Mechanical properties and durability of volcanic ash based geopolymer mortars

The mechanical properties and durability of volcanic ash based geopolymer mortars synthesized at 27 degrees C and 80 degrees C were evaluated. The water absorption and apparent porosity increase up to 28 days, then become almost constant with time. The bulk density of specimens cured at 27 degrees C decreases continuously with time, whereas it doesn't change considerably with time for specimens cured at 80 degrees C. Geopolymer specimens cured at 27 degrees C achieved the compressive strength of 20.5 MPa after 28 days and it no longer increases significantly with time. While a maximum strength of 37.9 MPa is reached at 90 days for specimens cured at 80 degrees C. Specimens performed well in wetting and drying conditions. Geopolymer specimens obtained at 27 degrees C developed a better resistance to 5% sulfuric acid than the ones cured at 80 degrees C. The microstructure of geopolymer specimens after acid exposure revealed the formation of gypsum as a secondary phase due to the reaction between sulfuric acid and calcium from geopolymer gel. The presence of Na-rich gel in specimen cured at 27 degrees C enhances its acid resistance. The pore structure and permeability are the key factors affecting the durability of volcanic ash based geopolymer mortars. (C) 2016 Elsevier Ltd.. All rights reserved.