Microstructural analysis of geopolymer pastes contaminated with crude oil: Impact on efflorescence, physical properties, and mechanical performance

Geopolymer concrete represents a more sustainable alternative to traditional cement in particular production processes, reducing carbon emissions, recycling industrial by-products, and promoting energy efficiency. However, a notable challenge is the potential for efflorescence, which can impair material performance due to microstructural changes from alkali leaching and carbonation. Various additives have been explored to mitigate efflorescence. Using oil-contaminated sand in geopolymer and concrete cement production is emerging as a cost-effective rehabilitation strategy that also addresses environmental concerns. This study investigates the impact of crude oil contamination on geopolymer pastes, focusing on efflorescence susceptibility. Under normal ambient conditions, the geopolymer pastes did not show signs of efflorescence. However, exposure to water led to the formation of efflorescence-type products. Notably, crude oil contamination significantly influenced this outcome. Crude oil significantly decreased the occurrence of efflorescence, mainly when contamination levels ranged from 2 % to 10 %. This reduction is attributed to the oil's effects on the paste's pore structure, fluid migration dynamics, and viscosity, which affected water adhesion and movement through the paste. Additionally, crude oil contamination altered the chemical properties of the geopolymer pastes, causing fluctuations in the pH of leaching solutions, which affected chemical equilibrium and electrical conductivity. Compressive strength improved with 1 % crude oil contamination but decreased with higher contamination levels. Geopolymer paste with 1 % crude oil content generally increases material density and reduces porosity, enhancing mechanical properties and reducing efflorescence. However, excessive contamination undermined these benefits and negatively impacted material performance. Therefore, moderate oil contamination can be effectively used as an additive to reduce efflorescence and enhance geopolymer concrete's physical and mechanical properties. The findings provide valuable insights into the potential applications and limitations of using fly ash-based geopolymers in environments prone to oil contamination.