Influence of Liquid-to-Solid and Alkaline Activator (Sodium Silicate to Sodium Hydroxide) Ratios on Fresh and Hardened Properties of Alkali-Activated Palm Oil Fuel Ash Geopolymer

Abstract

Malaysia is one of the largest palm oil producers in the world and its palm oil industry is predicted to generate a large amount of waste, which increases the need to modify it for sustainable reuse. The green geopolymers produced from industrial waste can be a potential substitute for cementitious binders. This type of polymer helps reduce dependency on cement, a material that causes environmental problems due to its high carbon emissions. Palm oil fuel ash (POFA) geopolymer has been widely investigated for its use as a sustainable construction material. However, there is still uncertainty regarding the total replacement of cement with POFA geopolymer as a binder. In this study, we examined the effects of different material design parameters on the performance of a POFA-based geopolymer as a building material product through iterations of mixture optimisation. The material assessed was a single raw precursor material (POFA) activated by an alkaline activator (a combination of sodium hydroxide and sodium silicate with constant concentration) and homogenised. We conducted a physical property test, compressive strength test, and chemical composition and microstructural analyses to evaluate the performance of the alkali-activated POFA geopolymer at 7 and 28 days. According to the results, the optimum parameters for the production of alkali-activated POFA paste binder are 0.6 liquid-to-solid ratio and 2.5 alkaline activator ratio. Our results show that the use of alkali-activated POFA geopolymer is technically feasible, offering a sustainable and environmentally friendly alternative for POFA disposal.

Potential of Soil Stabilization Using Ground Granulated Blast Furnace Slag (GGBFS) and Fly Ash via Geopolymerization Method: A Review

“…Previous research has employed the merger of sodium hydroxide and sodium silicate as an alkali activator [ 48 , 51 , 74 , 83 , 88 , 106 , 107 , 108 , 109 , 110 ]. As reported by Tempest et al [ 111 ], the degree of reactivity of raw geopolymer material decreases when the sodium silicate (Na 2 SiO 3 )/sodium hydroxide (NaOH) ratio is too high.…”

“…This is because sodium hydroxide solution plays an essential role in dissolving the raw materials [ 111 ]. However, higher sodium silicate (Na 2 SiO3)/sodium hydroxide (NaOH) ratios are encouraged to be studied for geopolymer systems due to commercial and marketing interest, lowering the workability and strength of the mixture [ 51 , 74 , 78 , 102 , 103 , 109 , 110 ]. This is supported by multiple another study, which also found that sodium silicate (Na 2 SiO 3 )/sodium hydroxide (NaOH) ratio at 2.0 in soil stabilization using fly-ash-based geopolymer process shows the best performance [ 51 , 74 ].…”

Artificial Lightweight Aggregates Made from Pozzolanic Material: A Review on the Method, Physical and Mechanical Properties, Thermal and Microstructure

“…In addition, pozzolanic materials with high SiO 2 , Al 2 O 3 , and CaO content have a high potential to be utilized in producing artificial aggregates with the addition of an alkaline activator [ 23 ]. The usage of alkaline activator as an additive for pozzolanic materials will help to influence the formation of C-S-H binding gel and sodium aluminosilicate hydrates during the geopolymerization process [ 41 ]. The formation of geopolymer aggregate by mixing pozzolanic material with alkaline activator will decrease the porosity of aggregate and improve the strength due to the extra C-S-H and calcium reaction during the reaction process alongside the denser microstructure produced [ 33 ].…”

Using Fly Ash Wastes for the Development of New Building Materials with Improved Compressive Strength

“…The long attack time determines the dissolution of aluminum oxide and the formation of silica-rich products, favorable over the final resistance properties of the materials. On the other hand, the alkaline activator has a significant influence [42], and the polymerization degree depends on the SiO 2 :Na 2 O ratio [43]. The most commonly ash activators are sodium hydroxide, potassium hydroxide and sodium silicates.…”