Search

Low‐field nuclear magnetic resonance is adopted in this paper for the study of the hydration process of early‐age pure and composite cement paste by monitoring the longitudinal relaxation time (T1) of water constrained in the paste. Based on the correlation between the changes of weighted average T1 and the hydration process of paste, the hydration process can be divided into four stages, i.e., initial period, dormant period, accelerated period, and steady period. The effect of water‐to‐cement ratio (w/c) and admixtures to hydration is discussed in detail. Compared to WC04, the weighted average T1 at the end of the dormant period increased by 4.79, 1.74, and 0.05 ms when 30% fly ash, 30% slag, and 10% silica fume were added, respectively. Based on experimental data and the Avrami–Erofeev equation, a hydration model for both pure and composite cement pastes is proposed, with a correlation that is higher than 0.96, which can describe the hydration process of paste well. [ABSTRACT FROM AUTHOR]

In this work, a particular type of carbon nano-material, like graphene oxide (GO), is synthesized in different batches by varying oxidation times, ranging from 1 to 4 days. The synthesis process initially starts with the oxidation of commercially available graphite powder and subsequently exfoliates the obtained graphite oxide in an aqueous solution using a high-frequency ultrasonication process. The synthesized GO batches were characterized using different characterization techniques to authenticate the formation of GO. The highly oxidized GO in an aqueous solution was selected and used as a strength-enhancing additive in concrete. The concrete mixes containing highly oxidized GO at the dosage of 0.01% 0.03%, 0.05%, 0.07%, and 0.09%bwoc were prepared to assess the strength and durability parameters. The GO (4 d) with 0.09%bwoc in concrete increases compressive strength by 58%, tensile strength by 41%, and flexural strength by 43% at 56 days. The results proved that the 0.09%bwoc GO dosage in cement concrete could effectively improve mechanical and durability performances compared to other mixes. Furthermore, the results are verified with the microstructural investigation using FE-SEM in secondary electron (SE) and backscattered electron (BSE) mode to monitor the microstructural changes and thickness of the interfacial transition zone (ITZ) during cement hydration. [ABSTRACT FROM AUTHOR]

The mechanical response and fracture behavior of two architected 3D-printed hardened cement paste (hcp) elements, 'lamellar' and 'Bouligand', were investigated under uniaxial compression. A lab-based X-ray microscope was used to characterize the post-fracture crack pattern. The mechanical properties and crack patterns were analyzed and compared to cast hcp. The role of materials architecture and 3D-printing-induced weak interfaces on the mechanical properties and fracture behavior are discussed. The pore architecture that inadvertently forms in the design of solid architected materials dictated the overall mechanical response and fracture behaviors in both 3D-printed architected materials. While no specific crack pattern or microcracking was observed in the cast element, lamellar architecture demonstrated a crack pattern following weak vertical interfaces. Bouligand architectures, on the other hand, exhibited a helical crack pattern with distributed interfacial microcracking aligned with the helical orientation of filaments. As a result, the bouligand architected elements showed a significant 40% increase in work-of-failure compared to cast counterparts. The enhanced energy absorption was obtained without sacrificing the strength and was attributed to higher fractured surface and microcracking, both of which follow the weak helical interfaces. [ABSTRACT FROM AUTHOR]

Structural health monitoring applications have gained significant attention in recent research, particularly in the study of the mechanical–electrical properties of materials such as cement-based composites. While most researchers have focused on the piezoresistive properties of cement-based composites under compressive stress, exploring the electrical impedance of such materials can provide valuable insights into the relationship between their mechanical and electrical characteristics. In this study, we investigated the connection between the mechanical properties and electrical impedance of cement-based composites modified with Au nanoparticles. Cylindrical samples with dimensions of 3 cm in diameter and 6 cm in length were prepared with a ratio of w/c = 0.47. The Au nanoparticles (Au NPs) were synthesized using pulsed laser ablation in liquids, and their size distribution was analyzed through dynamical light scattering. Mechanical properties were evaluated by analyzing the Young modulus derived from strain–stress curves obtained at various force rates. Electrical properties were measured by means of electrical impedance spectroscopy. The experimental results revealed a notable reduction of 91% in the mechanical properties of Au NPs-cement compounds, while their electrical properties demonstrated a significant improvement of 65%. Interestingly, the decrease in mechanical properties resulting from the inclusion of gold nanoparticles in cementitious materials was found to be comparable to that resulting from variations in the water/cement ratios or the hydration reaction. [ABSTRACT FROM AUTHOR]

Mechanical grinding is a common method used to enhance the pozzolanic activity of tailings, and these activated tailings can be used as supplementary cementitious materials in cement production. However, the addition of activated tailings usually reduces the workability of cement paste, and the mechanism of influence of different minerals in tailings on workability varies. In this study, three kinds of principal silicate minerals in tailings—quartz, feldspar, and mica—were mechanically activated. The influence of these activated minerals on the rheological properties of cement paste were studied in the absence or presence of PCE (polycarboxylate ether) superplasticizers, and the influence mechanism was investigated using rheology, TOC, contact angles, zeta potential, XPS, ICP-OES, and XRD. The results showed that quartz has the highest fluidity, and mica has the lowest. An increase in hydrophilicity decreased the flowability of the blended cement paste. The increase in the metal cation dissolution rate was the main reason for the decrease in the fluidity of PCE-blended cement pastes. The knowledge gained provides a valuable reference for the utilization of activated tailings in cement production. [ABSTRACT FROM AUTHOR]

In this study, a viscosity-reducing polycarboxylic acid superplasticizer (VRPCE) was synthesized using methylallyl polyoxyethylene ether (HPEG), acrylic acid (AA), and maltodextrin maleic acid monoester (MDMA) as the main raw materials. The influences of the VRPCE on the microscopic properties of cement paste were studied by gel permeation chromatography (GPC), total organic carbon test (TOC), zeta potential, laser particle size analysis, XRD, MIP, TG, and SEM. Finally, the effects of the VRPCE on the macroscopic properties of cement mortar were evaluated through flow time, slump flow, compressive strength, shrinkage, and creep. The results showed that the VRPCE can improve the hydration degree of the cement, optimize the pore structure, increase the porosity, improve the fluidity, compressive strength, and creep, and decrease the shrinkage resistance of the cement mortar. [ABSTRACT FROM AUTHOR]

The aim of this study is twofold. First, to assess the effect of the sonication process on the optimal dispersion of GO sheets for nanostructural reinforcement of cement pastes, as there is currently no clear criterion on this effect in the literature. For this purpose, in the first stage, the GO content in distilled water was fixed at 0.03% by weight, and the sheets were dispersed using different levels of ultrasonic energy, ranging from 0 J/mL to 2582 J/mL. In the second stage, to analyze the modification of pore structure due to the addition of GO sheets in different ratios (0–0.06% by weight) and its relationship with the mechanical and fracture properties of reinforced cement pastes. According to the results, it has been determined that the incorporation of GO sheets into the matrix alters the mechanical and fracture behavior, varying depending on matrix pore size and GO particle size. The addition of GO leads to a reduction in the average size of macropores (greater than 8 µm) of 13% for a dosage of 0.45% in weight and micropores (between 8 and 0.5 µm) in a 64% for the same composition with non-sonicated GO, although the total volume of pores in these ranges only decreased slightly. This reduction is more pronounced when the GO has not been sonicated and has larger particle size. Sonicated GO primarily modifies the range of capillary pores (<0.5 µm). The addition of GO with the highest degree of dispersion (465 nm) did not show significant improvements in compressive strength or Young's modulus, as the cement used contains a significant volume of macropores that are not substantially reduced in any composition. Adding 0.030% ultrasonicated GO achieved a 7.8% increase in fracture energy, while an addition of 0.045% resulted in a 13.3% decrease in characteristic length, primarily due to the effect of capillary and micropores. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study aimed to experimentally investigate the compressive strength and air voids of cement pastes with varying dosages of Superabsorbent Polymer (SAP) and water-to-cement (w/c) ratios. Cement pastes were prepared using three different w/c ratios of 0.4, 0.5, and 0.6, along with different dosages of SAP ranging from 0.2% to 0.5% by weight of cement. Additionally, SAP was introduced in two forms: dry and wet. After casting the cubes, two distinct curing conditions were employed: curing at a temperature of 20 °C with a Relative Humidity (RH) of 60% (Curing 1), and water curing (Curing 2). The results revealed that the addition of SAP increased early strength when subjected to Curing 1, followed by a decrease in later strength. On the other hand, samples with SAP and water curing exhibited higher strength compared to those without SAP, especially with w/c ratios of 0.4 and 0.5. However, at a w/c ratio of 0.6, nearly all samples showed a reduction in strength compared to those without SAP. Furthermore, air void analysis was performed on all samples cured for 28 days using an image analysis technique. The samples containing wet SAP resulted in a higher total air content compared to the samples with dry SAP. Additionally, the incorporation of wet SAP in cement paste led to lower specific surface areas and a higher spacing factor than the samples with dry SAP. These findings suggest that the clumping of wet SAP particles during presoaking resulted in coarser air voids compared to the samples containing dry SAP. [ABSTRACT FROM AUTHOR]

To explore the problem of additional shrinkage cracking caused by long water vapor balance of large specimens, a new in-situ micromechanical test method was proposed to study the micro creep and shrinkage of cement paste. Combined with digital image correlation (DIC) observation, uniaxial-biaxial compression creep and shrinkage tests were carried out on thin cement blocks in environmental scanning electron microscope (ESEM) and climate chamber (CC). The test results show that compared with the traditional test method, the new test framework significantly shortens the drying time by at least 200 times, thus effectively reducing the risk of cracking. There is a high linear correlation between the free drying shrinkage of cement paste and the mass loss when the relative humidity(RH) is higher than 60%. In the relative humidity of 50% ~ 60%, the cavitation of water influences the drying shrinkage. Compared with the ambient air-drying conditions in the climate chamber, the drying conditions in the environmental scanning electron microscope have lower air pressure, which causes forced convection flow and leads to a significant increase in the drying rate. However, under the equilibrium state of relative humidity of 20% RH, the shrinkage deformation of the two is basically the same. The rapid drying specimens have larger pores than the slow drying specimens, and the pores of the unloaded specimens are larger than those of the loaded specimens. In the uniaxial compression test, the change of drying creep with drying shrinkage shows a bilinear trend. In the biaxial compression test, the drying creep shows a linear relationship. The Poisson's ratio of drying creep is negative in both compression tests. When the Poisson's ratio is between - 0. 1 to 0, the creep properties obtained by CC test are basically consistent with the results of ESEM method. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Railway Science & Engineering is the property of Journal of Railway Science & Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract High-Performance Concrete (HPC) offers better workability, compressive strength, and durability compared to ordinary concrete. One type of high-strength concrete is magnetic concrete. The primary objective of this empirical research is to investigate the potential of magnetized concrete in enhancing the seismic properties of concrete structures, in this technology, the physical structure of water is altered by inducing a magnetic field. The research employs empirical methods, including experimental testing and analysis, to assess the seismic performance of magnetized concrete compared to traditional concrete. As a result, the number of molecules in a molecular cluster decrease from 13 to 5 or 6, and the surface tension of the water is reduced. Using this water in concrete preparation increases the workability of the concrete mix and reduces the required water. Additionally, by facilitating cement hydration, it increases the compressive strength and durability of the concrete. This increased compressive strength enhances the stability and resistance of the structure against earthquake forces. Moreover, maintaining the compressive strength of the concrete while using magnetic water can reduce cement consumption. This reduction in cement consumption can lower the weight of the structure, which is very effective in reducing earthquake forces in tall buildings.

In this study, the effect of curing humidity on mechanical performance, hydration as well as microstructure for cement paste containing metakaolin (MK) and limestone powder (LP) with various water to binder (w/b) ratios, such as 0.24, 0.36, and 0.48, were investigated. A total of 18 types of slurries were prepared and cured under three levels of humidity [55% relative humidity (RH), 95% RH, and water curing at 20°C] for 28 days. The compressive and flexural strengths were measured to evaluate the influence of humidity on the strength performances of pastes. The MK reaction degree of pastes was tested using the method of selective dissolution in hydrochloric acid. X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM) tests were employed to evaluate the hydration and microstructure of paste. Research results demonstrated that the strengths of pastes generally decreased with curing humidity. Curing at 55% RH can obviously degrade the flexural strength of pastes compared with curing at 95% RH and water curing. The influence of humidity on the compressive strength of MK-containing pastes decreased with the decrease of w/b. The compressive strength of 0.24 w/b pastes containing MK at various humidities were similar. Increasing humidity can enhance the MK reaction degree of pastes with different w/b ratios, which is responsible for the enhanced strength tendency of pastes with humidity. Similar to the compressive strength tendency, humidity had insignificant effects on the MK pozzolanic reaction of pastes with a low w/b ratio. XRD results demonstrated that raising humidity can further increase the synergistic effect of MK and LP. The quantities of monocarboaluminate (Mc) and hemicarboaluminate (Hc) in paste with a high w/b under water curing were greater than those in pastes cured at 55% RH. The microstructures of pastes investigated using MIP and SEM tests also corresponded well to the results of mechanical performances. The findings of this study can provide some guidance for manufacturing normal concrete (NC), high-performance concrete (HPC) and ultrahigh-performance concrete (UHPC) incorporating MK and LP under different levels of humidity. [ABSTRACT FROM AUTHOR]

Cementitious materials can capture CO2 through carbonation reaction during their service life and post-demolition. Indeed, construction and demolition waste (CDW) still have some potential for carbonation as they contain concrete and cement-based mortars. This research consists of an experimental programme to evaluate the CO2 capture of recycling aggregates (RAs) from CDW. Two types of CDW were studied, namely mixed recycled aggregates (MRAs) and recycled concrete aggregates (RCAs). The recycled aggregates were submitted to forced and accelerated carbonation at 23 °C, 60% relative humidity and 25% of CO2 concentration. This study contributes to the existing literature by investigating more realistic RA sources that have already absorbed atmospheric CO2 during their service life. From the experimental campaign, the results show that RCAs have higher carbonation potential when compared to MRAs due to the higher cementitious material content (Rc) and to the degree of natural carbonation. The recycled aggregates' maximum CO2 capture was assessed by thermogravimetric analysis (TGA) at different CO2 exposure times. It was verified that the maximum CO2 capture, respectively, for MRAs and RCAs, occurred after 5 h and 12 h of exposition. In short, CDW captured from 5 wt.% to 35 wt.% of CO2 per tonne of cement paste, which corresponds to 0.6% to 4.1% per tonne of aggregate. It was concluded that the carbonation process of CDW has the potential to sequester from 123 kg to 225 kg of CO2 per tonne of cement paste for MRAs and 52 up to 491 kg of CO2 per tonne of cement paste for RCAs. [ABSTRACT FROM AUTHOR]

In this study, the effect on the compressive strength of cement with the addition of 1–5 wt% nano-magnetite particles (nano-Fe3O4) is identified at the age of 7 days and 28 days of curing. In addition, an approach of aligning these nano-magnetite particles within cement using an external magnetic field is presented, where the orientation of nano-magnetite particles is aligned parallel to the compressive load. The effect of the compressive strength on cement mortar with the aligned nano-magnetite particles is compared with the non-aligned samples. Both aligned and non-aligned samples show positive effects on the compressive strengths as compared to the control samples, where the cement mortar with aligned nano-magnetite shows significant improvement on compressive strength up to 21%. This study also shows that the addition of 3 wt% nano-magnetite particles to cement mortar is the optimal amount to achieve maximum enhancement of compressive strengths. [ABSTRACT FROM AUTHOR]

Red mud has been used as a supplement substitute material in the fabrication of concrete. However, the influence mechanism of red mud on the film-forming performance of cement paste is still unclear. In this study, red mud with different substitution rates (by cement mass) was added to cement paste to investigate the influence of red mud on the film-forming performance. The addition of red mud increased the cohesiveness and reduced the fluidity of cement paste. It showed that low fluidity reduced the film thickness of cement paste, and the film thickness decreased gradually with the increase of red mud substitution. Moreover, thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy results demonstrated that red mud promotes the hydration process of cement by providing hydration nucleation sites, making the interfacial transition zone denser, which is important for improving the mechanical properties of cement paste. It is expected that this study improves the application of red mud in concrete. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Compressive strength, a crucial mechanical property of cement mortars, is typically measured destructively. However, there is a need to evaluate the strength of unique cement-based samples at various ages without causing damage. In this paper, a predictive framework using a genetic algorithm (GA) is proposed for estimating the compressive strength of ordinary cement-based mortars based on their dynamic elastic modulus, measured non-destructively using the impulse excitation technique. By combining the Popovics model (PM) and the Lydon–Balendran model (LBM), the static elastic modulus of samples was calculated using constant coefficients, representing an equivalent compressive strength. A GA was then employed to determine optimal values for these coefficients. The results showed that the LBM-based strength was dominant in the middle range of the dynamic Young's modulus while the PM-based strength was dominant for higher and lower values of the dynamic Young's modulus. The model was found to have a small root mean square error (3.1%). The findings suggest that this non-destructive model has potential for predicting the mechanical properties of cement mortars. It allows efficient evaluation of compressive strength without destructive testing, offering advantages for reliable assessments of cement-based materials. [ABSTRACT FROM AUTHOR]

Improving the flexural strength of a cement-based composite (CBC) reinforced with chopped carbon fibre (CF) while maintaining good workability is highly attractive for building high-rise large-span structures. A sulfoaluminate-based expansive agent (EA) was used to optimise the mechanical properties of CBCs reinforced with chopped CF by improving the fibre–matrix interfacial properties. The results of single-fibre pull-out tests showed that the interfacial frictional bond strength was improved by up to 51% owing to the addition of the EA, whereas the chemical debonding energy remained nearly unchanged. The effects of various concentrations of EA on the strength of cement pastes containing various lengths and volume fractions of CF were then investigated. The results indicated that, benefitting from the EA-induced high interfacial bond strength, the flexural strength and fluidity of the CF-reinforced cement paste could be further optimised. For example, utilising the EA, the flexural strength could be improved by 28% for a cement paste containing 0.5% CF of length 15 mm. [ABSTRACT FROM AUTHOR]

This study investigates the effect of nanofibrillated cellulose (NFC) on the total and autogenous shrinkage deformation of cement pastes. Three different water-to-cement ratios (w/c) were used, namely 0.30, 0.35, and 0.40, along with NFC inclusion percentages of 0.000%, 0.025%, and 0.050%. The effects of NFC were evaluated through total and autogenous shrinkage measurements. Total shrinkage evolution was measured using 24-h-old prisms while autogenous shrinkage deformation was monitored using sealed prisms and corrugated tubes; their results were then compared. The corrugated tube method provided early-age deformation measurements, while the sealed prism method allowed for direct comparison with free-drying shrinkage specimens. Flow table and bleed water tests were conducted to support the understanding of the impact of NFC on the cementitious system. The NFC reduced the expansion by up to 85%. Regarding total shrinkage deformation, there was a 36% decrease at the end of 28 days for specimens with a w/c of 0.30 and NFC inclusion of 0.050%. However, this outcome varied for different combinations of w/c and nanocellulose content. The presence of NFC modified the fresh state properties of cement pastes, significantly reducing bleed water and decreasing the expansion. These findings highlight the potential of NFC as a material for controlling shrinkage deformation depend on the dosage and emphasize the importance of considering different measurement methods for accurate assessment. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In rheological testing, different test regimes can result in large differences in the rheological curves, and the pre-shear procedure is one of the most important parts of the test. In order to investigate the effect of the pre-shear regime on the rheological properties of cement pastes, an Anton Paar 102 rotary rheometer was used for the test. Two different pre-shear regimes (RF and CP pre-shear), three different pre-shear duration times (50 s, 100 s, 150 s), and four different pre-shear rates (25 s-1, 50 s-1, 100 s-1) are carried out for the test. The results showed that with the increase of pre-shear duration or rate, the four rheological parameters (plastic viscosity, yield stress, rheological index, and thixotropy) of the pastes decrease in different degrees. RF pre-shear was more influenced by shear time, while CP pre-shear was influenced by shear time and rate. The pre-shear regimes led to different changes in the flocculation structure of the cement paste, which had a great influence on rheological parameters ultimately. Based on the improved Krieger-Dougherty model, the effective solid volume fraction of cement paste was calculated. Analysis shows that the phenomenon of "deflocculation" and "re-flocculation" occurs when the cement paste is subjected to shear action, thus, the pre-shear regimes destroy the structure of the pastes. With the increase of pre-shear duration or rate, the effective volume fraction decreased, which indicated that the initial flocculation structurewas broken. The greater the damage degree of pre-shear, the slower the establishment rate of the internal structure of the pastes in dynamic shear, resulting in lower rheological parameters. [ABSTRACT FROM AUTHOR]

Seawater-mixed concrete (SWC) is a proposed solution for catering to the needs of developing nations facing extremely severe water stress. Recent research works advocate the feasibility of producing SWC by adding supplementary cementitious materials (SCMs) and alternative reinforcements without reducing the engineering properties of the same. However, limited information is available for optimising the type and amount of SCMs in binary and ternary blended SW-mixed cementitious systems for achieving desirable strength development and early-age hydration. A comprehensive study to understand the evolution of heat of hydration and strength up to 28 days was conducted on 31 binder compositions mixed with both fresh water (FW) and seawater (SW). Fly ash, slag, metakaolin, and limestone are the supplementary cementitious materials used with CEM I as a primary binder at a replacement level between 10 and 70%. Isothermal calorimetry results revealed an increase in total heat of hydration and a reduction in setting time with SW-mixed cement pastes compared to their FW-mixed counterparts. Similarly, a significant increase in strength between 0 and 50% was observed in SW-mixed cement pastes. Suitable binder combinations showing an increase in compressive strength and not a significant reduction in strength compared to the CEM I reference mix were identified using the strength improvement factor approach. Binary and ternary blended cementitious, consisting of fly ash, slag, and metakaolin at different replacement levels, are amongst the chosen binder combinations. [ABSTRACT FROM AUTHOR]

The utilization of bio-fiber materials in building components has become imperative for improving sustainability, controlling global warming, addressing environmental concerns, and enhancing concrete properties. This study is part of a wide-range investigation on the use of Phragmites-Australis (PhA) fibers in construction and building materials. In this paper, the volume stability and mechanical properties of paste containing PhA fibers and exposed to high temperatures were investigated. Four mixes were made with 0, 0.5, 1, and 2% fibers by volume. To evaluate the volume stability and mechanical properties, the chemical shrinkage, autogenous shrinkage, drying shrinkage, expansion, ultrasonic pulse velocity, compressive strength, and flexural strength were tested. The curing duration and temperature were 180 days and 45 °C, respectively. The results indicated that an addition of PhA fibers of up to 2% resulted in a reduction in all the shrinkage parameters at 180 days. The presence of PhA fibers in the paste tended to reduce the compressive strength, with the lowest value observed at 2%. Apart from the values at 90 days, the optimal flexural strength seemed to be achieved by the paste with 1% PhA fibers. To further elucidate the experimental results, a hyperbolic model was employed to predict the variation in the length change as a function of the curing age with a high accuracy. Based on the results obtained, PhA fibers can play a crucial role in mitigating the shrinkage parameters and enhancing the mechanical properties of cement paste. [ABSTRACT FROM AUTHOR]

Concrete, essential to global infrastructure, confronts urgent environmental challenges due to its high carbon footprint and resource-intensive production. In response, researchers are exploring nanoparticles, such as nano-silica (nS) and nano-titanium dioxide (nT), to enhance sustainability and performance. This review examines recent advances in their application. Nano-silica, prized for rapid hydration and enhanced strength, emerges as a promising additive. Studies indicate nS accelerates cement hydration, densifies the matrix, and improves durability and impermeability. Silica-based nano-coatings on glass textile-reinforced composites bolster bond strength and resilience. Similarly, nT offers diverse benefits to concrete. Beyond its traditional applications in photocatalysis, nS has been proven to refine pore structure, increase compressive strength, and enhance resistance to elevated temperatures. Additionally, nT adds to the self-cleaning properties of concrete surfaces, making it a promising additive for sustainable construction practices. Despite these advancements, challenges persist in the effective dispersion of nanoparticles within concrete matrices and ensuring their economic feasibility and regulatory compliance. Addressing these challenges will require interdisciplinary collaboration and innovative approaches to optimize dispersion methods, mitigate health risks, and develop robust regulatory frameworks. Future research directions should focus on developing multifunctional nanomaterials capable of imparting multiple desirable properties to concrete simultaneously, such as self-sensing, self-cleaning, and energy harvesting capabilities. Furthermore, efforts to optimize manufacturing processes and scale up production will be essential to realizing the full potential of nano-modified concrete in addressing the sustainability challenges facing the construction industry.

A promising, supplementary material, highly reactive silica nanoparticles tend to react with calcium species (Ca2+) in cement, which produces more hydrated phases. The high amount of calcium species and the potential of capturing carbon dioxide (CO2) through carbonation implies the suitability of cement paste as a CO2 sorbent material. However, limited studies could be found highlighting the effect of silica nanoparticle inclusion on the CO2 capture property of hardened cement paste. Thus, this study investigates the effect of silica nanoparticle partial replacement on the CO2 capture capacity and regeneration performance of hardened cement paste. XRD and SEM analysis proved the formation of more hydrated phases upon partially replacing silica nanoparticles in cement. Partial replacement of 3 % with silica nanoparticles significantly improved CO2 regeneration capture at room temperature among the other cement paste samples. This study found that the presence of silica nanoparticles in cement paste triggered the formation of more hydrated phases, which served as active sites for CO2 capture to occur and, thus, improved the CO2 capture capacity and regeneration performance. ABSTRAK: Sebagai salah satu bahan tambahan yang berpotensi, nanozarah silika sangat reaktif dan cenderung bertindak balas dengan spesies kalsium (Ca2+) dalam simen di mana terhasilnya lebih banyak fasa terhidrat. Jumlah spesies kalsium yang tinggi dan berpotensi menangkap karbon dioksida (CO2) melalui pengkarbonan menunjukkan kesesuaian pes simen digunakan sebagai bahan penyerap CO2. Walau bagaimanapun, kajian adalah terhad terhadap kesan kemasukan nanozarah silika pada sifat tangkapan pes simen CO2 yang dikeraskan. Oleh itu, kajian ini adalah berkenaan kesan penggantian separa nanopartikel silika ke atas kapasiti tangkapan CO2 dan prestasi penjanaan semula pes simen yang dikeraskan. Analisis XRD dan SEM membuktikan pembentukan lebih banyak fasa terhidrat apabila penggantian separa nanopartikel silika pada simen. Penggantian separa nanopartikel silika 3% menunjukkan peningkatan ketara tangkapan penjanaan semula CO2 pada suhu bilik di antara sampel pes simen lain. Kajian ini mendapati bahawa kehadiran nanozarah silika dalam pes simen mencetuskan pembentukan lebih banyak fasa terhidrat yang berfungsi sebagai tapak aktif bagi penangkapan CO2 berlaku dan dengan ini, membawa kepada peningkatan kapasiti penangkapan CO2 dan prestasi penjanaan semula.

Green cementitious materials are usually developed by the addition of high volumes of mineral fillers. However, the addition of minerals can result in the reduction of mechanical strength. ECCs obtain their superior mechanical behavior from a high volume fraction of fibers. In ECCs, the matrix’s strength and the bond between the fibers and the matrix is a critical parameter, and if it becomes weak, the whole composite becomes weak or fibers may pull out of the matrix. In this study on green ECCs, to increase mechanical strength and also fiber/matrix bonding, the acrylic resin is used in 4 contents (e.g., 0, 2, 4, and 6 % in weight). The tests performed on ECC and plain cement paste (PCP) included tensile, compressive, and flexural. The results show that the acrylic increases the tensile strength, from about 2.0 MPa, up to 20 %, and compressive strength increased from about 88 MPa to 100 MPa. Due to the increase in ductility, the energy-based indexes increase more significantly. Acrylic resin optimum content was measured as 1.5–2.7 % (by weight). The trends show that acrylic resin is more effective for ECCs, because, in addition to enhancing the matrix strength, the resin increases the bonding strength between the matrix and fiber. Seeking the relationship between the results, nonlinear regression was used, and governing equations were presented. Also, using a regression model, the mechanical parameters were predicted successfully using input parameters.

Purposes The high-value utilization of coal gangue has attracted attention, and the activation and action of coal-bearing kaolin have great significance value for utilization of coal gangue. Methods The thermal activation parameters of kaolinite in coal gangue were optimized by orthogonal test, and the compressive strength and microstructure of paste consisting of cement and metakaolin formed under the optimal activation conditions were studied. Findings The experimental results show that the optimum thermal activation conditions of metakaolin are calcination temperature 800 ℃, holding time 2 h, and grinding fineness of 2.82 μm. Calcination temperature has the greatest influence on the activity of metakaolin, followed by grinding fineness and holding time. By using metakaolin instead of 20% (mass fraction) cement, the compressive strength of cement paste at all curing ages, especially in the early age, can be improved effectively. XRD and SEM test results show that the pozzolanic reaction of metakaolin consumes a lot of calcium hydroxide, and forms calcium silicate hydrate with lower calcium-silicon ratio and denses structure.

Introduction. The study addresses the effect of nanofibrillar cellulose (NFC) on the setting process of cement paste during the first hours of gauging. A brief justification of the research topic relevance is given. It has been noted that the modification of cement materials by nanoscale additives has sparked significant scientific and practical interest in recent years. NFC has emerged as one such additive, and the potential impacts of its incorporation into cement systems are currently under active investigation. The study aims at investigating the effect of NFC on the cement paste setting kinetics during the first hours of gauging. Materials and methods. We present the materials used in the research and their characteristics, in particular, two types of cement characterized by the presence or absence of false setting, as well as cement paste compositions with different NFC consumption (from 0 to 0.24% of dry matter by weight of cement). The technique of measuring conditional viscosity in time with a laboratory rheometer and a special measuring system is described. Results. The results of cement paste tests are presented in the form of setting process diagrams. Discussion. The results obtained and experimental data are given. The complex character of NFC influence on the cement paste setting kinetics has been noted, which depends on the cement quality and additive consumption. For cement without signs of false setting, a decrease in setting onset time was observed when increasing the NFC content. Conversely, increase in the amount of NFC leads to an increase in the setting onset time for cements with signs of false setting. Conclusion. NFC has a noticeable effect on cement paste setting kinetics in the first 3 hours: it accelerates the process when using cement without false setting and slows down the setting when using cement with false setting.

The beneficial effect of carbon nanotubes (CNTs) to enhance the electrical conductivity and piezoresistivity of cement-based materials was highly contingent upon its dispersion. To achieve an appropriate dispersion of CNTs, ultrasonication, high-speed stirring, and chemical dispersion were commonly used, which raises the risk of structural damage of CNTs caused by the excessive energy. In this study, electrostatic self-assembly of Fe3O4 nanoparticles on CNTs was employed to efficiently disperse CNTs. To optimize the dispersion effect of conductive fillers in cement paste, the mix proportions including sodium dodecyl sulfate (SDS) concentration, CNTs concentration, and Fe3O4/CNTs ratios were adjusted. The dispersion degree and electrical property were evaluated by UV–vis absorption and zeta potential. In addition, the effect of self-assembled conductive filler dosage on the electrically conductive property of cement pastes was examined. The results show that the occurrence of electrostatic self-assembly was proved by the change of zeta potential, and the grape-bunch structure was observed by transmission electron microscopy. Further, the optimal proportions of self-assembled conductive fillers were 0.20 wt% SDS concentration, 0.05 wt% CNTs concentration, and 1:1 Fe3O4/CNTs ratio. The self-assembled conductive filler dosage between 0.02 and 0.10 wt% can effectively improve the electrical conductivity of cement paste with up to 68% reduction of resistivity.

During construction at low temperatures, fresh concrete is susceptible to early freeze damage, which can permanently damage the concrete structure. Therefore, this study aimed to enhance the early-age strength and durability properties of the cement paste at −5 ℃ by incorporating calcium nitrite (CN) antifreeze and nano-silica (NS). First, the effects of CN and NS on the fresh properties of the cement paste were measured by setting time and bleeding rate tests. Subsequently, the mechanical properties and chloride content after salt solution erosion were tested for each group of specimens, and the change in slurry densification was further observed by ultrasonic pulse velocity and resistivity tests. Finally, the hydration products and microstructure of the specimens were analyzed using XRD and SEM tests. The results showed that the addition of CN and NS could reduce the setting time of cement paste and avoid the bleeding phenomenon of cement paste under negative temperature environment. The decrease in curing temperature and the use of NS both inhibited the promotion of C3A hydration by nitrite ions, which led to a decrease in nitrite-AFm content. However, NS can compensate for the reduced nitrite-AFm content by promoting the production of hydrated C-S-H through nucleation and pozzolanic effects. Ultimately, the strength and resistance of the slurry to chloride erosion are improved.

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. [ABSTRACT FROM AUTHOR]

Sisal fibers (SF) and polycarboxylate superplasticizers (PCE) contribute to the sustainable development of cementitious materials by improving and optimizing their hardening properties. In this study, the impact of SF and PCE on the workability of cement pastes was investigated. The workability was evaluated through spreading diameter, yield stress, and plastic viscosity measurements, and the adsorption behavior of PCE was analyzed. The results showed that the introduction of SF had a negative effect on the workability of PCE plasticized cement pastes, reducing flowability and increasing yield stress and plastic viscosity, regardless of aspect ratio or dosage. A contact angle tester and a scanning electron microscope (SEM) were employed to examine the surface properties of SF. The mechanism behind this interaction of cement-PCE-SF was explored and found to be due to the rough surface of SF, which increased the consumption of PCE, and the formation of hydrogen bonds between PCE and SF. Additionally, PCE modified the interfacial structure between SF and the cement matrix, strengthening the relationship between the different phases. These findings provide new insights into the modification of fiber-reinforced cementitious materials. This paper presents a comprehensive study on the workability and rheology behavior of cementitious material that coupled PCE superplasticizer and SF. The interaction between PCE and SF was experimentally studied by suitable tests, and the results and mechanism behind were well explained. The fresh properties were evaluated through a mini slump test, rheological properties, and the adsorption behavior of PCE on the surface of cement and SF was analyzed. The results showed that the introduction of SF decreases the spread diameter and increases the yield stress and plastic viscosity, regardless of aspect ratio and dosage, which indicate that a negative effect on the workability of PCE plasticized cement pastes. The mechanism behind the cement-PCE-SF interaction was explored in depth by the surface properties of SF, which revealed that the rough surface of SF increased the consumption of PCE. In addition, the formation of hydrogen bonds between PCE and SF provides an additional explanation. The significance of this study provides valuable guidance in using fibers and PCE together in cementitious materials. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In order to study the effect of interfacial agent on the bonding properties of wet joints, the optimal dosage of silica fume in the interfacial agent of silica fume cement paste was determined through mechanical property test. Then, the splitting tensile strength test, three-point bending test and shear strength test were conducted to explore the use of ordinary cement paste, cement paste with optimal dosage of silica fume and epoxy resin as interfacial agent. Effect on bonding properties of wet joints. The results show that the mechanical properties of the cement paste are the best when the optimal content of silica fume is 8% . The effects of different interfacial agents on the bonding properties of wet joints are analyzed from the tensile and shear angles, and the order from the largest to the smallest is: epoxy resin interfacial agent > 8% silica fume cement interfacial agent > ordinary cement interfacial agent > no interfacial agent. It is concluded that the interface agent of ordinary cement paste has little improvement on the bonding property of wet joints, while the interface agent of epoxy resin and 8% silica cement paste has obvious improvement on the bonding property of wet joints. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The present study examined the effects of colloidal nanosilica on the performance of cement paste samples exposed to nitric acid for a continuous period of 28 days. Compressive strength and weight losses in paste samples as a result of this attack were determined to be 66% and 27%. The inclusion of nanosilica up to 6% by weight reduced these sample losses by densifying the microstructure with its pore filling and pozzolanic effects. The addition of nanosilica decreased the flow of cement paste by 30%, but improved compressive and flexural strengths at the end of 28 days by up to 45% and 118%. The acid attack on the cement sample resulted in the formation of a degraded layer surrounding the unaltered core material. X‐ray tomography images showed this zone formation, and the scanning electron microscopy images revealed the degraded microstructure. The results of the x‐ray diffraction and nanoindentation tests confirmed the complete decalcification of the main cement hydrates, including calcium silicate hydrate and portlandite, as a result of acid attack. The results obtained suggest that the incorporation of nanosilica strengthens the microstructure of the cement matrix, thus improving the service life of structural concrete operating in chemical environments. [ABSTRACT FROM AUTHOR]

The ultrasonic pitch–catch method was used to study the hydration behaviour of Portland cement paste with sodium gluconate (SG) additive using a tailor-made piezoelectric transducer. X-ray diffraction analysis showed that the intensity of the diffraction peak of calcium hydroxide decreased with increasing SG content (CSG), especially for CSG > 0.10 wt%. The compressive strength of the hardening cement pastes decreased remarkably for the pastes with CSG > 0.05 wt%. Ultrasonic waveforms appeared after 2 h of hydration and the waveform amplitudes of cement pastes with SG contents of 0.15 wt% and 0.20 wt% were obviously larger than those of cement pastes with CSG = 0.05 wt% in the early hydration stage. The hydration process of the cement paste over 300 h was classified into three stages based on the head wave amplitude variation – the fluctuation period, the rapidly increasing period and the smoothly increasing period. The acoustic propagation time changed greatly with hydration before a hydration age of 48 h, indicating that the hydration and hardening process of the cement paste was intense in the first 48 h. The proposed ultrasonic monitoring method opens a new perspective for studying the hydration behaviour of SG-blended cement paste. [ABSTRACT FROM AUTHOR]

Fused cement clinker can be produced from molten basic oxygen furnace slag (BOFS) by way of a reductive thermochemical treatment. During the thermochemical treatment, oxidic iron is reduced to metallic iron and separated. The resulting low-iron slag has a chemical and mineralogical composition similar to ordinary Portland cement (OPC) clinker. In this study, the hydraulic reactivity of the fused clinker from BOFS with and without gypsum was investigated using isothermal calorimetry, differential scanning calorimetry, in situ X-ray diffraction and powder X-ray diffraction. Furthermore, a synthetic fused clinker without foreign ions and fused clinker produced by a mixture of both materials was studied. The hydraulic reaction of the fused clinker from BOFS was considerably slower than that of OPC. However, the reaction can be accelerated by adding gypsum as a sulfate carrier. Furthermore, the results showed an increased reaction rate with decreasing content of foreign ions such as Fe, P or Mn. [ABSTRACT FROM AUTHOR]

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 k Ω , almost four times lower than the reference specimens. In the realm of piezoelectricity, the piezoelectric voltage parameter g 33 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. [ABSTRACT FROM AUTHOR]

Sargassum muticum, a Japanese brown seaweed, has recently invaded various shorelines throughout the world, including the Atlantic coast of Morocco, where it has developed significant populations. We report on the use of these algae as a partial replacement of Portland cement in cement paste as part of a long-term plan to combat this invasive seaweed. With a fixed water to cement ratio (W/C = 0.45), algae powder is added at 5%, 10%, 15% and 20% from the cement content in producing cement pastes. The hydration process was assessed using impedance spectroscopy throughout the setting period from 10 min to 28 days. Compressive strength tests were performed at 7, 14 and 28 days. An equivalent circuit model has been proposed. The results showed that the various strength properties of the cement paste increased or decreased with addition of algae powder. The compressive strength tends to increase with the addition of algae powder. This study shows that 10% addition of algae powder to cement paste showed an increase in compressive strength and when the addition increased to 20% the properties started to decrease. [ABSTRACT FROM AUTHOR]

With more infrastructures being built in high-altitude regions, the impact of low atmospheric pressure on the stability of air bubbles in cementitious materials has aroused extensive attention. However, its influence is still inconclusive since it is difficult to isolate the factor of air pressure and study it. To solve this problem, the study investigated the bubble dynamic evolution in cement paste at standard atmospheric pressure (P = 0.1 MPa) and low atmospheric pressure (LAP = 0.8P, 0.6P, 0.4P, 0.2P) and revealed the mechanism of bubble instability under low atmospheric pressure. We established the bubble dynamic evolution equation in cement paste, computed the real-time bubble radius, resultant force, and critical time at different air pressure by MATLAB software. Results show that the maximum resultant force decreases by 50.0–57.7% when air pressure drops from P to 0.2P; both critical time (t ) and radius increment ( Δ R ) increase with the reduction of air pressure and the increase of initial radius. It indicates that when at 0.2P, the resultant force which inhibits bubble expansion is reduced, the time required to prevent bubble expansion increases by 94–137%, and Δ R grows 122–140% larger than that at P, and the bubble is more prone to instability and rupture than that at P. The key to improving bubble stability in low atmospheric pressure is to reduce the initial radius of bubbles and increase the strength of the bubble film. This work firstly discovered the impact of low atmospheric pressure on bubble dynamic evolution in cement paste and proposed a new perspective to explore bubble stability at low atmospheric pressure. [ABSTRACT FROM AUTHOR]