V3I9P18

Experimental Investigation of E-Waste Plastic as Partial Coarse Aggregate Replacement in Ambient-Cured Metakaolin–Fly Ash Geopolymer Concrete

Dr. Rajiv Khatri¹, Rakesh Kumar Rathore², Dr. Parth Verma^3*, Dr. Chandra Prakash Gour⁴

Abstract

The construction sector requires substantial quantities of cementitious materials and natural aggregates, while the rapid turnover of electrical and electronic equipment generates an increasingly difficult waste stream. This study investigates the feasibility of incorporating processed e-waste plastic (EWP) as a partial replacement for natural coarse aggregate in ambient-cured metakaolin–fly ash geopolymer concrete (MK–FA GPC). The experimental programme first optimized the geopolymer matrix through sequential variation of binder ratio, sodium hydroxide molarity, liquid-to-binder ratio, and sodium silicate-to-sodium hydroxide ratio. The optimum matrix consisted of 60% metakaolin and 40% fly ash, 10 M NaOH, liquid-to-binder ratio of 0.60, and Na₂SiO₃/NaOH ratio of 2.5. EWP was subsequently introduced at 0, 2.5, 5, 7.5, 10, 12.5 and 15% replacement of natural coarse aggregate. The EWP had a maximum particle size of 10 mm, specific gravity of 1.10 and water absorption of 0.10%, and exhibited a flaky/elongated morphology. Increasing EWP increased slump from 78 to 116 mm, but progressively reduced mechanical strength. At 28 days, compressive strength decreased from 42.31 MPa for the control mixture to 39.34 MPa at 5% EWP and 26.86 MPa at 15% EWP. Corresponding split tensile and flexural strengths at 5% EWP were 3.48 and 3.59 MPa, respectively. In contrast, water absorption, sorptivity and chloride charge passed decreased with EWP addition. At 5% EWP, 28-day water absorption decreased from 4.97 to 4.38%, 120-min sorptivity decreased from 0.060 to 0.047, and 90-day RCPT charge decreased from 881 to 863 C. Acid, sulphate and saltwater exposure also showed lower mass/strength losses for EWP-containing mixtures. Petrographic, SEM, EDS and elemental-mapping observations indicated that the geopolymer matrix remained continuous and that the principal N–A–S–H/C–A–S–H gel system was not disrupted by 5% EWP, although the carbon-rich plastic fraction reduced the relative proportion of geopolymeric gel. The results indicate that 5% EWP provides the most balanced combination of mechanical performance and durability within the investigated range. The study demonstrates a technically feasible route for converting a selected e-waste plastic fraction into a construction material, while also identifying the need for polymer-specific characterization, leaching assessment, thermal testing and life-cycle analysis before field-scale deployment.

Keywords:

e-waste plastic; geopolymer concrete; metakaolin; fly ash; recycled aggregate; durability; ambient curing; circular economy.