Hydration Reaction Research Articles

Effect of additional Al sources on early-age strength of fly ash-based geopolymer containing calcium carbide residue and Glauber’s salt as activators

Alkali-activated materials are more environmentally friendly than cementitious composites and are used in the construction and building sector. However, their intrinsic low early strength under ambient temperatures hinders their practical applicability. More research is needed on the possibilities of increasing early strength at ambient temperatures. In this study, aluminum sulfate (AS) was used as an additional aluminum source to improve the early-age properties of fly ash (FA)-based geopolymers incorporating calcium carbide residue (CCR) and Glauber’s salt (GS) as activators. XRD, TG, SEM, ICP and isothermal calorimetry analyses were carried out to characterize the phase composition, microstructure and hydration process of the prepared materials. The results showed that the 1d strength of AS1-CCR10 was increased by 260.7 % compared with the control material, and the effect on the late strength was negligible. The relative content of AFt increased by 2.97 %, creating a more compact microstructure. During the extraction process, insufficient dissolved Al3+ in the composite led to a decrease in initial strength. In the hydration process, the induction period of AS1-CCR10 was advanced by 40.92 % and that of t50 was advanced by 57.74 %, which accelerated the early reaction rate. However, the Krstulovic-Dabic model could not accurately describe the initial stage of the hydration reaction of composite materials. This study is helpful to broaden the utilization of geopolymer composites and provide a theoretical basis for the preparation and reaction mechanism of alkali-activated materials.

Injectable bone cement based on magnesium potassium phosphate and cross-linked alginate hydrogel designed for minimally invasive orthopedic procedures

Bone cement based on magnesium phosphate has extremely favorable properties for its application as a bioactive bone substitute. However, further improvement is still expected due to difficult injectability and high brittleness. This paper reported the preparation of novel biocomposite cement, classified as dual-setting, obtained through ceramic hydration reaction and polymer cross-linking. Cement was composed of magnesium potassium phosphate and sodium alginate cross-linked with calcium carbonate and gluconolactone. The properties of the obtained composite material and the influence of sodium alginate modification on cement reaction were investigated. Our results indicated that proposed cements have several advantages compared to ceramic cement, like shortened curing time, diverse microstructure, increased wettability and biodegradability and improved paste cohesion and injectability. The magnesium phosphate cement with 1.50% sodium alginate obtained using a powder-to-liquid ratio of 2.5 g/mL and cross-linking ratio 90/120 of GDL/CC showed the most favorable properties, with no adverse effect on mechanical strength and osteoblasts cytocompatibility. Overall, our research suggested that this novel cement might have promising medical application prospects, especially in minimally invasive procedures.

Fluid-rock interaction related to alpine subduction of Allalingabbro deduced from large-size μXRF element maps

Alpine subduction of a block of olivine gabbro produced a plethora of different assemblages and local structures typical of high-pressure and low-temperature metamorphism. However, gabbro with the locally well-preserved igneous assemblage olivine - augite - plagioclase occurs in some domains of a 2 km long outcrop (Allalinhorn, western Alps).A large variety of hydrate minerals including zoisite, glaucophane, talc, Mg-chloritoid, chlorite, paragonite and muscovite formed during Alpine subduction of the metagabbro. The three primary igneous minerals have been replaced by hydration reactions during Eocene subduction. Talc, omphacite, and zoisite + jadeite and are the main minerals in the local domains after olivine, augite and plagioclase respectively. The rocks preserved the coarse grained igneous texture.An excellent overview of the complex coarse textures of the eclogite facies rocks has been provided by element distribution maps produced from up to 25 cm large polished slabs of typical samples of Allalingabbro using a μXRF instrument. The RGB images suggest that the minerals formed at the high-pressure in the presence of an aqueous fluid. The pseudomorphing reactions progressed close to volume conservation. The hydration reactions required an H2O fluid containing dissolved solids. The mapped distribution of elements including trace elements provides important clues on the origin and mobility of these elements in the hydration fluid. The homogeneously distributed immobile Cr in omphacite portrays primary augite. The irregular patchy Sr distribution resulted from small-scale migration of components replacing plagioclase by Sr-bearing zoisite and jadeite. Coherent Ni signals are related to the presence of talc. The talc occurs as a late infill of structures produced by dissolving olivine. Mg-chloritoid, kyanite and mica coat the former grain-boundary of olivine and plagioclase suggesting that olivine dissolved at eclogite facies conditions. Talc formed at distinctly lower pressures, however, as implied by computed model reactions. The olivine replacement structures are often larger than the size thin section and can be excellently studied by the large size μXRF patterns used in this study.The fractured surroundings of the locations of olivine provided the necessary hydraulic conductivity for hydration reactions to progress. The fractures and small veinlets contain late Ni-bearing talc. Cl is only present in very late vein amphibole suggesting that hydration fluids in the subduction zone transported dissolved components as hydrous complexes (and their dissociated ions). There is no evidence for the presence of a Cl-brine during subduction. In addition to primary olivine as a local Ni source, the element may also have partly been imported with the hydration fluid and originate from dehydration of ophiolitic serpentinites in the slab.

Effect of raw material fineness on the properties of inorganic foam materials from solid waste

Solid waste inorganic lightweight materials not only compensate for the flammability of organic materials but also have a lower carbon footprint. They are environmentally safe and cost-effective compared with cement-based foaming materials, and they have good development prospects. This study aimed to improve the chemical foaming reaction kinetics by reducing the particle size of aluminum powder and alkaline solid waste, thereby increasing the expansion degree of solid waste slurry, to further reduce the absolute dry density of inorganic lightweight materials for solid waste and optimize their performance. The influence of the particle size of raw material on the absolute dry density, water absorption, and compressive strength of lightweight materials was investigated. The influence of the particle size of raw material on the macroscopic pore structure of foamed materials was analyzed through binarization of cross-sectional images of specimens. Furthermore, the hydration products and microstructure of materials were characterized using XRD, FTIR, TG-DTG, and SEM to provide a theoretical basis for related research. The experimental results showed that the smaller the particle size of the raw material, the easier it was to carbonize and the lower the flowability of the corresponding cementitious material slurry. Reducing the particle size of raw materials and aluminum powder increased the degree of slurry expansion, thereby reducing the absolute dry density of foaming materials. In addition, reducing the particle size of raw materials and using carbide slag wastewater instead of tap water increased the degree of foaming reaction and hydration reaction, which helped C-(A)-S-H gel formation and promoted the development of sample strength. Finally, the absolute dry density of inorganic lightweight materials was reduced to 0.35 g/cm3 at the minimum, and the corresponding 28-day compressive strength was 0.28 MPa, which met the requirements of the JG/T 266–2011 “foam concrete” specification.

Enhancing the mechanical and thermal properties of foam concrete by incorporating glass lightweight microspheres

The inferior mechanical strength and thermal resistance of foam concrete limited its application in thermal insulation engineering. This study focused on enhancing the mechanical strength and thermal resistance of foam concrete by incorporating glass lightweight microspheres (GLM) to partially replace foam. The roles of GLM in foam concrete were investigated through physical, mechanical, and thermal properties tests. The improvement mechanism behind the mechanical strength and thermal resistance was further revealed. Results indicated that the addition of GLM enhanced mechanical strength of foam concrete by promoting hydration reaction, optimizing pore structure, and improving GLM-paste interfaces. The mechanical strength of foam concrete with 20 % GLM increased by about 40 %. Moreover, GLM improved the residual compressive strength after exposure to 800°C, with an enhancement of 39.8 %. The inclusion of GLM reduced the risks of crack formation, densified the paste, and strengthened the foam wall due to its hollow structure, pozzolanic reactivity, melting and filling effects, and the phase transformation of additional C-S-H into well-packed wollastonite. Additionally, GLM with closed and isolated pores reduced the drying shrinkage and water absorption rate of foam concrete. The finding suggests that incorporating an appropriate amount of GLM can produce high-strength, low-density, and thermal-resistant foam concrete.

Establishing the Regioselectivity of a Small-Scale Alkene Hydration Reaction Using TLC Co-spotting

Establishing the Regioselectivity of a Small-Scale Alkene Hydration Reaction Using TLC Co-spotting

Thermal, electrical, and mechanical performances of ultrahigh-performance cementitious composites with multiwalled carbon nanotubes

This study examines the influence of multiwalled carbon nanotubes (MWCNTs) on cementitious composites, specifically focusing on the fabrication of multifunctional cementitious composites known as ultrahigh-performance cementitious (UHPC) composites. Key properties such as compressive strength, thermal performance, and electrical resistance were examined with varying MWCNT contents, curing methods, curing duration, and supply voltage. The effects of the incorporation of MWCNTs on the hydration reactions of the cementitious composites were analyzed using field-emission scanning electron microscopy, thermogravimetric analysis, and X-ray diffraction. The study revealed that MWCNT UHPC composites can achieve a maximum ultrahigh strength of 120.8 MPa. Additionally, the incorporation of MWCNTs enabled the composites to reach a maximum surface temperature of 90.6 °C during heating. Furthermore, the power consumption of MWCNT UHPC composites was found to be predictable based on the curing type and the duration of curing. Notably, the hydration reactions in MWCNT UHPC composites remained unaffected by the MWCNT content. The findings emphasize the potential of multifunctional MWCNT UHPC composites by offering exceptional strength, heating capabilities, and electrical performance in construction materials.

Study on the Effect of Silica–Manganese Slag Mixing on the Deterioration Resistance of Concrete under the Action of Salt Freezing

The use of silico-manganese slag as a substitute for cement in the preparation of concrete will not only reduce pollution in the atmosphere and on land due to solid waste but also reduce the cost of concrete. To explore this possibility, silico-manganese slag concrete was prepared by using silico-manganese slag as an auxiliary cementitious material instead of ordinary silicate cement. The mechanical properties of the silico-manganese slag concrete were investigated by means of slump and cubic compressive strength tests. The rates of mass loss and strength loss of silico-manganese slag concrete were tested after 25, 50, and 75 cycles. The effect of the silica–manganese slag admixture on the microfine structure and properties of concrete was also investigated using scanning electron microscopy (SEM). Finally, the damage to the silica–manganese slag concrete after numerous salt freezing cycles was predicted using the Weibull model. The maximum enhancement of slump and compressive strength by silica–manganese slag was 17.64% and 11.85%, respectively. The minimum loss of compressive strength after 75 cycles was 9.954%, which was 34.96% lower than that of the basic group. An analysis of the data showed that the optimal substitution rate of silica–manganese slag is 10%. It was observed by means of electron microscope scanning that the matrix structure was denser and had less connected pores and that the most complete hydration reaction occurred with a 10% replacement of silica–manganese slag, where an increase in the number of bladed tobermorite and flocculated C-S-H gels was observed to form a three-dimensional reticulated skeleton structure. We decided to use strength damage as a variable, and the two-parameter Weibull theory was chosen to model the damage. The final comparison of the fitted data with the measured data revealed that the model has a good fitting effect, with a fitting parameter above 0.916. This model can be applied in real-world projects and provides a favorable basis for the study of damage to silica–manganese slag concrete under the action of salt freezing.

Lime reactivity and overburning: the case of limestones belonging to Tuscan Nappe sequence (NW Tuscany, Italy)

This study examines limestone properties and calcination process to enhance product quality. Limestone burning produces lime (CaO, calcium oxide) and carbon dioxide (CO2). Lime is a substance highly reactive and turns into slaked lime (Ca(OH)2, calcium hydroxide) when exposed to water. Six limestone samples from Tuscan Nappe sedimentary sequence, outcropping in the Monti d’Oltre Serchio area (NW Tuscany, Italy), were selected and calcined at different temperatures (800, 900, 1000 and 1100 °C). The obtained lime was slaked, and chemical, mineralogical and petrographic analyses were conducted to study its reactivity during slaking process. Key factors influencing lime reactivity were identified: calcination temperature/time and limestone characteristics (chemical and mineralogical composition). The lime reactivity was measured through the rate of lime hydration reaction. Results showed that higher reactivity in lime, lower calcination temperature. The increase in temperature and time leads to an increase of CaO grain size and, consequently, to a decrease in reactivity. Temperature increase has a more significant effect on the increasing of grain size and reactivity than time. The optimal calcination temperature was found to be 900 °C, like that of ancient limekilns. The study emphasized the close link between lime reactivity and chemistry/mineralogy of limestone. Overall, the research provides insights for improving limestone calcination processes and obtaining superior products.

Sustainable Stabilization of Cadmium (Cd)-Contaminated Soil with Biochar-Cement: Evaluation of Strength, Leachability, Microstructural Characteristics, and Stabilization Mechanism

ABSTRACT To facilitate the solid waste reuse of cadmium (Cd)-contaminated soil and biochar and reduce the high emission of cement materials, we employed biochar-cement composite stabilizer to remedy Cd-contaminated soil. We assessed the effects of the biochar-cement composite stabilizer dosage and curing time on stabilized soil strength by using unconfined compressive strength (UCS) tests, leaching concentration and stabilization rate in Cd-contaminated soil stabilized by biochar-cement by using toxicity characteristic leaching procedure, and mechanism of change in strength and leaching characteristics by using scanning electron microscopy and X-ray diffraction. The research results demonstrate that biochar addition to cement-stabilized soil promoted cement hydration reaction and increased particle agglomeration. A low dosage of biochar improved stabilization effects. The optimal biochar dosage was 5%, which enhanced the early growth speed of the UCS. More cement improved the stabilized soil’s UCS. At a 5% cement dosage, adding biochar significantly reduced Cd leaching concentration, and improved the stabilization rate. At a 10% cement dosage, the biochar-cement composite stabilized soil’s stabilization rate was >99.8%. Calcium silicate hydrate, calcium aluminate hydrate, and ettringite were the main products of biochar-cement stabilized soil that filled soil and biochar pores; these substances encapsulated, adsorbed, or exchanged ions of Cd2+, achieving stabilization effects.

Synthesis of calcium sulfate whiskers via acidification exploiting FGD gypsum for improved binder properties

This research focuses on the synthesis of calcium sulfate whiskers using FGD (Flue Gas Desulfurization) gypsum as raw material through the acidification method and their utilization in gypsum binders. The acidification method using H2SO4 (1.5 mol/L) is distinguished by its sustainability and resource efficiency. The addition of Calcium Sulfate Whisker as an activator enhances the binder's properties by increasing its strength, durability, resistance to environmental factors, and overall structural integrity. The effects of different reaction parameters on the properties and microstructure of CSW have been studied. This research has the potential to bring about significant improvements in various applications, from construction materials to industrial products. Calcium Sulfate Whiskers act as pore fillers within the binder matrix which reduces the porosity and helps to decrease water absorption up to 12%. CSW is characterized by its needle-like structure, which provides an intricate network within the binder matrix. SEM images showed the strong interfacial bonding between the whiskers and the binder matrix, enhanced by the rough surface of the whiskers, which improves mechanical interlocking and adhesion. CSW demonstrates its potential as a highly active component in the binder. The whiskers facilitate efficient nucleation sites, accelerating the hydration reactions within the binder and enhancing the overall performance of the binder. CSW incorporation in the binder increases the compressive strength by up to 21.6% and flexural strength by 37%. The exceptional mechanical strength and efficient nucleation sites provided by CSW contribute to an increase in the workability of the binder and make it suitable for interior as well as exterior applications. These interconnected facets collectively position the project as a valuable and highly pertinent contribution, where sustainable innovation and improved material properties are of paramount importance. It potentially reduces the need for traditional additives with higher environmental impacts, making the binder formulation more eco-friendly.

New magnesium cement optimized in MgO-K2HPO4-SiO2 system and its hardening performance

Silica fume (SF) is commonly used in producing magnesium potassium phosphate cement (MPC) and magnesium silicate hydrate cement (MSHC). However, its roles in magnesium cement would differ from each other when mono hydrogen phosphate was involved. This paper aims to find optimized compositions in MgO-K2HPO4 DKP- SF system with comprehensive considerations of the micro and macro performances. Ternary contour maps were designed to determine the optimized proportions of MgO, DKP and SF. The hydration reaction mechanism was analyzed with a variety of techniques including XRD, SEM, TG-DTG and NMR. Magnesium cement containing 60–75 % dead-burnt MgO, 10–25 % DKP and 12.5–25 % SF exhibited excellent compressive strength and volume stability. K-struvite and M-S-H were confirmed to promote the hydration and hardening performance of the blended MgO-DKP-SF system with optimized proportions. An excess of soluble K+ from DKP may precipitate as KOH and then dissolute in solution, increasing pH and release of Si from SF.

Impact of curing conditions on the mechanical properties and micro characteristics of alkali-activated material synthesized from industrial waste soda residue

Alkali-activated materials (AAM) are considered a type of green cementitious material because they are produced without the grinding and calcining required for cement production, significantly reducing carbon emissions. However, their production typically involves the use of commercial alkalis, which are often corrosive, irritating, and expensive. As an industrial waste from sodium carbonate production, soda residue (SR) has a large reserve and is challenging to dewater and utilize, making its disposal a widespread technical challenge. In this paper, considering the alkaline nature and high salt content of SR, a soda residue activated granulated blast-furnace slag cementitious material (SAG) was synthesized directly using undried and unground SR slurry as the alkali activator, with a mass ratio of SR to granulated blast-furnace slag (GBFS) of 30:70. The effects of ambient temperature (AT) curing, water curing, various heat curing temperatures (45°C, 60°C, 75°C, and 90°C), and different heat curing durations (6 h, 12 h, 18 h, and 24 h) on the properties of SAG were investigated. Specifically, the effect of curing conditions on the mechanical properties of SAG was analyzed through unconfined compressive strength (UCS) testing of mortar specimens. The impact of curing conditions on the phase composition and changes in SAG was characterized using XRD, TG, and FTIR, while the effect on the microstructure of SAG was characterized using SEM. The results showed that SAG achieved the highest UCS (3 d/56 d: 28.1 MPa/36.7 MPa) when subjected to heat curing at 75°C for 12 h. The UCS increased significantly by 3022 % and 321 %, respectively, compared to those under AT sealed curing. This was attributed to the fact that SAG under heat curing produced more C-(A)-S-H gels and hydrocalumite crystals, optimizing pore structure and resulting in a denser microstructure. However, exceeding the threshold temperature of 75°C led to an excessively rapid hydration reaction that adversely affected the further dissolution of GBFS and the uniform distribution of hydration products, thereby diminishing the positive effects of heat curing on UCS. In addition, excessively prolonging the heat curing time exacerbated the development of microcracks within the SAG, leading to a deterioration of UCS over age. In this paper, a novel AAM was synthesized using undried and unground industrial waste without the addition of commercial alkali, and the impact of curing conditions on their properties was studied. This broadens the range of applications for SAG, fills a gap in research on the impact of curing conditions on AAM without commercial alkali, and provides a theoretical basis for the low-carbon utilization of industrial waste.

Utilization of eggshell powder in one-part alkali-activated metakaolin based binder

Eggshell is a waste of poultry and the proper disposal of such waste products is a worldwide issue. Alkaline activation of calcium-rich eggshell powder (ESP) as a binder with a suitable aluminosilicate source offers the opportunity to produce viable materials. Thus, this paper reports the innovative use of ESP as a precursor in metakaolin (MK)-based one-part alkali-activated materials (AAMs). The impact of ESP on the fresh, physical, mechanical, and microstructural properties of one-part AAMs was studied. Upon the addition of ESP, the setting time was extended and a consistent reduction in semi-adiabatic heat release was observed. ESP favored the rheological characteristics of the mixtures by lowering viscosity and yield stress which enabled a decrease in the water content of ESP containing mortars. The incorporation of ESP up to 40 % improved the compressive strength by 22 % and 46 % for paste and mortar samples, respectively, and resulted in a notable mitigation of mortar shrinkage (only 300 µɛ at 56th days). ESP plays dual function in microstructure of AAM as a binder and micro-aggregate. C-A-S-H type gels were observed in ESP-rich mixes due to its calcium-rich structure, and the contribution of ESP on the hydration reactions were clarified in detail via X-Ray diffraction and thermogravimetric analysis. Life cycle analysis results indicated that incorporating ESP could obtain similar compressive strength while reducing the ecological impact.

Low-calcium CO2 sequestration materials prepared with full-component solid waste based on lithium slag as crystal regulator

High performance low calcium CO2 sequestration materials (LCCSM) were prepared by using carbide slag (CS), copper tailings (CT) as main raw materials and lithium slag (LS) as crystal regulator at 1260 °C for 1 h. The effects of lithium slag content on the crystal transformation and carbonation hardening behavior of low calcium CO2 sequestration material (LCCSM) were studied. The results show that with the increase of LS content (i.e. from 0 % to 3 %), the C3S2 content was increased continuously, and the sum of C2S (i.e., β-C2S and γ-C2S) content was decreased continuously. Due to the activity energy of β-C2S was lowest in first stage carbonation, which accelerates carbonation reaction of the overall LCCSM clinkers and releasing a large amount of heat. Thereafter, the hydration reaction of β-C2S was accelerated significantly and the hydration products will be further carbonated. The minor LS (i.e., 1 %) significantly improved the carbonation activity of LCCSM clinker. Thus, the compressive strength development and degree of carbonation of carbonated compact made by LS-1% was obviously enhanced than that of other LCCSM clinker during the first 24 h. This finding could provide guidance for the obtaining high performance low-calcium CO2 sequestration material based on multiple solid wastes. And also proposed a new perspective for the mechanism among the multi-phase coexistence, crystal transformation and their synergistic carbonation sequestration of calcium silicate clinkers.

Effect and mechanism of activators on the properties of Yellow River sediment/fly ash/cement-based alkali-activated cementitious materials used for coal mine filling

Preparing Yellow River sediment/fly ash/cement-based alkali-activated cementitious materials for coal mine filling can realize the large-scale consumption of Yellow River sediment and reduce the cost of coal mine filling materials. This paper studied the effects of Ca(OH)2, NaOH, and water glass on the properties of coal mine filling materials. Adding activators Ca(OH)2, NaOH, and water glass can improve the compressive strength and shorten the setting time of the filling materials. NaOH and water glass can also significantly reduce the bleeding rate. The mechanism of activators' influence on the mechanical properties of filling materials was explored based on XRD, TGA, FTIR, MIP, and SEM. The alkaline environment provided by NaOH and Ca(OH)2 accelerated the hydration reaction of cement, and the SiO32- from the hydrolysis of water glass can bind to Ca2+ to form C-S-H gel. The co-mixing of water glass and NaOH can make fly ash and Yellow River sediment's active components react more fully, generating more C-S-H and C-A-S-H gels. This can refine the pore size distribution of the filling materials, reduce the content of harmful pores, make the matrix dense, and improve the filling materials' working and mechanical properties. When the NaOH is 0.5 wt%, and the water glass is 13 wt%, the strength of the filling materials prepared by compound doping was the highest, and the working performance met the requirements. The results had broad application prospects and economic value, contributing to ecological and environmental protection and sustainable development.

Effect of steam curing system on compressive strength of recycled aggregate concrete

Abstract Steam curing prefabrication is a feasible way to promote the application of recycled aggregate in the background of building industrialization. The combined use of slag and fly ash contributes to the comprehensive improvement of both the early and later-stage performance of recycled aggregate concrete (RAC). However, the steam curing regime for RAC composed of slag and fly ash remains unclear, including appropriate curing temperatures and time. In this study, the influences of curing temperatures (20, 40, 60, and 80°C), steam curing time (6, 9, and 12 h) and mineral admixtures (slag powder and fly ash) on the demoulding strength and strength development of RAC were investigated. Based on the Arrhenius formula, the hydration reaction rate was characterized by the development of compressive strength, the apparent activation energy related to the steam curing time was calculated, and the energy-based compressive strength model was proposed to realize the early strength prediction of the steam-cured RAC.

Preparation and characterization of low-activity coal bottom ash-based cementitious materials via orthogonal experiment

The effective use of coal bottom ash produced by burning coal can reduce the pollution of solid waste to land and water resources. Meanwhile, the use of coal bottom ash as cementitious materials can reduce the demand for traditional resources and carbon emissions, availing to promoting the sustainable development of the construction industry. However, the application and popularization of coal bottom ash-based cementitious materials are facing many practical problems. For example, the utilization rate of coal bottom ash is low, and the traditional alkali activation method has some limitations such as high cost and poor safety. For this reason, through orthogonal experiment and range analysis, new calcium combination activators were explored for the preparation and optimization of coal bottom ash-based cementitious materials. The coal bottom ash-based cementitious materials with compressive strength up to 17 MPa was prepared, when the mass ratio of CaO: Ca(OH)2: AlPO4 was 1: 0.15: 0.10 : 0.05 and preparation temperature was 15 °C. Furthermore, the influence of various factors on the compressive strength of the products was evaluated comprehensively: AlPO4 > CaO and Ca(OH)2 > preparation temperature. The action effect and reaction mechanism of various factors were revealed by means of fluidity test, setting time test, XRD, FTIR and SEM-EDS. The results show that calcium combination activators react with coal bottom ash to mainly form C-A-S-H gel. Among the calcium combination activators, CaO greatly improves the rate of early hydration reaction, Ca(OH)2 is conducive to the sustained and stable development of late hydration reaction, and AlPO4 can improve the fluidity and setting time of the slurry. Moreover, although the water and environment temperature show the weakest influence in the laboratory stage, the influence of this factor on the property of the cementitious materials in the actual project cannot be ignored. This research has important scientific and engineering significance for promoting coal bottom ash-based cementitious materials in economic development and environmental protection.

Comparison of thermogravimetry response of alkali-activated slag and Portland cement pastes after stopping their hydration using solvent exchange method

AbstractThe critical step for any subsequent instrumental analysis of cementitious binders is to stop their hydration reactions, i.e., to remove free water. One of the most available techniques is a solvent exchange method. However, the solvents are known to be strongly bound in ordinary Portland cement (OPC) paste and alter the results of thermogravimetric analysis (TGA) and sensitive hydrates, while their effect on TGA response of alkali-activated slag (AAS) has not been comprehensively investigated. Therefore, the objective of this paper is to track the effects of fundamental aspects of the solvent exchange on the TGA response of AAS with different sodium activators (hydroxide, carbonate, waterglass) and to support these results by X-ray diffraction and effluent gas analysis. All solvents used (acetone, diethyl ether, isopropyl alcohol, ethanol, and methanol) affected the TGA response of all tested pastes, and their effect was enhanced by prolonged immersion time. All solvents induced an additional mass loss at around 800 °C and, especially for OPC paste, increased in situ carbonation, even in an inert atmosphere. Methanol and ethanol had a detrimental effect on ettringite and decreased the basal distance of the C–(A)–S–H gel, while they only marginally affected gaylussite. For AAS, hydration stoppage by washing out the alkali-rich pore solution with water was also investigated and can usually be recommended (except for its detrimental effect on gaylussite), as it is more efficient than organic solvents, which lack solubility for activators. Methanol and ethanol are the most suitable alternatives, particularly for NaOH.

Mechanical properties and microscopic analysis of water-castable engineered cementitious composites (WECC)

To address the difficulties in repairing underwater concrete panels and the unsatisfactory results of existing repair methods and materials, water-castable engineered cementitious composites (WECC) are developed. The effects of flocculant dosage on anti-dispersibility, fluidity, tensile behaviors, flexural behaviors, and fracture behaviors were investigated. XRD, MIP, and SEM tests were conducted on the WECC. Excellent tensile properties, flexural energy absorption capacity, and crack resistance are exhibited by the WECC. The increase in flocculant dosage decreases the dispersion degree during the underwater casting process of WECC, reduces the early hydration reaction rate, increases the internal porosity, resulting in a decrease in various mechanical properties. By comparing the tensile properties of WECC and WECC(L), while integrating microscopic analysis results, the performance loss mechanism of WECC and the tensile constitutive model have been identified. Additionally, the effects of (washed sea sand) sand-colloid ratio on workability and mechanical properties were investigated. When the sand-colloid ratio is 0.25, a higher level of compatibility between the fibers and the matrix is observed, and good ductility is demonstrated. Considering various performance factors, two mixed proportions have been established. The time, resources, and labor required for the repair process can be significantly reduced by using WECC for repairing underwater components, and the hydraulic structures can operate normally. The externally generated complex stress can be effectively released by WECC. The tested results provide crucial references for the underwater reinforcement of WECC.