Experimental Study in Compressive Strength of Geopolymer Concrete Using Sodium Hydroxide and Sodium Silicate Solution

Abstract: Concrete is one of the most widely used construction materials in the civil engineering industry because of its strength, durability, versatility and suitability for a wide range of structural applications. However, the production of Ordinary Portland Cement (OPC), which acts as the principal binding material in conventional concrete, is associated with significant carbon dioxide (CO₂) emissions, high energy consumption and environmental degradation. The increasing demand for sustainable construction materials has encouraged researchers to investigate alternative binders that can reduce the environmental impact of conventional cement-based concrete. Geopolymer concrete is one such alternative, in which aluminosilicate-rich materials are activated using alkaline solutions to form a hardened binder. Industrial by-products such as fly ash and Ground Granulated Blast Furnace Slag (GGBS) can be utilized as source materials, thereby promoting waste utilization and reducing dependence on conventional cement.

The present research work, entitled “Experimental Study in Compressive Strength of Geopolymer Concrete Using Sodium Hydroxide and Sodium Silicate Solution,” focuses on the experimental investigation of the compressive strength of geopolymer concrete prepared using fly ash and GGBS as binder materials and sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) as alkaline activators. Particular emphasis is placed on the use of a 14 molarity sodium hydroxide solution to investigate the strength development of the geopolymer concrete. Fine aggregate and coarse aggregate are incorporated to produce the concrete mixture, while the alkaline activators initiate the geopolymerization process by dissolving and reacting with the silica- and alumina-containing source materials.

The experimental programme involves the selection and proportioning of constituent materials, preparation of the alkaline activator solution, mixing of geopolymer concrete, casting of standard concrete cubes of 150 mm × 150 mm × 150 mm, curing, and determination of compressive strength. The compressive strength of geopolymer concrete is evaluated at 7, 14 and 28 days to understand its strength development with age. The results are compared with the corresponding strength values of conventional M25 grade concrete to assess the suitability of geopolymer concrete as an alternative construction material. In addition to mechanical performance, the study considers the material cost of geopolymer concrete and conventional concrete, including the influence of binder materials, alkaline activators and aggregates on the overall cost.

The recorded compressive strengths of geopolymer concrete are 14.38 N/mm² at 7 days, 20.22 N/mm² at 14 days and 23.45 N/mm² at 28 days. The corresponding reference values for conventional M25 grade concrete are 16.25 N/mm², 22.50 N/mm² and 25.00 N/mm², respectively. The 28-day strength of 23.45 N/mm² demonstrates the potential of the investigated mixture while also indicating the need for further mix optimization to achieve or exceed the target strength of M25 grade concrete.

The study highlights the potential environmental benefits of utilizing fly ash and GGBS as alternative binder materials and reducing the consumption of Ordinary Portland Cement. It also emphasizes that the performance and economic feasibility of geopolymer concrete depend on material proportions, alkaline activator concentration, solution ratio, water content, curing conditions and the prevailing cost of raw materials. The findings contribute to understanding the compressive strength development of geopolymer concrete prepared with sodium hydroxide and sodium silicate solutions and provide a basis for further investigations into sustainable concrete technology and its potential applications in the construction industry.

Keywords: Geopolymer concrete, fly ash, GGBS, sodium hydroxide, sodium silicate, compressive strength.