A state-of-the-art review of the physical and durability characteristics and microstructure behavior of ultra-high-performance geopolymer concrete

This paper provides a comprehensive review of ultra-high-performance geopolymer concrete (UHPGPC), an innovative, eco-friendly, and cost-effective variant of ultra-high-performance concrete (UHPC), devised to meet the rising request for ultra-high-strength construction materials. Previous research papers have not thoroughly analyzed and compared the rheological, physical, durability, and microstructural properties of UHPGPC with UHPC. Similarly, review articles scarcely investigate UHPGPC's strength properties and microstructural behavior under high temperatures. This paper includes an assessment of the correlation between compressive strength, splitting tensile strength, and modulus of elasticity (MOE). The current study also compares chloride ion penetration test outcomes, elevated temperature, electrical resistivity, and porosity tests to evaluate durability. To analyze the microstructure of UHPGPC, the paper assesses results from Fourier Transform Infrared Spectroscopy (FT-IR), Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), and Mercury Intrusion Porosimetry (MIP). The findings from the present paper suggest that UHPGPC effectively meets the ideal mechanical property specifications of UHPC. Compared to UHPC, UHPGPC displayed a higher ion passage propensity due to larger pores (>100 nm). Geopolymer technologies present a greener path for producing UHPC by consuming less energy and emitting reduced CO2. Introducing mineral fillers like silica fume impacts the mixture's flowability and increases its water needs. However, adding an optimal ratio of micro-silica as a partial substitute for granulated blast furnace slag further bolsters the strength characteristics of UHPGPC. The strength of UHPC can also be notably improved by adjusting the water-to-binder ratio, with specific ratios yielding considerable enhancements in compression strength. The selection of an alkaline activator plays a pivotal role in UHPC's heat resilience. Among them, a combination of potassium hydroxide and sodium silicate is the prime chemical activator for boosting strength performance, durability behavior, and microstructural attributes, particularly at temperatures beyond 600 °C. Eco-friendly Geopolymer Composites (EGCs) offer lower embodied energy and CO2 emissions than traditional composites, with certain components like polyvinyl alcohol fibers being key contributors to these emissions. Progress in self-healing materials is driving sustainability in construction through innovative techniques, such as bacterial applications and specific chemical reactions. The strength and workability of Engineered Geopolymer Composites are influenced by their fiber content, with certain fibers interacting weaker than others. On a microstructural level, UHPGPC has a relatively weaker structure than UHPC due to differences in pore size, but its durability is improved when reinforced with fibers.

Performance of Porous Asphalt Mixtures Containing Recycled Concrete Aggregate and Fly Ash

This study investigates the effects of two waste materials from construction and industry, namely recycled concrete aggregate (RCA) and Type C fly ash, on the overall performance of a special type of pavement surface mixture, porous asphalt mixture. Mixtures of different combinations of RCA (for partial aggregate replacement) and fly ash (for filler replacement) were prepared in the laboratory and tested for a variety of pavement surface performance parameters, including air-void content, permeability, Marshall stability, indirect tensile strength, moisture susceptibility, Cantabro loss, macrotexture, and sound absorption. The analysis of the results showed that incorporating RCA or fly ash in a porous asphalt mixture slightly reduced the air-void content, permeability, and surface macrotexture of the mixture. A 10% replacement of granite aggregates with RCA in the porous asphalt mixtures led to a reduction in mixture stability, indirect tensile strength, resistance to raveling, and sound absorption. The further substitution of mineral filler with fly ash in the mixture, however, helped to offset the negative impact of RCA and brought the mechanical properties of the mixture with 10% RCA to levels comparable to those of the control mixture.

Laboratory Evaluation of the Use of Florida Washed Shell in Open-Graded Asphalt Mixtures

This study investigates the substitution of conventional aggregate with a Florida washed shell in open-graded asphalt mixtures and evaluates the optimal substitution percentage in aggregate gradations of various nominal maximum aggregate sizes (NMASs) (i.e., 4.75, 9.5, and 12.5 mm). Laboratory experiments were performed on open-graded asphalt mixture specimens with the coarse aggregate of sizes between 2.36 and 12.5 mm being replaced by the Florida washed shell at various percentages (0, 15, 30, 45, and 100%). Specimen properties relevant to the performance of open-graded asphalt mixtures in the field were tested, evaluated, and compared. Specifically, a Marshall stability test, Cantabro test, indirect tensile strength test, air void content test, and permeability test were conducted to evaluate the strength, resistance to raveling, cracking resistance, void content, and permeability of open-graded asphalt mixtures. The results show that there is no significant difference in the Marshall stability and indirect tensile strength when the coarse aggregates are replaced with Florida washed shell. This study also found that the optimum percentages of Florida washed shell in open-graded asphalt mixture were 15, 30, and 45% for 12.5, 9.5, and 4.75 mm NMAS gradations, respectively.