Mechanical properties and microstructure of alkali activated Pisha sandstone geopolymer composites

Pisha sandstone is an underdevelopment mudstone/sandstone formed during the Tertiary period. It is the major source of Yellow River sediment. The purpose of this study is to investigate the feasibility of producing a new structural material by using Pisha sandstone via alkali activation process. The variables of this study are alkali dosage, admixture content, curing conditions and curing age. SEM, TG-DTG and XRD observations were used to analyze the microstructure and indentify the crystalline phases of the alkali-activation products respectively. Compressive strength was tested to evaluate the mechanical performance of the fabricated composites. It was shown that mechanical properties of the Pisha sandstone geopolymer composites will be significantly influenced by the curing age, alkali dosage and admixture content. The highest compressive strength of the composites is 20.3 MPa, and the corresponding softening coefficient at 90 days is 0.86. The main alkali-activation products of Pisha sandstone geopolymer composites is an amorphous C-S-H gel. These results suggest that it is possible to utilize Pisha sandstone to fabricate inexpensive construction materials with reliable strength.