Optimising Durability Performance of Dehydroxylated Kaolin Geopolymer Concrete Using Central Composite Design

Abstract

Geopolymer concrete has emerged as a sustainable and high-performance alternative to Ordinary Portland Cement (OPC) concrete due to its lower carbon emissions and the potential for incorporating industrial waste materials. This environmentally friendly binder system significantly reduces greenhouse gas emissions, primarily CO₂, associated with the production of traditional cement. This study investigates the durability of dehydroxylated kaolin (DHK) geopolymer concrete (DHKGPC) in terms of water absorption capacity, utilising the central composite design (CCD) method. The research focused on five key parameters: activator/DHK ratio, sodium hydroxide-sodium silicate (SS/SH) ratio, sodium hydroxide concentration, curing period, and curing temperature. The CCD technique was used to formulate optimisation models with the ordinary least squares method for precise calibration. The analysis revealed that DHKGPC exhibits a low water absorption capacity, ranging from 121.48 kg/m³ to 210.37 kg/m³, all below the ASTM C140 threshold of 240 kg/m³. The optimisation model demonstrated a strong R² value of 92.55%, confirming the model's reliability in predicting the impact of various factors on water absorption capacity. Key findings indicate that the activator/DHK ratio significantly impacts water absorption capacity, with higher ratios leading to increased absorption due to a less dense microstructure. Optimal sodium hydroxide concentration and SS/SH ratios helped minimise absorption, while curing time and temperature enhanced the geopolymeric reaction, lowering water absorption capacity. The optimised conditions yielded a minimum water absorption capacity of 117.56 kg/m³, fulfilling ASTM C140 durability standards. Furthermore, compared to traditional Portland cement concrete, DHKGPC exhibited slightly better durability, with a 2% lower water absorption rate, indicating enhanced resistance to water penetration and environmental degradation. The results align with previous studies on geopolymer concrete, reinforcing its potential as a durable alternative to traditional cement-based concrete. The low water absorption is attributed to the enhanced pozzolanic reactivity of dehydroxylated kaolin. In conclusion, DHKGPC’s optimised formulation presents a promising material for sustainable construction, with its improved durability and environmental benefits.