Experimental investigation on the effect of integral hydrophobic modification on the properties of fly ash-slag based geopolymer concrete

Geopolymer Concrete (GC) is an innovative, environmentally friendly alternative to conventional concrete. The use of geopolymer as binder compared to Portland Cement has the potential to greatly reduce the carbon dioxide emissions and save natural resources being used in the production of building materials. GC, despite its many benefits, is susceptible to water penetration giving rise to durability and longevity issues in structures. Water can carry hostile ions like chlorides and sulphates among other deleterious substances which have the potential to undermine the structural integrity of the material. Therefore, it becomes imperative to address the vulnerability of GC to water penetration induced deterioration to guarantee long-term durability and dependability. The primary focus of this study is to investigate the impact of hydrophobic modification on the fresh state, mechanical, wettability and microstructure properties of GC. The microstructure was studied using Scanning Electron Microscopy (SEM) coupled with Energy Dispersive X-Ray Spectroscopy (EDS) analysis. The hydrophobic modification in GC is carried out by making use of polydimethylsiloxane (PDMS) as a hydrophobic additive to produce integral hydrophobic GC. The findings indicate that as the PDMS content increases, the Water Contact Angle (WCA) on the GC initially increases rapidly and then shows a gradually decreasing trend. PDMS inclusion in into GC showed a reduction in the compressive strength as well as the split tensile strength. Based on the experimental results and considering hydrophobicity as well as the mechanical properties, a PDMS content of 4 % is suggested as the most suitable, yielding a WCA of 132.18 & ring;.