Limestone calcined clay cement (LC³) has garnered significant interest due to its low clinker factor and reduced carbon footprint. However, its scalability is compromised by the scarcity of high-grade clays and the energy-intensive, multi-step nature of conventional calcination. To circumvent these bottlenecks, this study introduces a suspension flash co-calcination process that simultaneously dehydroxylates bauxite tailings (BT) and partially decomposes limestone (LS) within seconds, directly yielding a composite supplementary cementitious material (SCM). With a fixed 7 s holding time,, the parametric effects of the LS/BT ratio (1:4-1:1) and temperature (650-850 ℃) on phase evolution and hydration performance were rigorously assessed. Optimized at 850 ℃ with LS:BT = 1:4, the resulting LC³ mortar achieves a 28-day compressive strength of 47.5 MPa and pozzolanic activity indices of 75%, 110%, and 109% at 3, 7, and 28 days, respectively. This outstanding performance originates from a triple synergistic mechanism—portlandite consumption by highly reactive metakaolin, heterogeneous nucleation on micro-calcitic surfaces, and nanopore infilling by mono-/hemi-carboaluminates，which collectively drives a fundamental pore structure refinement. The fraction of harmless pores (<20 nm) increases from 13.4% to 54.1%, while total porosity decreases by 30.5%. These findings confirm flash co-calcination as a transformative single-step strategy to upgrade low-grade industrial tailings into high-performance SCMs, offering a viable pathway to lower both the carbon and energy footprint of LC3 production.

Accelerated carbonation curing is recognized as a pivotal strategy for reducing the embodied carbon of cementitious materials in the context of global carbon neutrality. Foamed concrete, despite its high porosity, often exhibits limited CO2 sequestration efficiency due to transport barriers imposed by isolated macropores and insufficient micro/nano-pore connectivity. To overcome this limitation, this study engineered a percolating micro/nanoporous network within foamed concrete using a silicon-based nanoporogen integrated with a protein foaming agent. Micro/nanopore-enriched foamed concrete (MNFC) specimens with dry densities of 300-700 kg/ m3 were prepared and subjected to carbonation at 25 degrees C and 50 degrees C. The results demonstrate that the enhanced pore connectivity reduced the time to full carbonation from 32 h to merely 2 h at 25 degrees C for 300 kg/m3, while achieving a consistent CO2 uptake of 35-39% across all densities. An increase in thermal conductivity was observed, attributed to CaCO3 precipitation and matrix densification. This work establishes pore-architecture design as a critical enabler of efficient carbonation curing, offering a practical route for low-carbon building envelope and infill systems.

Limestone calcined clay cement (LC3) is a representative low-clinker and low-carbon cement that has received considerable attention. However, its use is largely restricted by the quality/distribution of the required clay resources and the energy consumption/CO2 emissions during clay calcination. Herein, a solid waste, named circulating fluidized bed combustion ash (CFBA), discharged by a circulating fluidized bed coal-fired power plant, which has compositions and properties similar to those of calcined clay, is proposed as a substitute for calcined clay in the preparation of low-clinker and low-carbon cement. In this study, the mix of the low-clinker cement based on CFBA was designed and optimized using Design Expert 13.0 software. The physical properties, hydration, hardened matrix structures, and carbon footprint of the low-clinker cement were investigated in detail. The results showed that the optimized mix design for low-clinker cement was 60 % clinker, 27.37 % CFBA, 7.379% limestone, and 5.251 % gypsum. In this case, the physical properties of the low-clinker cement were comparable to those reported for 42.5 grade LC3-50. The apparent activation energy of the low-clinker cement was 43.79 kJ/mol, indicating that the hydration reaction occurred more easily and the reaction rate was less sensitive to temperature than that of 42.5 grade ordinary Portland cement. The synergic hydration effect of the aluminum phase in the CFBA and limestone stabilized the AFt phase, refined the pore structure, and reduced the critical pore size of the cement matrix, thereby improving the later strength of the low-clinker cement. The embodied energy (EE) and embodied CO2 emissions (ECO2-e) of the low-clinker cement with 60 % clinker were 2.79 GJ/t and 0.51 t-CO2-e/t, respectively, representing reductions of 13.35% and 3.77%, respectively, compared with those reported for LC3-50 with 50 % clinker.

With the increased requirement of lithium salts in lithium battery, large amount of lithium slag (LS) discharged during lithium salts extraction process by using spodumene. High content of aluminosilicates and gypsum in LS make it an ideal alternative for mineral admixture and retarder in ordinary Portland cement. Based on above, a ternary compound cement by using clinker, LS and limestone (CC) was proposed in the study. Results showed that the LS could be substituted for calcined clay and gypsum simultaneously to prepare a ternary compound cement similar to limestone calcined clay cement. The prepared cement had longer setting time and better fluidity, and more than 120 % of 28 days compressive strength increasing rate compared to that of 3 days was also observed. The addition of CC could shorten the setting time and improve the workability of the ternary compound cement compared to that of cement with LS alone, due to the nucleation and filling effect of CC. Slow pozzolanic reaction of aluminosilicates in LS and the formation of monocarboaluminate (Mc) might contribute to the higher later mechanical performances of the ternary compound cements. In addition, synergistic hydration effect among clinker, LS and CC would hinder the transformation from AFt to AFm, increase the hydration products and refine the pore structures of the hydrated ternary compound cement system.

In the context of global carbon neutrality efforts, calcium carbide slag has emerged as a promising CO2 adsorbent due to its high absorption capacity. However, kinetic limitations in carbonation hinder its efficiency. Existing research has explored various additive strategies, yet the application of alcohol-amine compounds in solid-phase calcium carbide slag carbonation remains underexplored. This study aims to evaluate the effects of different additive types (MEA, DEA, TEA, NaHCO3), dosages, and CO2 flow rates on the carbonation kinetics and product characteristics of calcium carbide slag. Key findings indicate that NaHCO3 accelerates initial carbonation by directly supplying CO23 ions (269 kg/t CO2 uptake at 1 h), while MEA enhances mid-stage efficiency (389 kg/t at 5 h) through carbamate-mediated CO2 hydration. The performance of DEA is limited by steric hindrance from hydroxyl groups, and high doses of TEA reduce uptake by 32 % due to viscosity-induced diffusion barriers. All additives yield pure calcite, albeit with varied morphologies. MEA promotes the formation of high-aspect-ratio needle/plate crystals, while NaHCO3 results in tightly packed cubic structures. A CO2 flow rate of 160 mL/min significantly boosts carbonation rates, validating mass transfer as a critical driver. This work underscores the potential of calcium carbide slag as a carbon sink via MEA's catalytic pathway and NaHCO3's ion supply. However, challenges remain regarding additive recycling, residual impacts on cement performance, and fixed operational conditions. Future studies should focus on optimizing recycling protocols and evaluating performance under diverse scenarios to enhance industrial scalability.

Considerable blast furnace titanium slags (BFTS) are generated during the V-Ti magnetite smelting process, which had been low-value utilized as aggregates in construction and building areas. In this study, an air-quenching process was proposed to treat BFTS melts directly to obtain spherical BFTS particles. The obtained BFTS spheres (ATS) were sieved into 16-30 mesh (S1), 40-70 mesh (S2) and 70-140 mesh (S3). The morphological parameters (including roundness and sphericity), mineral and chemical compositions of all ATSs were determined by image analysis, scanning emission microscopes (SEM), X-ray fluorescence spectrometry (XRF), and X-ray diffraction (XRD), etc. While their properties were also measured experimentally. It is concluded that all ATSs have a smooth spherical shape with relatively higher sphericity and roundness. ATSs exhibit a better close packing and lower water absorptions as compared with raw BFTS. ATS S3 showed relatively lower acid solubility and excellent crushing resistance as compared with those of ATS S1 and ATS S2. A secondary thermal treatment method is proposed to further improve the acid solubility and crushing resistance of ATSs. Glass phases in ATSs are transformed into crystalline phases, thus improved the acid solubility and crushing resistance of the ATS samples, excluding the crushing resistance of ATS S3. It is expected that the preparation of ATS through air-quenching and the consequent secondary thermal treatment was one of the most proper way in the treatment and high-value utilization of BFTS. And the obtained ATS can be used as a special and functional high-performance aggregate/filler in the construction field or others.

This research investigates the effects of various curing regimes, the incorporation of titanium slag, and the utilization of quartz sand on the strength properties and shrinkage behavior of ultra-high-performance concrete (UHPC). By using low-heat silicate cement to prepare UHPC, this study conducted standard curing and steam curing, and comprehensively analyzed the macro and micro performance of UHPC under different curing conditions. The findings indicate that the application of steam curing markedly enhances the mechanical attributes of UHPC while efficiently decreasing its drying shrinkage. In the comparative tests, we found that the compressive strength of concrete that had undergone 2 days of steam curing was 9.15% higher than that of concrete cured for 28 days under standard conditions. In addition, under the same curing conditions, titanium slag sand had higher mechanical properties than quartz sand. Under standard curing conditions, the 28-day compressive strength of UHPC using titaniferous slag aggregate was 12.64% higher than that of UHPC using standard sand. Through the data analysis of XRD, TG, and MIP, we found that the content of Ca(OH)2 in the hydration products after steam curing was reduced compared to the standard curing conditions, and the pore structure had been optimized. The UHPC prepared with titanium slag sand has greater advantages in mechanical properties and drying shrinkage, and has a smaller pore structure than the UHPC prepared with quartz sand. Moreover, the use of titanium slag sand offers ecological and economic benefits, making it a more sustainable and cost-effective option for high-performance construction applications.

Metakaolin (MK) finds extensive use in cement, mortar, and concrete due to its exceptional pozzolanic activity, which has been found to significantly improve the long-term mechanical performance, impermeability, corrosion resistance, and other material properties. However, the high adsorption and low dispersion of MK lead to an increased demand for water and superplasticizers to achieve the necessary workability, which poses a challenge for the large-scale application of MK in cementitious materials. In this study, we propose the use of local solid waste titanium slag (TS) as a low-hydration-activity filler and water-reducing mineral admixture to mitigate the adverse effects of MK in Portland cement. The hydration process and performances of the blended cements containing ordinary Portland cement (OPC), MK and/or TS were analysed. Results showed that MK actively participated in the cement hydration process and refined pore structures of hardened pastes. However, the mechanical performance enhancement was accompanied by a dramatic reduction in fresh mortar fluidity. The addition of TS to the blended cement containing OPC and MK effectively improved mortar fluidity, and at the same time, resulted in slightly higher compressive strength compared to OPC. The addition of TS did not change the hydration products. However, it did enhance the filling and lubricating effects, resulting in a denser structure in the hardened paste.

Using recycled concrete fines (RFs) as a supplementary cementitious material in blended cement systems offers potential benefits for the construction industry. This study investigated the mechanical properties, hydration development, and microstructural evolutions of blended Portland cement systems incorporating different particle-size distributions of untreated RFs. The results highlighted that finer RFs improved the compressive strength of mortar and influenced hydration by promoting monocarbonate formation. The incorporation of RFs optimizes the pore structure in the early stage but increases porosity. RFs affected the distribution of capillary pores and created a rougher and more complex surface compared to inert mineral admixtures. Furthermore, the particle size of RFs impacted the fractal dimension of multi-scale pore sizes.

The utilization of construction demolition waste as recycled mineral admixtures can simultaneously reduce cement consumption and the environmental impact on the construction industry. Thus, recycled mineral admixtures based on recycled clay brick powder (CBP) were prepared and circulating fluidized bed combustion (CFBC) fly ash was introduced as the activity compensation and sulfate excitation component. The effects of the hydration of recycled mineral admixtures on the mechanical performance and drying shrinkage of mortar were investigated. The results indicated that the incorporation of CFBC fly ash into the blended cement paste accelerated the hydration of C3S and shortened the induction period. The fly ash also promoted the secondary hydration of C3A and the conversion of ettringite to the monosulfate phase. The CBP consumed portlandite to form a calcium–silicate–hydrate gel at a later age, whereas CFBC fly ash promoted the pozzolanic reaction to occur earlier. The incorporation of the CBP and CFBC fly ash increased the porosity and pore volume of the blended paste.

Considering CO2 emissions during production and re-mineralization during hardening, natural hydraulic lime (NHL) has been deemed an ideal cementitious material based on CO2 cycling. However, the preparation of NHL has rarely been reported. In this study, NHL clinker was prepared by calcining calcite tailings, and NHL was obtained by digesting the clinker. The results showed that the performance of the prepared NHL when calcining the calcite tailings at 1,200 degrees C for 1 h and digesting the clinker at 20 degrees C 1 2 degrees C and 70% 1 5% RH (relative humidity) for 8 days met the requirements of NHL5 standard lime mortar. Furthermore, carbonation of the prepared NHL5 was studied, showing that the pore size of the hardened NHL5 mortar was refined during carbonation, and its compressive strength also improved. The prepared NHL5 could be an environmentally friendly cementitious material owing to its utilization of waste, relatively lower energy consumption, and higher CO2 recycling rate. DOI: 10.1061/(ASCE)MT.1943-5533.0004580. (c) 2022 American Society of Civil Engineers.

地聚合物具有轻质、高强、低导热、耐火、防腐蚀等特性,是钢结构无机防火防腐涂料粘结剂的优良备选.以偏高岭土基地聚合物为主要胶凝材料制备了无机防火涂料,探讨了硅灰掺入对防火涂料结构和性能影响.研究结果表明,硅灰掺入可进一步降低防火涂料干密度和导热系数,但其力学性能和防火性能则有较大提高.此外,硅灰掺入大幅提高了防火涂料的粘结强度,避免了偏高岭土地聚合物薄型防火涂层表面开裂和剥落问题.质量比为1:1的偏高岭土与硅灰制备的防火涂料综合性能最佳,涂料干密度619 kg/m3、导热系数0.1388 W/(m·K)、抗压强度6.1MPa、粘结强度达0.4MPa,燃烧1h内防火涂层背火面最高温度不超过251℃.亚微米级硅灰颗粒堆积孔孔径较小,且可填充地聚合物基体大孔;另一方面,硅灰可参与地聚合反应,提高地聚合物凝胶硅铝比,增加凝胶相含量,使得掺硅灰偏高岭土基地聚合物防火涂料性能表现优异.

早期水化活性过低是限制冶炼渣在胶凝材料体系中大掺量应用的重要因素之一.利用固硫灰(CFBA)中的硫酸盐激发硅锰渣(SM)水化活性,并研究硅锰渣-固硫灰复合辅助性胶凝材料的水化过程及活性发展.结果表明:随着固硫灰掺量增加,胶砂流动度大幅下降,但其早期和后期活性得到有效提升;当固硫灰掺量为10％(质量分数)时,复合辅助性胶凝材料3 d、7 d和28 d活性指数分别达到61％、71％和95％,均高于单独使用硅锰渣体系(3 d、7 d和28 d活性指数分别为50％、53％和81％).固硫灰的掺入激发了水泥和辅助性胶凝材料的早期水化,延缓了水化过程中钙矾石转变为单硫型水化硫铝酸钙(AFm),使得胶凝材料早期水化形成更多钙矾石.

The preparation of lime-based materials through calcining limestone or siliceous/clay limestone (including air lime and hydraulic lime) directly/indirectly emits large amounts of CO2 due to limestone decomposition and energy consumption. In this study, a sinter-free hydraulic lime (HL) was proposed by mixing carbide slag (CS) and white Portland cement (WPC), which can effectively utilize solid wastes and in future that may prove to be effective for CO2 mitigation. Results showed the flexural strength of HL mortars decreased from 6.3 MPa to 0.5 MPa, compressive strength decreased from 42.0 MPa to 2.2 MPa, air permeability increased from 0.440 to 2.468 Ln (pressure)/min and water permeability increased from 6.576 x 10(-7) to 47.362 x 10(-7) m(3)/min(0.5) with the increase of CS from 20% to 40%, 60% and 80% in HL. However, the mechanical properties still meet the standard requirements when the CS content is 80%. Carbonation treatment can refine pore size and improve mechanical properties of HL mortar. CS is expected to become the main raw material for HL preparation.

Foaming agent is an indispensable component in preparation of foam concrete by using prefabricated foams. In this study, four types of foaming agents were used to prepare foam concrete. Effect of foaming agent on properties of fresh and hardened foam concrete, interaction between foaming agent and cement, and the gas-liquid interface in foam concrete were studied. It is observed that the interaction between foaming agent and cement played a greater role in the formation process of foam concrete. The property of gas-liquid interface of foam concrete was the most important factor for the performance of in foam concrete, which determined the stability of fresh foam concrete, the pore structure and the products on the pore wall of hardened foam concrete. Finally, the evolution mechanism of foams in new foam concrete w discussed. (C) 2021 Elsevier Ltd. All rights reserved.

Cs-defined ceramics are considered to be ideal solidification forms for 137Cs with high solubility, high volatility, and high mobility in Cs-containing nuclear wastes. In this study, a process consisting of low-temperature solidification and subsequent rapid microwave sintering was proposed to treat the simulated nuclide 137Cs. Csgeopolymer (CsGP) precursors were first prepared to form solidified forms containing simulated 137Cs under ambient conditions. Afterwards, a rapid transformation from CsGP to Cs-defined ceramics was realized by microwave sintering below 1100 degrees C for 30 min, which could effectively avoid the Cs volatility while Cs entered into Cs-defined ceramic lattices under conventionally long-term and high-temperature sintering. As-prepared Csdefined ceramics exhibited superior chemical durability, and the normalized Cs+ leaching rate was as low as 3.06 x 10-4 g/(m2.d).

Hardened hydraulic lime with proper strength, high porosity and large carbonation capacity is considered to be an ideal candidate for CO2 adsorption and in-situ solidification. In this study, hydraulic lime (HL) was obtained by mixing of hydrated lime (Ca(OH)(2), CH) and white Portland cement (WPC). Foamed HLs with dry bulk densities of 300 kg/m(3) and 600 kg/m(3) were prepared in order to increase the CO2 permeability in hardened matrix. Then, CO2 was rapidly captured by foamed HLs to form CaCO3 due to the air-hardening reaction. Results indicated that the CO2 captured capacity and the thermal insulation performance of foamed HLs was increased, but the compressive strength was reduced with the increase of CH in HLs. Carbonation rate was further accelerated under accelerating carbonation condition. Pore size of foamed HLs was refined with the cement hydration and carbonation process, which was beneficial to the increase of compressive strength and thermal insulation performance of foamed HLs. It is expected that foamed HLs could be used as building insulation materials with superior capacity and rate for CO2 adsorption and solidification. (C) 2021 Elsevier Ltd. All rights reserved.

Separation and removal of Cs-137 with long decay period and high decay heat will be beneficial to the subsequent treatment and disposal of radioactive wastes. In this study, geopolymer foams (GFs) with proper mechanical performance and density of 300-600 kg/m(3) have been prepared through prefabricated foam method, which were proposed to be used as the adsorbent monoliths for Cs-137 based on its zeolite-like and hierarchical micro- and meso- pore structures. The prepared bulk GF exhibited remarkable adsorption capacity (192.14 mg/g) and desorption efficiency (64.92%) for simulated Cs-137 in aqueous solution. Furthermore, the adsorption process followed Pseudo-second-order kinetic and Langmuir isotherm models, which was also spontaneous, endothermic, and entropy increased. Finally, the adsorption and enrichment mechanism of simulated Cs-137 in GFs was thus proposed.

Combination of nanoparticles and polycarboxylate superplasticizers (PCE) is expected to synchronously improve the workability, mechanical properties and durability of the mortars and concretes. In this study, nanosilica (NS) has been introduced and grafted onto PCE molecular chains through radical polymerization. Nanosilica-doped polycarboxylate superplasticizer (NS/PCE) was thus obtained and used as the modified water reducer in cement pastes and mortars. The effect of NS/PCE on adsorption, dispersion and mechanical properties of cement pastes or mortars has also been investigated. Results showed that PCE had been chemically bonded to anchor onto the surface of NS by Si-O-. NS was uniformly dispersed in PCE due to the steric resistance and electrostatic repulsive force. The as-obtained NS/PCE had better dispersion and enhanced adsorption performance compared to that of the undoped PCE. NS/PCE can effectively reduce the amount and orientation coefficient of Ca(OH)(2) crystals in cement-based materials, which is beneficial to the microstructure refinement and the mechanical properties improvement of cement matrix. (C) 2020 Elsevier Ltd. All rights reserved.