Strength and Microstructure of Clay Geopolymer Non-Load-Bearing Masonry Units Using Fine-Clay Brick Waste and Palm Oil Fuel Ash

Abstract

This research studies the applicability of alkali-activated cement with a mixture of fine-clay brick waste (FCBW) and palm oil fuel ash (POFA) to manufacture environmentally friendly masonry units. FCBW and POFA were used as a precursor, while a dredged soft clay (SC) was used as aggregate. Sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) solutions were used as the liquid alkaline activator. Effects of NaOH concentration, initial SiO2/Al2O3 mole ratio, Na2SiO3/NaOH ratio, and curing conditions on the strength and microstructure of the FCBW-POFA-SC geopolymers were evaluated. The FCBW-POFA-SC geopolymers had a lower total unit weight than compacted SC because NaOH in the geopolymer binder caused a flocculated soil structure. It was found that Na2SiO3/NaOH=70/30, 10 M NaOH, and FCBW/POFA=70/30 were the best ingredients providing the rigid network of the geopolymer structures. The suitable heat duration of 48 h at 80°C accelerated the dissolution rate of the Si and Al and polycondensation in the geopolymer structure, resulting in denser geopolymer gels and early strength gain. With this optimum ingredient and suitable heat condition, 7-day unconfined compressive strength (UCS) of the FCBW-POFA-SC geopolymers achieved the requirement of the Thailand industrial standard for non-load-bearing masonry units (UCS>2.5 MPa). The geopolymer products were found to be sodium aluminum silicate hydrate (N─ A─ S─ H) and calcium aluminum silicate hydrate (C─ A─ S─ H). The research outcome will promote the usage of waste materials for manufacturing environmentally friendly infrastructure in Thailand and other countries.