[Objectives] With the rapid development of the iron and steel industry, steel slag as a by-product in the process of iron and steel smelting, its resource utilization has become an important topic of environmental protection and sustainable development, and the low activity of steel slag will lead to the decrease of early strength of concrete. C-S-H not only shortens or even eliminates the induction period through the homogeneous nucleation effect, but also provides excellent physical filling effect, and does not have a negative impact on the later strength. This feature makes it have broader application potential and prospects than traditional early strength agents. However, C-S-H is prone to agglomeration due to its small particle size and large specific surface area, which affects its acceleration effect.

[Methods] In this study, C-S-H / PCE materials were synthesized and the effects of different dosages of C-S-H / PCE on the setting time, compressive strength, pore structure and cement hydration of steel slag cement mortar were systematically discussed. The setting time of cement mortar was tested according to the standard consistency water consumption, setting time and stability test method of cement (GB / T 1346). According to the cement mortar strength test method (GB / T 17671 − 2021), the compressive strength of cement mortar at 6h, 8h, 12h, 18h, 1d, 3d, 7d and 28d was tested. The Autopore IV 9520 mercury porosimeter was used to test the porosity of cement mortar after curing for 1 d, 3 d and 7 d. The thermal stability of mortar at 3 d, 7 d and 28 d was analyzed by NETZSCHSTA 2500 thermogravimetric analyzer. The mineral composition of steel slag cement mortar with different contents of C-S-H / PCE was qualitatively studied by Shimadzu XRD-6100 X-ray diffractometer.

[Results] The adsorption of Ca2+ by C-S-H / PCE conforms to the Langmuir adsorption model. The results show that the adsorption of Ca2+ by C-S-H / PCE is monolayer adsorption, and the maximum adsorption capacity (Qmax) can reach 26.19 mg / g. Adding a certain amount of C-S-H / PCE to steel slag cement mortar can effectively accelerate its setting time. And the incorporation ratio of C-S-H / PCE is proportional to the reduction of the setting time of the mortar, that is, the higher the C-S-H content, the shorter the time required for the cement mortar to reach the initial setting and final setting state. The addition of C-S-H / PCE can improve the compressive strength of steel slag cement mortar, especially in the early stage (before 1 d). The more C-S-H / PCE content, the higher the early compressive strength of steel slag cement mortar, and with the increase of curing age, the compressive strength growth rate of cement mortar decreases. The addition of a certain amount of C-S-H / PCE can effectively improve the compactness of steel slag cement mortar and refine its pore structure. Especially in the early stage of mortar test block, the improvement effect of C-S-H / PCE on porosity is more significant. With the increase of C-S-H / PCE content, the number of macropores in cement mortar decreased significantly, while the number of gelled pores and mesopores increased correspondingly, which promoted the pore structure to evolve towards a denser and smaller direction.

[Conclusions] C-S-H / PCE can not only stimulate cement to produce more hydration products and accelerate the overall hydration process, but also the types of hydration products in this process have not changed, which ensures the stability and controllability of cement properties and opens up a new path for the performance optimization of steel slag cement mortar.This study aims to provide a solid theoretical basis and technical guidance for the scientific and rational use of steel slag in concrete, so as to promote the in-depth development and practical application of steel slag resource utilization.