To explore the basic mechanical properties and size effects of recycled aggregate concrete (RAC) with different substitution ratios of coarse recycled concrete aggregates (CRCAs) to replace natural coarse aggregates (NCA), the failure modes and mechanical parameters of RAC under different loading conditions including compression, splitting tensile resistance and direct shear were compared and analyzed. The conclusions drawn are as follows: the failure mechanisms of concrete with different substitution ratios of CRCAs are similar; with the increase in substitution ratio, the peak compressive stress and peak tensile stress of RAC decrease gradually, the splitting limit displacement decreases, and the splitting tensile modulus slightly increases; with the increase in the concrete cube’s side length, the peak compressive stress of RAC declines gradually, but the integrity after compression is gradually improved; and the increase in the substitution ratio of the recycled aggregate reduces the impact of the size effect on the peak compressive stress of RAC. Furthermore, an influence equation of the coupling effect of the substitution ratio and size effect on the peak compressive stress of RAC was quantitatively established. The research results are of great significance for the engineering application of RAC and the strength selection of RAC structure design.

This study focuses on the chloride ion penetration resistance of a magnesium phosphate cement (MPC)-based composite material coating on the surface of silicate material. By means of electrical flux method and electric acceleration corrosion tests, the anti-chlorine ion permeation and reinforcement properties of MPC-based materials and Portland cement (OPC) mortar were compared and analyzed. The experimental results show that the electrical flux of the hardened body of the MPC-based material is much lower than that of the Portland cement mortar, and the electrical flux of the hardened body of the MPC mortar can be obviously reduced by adding silica-fume (SF) and fly ash (FA), which, when combined in a suitable proportion, will make the MPC’s hardened body more dense and impermeable. The addition of short cut fibers increases the number of pores, the pore size, and the electrical flux of the cement mortar’s hardened body. The adverse effects of the three fibers on the permeability of the MPC mortar against chlorine ions were as follows: polyvinyl alcohol fiber > glass fiber > basalt fiber. The electrical flux of MPC mortar or MPC paste coated on the surface of the OPC mortar was greatly reduced. Compared with silicate mortar, the MPC-based material has excellent protective performance under the condition of accelerated corrosion.

In order to study the synergistic effect of polymer and conductive functional materials on the properties of cement-based materials, polymer conductive cement-based materials were prepared by mixing four polymer lotions of silicon–acrylate emulsion (SG), phenylacrylic emulsion (SR), waterborne epoxy resin emulsion (SH), and acrylic emulsion (SX) with carbon fiber (CF) and carbon black (CB), two conductive functional materials, in a certain proportion. The effects of the different polymer–cement ratios (P/C) of the four polymers on the physical, mechanical, and electrical properties of conductive cement-based materials were studied. The results illustrated that SH improved the fluidity of cement paste, and the four polymers all had a delaying effect, which led to the hardening of the specimens and the extension of the demoulding specimens to varying degrees. SH and SR can increase the ratio of flexural strength to compressive strength (F/C) in cement paste and improve the toughness of materials, and the maximum value is reached when the P/C is 0.15. Except for SX, the other three polymer lotions can reduce the resistivity of cement paste, which is beneficial to the improvement of conductivity. The improvement sequence is SH > SR > SG. Among them, both SH group and SR group achieved the lowest electrical resistivity at the P/C of 0.15. The four kinds of polymer lotion can significantly reduce the water absorption of the specimen and promote the waterproof performance. The improvement effect: SH > SR > SG > SX. Among them, both the SH group and SR group achieved the minimum water absorption at the P/C of 0.15.

This paper experimentally investigated the effects of varying contents of Na₂O in a modified sodium silicate, sodium silicate moduli (M_s), and contents of granulated blast furnace slag (GBFS) on the compressive strength and drying shrinkage of fly ash (FA)-based geopolymer grouting materials at different ages. X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), and scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDS) were used to study the influences of different amounts of GBFS on the microstructure and product compositions of FA-based geopolymer grouting materials. The results show that the content of Na₂O in modified sodium silicate, M_s, and the content of GBFS play a significant role in compressive strength and drying shrinkage of FA-based geopolymer grouting materials. In addition, the influence of M_s as well as the content of GBFS on the compressive strength and drying shrinkage of FA-based geopolymer grouting materials was deeply affected by curing age. The micro-performance tests and analysis clearly showed that incorporating 30 wt% GBFS can decrease the proportion of pores with large pore sizes, improve pore size distribution, and enhance the solubility of FA and further promote the formation of C-A-S-H gel within FA-based geopolymer grouting materials.

To improve the safety of orthotropic steel bridge decks and the construction efficiency of bridge deck pavement by enhancing the performance of pavement materials, a new-generation, high-performance cold-mix resin was prepared by carrying out the combination of micro-characteristic analysis and performance test. Meanwhile, the pavement performance and fatigue performance of high-performance cold-mix resin mixtures and hot-mix epoxy saphalt mixtures as a control group were studied experimentally. The results show that different kinds of epoxy resins show bisphenol structure in essence. The curing exothermic peak temperature of the cold-mix resin increases with the heating rate. Both the specific heat capacity (△C_P) of cold-mix resin and cold-mix resin asphalts exhibit a sudden change between −20 °C and 40 °C. In resin asphalt mixtures, cold-mix resin forms the network structure skeleton whereas the asphalt distributed in the form of tiny particles. The dosage of respective component has a significant effect on the tensile strength and elongation at break of cold-mix resin. Compared with hot-mix epoxy asphalt mixtures, cold-mix resin mixtures exhibit comparable water stability and high and low-temperature performance, as well as greater fatigue life.