Search

In order to investigate the mechanism of the effect of Mg2+ on the solidification of chloride ions in hardened Portland cement slurry, a NaCl-MgCl2 composite solution was used to soak and corrode the hardened Portland cement slurry. Under the condition of fixed total chloride ion concentration of 0.6mol/L, the effects of Mg2+ concentration (0.1mol/L, 0.2mol/L, 0.3mol/L) and soaking time in environmental solutions on Friedel salt production, leaching Ca2+ ion concentration, and leaching of hardened Portland cement were studied The influence law of pH value and other properties in erosive environments. The results showed that in the early stage of immersion erosion, Mg2+ had little effect on the rate of pH increase of the erosion solution; After the pH value of the solution stabilizes, the final pH value of the solution decreases with the increase of Mg2+ concentration; As the concentration of Mg2+ in the erosion solution increases, Mg2+ promotes the dissolution of hydration product Ca(OH)2 and the dissolution of Ca2+, while generating Mg(OH)2 precipitates, resulting in a decrease in solution alkalinity and an increase in the amount of chloride ions solidified; When the pH of the solution exceeds 12.1, a lower pH value will promote the formation of Friedel salts; When the pH of the solution is less than 12.1, higher concentrations of Mg2+ cause Friedel salt to decompose.

Children's eating behaviors, body shape and body image cognition may be more susceptible to the influence of their parents, but these influences may be weakened with age. There may be different association pathways between parental pressure on children’s body image (PPCBI), body mass index (BMI), body image dissatisfaction (BID) and eating disorders (EDs) among children and adolescents at different developmental stages. This study aims to analyze the association pathways between PPCBI, BMI, BID and EDs among children and adolescents at different developmental stages. The stratified cluster sampling method was used to select 486 students aged 8–15 years in two 9-year schools. Children’s body height, weight, testicular volume and breast development were measured. PPCBI, BID, and EDs were investigated using the Appearance-related Social Stress Questionnaire, Body Size Questionnaire (BID-14), and EDI-1 scale, respectively. The boys with testicular volume Pβ=0.035, Pβ=0.059, Pβ=0.032, Pβ=0.175, Pβ=0.026, Pβ=0.172, Pβ=0.30, Pβ=0.176, P

Keke Liu, Juan Zhang, Songhui Liu, Jiaoyan Chen, Ya Zhang, Wenxiu Li, Han Fu, Lianguo Fu Department of Child and Adolescent Health, School of Public Health, Bengbu Medical College, Bengbu, Anhui, People’s Republic of ChinaCorrespondence: Lianguo Fu, Tel +86-13195529639, Fax +86-5523175215, Email lianguofu@163.comPurpose: This study aimed to analyze the association pathways of parental stress on children’s appearance, body dissatisfaction, and eating behaviours in Chinese children and adolescents.Patients and Methods: The children aged 8– 15 years were selected from 2 nine-year schools using stratified cluster random sampling. The appearance-related social stress questionnaire and the body dissatisfaction subscale of EDI-1 were used to investigate parental stress on children’s appearance and body dissatisfaction, respectively. The self-administered eating frequency questionnaire was used to investigate children’s eating behaviours.Results: Body dissatisfaction in girls mediated associations between BMI, parental teasing, parental injustice and ignorance, parental encouragement and healthy eating behaviour: BMI → body dissatisfaction → healthy eating behaviour, parental teasing → body dissatisfaction → healthy eating behaviour, parental injustice and ignorance → body dissatisfaction → healthy eating behaviour, parental encouragement → body dissatisfaction → healthy eating behaviour. Parental injustice and ignorance directly and negatively predicted healthy eating behaviour in girls. In boys and girls, parental teasing was a direct predictor factor of unhealthy eating behaviour.Conclusion: Parental teasing, parental injustice and ignorance, parental encouragement, and BMI through body dissatisfaction positively predicted healthy eating behaviour in girls, parental injustice and ignorance directly negatively predicted healthy eating behaviour in girls, and parental teasing directly positively predicted unhealthy eating behaviour in girls and boys. Therefore, parental pressure on children’s appearance may pay important role in children’s eating behaviours.Keywords: parental stress on children’s appearance, body dissatisfaction, eating behaviour, children and adolescents

Background: The purpose of this study was to analyze the association pathways between parental pressure on children’s body image (PPCBI), body mass index (BMI), body image dissatisfaction (BID) and eating disorders (ED) among children and adolescents with different developmental stages. Methods: The stratified cluster sampling method was used to select students aged 8–15 years in two 9-year schools. Children's body height, weight, testicular volume and breast development were measured. PPCBI, BID, and ED were investigated using the Appearance-related Social Stress Questionnaire, Body Size Questionnaire (BID-14), and EDI-1 scale, respectively. Results: The boys with testicular volume Conclusions: Parental pressure on children's body image may positively predict children's eating disorders through BMI and body image dissatisfaction in boys and girls after puberty initiation and directly predict eating disorders in boys before puberty initiation; however, it indirectly predicts eating disorders only through BID in girls before puberty initiation.

A novel double-sulfate composite early strength agent (DSA) incorporating aluminum sulfate and sodium sulfate was developed to improve the early strength of Portland cement paste. The effect of the DSA dosage on the setting and hardening properties, hydration process, hydration product composition, microstructure, and pore structure of the Portland cement paste was investigated to reveal its synergistic enhancement mechanism. The results show that the 3 d and 28 d compressive strengths of the Portland cement paste incorporating with 1.0% aluminum sulfate and 1.5% sodium sulfate performed the best, with a 21.3% and 29.7% increase, respectively, compared to the control group. The heat of hydration, XRD, TG, SEM, and MIP tests showed that aluminum sulfate and sodium sulfate acted synergistically, with more AFt (Ettringite) being produced by the synergistic use of 1.0% aluminum sulfate and 1.5% sodium sulfate. Moreover, the hydration of C3S and C2S was accelerated, which resulted in a denser microstructure.

The production of concrete based on Portland cement consumes huge amounts of water every year, but water conservation is becoming a global concern. To address this issue, a special bonding material activated by carbon dioxide instead of water was prepared. The hardening performance, the composition and microstructure of the reaction products and the hardening mechanism of this bonding material were evaluated. It was found that the compressive strength of the material reached 78·2 MPa after the carbon-dioxide-activated curing (CDAC) process. The main reaction products were determined to be calcite and polymerised silicon dioxide gels, which formed a dense microstructure and thus contributed to the material's excellent mechanical strength. Furthermore, in this process, water is not chemically consumed and can be easily recovered during the CDAC. The results indicate that this is an ideal bonding material for buildings in water-scarce areas.

Carbonation is an effective method to promote the quality of the steel slag binder. In this article, two carbonation approaches, namely hot-stage carbonation and accelerated carbonation, were employed to leach the metals, and the influence mechanism on the metal sequential leachability of the binders composed of 80 wt% of EAF slag incorporating 20 wt% of Portland cement (PC) was revealed. The carbonate products, microstructures, and chemical states were investigated, and the results indicated that chromium, vanadium, and titanium gradually transformed into inactive phases after two carbonation approaches, while zinc appeared the opposite trend. The sequential leachability of chromium declined with the increase of the carbonation efficiency, in which the exchangeable chromium decreased from 1.99 mg/kg in the A2A binder to below the detection limit in the A2C binder and C2C binder. Hot-stage carbonation treatment facilitated particle agglomeration, minerals remodeling, and calcite formation. The carbonation curing of the steel slag paste resulted in the formation of amorphous CaCO3, calcite crystalline and Si-bearing hydrates that covered the pores of the matrix, and silicate structure with a higher disorder. The hot-stage carbonation and accelerated carbonation curing methods were adopted to jointly prevent the leaching of harmful metals and facilitate promising high-volume steel slag-based binders with structural densification and CO2 storage.

Optimization of pretreatment and various gas-solid interaction conditions is necessary for effective carbonation of recycled coarse aggregates derived from concrete wastes (RCA). This study demonstrated the use of linear weighted sum method to simultaneously optimize the pretreatment and carbonation test conditions. The optimization of the test conditions produced simplified, and eco-friendly pretreatments and drastically reduced the carbonation duration of RCA from 72 h to 3 weeks in previous studies to 18 h in this study. In addition, the optimum experimental conditions were validated by casting concrete using the carbonated RCAs. The optimized pretreatment and carbonation conditions were spraying Ca2+-rich wastewater at a level of 60% of the 24 h water absorption of RCA, 12 h air drying and 6 h carbonation at 60 °C. This study also demonstrated that wastewater derived from ready-mix concrete batching plants can be utilized for spraying the RCAs to improve carbonation efficiency. Also, the mechanical and durability properties of concrete prepared with RCAs produced from the optimized conventional carbonation and pressurized carbonation were similar. Therefore, optimized conventional carbonation can be utilized as an alternative to pressurized carbonation. The improved mechanical and durability properties of concrete prepared with carbonated RCAs were attributed to the improved physical properties of carbonated RCAs and improved microhardness of the interfacial transition zone of the new mortar. The simplified, faster, ecofriendly, optimized pretreatment and carbonation conditions opens a new vista for industrial carbonation applications and optimization of gas-solid interactions.

The present work presents the microstructure of β-Ca2SiO4 (β-C2S) after accelerated carbonation. The synthesis procedure of β-C2S was examined first, and the crystalline and amorphous structure, the distribution and the pore structure of β-C2S carbonation products were also determined by X-ray diffraction (XRD) quantitative analysis, simultaneous thermal analyzer (TG/DTA), Fourier transform-infrared spectroscopy (FT-IR), high resolution 29Si magic angle spinning nuclear magnetic resonance (29Si NMR), N2-sorption techniques, and scanning electron microscopy (SEM), respectively. Test results indicate that carbonation products are dramatically formed in the initial 2 h. The main carbonation products are crystalline calcite and amorphous three-dimensional network silica gels, which contain nanometer-sized pores. The calcite, silica gels and un-carbonated β-C2S are distributed hierarchically.

In order to increase the application of CO2 in cementitious materials and to develop new additives for cement-based materials, the effect of lithium carbonate (Li2CO3) on the properties of Portland cement (PC) paste was investigated. The hydration heat of fresh paste was tested and the hydration products were characterized using XRD, TG–DTA, SEM and MIP. The results showed that both the initial and final setting time of the PC paste was prolonged with increasing Li2CO3 content. While, the compressive strength of the hardened PC paste at 1 day, 7 days and 28 days increased initially and then decreased. When the content of Li2CO3 was 0.09wt%, the initial and final setting time was increased by 19.8% and 27.7%, and the compressive strength at the age of 1 day, 7 days and 28 days was increased by 47.6%, 21.2% and 14.0%, respectively. Hydration heat, TG–DTA, XRD, SEM, pore structure and other tests showed that Li2CO3 promoted the formation of AFt, and prolonged the arrival time of hydrated calcium silicate peak, but increased the formation of hydrated calcium silicate. Especially when the Li2CO3 content was below 0.09wt%, the pore structure was also optimized. Based on the above results, when the content of Li2CO3 is not greater than 0.09wt%, not only the setting of the Portland cement paste can be retarded, but also the early strength can be enhanced. This can provide a good reference for the use of Li2CO3 in the preparation of new Portland cement-based material admixtures.

In this paper, the effect of triethanolamine content on chloride binding capacity of cement fly ash composite cement paste after curing for 7 days and 28 days was studied. The hydration product composition and pore structure evolution of the hardened paste were studied by hydration heat test, XRD, TGA and nitrogen adsorption test. In addition, the effects of triethanolamine on ion dissolution and microstructure of fly ash were studied by ICP and SEM. The results show that with the increase of triethanolamine content at the same age, the ability of composite cement paste to bind chloride ions is strengthened, and the ability to bind chloride ions is also increased with the increase of age.

This study compared the efficiencies of five recycled aggregate treatment methods (pressurized gas–solid carbonation (PC), flow-through gas–solid carbonation (FC), wet carbonation (WC), nano-silica (NS) spraying and combined PC with NS spraying (PCNS)) in enhancing the performance of recycled aggregate concrete (RAC). Mechanical properties, durability and microhardness of RACs were evaluated. The results showed that PC method recorded higher enhancing efficiency than both FC and WC method. NS spraying method caused higher improvement in mechanical properties of RAC than three carbonation methods. Because of the synergistic effect of enhanced old mortar and new ITZ, PCNS method recorded the highest efficiency.

In this work, a two-step wet carbonation process was developed to synthesize amorphous nano-silica by extracting the silicon phase from recycled cement fines (RCF), aiming to convert RCF into value-added products and sequester CO2. The phases evolution and their microstructure during carbonation were investigated. The results indicated that the RCF was carbonated rapidly to form a mixture of calcite and amorphous silica gel, followed by the formation of silica bearing gel containing aluminosilicate gel and silica gel after two-step wet carbonation. An amorphous silica with a purity of 98.8% and in the form of aggregated nanoparticles (

To enhance the carbonation reactivity of wollastonite (CS), three different calcination processes were adopted to synthesis CS with different crystal structures. The effects of the cooling process on the polymorphs, carbonation reactivity, and CO2 sequestration capacity of CS were measured and evaluated, and its carbonation hardening properties and microstructure evolution were also explored. The results indicated that the carbonation reactivity of CS was enhanced by the rapid cooling process due to the inhibition of the polymorphic transition of α-CS to β-CS. The enhanced carbonation reactivity was attributed to the distorted CaOx polyhedra and extended Ca-O distance in α-CS, which made the dissolution of α-CS to leach Ca2+ easier. The CO2 sequestration capacity and compressive strength of highly reactive CS reached 27.2% and 92.3 MPa, respectively, after carbonation for 24 h. Therefore, it was demonstrated that highly reactive CS can be adopted as ultra-low calcium and CO2 sequestration binder.

Although the research of coal gangue as construction aggregate has been conducted for many years, the fundamental knowledge about the links between the microscopic properties of coal gangue and the macroscopic properties of concrete has not been discovered yet. In this paper, gravel was entirely replaced by coal gangue to improve the utilization rate. The compressive strength, fluidity, and compactness of concrete were studied to explore the macro performance of coal gangue concrete (CGC). Meanwhile, mercury intrusion porosimeter (MIP), scanning electron microscope (SEM), and nanoindentation were used to comprehensively analyze the pore structure, morphology, and micromechanical properties of coal gangue as aggregate. The experimental results showed that coal gangue has a hierarchical structure, wide pore distribution, and poor mechanical properties in microcosmic. Compared with ordinary concrete (OC), both the fluidity and compressive strength of CGC were lower. However, due to the large porosity and water absorption of coal gangue, the bonding surface between coal gangue and cement was denser, which makes the overall compactness of CGC better than OC. The width of the interface transition zone (ITZ) of CGC did not change significantly with the water-cement ratio (w/c), while that of OC did. When w/c was greater than 0.4, the compressive strength of CGC was only about 10% lower than that of OC. The pore structure and micromechanical properties of coal gangue determined the compactness and strength of CGC.

A novel composite admixture (N-A admixture) including sodium bicarbonate (NaHCO3) and aluminum sulfate (Al2(SO4)3) was developed for the in situ generations of calcium carbonate (CaCO3) nano-reinforced particles in Portland cement paste. The effect of N-A admixture dosage (0%, 1%, 2%, 3%, 4%, 5%) on the hydration and hardening properties of Portland cement paste such as setting time and compressive strength was systematically investigated. The enhancement mechanism of the N-A admixture was also revealed by using XRD, TGA, SEM, MIP, and ICC. The results indicated that the N-A admixture can effectively accelerate the hydration reaction process of Portland cement paste and shorten its setting time. When the N-A admixture was added at 3%, the compressive strength at 1 day was 86.9% higher than that of the control Portland cement paste, and there was no inversion of strength at 90 days. N-A admixture promoted the formation of more hydration products. At the early stage of hydration, in situ CaCO3 with a grain size ranging from 25.53 to 42.98 nm was generated, the amount of which increased with the addition of N-A admixture. Moreover, the in situ CaCO3 also reacted with the aluminum phase to form mono-carbonate (Mc) in the late stage, which effectively reduced the proportion of large pores, resulting in a dense microstructure of the hardened Portland cement paste. The results of this work provide a novel and facile method for the generation of in situ CaCO3, which can be used to greatly improve the performance of cement concrete.

Deep coal mining requires grouting reinforcement materials with adjustable setting time, high early strength and toughness. Sulphoaluminate cement-based grouting materials (SCGM) have been widely used due to their low cost, but still suffer from poor deformation and toughness. To solve this problem, in-situ polymerization of acrylamide was developed to modify SCGM, and the effects of acrylamide addition on the fluidity, setting time, mechanical properties, and microstructure evolution of SCGM were systematically investigated. The results indicated that the addition of acrylamide significantly improved the toughness of SCGM. When the acrylamide content reached 35 wt%, the flexural strength of SCGM increased to 10 MPa and the compressive strength reached 35 MPa. In light of microstructural analysis, the exothermic heat of SCGM hydration promoted the free radical polymerization of acrylamide to form inorganic–organic hybrid grouting material with a three-dimensional interpenetrating network structure, which was responsible for the enhanced toughness of SCGM. Those results provided a new method to enhance the toughness of SCGM, making it more suitable for grouting reinforcement engineering.

As a 3D micro-nano material, layered double hydroxides have been widely used in many fields, especially for reinforced composite materials. In this paper, LiAl-LDHs was obtained by a hydrothermal method. In order to investigate the effects of LiAl-LDHs on the early hydration of calcium sulphoaluminate (CSA) cement paste, compressive strength, setting time and hydration heat were tested while X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scaning electron microscopy (SEM) and differential scanning calorimetry (DSC) analysis were employed. The results indicated that LiAl-LDHs could significantly improve the early compressive strength and shorten the setting time of calcium sulphoaluminate cement paste with 3wt% concentration. Besides, the hydration exothermic rate within 5 h was accelerated with increasing LiAl-LDHs content. Moreover, the addition of LiAl-LDHs did not result in the formation of a new phase, but increased the quantity of hydration products providing higher compressive strength, shorter setting time and denser microstructure.

Bayer red mud based ceramic bricks (RMCB) were produced by normal sintering and the effects of sintering temperature on their physical and mechanical properties, mineral composition and microstructure were analyzed. The water permeability and interconnected pores formation mechanism was also analyzed, as well as the pH and conductivity of RMCB leaching solution to evaluate environmental effects. The results show the RMCB to have excellent performances (compressive strength, 22.69 MPa; bulk density, 1.68 g/cm 3 ; total porosity, 47.12%; Linear shrinkage, 7.29%) when sintered at 1125 ℃. Nepheline and anorthite phases formed during sintering are felt responsible for the strength of RMCB. The excellent water permeability is attributed to the creation of a network of interconnected pores within the RMCB. The pH and conductivity of RMCB are greatly reduced compared to the raw Bayer red mud leaching solution due to the stabilized aluminosilicates formed during the sintering process, thus avoiding alkaline harm to the environment.

Carbonation of industrial solid wastes containing calcium silicate can reduce CO2 emissions as well as produce useful building materials. However, until a fully understanding of the hardening and solidification mechanism of solid wastes is obtained, their utilization in engineering applications may remain limited. In respect of this, the present work examined the effect of sodium hydroxide (NaOH) on the carbonation degree and carbonation products structure of β-dicalcium silicate (β-C2S) by using the X-ray diffraction (XRD), Fourier transform infrared spectrometer (FT-IR) and scanning electron microscopy (SEM-EDS), respectively. Moreover, the soluble sodium ions content and pH values of samples suspension were also monitored by using a five channel flame photometer and a digital pH meter, respectively. The results indicated that sodium hydroxide was adverse to the carbonation of β-C2S. In the presence of NaOH, stabilized vaterite phase was formed and the polymerization degree of silicon dioxide gels was also decrease. In turn, soluble sodium ions could be solidified in vaterite crystal structure and the pH values after carbonation was also decreased, providing a new insight into potential means to utilize alkaline solid wastes by carbonation, safely.

β-dicalcium silicate (β-C2S) minerals were prepared. The compositions, microstructures, and distributions of the carbonation products of hardened β-C2S paste were revealed by X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, and backscattered electron (BSE) image analysis. The results show that a dense hardened paste of β-C2S can be obtained after 24 h of carbonation curing. The hardened pastes are composed of pores, silica gel, calcium carbonate, and unreacted dicalcium silicate, with relative volume fractions of 1.3%, 42.1%, 44.9%, and 11.7%, respectively. The unreacted dicalcium silicate is encapsulated with a silica gel rim, and the pores between the original dicalcium silicate particles are filled with calcium carbonate. The sufficient carbonation products that rapidly formed during the carbonation curing process, forming a dense microstructure, are responsible for the carbonation hardening of the β-C2S mineral.

To enhance the properties of recycled concrete aggregates (RCA), a liquid-solid carbonation process was developed and compared with the conventional gas-solid pressurized carbonation method. The performance of RCA and the recycled aggregate concrete (RAC) prepared with the carbonated RCA by the two aforementioned carbonation methods was evaluated. The carbonation products assemblage, microstructure and porosity evolution were first characterized. The results indicated that after subjecting to a 10-min liquid-solid carbonation process, a reduction of 12.2% in RCA water absorption and an increase of 2.6% in density were achieved, which were more efficient when compared to the 24-h gas-solid pressurized carbonation. More importantly, the compressive strength of RAC prepared with the 6-h liquid-solid carbonated RCA was significantly improved. In light of microstructural analysis, the enhanced performance of RAC was attributed to more additional mono-carbonate (Mc) and C–S–H gel formed at the interface between the liquid-solid carbonated RCA and the new cement pastes.

This study proposes a novel design concept of high strength pervious concrete, aiming at improving its compressive strength with adequate permeability. An ultra-high performance paste was developed and used as the binder of the high strength pervious concrete. The effects of aggregate characteristics and membrane-forming ability of the paste on the performance were investigated and their compatibility was evaluated. The experimental results showed that the use of ultra-high performance paste, improvement of homogeneity and compatibility between the paste and the aggregates by elimination of coarse aggregates could improve the mechanical properties. The combined use of aggregates with two-size ranges also resulted in an increase of compressive strength due to the increase of homogeneity and interlocking effect between the aggregates. The enhancement of the membrane-forming ability could optimize the bonding area and thickness of the cement paste between the aggregates. Therefore, the application of the proposed design concepts was able to produce a high strength pervious concrete with a compressive strength of 60.93 MPa and a water permeability of 0.37 mm/s, which would potentially broaden the scope of application of pervious concrete.