ASSESSMENT OF THE STRENGTH AND DURABILITY OF GEO-POLYMER CONCRETE CURED IN LAGOON WATER

Abstract

ABSTRACT Geopolymer Concrete (GPC) presents a suitable alternative to Portland Cement Concrete (PCC) in infrastructure projects due to its friendly production effect to the environmental. The production of Portland Cement (PC) contributes significantly to greenhouse gas emissions, and its poor performance in aggressive environment. This study investigated the strength and durability of GPC in Lagoon water. With the target strength of 50 Mpa.The GPC comprises of fine and coarse aggregates, metakaolin (MK) with ground granulated blast furnace slag acting x as the binders, sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) which provided the alkaline medium. Reinforced GPC 100 × 100 × 600 mm beams, 100 × 100 x 100 mm cubes and 100 × 200 mm cylinders were prepared for flexural, compressive and split tensile testrespectively. Two specimens were prepared; the main specimen was cured in lagoon water (GPCW), while the control specimen was cured at ambient temperature (GPCD), for 28, 90, 180, 270 and 365 days. A finite Element program ANSYS was used to simulate the mechanical properties of both specimen. Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy were used to determine the microstructural and elemental composition of the specimens, respectively.Results showed an increase (111.31 to 146.22 Mpa)in compressive, flexural and splitting tensile on an average of 38.8% from 28 to 180 days, with a decrease of (146.22 to 205.25 Mpa) 23.6% by the 365th day for the GPCD samples. The GPCW showed a reduced strength of (45.02 to 40.01 Mpa) 43% when compared with GPCD, and it experienced reduction in strength at an average of 11% from 28 to 365 days. Deflection of the reinforced beams indicated a steady increase from 28 to 365 days, mirroring the general deflection behaviour of conventional concrete's linear elasticity. SEM revealed differences in GPCD and GPCW with the latter displaying less dense structures with larger voids, consistent with the reduction in compressive strength over time. Conversely, GPCD samples had a denser microstructure, resulting in higher strength. Unreacted MK particles were visible in SEM images, indicating incomplete geopolymerisation in certain areas of the GPCW.XRD analysis highlighted a stable calcium-to-silicon (Ca:Si) ratio in GPCW, with variations in the silicon-to-aluminum (Si:Al) ratios between GPCW and GPCD specimens. Efflorescence substance was observed in the GPCD samples after 180 days. The analysis of the substance revealed a high level of calcium oxide (CaO) and iron oxide (Fe2O3). These oxides led to the reduction in strength after 180 days. The simulation of both GPC samples revealed the elastic strain, normal stress and the deformation generated within the concrete samples during the experiment. Statistical analysis showed the difference between the experimental and simulation strength results to have P ≤ 0.05 confidence interval. This confirmed that the stress-strain obtained in the ANSYS simulation is a true reflection of what happened in the experiment. The study found that Geo-polymer Concrete had weak durability and mechanical properties in an aggressive environment, but strong mechanical strengths in non-aggressive environment making it a promising alternative to PortlandCement.