ORIGINAL ARTICLE Study of aluminum sulfate and anhydrite on cement hydration process Jianguo Han . Kejin Wang . Yue Wang . Jiyao Shi Received: 8 May 2014 / Accepted: 9 February 2015 Ó RILEM 2015 Abstract The influences of aluminum sulfate (AS) introduction and dosage on setting time, hydration heat evolution, hydration product type and pore structure of Portland cement were studied, and the influence of AS on concrete strength was investigated also. The results indicate that AS can effectively accelerate setting time of Portland cement and enhance concrete at early age (1 day) strength. AS can promote hydration process of calcium aluminate but inhibit that of calcium silicate. The effect of AS on hydration process becomes more significant along with the increased dosage; and the introduction of AS can promote the formation of AFt. The research results of this paper favor the opinion of the existence of AFt precursor; and the AFt precursor is amorphous AFm which could not be identified by XRD. With anhydrite as setting regulator, the amorphous AFm retention time is prolonged, and the endothermal peaks pro- duced by amorphous AFm during DSC–MS measurement correspond to 80–160 and 830–910 °C, losing H 2 O and SO 2 respectively. Keywords Cement Á Aluminum sulfate Á Anhydrite Á Hydration Á AFt Á Amorphous AFm Á MS 1 Introduction Accelerating admixtures, or accelerators, are common- ly used in concrete to increase setting and/or early age strength development [1]. Depends on the characteristic of accelerator, it will act on the reaction of either C 3 A or C 3 S. For example, sodium aluminate can expedite the hydration process of C 3 A and calcium formate can expedite that of C 3 S[2, 3]. Meanwhile, there are still some other materials which can be utilized as accel- erator and its working objective is not the phase in clinker. Such materials can take effect by enhancing the viscosity of pore solution or cement paste, such as viscosity modifying agent (VMA) and silica fume; by enhancing the thixotropy of cement paste, such as zeolite and metakaolin powder [4, 5]; by producing hydration product which can promote the hardening of cement paste, such as calcium aluminate [2]. Except the composition and dosage of accelerator, the working effect of accelerator can also be influenced by compo- sition and physical characteristics of clinker, properties of mineral admixture, characteristics of setting regula- tor, particle fineness of cement and environmental J. Han (&) Department of Civil Engineering, Tsinghua University, Beijing 100084, China e-mail: hanjg@mail.tsinghua.edu.cn J. Han Á K. Wang Department of Civil, Construction and Environmental Engineering, Iowa State University, Ames, IA 50014, USA Y. Wang Á J. Shi Technology Center of China Railway Tunnel Co., Ltd, Luoyang 471000, China Materials and Structures DOI 10.1617/s11527-015-0561-2