Khawar Ali’s research while affiliated with University of Engineering and Technology Taxila and other places

Plastic waste has increased significantly in recent years as a result of fast population growth and urbanization. Studies on the incorporation of plastic aggregates as a substitution for natural aggregates in concrete are needed to successfully reduce both adverse environmental impact and the depletion of natural resources. The objective of this research was to investigate the use of plastic as a partial substitution for natural coarse aggregates in concrete. For this purpose, seven concrete mixes were produced using 0, 10, 15, and 20% plastic coarse aggregates to replace natural aggregates with and without silica fume of similar replacement levels with cement. Fresh density, workability, compressive strength, splitting tensile strength, stress–strain response, and Poisson’s ratio were observed to study the fresh as well as hardened properties of concrete mixtures. Indoor and outdoor thermal performance and thermo-gravimetric analysis were also investigated. The results revealed that the plastic aggregates’ incorporation improved the workability of concrete; however, it negatively influenced the fresh density and mechanical properties of concrete. The compressive and tensile strengths of plastic aggregate concrete without silica fume were reduced by 32 and 33%, respectively. The reduction in strength could be associated with the smooth texture of plastic aggregates. The addition of silica fume with plastic aggregates resulted in denser concrete and improved mechanical properties. In general, the performance of plastic aggregates as a partial replacement for natural aggregates was satisfactory, which suggests their possible use to produce eco-friendlier concrete.

Cement demand has steadily increased around the world, negatively impacting the environment by consuming a substantial amount of energy, depleting raw materials, and contributing to climate change. Supplementary cementitious materials (SCMs) can be a potential way to deal with environmental issues by providing an alternative to the cement industry, resulting in more efficient, sustainable, and long-lasting concrete while keeping the environment safe for subsequent generations. The effect of individual and combined integration of bentonite and silica fume as a partial replacement for cement in concrete mixes with polypropylene fibers (PPF) was investigated by determining the mechanical and durability properties of concrete mixes. Binary mixes, containing either bentonite or silica fume as a partial replacement of cement, were prepared along with ternary mix incorporating both the SCMs. Additionally, PPFs were added to the ternary blends in increments of 0.25%, resulting in nine distinct concrete mixtures. Compressive, splitting tensile and flexural strength tests were carried out to study the hardened concrete properties. UPV, sorptivity, porosity, water permeability, abrasion resistance, acid attack resistance, and chloride penetration tests were performed to examine the durability properties. The experimental results exhibited that the addition of silica fume and bentonite resulted in enhanced compressive, splitting tensile and flexural strengths. The durability properties of SCM concrete mixtures also improved compared to the control mix. The microstructure investigation depicted a denser concrete in the case of SCM incorporated mixes. PPF mixes showed satisfactory performance up to a certain percentage of PPF (i.e., 0.5%).

h i g h l i g h t s Plastic fine aggregate (PFA) is used to replace natural sand from 0 to 20%. PFA is found to degrade the mechanical and improve the thermal characteristics. Silica fume is found to reduce the adverse impacts of PFA on strength properties. Stress-strain curves and moduli of elasticity of resulting concrete are presented. Eco-friendly alternative with comparable strength and superior thermal properties. a b s t r a c t Production of plastic and the resulting plastic waste is on the rise due to the rapid increase in population and urbanization. In this context, studies investigating the recycling and reuse of plastic waste in construction industry provides an avenue to reduce adverse environmental impacts of waste plastic and to save natural resources. This research work investigates the use of plastic fine aggregate (PFA) manufactured from electronic waste as a replacement of natural fine aggregate in concrete. Concrete mixes with 10%, 15%, and 20% replacement of natural sand with PFA are prepared and tested. Fresh properties are studied based on workability and density while mechanical properties are studied based on compres-sive strength, split tensile strength, stress-strain behavior, Poisson's ratio, and lateral-to-axial strain ratio. The results revealed that manufactured PFA improves the workability of concrete but as expected, the compressive and tensile strength was reduced significantly. To improve the strength properties, silica fume (SF) is incorporated in the concrete mix as a replacement of cement with same replacement percentage as for PFA. Addition of silica fume minimized the effects of plastic aggregate on strength properties with compressive and tensile strength of concrete showing a reduction of only 4.7% and 1.1%, respectively, for maximum replacement of plastic aggregate and silica fume. Indoor and outdoor thermal performance tests showed that concrete with 20% replacement percentage of PFA and silica fume exhibits better thermal performance with an average reduction of 8% in the thermal conductivity. Results from thermogravimetric analysis showed an increased loss of mass at around 300°C to 480°C in addition to the usual weight loss that concrete exhibits from 600 to 800°C. Overall results suggest that plastic aggregate can be utilized as a natural fine aggregate replacement to produce eco-friendly concrete with comparable strength properties and improved thermal properties.