Layered double hydroxides (LDHs) have attracted considerable interest as versatile functional materials for energy and environmental applications. However, the primary challenges in LDHs application were their tendency to agglomerate, as well as the difficulty in separation. In this study, a high-performance AC/CaFe-LDH composite was fabricated by immobilizing nano-sized CaFe-LDH particles onto polydopamine-decorated activated carbon (AC). Comprehensive characterization (SEM, XRD, and FTIR) confirmed the successful formation of the AC/CaFe-LDH composite, revealing well-dispersed LDH nanoparticles anchored within the porous matrix and surface of the AC. Compared to pristine CaFe-LDH (286.4 m(2)/g), the AC/CaFe-LDH composites achieved not only an approximately twofold enhancement in BET surface area but also maintained a predominantly mesoporous structure with an average pore diameter of 5.8 +/- 0.4 nm. This unique architecture effectively prevented CaFe-LDH aggregation while maximizing accessible active sites, leading to superior sorption capacity (13.25 mg-P/g at 25 degrees C). Isotherm analyses showed a strong correlation with the Langmuir and Freundlich models, indicating a complex sorption process involving both homogeneous and heterogeneous mechanisms. Investigation of the thermodynamic parameters revealed that the sorption process was spontaneous and endothermic, pointing to an increase in randomness at the solid-solution interface. The superior fit of the Elovich model (R-2> 0.98) suggested a synergistic sorption mechanism where ion exchange predominated, assisted by interface interactions for phosphate removal from aqueous system. LDH-incorporated porous matrix composite offered an effective strategy to enhance performance, while also serving as a valuable reference for developing high-performance functional materials.

This study aims to investigate the influence of amorphous silica on the mechanical properties and fire resistance of gypsum boards, as well as the water-to-gypsum ratio and setting time of gypsum. The results indicate that amorphous silica has a negligible impact on the water-to-gypsum ratio and setting time of gypsum, while it can enhance the mechanical properties and fire resistance to some extent. With the incorporation of 4 wt% amorphous silica, the breaking load of the gypsum board parallel to the long side increases from 311 N to 324 N, while the breaking load perpendicular to the long side rises from 622 N to 682 N. The edge hardness of the gypsum board increases from 116 N to 136 N, while the end hardness rises from 143 N to 165 N. In addition, the fire stability of the gypsum boards is also clearly enhanced, with the fire resistance time increasing from 326 min to approximately 520 min at 800°C. This is attributed to the filling of amorphous silica particles between gypsum crystals, which inhibits crack propagation of the gypsum board under stress. In addition, under elevated temperature conditions, amorphous silica undergoes sintering, transforms from amorphous to crystalline, compensates for shrinkage, and improves the fire resistance of the gypsum board.

To overcome dual technical constraints-setting inhibition and freeze-thaw damage-in cold-region concrete construction while maximizing performance-cost efficiency, this study integrates alkali-activated slag concrete (AASC) and recycled fine aggregate (RFA) two green technologies, conducting comprehensive low-temperature performance investigations. Research examines early-age strength development under subzero conditions and long-term frost resistance at the strength stabilization stage. Air-entraining agents (AEA) were selected to counteract RFAinduced negative impacts by optimizing the air content, demonstrating the dual influences of the RFA-AEA synergy on concrete strength and durability. Critical findings reveal that. (1)RFA significantly shortens setting time and impairs air-entraining efficacy, substantially reducing AASC workability. At 100% replacement, the setting time is reduced by 68.4% and the air content declines by 34.5%, together causing a pronounced deterioration in workability. (2)Under low-temperature curing, AASC hydration is governed primarily by the alkali-activator dosage, and its early-age strength development is strongly dependent on the initial temperature of the raw materials. Therefore, preheating combined with thermal protection enables the 4% alkali-activator AASC to reach the critical strength. (3)RFA enhances early-age strength at low temperatures through its alkali-supplying effect, increasing the 24-h compressive strength by 57% in a 3% alkali-activator AASC system. This strength-enhancing effect diminishes as the alkali-activator dosage increases. In contrast, traditional AEA provides no early strength enhancement at-15 degrees C. (4)AASC with RFA replacement maintains excellent freeze-thaw resistance, but high replacement reduces air-entraining efficiency, thus diminishing the frost resistance improvement. At 50% replacement, RFA and AEA exhibit optimal synergistic compatibility in AASC, as evidenced

The combination of solid waste into lightweight aggregates is a promising strategy for solid waste resource utilization and an effective method for carbon reduction. Herein, the lightweight aggregate with high CO2 adsorption and mineralization performance was prepared by multi-source solid waste combined with porous structural material. Based on the basic property parameters (density, water absorption and porosity) of lightweight aggregates, the effectiveness of multi-source solid waste (fly ash (FA), desulfurization gypsum (DG), coal gangue (CG), blast furnace slag (BFS) and steel slag (SS)) to improve the aggregate performance was determined. The water absorption rate reduced by 20 % and the mechanical strength increased by 49.1 % with the addition of five multi-source solid waste. Moreover, the amount of CO2 absorption could be steadily maintained above 20 % throughout the carbonization curing at room temperature. The decrease in bulk density and water absorption, as well as the increase in skeleton density and mechanical strength of aggregates, were the results of the synergistic effect of multi-source solid waste. This could be attributed to the correlation between the physical properties of the aggregate. The pathway of increasing carbon absorption was proposed based on product analysis and pore characterization. The inability of CO2 to diffuse into aggregate was referred to the accumulation of carbonate on the aggregate surface, resulting in a low carbon absorption rate. The porosity of aggregates was increased and the carbon absorption rate was improved by adding porous materials (diatomite and zeolite). The CO2 absorption of multi-source solid waste coupled with porous materials was increased to 26.3 % under 20 % CO2 (v/v) in nitrogen. Additionally, the synergistic effects of solid waste inhibited the content of heavy metals, and porous materials showed notable inhibiting effect on 8 heavy metals. Zn decreased by 28.7 % due to the addition of DE, and ZE had a better reduction effect by 42.9 %. This study provides a significant understanding of the porous materials modified cold-bonded aggregates by the utilization of multi-source industrial solid waste coupled with CO2 for building materials in engineering applications.

In the current CO2 curing process, pure CO2 gas with a concentration exceeding 99% is primarily used. However, flue gas, which typically contains 10-30% CO2, can also be utilized for carbonization. This study sought to explore the viability of employing flue gas for carbonation and assessed the impact of impurity gases such as SO2. Two typical industrial solid wastes (fly ash and coal gangue) were used to substitute a portion of the cement to prepare light aggregates, which were carbonized under varying concentrations of CO2 and SO2. The porosity and water absorption of the samples decreased after carbonation. A higher degree of carbonation was observed at increasing CO2 concentration. Aggregates carbonated with 15% CO2 improved the CO2 absorption by 48%. The actual CO2 uptake reached up to 58.3% of the theoretical value. The presence of SO2 has been found to impact the uptake of CO2. The CO2 uptake initially declined and then increased as the SO2 concentration increased. The existence of SO2 led to varied increases in the leaching concentrations of the aggregates following the process of carbonation, and some even exceed standard limits. In the presence of both CO2 and SO2, SO2 reacted with the aggregates, resulting in the creation of calcium sulfate. This reaction disrupted the structure of the aggregate, facilitating the diffusion of CO2 into the samples.

The carbonation behavior of concrete with different blast furnace slag replacement ratios (0 %, 50 % and 70 %) at different CO2 concentrations (natural carbonation at 0.04 % and accelerated carbonation at 1 % and 2 %) was investigated in terms of carbonation rate, carbonation products assemblage and pore structure. The results show that the porosity of concrete decreases with the increase in CO2 concentration regardless of mix proportion. The lower porosity at a higher CO2 concentration can lead to an underestimation of the natural carbonation coefficient from accelerated carbonation tests. The carbonation degree of the C-S-H is one of the key factors that determine the carbonation behavior at different CO2 concentrations. A higher CO2 concentration enhances the consumption of the high-density C-S-H and therefore the carbonation of unreacted clinker. However, the C-S-H formed from GGBFS hydration is carbonated to a more advanced state (considerable silica gel is formed) under natural carbonation.

Durability of concrete with supplementary cementitious materials (SCMs) is crucial to the longevity of our built environment. Current research on the carbonation performance of concrete focuses on determining changes in microstructure induced by the chemical and physical interactions of CO2 with the cement phase in samples that do not undergo loading. Although this approach has enabled us to understand the chemical carbonation durability of concrete, the deterioration process is certainly not realistic considering the in-service conditions of structural concrete. Therefore, five different laboratories from RILEM TC 281-CCC WG4 conducted comparative testing of Portland cement concrete with/without SCMs under the combined action of carbonation and mechanical loading. The results indicated that the carbonation depth of concrete undergoing mechanical loading is lower in the case of a limited compressive load, and higher in the case of a high compressive load or tensile load, compared with unloaded specimens. The relative carbonation depth was decreased by 9–16

The combination of environmental actions and mechanical load, which most structural concretes are subjected to, has a synergetic effect on the durability of concrete. The comparative test conducted by RILEM TC 281-CCC WG4 demonstrated and quantified the effect of an applied mechanical load on carbonation performance of concrete with supplementary cementitious materials. Although the effect of loading on the chemical durability of concrete should be taken into consideration for the development of realistic service life predictions, they have been widely overlooked so far. This recommendation proposed by RILEM TC 281-CCC WG4 proposes a testing method for determining the effect of applied load on the carbonation rate of concrete. It specifies a detailed experimental procedure to determine the carbonation development of concretes subjected to compressive and tensile loads. Therefore this recommendation will support the consideration of such combined effects in design codes.

ABSTRACT Shale reservoirs are usually developed by horizontal wells and staged fracturing, and severe casing deformation occurs during development. The main deformation form is shear deformation. The main reason for casing shear deformation is that during hydraulic fracturing, when the fracturing fluid enters the natural fracture or weak cementation surface, the normal stress between the fracture surface or bedding surface will be significantly reduced, and the friction coefficient between the two will also be substantially reduced, which will lead to relative sliding of the rock mass on both sides of the fracture or bedding. Once the rock mass slips, it will lead to shear deformation of the casing. Given this, a method of reducing casing shear deformation using composite cement slurry column structure is proposed: inject conventional cement slurry, elastic and ductile cement slurry, and cement slurry containing hollow glass beads into the wellbore in sections. The high porosity cement sheath formed by cement slurry containing hollow glass beads can effectively reduce the degree of casing shear deformation during formation slip, and the elastic and ductile cement slurry can effectively seal the possible gas channeling problem. During the research, the optimal rheological model of the composite cement slurry column was optimized, the change of the annulus pressure loss caused by the mixing was calculated, and the influence of the cement sheath formed by the structure solidification of the composite cement slurry column on the reduction of the shear deformation of the casing was analyzed. The research results show that the established rheological composite cement slurry column model can be well applied to the project site. Still, the influence of the cement slurry system on friction should be considered in the use process. The cement sheath formed by cement slurry containing hollow glass beads can effectively reduce the shear deformation of the casing. With the continuous increase of the content of hollow glass beads, the ability to reduce the shear deformation of the casing is continuously improved. The research results provide a new way to solve the problem of casing deformation caused by interlayer slip and shear during hydraulic fracturing.

The C30 concrete specimens were exposed in a 20vol% CO 2 atmosphere at different ages for the accelerated carbonation test. The carbonated concrete’s gas permeability coefficient(k Au ) and pore structure parameters were measured by the Autoclam test system and the mercury intrusion porosimetry（MIP）. The relationship between k Au and pore structure parameters was studied by grey correlation analysis（GRA）. The test results showed that the air permeability coefficient of the carbonated concrete increased exponentially with the increase of exposure time. The porosity, characteristic pore size and pore connectivity of the carbonated concrete increased with the exposure time as well. For the change of pore distribution with the exposure time, the volume ratio of pores smaller than 200 nm decreased, the volume ratio of pores with the diameter of 200—1 000 nm increased, and the volume ratio of pores larger than 1 000 nm was unchanged. The GRA results showed that the pore structure parameters with the highest correlation with the k Au are the volume ratio of 50—200 nm pores, pore connectivity, and porosity. The grey correlation coefficients of the above three parameters are 0.932, 0.907 and 0.888, respectively. The linear relation model between k Au and the three parameters was established by regression, laying the foundation for future work on establishing a service life prediction model based on gas permeability coefficient.

The carbonation behavior of concrete with different blast furnace slag replacement ratios (0%, 50% and 70%) at different CO 2 concentrations (natural carbonation at 0.04% and accelerated carbonation at 1% and 2%) was investigated in terms of carbonation rate, phase assemblage and pore structure. The results show that the porosity of concrete decreases with the increase in CO 2 concentration regardless of mix proportion. The lower porosity at a higher CO 2 concentration can lead to an underestimation of the natural carbonation coefficient from accelerated carbonation tests. The carbonation degree of the C-S-H is one of the key factors that determine the carbonation behavior at different CO 2 concentrations. A higher CO 2 concentration enhances the consumption of the high-density C-S-H and therefore the carbonation of unreacted clinker. However, the C-S-H formed from BFS hydration is carbonated to a more advanced state (considerable silica gel is formed) under natural carbonation.

通过溶液法合成钙矾石(AFt),然后采用X射线衍射(XRD)、热分析(TG-DSC)和红外光谱(IR),对比研究了NaCl溶液和模拟海水溶液对AFt与氯离子结合的影响.结果表明:在纯NaCl溶液中,未发生AFt与氯离子的化学结合;当模拟海水溶液中氯离子的浓度升至0.270 mol/L时,有少量Friedel盐形成,同时AFt衍射特征峰的位置发生偏移;当模拟海水溶液中氯离子的浓度升至0.540、1.700 mol/L时,AFt的衍射特征峰消失,水化产物主要为CaSO4·2H2O及Friedel盐;AFt对氯离子的结合在纯NaCl溶液中主要为物理吸附,在模拟海水溶液中不仅有物理吸附,还有化学结合.

Carbonation of concrete, in which 0%, 50% and 70% of cement was replaced by blast furnace slag (BFS), under different levels of sustained compressive load (0, 0.25, 0.5 and 0.75 times the breaking load) was investigated. The results show that the carbonation rate first decreases with load level and then above a threshold value (approximately 0.25–0.5 times the breaking load) increases with load level. The carbonation rate of BFS concrete becomes closer to that of Portland cement concrete under sustained compressive load. An investigation of the load-induced microstructure changes showed that the densification effect dominates in the carbonated zone in terms of lower porosity, denser interfacial transition zone, lower crack width and autogenous healing of fine cracks. The cracking effect plays a more significant role in the non-carbonated zone and leads to a notable increase in the carbonation rate at a high load level. The average major principle strain obtained by digital image correlation can be used to evaluate the combined effect of densification and cracking.

The carbonation behavior of concrete with different blast furnace slag replacement ratios (0%, 50% and 70%) at different CO 2 concentrations (natural carbonation at 0.04% and accelerated carbonation at 1% and 2%) was investigated in terms of carbonation rate, phase assemblage and pore structure. The results show that the porosity of concrete decreases with the increase in CO 2 concentration regardless of mix proportion. The lower porosity at a higher CO 2 concentration can lead to an underestimation of the natural carbonation coefficient from accelerated carbonation tests. The carbonation degree of the C-S-H is one of the key factors that determine the carbonation behavior at different CO 2 concentrations. A higher CO 2 concentration enhances the consumption of the high-density C-S-H and therefore the carbonation of unreacted clinker. However, the C-S-H formed from BFS hydration is carbonated to a more advanced state (considerable silica gel is formed) under natural carbonation.

The effect of the interfacial transition zone (ITZ) on carbonation of stress damaged concrete is investigated by a joint simulation using ABAQUS and COMSOL. Two FEM software use identical mesh and respectively determine the stress damage and carbonation depth. The parameters utilised in the simulation are obtained by a uniaxial test of mortar cylinders and a 450-day carbonation test of cubic concrete. The influence of ITZ and its width (20-100 mu m) on carbonation are studied. For undamaged concrete, ITZ reduces the aggregate-phile effect by 10%. For stress damaged concrete, uneven carbonation fronts are observed, and ITZ increases the maximum carbonation depth by 7-11 and 6.8 times within 1000 days under compression and tension, respectively. An increasing ITZ width also spreads the concentrated damage and promotes the carbonation depth. Comparing the result of ITZ = 100 mu m to that of 20 mu m, the maximum carbonation depth is doubled, and the average carbonation depth is increased by 37%.

目前测定混凝土碳化深度的常规方法是酚酞酒精法(以质量分数为1％的酚酞酒精溶液为显色剂),它能确定混凝土中pH值小于10的完全碳化区域.混凝土的部分碳化区(PCZ)介于完全碳化区(FCZ)和未碳化区(NCZ)之间,其孔溶液碱度因碳化pH值下降至小于11.5时会导致钢筋钝化膜失稳,影响混凝土结构服役寿命,但常规碳化深度测定方法检测不出这一区域,因此未能完整反映混凝土实际碳化损伤.本工作探索了逐层磨粉测定混凝土pH值以确定混凝土碳化深度的方法,测试了碳化7 d、14 d、28 d和56 d混凝土中FCZ和PCZ的厚度,利用热重分析(TG)测定了碳化混凝土内部各层Ca(OH)2与CaCO3分布,建立了混凝土中Ca(OH)2与pH值的对应关系.结果表明:磨粉逐层测试pH值确定的混凝土碳化深度是酚酞酒精法的1.5～2倍,酚酞酒精法忽略了PCZ中可能导致钢筋钝化膜失稳的区域,pH值法测定混凝土碳化深度更为准确.试验还发现混凝土逐层pH值与该层Ca(OH)2含量呈正相关,与该层CaCO3含量呈负相关,通过逐层pH值的变化可反映混凝土碳化反应的进程.本研究为碳化混凝土结构服役寿命预测提供更准确的碳化深度数据.

Concrete structures have to withstand the combined effects of external load and environmental factors. Therefore, it is meaningful to study the durability of concrete under compression and carbonation. The air permeability coefficient (kAu) and pore structure of concrete under uniaxial compression and carbonation were measured by the Autoclam method and mercury intrusion porosimetry (MIP). The Autoclam test results showed that the concrete kAu changed in a concave parabolic manner with the compressive stress level, and the inflection point of the stress level was 45%. The MIP results showed that the characteristic pore structural parameters (porosity, average pore diameter, median pore diameter by area, and median pore diameter by volume) first decreased and then increased with the stress level change. The change in concrete microstructure was a result of the combined effect of pore filling, decalcification, and densification, as well as the split effect. The key pore structural parameters affecting kAu were confirmed using gray relational analysis (GRA). The top three parameters with the highest correlation with the carbonated concrete kAu were porosity (gray relational grade γi = 0.789), median pore diameter by volume (γi = 0.763), and proportion of transition pore volume (γi = 0.827). Furthermore, the regression analysis showed a good linear relation between kAu and the important pore structural parameters.

A numerical method is proposed to determine the semi-carbonated and fully-carbonated depth of concrete subjected to sustained loads. The method modified the diffusivity of each element by multi-axial load levels and stress damages. Based on 1000-day carbonation results of 2D mesoscale concrete, it was indicated that the external load causes highly uneven carbonations and has a similar influence on the semi-carbonated and fully-carbonated depth. However, the tensile and compressive loads have distinctly different influences. Moreover, the relationship between carbonation depths and exposure times which is consistent with Fick’s first law will be broken in the post-peak segment due to severe damages’ propagation.

In order to compare the compensation effect of expansive materials with different mineral sources on the temperature stress of concrete,we investigated the temperature stress of concrete when adding calcium sulfoaluminate type expansive materials (CSA) or CaO and calcium sulfoaluminate mixed type expansive materials (HCSA) at different temperatures by temperature-stress testing machine (TSTM) considering the influence of temperature history on the expansion.The experimental results show that the expansion characteristics of the two kinds of expansive materials with different mineral sources significantly vary.When adding expansive materials,the growth rate of compressive stress during the heating stage increases obviously,the maximum compressive stress is higher,while the decline rate of tensile stress in the late cooling stage becomes slow,and finally cracking temperature decreases.It is proved that concrete with HCSA has lower cracking temperatures and better temperature shrinkage compensation effect.Therefore,it is rational to choose HCSA when preparing concrete with high expansion energy to reduce thermal cracking.

Hydration-heat-inhibiting materials(HIM) with polysaccharide as core material was prepared using microcapsule sustained-releasing technology, through a centrifugal spray granulation process after melting together. The preparation process parameters of HIM were selected by the semi-adiabatic temperature rise test of cement paste. TAM air microcalorimeter was used to investigate the regulation performance of HIM on the hydration of cement. The influence of HIM on the microstructure of cement was investigated by XRD, SEM, and TG-DSC.The results showed that the most suitable wall material for HIM was polyethylene wax, the optimum polyethylene wax/polysaccharide mass ratio was 1, and the most effective particle size was 0.16–0.30 mm. Polysaccharide coated by polyethylene wax released slowly, and the peak heat release rate of cement could be reduced by 55.2% after continuous regulaion. The regulation period continued to 120 h. HIM mainly decreased the C3S reaction rate, which resulted in a 39.2% peak value reduction of hydration heat release rate. However, HIM had little regulation on C3A. The hydration heat release process of cement-based materials can be designed by adjusting the dosage of HIM.