Study On Nascent Microcrystalline Modified Alkali-activated Cement

Since the19th Century, the alkali-activated cement has got widespread attentionfor its superior performance, such as high early strength, fast strength development,good pore structure, low hydration heat, excellent corrosion resistance. Yet theapplication of alkali-activated cement to industry is limited because of high shrinkageand cracking sensitivity resulted from the hydration products, which mostly consist ofgel. Aiming to solve these defects two new kinds of nascent alkali-activated cementare researched, including Mg(OH)2Alkali Activated Cement (MAAFS) and SteelSlag Alkali Activated Cement (SAAFS). This paper reveals many factors related tothe performance of the nascent microcrystalline modified alkali-activated cement.The performance is just mentioned, such as physicochemical properties, dryingshrinkage and cracking sensitivity, et al. Conclusions are as follows:1. The optimum composition of MAAFS:6%(in Na2O+SiO2, Ms=1.0)activator+MgO (burned by the way of M, T=750℃)+slag: fly ash:magnesia=54:36:10. The initial setting time is2hours and the final setting time is3.5hours. The strength can reach to62.5Mpa. Compared with ordinary alkali-activatedcemen the cracking resistance of MAAFS is superior, although compared with OPC itis inferior.2. When the activator is6%, not only can strength of the MAAFS increasewhich is higher than OPC, especially the early strength, but also drying shrinkage rateis lower and cracking resistance is better through N and B burning methods. Dburning method is just the opposite however.3. The optimum composition of SAAFS:6%(Ms=1.0) activator+slag: steelslag: fly ash=60:20:20. The initial setting time is1hour and the final setting time is2hours. The strength can reach to62.5Mpa, the cracking resistance of SAAFS is betterthan that of ordinary alkali-activated cement.4. The hydration products of MAAFS primaryly consist of calcium silicatehydrate gel (C-S-H gel), magnesium carbonate (MgCO3) and magnesium hydroxide(Mg(OH)2). Hydration products like Mg(OH)2from MgO and MgCO3from carbonization can produce relatively large volume expansion to compensate theshrinkage caused by C-S-H gel, and mitigate cracking sensitivity of cement paste.5. SAAFS hydration products predominantly consist of calcium silicate hydrategel (C-S-H gel), Mg(OH)2and Ca(OH)2. Both Mg(OH)2and Ca(OH)2can bringrelatively large volume expansion to compensate the shrinkage of C-S-H gel andreduce cracking sensitivity of cement paste.6. MAAFS and SAAFS have modification on AAS obviously with the volumeeffect and micro-aggregate effect of Mg(OH)2and Ca(OH)2。...