Study on early shrinkage of concrete under different aggregate types based on thermo-mechanical model

Under the combined effects of heat and mechanical loading, the early shrinkage and microcracking of concrete with different non-calcined materials and aggregate types significantly affect its macroscopic properties. In this study, 12 types of concrete specimens were prepared, including three types of cement (Portland slag cement PSC, Portland fly ash cement PAC, and Portland composite cement PCC) and four types of aggregates (gravel, limestone, basalt, and granite) with a particle size range of 2-30 mm. The compressive and tensile strengths, shrinkage, and creep properties at different ages were systematically tested. Additionally, a numerical model that accounts for hydration heat and equivalent age was established to analyze the early thermal-mechanical behavior of concrete, and the influence of aggregate type on the hardening temperature, shrinkage strain, and creep development of concrete was predicted and analyzed. The results show that the compressive strength and shrinkage strain of concrete increase with the Langmuir function with the curing time (R²>0.90). Under the same cement type and age, the granite aggregate concrete exhibits the highest compressive and tensile strengths; the shrinkage and creep strain of gravel aggregate concrete are the largest, while the shrinkage strain of basalt aggregate concrete is the smallest, and the creep strain of granite aggregate concrete is the smallest. The performance indicators of limestone aggregate concrete are generally between those of gravel and basalt/hard granite. For example, the 28-day compressive strength is approximately 11.9% higher than that of gravel, and the ultimate shrinkage is approximately 7.9% to 23.7% lower than that of gravel. Compared with cement containing slag, cement containing fly ash can increase the ultimate compressive strength of concrete by 3.2% to 10.6%, but it also increases the early and later creep strains. The calculation results of the numerical model are in good agreement with the measured values in terms of trend and quantitative values. Considering the hardening temperature, shrinkage, and creep performance, basalt can be selected as the preferred aggregate for silicate fly ash cement concrete.