Axial compression performance and bearing capacity of reinforced concrete column is crucial to concrete structure. Lateral Impact load could pose severe danger to the security and service life of reinforced concrete column. Impact dynamic response, axial compression performance and residual bearing capacity of reinforced concrete columns after lateral impact load were investigated in this paper. Investigation results indicated that with the increase of impact energy, residual displacement and crack width on column increased, impact damage on column exacerbated. It was proved that impact resistance performance of reinforced concrete column could be enhanced by preload axial force. Residual bearing capacity of reinforced concrete column degenerated obviously after subjected to lateral impact load. And RC column would be under elastic stage when impact energy was low. According to analysis results on the correlation between residual displacement and residual bearing capacity, prediction model on residual bearing capacity of reinforced concrete column after lateral impact load was proposed.

The mesoscopic-scale discrete element method (DEM) modeling approach demonstrated high compatibility with macroporous recycled concrete (MRC). However, existing DEM models failed to adequately balance modeling accuracy and computational efficiency for recycled aggregate (RA), replicate the three distinct interfacial transition zone (ITZ) types and pore structure of MRC, or establish a systematic calibration methodology. In this study, PFC 3D was employed to establish a randomly polyhedral RA composite model and an MRC model. A systematic methodology for parameter testing and calibration was proposed, and compressive test simulations were conducted on the MRC model. The model incorporated all components of MRC, including three types of ITZs, achieving an aggregate volume fraction of 57.7%. Errors in simulating compressive strength and elastic modulus were 3.8% and 18.2%, respectively. Compared to conventional concrete, MRC exhibits larger strain and a steeper post-peak descending portion in stress–strain curves. At peak stress, stress is concentrated in the central region and the surrounding arc-shaped zones. After peak stress, significant localized residual stress persists within specimens; both toughness and toughness retention capacity increase with rising porosity and declining compressive strength. Failure of MRC is dominated by tension rather than shear, with critical bonds determining strength accounting for only 1.4% of the total. The influence ranking of components on compressive strength is as follows: ITZ (new paste–old paste) > ITZ (new paste–natural aggregates) > new paste > old paste > ITZ (old paste–natural aggregates). The Poisson’s ratio of MRC (0.12–0.17) demonstrates a negative correlation with porosity. Predictive formulas for peak strain and elastic modulus of MRC were established, with errors of 2.6% and 3.9%, respectively.

In saline soil and alpine regions of northwest China, fiber-reinforced recycled aggregate concrete (FR-RAC) beams are subjected to coupled degradation from a chloride–sulfate composite salt attack and freeze–thaw cycling. Existing studies predominantly focus on natural aggregate concrete in freshwater environments or single-salt solutions, with limited documentation on the shear performance of FR-RAC beams after freeze–thaw exposure in chloride–sulfate composite salt solutions. To investigate the durability degradation patterns of FR-RAC beams in Xinjiang’s saline soil regions, two exposure environments (pure water and 5% NaCl + 2.0% Na₂SO₄ composite salt solution) were established. Shear performance tests were conducted on nine groups of FR-RAC beams after 0–175 freeze–thaw cycles, with measurements focusing on failure modes, cracking loads, and ultimate shear capacities. The results revealed that under composite salt freeze–thaw conditions: after 100 cycles, the cracking load and shear capacity of tested beams decreased by 39.8% and 22.2%, respectively, compared to unfrozen specimens representing reductions 29.6% and 82.0% greater than those in freshwater environments; at 175 cycles, cumulative damage intensified, with total reductions reaching 56.8% (cracking load) and 36.1% (shear capacity). A shear capacity degradation prediction model for FR-RAC beams under composite salt freeze–thaw coupling was developed, accounting for concrete strength attenuation and interfacial bond degradation. Model validation demonstrated excellent agreement between predicted and experimental values, confirming its robust applicability.

With global sustainable construction growth, fully recycled coarse aggregate concrete (RCAC)—eco-friendly for cutting construction waste and reducing natural aggregate over-exploitation—has poor durability in seasonally freezing saline-soil regions (e.g., Tumushuke, Xinjiang): freeze-thaw and salt ions (NaCl, Na₂SO₄) cause microcracking, faster performance decline, and shorter service life, limiting its use and requiring better salt freeze resistance. To address this, a field survey of Tumushuke’s saline soil was first conducted to determine local salt type and concentration, based on which a matching 12% NaCl + 4% Na₂SO₄ mixed salt solution was prepared. RCAC specimens modified with fly ash (FA), silica fume (SF), and polypropylene fiber (PPF) were then fabricated, cured under standard conditions (20 ± 2 °C, ≥95% relative humidity), and subjected to rapid freeze-thaw cycling in the salt solution. Multiple macro-performance and microstructural indicators (appearance, mass loss, relative dynamic elastic modulus (RDEM), porosity, microcracks, and corrosion products) were measured post-cycling. Results showed the mixed salt solution significantly exacerbated RCAC’s freeze-thaw damage, with degradation severity linked to cycle count and admixture dosage. The RCAC modified with 20% FA and 0.9% PPF exhibited optimal salt freeze resistance: after 125 cycles, its RDEM retention reached 75.98% (6.60% higher than the control), mass loss was only 0.28% (67.80% lower than the control), and its durability threshold (RDEM > 60%) extended to 200 cycles. Mechanistic analysis revealed two synergistic effects for improved performance: (1) FA optimized pore structure by filling capillaries, reducing space for pore water freezing and salt penetration; (2) PPF enhanced crack resistance by bridging microcracks, suppressing crack initiation/propagation from freeze-thaw expansion and salt crystallization. A “pore optimization–ion blocking–fiber crack resistance” triple synergistic protection model was proposed, which clarifies admixture-modified RCAC’s salt freeze damage mechanism and provides theoretical/technical guidance for its application in extreme seasonally freezing saline-soil environments.

Structures or chemical engineering facilities can be subjected to the combined effects of sulfate corrosion and high temperature in the event of fire. This paper presents experimental results on compressive stress–strain relationships of recycled coarse aggregate concrete (RAC) and normal aggregate concrete (NAC) after dry–wet cycles of sulfate corrosion and high-temperature exposure. First, RAC and NAC specimens were subjected to 0, 20, 40, 60, 80, 100, and 120 dry–wet cycles of sulfate corrosion, respectively. Then, RAC and NAC specimens were subjected to 0 °C, 200 °C, 400 °C, 600 °C, and 800 °C temperature exposures, respectively. At last, RAC and NAC specimens were loaded by uniaxial compressive test. The test results show that the shapes of the stress–strain curves of RAC and NAC specimens after the 200 °C exposure and dry–wet cycles of sulfate corrosion were basically the same as those at room temperature. When the temperature was in the range of 200–400 °C, the elastic modulus and peak stress of RAC decreased with the number of dry–wet cycles of sulfate corrosion, while the corresponding peak strain gradually increased. When the temperature was lower than 400 °C, the number of dry–wet cycles of sulfate corrosion had a greater impact on the peak strain of RAC, while the temperature had a greater impact on the peak strain of RAC when the temperature exceeded 400 °C. After the temperature exceeded 400 °C, the elastic part in the ascending section of the stress–strain curve of RAC gradually shortened, and the peak point of the curve also shifted significantly to the lower right. The increase in peak strain of the RAC was larger than that of NAC. Based on the test results, a compressive stress–strain relationship model of RAC after sulfate corrosion and high temperature is established.