Properties of high calcium fly ash geopolymer incorporating recycled brick waste and borax

Geopolymer has attracted various interests all around the world since its introduction. It is known as a beneficial alternative to cement as it can be produced at room conditions, effectively cutting down CO2 emissions compared to the high temperature calcination process in cement production. Moreover, industrial waste or by-products can be upcycled by incorporating as the precursor in geopolymer production, reducing the environmental burden of waste disposal. High calcium fly ash is emerging as a viable option to produce geopolymer binder material. Recycled brick waste (RBW) on the other hand, may be a good source of aluminosilicate, which is vital to produce geopolymer binder material. However, the incorporation of both materials in the production of geopolymer binder materials has not been well-studied. Hence, this paper presents a study on the properties of geopolymer mortar made with high calcium fly ash incorporating 10 % RBW and borax additive at dosages of 3 % and 6 %. In the fresh state, the geopolymer with 10 % RBW and higher borax dosage had a lower temperature, but all mixes gradually exhibited a similar temperature range between 31.3 °C and 31.9 °C. The geopolymer containing RBW exhibited a 13 % higher compressive strength compared to the RBW-absent counterpart in both mixes with 3 % and 6 % borax while the inclusion of borax from 3 % to 6 % reduced the compressive strength by 22 %. The geopolymer had compressive strengths of about 11.8–15.9 MPa after prolonged exposure to an acidic solution, showing a decreasing trend due to the acid attack on the reaction products. The geopolymer mixes containing 6 % borax exhibited lower strength loss (30.2 % and 28.2 %) compared to those with 3 % borax (40.3 % and 42.3 %) on 800 °C heat resistance while the effect of RBW was negligible. On the other hand, the drying shrinkage of geopolymer did not benefit from the inclusion of either RBW or higher borax dosage. The study provided important insights into the incorporation of these materials in the properties of the geopolymer.