| Metakaolin is a kind of artificial pozzolanic material with high-activity, which can take pozzolanic reaction in alkaline environment. The paper presents studies on preparation of metakaolin based geopolymer using water glass and sodium hydroxide to, it focus on geopolymer strength development and early strength influence factors. Firstly, to study on water glass modulus and activator alkalinity to geopolymer strength development influence; secondly, to study how fly ash and slag as admixture compound mixture affect on performance of geopolymer; thirdly, study on curing temperature; finally, discusses the drying shrinkage of geopolymer. Research results show that:(1) Change the water glass modulus and alkalinity of activator produced marked effects on the compressive strength of geopolymer. When water glass modulus is1.4and the introduction of Na2O is18%. The highest compressive strength of geopolymer reaches46.3MPa at28day.(2) As mineral admixture, fly ash and slag have a significant effect on fluidity and compressive strength of geopolymer, fly ash can improve the fluidity of geopolymeric cement. Under the same water-cement ratio,15%fly ash can improve21%of the fluidity of paste; Slag can improve the geopolymer early strength development.15%slag can improve9.3%compressive strength of geopolymer at3d.(3)Curing temperature has an essential effect on setting and hardening of metakaolin-based geopolymer. Both early-age and final mechanical properties of geopolymer material are greatly dependent on curing temperature. Higher curing temperatures increase the early-age compressive strengths, which can even reach their target values within1day. Curing temperature at60℃can increase compressive strength66.7%to20℃at Id.But the high temperature and quick formation of the hard structure probably can make cracks. Moreover, the effect of temperature depends on curing time. Curing for just1h at an elevated temperature did not cause remarkable changes in strengths development but longer treatment was responsible for a considerable acceleration of the reaction rate and increase in early-age strengths.(4)As similar as ordinary concrete, drying shrinkage is the main reason for geopolymer to make cracks. As geopolymer paste has a higher water-cement ratio than cement paste and the reaction of water, the dry shrinkage ratio is higher than cement paste. The addition fly ash can reduce the dry shrinkage. When fly ash admixture takes up to15%of cement, the geopolymeric cement shrinkage is decreased38%; the slag admixture can raise geopolymeric cement dry shrinkage. When the slag admixture takes to15%in cement, geopolymer shrinkage is increased19.9%. |
