C-S-H/PCE对钢渣水泥砂浆早期水化及力学性能的调控机制

[Objective] With the rapid development of the iron and steel industry, steel slag, a by-product of iron and steel smelting, has become a key focus for environmental protection and sustainable development. However, its low activity can lead to a reduction in the early strength of concrete. Calcium silicate hydrate (C-S-H) not only shortens or even eliminates the induction period through homogeneous nucleation but also provides an excellent physical filling effect without negatively affecting later strength. This feature gives C-S-H broader application potential and greater prospects compared with traditional early-strength agents. However, C-S-H tends to agglomerate due to its small particle size and large specific surface area, which reduces its accelerating effect. [Methods] In this study, calcium silicate hydrate/polycarboxylate ether (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 investigated. The setting time of the cement mortar was measured following the standard test methods for water consistency, setting time, and stability of cement (GB/T 1346). Following the cement mortar strength test method (GB/T 17671-2021), the compressive strength of cement mortar was measured at 6 h, 8 h, 12 h, 18 h, 1 d, 3 d, 7 d, and 28 d. The porosity of the cement mortar after 1 d, 3 d, and 7 d of curing was determined using an Autopore IV 9520 mercury porosimeter. The thermal stability of the mortar at 3 d, 7 d, and 28 d was analyzed using a NETZSCH STA 2500 thermogravimetric analyzer. The mineral composition of steel slag cement mortar with varying C-S-H/PCE content was qualitatively analyzed using a Shimadzu XRD-6100 X-ray diffractometer. [Results] The adsorption of Ca2+ by C-S-H/PCE followed the Langmuir adsorption model. The results indicated that Ca2+ adsorption by C-S-H/PCE was monolayer, with a maximum adsorption capacity (Qmax) of 26.19 mg/g. Incorporating an appropriate amount of C-S-H/PCE into steel slag cement mortar effectively accelerated its setting time. The reduction in setting time was proportional to the C-S-H/PCE dosage. Higher C-S-H levels led to shorter times for the cement mortar to reach both initial and final setting. Adding C-S-H/PCE enhanced the compressive strength of steel slag cement mortar, particularly at early stages (within 1 day). Higher C-S-H/PCE content resulted in greater early compressive strength, while the rate of compressive strength increase decreased with curing age. Incorporating an appropriate amount of C-S-H/PCE effectively improved the compactness of steel slag cement mortar and refined its pore structure. This effect was particularly pronounced at early stages of mortar curing, during which C-S-H/PCE significantly reduced porosity. As C-S-H/PCE content increased, the number of macropores decreased significantly, while the proportion of gel pores and mesopores increased, promoting a denser and finer pore structure. [Conclusion] C-S-H/PCE not only stimulates the formation of additional hydration products and accelerates the overall hydration process but also does not alter the types of hydration products, ensuring the stability and controllability of cement properties, and providing a new approach for optimizing steel slag cement mortar performance. This study provides a solid theoretical foundation and technical guidance for the scientific and rational utilization of steel slag in concrete, promoting its practical application and the sustainable development of steel slag resources.