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The preparation of new-generation concrete from recycled coarse aggregate (RA) is an effective way to realize the resource utilization of construction waste. However, loose and porous attached mortar leads to RA showing low-density, high-water absorption, and high crushing value. However, carbonation modification treatment can effectively improve the performance of RA. This paper studied the effects of carbon dioxide (CO2) concentration, gas pressure, and moisture content on the RA physical properties (apparent density, water absorption, crushing value, and soundness) of waste concrete. The results showed that, when the (CO2) concentration increased from 20% to 60%, the apparent density of RA after carbonation increased by 0.23–0.31%, the water absorption decreased by 0.57–0.93%, the crushing value decreased by 0.36–0.61%, and the soundness decreased by 0.47–0.85%. When the (CO2) concentration was further increased from 60% to 80%, the apparent density of RA after carbonation was increased by 0.04–0.05%, the water absorption was improved by 0.15–0.31%, the crushing value was reduced by 0.06–0.07%, and the soundness was reduced by 0.09–0.11%. During the carbonation modification process, the performance of RA was significantly enhanced when the moisture content was 3.4% and the dissolution of hydration products was accelerated. The diffusion rate of CO2 and the carbonation reaction rate decreased with the high moisture content of RA. As gas pressure increases to 0.01 MPa, the physical properties of RA change significantly, because gas pressure promotes the carbonation reaction between hydration products and CO2 in attached mortar. As the gas pressure increased to 0.5 MPa, RA's apparent density gradually increased, while its water absorption, crushing value, and stability gradually decreased. The result improved RA's performance. SEM images show that carbonation modification of RA under different gas pressures increases CaCO3 in attached mortar, filling the Interfacial Transition Zone (ITZ), and decreasing crack width and number. Gas pressure accelerates CO2 diffusion and reaction with hydration products, resulting in narrower ITZ and dense mortar. [ABSTRACT FROM AUTHOR]

Traditional pervious concrete poses significant challenges in optimizing both mechanical properties and permeability. To address this issue, a novel type of self-compacting recycled pervious concrete (SCRPC) featuring vertical and penetrating channels has been developed. The vertical channels were created by pulling out the reinforcement in the pre-drilled holes that were artificially created in the mold, after the concrete had been poured. However, whether this concrete has superior durability and can be employed in different sulfate drying–wetting situations remains to be investigated. This study explored the sulfate resistance and permeability of SCRPC under five drying–wetting exposure regimes: full soaking in Na2SO4 solution with drying–wetting ratios of 3:18, 9:12, and 18:3; semi-soaking in Na2SO4 solution; and full soaking in MgSO4 solution. The results showed that the SCRPC soaked in MgSO4 solution suffered the largest compressive strength loss (13.4%) after 150 drying–wetting cycles. Furthermore, as the drying–wetting ratio increased, the sulfate degradation of the SCRPC increased. Despite the comparable relative dynamic modulus of elasticity of SCRPC after full soaking (95.54%) and semi-soaking (92.89%), ettringite and gypsum were identified as the predominant sulfate deterioration products of SCRPC, respectively. In contrast to the two stages for traditional pervious concrete, the effective porosity of SCRPC was divided into three stages during sulfate attack: an initial rapid decline stage, a subsequent increase stage, and a final slow decline stage. The permeability coefficient of SCRPC varied from 6.00 to 6.82 mm/s under different sulfate drying–wetting exposures. In summary, SCRPC has superior sulfate resistance and permeability, and it could be more applicable in environments containing Na2SO4 compared to MgSO4. This study provides basic data for the enhancement and application of pervious concrete with artificial vertical and penetrating channels. [ABSTRACT FROM AUTHOR]

In this paper, a novel pervious concrete (PC) has been proposed, which combines a high-strength self-compacting concrete matrix with artificial pore channels, to prepare a novel self-compacting recycled pervious concrete (NSRPC) with vertically and uniformly distributed pore channels. Then, an analysis was conducted to assess the flexural performance, permeability, and resilience to rainstorm of NSRPC after flexural fatigue load, which was carried out to ascertain the fluctuations in strength and drainage efficiency over the anticipated service life. The experimental results of NSRPC with porosity levels of 0.28%, 0.56%, 0.84%, and 1.12% show that the reduction in rainstorm will first decrease and then increase with the increase of fatigue cycles. After 2×105 fatigue cycles, the corresponding NSRPC flexural strength was 5.9, 5.6, 5.4, and 4.5 MPa, respectively, and the ultimate displacement decreased by 20.2%, 25.1%, 28.0%, and 33.1%, respectively. After 2×105 fatigue cycles, NSRPCs still demonstrate good storm waterlogging resistance under 20-, 50-, and 100-year rainstorms. The maximum water retention dissipation rate of NSRPC can reach 0.13 mm/min , and the maximum water retention depth is less than 2.5 mm. Additionally, the permeability coefficient of NSRPC remains almost unchanged with an increase in fatigue cycles. When the permeability coefficient is greater than 4.5 mm/s , the depth of stagnant water remains almost constant with the increase of the permeability coefficient. The research in this project provides a new material and direction for the study of pervious concrete to control rainstorms and waterlogging. [ABSTRACT FROM AUTHOR]