Experimental Study on the Optimization of Concrete Mix Ratio in Freeze-Thaw Environment

In order to screen the good proportions of concrete under freeze-thaw environment, cement heat of hydration tests and uniaxial compression tests of concrete after freeze-thaw are carried out under different conditions to investigate the effects of admixture and water-cement ratio on the structural properties of concrete, to determine the good proportions of concrete in cold areas, and to establish the stress-strain prediction curve of the whole process after freeze-thaw. The results show that: (1) The total heat of hydration decreases with increasing mineral admixture content. However, a small dosage of silica fume can enhance early-age heat release. The reactivity of the materials at early ages follows the order: cement > silica fume > fly ash; (2) A small amount of fly ash and silica fume admixture into concrete can play the microaggregate and volcanic ash effect, improve the concrete compactness, and strengthen the structural frost resistance and mechanical properties; (3) Low admixture (0~10%) silica fume incorporation is beneficial to structural frost resistance, fly ash (0~20%) incorporation leads to first increase and then decrease in structural frost resistance, so there is an optimum value of fly ash incorporation, water-cement ratio leads to significant decrease in structural frost resistance, 15% fly ash—10% silica fume—0.36 water-cement ratio is an excellent concrete ratio applicable to cold regions; (4) The prediction curve of compressive stress-strain of concrete after freeze-thaw is proposed, which can be applied to the nonlinear analysis of concrete in cold regions.