Search

Synthesized nanocalcium-silicate-hydrate (C─ S─ H) was successfully employed as an accelerator in portland cement. C─ S─ H nanomaterials were produced in this study utilizing a process that used separate nucleation and growth steps with varied solvent compositions. The effects of the water/alcohol volume ratio (W/A) in the combined solvent on the calcium silicon ratio, particle size, morphology of C─ S─ H nanomaterials, and compressive strength of portland cement were studied. The results reveal that when the W/A ratio decreased, the calcium to silicon (Ca/Si) molar ratio reduced, and the morphology of the C─ S─ H nanomaterials turned from micalike to mixed lamellar and granular, then to granular with a wrinkled surface, and finally to foillike. When the W/A was 3∶1 , the small particles (100 nm) of C─ S─ H nanomaterials had the highest W/A, whereas the large particles (>200 nm) had the highest W/A. C─ S─ H nanomaterials offered calcium silicate hydrate nucleation sites, altered C─ S─ H gel development modes, and enhanced the number of hydration products. The composition, particle size, and shape of C─ S─ H nanomaterials all influenced the compressive strength of the cement paste. [ABSTRACT FROM AUTHOR]

This present study mainly focuses on the influence of low-calcium circulating fluidized bed fly ash (LCFA) on the mechanical property and microstructure of cement-based materials under different curing conditions. The mechanical properties test was conducted by changing variable parameters, such as LCFA content, the internal mixing ratio of LCFA and fly ash (FA), and dry and water curing conditions. Further, the hydration products and pore structure were analyzed using XRD, FT-IR, TG-DTG, NI, SEM, and BET micro-testing technology. The strength development law of LCFA on cement-based materials is discussed. The research results show that LCFA has a certain degree of self-hardening and can be used as a cementitious material in cement-based materials. Still, the loose and porous microstructure of LCFA leads to higher water requirements, which reduces the fluidity of cement-based pastes. Water curing is favorable for promoting the development of LCFA on the long-term compressive strength of cement-based materials. When the LCFA was added to the cement, the optimal substitution ratio was 20%, and the compressive strength at 91 days reached 101 MPa. In the case of compounding LCFA and FA, when the internal mixing ratio of LCFA/FA was 3 and the total content was 20%, the mechanical properties were the highest, and the compressive strength at 91 days was 92 MPa. The microscopic analysis result shows that the cumulative hydration heat of the samples decreased significantly with the increase of dosage of LCFA. The main hydration products of cement-based materials mixed with LCFA were AFt, C-S-H gel, and Ca(OH)2. AFt and C-S-H gels are critical to the strength development of OPC-LCFA samples. The active Al2O3 and active SiO2 in LCFA were involved in hydration reactions to promote the formation of C-A-H and C-S-H gel and effectively promote the development of the mechanical properties. Overdosages of LCFA would reduce the ettringite formation rate. FA is not conducive to AFt formation in the hydration process of OPC-FA samples. [ABSTRACT FROM AUTHOR]

Delaminated MXene was incorporated into cement to improve the properties of cement composites, and its effects on the hydration process, microstructures, and mechanical properties were investigated, respectively. The investigation results showed that delaminated MXene was well-dispersed in the cement matrix and significantly reinforced the compressive strength of cement, especially when the addition is 0.01 wt%. Meanwhile, the total hydration heat of cement hydration and the quantity of hydration products were increased with the addition of delaminated MXene. In addition, the formation of HD C-S-H gel was promoted, and the microstructure of hydrated cement became more compact. [ABSTRACT FROM AUTHOR]

Abstract: Fineness is one of the key factors in determining the hydration activity factor of slag. The present research investigates the effect of particle size distribution (PSD) of slag on water requirement, setting time, and compressive strength. For this purpose, a reference and 17 cement samples containing different blast furnace slag are made and the properties are tested. When slags with proper PSD are prepared the cement properties can be better than the reference. [Copyright &y& Elsevier]

In this paper, in order to improve the wear resistance of road cement, nano-Si3N4 (NSN) was incorporated into cement, and the effect of NSN on compressive strength and wear resistance of road cement was investigated. The main variable of the experimental investigation was the dosage of NSN. The experimental results showed that the addition of NSN could significantly improve the compressive strength and wear resistance of cement paste. Compared with the reference group, the wear resistance can be improved by 46.5% and the compressive strength of cement paste can be improved by 12.3% when the addition of NSN is 0.16% by weight. In addition, the improvement mechanisms of NSN on cement paste were revealed by hydration heat, XRD, DTA-TG, nanoindentation, nitrogen adsorption, and SEM for microscopic phase tests. Through the microscopic analysis, the addition of NSN can accelerate the hydration reaction and promote the hydration degree, optimize the pore structure, and make the cement paste more compact. Additionally, NSN can improve the performance of the interface transition zone (ITZ) and increase the content of HD C-S-H gel. The action mechanism of NSN is mainly dominated by the surface effect, filling effect, and larger surface energy of NSN thereby improving the mechanical properties of cement-based materials. These research results have guiding significance for the design of the high wear resistance and high compressive strength of cement-based materials. [ABSTRACT FROM AUTHOR]

Sintering red mud (SRM) is an industrial alkaline waste residue generated from the sintering process in alumina production, which is often directly discarded and causes environmental issues. In this study, an innovative magnesium-modified wet carbonation method was proposed to convert sintering red mud to valuable calcium carbonate whiskers using CO 2 -containing flue gas. The effects of carbonation conditions including temperature, MgCl 2 concentration, and duration on the composition, microstructure, and morphology of carbonated products were systematically investigated. It was found that a high whisker content of 60% with an aspect ratio of ∼6 could be obtained under the optimal conditions of 80 °C, 0.4 M MgCl 2 , and 2 h reaction time. Besides the formation of whiskers, amorphous aluminosilicate gel was also generated during SRM carbonation. The effects of the as-prepared whisker-rich materials as partial cement replacement on the mechanical properties of cement paste were evaluated with 5 wt% replacement, the 28 d compressive strength was significantly improved by 20.5% compared to the control specimen. The effective reinforcement was ascribed to the fibrous whiskers and enhanced interfacial bonding. This method enables high-value utilization of SRM waste and CO 2 fixation, providing a green and low-cost approach to producing high-performance cementitious materials. [ABSTRACT FROM AUTHOR]

Numerous studies have investigated the carbonation process of tricalcium silicate (C 3 S). However, research on the carbonation of its different crystal forms remains relatively limited. This study explored the effects of accelerated carbonation on the performance and microstructure of T-C 3 S and M-C 3 S. The findings indicated that both T-C 3 S and M-C 3 S exhibited a rapid carbonation reaction rate during the initial 12 h, which subsequently declined gradually. The carbonation products of T-C 3 S and M-C 3 S primarily consisted of calcite, with T-C 3 S also containing a proportion of aragonite calcium carbonate. The decomposition peak temperature of calcium carbonate weight loss increased with prolonged carbonation time for both C 3 S crystal forms. Prismatic or cubic morphology calcite formed in T-C 3 S and M-C 3 S during the initial carbonation stages, leading to a denser microstructure. As the carbonation duration increased, the particle size of calcite also grew, displaying a more irregular morphology. Furthermore, needle-like or rod-like aragonite calcium carbonate was observed in T-C 3 S. T-C 3 S exhibited superior compressive strength compared to M-C 3 S at all stages of carbonation. Additionally, a relationship was established between compressive strength, calcium carbonate content, and CO 2 uptake. This study provided evidence that the crystal structure of C 3 S not only influenced the rate of the carbonation reaction but also impacted the type and morphology of calcium carbonate products and the development of compressive strength. • Effects of accelerated carbonation on the performance and microstructure of T-C 3 S and M-C 3 S were investigated. • T-C 3 S showed a higher carbonation reactivity compared to M-C 3 S. • T-C 3 S had a higher compressive strength compared to M-C 3 S. [ABSTRACT FROM AUTHOR]

Sulfoaluminate cement-based materials (SCBMs) are widely used for grout reinforcement. It is common to use a large water-to-binder ratio in the construction of sulfoaluminate cement-based materials (SAGMs) to obtain good workability and permeability, which results in poor early strength. Nanotechnology has been increasingly employed to enhance the mechanical properties of cementitious materials. Nano Zn-Mg-Al hydrotalcite-like (LDHs) and nano Mg-Al LDHs increased the early compressive strength, while nano Zn-Al LDHs had the opposite effect. However, the reason for this observation remains unclear. In this study, the influence of LDHs structures with different laminar element compositions on the hydration and hardening processes of SCBMs was analysed. The results showed that nano-ZnAl-LDHs, ZnAl-LDHs, and MgAl-LDHs could provide nucleation sites for ettringites. The three hydrotalcite-like materials slowly released different concentrations of zinc and/or magnesium ions and carbonate ions in the cement paste. Zinc ions entered the hydration product of ettringite and aluminum gel and promoted the transformation of amorphous aluminum gel to bayerite, which inhibited the hydration reaction of SCBMs. Magnesium ions could also enter the ettringite, and carbonate ions promoted the formation of calcium carbonate, which facilitated the hydration reaction of SCBMs. The nucleation effect and the release of zinc and/or magnesium ions and carbonate ions acted synergically to influence the hydration rate, pore size distribution, and compressive strength of SCBMs. • Nano MgAl-LDHs, ZnMgAl-LDHs and ZnAl-LDHs could provide nucleation sites for AFt. • The three LDHs released different concentrations of Zn2+ and/ or Mg2+ and CO 3 2-. • Cement hydration was affected by both nano crystal nucleus and the released ions. [ABSTRACT FROM AUTHOR]

• Carbonation properties of mortar with SPLCC and 4 types of aggregates were studied. • Manufactured sand mortar showed highest strength, lowest absorption, narrowest ITZ. • Stone powder improved binding and accelerated calcium carbonate accumulation in ITZ. • Ca:Si ratio in ITZ strongly correlated with strength and absorption of mortar. This study investigated the effects of four aggregates - standard sand, manufactured sand, slag, and coal gangue - on the properties of carbonated self-pulverized low-calcium clinker (SPLCC) mortars. The SPLCC, aggregates, and water were mixed in a mass ratio of 1.00:2.50:0.15 and compaction molded, then carbonation cured by 99.99 % CO 2 exposure at 0.2 MPa. Tests determined the weight gain, compressive strength, water absorption, and interfacial transition zone (ITZ) microstructure after 1, 4, and 24 h of curing. Results showed the manufactured sand mortar had the highest compressive strength (39.7 MPa) and lowest water absorption (3.50 %) at 24 h, indicating the best macroscopic performance. This was due to the manufactured sand's stone powder content improving SPLCC binding and accelerating calcium carbonate accumulation in the ITZ. Nanoindentation revealed the manufactured sand mortar had the narrowest ITZ width (15 μm). SEM-BSE also showed higher Ca content in its ITZ. The Ca: Si ratio in the ITZ strongly correlated with strength and absorption. Overall, manufactured sand as aggregate can enhance carbonated SPLCC mortar properties, providing potential for precast products. [ABSTRACT FROM AUTHOR]

• Influence of LCFA on the properties of cement-based materials was investigated. • Appropriate LCFA is positive to the strength and chloride resistance of cement-based materials. • Early strength of cement-based materials with LCFA can be increased by WG. • LCFA can fill the coarse pores and make the pore structure more compact. To enhance the utilization of circulating fluidized bed fly ash in construction materials, this study investigated the influence of low-calcium circulating fluidized bed fly ash (LCFA) on the properties of cement-based materials. In addition, an alkali activator was added to improve the properties of cement-based materials mixed with LCFA and the synergistic effect was also investigated. The results show that an appropriate amount of LCFA can improve the compressive strength of cement-based materials in underwater curing conditions. The addition of LCFA can improve the physical properties and carbonization resistance of cement-based materials. Whereas, the addition of water glass (WG) can appropriately shorten the setting time and effectively increase the compressive strength of cement mixtures with LCFA. In addition, adding WG can effectively improve the resistance of chloride ion penetration and carbonation. It is speculated that adding appropriate amount of LCFA enhanced the amount of hydration products generated, filled the coarse pores, and made the pore structure of samples more compact. Appropriate addition of LCFA and WG increases the concentration of hydroxyl groups in the system, accelerates the rupture of Si-O and Al-O bonds on the surface of LCFA particles, and forms free and unsaturated active bonds on the surface of LCFA, which is easier to react with Ca(OH) 2 to form hydration products such as C-S-H and C-A-S-H. At the same time, gelatinous hydration products migrate and diffuse with the change of ion concentration in the system, and gradually fill and compact the internal structure. [ABSTRACT FROM AUTHOR]

• The carbonation reactivity of CS was enhanced by the rapid cooling process. • The compressive strength of highly reactive CS after carbonation reached a maximum of 92.3 MPa. • Highly reactive CS can be adopted as ultra-low calcium and CO 2 sequestration binder. 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 CO 2 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 CaO x polyhedra and extended Ca-O distance in α-CS, which made the dissolution of α-CS to leach Ca2+ easier. The CO 2 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 CO 2 sequestration binder. [ABSTRACT FROM AUTHOR]