Parallel Bar Compressive Strength Model for Pumice Concrete Considering Frost-Heave Stress

Pumice concrete is a lightweight porous building material. Under the continuous low temperature in permafrost regions, the interstitial water of concrete is frozen, which can improve its mechanical properties. In this research, the interstitial water freezing law of pumice concrete is obtained by nuclear magnetic resonance, the frozen-heave stress and compressive strength of pumice concrete under a low-temperature environment are tested, and the relationship among the three is studied. A compressive strength model for pumice concrete considering frost-heave stress is also established using parallel bar theory. Finally, the hydrothermal coupling frost-heave model of concrete is established. Results showed that in the rapid change stage of 0°C to $-10°\mathrm{C}$, the interstitial water with the largest proportion of medium pores (0.1–1 μm) in this temperature range is rapidly frozen and expanded, which makes the frost-heave stress and compressive strength increase rapidly. The frost-heave stress caused by pore-water freezing can be regarded as prestressing force against external load, which is the main reason for the increase in low-temperature compressive strength of pumice concrete. The maximum error between the calculated value of the parallel bar compressive strength model and the experimental value was 7.42%, indicating that the model has good accuracy and certain rationality. The hydrothermal coupling model can reflect the frost-heave process of concrete, and the error between the simulated and experimental values of frost heaving strain was small, which proves that the model has high accuracy.