Steel slag is the main by-product of steelmaking, and its stacking and burying cause serious pollution to soil and water. Meanwhile, the exploitation of gravel is restricted with the implementation of ecological environment protection, resulting in the lack of nature aggregate. Based on the good engineering properties of steel slag aggregate, many researches attempted to substitute natural aggregate with steel slag applied to concrete. Therefore, this article summarizes the composition and properties of steel slag and discusses the effect of steel slag on properties and microstructure of cement concrete. Extensive literatures verify the feasibility of steel slag substituting part of natural aggregate in concrete. Steel slag affects the workability and volume stability of concrete but improves compressive strength, frost resistance and wear resistance, whereas it is controversial in flexural strength and permeability. Finally, the future research trends of concrete with steel slag aggregate are put forward.

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 (D_m) 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 D_m showed positive correlations with strength and fracture energy, with increasing D_m 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 (D_t) 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.

Crushed brick-concrete recycled aggregate (BCRA) represents a sustainable and environmentally friendly alternative to natural aggregates (NAs) in practical engineering. However, compared with NA, the high porosity and low strength of BCRA means it struggles to meet engineering requirements, which limits its large-scale application. This paper reports upon an experimental study to enhance the quality of BCRA via soaking in different types of solutions (pozzolanic materials, sodium silicate, polyvinyl alcohol, and silicon-based additive). The physical and mechanical properties of treated and untreated BCRA were evaluated by testing the apparent density, water absorption, and crushing value. Meanwhile, the optimization schemes for different treatment techniques were recommended using the multi-objective grey target decision method. In addition, the surface morphology of BCRA was characterized by X-ray diffraction and scanning electron microscopy with energy dispersive spectroscopy, to examine the microstructure of the BCRA surface before and after different treatment processes. The results show that 80% cement, 10% fly ash, and 10% silica fume slurries had notable effects on the apparent density and mechanical strength of BCRA, in which the apparent density increased by 0.6–1.8% and the crushing value decreased by 3.5–19.7%; however, the water absorption of BCRA increased by 1.7–8.5%. The physical and mechanical properties of BCRA increased under an increase of sodium silicate concentration and soaking time, though its strengthening effects were limited. Polyvinyl alcohol and silicon-based additives were best able to improve the waterproofing of BCRA, and the water absorption of the BCRA after treatment was reduced by 5.1–17.8% and 30.5–44.9%, respectively. Clear microstructural improvements can also be observed on the treated BCRA surface. To summarize, the BCRA treated by the four treatment methods exhibited surfaces that were denser, less porous, and more homogeneous and regular. These results will provide a useful reference for the future engineering applications of treated BCRA.

The performance of waterproof bonding layer systems significantly affects the service life of concrete bridge deck pavement. This article aims to compare the bonding properties and composite structure mechanical properties of different waterproof bonding layer systems in bridge deck pavement to recommend appropriate structures based on service conditions. To fulfill this objective, four kinds of waterproof bonding material composite systems were designed, and test samples were fabricated. Then, the waterproof bonding layer properties were studied by penetration resistance tests, scalding resistance tests, and corrosion resistance tests. Pull-off tests were conducted to compare the bonding properties. Then, dynamic modulus tests, Hamburg wheel tracking tests, and static load creep tests of composite structure specimens were implemented to evaluate the dynamic and static mechanical performances and water-temperature stability. The findings showed that the four schemes had good impermeability. The pull-off strengths of scheme III at 25 °C were about 2.5-, 2.5-, and 4-times those of schemes I, II, and IV, respectively, and the pull-off strengths at 50 °C were about 1.6-, 2-, and 1.6-times those of schemes I, II, and IV, respectively, and the bonding performances and dynamic modulus of different schemes were ranked as follows: III > I > II > IV. The results of the Hamburg wheel tracking test were consistent with the static load creep test. The high-temperature stability of scheme IV was the best, while the stabilities of scheme III and I were better than that of scheme II. In conclusion, the scheme of concrete bridge deck pavement can be selected based on the environmental conditions and traffic load, and schemes III and I should be considered first. The findings of this research could provide technical support for the future design of bridge deck waterproof bonding systems.