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This study focuses on the influence of salt crystallization from sodium sulfate on uniaxial compressive properties of concrete subjected to the coupling action of dry–wet cycles and freeze–thaw cycles. Eight groups of concrete specimens with different concentrations of sodium sulfate solution (CSSS) and different numbers of drying and wetting cycles (NDWC) were designed. Three groups of specimens with different numbers of freezing and thawing cycles (NFTC) exposed to same dry–wet cycles and same sulfate concentration were prepared to study the effects of combined environmental conditions. Salt crystallization from sodium sulfate was generated under a cyclical dry–wet time ratio of 3:1. Scanning electron microscopy and X-ray diffraction analysis were used to analyze reaction products of sulfate and concrete matrix. The results show that under single sulfate dry–wet cycles, with the increase of CSSS and NDWC, the uniaxial compressive strength of concrete degrades as a parabola and corresponding strain increases as a parabola, except for the linear increase of CSSS strain. Subjected to the combined action of sulfate dry–wet cycles and freeze–thaw cycles, it shows that the uniaxial compressive strength of concrete decreases as a parabola with the increase of NFTC, but corresponding strains have no obvious variation. The sulfate salt attack in advance greatly accelerates the deterioration of specimens after freeze–thaw cycles. The common dimensionless predication model of stress–strain relationship of concrete subjected to the combined action of dry–wet cycles and freeze–thaw cycles has been established. [ABSTRACT FROM AUTHOR]

• The bond behavior between deformed rebar and surrounding concrete under the combined actions of sulfate, dry-wet cycle and freeze–thaw cycle was investigated. • The bond-slip relationships of deformed rebar and surrounding concrete under different variables before and after yielding were obtained. • The expansive force caused by sulfate crystallization under different variables were calculated. • The bond strength models of post-yielding deformed rebar and surrounding concrete under single and multiple environmental factors were established. The bond-slip behavior of deformed rebar with medium embedded length and surrounding concrete without stirrup under sulfate salt, dry-wet cycle and freeze–thaw cycle was investigated in this study. Physical crystallization of sulfate was produced by using a 3:1 drying/wetting time ratio in erosion specimens. Different concentrations of sodium sulfate solution (CSSS), different drying and wetting cycles (DWC), and different freeze–thaw cycles (FTC) were considered as environmental variables in central pull-out tests. The bond characteristics of post-yielding rebar and surrounding concrete under combined environmental factors were obtained. Scanning electron microscope and x-ray diffraction analysis were conducted to identify reaction products. The experimental results showed that CSSS and DWC had both beneficial and adverse effects on the bond strength.1% CSSS and 25 DWC were the turning points of increasing and decreasing of bond strength. The expansion force caused by Na 2 SO 4 physical crystals improved the bond strength in the initial stage, but impaired it after the crack of pore wall of concrete in the later stage. After superimposed FTC, the bond strength was greatly reduced. Sulfate crystallization significantly accelerated the deterioration of bond strength under freeze–thaw cycles. The prediction models of the bond strength between deformed rebar and surrounding concrete after yielding in terms of single and multiple environmental factors had been established. The models can be used to predict the bond strength of post-yielding rebar and surrounding concrete in complex environments of sulfate, dry-wet cycle and freeze–thaw cycle. [ABSTRACT FROM AUTHOR]