Fly Ash Geopolymer Lightweight Concrete Containing Glass Fiber Reinforce Plastic Waste and Polypropylene Terephthalate Recycled Plastic Pellets

Abstract

This research focuses on studying the properties of fly ash geopolymer lightweight concrete that uses fine aggregates as lightweight aggregates (LWFA) derived from a mix of glass fiber reinforced plastic waste from water tank industry (GFRP) and recycled polyethylene terephthalate (PET) pellets. Six mixtures were selected for the study, with a controlled concentration of NaOH solution at 15M and Na2SiO3 type 2 solution as per Thai Industrial Standard TIS 433-2539. The NS/NH ratio was 1.5, and the ratio of alkaline solution to fly ash (L/A) was 0.85. The replacement amount of paste and RCA with LWFA was varied to achieve and calculate equilibrium density of 1497, 1431, 1401, 1378, 1340, and 1323 kg/m³, with paste volumes of 61.8%, 60.4%, 59.1%, 58.1%, 56.4%, and 55.6%. The results showed that workability tended to vary with the paste volume in the mixtures. Water absorption and porosity were not linearly related to the paste content and density. Compressive strength ranged from 1.48 to 9.82 MPa, showing a trend related to paste volume. When the paste content was reduced from 61.8% to 60.4%, 59.1%, 58.1%, 56.4%, and 55.6%, the compressive strength decreased by 23%, 29%, 23%, 85%, and 85%, respectively. The tensile strength ranged from 0.66 to 1.33 MPa, with an inverse relationship to porosity. The distribution of the mixture was another significant factor influencing tensile strength. All six mixtures passed the criteria for compressive strength and water absorption for non-load-bearing concrete blocks according to TIS 58-2530, with some mixtures passing the criteria for load-bearing concrete blocks according to TIS 57-2530. However, none of the mixtures met the strength requirements of ASTM C330/C330M for structural lightweight concrete. This study contributes to the development of environmentally friendly concrete using industrial waste materials and promotes a circular economy.