Research on the purification efficiency and mechanism for road runoff pollutants in pervious concrete with recycled aggregates.

The use of recycled aggregate (RA) in pervious concrete (PC) is a green approach that can effectively mitigate urban waterlogging, excessive RA, and runoff pollution, thereby enhancing the urban ecological environment. This article focuses on the long-term purification efficiency of runoff pollutants by PC at different porosities and RA dosages. Moreover, the purification mechanism of pollutants by recycled aggregate pervious concrete (RAPC) was revealed utilizing particle size analysis, microstructure, and elemental analysis. Finally, the recovery effects of different maintenance approaches on the purification capacity of RAPC were explored. The results indicate that an increase in the RA dosage reduced the effective porosity of PC, thereby decreasing the permeability of RAPC. In addition, PC with a lower porosity demonstrated a slightly greater purification effectiveness for pollutants. However, the utilization of RA significantly enhanced the purification capacity of PC for various pollutants, primarily by leveraging advantages in terms of pore structure, micromorphology, and surface chemical composition. Additionally, RAPC exhibited nearly 100 % retention effectiveness for particles larger than 68.95 µm but relatively lower purification efficiency for particles ranging from 1.541 to 17.11 µm. In particular, it displayed the poorest purification performance for particles with a diameter of 6.396 µm. The surface of RAPC's pore channels exhibited a loose state with high porosity and appeared rough and uneven with numerous pits and grooves. RAPC had a larger surface area and contained more components, such as SiO2, CaCO3, and Al2O3, than regular PC. Therefore, RAPC possessed a higher purification capacity. High-pressure flushing (HPF) and sodium citrate flushing (SCF) under different maintenance frequencies significantly contributed to the recovery of the purification efficiency of RAPC. However, overall, a lower maintenance frequency led to a less favorable recovery effect. Furthermore, SCF had a better recovery effect than HPF.

Measurements, emission characteristics, and control methods of fire effluents generated from tunnel asphalt pavement during fire: a review.

Tunnels are widely used in high-grade roads, particularly in mountainous areas; however, tunnel fires often result in severe economic losses and casualties. The fire effluents produced from asphalt pavement have attracted significant research attention. The main objective of this study is to assimilate information on various aspects of bituminous mixture emissions during fires. In this study, the fume emissions of bitumen and bituminous mixtures during combustion are comprehensively reviewed and summarized. First, the test methods for fire effluents produced by bitumen and bituminous mixtures after combustion are summarized. Second, the factors influencing the fume concentration and composition are determined. In addition, different methods to reduce the emission of fire effluents are compared, particularly for the suppression of toxic gas emissions. Then, reasonable suggestions are proposed to reduce the damage caused by hazardous gases to humans and the environment. This review is beneficial for comprehensively understanding the fume emission behaviour and future research on the smoke suppression of highway tunnel asphalt pavements during fires.

Effect of Sulfate Concentration on Chloride Diffusion of Concrete under Cyclic Load.

The existence of chloride ions, sulfate ions, and vehicle dynamic loads may lead to a shortened service life and premature failure of the road and bridge structures in northwestern China. Immersed in a dual-salt solution while simultaneously applying cyclic flexural loads, the free chloride ion concentration and erosion depth in concrete specimens were measured. The influence of the sulfate concentration on the apparent surface chloride concentration (Cs) and apparent diffusion coefficient (Dapp) was studied. An exponential model was used to fit the Cs, and the influence of sulfate concentration on the Cs was analyzed. The result showed that cyclic loading and solution concentration were two primary factors affecting chloride diffusion. Meanwhile, compared with the emersion conditions, dynamic loading would induce significantly accelerated chloride ion penetration. Under the coupling effect of sulfate and dynamic loading, as the sulfate concentration increased, the chloride ion concentration and erosion depth were both decreased. The existence of sulfate ions improved the chloride ion penetration resistance of concrete. The results provide insight in designing concrete in regions where multiple salt ingression (sulfate and chloride) is a major durability issue of the structures.

Meso- and Macro-Mechanical Analysis of the Frost-Heaving Effect of Void Water on Asphalt Pavement.

In cold regions, many types of structural damages are caused by the frost heaving of asphalt pavements. Hence, it is important to quantitatively determine the frost-heaving effect of asphalt pavement using a mechanical method to control frost-heaving damage. In this study, first, the internal voids of the asphalt mixture were regarded as a single void, and the water phase transition generating the freezing water in the voids was simulated using a simplified hollow sphere model to create a uniform internal pressure. Second, the prediction equation of the equivalent linear expansion coefficient was proposed by taking the phase transition of water in the saturated asphalt mixture voids into account. A step function was used during the phase transition of water to determine the sudden change in the equivalent linear expansion coefficient, heat capacity, density, and thermal conductivity. Finally, the typical cooling conditions were simulated with the water phase transition and the nonwater phase transition. The experimental results showed that the proposed model could accurately simulate the effect of frost heaving. Higher stress and strain were generated on the surface and in the interior of the pavement, and the positions of maximum stress and strain occurred on the pavement surface under the frost-heaving conditions. The compressive strength of the asphalt mixture in a uniaxial compression test is about 4.5-6 MPa with a single freeze-thaw cycle. Furthermore, when frost heaving occurs on the asphalt pavement between 5.8 and 6.5 MPa, the numerical simulation method can be used to calculate the internal stress of the structure, which found that the compressive stress under the frost-heaving condition was the same magnitude as the compressive strength under the freeze-thaw testing condition.

Fractal Dimension of Basalt Fiber Reinforced Concrete (BFRC) and Its Correlations to Pore Structure, Strength and Shrinkage.

In this study, we focused on exploring the correlations between the pore surface fractal dimensions and the pore structure parameters, strength and shrinkage properties of basalt fiber-reinforced concrete (BFRC). The pore structure of BFRCs with various fiber contents and fiber lengths was investigated using mercury intrusion porosimetry (MIP) measurements. Through Zhang's model, the fractal characteristics of BFRCs in the whole pore size range and in different pore size ranges were calculated from the MIP test data. The results showed that the addition of BF increased the total porosity, total pore volume and pore area but decreased the average pore diameter, indicating that BFs refined the pore structure of the concrete. BFRC presented obvious fractal characteristics in the entire pore-size range and individual pore-size ranges; generally, the fractal dimension increased with increasing fiber content. Moreover, correlation analysis suggested that the fractal dimension of BFRC in the whole pore-size range (FD) was closely related to the fractal dimension in the macropore region (Dm) and average pore diameter (APD). The influence of pore structure factors on mechanical strength and shrinkage was studied by grey correlation theory, and the results showed that Dm showed positive correlations with strength and fracture energy, with increasing Dm tending to strengthen and toughen the concrete. An increase in fiber content and length was detrimental to reducing the drying shrinkage strain. In the transition pore region, the fractal dimension (Dt) at diameters ranging from 20 to 50 nm and shrinkage strain exhibited a highly linear relation. These results merit careful consideration in macro-property evaluation by using the pore surface fractal dimension in a specific region instead of the whole region. Finally, grey target theory was applied to evaluate the rank of the mechanical strength and shrinkage of concrete, and the results showed that the overall properties of concrete with a BF length of 18 mm and a BF content of 0.06% ranked the best.