EFFECT OF SODIUM HYDROXIDE (NAOH) MOLARITY ON WORKABILITY AND 28 DAY COMPRESSIVE STRENGTH OF SILICA FUME AND COAL FLY ASH BASED GEOPOLYMER CONCRETE

Abstract

The production of ordinary Portland cement (OPC) is one of the main causes linked with carbon dioxide (CO₂) emissions which results in climate instability and environmental degradation, motivating exploration of industrial by products as sustainable supplementary Cementous materials (SCMs). This research focuses on experimental assessment of the geopolymer concrete (GPC) produced with silica fume and coal fly ash with alkaline solutions of NaOH and Na₂SiO₃. This study evaluates the effect of sodium hydroxide (NaOH) molarity and AA/B on the workability and 28 day compressive strength of geopolymer concrete made with silica fume and coal fly ash. Eighteen mix designs were prepared with three different NaOH molarities (10M, 12M, and 14M), Na₂SiO₃/NaOH ratios (1.5, 2.0, and 2.5), and alkaline activator-to-binder ratios (0.50 and 0.67). Three standard 100 mm cubes were cast for each mix, producing a total of 54 specimens. All specimens were heat cured at 90°C and then stored under ambient laboratory conditions until testing at 28 days. Workability was measured by slump, and compressive strength was determined by dividing the maximum failure load by cross sectional area of the cube. The results revealed GPC workability decreased with higher NaOH molarities, slump values averaged of 84.17 mm at 10M, 69.00 mm at 12M, and 54.00 mm at 14M. The 28 day compressive strength followed non trend, it increased from 21.92 MPa at 10M to 24.41 MPa at 12M before declining slightly to 23.63 MPa at 14M series. The highest strength mix was GPC-14, which combined 12M NaOH, Na₂SiO₃/NaOH = 2.0, and an activator-to-binder ratio of 0.50 and achieved 32.62 MPa. Finally, the identifies optimum mix demonstrates high potential for environment friendly construction. By substituting OPC with industrial by products this research contributes to the mitigation of global CO₂ emissions and offers a sustainable solution for the modern construction industry.