Improving the durability of pumice-fly ash based geopolymer concrete with calcium aluminate cement

This study aims to improve the durability of pumice (70 wt%) and fly ash (30 wt%) based geo-polymer concretes (PGCs) by replacing pumice with calcium aluminate cement (CAC) up to 20 wt % of the total powder binder. In this context, durability characteristics (wetting-drying, freeze-thaw, sulfuric acid, resistance to water-penetration, and abrasion) and microstructure (by performing XRD, FTIR, and SEM-EDS analyses) of PGCs were examined and compared with Portland cement-based concrete (PCC) to control. As a result, CAC substitution of 20% increased the 28-day compressive strength of PGC from 20.0 MPa to 70.0 MPa. The abrasion resistance of PGCs was better than that of PCC, regardless of CAC replacement levels. Since PGC without CAC is highly permeable, wetting-drying cycles, freeze-thaw action, and sulfuric acid attack reduced the strength of this concrete by easily leaching the weakly bound Na cations in the geopolymer matrix and forming -OH and H-O-H type bonds. On the other hand, C-A-S-H type gels formed in PGC with 20% CAC reduced the water penetration depth up to 33 mm by reducing the permeability. In addition, upon 20 wetting-drying and 100 freeze-thaw cycles, compressive strength losses with the CAC replacement level increasing from 0% to 20% decreased from 36.7% to 1.4% and from 43.4% to 4.6%, respectively. Exposure to 5% sulfuric acid solution for 120 days resulted in 0.5% and 16.6% weight loss and 47.4% and 72.6% compressive strength loss in PGCs and PCC, respectively.