In this paper, we randomly select 75 sets data of calcium sulfate hemihydrate (CSH) content and initial setting time, and the traditional test method of CSH and analyses initial setting time was used by complexometric titration. So the close relationship between them was studied in depth, which classification fitting data to be analyzed by regression analysis. The result shows that this regression analysis method can accurately determine CSH content in modified industrial by-product gypsum. The determination method has the advantages of simplification and rapid operation. As well as, the XRF quantitative analytical method was used to test the CSH content, which verified the accuracy of regression analysis method. The results also show that this method has high accuracy, and can simplify the traditional experimental process. The method developed is easier and more convenient and has broad prospects in application.

Setting time in geopolymers is known as the time taken for the transition phase of liquid to solid of the geopolymer system in which is represented in the initial setting and final setting. Setting time is significant specifically for application in the construction field. This study intends to determine the setting time of high calcium fly ash geopolymers and the properties of the geopolymers after setting (1-day age). This includes the determination of heat evolved throughout geopolymerization using Differential Scanning Calorimeter. After setting properties determination includes compressive strength and morphology analysis at 1-day age. High calcium fly ash was used as geopolymer precursor. Meanwhile, for mixing design, the alkali activator was a mixture of sodium silicate and sodium hydroxide (concentration varied from 6M-14M) with a ratio of 2.5 and a solid-to-liquid ratio of 2.5. From this study, it was found that high calcium fly ash geopolymer with 12M of NaOH has a reasonable setting time which is suitable for on-site application as well as an optimal heat evolved (–212 J/g) which leads to the highest compressive strength at 1-day age and no formation of microcracks observed on the morphology. Beyond 12M, too much heat evolved in the geopolymer system can cause micro-cracks formation thus lowering the compressive strength at 1-day age.