Effective of alkaline additives on the geopolymer cements properties as alternative to Portland cement in order to protect environment

Geopolymers are inorganic alumina-silicate materials produced from raw materials, rich in silica (SiO2) and alumina (Al2O3), in combination with an alkaline activator solution. In this study, geopolymer of class C flay ash in ambient curing condition were used form geopolymer mortar and effects of different alkaline activator solutions and variations of associated parameters, were investigated. The obtained results indicated that in ambient curing condition (23±2°C), using sodium hydroxide and sodium silicate as an alkaline activator solution, result in higher 7- and 28-day compressive strength of geopolymer mortar compared to potassium-based (potassium hydroxide and potassium silicate) and combination of sodium and potassium-based alkaline activator solutions, approximately 49% and 145%, respectively. But, in term of 90°C curing condition, potassium-based alkaline activator subject to higher 7- and 28-day compressive strengths. Additionally, simultaneous inclusion of NaOH and KOH led to decline the compressive strength. Also, obtained results of experimental data show that optimal ratio 1.5–2 of SiO2/Na2O were highest compressive strength.