Roles of Waste Glass and the Effect of Process Parameters on the Properties of Sustainable Cement and Geopolymer Concrete-A State-of-the-Art Review

Novel f-CaO soft sensor for cement clinker based on integrated model of dual-parallel structure

Aiming at the problem that the cement production process is inherently affected by uncertainty, time delay, and strong coupling among variables, this paper proposed a novel soft sensor of free calcium oxide in a cement clinker. The model utilizes a dual-parallel integrated structure with an optimized integration of one-dimensional convolutional neural networks, long and short-term memory networks, graphical neural networks, and extreme gradient boosting. The proposed model can mitigate the risks associated with overfitting while incorporating the strengths of each individual model and excels in extracting both local and global features as well as temporal and spatial characteristics from the original time series data, ensuring its stability. The experimental results demonstrate that this dual-parallel integrated model exhibits superior robustness, predictive accuracy, and generalization capabilities when compared to single models or enhancements made to other deep learning algorithms.

Influence of Waste Glass Addition on the Fire Resistance, Microstructure and Mechanical Properties of Geopolymer Composites

Nowadays, humanity has to face the problem of constantly increasing amounts of waste, which cause not only environmental pollution but also poses a critical danger to human health. Moreover, the growth of landfill sites involves high costs of establishment, development, and maintenance. Glass is one of the materials whose recycling ratio is still insufficient. Therefore, in the presented work, the influence of the particle size and share of waste glass on the consistency, morphology, specific surface area, water absorption, setting time, and mechanical properties of geopolymers was determined. Furthermore, for the first time, the fire resistance and final setting time of such geopolymer composites were presented in a wide range. Based on the obtained results, it was found that the geopolymer containing 20% unsorted waste glass obtained a final setting time that was 44% less than the sample not containing waste glass, 51.5 MPa of compressive strength (135.2% higher than the reference sample), and 13.5 MPa of residual compressive strength after the fire resistance test (164.7% more than the reference sample). Furthermore, it was found that the final setting time and the total pore volume closely depended on the additive's share and particle size. In addition, the use of waste glass characterized by larger particle sizes led to higher strength and lower mass loss after exposure to high temperatures compared to the composite containing smaller ones. The results presented in this work allow not only for reducing the costs and negative impact on the environment associated with landfilling but also for developing a simple, low-cost method of producing a modern geopolymer composite with beneficial properties for the construction industry.

Influence of Waste Glass Particle Size on the Physico-Mechanical Properties and Porosity of Foamed Geopolymer Composites Based on Coal Fly Ash

In order to protect the environment and counteract climate change, it is necessary to take any actions that enable a reduction in CO₂ emissions. One of the key areas is research focused on developing alternative sustainable materials for construction to reduce the global demand for cement. This work presents the properties of foamed geopolymers with the addition of waste glass as well as determined the optimal size and amount of waste glass for improving the mechanical and physical features of the produced composites. Several geopolymer mixtures were fabricated by replacing coal fly ash with 0%, 10%, 20%, and 30% of waste glass by weight. Moreover, the effect of using different particle size ranges of the addition (0.1-1200 µm; 200-1200 µm; 100-250 µm; 63-120 µm; 40-63 µm; 0.1-40 µm) in the geopolymer matrix was examined. Based on the results, it was found that the application of 20-30% of waste glass with a particle size range of 0.1-1200 µm and a mean diameter of 550 µm resulted in approximately 80% higher compressive strength in comparison to unmodified material. Moreover, the samples produced using the smallest fraction (0.1-40 µm) of waste glass in the amount of 30% reached the highest specific surface area (43.711 m²/g), maximum porosity (69%), and density of 0.6 g/cm³.

Modeling, multi-response optimization, and performance reliability of green metal composites produced from municipal wastes

For the purpose of reducing and reusing municipal wastes, used aluminum products, waste glass, and rice husk were selected and reprocessed into green-metal composite. The process entailed recycling of waste glass and rice husk into glass powder (GP) and rice husk ash (RHA), respectively. These were employed as additives in recycled aluminum melt. Composite samples development entailed group mixes A, B, C, and D. Group mix A was prepared by the blend of 3 wt.% RHA at constant proportion with 2, 4, 6, 8, and 10 wt.% GP. Regarding group mixes B, C, D, the same proportion of GP was blended with 6, 9, 12% RHA at constant dosage respectively. Mechanical properties; tensile, impact, flexural and compressive strengths, and fracture toughness were investigated. The significance of the additives on the composites was appraised via performance reliability index (PRI) as a measure of effective property based on variable experimental inputs. From the results, the commix of 3% RHA and 4, 6, 8% GP; 6% RHA and 2, 4, 6% GP; 9% RHA and 2, 4% GP exhibited enhancement of effective property. The compressive strength of the composites was showcased to be the most improved mechanical property. Maximum improvement was obtained at the collage of 4% GP and 6% RHA, yielding a PRI of 1.35. Results of the ANOVA revealed that the experimental inputs had significant contribution on each property response. Mathematical models were developed for each property response, and multi-response optimization predicted an optimum mix of 3.93 wt.% GP and 6.14% RHA. The difference between the property value of the predicted and confirmation experiment is <  ± 0.05, validating the models.

Evaluation of the Effect of Recycled Polypropylene as Fine Aggregate Replacement on the Strength Performance and Chloride Penetration of Mortars

Nowadays, the re-use and recycling of industrial wastes to reduce the environmental impact and landfill problems are the main concerns of researchers. Plastics are one of the main waste materials worldwide, with considerable impacts on health and environmental conditions. Recycling plastic wastes in the concrete industry is one of the adopted ways to reduce such impact and increase the economic recyclability of plastics. In this study, the utilization of recycled polypropylene (rPP) as a fine aggregate in the preparation of cement mortars was evaluated. The river sand was replaced with 10, 20, 30, 40, and 50%, volumes of rPP. The results showed that the inclusion of rPP reduced the mortar's workability and fresh density. Fresh density dropped from 11% to 35% as the rPP content increased. Furthermore, the compressive strength at early and late age was significantly influenced by the rPP content. At 28 days of curing age, the results showed that the inclusion of 50% of rPP in the mortar matrix led to a drop in the compression strength from 40 MPa to 10 MPa. A similar trend of results was obtained for the flexural (from 8.3 MPa to 2.9 MPa) and tensile strengths (from 3.4 MPa to 1.21 MPa). The chloride ion penetration went through a maximum of 5000 Coulombs between 10% and 50 % of rPP. Therefore, it can be concluded that the use of 10% of rPP as a river sand replacement can achieve acceptable strength (25 MPa) for several applications in the construction industry.

Chemical and Microstructural Properties of Fly Ash and Fly Ash/Slag Activated by Waste Glass-Derived Sodium Silicate

Sodium silicate is commonly used for activating alumina silicates to produce alkali-activated binders that can compete with conventional Portland cement in concrete. However, the cost and emissions related to activators can hinder the use of alkali-activated materials in the industry. The novel, waste-based activators have been developed in the last years, using Si-rich waste streams. Processing waste glass cullet not only reduces the glass landfill disposal but also allows the production of sodium silicate for alkali activation. In this article, the chemical and microstructural properties of neat fly ash and blended 60 fly ash/40 slag pastes activated by sodium silicate produced from glass cullet were studied and compared to equivalent ones activated by commercially available sodium silicate and sodium hydroxide solutions. Fourier transform infrared (FTIR) spectroscopy, X-ray powder diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) coupled with energy dispersive X-ray (EDX) were used to determine the microstructure and composition of the gel phase. Findings have confirmed that pastes activated by the processed waste glass showed chemical and microstructural properties comparable to pastes produced with commercially available activators.

Geopolymers-Design, Preparation, and Applications

Concrete is the most commonly used construction material worldwide, and many efforts have been carried out in recent years to improve its functional properties while also trying to increase its sustainability [...].