Thermal Reactivation of Hydrated Cement Paste: Properties and Impact on Cement Hydration.

In this research, the properties and cementitious performance of thermally activated cement pastes (referred to as DCPs) are investigated. Hydrated pastes prepared from Portland cement and slag blended cement were subjected to different thermal treatments: 350 °C for 2 h, 550 °C for 2 h, 550 °C for 24 h and 750 °C for 2 h. The properties and the reactivity as SCM of the DCPs were characterised as well as their effect on the mechanical performance and hydration of new blended cements incorporating the DCPs as supplementary cementitious materials (SCMs). It was observed that the temperature and duration of the thermal treatment increased the grindability and BET specific surface area of the DCP, as well as the formation of C2S phases and the reactivity as SCM. In contrast, the mechanical strength results for the blended cements indicated that thermal treatment at 350 °C for 2 h provided better performance. The hydration study results showed that highly reactive DCP interfered with the early hydration of the main clinker phases in Portland cement, leading to early setting and slow strength gain. The effect on blended cement hydration was most marked for binary Portland cement-DCP blends. In contrast, in the case of ternary slag cement-DCP blends the use of reactive DCP as SCM enabled to significantly increase early age strength.

Incorporation of spent ion exchange resin simulate into cement composites.

Solidification/Stabilization (S/S) of spent radioactive ion exchange resins (IER) is one of many critical problems facing developing nuclear industries all over the world. Immobilization technology using Ordinary Portland Cement (OPC) as an inert matrix, has been widely applied for the solidification/stabilization of spent ion exchange resin. In this study incorporation of simulated IER into cement matrix and characterization of the final solid waste form (FWF) had been searched practically in laboratory scale experiments. Factors that can affect the properties of the FWF including the water/cement (w/c) ratios and the resin concentration were studied systematically. Mechanical integrities, thermal analysis, and mass loss during hardening and curing for 28 days were evaluated for FWF hard blocks. Scanning Electron Microscope (SEM) and X-Ray Diffraction (X-RD) examinations were performed to investigate the internal architecture of the FWF. Moreover, the heat of cement hydration reactions was recorded during the IER solidification process. Based on the experimental results obtained, it is worth to state that according to its acceptable characteristics and advantages of cement as an inert matrix, it can be suggested safely for the immobilization of untreated spent radioactive ion exchange resins.

The Effects of Calcium Nitrite on the Mechanical Properties and Microstructure of Early-Age Frozen Cement Paste.

The objective of this paper is to investigate the effect of calcium nitrite (CN) on improving the mechanical properties and microstructures of early-frozen cement paste. Cement pastes containing 1%, 1.5%, 2%, 2.5%, and 3% CN were prepared. One batch of samples was frozen at -6 °C for 7 days and then cured at 20 °C, and the other batch of samples was directly cured at 20 °C as a control. The compressive strength, ultrasonic pulse velocity, and resistivity of all specimens at different target ages were measured under these two curing conditions. The hydration products and microstructures of typical samples were observed using XRD and scanning SEM. The results showed that the addition of 1.5% CN could promote cement hydration and enhance slurry densification, thereby increasing the compressive strength, ultrasonic pulse velocity, and electrical resistivity of the slurry, and positively affecting the early freezing resistance of the slurry. However, when the CN dosage exceeded 1.5%, the internal structure of the slurry was loose and porous due to the generation of a large amount of nitrite-AFm, which negatively affects the properties of the cement paste. In addition, the effectiveness of CN is only limited to temperature environments above -6 °C. Concrete antifreeze suitable for lower temperatures still requires further research.

Low Concentrations of Gold Nanoparticles as Electric Charge Carriers in Piezoelectric Cement-Based Materials.

Piezoelectric cement-based composites could serve to monitor the strain state of structural elements or act as self-powered materials in structural health monitoring (SHM) applications. The incorporation of piezoelectric materials as an active phase within cement matrices has presented a highly attractive avenue until today. However, their application is challenged by the low electrical conductivity of the hydrated cement matrix. Gold nanoparticles (Au NPs) possess substantial potential for elevating the free electrical charge within the matrix, increasing its electrical conductivity between the Au NPs and the cement matrix, thereby enhancing the piezoelectric response of the composite. In this sense, the objective of this study is to investigate the effects of incorporating low concentrations of gold nanoparticles (Au NPs) (442 and 658 ppm) on the electrical and piezoelectric properties of cement-based composites. Additionally, this study considers the effects of such properties when the material is cured under a constant electric field. Electrical impedance spectroscopy was used to evaluate the polarization resistance and piezoresistive properties of the material. Additionally, open-circuit potential measurements were taken alongside the application of mechanical loads to assess the piezoelectric activity of the composites. The findings revealed a notable decrease in the composite's total electrical resistance, reaching a value of 1.5 ± 0.2 kΩ, almost four times lower than the reference specimens. In the realm of piezoelectricity, the piezoelectric voltage parameter g33 exhibited a remarkable advancement, improving by a factor of 57 when compared to reference specimens. This significant enhancement can be attributed to both the concentration of Au NPs and the electrical curing process. In summary, the outcomes of this study underscore the feasibility of creating a highly electrically conductive cement-based matrix, using low concentrations of gold nanoparticles as electric charge carries, and indicate the possible piezoelectric behavior of the studied compposite.

Synthesis and Modification of Polycarboxylate Superplasticizers-A Review.

The molecular-scale structural changes in polycarboxylic superplasticizer (PCE) can influence dispersion and water retention. Polycarboxylate superplasticizer, synthesized using different methods, may alter dispersion and water-reducing effects. The synthesis of PCE involves creating a novel macromolecular monomer with a controllable molecular mass, adjustable lipophilic, and hydrophilic moieties, as outlined in this study. This article reviews processes for synthesizing polycarboxylates and identifies the optimal method through orthogonal experiments to produce a modified polycarboxylate superplasticizer (PCE-P). The study investigated the effects of different PCE types and concentrations on the surface tension, fluidity, and ζ potential of cement paste. PCE-P, synthesized at room temperature, showed comparable performances in initial hydration and conversion rate in cement to PCE synthesized at high temperatures. PCE-P exhibited an increased slump but had a wider molecular weight distribution and longer main and side chains, leading to a 24.04% decrease in surface tension, indicating a good dispersibility.

Shrinkage Reduction in Nanopore-Rich Cement Paste Based on Facile Organic Modification of Montmorillonite.

The organic modification of montmorillonite was successfully achieved using cetyltrimethyl ammonium bromide under facile conditions. The modified montmorillonite was subsequently used for the fabrication of montmorillonite-induced nanopore-rich cement paste (MNCP), and the shrinkage behavior and fundamental performance of MNCP were also investigated. The results indicate that alkali cations on a montmorillonite layer surface were exchanged by using CTAB under 80 °C, successfully achieving the organic modification of montmorillonite. As a pore-forming agent, the modified montmorillonite caused a reduction in shrinkage: the 28-day autogenous shrinkage at a design density of 400 kg/m3 and 800 kg/m3 was reduced to 2.05 mm/m and 0.24 mm/m, and the highest reduction percentages during the 28-day drying shrinkage were 68.1% and 62.2%, respectively. The enlarged interlamellar pores and hydrophobic effects caused by the organic modification of montmorillonite aided this process. Organic-modified montmorillonite had a minor influence on dry density and thermal conductivity and could contribute to an enhancement of strength in MNCP.

Structural Study of the Thermoelectric Work Units Encapsulated with Cement Paste for Building Energy Harvesting.

Cement-based material encapsulation is a method of encapsulating electronic devices in highly thermally conductive cement-based materials to improve the heat dissipation performance of electronic components. In the field of construction, a thermoelectric generator (TEG) encapsulated with cement-based materials used in the building envelope has significant potential for waste heat energy recovery. The purpose of this study was to investigate the effect of cement-based materials integrated with aluminum heatsinks on the heat dissipation of the TEG composite structure. In this work, three types of thermoelectric work units encapsulated with cement paste were proposed. Moreover, we explored the effect of encapsulated structure, heat dissipation area, the height of thermoelectric single leg, and heat input temperature on maintaining the temperature difference between the two sides of the thermoelectric single leg with COMSOL Multiphysics. The numerical simulation results showed that under the conditions of a heat source temperature of 313.15 K and ambient temperature of 298.15 K, the temperature difference between the two sides of the internal thermoelectric single leg of Type-III can maintain a stable temperature difference of 7.77 K, which is 32.14% higher than that of Type-I and Type-II (5.88 K), and increased by 26.82% in the actual experiment. This work provides a reference for the selection and application of TEG composite structures of cement-based materials combined with aluminum heatsinks.

Rheological and Flexural Strength Characteristics of Cement Mixtures through the Synergistic Effects of Graphene Oxide and PVA Fibers.

This study investigates the synergistic effects of incorporating graphene oxide (GO) and polyvinyl alcohol (PVA) fibers into cement paste mixtures, aiming to modify their rheological properties and flexural behaviors with resistance to crack formation. The relationship between static yield stress and critical shear strain was examined in ten cement paste mixtures with varying concentrations of 6 mm and 12 mm PVA fibers and 0.05% GO. Additionally, viscosity analyses were performed. For the specimens fabricated from these mixtures, flexural strength tests were conducted using the Digital Image Correlation (DIC) technique for precise strain analysis under load history. The results indicated a significant increase in static yield stress, viscosity, and critical shear strain due to the combined addition of GO and PVA fibers, more so than when added individually. Notably, in PVA fiber-reinforced cement mixtures, the integration of GO increased the crack initiation load by up to 23% and enhanced pre-crack strain by 30 to 50%, demonstrating a notable delay in crack initiation and a reduction in crack propagation. Microstructural analyses using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) revealed a concentrated presence of GO around and on the PVA fibers. This promotes increased C-S-H gel formation, resulting in a denser microstructure. Additionally, GO effectively interacts with PVA fibers, enhancing the adherence of hydration products at their interface.

The Slump Flow of Cementitious Pastes: Simulation vs. Experiments.

Understanding the transient properties of cementitious pastes is crucial for construction materials engineering. Computational modeling, particularly through Computational Fluid Dynamics (CFD), offers a promising avenue to enhance our understanding of these properties. However, there are several numerical uncertainties that affect the accuracy of the simulations using CFD. This study focuses on evaluating the accuracy of CFD simulations in replicating slump flow tests for cementitious pastes by determining the impact of the numerical setup on the simulation accuracy and evaluates the transient, viscosity-dependent flows for different viscous pastes. Rheological input parameters were sourced from rheometric tests and Herschel-Bulkley regression of flow curves. We assessed spatial and temporal convergence and compared two regularization methods for the rheological model. Our findings reveal that temporal and spatial refinements significantly affected the final test results. Adjustments in simulation setups effectively reduced computational errors to less than four percent compared to experimental outcomes. The Papanastasiou regularization was found to be more accurate than the bi-viscosity model. Employing a slice geometry, rather than a full three-dimensional cone mesh, led to accurate results with decreased computational costs. The analysis of transient flow properties revealed the effect of the paste viscosity on the time- and shear-dependent flow progress. The study provides an enhanced understanding of transient flow patterns in cementitious pastes and presents a refined CFD model for simulating slump flow tests. These advancements contribute to improving the accuracy and efficiency of computational analyses in the field of cement and concrete flow, offering a benchmark for prospective analysis of transient flow cases.

Numerical Analysis of the Freezing Behavior of Saturated Cementitious Materials with Different Amounts of Chloride.

The freezing behavior of cement paste saturated with different chloride concentrations is investigated numerically with a coupled 3D hygro-thermo-mechanical FE analysis. The mathematical formulation of the freezing processes in the context of poromechanics takes into account the water (hydraulic) and ice pore pressures, as well as the distribution of heat (temperature) and strains. These quantities are calculated numerically based on three coupled differential equations, namely the static equilibrium equation and the equations for the transport of water and heat. The coupling between the mechanical (loading) and the non-mechanical processes (freezing) is performed using a staggered solution scheme. The proposed numerical approach is first validated using numerical and experimental studies from the literature dealing with two different cement pastes saturated with different amounts of chloride. The validated model is then used to investigate the effects of liquid water permeability, total porosity and pore size distribution on the freezing behavior of hardened cement paste. The results show that liquid water permeability has a strong effect on the pore pressure and deformation of the hardened cement paste. It is also shown that by decreasing the total porosity, the material becomes denser and contracts more as the temperature decreases, leading to a decrease in freezing strain. The results of this paper will provide important findings for the development of a simplified engineering model to investigate the mechanism that leads to freeze-thaw salt-induced damage to concrete structures in the framework of the DFG-funded research project.

Recycling Local Waste Glass Bottles into Cement Paste: Effect on Hydration, Microstructure, and CO2 Emission.

Large amounts of waste glass are generated along with the manufacturing of glass products, causing detrimental effects on the environment. Through crushing and ball-milling, waste glass powder (WGP) can be acquired from glass bottles and has been suggested in cementitious systems due to its potential pozzolanic activity. To better understand the impact of WGP on cementitious composites, experimental tests of rheology, heat of hydration, and strength development were conducted on cement pastes with and without WGP. Results show that the rheological performance of cement paste is improved when WGP with particles passing through 80 µm sieves is incorporated. The retarding effect and pozzolanic reaction were observed through X-ray diffraction patterns and thermo-gravimetric parameter analyses. A calcium hydroxide (CH) content calculation further confirms the secondary reactivity of WGP in cement pastes. Compared with the samples without WGP, the normalized CH content of binder per unit mass containing 35% WGP decreased by 21.01%, 24.94%, and 27.41% at the ages of 1, 28, and 90 days, respectively, which contributes to late-age strength development of pastes. At the same time, the hydration per unit of cement was increased by 21.53%, 15.48%, and 11.68%, which improved the cement efficiency. In addition, WGP particles provide nuclei for hydration products, facilitating the subsequent growth of C-S-H and strength development in late ages. Based on value engineering analysis, WGP was found to reduce the impact of Portland cement on the environment by 34.9% in terms of carbon dioxide emissions, indicating a bright prospect for WGP in the cement industry.

Environmental, economic and engineering performances of aqueous carbonated steel slag powders as alternative material in cement pastes: Influence of particle size.

The low reactivity and volume expansion issue of steel slag limits its application as alternative to cement. Studies demonstrated that aqueous carbonation (AC) can enhance the cementitious properties of finely sized steel slag as a cementitious supplementary material (SCM). However, the impact of particle size on the CO2 uptake capacity and its association of performance of carbonated steel slag remains unexplored. This study aims to optimize the grinding levels by examining the fineness of the steel slag used as SCM to reduce the high-energy consumption while maintaining the CO2 sequestration and properties of SCM. The results show that reducing the size of steel slag is favorable for CO2 sequestration (particle size 22.4-112.6 µm corresponds to sequestration of ∼88.5-37.9 kg CO2/t steel slag) and improve the leaching of Mg ions for mineralization. The life cycle assessment shows that the global warming potential of AC of steel slag is ∼96.2-24.9 kg CO2-eq/t steel slag, which can offset the carbon emissions due to further grinding. The 28-day compressive strength of the cement pastes blended with finer carbonated steel slag was also relatively higher due to the formation of mono-carboaluminates and stabilization of ettringite in facilitating the bond strength between the carbonated steel slag particle and the cement paste matrix. According to 3E (engineering, environmental and economic) triangle model, 22.4 µm steel slag powder showed the best comprehensive performance, including an increased revenue of 40.8 CNY/ton steel slag.

Developing Innovative Cement Composites Containing Vine Shoot Waste and Superplasticizers.

The expansion of the construction industry requires large quantities of construction materials; therefore, the utilization of alternative raw materials that reduce the environmental impact and enhance the quality of the construction materials has received increasing interest. The comparative performance of 1% Dynamon SR3 or Dynamon SR41 superplasticizers on the properties of cement paste with 1 wt.% vine shoot waste addition (VSW) was investigated after 28 days using Fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), and solid-state 27Al and 29Si nuclear magnetic resonance (NMR) spectroscopy. VSW does not delay the formation of calcium hydroxide and C-S-H and a slight decrease of the -OH band in samples containing superplasticizers, suggesting that free lime is converted to carbonates. The highest degree of crystallinity was remarked for the samples with superplasticizers. The structure of the cement paste with VSW and superplasticizers was corroborated with mechanical properties, showing increased strength in using VSW and superplasticizers. The results showed that adding 1% VSW and superplasticizers does not change the performance of the cement paste but reduces the water-cement ratio. The combination of VSW and superplasticizers led to cement composite with improved structural and mechanical properties suitable for construction.

Mechanical Characterization of MWCNT-Reinforced Cement Paste: Experimental and Multiscale Computational Investigation.

Computational approaches could provide a viable and cost-effective alternative to expensive experiments for accurately evaluating the nonlinear constitutive behavior of cementitious nanocomposite materials. In the present study, the mechanical properties of cement paste reinforced with multi-wall carbon nanotubes (MWCNTs) are examined experimentally and numerically. A multiscale computational approach is adopted in order to verify the experimental results. For this scope, a random sequential adsorption algorithm was developed to generate non-overlapping matrix-inclusion three-dimensional (3D) representative volume elements (RVEs), considering the inclusions as straight elements. Nonlinear finite element analyses (FEA) were performed, and the homogenized elastic and inelastic mechanical properties were computed. The use of a multiscale computational approach to accurately evaluate the nonlinear constitutive behavior of cementitious materials has rarely been explored before. For this purpose, the RVEs were analyzed both in pure tension and compression. Young's modulus as well compressive and tensile strength results were compared and eventually matched the experimental values. Moreover, the effect of MWCNTs on the nonlinear stress-strain behavior of reinforced cement paste was noted. Subsequently, three-point bending tests were conducted, and the stress-strain behavior was verified with FEA in the macro scale. The numerical modeling reveals a positive correlation between the concentration of MWCNTs and improved mechanical properties, assuming ideal dispersion. However, it also highlights the impact of practical limitations, such as imperfect dispersion and potential defects, which can deteriorate the mechanical properties that are observed in the experimental results. Among the different cases studied, that with a 0.1 wt% MWCNTs/CP composite demonstrated the closest agreement between the numerical model and the experimental measurements. The numerical model achieved the best accuracy in estimating the Young's modulus (underestimation of 13%), compressive strength (overestimation of 1%), and tensile strength (underestimation of 6%) compared to other cases. Overall, these numerical findings contribute significantly to understanding the mechanical behavior of the nanocomposite material and offer valuable guidance for optimizing cement-based composites for engineering applications.

Research of Water Absorption and Release Mechanism of Superabsorbent Polymer in Cement Paste.

The water absorption and release properties of superabsorbent polymers' (SAP) internal curing agent are affected by many factors, such as solution properties, the ambient temperature and humidity and the particle size of SAP, which determine the curing effect and the durability of cement concrete structures directly. In this paper, the variation rule of the water absorbing capacity of SAP in simulated cement paste under different solutions and environmental conditions was studied. Based on microscopic image technology, the dynamic swelling behavior of the SAP particles was explored. The water release performance of SAP in cement paste was analyzed by both the tracer method and the negative pressure method. The results show that the water absorption of SAP in cement paste varied from 27 to 33 times. The ionic valence had a significant effect on the water absorption capacity of SAP, which suggests that the larger the ionic radius, the lower the absorption of SAP. The higher the temperature of the solution, the greater the water absorption rate of SAP. While the SAP particle size was less than 40-80 mesh, a slight 'agglomeration effect' was prone to occur, but the absorption state of SAP was more stable. Based on the swelling kinetic equation of SAP and the time-dependent swelling morphology of SAP in cement paste, a swelling kinetic model was established. The water release performance of SAP was less affected by the capillary negative pressures, and it would not release the water prematurely during the plastic stage, which was conducive to the continuous internal curing process of hardened paste in the later stage.

Analysis of Pore Structure in Cement Pastes with Micronized Natural Zeolite.

The continuous development of urban areas around the world led to an increase in construction material use and demand, with concrete seeing significant market uptake. Although significant progress has been made to reduce the environmental impact of concrete, there is still a stringent need for improvement. One of the most widely used methods to reduce the environmental impact of the cement industry and the construction industry alike is the replacement of ordinary Portland cement (OPC) by supplementary cementitious materials (SCM). Aside from by-products of industry, SCMs could also come from natural sources. Taking into account the porous structure of zeolites and their contribution to the improvement of the mechanical and durability properties of cement-based materials, the analysis of pore structure in cement pastes incorporating micronized natural zeolite is deemed necessary. In this research, the OPC was replaced by zeolite in three different percentages: 10%, 20%, and 30% by mass. The evolution of pore structure was investigated by means of nuclear magnetic resonance relaxometry at the curing ages of 1, 7, and 28 days. The microstructure of cement pastes was assessed by scanning electron microscopy investigations at 1, 7, 14, 21, and 28 days. The obtained results show that smaller pore sizes are present in cement pastes containing zeolites during the first 7 days. However, at the age of 28 days, the reference mix exhibits a similar pore structure to the mix containing 10% micronized zeolite due to the presence of larger amounts of hydration products. Increasing the replacement percentage to 30% results in larger pores, as indicated by larger values of the relaxation time.

Evaluation of the Fresh Properties of Cement Pastes: Part I-Response Models Applied to Changes in the One-Variable-at-a-Time Method.

The workability of cement-based materials is one of the features that makes these construction materials the most used worldwide. Measuring and understanding how cement-based constituent materials affect fresh properties depends on the experimental plans. The experimental plans deal with the constituent materials used, the tests carried out, and the run of experiments. Here, the fresh properties (workability) of cement-based pastes are evaluated based on the diameter in the mini-slump test and the time in the Marsh funnel test being measured. This overall study is composed of two parts. In Part I, tests were carried out on several cement-based paste compositions incorporating distinct constituent materials. The effects of the distinct constituent materials on the workability were analyzed. Furthermore, this work deals with an approach to the run of experiments. A typical run of experiments was applied, with basic sets of mixed compositions being studied by only changing one input parameter at a time. This approach used in Part I is faced with a more scientific approach applied in Part II of the work where, based on the design of experiments, multiple input parameters were changed at a time. This work showed that a basic run of experiments is quick and easy to apply and leads to results for simple analyses; conversely, it lacks information for advanced analyses and scientific conclusions. The tests carried out included studies on the effect on the workability caused by changes in the limestone filler content, the type of cement, the water-to-cement ratio, distinct superplasticizers, and shrinkage-reducing admixture.

Diffusion potentials in saturated hardened cement paste upon chloride exposure.

The diffusion potentials can cause significant errors in corrosion-related investigations of reinforced concrete structures (half-cell potential mapping, potentiometric sensors). Therefore, an improved understanding of the diffusion potentials in cement-based materials is needed. This study investigates the permselective behavior and its implication for the arising diffusion potentials. A diffusion cell is used to study the diffusion potentials in hardened cement pastes with imposed NaCl gradients. The cement pastes consist of ordinary Portland cement (OPC) and blast furnace cement (BFC) with water-cement ratios of 0.30-0.70. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is used to determine the concentration profiles of Cl, Na, K and Ca in the cement pastes with a high spatial resolution (100 µm). For the BFC pastes, considerable differences in the Cl- and Na+ mobilities are found, indicating their permselective behavior. Despite the permselective behavior, the measured diffusion potentials are small (- 6 to + 3 mV) for all investigated cement pastes due to the high pH levels (13-14) in the pore solutions. However, when using the diffusion cell, the pH differences interfere with the measured diffusion potentials. The interfering pH differences need to be considered for an accurate measurement of the diffusion potentials in cement pastes.

Rheological and Mechanical Properties of Bentonite-Cement Paste Reinforced with Basalt Fibers.

Bentonite cement paste (BCP) is among the grouting materials used widely in large-pore grouting and karst cave treatment. The mechanical properties of bentonite cement paste (BCP) will be improved by additional basalt fibers (BF). In this study, the effects of basalt fiber (BF) contents and their lengths on the rheological and mechanical properties of bentonite cement paste (BCP) have been examined. Yield stress (YS), plastic viscosity (PV), unconfined compressive strength (UCS), and splitting tensile strength (STS) were used to evaluate the rheological and mechanical properties of basalt fiber-reinforced bentonite cement paste (BFBCP). Scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS) characterize microstructure development. The results indicate that the Bingham model can provide the rheological behavior of basalt fibers and bentonite cement paste (BFBCP). The yield stress (YS) and plastic viscosity (PV) increase as the content and length of basalt fiber (BF) increase. The effect of fiber content on yield stress (YS) and plastic viscosity (PV) is greater than that of fiber length. The addition of basalt fiber (BF) enhanced the unconfined compressive strength (UCS) and splitting tensile strength (STS) of basalt fiber-reinforced bentonite cement paste (BFBCP) at the optimum basalt fiber (BF) content of 0.6%. The optimum basalt fiber (BF) content tends to increase as curing age increases. The basalt fiber length of 9 mm is the most effective for improving unconfined compressive strength (UCS) and splitting tensile strength (STS). The large increments in unconfined compressive strength (UCS) and splitting tensile strength (STS) were 19.17% and 28.21% for the basalt fiber-reinforced bentonite cement paste (BFBCP), with a basalt fiber length of 9 mm and content of 0.6%. Scanning electron microscopy (SEM) shows that the randomly distributed basalt fiber (BF) forms a spatial network structure in basalt fiber-reinforced bentonite cement paste (BFBCP), which composes a stress system under the action of cementation. Basalt fibers (BF) used in crack generation processes slow down the flow through bridging and occur in the substrate to improve the mechanical properties of basalt fiber-reinforced bentonite cement paste (BFBCP).

Study on Kinetics of Carbonization Reaction of Hardened Cement Paste Powder Based on Carbonization Degree.

The hardened cement paste powder (HCP) powder, devoid of the hydration cementing property, can be regenerated and cemented into a test block with practical strength of almost 60 MPa via CO2 carbonization using appropriate means. This study established a kinetic model of CO2 curing of an HCP powder test block based on the degree of carbonization to study the carbonization reaction kinetic characteristics of the test block. The model was modified according to the characteristics of the evident temperature differences in the reaction kettle in the early, middle, and late stages of the carbonization process. The proposed model can be used to formulate and control the carbonization and cementation processes of HCP powder and can also be applied to describe the kinetics of the reaction processes of other similar systems.