Influence of Calcium Aluminate Cement and Ground Granulated Blast Furnace Slag on the Synthesis of Rice Husk Ash-Based Geopolymer Mortars

The manufacture of Portland cement is energy intensive and is associated with carbon dioxide emission of approximately 7% of total global emission. The process also produces pollution in the forms of dust, noise, and vibration with operating machinery during blasting in quarries. Geopolymer material is formed through the reaction of silica and alumina oxides with alkali activator and has appeared as a viable alternative to the Portland cement in the construction field due to good properties such as high compressive, low permeability, more resistance to corrosion and fire, and good acid resistance. Furthermore, the production of geopolymer concrete offers a solution to the environmental issue as it utilized the industrial by-product materials that consist of silicon and aluminium such as fly ash and rice husk ash (RHA) from power plants. Being rich in silica, RHA can be used as a source material for making geopolymers. However, RHA contains very little aluminium, an additional source of aluminium is needed. Calcium aluminate cement (CAC) and ground granulated blast furnace slag (GGBFS) are aluminium-rich materials, which might be suitable as a source of aluminium when added to RHA to synthesize geopolymers. This dissertation consists of three main parts. The first part is to investigate the possibility of using RHA, CAC, and GGBFS to develop the RHA-CAC and RHA-GGBFS geopolymer mortars at ambient environment. The results showed that the RHA-based geopolymer mortars incorporated with CAC or GGBFS possessed the compressive strength varied from 11 to 73 MPa. The characteristics of CAC and GGBFS can significantly affect the strength development of the geopolymer mortars. The mortar specimens containing KOH had higher compressive strength at various ages up to 120 days when compared with the mortar specimens containing NaOH. The second part of the dissertation examines the durability properties of RHA-CAC and RHA-GGBFS geopolymer mortars in terms of fire and sulfuric acid conditions. For fire resistance, the geopolymer mortars were heated in an electric furnace to temperatures of up to 500°C, 750°C, and 1000°C for 60 min at a heating rate 5°C/min. It was found that both types of the geopolymer mortars suffered strength loss after elevated temperature exposures. However, after exposure to 500°C, the geopolymer mortars prepared using CAC gained strength. The behavior of geopolymers exposed to high temperatures is attributed to two opposing effects: ongoing geopolymerization reaction and/or sintering leading to strength gain; thermal incompatibility leading to strength loss. Hence, the geopolymer mortar strength can either be increased or reduced depending on the dominant process. For sulfuric acid resistance, the geopolymer mortars were exposed to pH 1 and pH 2 sulfuric acid solutions by immersion up to 1, 2, 3, and 4 weeks. The results revealed that both types of the geopolymer mortars had no significant visual signs of deterioration after exposure in the solutions. Some minor corrosion could be observed in the specimens by the acid attack. The mortar specimens showed no noticeable change in color and were seen to remain structurally intact. The important factors identified, which contribute to better resistance to sulfuric attack include the low content of calcium and low porosity that results in low permeability. The third and last part presents the lightweight foamed RHA-based geopolymer mortars using aluminium powder as foaming agent. In addition, lightweight expanded clay aggregate was used to partially replace quartz sand at 50% by volume. The findings indicated that the compressive strength of the lightweight foamed RHA-based geopolymer mortars in the range of 1 to 5 MPa and the density between 660 and 1100 kg/m3 could be made, suggesting that the lightweight foamed RHA-based geopolymers are comparable to those of the lightweight foamed ordinary Portland cement. As described above, in terms of mechanical and durability properties, the RHA-based geopolymers could be a cementitious material to replace Portland cement in infrastructure applications, such as roadway construction, building materials, as well as sewage pipes, which bring economic and environmental benefits.