Turning waste expanded polystyrene into lightweight aggregate: Towards sustainable construction industry

Effect of SiO2 aerogel and perlite on properties of foamed concrete

To enhance the insulation performance, strength, and fire resistance performance of foamed concrete, this paper investigates the effects of incorporating nano-silica aerogel and expanded perlite. A comprehensive comparison and analysis were conducted on the dry density, water absorption, mechanical performance, thermal conductivity, fire-resistant insulation, and microstructure of both Nano-SiO2 Aerogel Foamed Concrete (NSAFC) and Expanded Perlite Foamed Concrete (EPFC). The findings indicate that as the Nano-SiO2 Aerogel (NSA) content increases, the water absorption of the foamed concrete gradually rises. Conversely, the water absorption of the foamed concrete test blocks first increases and then decreases with an increase in Expanded Perlite (EP) content. It is noteworthy that, incorporating 10% NSA and EP reduces the dry density of foamed concrete by 12.7% and 7.8%, respectively. When EP content reaches 6%, the 28-d flexural and compressive strengths of the foamed concrete test blocks increase by 73.5% and 54.2%, respectively. Similarly, at NSA content of 6%, the 28-d flexural and compressive strengths increase by 70.5% and 39.6%, respectively. The fire-resistant insulation tests demonstrate that NSAFC exhibits superior thermal insulation and fire resistance performance compared to EPFC. Furthermore, SEM images demonstrate that the pore structure of NSAFC is more uniform.

Reduction of polystyrene/polyurethane plastic wastes from the environment into binders for water-resistant emulsion paints

Waste management is fundamental to resource and environmental sustainability. Expanded polystyrene (EPS) and polyurethane (PU) waste plastics were recycled and applied as binder in emulsion paint formulation. The recycled polystyrene (rPS) and polyurethane (rPU) were blended into composite resins, where toluene was used as the solvent. The blends of rPS and rPU were optimized, while some physicochemical properties of the composite blends (rPS/PU) were evaluated. The results showed that the incorporation of rPU into rPS increased the viscosity (1818 mPa-3924 mPa), rate of gelation (dry-to-touch time: 15 min-0.25 min), moisture content (2.7%-8.1%), moisture uptake (3.2%-5.0%), solid content (48%-53.4%) and density (0.82 g/cm3 to 1.050.82 g/cm3) of the rPS/PU composite resins. Characterization was carried out using Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscope (SEM), and atomic force microscopy (AFM). The results summarily showed that there are interactions among the rPS and rPU molecules in the composite, where complimentary structural and morphological characteristics were also achieved. The composite resin also exhibited superior bond strength (0.5-4.24 Mpa) on wood, cast mortar, ceramic, and steel surfaces due to its stronger intra- and inter-surface interactions compared to the neat rPS resin. The composite resin was used as a binder in the formulation of emulsion paint. The paint exhibited stronger resistance to water, among other superior properties, when compared to the paints formulated using neat rPS and conventional polyvinyl acetate (PVA) resins. The reduction of plastic waste in this study holds potential for the production of highly water-resistant emulsion paint for outdoor and indoor applications.

Enhancing Water Resistance in Foam Cement through MTES-Based Aerogel Impregnation

The propensity of foamed concrete to absorb water results in a consequential degradation of its performance attributes. Addressing this issue, the integration of aerogels presents a viable solution; however, their direct incorporation has been observed to compromise mechanical properties, attributable to the effects of the interface transition zone. This study explores the incorporation of MTES-based aerogels into foamed cement via an impregnation technique, examining variations in water-cement ratios. A comprehensive analysis was conducted, evaluating the influences of MTES-based aerogels on the thermal conductivity, compressive strength, density, chemical composition, and microstructure of the resultant composites across different water-cement ratios. Our findings elucidate that an increment in the water-cement ratio engenders a gradual regularization of the pore structure in foamed concrete, culminating in augmented porosity and diminished density. Notably, aerogel-enhanced foamed concrete (AEFC) exhibited a significant reduction in water absorption, quantified at 86% lower than its conventional foamed concrete (FC) counterpart. Furthermore, the softening coefficient of AEFC was observed to surpass 0.75, with peak values reaching approximately 0.9. These results substantiate that the impregnation of MTES-based aerogels into cementitious materials not only circumvents the decline in strength but also bolsters their hydrophobicity and water resistance, indirectly enhancing the serviceability and longevity of foamed concrete. In light of these findings, the impregnation method manifests promising potential for broadening the applications of aerogels in cement-based materials.

Assessment of plastic pollution in coastal areas of Karachi: Case study of West Warf, Kemari Jetty, and Manora

This study focused on marine pollution in coastal areas of Karachi, particularly West Warf, Kemari Jetty, and Manora. The research examined the sources and quantities of waste, from boat manufacturing, export units, and local commercial activities. Stakeholder interviews were conducted to understand waste management practices and identify the key contributors to ocean litter. The results indicated that restaurants, export units, boat construction, and tourist and commuter activities were the primary sources of marine pollution. Plastic was found to be the most prevalent litter category, with LDPE (e.g., single-use bags) and polystyrene (e.g., material in floating docks) being the most common types. Additionally, multi-layer packaging, such as chip wrappers, was frequently observed in the surveyed areas. Overall, this research highlights the urgent need for improved waste management and compliance measures in coastal regions to mitigate marine pollution.

A two-step approach for calculating chloride diffusion coefficient in concrete with both natural and recycled concrete aggregates

This paper presents an analytical approach to calculate the effective diffusion coefficient of chlorides in concrete with both natural and recycled concrete aggregates. In the approach the concrete is treated as a composite consisting of three phases, namely mortar, natural aggregate plus interfacial transition zone, and recycled concrete aggregate plus interfacial transition zone. The effective diffusion coefficient of chlorides in the composite is calculated through two steps. The first step is to calculate the effective diffusion coefficients of chlorides in the natural aggregate plus interfacial transition zone and in the recycled concrete aggregate plus interfacial transition zone by using multilayer spherical approximation, the results of which provide the information about the quality of recycled concrete aggregate in terms of chloride penetration resistance. The second step is to calculate the effective diffusion coefficient of chlorides in the three-phase concrete composite by using effective medium approximation, the results of which provide the information about the influence of recycled concrete aggregate on the diffusivity of recycled aggregate concrete. The analytical expression of the effective diffusion coefficient is derived and carefully compared with the results obtained from both the experiments and numerical simulations, which demonstrates that the present analytical model is rational and reliable. The analytical expression presented can be used to predict the service life of recycled aggregate concrete exposed to chloride environment.