases with increasing curing age, and the main pore types transition from multi-harmful pores (>200 nm) to harmless pores (<20 nm) and less harmful pores (20–50 nm). The multiple correlation coefficient of the long-term strength prediction model established by using the combined exponential prediction model ranges from 0.9152 to 0.9765, which indicates that the combined exponential prediction model based on the strength at the curing age of 28 days better replicates the long-term performance of hydraulic concrete.