The C4A3$-C4AF-C2S-C5S2$ cement system, as a low-carbon cement, relies critically on mineral composition for hydration and performance, yet specific impact has not been thoroughly investigated. In this study, C4A3$-C4AF-C2S-C5S2$ clinkers with different mineral compositions were calcined to evaluate the influence of the mineral compositions on the cement performance. After identifying the optimal mineral proportion, the effects of the gypsum type and dosage on the cement performance were further investigated. The workability, strength, and drying shrinkage were tested, and the hydration behaviour of C4A3$-C4AF-C2S-C5S2$ cement was also analysed using XRD, hydration heat, and TG-DSC. The results indicate that a balanced C4A3$/C5S2$ ratio of 1:1 yields the optimal performance, with the composition of 35 wt. % C4A3$ and 35 wt. % C5S2$ achieving a 28-d compressive strength of 48.6 MPa and low drying shrinkage. A microstructural analysis revealed that the continuous formation of AFt, sustained by SO42- released from the gradual hydration of C5S2$, is the key mechanism ensuring the long-term strength development and volume stability. Furthermore, 15 wt. % natural gypsum is identified as the optimal dosage to regulate the early hydration and shrinkage, while desulfurisation gypsum leads to increased later shrinkage due to its lower dihydrate content and insufficient AFt formation.
To realise the resource-oriented utilisation of poly-aluminium chloride (PAC) residue rich in SiO2 and Al2O3, the residue was dechlorinated, dried, and used to partially replace cement by mass to fabricate static-press concrete bricks. The compressive and flexural strengths at 28 days and durability after 50 freeze-thaw cycles were tested, and a microstructural characterisation was performed by X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results show that, after pre-treatment, the cumulative content of SiO2 and Al2O3 in the PAC residue reaches 73.52 %, confirming its potential as a reactive pozzolanic material. When the replacement ratio is <= 20 %, the 28-day compressive strength remains 85 - 95 % of the control, and the strength loss after 50 cycles is below 20 %, meeting specific standards. At replacement ratios > 20 %, both the mechanical and durability performances decline markedly. The microstructural analysis suggests that, at low replacement ratios, the residue refines the pore structure via microaggregate effects and secondary hydration, whereas at high levels, dilution effects and residue morphology increase the porosity. This verifies the feasibility of PAC residue (<= 15 % replacement) in static-press bricks and provides guidance for its industrial valorisation in green building materials.
Supersulfated cement (SSC), a binder with significantly low carbon emissions, exhibits excellent chemical resistance and considerable potential for marine engineering and other infrastructure applications. However, its intrinsic low early-age strength deficit has limited its broader adoption. This study proposes an innovative solution to this limitation by synergistically applying chemical activation (calcium formate) and thermal activation (steam curing at 50 degrees C). It also contributes, through the development of a support vector regression (SVR) model, to jointly optimizing compressive strength and carbon footprint, as experimentally validated. The results show that the dual-activation blend containing 20 % fly ash (FA) reduces CO2 emissions by 29.4 % (8.5 kg CO2/100 kg) compared to conventional SSC, while achieving a 7-day strength of 63.6 MPa. This leads to an outstanding eco-mechanical index of 0.89 kg CO2/(MPa & centerdot;100 kg). By integrating chemical activation, thermal curing, and multi-objective machine learning, this study provides a promising route to advance SSC's potential as a low-carbon, high-performance infrastructure material.
High-performance 95 wt. % alumina structural ceramics are key materials for mechanical seals, semiconductor equipment and new energy components. However, their industrial production still faces challenges such as high sintering temperature, large batch-to-batch performance fluctuations and low yield. In this study, the integrated preparation process including powder pretreatment, composite forming and multi-stage gradient sintering was systematically optimized through orthogonal experiments, and the effects of process parameters on phase composition, microstructure and mechanical properties were revealed. The results show that the optimized process achieves low-temperature densification sintering at 1580 degrees C, and the prepared ceramics have a relative density of 99.6 +/- 0.1 %, bending strength of 485 +/- 12 MPa, fracture toughness of 5.2 +/- 0.3 MPa & centerdot;m0.5 and Vickers hardness of 18.2 +/- 0.4 GPa, with comprehensive mechanical properties improved by more than 22 %. In pilot-scale industrial production, the batch yield increased from 82.3 % to 96.7 %, the single-piece production cycle was shortened by 31.2%, and the relative standard deviation of flexural strength between batches decreased from 8.7 % to 2.1 %. This study provides a scientific basis for the stable and efficient industrial production of high-performance alumina structural ceramics.
Concrete is prone to cracking during hardening due to shrinkage, which significantly impairs its mechanical properties and durability, particularly under freeze-thaw cycles. Urea, with inherent hygroscopicity and recrystallisation characteristics, can effectively mitigate concrete shrinkage, thereby enhancing its mechanical performance and frost resistance. This study analysed ureas' effects on concrete properties, including the slump, hydration heat flow, mechanical strength, crack index, pore structure, water absorption, and freeze-thaw durability. The results show that the concrete performance was notably improved when urea content reached 0.01 wt. %. After 28 days, the cracking index, drying shrinkage restriction rate, restrained shrinkage stress, porosity, and water absorption were reduced by 37.90, 27.97, 27.72, 27.96, and 13.08 %, respectively. Meanwhile, the compressive strength loss rate and mass loss rate after 200 freeze-thaw cycles decreased by 39.84 and 34.44 %, respectively. Additionally, the flexural strength and splitting tensile strength of concrete with 0.01 wt. % urea reached 9.70 and 6.20 MPa, representing increases of 38.57 and 16.98 % compared to the control group. The enhanced crack resistance and mechanical properties are attributed to pore structure optimisation induced by the urea decomposition, while the improved frost resistance stems from the increased cumulative hydration heat and reduced water freezing point.
