This research investigates the possibility of using municipal solid waste incineration fly ash (MSWI FA) geopolymer to stabilise the strength of recycled concrete aggregate (RCA) in pavement applications. The unconfined compressive strength (UCS) and scanning electron microscope were studied in this research. The maximum dry unit weight of RCA-MSWI FA geopolymer specimens increased as MSWI FA replacement increased due to the filler effect of MSWI FA. For MSWI FA higher than 20, the maximum dry unit weight of samples decreased with MSWI FA replacement due to the lower specific gravity of MSWI FA. The optimum ingredient of RCA-MSWI FA geopolymer specimens is at optimum liquid content (OLC), RCA/MSWI FA of 90/100, and all sodium silicate (Na₂SiO₃)/sodium hydroxide (NaOH) ratios which meet the 7-day UCS requirement of pavement base material for the low-volume road. There is one ingredient for the high-volume road: OLC, RCA/MSWI FA of 90/100, and Na₂SiO₃/NaOH of 60/40.

The use of concrete in road construction has grown over the past decade due to the material’s great durability. However, concrete has poor tensile strength, ductility, and energy absorption. This paper aims to investigate the utilization of plastic waste, namely polypropylene (PP), to create a novel fiber to enhance the engineering properties of fiber reinforced concrete (FRC), an eco-friendly concrete that can reduce environmental problems. The 28-day design strengths of 28 and 32 MPa were used in this study because the compressive strength requirements for concrete footpaths and pavement specified by Austroads and the Department of Highways, Thailand, were at least 25 and 32 MPa, respectively. The fiber (F) was a mixture of virgin PP and recycled PP (RPP). The study used F contents of 0.25, 0.50, 0.75, and 1% by weight of cement and PP:RPP ratios of 100:0, 75:25, 50:50, 25:75, and 0:100. The compressive strength, flexural strength, leaching, and CO₂ emissions savings of FRC were evaluated. Improvements in the compressive strength, flexural strength, and toughness of the samples with F were observed in comparison to the control concrete samples for all design strengths. All mixtures met the compressive strength requirements for concrete footpaths, except for F contents of 0.75 and 1% and a PP:RPP ratio of 0:100. By contrast, the 32 MPa FRC samples with F contents of 0.25 and 0.5% and all PP:RPP ratios met the requirements for rigid pavement. From an environmental perspective, the heavy metal contaminants of the 32 MPa FRC sample were within the allowable limits for all mixtures. Regarding incineration disposal, the maximum CO₂ emissions savings of 28 MPa and 32 MPa FRC with an F content of 0.5% and a PP:RPP ratio of 0:100 were 1.0 and 1.11 kg CO₂-e/m³, respectively. This research will enable plastic waste, traditionally destined for incineration and landfill disposal, to be used as a sustainable fiber in the construction industry.

In this research, water treatment sludge (WTS) calcium carbide residue (CCR) geopolymers were evaluated as a sustainable masonry nonbearing unit. The WTS was a by-product from a water treatment plant, whereas CCR was a by-product from an acetylene gas factory in Thailand. Sodium hydroxide solution (NaOH) and sodium silicate solution (${\mathrm{Na}}_2{\mathrm{SiO}}_3$ ) were used for the geopolymerization process. The unconfined compressive strength (UCS), water absorption, and durability of WTS-CCR geopolymer were studied in this research. The test results indicate that the optimal liquid alkaline activator (L)/CCR ratios provided the maximum unit weight decrease with CCR contents for all of the ${\mathrm{Na}}_2{\mathrm{SiO}}_3/\mathrm{NaOH}$ ratios evaluated. The optimal L/CCR ratios were found to be 16, 8, 5.33, 4, 3.2, and 2.67 for CCR contents of 5, 10, 15, 20, 25, and 30%, respectively. The ${\mathrm{Na}}_2{\mathrm{SiO}}_3/\mathrm{NaOH}$ ratio of 70:30 was found to give the highest maximum unit weight and UCS among all of the WTS/CCR ratios tested. Three zones of UCS development with CCR content were evident: the active, inert, and deterioration zones. In the active zone, the UCS increased significantly as the CCR content increased, and the maximum UCS was attained at 10% CCR. In the inert zone, the UCS development was gradual. When the CCR content was more than 20% in the deterioration zone, a subsequent strength decrease was observed. The wet–dry (w–d) cycle strength, ${\mathrm{UCS}}_{(w-d)}$ , depends primarily on the initial soaked strength, ${\mathrm{UCS}}_0$ . A ${\mathrm{UCS}}_{(w-d)}$ predictive equation was proposed for the assessment of initial strength to attain the required w–d strengths. Based on the UCS and water absorption requirements, an optimum ingredient consisting of 10% CCR and 70:30 ${\mathrm{Na}}_2{\mathrm{SiO}}_3/\mathrm{NaOH}$ at room temperature curing can be recommended for nonbearing masonry units.

Spent coffee ground (CG) geopolymers are novel cementitious materials, which utilise industrial wastes such as fly ash and ground granulated blast furnace slag as precursors. Several past studies have investigated the strength development of these recycled products, and established their suitability as road subgrade construction materials. This paper evaluates the incorporation of recycled glass (RG) into the CG geopolymer blend to further enhance the strength of the mix, as well as investigates the resilient modulus (M_R) properties of CG+RG. Repeat Load Triaxial (RLT) tests were undertaken to investigate the flexibility and deformation pattern of CG+RG geopolymer subgrades under repeated traffic loading. The relationship between RG replacement ratio and material stiffness was furthermore established. California Bearing Ratio (CBR) tests on the CG+RG geopolymers indicate that the CBR value of these materials exceeds those of naturally occurring subgrade materials. The CBR and M_R values of the CG+RG geopolymers are essential design parameters for the usage of this novel construction material in subgrades.

This research investigates the possibility of using high-density polyethylene (HDPE) plastic waste to improve the properties of asphalt concrete pavement. HDPE plastic waste contents of 1, 3, 5, and 7% by aggregate weight were used. HDPE plastic waste=stabilized asphalt concrete pavement (HDPE-ACP) was evaluated by performance testing for stability, indirect tensile strength, resilient modulus (MR), and indirect tensile fatigue (ITF). In addition, microstructure, pavement age, and CO₂ emissions savings analyses were conducted. The performance test results of the HDPE-ACP were better than those without HDPE plastic waste. The optimum HDPE plastic waste content was 5%, offering the maximum MR, ITF, and pavement age. Scanning electron microscope images showed that the excessive HDPE plastic waste content of 7% caused a surface rupture of the sample. Improvements in the pavement age of the HDPE-ACP samples were observed compared with the samples with no HDPE plastic waste. The highest pavement age of the HDPE-ACP sample was found at an HDPE plastic waste content of 5% by aggregate weight. The CO₂ emissions savings of the sample was 67.85 kg CO₂-e/m³ at the optimum HDPE plastic waste content.