This study aims to evaluate the impact resistance and mechanical properties of a number of developed lightweight self-consolidating concrete (LWSCC) mixtures under cold temperatures. To achieve LWSCC mixtures with minimum possible density, the authors explored different replacement levels of normalweight fine or coarse aggregates by lightweight fine and coarse expanded slate aggregates. The studied parameters included testing temperature (+20°C, 0°C, and –20°C), type of lightweight aggregate (either fine or coarse expanded slate aggregates), binder content (550 and 600 kg/m3 [34.3 and 37.5 lb/ft3]), coarse-to-fine (C/F) aggregate ratio (0.7 and 1.0), and the use of polyvinyl alcohol (PVA) fibers (fibered and nonfibered mixtures). The results indicated that for all tested mixtures, decreasing the temperature of concrete below room temperature significantly improved the mechanical properties and impact resistance. Increasing the percentage of lightweight fine or coarse aggregate in the mixture showed more improvement in the mechanical properties and impact resistance under cold temperatures. However, the failure mode of all tested specimens appeared to be more brittle under subzero temperatures. It was also observed that the inclusion of PVA fibers helped to compensate for the brittleness that resulted from decreasing the temperature, and it further enhanced the impact resistance and mechanical properties under low temperatures.

Freezing-and-thawing (F-T) resistance is a key parameter in evaluating the durability of concrete. The response of concrete under F-T environment varies depending on the mixture proportion and materials used. This paper focuses on the F-T behavior and damage resistance of normal-strength (NC), high-strength (HSC), high-performance (HPC), and ultra-high-performance (UHPC) concrete. The mechanisms causing F-T damage are discussed, specifically based on expansion of freezable water under negative temperature and thermal stress arising from differences in the coefficient of thermal expansion of cement and aggregates. To quantify damage, two parameters—namely, mass loss ratio (MLR) and relative dynamic elastic modulus (RDEM)—are compiled for different classes of concrete. Results show that UHPC exhibited much lower increase in MLR and reduction in RDEM than NC and HPC, respectively. The effects of F-T loading on other mechanical properties of concrete such as compressive strength, flexural strength, tensile strength and stress-strain relationship are also investigated in this paper as possible parameters to help characterize F-T resistance. It is found that F-T will decrease the peak stress but increase the peak strain, and the flexural strength has the fastest loss rate for NC, HPC, HSC and UHPC, respectively. As concrete under F-T environment is often exposed to chloride, the significance of sodium chloride (NaCl) concentration and chloride diffusion coefficient (CDC) on HSC and UHPC under NaCl solution are studied. UHPC exhibits better resistance on chloride diffusion after F-T action due to denser internal pore structure. To improve the F-T resistance of concrete, the performance of two supplementary cementitious admixtures, fly ash and silica fume, to partially replace cement are studied. Results show that the appropriate fly ash replacement of 10 to 30% or silica fume replacement of 5 to 10% is found to enhance the F-T resistance. In addition, introducing fibers such as PVA or PP can improve the F-T resistance significantly, although using the wrong proportion may have a negative effect. Using combined admixture of polyvinyl alcohol and polyethylene fiber with 1.5% volume in cement-based composites reduces strength degradation caused by F-T loadings.