The development of prefabricated buildings increases the demand for using early strong agents in the production of prefabrication. As a new type of crystal early strength agent, synthetic calcium silicate hydrate (C-S-H) can significantly enhance the early strength of cement-based materials, but its poor dispersibility limits its application. In this paper, the polycarboxylate superplasticizers (PCE) with different side chain density were used as a dispersant to synthesis a series of C-S-H/PCE by means of co-precipitation method. The influence of C-S-H/PCE on the structure of C-S-H was studied with XRD, FT-IR, DLC. Moreover, its influence on the cement hydration behavior, hardened body strength and composition structure was investigated. The results show that the smaller the side chain density of PCE, the better the dispersion of C-S-H seeds and the smaller the particle size; the median particle size can reach 339.5 nm; the increase of the number of seed particles can provide more nucleation sites. The incorporation of C-S-H/PCE can significantly accelerate cement hydration, advance the exothermic peak of hydration acceleration by 1.3 h, and increase the heat release by 10.8% at 8 h. After the incorporation of C-S-H/PCE, the porosity of the hardenite of the cement slurry decreases at 8 h and 1 d and the compressive strength increases by 13% and 15%, respectively.

The cement industry is a high energy consuming industry, and the use of mineralizers in the calcination process of cement clinker is an effective energy-saving method. Using solid waste as a mineralizer can also turn waste into treasure and achieve its resource utilization. With pyrite tailings as mineralizer, this study prepared Portland cement clinker with 0, 1.5%, 2.0% and 2.5% SO₃ at calcination temperature of 1350 ℃ , 1400 ℃ and 1450 ℃. Thermal analysis, X-ray diffraction (XRD), polarizing microscope, and other methods were used to analyze the effects of SO₃ addition on the calcination process, mineral composition, petrographic structure, and physical properties of the clinker. The results show that the best effect is achieved when the content of SO₃ is 2.0%. Under this proportion, the content of f-CaO in cement clinker decreases from 1.84% to 1.18%, which can significantly improve the burnability of raw meal. The addition of pyrite tailings can reduce the initial and peak temperatures of CaCO₃ decomposition in raw meal, and form two transition phases of calcium sulphosilicate (2C₂S·CaSO₄) and calcium sulphoaluminate (4CaO·3Al₂O₃·SO₃) at low temperature. This reduces the temperature of liquid phase by 35 ℃, promoting the formation and development of clinker minerals, and has a significant mineralization effect. The cement clinker obtained by calcination with pyrite tailings has good performance, and its compressive strength after curing for 3 days and 28 days is 33.1 and 61.8 MPa, respectively.

Steel slag contains metallic iron and its oxide, which are high value-added renewable resources, and it can be utilized as a mineral admixture in the building materials industry. After different cooling treatment processes, the phase of steel slag evolves, thus affecting the recovery of iron in steel slag and the cementitious activity of tailings. In order to improve the recycling of iron resources in steel slag and the effective utilization of tailings, this paper studied the steel slag of three different treatment processes, namely, hot splash, roller crushing-pressurized hot stewing and roller crushing-hot splash. It used petrography analysis, XRD, SEM-EDS, and chemical phase-selective dissolution, and other methods to analyze the distribution of the iron phases and the state of enrichment of steel slags, and to determine the rate of magnetic separation powder and iron grade, and the cementitious activity of tailings. The results show that: the metal iron is easier to be enriched and deposited under the hot splash process, and the iron phase is mainly in the form of FeO uniformly distributed in the RO phase and the ferrite phase, with less Fe in the phase, and the yield of magnetic separation powder is higher, but the grade is poorer, which is 32.22% and 33.43%, respectively. After roll crushing-pressurized hot stewing, no obvious metal iron particles can be seen in the slag; Fe in the phase accounts for more, and the yield of the magnetic separation powder is low but the grade is higher, which is 28.37% and 37.12%, respectively; after roll crushing-hot splashing, the iron phase mainly exists in calcium ferrite phase and silicate phase in the form of Fe₂O₃, Fe in the phase accounts for more and contains Fe₃O₄, and the magnetic separation powder has high yield and high iron grade, which is 37.60% and 39.69%, respectively. Under roll crushing-pressurized hot stewing, the C₂S content in steel slag is relatively more and better developed, and has high cementitious activity, 7 d and 28 d activity index of tailings is 78% and 92%, respectively; the 7 d activity index of the roll crushed-hot splash slag is low at 66%, but the 28 d activity index grows to 92%; the cementitious activity of the hot splash slag is in the middle.