Search

Three groups of composite cementitious materials (CCMs) were prepared by separate grinding, mixed grinding, and cascade grinding using iron and steel solid waste (ISSW) materials (granulated blast furnace slag (GBFS), iron ore tailings (IOTs), steel slag (SS) and desulfurization gypsum (DG)), and the influence on the strength of CCMs was investigated under different water-binder ratios (w/b). Then, the hydration hardening mechanism of the CCMs was revealed via hydration heat analysis, phase composition and structural analysis of hydration products. The results show that the properties of the CCMs prepared by cascade grinding (CGC) is better than that prepared by separate grinding and mixed grinding. When the mass percentage of IOTs and SS in the CGC was 2:3, the mix proportion of CGC is SS+IOTs: GBFS: DG=36:51.5:12.5, mixed with 1.0 % Na 2 SO 4 and 1.2 % Na 2 SiO 3 ˑ9 H 2 O of the CGC, the compressive strength (CS) of mortar sample containing CGC in 28-days and 180-days reach 52.3 MPa and 70.7 MPa respectively under the conditions of standard curing and low water-binder ratios. The hydration degree of pure cement is higher than that of CGC, but types of the hydration products were similar with cement, mainly were Ca(OH) 2 , iolite, ettringite (AFt) and C-S-H gel. The CGC can greatly reduce the hydration heat of CCMs system in early age, and is suitable for massive concrete structures in which elevated temperature can be kept for a long time. [ABSTRACT FROM AUTHOR]

Phosphorus tailings are solid wastes generated from mineral processing. It limits the green development of phosphorus chemical industries. Phosphorus tailings mainly consist of dolomite, fluorapatite, and quartzite, so they are used as mineral admixtures to prepare concrete, which not only reduces carbon emissions but also eliminates phosphorus tailings and solves the issues caused by the large accumulation of phosphorus tailings. In this paper, C40 concrete was prepared with different content and fineness of phosphorus tailings, and the effects of phosphorus tailings on its workability, mechanical properties, and durability were investigated. The harm of heavy metals leaching of concrete mixing with phosphorus to the environment was evaluated. The mechanism of the effect of phosphorus tailings on concrete was also analyzed by using characterization methods such as heat of hydration, XRD, and SEM. The results showed that the workability of concrete increased with the phosphorus tailings amount increased, but the mechanical property of concrete decreased. The fineness of phosphorus tailings has little effect on the workability and mechanical properties of concrete. The durability properties of concrete were impaired with the increase in the admixture of phosphorus tailings, but the fineness of phosphorus tailings has no significant effect on the durability properties of concrete. With the increase of the curing time, the structure of the concrete mixed with phosphorus tailings became denser than the concrete without phosphorus tailings incorporated. The concrete mixing with phosphorus tailings had little detriment to the environment. Finally, using the particle size of 20 μm and the content of 20% of phosphorus tailing to replace the cement was suggested. [ABSTRACT FROM AUTHOR]

Hot stuffy self-disintegration has become an advanced and popular steel slag treatment method in recent years, presenting numerous advantages. Hot-stuffy steel slag (HSS) obtained by self-disintegration treatment technology with waste heat has different compositions and properties compared with ordinary steel slag (OSS). Although the properties of OSS as a mineral admixture have been reported by numerous articles, few researches focus on HSS, especially its effect on early cement hydration. In this paper, the early hydration of HSS-cement composite pastes is investigated from the insights of isothermal calorimetry and phase evolution. Effects of HSS on the setting time, hydration heat, reaction product, reaction degree, microstructure, and pore solution were systematically studied and compared with those of OSS. Results show that, unlike OSS, HSS hardly ever retards the early hydration of cement. This is caused by the differences in the composition of HSS and OSS due to the diversity in their production treatment processes. During the hot stuffy self-disintegration, the key retarding component in OSS, such as C12A7, reacts with water and their contents in HSS are reduced. It is found that hot stuffy self-disintegration is an effective method to mitigate the retardation effect of steel slag on the early hydration of cement. This study provides a better understanding of HSS, which is crucial for its utilization in cementitious materials. Highlights: The impact of HSS on the early hydration of cement paste was studied. Hydration kinetics and phase evolution of C-HSS paste were investgated. Unlike OSS, HSS hardly ever retards the early hydration of cement. During the hot stuffy process, the key retarding component in SS is reduced. Hot stuffy self-disintegration effectively mitigates the retarding effect of SS. [ABSTRACT FROM AUTHOR]

Using fly ash (FA) to modify magnesium phosphate cement (MPC) not only extends setting time and enhances MPC performance but also reduces costs. Currently, high‐quality FA is predominantly used, whereas the accumulation of low‐quality FA poses challenges for waste management and environmental protection. This study focuses on low‐quality FA with excessive sulfur content. Initially, X‐ray fluorescence spectroscopy was employed to select two types of FA with SO3 contents of 1.06% and 6.07%. FA replaced magnesium oxide in equal mass to prepare FA/MPC composite cementitious materials. The composite materials were studied for hydration heat, phase composition, infrared spectroscopy, mechanical properties, and microscopic morphology to explore SO3’s impact on MPC hydration processes, microstructure, and properties. The findings indicate that adding FA effectively dilutes reactants, extending setting time from 7 to 17 min and 18 min, aiding construction operations. In the FA/MPC composite cementitious materials, MPC hydration, along with FA's synergistic hydration, forms a new hydration product MgSiO3, improving material density and mechanical strength post‐hardening. Excessive SO3 in high‐sulfur FA accelerates MgO decomposition, providing ample Mg2+ for K‐struvite synthesis, promoting MPC hydration, and transforming K‐struvite from amorphous to crystalline, enhancing material strength. [ABSTRACT FROM AUTHOR]

In the last decades, nano-silica (NS), nano-alumina (NA), and nano-calcium oxide (NC) particles have been incorporated into cementitious materials, and it seems that each one of them contributes uniquely to the materials' properties. This research explores the influence of each nanomaterial on the fresh properties of cement pastes and their compressive strength evolution over one year. Low proportions (1.5% by weight) of nanomaterials were added to cement pastes, and their fresh properties, such as heat of hydration and X-ray diffraction patterns in the first hours, were analyzed. The compressive strength and open porosity were also measured long-term. The acceleration of hydration heat in NA-cement pastes is linked to enhanced hydration product formation at early ages. Among the tested nanomaterials, NA increased compressive strength by 10% at later ages. Although the fresh properties of NC-cement pastes remained unaffected, their open porosity decreased by 54% at 28 days. In contrast, the increase in heat of hydration in NS-cement pastes did not result in significant strength improvement. Based on these findings, NA was selected for ultra-high-performance cement (UHPC)-based material use. Its incorporation not only preserved the ultra-high-performance (UHP) properties but also provided additional benefits such as an increase in compressive strength under a CO2 atmosphere. Through detailed analysis, this research establishes that nano-alumina incorporation optimizes the microstructural development and compressive strength of ultra-high-performance cement-based systems, presenting a novel advancement in enhancing the mechanical properties and durability of these materials under various environmental conditions. [ABSTRACT FROM AUTHOR]

The objective was to assess if post‐exercise ingestion of carbonated water in a hot environment ameliorates hypotension, enhances cerebral blood flow and heat loss responses, and positively modulates perceptions and mood states. Twelve healthy, habitually active young adults (five women) performed 60 min of cycling at 45% peak oxygen uptake in a hot climate (35°C). Subsequently, participants consumed 4°C carbonated or non‐carbonated (control) water (150 and 100 mL for males and females regardless of drink type) at 20 and 40 min into post‐exercise periods. Mean arterial pressure decreased post‐exercise at 20 min only (P = 0.032) compared to the pre‐exercise baseline. Both beverages transiently (∼1 min) increased mean arterial pressure and middle cerebral artery mean blood velocity (cerebral blood flow index) regardless of post‐exercise periods (all P ≤ 0.015). Notably, carbonated water ingestion led to greater increases in mean arterial pressure (2.3 ± 2.8 mmHg vs. 6.6 ± 4.4 mmHg, P < 0.001) and middle cerebral artery mean blood velocity (1.6 ± 2.5 cm/s vs. 3.8 ± 4.1 cm/s, P = 0.046) at 20 min post‐exercise period compared to non‐carbonated water ingestion. Both beverages increased mouth exhilaration and reduced sleepiness regardless of post‐exercise periods, but these responses were more pronounced with carbonated water ingestion at 40 min post‐exercise (mouth exhilaration: 3.1 ± 1.4 vs. 4.7 ± 1.7, P = 0.001; sleepiness: −0.7 ± 0.91 vs. −1.9 ± 1.6, P = 0.014). Heat loss responses and other perceptions were similar between the two conditions throughout (all P ≥ 0.054). We show that carbonated water ingestion temporarily ameliorates hypotension and increases the cerebral blood flow index during the early post‐exercise phase in a hot environment, whereas it enhances mouth exhilaration and reduces sleepiness during the late post‐exercise phase. [ABSTRACT FROM AUTHOR]

The study of the cementitious material activity of industrial solid wastes is a key issue in the comprehensive utilization of its green building materials. In this study, mechanical activation was used to prepare cementitious materials from vanadium-titanium iron ore tailings (VTIOT) as the main raw materials, and the effects of grinding time, the key parameter, on the grinding characteristics of VTIOT, the mechanical properties of the VTIOT cementitious material, and the hydration mechanism were investigated by means of surface area analysis, particle size analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), alkali leaching, mechanical testing, hydration heat analysis, and thermogravimetric analysis (TGA). The results show that: the grinding time and specific surface area of VTIOT exhibit a linear correlation. Prolonging the grinding time, the fractal dimension of the particles gradually increases. The activity of Si4+ and Al3+ elements increases rapidly, reaching a Si4+ and Al3+ content of 96 mg·L−1 at 90 min of grinding. With a VTIOT mixing amount of 30 %, a mortar paste ratio of 1:3, and a water cement ratio of 0.5, the 50 min ground VTIOT mortar demonstrates 7 d and 28 d compressive strengths of 29 MPa and 38.7 MPa, corresponding to the highest values of the activity index, measured at 71.4 % and 75.2 %, respectively. Under standard curing conditions, the hydration products of cementitious materials at 7 d are ettringite (AFt), calcium silicate hydrate (C-S-H), alumina, ferric oxide, monsulfate (AFm), calcium hydroxide (Ca(OH) 2), and calcium silica (CS). In the hydration process of 7 d, the exothermic peak and exothermic amount of the 50 min VTIOT cementitious materials are greater than those observed for other grinding times, but lower than those of pure reference cement. [ABSTRACT FROM AUTHOR]

The aim of this research was to develop cost-effective and environmentally friendly ultra-high-performance concrete (UHPC) using fly ash (FA) and quartz powder (QP) as sustainable cement replacements. The performance of the various constituents was examined and their influence on fresh and hardened properties was investigated in order to determine the optimum trial mix design. A cube compressive strength of 144 MPa was achieved with 20% FA and 10% QP and other ingredients without any special heat treatment. Advanced characterisation studies, such as the heat of hydration and X-ray diffraction analysis, were performed to gain understanding of the performance of FA-blended UHPC. Various fracture properties (fracture toughness, fracture energy, brittleness etc.) were investigated considering geometrically similar notched beam specimens for UHPC mixes with steel fibre contents of 1.5% and 2.5%. The optimum UHPC mix achieved good scores in terms of the strength index and the embodied carbon dioxide emissions index, indicating that the concrete is eco-friendly and sustainable. [ABSTRACT FROM AUTHOR]

Compacted bentonite is under consideration as a backfill material for engineered barrier systems in a geological repository for high-level radioactive waste. Coupled THM (thermal–hydrological–mechanical) models for laboratory tests have been effective in understanding coupled processes and improving modeling capability. While studies on bentonite behavior under heating temperatures < 100 °C have been extensively conducted, models and tests for high temperatures are relatively sparse. A bench-scale laboratory experiment at a high temperature (200 °C) was conducted, which provided 3D visualization of the density distribution via frequent X-ray CT images during the experiment, and detailed characterization of bentonite samples after the column tests was running for 1.5 years. We present here a THM model to interpret the data observed from the test, particularly focusing on the effect of the soil–water retention curve (SWRC) and the thermal conductivity function (TCF) under high temperatures. Model results provide a decent match of measured temporal and spatial changes that are the result of heating-induced desaturation, capillary-regulated hydration, swelling/shrinkage induced by local water content, temperature and pressure change, and displacement from nearby areas. The model suggests that (1) the non-linear TCF function should be chosen, (2) temperature-dependent SWRC affects the simulation results in all aspects, and (3) the linear swelling model underperforms the state surface approach in matching the displacement data. It is challenging to explain the density distribution at an early time (< 10 days) at the hydration front where increases in water content, swelling at the hydration front, and compression from nearby areas leads to high density that cannot be fully explained by the current THM model. Refinement of the mechanical model is needed in the future. Highlights: A column experiment at a high temperature (200 °C) was conducted to track THM evolution of bentonite under heating and hydration. A coupled THM model was developed to interpret the dynamic change of temperature, density, displacement. The model suggests the non-linear thermal conductivity function should be used. Temperature-dependent soil–water retention curve affects the simulation results in all aspects. The linear swelling model underperforms the state surface approach in matching the displacement data. [ABSTRACT FROM AUTHOR]

Fly ash (FA) increases the performance of cement concrete through pozzolanic reaction and microstructure development at later ages. FA is usually associated with lower early age compressive strength especially at higher replacement levels. This study attempts at improving the early age strength of FA portland pozzolana cement with limestone calcined clay pozzolan (LC2). Different proportions of limestone and calcined clay (1∶1 , 1∶2 , and 2∶1) in tandem with FA at various replacements of cement clinker (30%, 40%, and 50%) were tested. The combined effect of using LC2 with FA has shown to enhance the early age hydration of cement along with improved compressive strength. Heat of hydration results showed increased heat release in FA mixes blended with LC2. Thermodynamic modeling analysis was used to study the change in phase assemblage of these mixtures. A higher solid volume observed in the thermodynamic simulations in the combined blends of FA and LC2 is hypothesized to be the cause of improved performance compared with only FA blended cement. Mercury intrusion porosimetry (MIP) results further confirmed an improvement in pore structure characteristics of FA cement blended with LC2. The possibility of reducing associated carbon emissions without compromising in strength are highlighted by using FA and LC2. [ABSTRACT FROM AUTHOR]

Cement grout is widely used in underground excavations and constructions. Recent research reveals that coal char, a sustainable coal-derived material, can enhance the engineering properties of traditional cement grouts, such as higher compressive strength and lower bleeding at room temperature. However, the effect of coal char addition on the heat of hydration and rheological behaviors of char-cement grouts at lower or higher temperatures remains unclear. In this study, considering different w/c ratios (0.8–1.2) and char contents (10%–30%), the heat of hydration of char-cement is investigated to understand the hydration mechanism of cement with adding char. The rheological behaviors of new char-cement grouts at two different temperatures of 5 and 35°C are studied. It is found that the addition of char at the same w/c ratio leads to a higher first heat flow peak in the initial reaction period and facilitates hydration reaction in cement grouts based on cumulative heat evolution over a longer period (typically >14 h). The effect of 5 and 35°C on rheological behaviors of char-cement grouts is consistent with the respective pure cement grouts. A simple model based on cumulative flow resistance is proposed for describing the rheological behavior and can well fit all pure cement and char-cement grouts with a relatively high average R2 value of 99.7%. [ABSTRACT FROM AUTHOR]

The paper presents the results of a study on the hydration heat of ultralight cementitious foams envisaged as insulation materials for building envelopes. The examined porous foam-cement material was additionally enhanced by embedded microencapsulated phase change material (PCM) to improve the desired thermal properties of the material. The heat emission and heat flow were measured at 20 °C and 30 °C for 168 h using the isothermal calorimeter. The experimental study comprised composites with dry densities of 240 kg m−3 and 480 kg m−3, two concentrations of protein-based foaming agent (2% and 4%) and two dosages of the embedded PCM material (10% and 20%). The reference composite without PCM was also tested. The effect of the necessary admixtures used to achieve the stability of ultralight cementitious foams was also examined. The results showed that hydration in ultralight foam-cement composites is retarded, and the values of heat released are lower than those of the paste used to produce the composites. In this regard, the main factors contributing to the lower heat released and its lower rate are the excess water from the foam, the dosage of the foaming agent and the admixtures introduced to achieve the stability of the ultralight composite. The stabiliser was found to be the most retarding admixture. Considering PCM, which was added at 10% and 20% of the paste volume, a rather low influence on the course of the hydration process was observed due to the overall composition of ultralight cementitious foams specially modified for each assumed content of PCM. [ABSTRACT FROM AUTHOR]

In this study, three hydration heat controlling materials (HHCMs), respectively, containing pure hydroxyl (polyvinyl alcohol, PVA), carboxylic (polyacrylic acid, PAA) and ester groups (maleic acid-ethylene glycol ester, P(MA-EG)) were synthesized and mixed with cement-based materials, and the hydration heat and setting time of cement pastes and the SEMI adiabatic temperature rise and strength of mortars were tested. The results showed that PAA and P(MA-EG) reduced the peak value of hydration exothermic rate by 77.45% and 62.28%, respectively, and prolonged 54.14 h and 15.56 h, respectively. Mechanism studies showed that HHCMs containing carboxylic or hydroxyl groups adsorbed on cement particles by Ca2+ complexation, while HHCMs containing ester groups hydrolyzed to carboxylic groups in alkaline cement pastes, which hydrolysis rate changed with the hydration temperature of cement-based materials to regulate the hydration process. This study aims to provide technical feasibility and theoretical basis for exploring new avenues of synthesizing HHCMs with different functional groups. [ABSTRACT FROM AUTHOR]

Under the action of cement hydration heat, the construction environment, thermal insulation measures, and pipe cooling systems, a mass concrete pile cap is subject to a complex internal temperature field, which makes it difficult to control its internal surface temperature difference (TISTD), the internal adiabatic temperature rise (TIATR), and the surface temperature (TST). In this study, a mass concrete pile cap of a very large bridge (the length, width, and height were 26.40 m, 20.90 m, and 5.00 m, respectively, and the central-pier pile cap was constructed with C40 concrete) was taken as the research object. The control factors affecting the temperature field of the pile cap were determined by comparing the field temperature measurements with the values calculated with finite element software simulation analysis. By using Midas Civil (2022 v1.2) and Midas FEA (NX 2022) finite element software, these factors (the concrete mold temperature, the concrete surface convection coefficient, the ambient temperature, the pipe cooling system parameters, etc.) were numerically analyzed, and their influence laws and degrees were determined. [ABSTRACT FROM AUTHOR]

With the rise in the marine industry and marine tourism, coral powder is increasingly used to make concrete for marine islands. This study proposes a three-parameter hydration model and a hydration kinetic model to predict the performance of coral powder concrete based on previous experimental data. The process of the proposed prediction model is as follows: 1. The input parameters of the three-parameter hydration model are calibrated for the first 7 days using the cumulative hydration heat per gram of cement. The maximum cumulative hydration heat (455.87 J/g cement) and the shape coefficient (−0.87) remain constant. In this study, the hydration rate coefficients for 0%, 10%, and 20% coral powder were 6.91, 6.19, and 5.55, respectively, showing decreases of 10.41% and 19.68% compared with the specimens without coral powder. 2. At 28 days, the cumulative heat release values per gram of cement for 0%, 10%, and 20% coral powder were 389.77, 395.69, and 401.62 J/g, showing increases of 1.52% and 3.04% for the specimens containing 10% and 20% coral powder, respectively. Meanwhile, the hydration degrees for 0%, 10%, and 20% coral powder were 0.855, 0.868, and 0.881, respectively, showing increases of 1.52% and 3.04%. Furthermore, the cumulative heat release values per gram of binder were 389.77, 356.12, and 321.29 J/g, showing decreases of 8.63% and 17.56% for specimens containing 10% and 20% coral powder, respectively. 3. Properties such as compressive strength, ultrasonic pulse velocity (UPV), and surface electrical resistivity were evaluated using the power function and the cumulative hydration heat per gram of binder. 4. At 28 days, the chemically bound water contents for samples with 0%, 10%, and 20% coral powder were 0.2402, 0.2197, and 0.1981 g/g binder, respectively. Moreover, the calcium hydroxide contents were 0.1848, 0.1690, and 0.1524 g/g binder, showing reductions of 8.53% and 17.52% in bound water and 8.54% and 17.53% in calcium hydroxide. 5. A hydration kinetic model is proposed, which can distinguish between the dilution effect and the nucleation effect of coral powder, unlike the three-parameter model, which cannot distinguish between the two effects. Furthermore, the input parameters of the hydration kinetic model remain unchanged for different mixtures, while the input parameters of the three-parameter model must be varied among mixtures. Parameter analysis of the hydration kinetic model indicated that a low water–binder ratio and a high coral powder substitution rate significantly improve the relative reaction level of cement. [ABSTRACT FROM AUTHOR]

Gold tailings is formed as an industrial waste during gold mining and processing. The aim of the current study is to use it to prepare foamed concrete as subgrade filler. The effect of wet density (600, 700 and 800 kg/m3) and tailings content (15, 30, 45 and 60 wt%) on fluidity, compressive strength, elastic modulus, drying shrinkage, freeze–thaw resistance, hydration heat and pore structure were investigated. It was found that incorporating tailings into foamed concrete decreases the compressive strength as tailings adversely affected the pore structure, resulting in increased porosity, enlarged and connected pores, and reduced sphericity. To meet the requirement of subgrade filler, the tailings content was limited to 30 wt% when the designed wet density was 600 kg/m3 and it was 45 wt% when the wet density increased to 700 and 800 kg/m3. Nevertheless, increasing the tailings content effectively reduced the drying shrinkage and early age hydration heat which are favorable for massive foamed concrete construction. Besides, the incorporation of gold tailings is helpful to the freeze–thaw resistance of 600 and 700 kg/m3 foamed concrete for application in seasonal frozen areas. [ABSTRACT FROM AUTHOR]

Recycled concrete paste (RCP) can be transformed to the carbonated RCP (cRCP) as supplementary cementitious materials (SCM). By blending cRCP with calcined clay prepared from excavated waste, a distinctive limestone calcined clay cement (LC3) was produced. The aim of this research was to assess the reactivity of LC3 produced from the cRCP utilizing different carbonation procedures, via isothermal calorimetry. The carbonation process occurred at 100% R.H. and 20 vol.% CO2 concentration. To investigate the effect of pre-wetting treatment on the carbonation degree, the RCP was pre-wetted using either deionized water or 0.1 mol L−1 NaOH solution. The carbonation degree and microstructure of cRCP were analyzed using thermogravimetric analysis, X-ray diffraction, and solid-state nuclear magnetic resonance. The results revealed that pre-wetting methods significantly impact carbonation degree, while the alkali solutions had moderate influence. Notably, the pre-wetting procedure aided in decalcifying other hydrates apart from portlandite, leading to compositional variations within the cRCP. Nevertheless, these variations did not significantly affect the cRCP's reactivity in LC3. [ABSTRACT FROM AUTHOR]

Tricalcium aluminate (C3A) and tricalcium silicate (C3S) with gypsums play an important role in the hydration of oil well cement. This study aims to assess the influence of C3S and C3A with various gypsums on the hydration of oil well cement at 30, 50, and 80 °C through the analyses of hydration heat evolution by isothermal calorimetry analysis, setting and thickening times, strength, and hydration products by X-ray diffraction. The result reveals that C3A hydrates, in the presence of gypsums, rapidly at 80 °C to produce the C3AH6 phase leading to higher heat evolution. The conversion of AFt to AFm is observed in oil well cement paste at 50 °C. An increase in C3A leads to an increase in compressive strength and a decrease in permeability at 80 °C. An increase of C3S leads to the reduction of cumulative heat evolution and early compressive strength before 28 d. Gypsums shorten cement setting and thickening times opposite to the commonly known retardation effect due to the lower content of C3A and its acceleration on C3S hydration. Dihydrate and hemihydrate gypsums show a greater promotion effect on strength at 30 and 50 °C, while anhydrous gypsum presents a greater enhancing effect at 80 °C. Gypsum increases the permeability while the others show an unobvious effect at 80 °C. [ABSTRACT FROM AUTHOR]

Recycled concrete paste (RCP) can be transformed to the carbonated RCP (cRCP) as supplementary cementitious materials (SCM). By blending cRCP with calcined clay prepared from excavated waste, a distinctive limestone calcined clay cement (LC3) was produced. The aim of this research was to assess the reactivity of LC3 produced from the cRCP utilizing different carbonation procedures, via isothermal calorimetry. The carbonation process occurred at 100% R.H. and 20 vol.% CO2 concentration. To investigate the effect of pre-wetting treatment on the carbonation degree, the RCP was pre-wetted using either deionized water or 0.1 mol L−1 NaOH solution. The carbonation degree and microstructure of cRCP were analyzed using thermogravimetric analysis, X-ray diffraction, and solid-state nuclear magnetic resonance. The results revealed that pre-wetting methods significantly impact carbonation degree, while the alkali solutions had moderate influence. Notably, the pre-wetting procedure aided in decalcifying other hydrates apart from portlandite, leading to compositional variations within the cRCP. Nevertheless, these variations did not significantly affect the cRCP's reactivity in LC3. [ABSTRACT FROM AUTHOR]

In this study, the effect of limestone content on the mechanical performance and the heat of hydration of ordinary Portland cement (OPC) was investigated. Changes in the phase assemblage were analyzed through XRD and thermodynamic modeling. The purpose of the study was to identify the optimal limestone content in OPC. As a result of the experiment, all samples were found to have equal fluidity. Increasing the limestone content accelerated the hydration of the cement before approximately 13 h and shortened the setting time due to the acceleration of the initial hydration reaction. The compressive strength of the cement mortar showed a dilution effect, with lower compressive strength compared to the reference sample at an early age, but it gradually recovered at a later age. This is because, as shown in the XRD and thermodynamic modeling results, the carboaluminate phases formed due to the chemical effect of limestone contributed to the development of compressive strength. As a result, within the scope of this study, it is believed that maintaining the limestone content in OPC within 10% is optimal to minimize quality degradation. [ABSTRACT FROM AUTHOR]

With the order of better understanding the early hydration process and reaction mechanism of CaO-MgO combined expansion agent-involved cement-based systems (CMEA-CBS), CMEA dosage, CaO to MgO ratio (Ca/Mg), MgO activity, hydration temperature, and water-binder ratios (w/b) were chosen as the influencing factor. Accordingly, isothermal calorimetry was implemented to analyze the hydration heat release law, and the Krstulovic–Dabic model was applied to investigate the hydration kinetic. Moreover, the activation energy of CMEA-CBS was calculated. The findings of this study are as follows. The incorporation of CMEA can accelerate the hydration of cementitious systems. Hydration temperature increase markedly promote the hydration reaction of CMEA-CBS. The hydration reaction of CMEA-CBS is a complex associated reaction process dominated by multiple reaction mechanisms in sequence. At both 20 °C and 45 °C, the hydration process of CMEA-involved cement-based systems experienced three stages of crystallization nucleation and crystal growth (NG), phase boundary reaction (I), and diffusion (D), and the hydration mechanism was NG → I → D. However, the hydration of CMEA-CBS at 65 °C switched from the NG stage to the D stage directly. The hydration promotion effect of increasing temperature on I and D process of CMEA-CBS is less than I and D process of pure cement. Compared to the other groups, the temperature increase had the least effect on the early hydration process of 10%-C1M1-M-0.4 with the lowest apparent activation energy. [ABSTRACT FROM AUTHOR]

This study aimed to comprehensively investigate the properties of a binder based on high-calcium fly ash and silica fume with a complex additive consisting of calcium nitrate and magnesium chloride. The strength characteristics, the characteristics of the hydration process, and the phase composition of the hydration products of the binder were investigated. Silica fume was used to suppress the expansion of fly ash during hydration. A complex additive (CA) consisting of Ca(NO3)2 and MgCl2 provided a higher strength of binder than each of these salts separately. When testing a mortar with sand, the CA additive ensured that the strength of the specimens was 43.5% higher than the strength of the mortar with the addition of Ca(NO3)2 and 7.5% higher than the strength of the mortar with the MgCl2 additive. Calcium nitrate greatly accelerated the process of heat release in the first 60 min of binder hydration, and subsequently, conversely, slowed it down. The addition of MgCl2 gave a significantly greater thermal effect than Ca(NO3)2. When the two salts acted together, even a small fraction of magnesium chloride (0.2 of CA) compensated for the retarding effect of calcium nitrate and provided heat release for the binder that was almost as good as that of MgCl2. [ABSTRACT FROM AUTHOR]

This study aims to propose a hydration kinetic model for the cement–eggshell powder binary system and predict the performance development of composite concrete through this model. The specific content and results of the model are as follows. First, based on the cumulative hydration heat of the cement and eggshell powder binary system in the first seven days, the parameters of the cement hydration model and the eggshell powder nucleation parameter are calibrated. These parameters remain constant regardless of the mix ratio. Secondly, the hydration heat of the cement–eggshell powder binary system over 28 days is calculated using the hydration model. The results show that at 28 days, for specimens with 0%, 7.5%, and 15% eggshell powder substitution, the cement hydration degrees are 0.832, 0.882, and 0.923, respectively. The hydration heat per gram of cement is 402.69, 426.88, and 446.73 J/g cement, respectively, while the hydration heat per gram of binder is 402.69, 394.86, and 379.72 J/g binder, respectively. Additionally, the hydration model is used to calculate the chemically bound water and calcium hydroxide content of the cement–eggshell powder binary system. At 28 days, for samples with 0%, 7.5%, and 15% eggshell powder, the chemically bound water content is 0.191, 0.188, and 0.180 g/g binder, respectively, and the calcium hydroxide content is 0.183, 0.179, and 0.173 g/g binder, respectively. Finally, a power function is used to regress the calculated hydration heat with experimentally measured compressive strength and surface electrical resistivity. The correlation coefficients for compressive strength and surface electrical resistivity are 0.8474 and 0.9714, respectively. This is because the strength weak point effect of eggshell powder has minimal impact on hydration heat and surface electrical resistivity experiments but significantly affects the strength experiment. [ABSTRACT FROM AUTHOR]

Micro-nanobubbles (MNBs) are tiny bubbles of water used in various industries. The production methods and properties of concrete containing MNBs and the applications of MNBs in different industries are reviewed. Then, the effect of MNBs on the properties of fresh and hardened concrete is described. Next, we assessed the advantages and disadvantages of using MNBs in different types of concretes, environmental and economic impact, and research gaps in the concrete containing MNBs. Even though the presence of MNBs in concrete has an undesirable effect on workability and rheology parameters, the results of workability are in the range of the European Guideline for Self-compacting Concrete regulations and the British Standard for conventional concrete. In contrast, using sulfo-aluminate cement instead of Portland cement and MNBs in concrete improves rheological characteristics. The review also shows that MNBs improve the mechanical properties of concrete by up to 31% for compressive strength, 10–20% for tensile, and 3–34% for flexural strength. Furthermore, concrete containing MNBs has performed better than conventional concrete in terms of durability properties such as electrical resistivity, ultrasonic pulse velocity, chloride penetration resistance, and resistance to freezing–thawing cycles (F-T cycle). MNBs in concrete reduce the porosity by 17% and decrease the size of the holes. Water absorption of MNB concrete at 28 days decreased by 20%, and chloride permeability reduced by 20%. MNBs in concrete help to develop the resistance of cement-based materials improve the elastic modulus at early ages and increase the ability to resist cracking, which can reduce the crack width. Still, it is necessary to carry out more experimental work for workability and durability, especially for SCC. Even though a few studies indicate a slight impact on the environment, environmental and economic effects, and production challenges need more investigations.

Synthetic zeolites that are obtained from the hydrothermal reaction of NaOH with fly ash have a well-defined pore structure and pozzolanic properties. This work examines the effect of the low-silica (Na-A) and high-silica (ZSM-5) zeolite structure on the kinetics of alite hydration and mineralogical characteristics of the reaction products. The addition of the Na-A and ZSM-5 zeolites reduced the rate of heat release during the hydration reaction, which is typical for commonly used pozzolanic additives. The ZSM-5 zeolite had a much higher Si/Al ratio relative to the Na-A zeolite, which translated into a higher pozzolanic activity and resulted in greater stability of the hydration reaction kinetics. The addition of zeolites caused the heat of hydration to decrease compared to the reference pastes (the alite reference paste—206 J/g): Na-A 15%—148.9 J/g; ZSM-5 15%—149.9 J/g. The concentration of calcium ions in the alite solution and the content of active silica were identified as the most important parameters affecting the kinetic, morphological, and structural characteristics of the C–S–H phase. The addition of zeolites increased the amount of C–S–H gel phases formed. At the same time, the proportion of portlandite in the hydration products of the alite–zeolite systems decreased. Pozzolans reduced the ratio of CaO/SiO2 in the C–S–H phase, which for pastes with the addition of the Na-A ranged from 1.61 to 1.37, and for the ZSM-5 from 1.91 to 0.47. This ratio decreased with the dosage and the age of alite paste. In summary, this research has shown that synthetic zeolites are a viable pozzolanic additives. [ABSTRACT FROM AUTHOR]

Since hydration heat generated during construction has been the cause of cracking and deformations in mass concrete structures, selecting appropriate thermal control plans is crucial in mass concrete construction. However, developing numerical models to predict the heat of hydration in mass concrete involves complex processes that demand extensive knowledge in thermodynamics and related fields, which can result in increased costs and extended timelines for construction methods and material selection. To address this problem, this research aims to develop a simple decision-making framework to select a cost-effective thermal control method using nomograms for materials and construction engineers. Several nomograms, including temperature and cost nomograms, were used to provide the most cost-effective thermal control plans while satisfying the maximum temperature limits of mass concrete. A case study of an actual construction project was used to validate and demonstrate the proposed framework. The effectiveness of this framework was demonstrated through a case study on a real construction project, which validated the approach and confirmed its potential to reduce the time required for developing thermal control plans in mass concrete construction projects. The findings from this study highlight the proposed framework's capability to streamline the thermal control method selection process, thereby facilitating a more intuitive understanding of thermal control options and markedly reducing both costs and time in mass concrete construction projects. [ABSTRACT FROM AUTHOR]

In the solidification of plasters, promptly identifying layering defects is vital to reduce later inspection and maintenance expenses. Traditional tapping methods for defect detection, while widespread, are inefficient and can damage walls. This study proposes an innovative method utilizing Infrared Thermal Imaging (IRT) for semi real-time detection of layering defects during the solidification phase. The method was applied within the first 48 h following the application of two different plasters (Cement and Gypsum, mixed on-site as needed, not pre-dosed, and applied in a single layer), systematically examining the effects of plaster composition and environmental temperature conditions. The results showed that all preset defects were successfully identified. It was observed that larger defects are more readily detectable at a given thickness, and conversely, thicker defects are more discernible at a fixed size, with the dimension of the defect having a more pronounced impact on absolute contrast than its thickness. Notably, cement plaster exhibited two distinct temporal windows for defect detection, primarily influenced by environmental temperatures. In contrast, gypsum mortar presented two detection phases, with the initial phase being predominantly governed by the heat of hydration and the latter by ambient temperature conditions. The application of IRT technology in this research demonstrates its efficacy in accurately detecting layering defects during the solidification of plasters. This method offers valuable insights and guidance for the application of plaster layers in real-world engineering scenarios, potentially reducing maintenance costs and improving construction quality. [ABSTRACT FROM AUTHOR]

Calcium sulfoaluminate (CSA) cements are a promising alternative to Portland clinker, however, a thorough understanding of their properties is needed for their broader use in the industry. One of the topics that requires a good understanding is the effect of the w/c ratio on the properties of CSA cements. To this end, the aim of this paper was to provide research into the effects of a w/c ratio in the range of 0.45–0.6 on the properties of fresh and hardened CSA pastes and mortars. For fresh mortars, consistency and setting time, as well as plastic shrinkage tests, were conducted, and were complemented by hydration heat tests, carried out on pastes. For hardened mortars, tests of compressive and flexural strength and dry shrinkage, as well as SEM photography, were conducted. It was found that, regardless of a higher hydration rate, the increase in w/c ratio decreased flexural and compressive strength, as well as shrinkage, while increasing consistency, setting time, and hydration heat. Also observed was a significant decrease in strength between 3 and 7 days of curing in mortars with a high w/c ratio. It can be concluded that, regardless of the hydration rate, low w/c ratios in CSA mortars provide better properties than high w/c ratios. [ABSTRACT FROM AUTHOR]

Although quartz powder is a common concrete filling material, the importance and originality of this study lies in the development of a hydration model for quartz powder–cement binary mixtures and the adoption of this model to predict the development of concrete material properties. The purpose of this study is to use this model to promote the material design of environmentally friendly concrete and to elucidate the relationships in the development of the various properties of quartz powder concrete. The method used in this study was as follows: The parameters of the hydration model were obtained through seven days of hydration heat experiments. The hydration heat up to 28 days was also calculated, and the various properties of the concrete were predicted from the heat of hydration. The main findings of this study were as follows: (1) The ultimate hydration heat released per gram of cement for the different quartz powder substitution rates and quartz powder particle fineness was the same, at 390.145 J/g cement, as was the shape index of the hydration model at −1.003. (2) Moreover, through the model calculations, we found that, at the twenty-eighth day of the curing period for the quartz powder specimens with different quartz powder substitution amounts and different fineness, the reaction level of the cement was similar, at 0.963, as were the values of the cumulative heat of hydration, with both at 375.5 J/g cement. (3) The model showed that, in the late stage (28 days) of hydration for quartz powders of different fineness and when the substitution amount was the same, the cumulative heat of hydration over 28 days was similar. (4) The properties of concrete were evaluated using the calculated hydration heat. Overall, the predictive performance of the power and linear functions was similar, with no significant differences being found. [ABSTRACT FROM AUTHOR]

Molybdenum tailings are accumulated in large quantities, occupying the land and polluting the environment. Therefore, the resource utilization of molybdenum tailings is imperative. In this paper, the influence of molybdenum tailings powder (MTs) as admixture on hydration characteristics, including hydration heat, hydration products, phase composition, and mechanical properties evolution of cement paste were investigated. Results showed that the early hydration of cement paste can be promoted when the content of MTs is not more than 15%. The compressive strength of cement paste with 15% MTs at 3, 28, and 120 days was 89.37%, 96.14%, and 91.68% of that of the portland cement (PC) group, respectively. When the content of MTs does not exceed 15%, the second exothermic peak of hydration heat of cement paste appears ahead of time and the peak value increases. With the increase of MTs content, the cumulative heat release of 72 h gradually decreased. The addition of MTs does not produce new hydration products, but introduces the mineral phase of MTs itself, and leads to the early transformation of ettringite (AFt) into monosulfoaluminate (AFm) in paste. There is still a close linear relationship between the compressive strength and cumulative heat release and chemically bound water content after addition of MTs into cement paste. It was also discovered that the pozzolanic activity of MTs in cement paste mainly occurred from 3 to 28 days. After 28 days, the particle-filling effect of MTs was dominant mainly. The research results are expected to provide basic research for the resource utilization of MTs. [ABSTRACT FROM AUTHOR]

This study focuses on the hydration kinetics of supersulfated cement (SSC). The hydration heat release characteristics are analyzed, and a kinetic model for hydration is established. Then, the hydration kinetic parameters, such as hydration mechanism constant N, reaction rate constant K, and reaction rate constant Ea, are discussed. The results show that increasing the temperature promotes the nucleation of hydration products, thereby leading to the early attenuation of SSC hydration. Meanwhile, the water-to-cement ratio has little effect on the hydration process. A new hydration kinetic model considering the time-varying nature of hydration is proposed. In this model, SSC hydration after the induction period is primarily controlled by diffusion rather than by the nucleation of hydration products. The hydration process of SSC consists of a finite number of hydration cycles, and the ettringite (AFt) crystallization pressure is responsible for overcoming the "coating effect" to allow a new hydration cycle to begin. Hence, weakening the "coating effect" and increasing the AFt crystallization pressure are promising strategies to improve the degree of slag hydration. Finally, the activation energy of SSC is higher than that of cement. [ABSTRACT FROM AUTHOR]

Rock-Filled Concrete (RFC) is formed by pouring High-performance Self-Compacting Concrete (HSCC) into gaps between pre-placed rocks (that form a strong rock skeleton) in the formwork. An in-depth analysis of RFC's elastic modulus must focus on its static and elastic modulus behavior, strength characteristics, and sustainability aspects. Mesoscopic finite element modeling effectively incorporates pre-positioned rocks, Self-Compacting Concrete (SCC), and the Interfacial Transition Zone (ITZ) to correctly predict performance. RFC is a promising alternative to traditional construction methods, offering combined advantages for masonry and concrete techniques while reducing cement usage. Studies continue to examine the creep properties of reinforced fiber composites, with promising signs of their effectiveness in reducing hydration heat and concrete shrinkage. Subaquatic conservation agents enhance environmental stewardship in wet situations. The elastic modulus of rock-filled concrete increases logarithmically, mostly influenced by the rock-fill composition. It is crucial to study the shape, size, and rock-fill ratio of rocks in RFC that impact its stability, strength, and resistance to static and dynamic loads. Irregularly shaped rocks can enhance interlocking and mechanical properties, while a well-graded mix of sizes improves compaction and uniformity. Studying these properties enables engineers to optimize design and construction for durability and performance. [ABSTRACT FROM AUTHOR]

Currently, oyster shell powder (OSP) is becoming more widely used in the production of cement-based materials. The purpose of this study is to propose a predictive model that can predict the properties of concrete materials incorporating oyster shell powder. The methods of this prediction model are given as follows. First, based on the measurement results of the heat of hydration in the first 7 days, the prediction parameters of the hydration model are obtained. Secondly, based on the hydration model, the measured results of the heat of hydration were extrapolated, and the heat of hydration from the start of stirring to day 28 was calculated. From the calculation results, the developments of compressive strength, ultrasonic velocity, and surface electrical resistivity were estimated. Finally, we evaluated the CO2 emissions of concrete incorporating oyster shell powder. The CO2 emissions corresponding to unit compressive strength and unit surface electrical resistivity were calculated. The important conclusions of the prediction model are given as follows. First, for different substitution amounts of oyster shell powder, the model result shows that the ultimate value of the heat of hydration corresponding to the unit cement mass is the same, i.e., 454.27 J/g. While the substitution amount of oyster shell powder increases from 0% to 30%, the model result shows that the cumulative 28-day hydration heat for 1 g cement increases the powder amount from 405.7 J/g to 419.3 J/g. Secondly, as the amount of substituted oyster shell powder increases from 0% to 30%, the model result shows that the cumulative 28-day heat of hydration per gram of cementitious material decreases this amount from 405.7 J/g to 293.4 J/g. Compressive strength, ultrasonic pulse velocity, and surface electrical resistivity can all be expressed as exponential functions of the heat of hydration. For compressive strength, ultrasonic pulse velocity, and surface electrical resistivity, the coefficients of determination for the simulation results and experimental results are 0.8396, 0.7195, and 0.9408, respectively. Finally, as the amount of substituted oyster shell powder increases from 0% to 30%, the model result shows that the CO2 emission per unit of compressive strength increases from 10.18 kg/MPa to 16.51 kg/MPa. As the amount increases from 0% to 30%, the model result shows that the CO2 emission corresponding to the unit surface electrical resistivity does not change significantly. In summary, the importance of this model is that it can predict various properties of concrete mixed with oyster shell powder, reduce the number of experiments, and promote the engineering application of oyster shell powder concrete. [ABSTRACT FROM AUTHOR]

The drive for continuous innovation in large-scale infrastructure necessitates advancements in techniques, addressing the challenges of constructing super-length concrete structures. This study investigated the emerging shift from traditional united expanding agent (UEA) to magnesia expansive agent (MEA) in conjunction with expansive strengthening bands (ESBs), marking a pivotal transition in ensuring monolithic integrity. Despite a decade of exploration, MEA–ESB implementation in real-world projects remains underdocumented, with scholarly focus primarily confined to material characterization. This research integrated empirical on-site tests of MEA–ESB with high-fidelity numerical simulations in ABAQUS. The finite element model (FEM) validation against actual test data underscored the precision of our modeling, capturing the complex thermomechanical behavior of the system. We introduced a sophisticated parametric analysis framework, elucidating the influence of critical parameters like the ESB-to-raft-width ratio and MEA concrete expansion rates. This granular understanding facilitated the fine-tuning of design parameters, advancing the practical application of MEA methodologies. A groundbreaking contribution entailed the formulation of predictive models for early-stage cracking, anchored in the guidelines of the ACI Committee 207 and refined through extensive parametric exploration. These formulae empower engineers to anticipate and mitigate cracking risks during the design phase, thereby enhancing project safety and efficiency. Notably, this study identified limitations in current prediction models, highlighting the need for future research to incorporate comprehensive lifecycle considerations, including hydration heat effects and time-dependent mechanical property evolution. [ABSTRACT FROM AUTHOR]

In the cement industry, the morphological control of calcium silicate hydrate (C-S-H) and its impact on cement hardening and hydration are important research topics. This study investigated the impact of template agents on C-S-H morphology and structure. By using chemical precipitation, amorphous, spherical, needle-like, and layered C-S-H with the template agents being sodium dodecyl benzene sulfonate (SDBS) and cetyl trimethyl ammonium bromide (CTAB) were prepared. An increase in SDBS concentration resulted in the transformation of the C-S-H morphology from disorderly to spherical, rod-shaped, and vesicular. When CTAB was used, an increased concentration resulted in the transformation of the C-S-H morphology from disorderly to spherical and layered. When the template agent concentration was greater than the critical micelle concentration (CMC), both the C-S-H crystallinity and CMC value decreased. The impact of different C-S-H morphologies on cement performance particularly cement hydration was also evaluated and analyzed. A significant correlation between cement hydration heat and strength was verified. Different microscopic C-S-H morphologies were used to design cement products, allowing the improvement of cement performance to varying degrees. Experimental results would provide an insight into the improvement of the performance of ordinary cement. [ABSTRACT FROM AUTHOR]

The effects of steel slag (SS) and fly ash (FA) on hydration heat, fluidity, setting time and rheological properties of alkali-activated slag (AAS) pastes with different silicate modulus (Ms) values were comparatively investigated. The results show that the incorporation of SS shortens the induction period, increases the cumulative hydration heat, improves the initial fluidity and decreases the setting time at low Ms, but the opposite trend is found at high Ms. FA significantly retards the reaction, reduces the hydration heat, increases the fluidity and prolongs the setting time. The addition of SS or FA reduces the yield stress and plastic viscosity of AAS paste. SS improves the rheological properties of AAS paste more significantly than that of FA at high Ms. The yield stress and plastic viscosity of AAS paste with SS or FA rise with the increasing Ms and decline with the increasing water/binder (w/b) ratio. [ABSTRACT FROM AUTHOR]

The production of manufactured sand and stone processing can cause dust pollution due to the generation of a significant amount of stone powder. This dust (mainly granite powder) was collected and incorporated as a cement replacement into mass-manufactured sand concrete in order to enhance the mechanical properties and microstructures. The heat of the hydration was measured by adding the granite powder into the cementitious material system. The mechanical properties, autogenous shrinkage, and pore structures of the concrete were tested. The results showed that the mechanical strength of the concrete increased first and then decreased with the increase in granite powder content. By replacing the 5% cement with the granite powder, the 28 d compressive and flexural strength increased by 17.6% and 20.9%, respectively. The autogenous shrinkage was mitigated by the incorporation of the 10% granite powder and decreased by 19.7%. The mechanism of the granite powder in the concrete was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP). The porosity decreased significantly within the 10% granite powder. A microstructure analysis did not reveal a change in the type of hydration products but rather that the granite powder played a role in the microcrystalline nucleation during the hydration process. [ABSTRACT FROM AUTHOR]

The production of flue gas desulfurization gypsum poses a serious threat to the environment. Thus, utilizing gypsum-based self-leveling mortar (GSLM) stands out as a promising and effective approach to address the issue. β-hemihydrate gypsum, cement, polycarboxylate superplasticizer, hydroxypropyl methyl cellulose ether (HPMC), retarder, and defoamer were used to prepare GSLM. The impact of mineral admixtures (steel slag (SS), silica fume (SF), and fly ash (FA)) on the physical, mechanical, and microstructural properties of GSLM was examined through hydration heat, X-ray diffractometry (XRD), Raman spectroscopy, and scanning electron microscopy (SEM) analyses. The GSLM benchmark mix ratio was determined as follows: 94% of desulfurization building gypsum, 6% of cement, 0.638% each of water reducer and retarder, 0.085% each of HPMC and defoamer (calculated additive ratio relative to gypsum), and 0.54 water-to-cement ratio. Although the initial fluidity decreased in the GSLM slurry with silica fume, there was minimal change in 30 min fluidity. Notably, at an SS content of 16%, the GSLM exhibited optimal flexural strength (6.6 MPa) and compressive strength (20.4 MPa). Hydration heat, XRD, and Raman analyses revealed that a small portion of SS actively participated in the hydration reaction, while the remaining SS served as a filler. [ABSTRACT FROM AUTHOR]

The advent of novel polyether macromonomer has garnered significant attention within the industrial domain. In this study, a range of polycarboxylate superplasticizers (PCEs) was produced via free radical polymerization, employing a new polyether monomer, 4‐hydroxybutyl vinyl polyethylene glycol ether (VPEG). This monomer served as the predominant component and was grafted with various functional monomers on its main chain. The molecular configuration of the resultant PCEs was discerned through Fourier infrared spectroscopy and gel permeation chromatography, while the surface tension underwent assessment via a surface tension meter. Both the initial and subsequent fluidity of cement paste and mortar were leveraged to ascertain the dispersion and retention efficacy of the synthetic PCEs. The ramifications of diverse functional group grafts of the new polyether monomer on the cement hydration procedure and strength attributes were elucidated via setting time, hydration heat assays of cement paste, SEM analysis, and compressive strength evaluations of mortar. Observations reveal that the carboxylic acid group significantly reduces surface tension, whereas the sulfonic acid group's effect remains minimal. The incorporation of both the amide and sulfonic acid groups marginally impacts the preliminary dispersion efficacy of PCEs but notably affects dispersion retention. Furthermore, these functional groups facilitate cement hydration, expedite the primary setting time of the cement paste, and bolster the initial compressive strength of the mortar. Specifically, the grafted of sodium methacrylsulfonate (SMAS) yields the most noticeable results. Finally, the working mechanism of PCEs with varying molecular structures has been explained in light both theoretical and experimental results. This research offers valuable insights for subsequent investigations into the fabrication of polycarboxylate superplasticizers using the VPEG macromonomer. [ABSTRACT FROM AUTHOR]

In order to enhance the utilisation efficiency of lithium slag (LS) in cement-based materials, calcification and thermal activation of LS were conducted, and the activation mechanism was analysed. Results showed that gypsum and spodumene in LS decomposed at high temperature by way of calcification and thermal activation, and spodumene as well as limestone calcination decomposed at high temperature, to generate more CS, CA and other mineral phases. Calcification and thermal activation could enhance the activity of LS to participate in pozzolanic reaction, and generate the formation of more hydration products. After calcification and thermal activation of LS, the hydration exothermic peak, the total amount of hydration heat and the hydration production of LS composite binder were significantly increased. The hardened matrix was more compact with less porosity. Compared with cement mortar incorporating raw LS, the incorporation of calcified and thermally activated LS enhanced the compressive strength of cement mortar at 3, 7 and 28 days by 25.8, 13.4 and 20.5%, respectively. [ABSTRACT FROM AUTHOR]

Polycarboxylate superplasticizer (PCE) is a common admixture in high performance concrete. In the design of PCE molecules, it is necessary to ensure that the molecular weight of the polymer is moderate and the acid‐ether ratio is appropriate to improve the dispersion effect. Chain transfer agent is usually added in the synthesis of PCE to adjust the molecular weight and distribution of PCE. In this study, three sulfhydryl chain transfer agents with different electron‐withdrawing groups or electron‐donating groups were synthesized by nucleophilic addition reaction based on sodium hydrosulfide method. Then, three kinds of PCE containing sulfhydryl chain transfer agent were prepared and compared with commercial β‐mercaptopropionic acid superplasticizers. The yield stress and plastic viscosity of cement paste samples prepared by PCE−A and PCE−M were close to those prepared by PCE−P. PCE−M and PCE−A prepared by chain transfer agent with electron‐withdrawing group had higher dispersion and retention capacity than PCE−P, and had more obvious delay of cement hydration and lower hydration accumulated heat. Therefore, the optimization of molecular structure of chain transfer agent is helpful to improve the properties of concrete superplasticizer. [ABSTRACT FROM AUTHOR]

Aiming to enhance the comprehensive utilization of steel slag (SS), a solid waste-based binder consisting of SS, granulated blast furnace slag (BFS), and desulfurization gypsum (DG) was designed and prepared. This study investigated the reaction kinetics, phase assemblages, and microstructures of the prepared solid waste-based cementitious materials with various contents of SS through hydration heat, XRD, FT-IR, SEM, TG-DSC, and MIP methods. The synergistic reaction mechanism between SS and the other two wastes (BFS and DG) is revealed. The results show that increasing SS content in the solid waste-based binder raises the pH value of the freshly prepared pastes, advances the main hydration reaction, and shortens the setting time. With the optimal SS content of 20%, the best mechanical properties are achieved, with compressive strengths of 19.2 MPa at 3 d and 58.4 MPa at 28 d, respectively. However, as the SS content continues to increase beyond 20%, the hydration process of the prepared binder is delayed. The synergistic activation effects between SS and BFS with DG enable a large amount of ettringite (AFt) formation, guaranteeing early strength development. As the reaction progresses, more reaction products CSH and Aft are precipitated. They are interlacing and overlapping, jointly refining and densifying the material's microstructure and contributing to the long-term strength gain. This study provides a reference for designing and developing solid waste-based binders and deepens the insightful understanding of the hydration mechanism of the solid waste-based binder. [ABSTRACT FROM AUTHOR]

Xinjiang has a temperature difference of 20°C between day and night, interannual temperature difference of 50°C, the control of the temperature cracks in mass concrete becomes difficult. Although low-heat portland (P·LH) cement concrete containing fly ash (FA) can reduce hydration heat, the mismatch between its mechanical and thermal properties is still not fully resolved. An attempt to explore the effect of FA on the competitive hydration reaction of C3A and C3S at super-early ages, and how this effect changes the physical and chemical properties of hardened cement pastes by electrical resistivity and zeta potential and common microstructure test methods, and to provide a theoretical basis for optimization of mechanical and thermal properties of P·LH cement concrete with FA. Results showed that in the fast dissolution stage, a numerous {Ca6[Al(OH)6]224H2O}6+ ions and a very small amount of H3SiO4−/H2SiO42− ions were formed, and incorporating 20%, 30%, 40% FA primarily inhibited the Al(OH)63− hydration and the {Ca6[Al(OH)6]224H2O}6+ generation, resulting in the generation time of AFt in comparison with pure cement, respectively, delayed by 44%, 140%, and 524%. This phenomenon decreased the nucleation and crystallization growth rate of AFt and Ca(OH)2 in the induction stage, and reduced the consumption of gypsum in the acceleration stage. Hence, monosulfoaluminate did not exist for pastes with more than 30% FA, and the number of particles involved in the reaction for the P·LH cement stone with 20%, 30%, and 40% FA decreased by 4.0%, 46.5%, and 52.0% in the deceleration stage compared with the pure cement. The research results can provide a theoretical reference for modifying chemical properties of FA to meet the matching of mechanical strength and thermal of P·LH cement. [ABSTRACT FROM AUTHOR]

Concrete-filled steel tube (CFST) members have been widely used in skyscrapers and long-span bridges. Non-uniformly distributed hydration heat during curing, inadequate compaction during construction and unavoidable shrinkage and creep of mass concrete in service most likely lead to interface debonding defects between concrete core and steel tube, which has been a common concern. The development of effective non-destructive inspection methods for interface bonding condition of existing CFST members is critical. In this study, an interface debonding defect detection method based on electromechanical impedance (EMI) measurement using surface-mounted piezoelectric-lead-zirconate-titanate (PZT) sensors is proposed at first. Then, experimental study on the feasibility of the proposed approach is carried out with scaled CFST specimens with artificially mimicked interface debonding defects. EMI of surface-mounted PZT sensors at different frequency bands are measured and compared to verify the detectability of the proposed approach for the mimicked interface debonding defects. Thirdly, a multi-physics CFST-PZT coupling finite element model (FEM) with interface debonding defects is established, and EMI of surface-mounted PZT sensors at different locations is simulated. The influence of interface debonding defects on EMI measurements is illustrated. Finally, a blind inspection on the interface bonding condition of selected CFST columns in an existing skyscraper in service using the proposed approach is carried out. Both bonding and debonding defect in the tested CFST columns are detected correctly and validated with drilling hole observation. Experimental, numerical and engineering application results show the proposed approach is effective for interface debonding detection of CFST members and sensitive to minor debonding defect of 0.3 mm in CFST members. [ABSTRACT FROM AUTHOR]

The utilization of desulfurized building gypsum as raw material for gypsum-based self-leveling mortar (GSL) is limited by its low strength and poor water resistance. The objective of this study is to enhance comprehensive properties of GSL and prepare qualified desulfurized building gypsum-based self-leveling mortar that can be effectively applied in practical engineering projects. The influence of cement on water consumption rate of initial fluidity (W/M ratio), fluidity, setting time, mechanical strength, and water resistance of GSL were evaluated. Additionally, rheological parameter, heat of hydration, crystal morphology, and pore structure were also analyzed. Cement significantly improved the fluidity of slurry. Moreover, the compressive strength and softening coefficient of GSL reached 20.6 MPa and 0.56 at 10% cement, respectively. Furthermore, cement reduced the 30-min-fluidity loss and improved fludity by reducing the yield stress and increasing the plastic viscosity of screed. The transformation of hydration kinetics of GSL could be due to Ca2+ and OH− released by cement, thus resulting in the shortening of initial setting time and the prolongation of the interval between initial and final setting time. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) showed that CSH gel and AFt crystal would generate on the surface of CaSO4·2H2O crystal, making the structure more compact. Mercury intrusion porosimetry (MIP) indicated that cement greatly reduced the porosity through the water reduction effect in the early stage and continuous hydration in the later stage. The continuous hydration of cement also increased the shrinkage rate. This work was expected to provide reference for promoting the application of desulfurized building gypsum as the high value-added screed. [ABSTRACT FROM AUTHOR]

Strain-hardening cementitious composites (SHCC) have been widely studied due to their high toughness and durability. The high cement content increases a huge burden on the cost and CO2 emissions of SHCC. To reduce the environmental impacts of SHCC, this study first develops low-carbon and lightweight SHCC by using high-volume recycled concrete powder (RCP) as supplementary cementitious materials and cenosphere waste as lightweight aggregate. The influence of RCP content (0%, 15%, 30%, and 45% by mass) on the hydration mechanism, mechanical properties, and sustainability of low-carbon and lightweight SHCC was investigated. The results showed that the incorporation of RCP in the SHCC matrix resulted in a decrease in hydration heat with increasing RCP content. The filling and pozzolanic effects of RCP were significantly lower than those of cement. The increased porosity and the presence of the interface transition zone due to RCP incorporation led to reduced compactness of the SHCC, which consequently led to decreased compressive strength and fracture toughness of the cement matrix. While the fracture toughness of the cement matrix was reduced, the SHCC still exhibited remarkable bending toughness and tensile ductility. The developed low-carbon and lightweight SHCC containing 45% RCP showed a density of 1482.5 kg/m3, a tensile strength of 3.94 MPa, and a tensile strain capacity of 6.80%, which successfully pushed the performance of low-carbon and lightweight SHCC. The replacement of cement with high-volume RCP in the low-carbon and lightweight SHCC resulted in a significant reduction in embodied carbon compared to conventional SHCC. Therefore, SHCC combines the advantages of lightweight, low-carbon, and highly ductile, making it a promising material for widespread utilization in concrete structures. [ABSTRACT FROM AUTHOR]

This study aimed to explore the impact of three corrosive ions—SO42−, Cl−, and Mg2+—on the hydration property of calcium sulphoaluminate (CSA) cement. Cement paste was prepared using three types of sea salt ion solutions with varying concentrations as mixing water. The experimental program encompassed assessments of porosity, compressive/flexural strength, heat of hydration, pH of pore solution, XRD, and SEM analysis. To modulate the hydration environment, Ordinary Portland cement (10%) was incorporated to elevate the pH and enhance the stability of ettringite, thereby facilitating the formation of additional C-S-H gel for the observation of M-S-H and other compounds. Findings revealed that the Cl− accelerated the hydration of CSA, resulting in heightened heat release. However, it also decreased the length-to-diameter ratio of ettringite, leading to cracking in CSA test blocks. The addition of SO42− resulted in elevated internal alkalinity, prompting alterations in hydration product types and subsequent reduction in CSA strength. Conversely, Mg2+ was observed to ameliorate the microstructure of CSA test blocks, diminishing porosity and augmenting strength. [ABSTRACT FROM AUTHOR]