Research On The Drying Shrinkage And Reaction Mechanism Of Geopolymer

Production of cement has negative effects on the environment. Geopolymer is a kind of green construction materials with good physical properties and getting more and more attention. However, the shrinkage of the geopolymer that synthetized at room temperature is greatly effected by the environment. Therefore the results about the shrinkage of geopolymer are different. And it restrains the application of geopolymer. This paper mainly studied the effects of activator content, fly ash size disrtibution, steam curing and some kinds of additives on the shrinkage of fly ash geopolymer and fly ash-slag geopolymer, as well as the compressive strength. Meanwhile, the FTIR, XRD and MIP were used to study the reaction mechanis m. It will provide usefull information for the apply of geopolymer.The results showed that the fly ash geopolymer being at standard curing condit ion showed a little expanding. In the condition of relative humidity being 30%, the 90 days’ drying shrinkage of geopolymer was more than 7 times of cement. And its early shrinkage was large, the first 7 days’ shrinkage was 80% of total 90 days’. The main pore size of fly ash geopolymer were micropore and mesopore, and the content was 60%. Decreasing the content of activator increased the expanding of geopolymer in the standard cruring condition, as well as its shringkage in the condit ion with relative humidity being 30%. And its pore distribution was more concentrated. The samples with smaller size of high calcium fly ash had lower early strength, but higher later strength. Its drying shrinkage was larger, however, it had smaller porosity. Addition of 10wt% of cement increased the early strength of geopolymer, and decreaced the drying shrinkage of the samples with more uniform pore distribution. The degree of crystallization of geopolymer gel increased with longer 90 celsius steam curing, however, the strength increased then decreased. And after steam curing, the strength kept decreasing. During the steam curing, the samples expanded. And its 30 days’ drying shrinkage decreased 83%.The drying shrinkage of fly ash-slag geopolymer was mainly happended in the first 7 days about 80% of 45 days’. And the porosity of the samples was around 19% with main pore size being larger than 100 nm. After 24 hours of 90 celsius steam curing, the strength was more than 80% of the samples’ which curied at standard condit ion for 28 days. And after steam curing, the strength kept growing. Steam curing decreased the 45 days’ drying shrinkage 90%. And the pore size was smaller with most pore size being smaller than 50 nm.