Mechanical Properties Of Cement Paste Research Articles

Study of the Structure and Properties of Concrete Modified with Nanofibrils and Nanospheres

The application of modifying nanoadditives in the technology of cement composites is currently a relevant and widely researched topic in global materials science. The purpose of this study was to investigate new nanoadditives—nanofibrils made from synthesized wollastonite (NF) and nanospheres from corundum (NS)—produced by LLC NPK Nanosystems (Rostov-on-Don, Russia) as a modifying additive. During the experimental investigations, the mechanical properties of cement pastes and concrete were examined. This included an analysis of the density, compressive and bending strength, as well as water absorption of concrete that had been modified with NF and NS additives. X-ray phase and microstructural analyses of concrete were performed. It was established that modification of cement composites with NF and NS additives had a beneficial effect on their properties, and the optimal amount for both types of additives was 0.3% by binder weight. The highest recorded enhancements in compressive and flexural strength of concrete with 0.3% NF were 7.22% and 7.04%, respectively, accompanied by a decrease in water absorption by 4.70%. When modifying concrete with 0.3% NS, the increases in compressive and flexural strength were 2.71% and 2.48%, and water absorption decreased by 1.96%. Modification of concrete with NF and NS additives did not have a significant effect on the change in concrete density, which was no more than 1%. Based on the results of phase analysis, it was established that concrete with NF and NS additives were characterized by the presence of five main phases: quartz, portlandite, calcite, larnite, and olivine-Ca. It was found that compositions with 0.3% NF and NS differed from the control composition by the presence of such a phase as olivine-Ca. Microstructural analysis confirmed the effectiveness of NF and NS additives. The microstructure of the modified concretes was distinguished by the extensive occurrence of clusters composed of calcium silicate hydrate zones. The conducted studies prove the possibility of using NF and NS as modifying nanoadditives in the technology of cement composites. The addition of nanofibrils from synthesized wollastonite is the most effective and promising and is recommended for use in real construction practice.

Study on the Modification Mechanism of Soap-Free Latex on the Microstructure and Mechanical Properties of Cement Paste

Abstract In view of problems such as the decline in strength of cement paste and latex exudation caused by the addition of conventional latex, JAS soap-free latex (JAS latex) was prepared by soap-free emulsion polymerization technology. JAS latex had the characteristics of low viscosity, uniform particle size, good dispersity of particles, and good compatibility with cement admixtures. JAS latex had little impact on the fluidity of oil-well cement paste. The free liquid of the cement paste with 10 % JAS latex was 0 %, and its liquid-loss content was 43 mL. When the JAS cement paste was cured at 90°C, its compressive strength was 34.08 MPa. When the curing temperature was 70°C, the bond strength between the paste and metal casing reached 4.95 MPa. Combining the results tested by X-ray diffraction, scanning electron microscopy, and atomic force microscopy showed that JAS latex did not affect the hydration process of oil-well cement, had good film-forming ability in cement paste, and improved the density and impact resistance of the cement paste. It is helpful to improve the sealing integrity and sealing ability of cement sheath in cementing engineering and ensure the safe and efficient development of oil and natural gas resources.

Effect of Different Concentration of CO2 Gas Injected into Fresh Cement Paste Along with the Addition of Superplasticizer on the Mechanical Properties of Cement

This paper focused on examining the impact of injecting varying concentrations of carbon dioxide (CO2) gas on the mechanical characteristics of both the fresh and hardened states of cement paste. This study also considered the influence of the presence or absence of polycarboxylate superplasticizer in cement mixture on these properties. Many researchers discovered the benefit of CO2 gas utilization in cement mixture to accelerate the early strength of cement or concrete hydration by its carbonation that form calcium carbonate (CaCO3). The application method is to directly inject CO2 gas in a curing chamber for air-curing of precast concrete. Alternatively, carbonated water is mixed with cement during concrete mixing. However, the use of CO2 gas does not significantly improve the 28-day strength of concrete. This study explores how to improve the carbonation impact on mechanical properties of cement paste and apply it to ground improvement. In this study, the method adopted is direct injection of CO2 gas during cement slurry mixing with different injection duration. The influence of CO2 in the presence of superplasticizer (SP) in cement slurry was also studied as SP is generally used for grouting. The results showed that the carbonation of cement paste with additional of superplasticizer significantly affect its flow, viscosity and bleeding properties. Unlike samples with SP addition, the samples without SP addition showed higher compressive strength after 28 days of curing up to certain CO2 injection time. For all CO2 gas injection time, smaller porosity rates were observed for 7-day cured samples with SP addition compared to those without SP addition. This is due to accelerated carbonation due to SP presence in cement mixture. From the results, the optimum of CO2 gas injection time for one liter mixture of cement paste to improve its compressive strength (up to 123% increase) have been discovered. It can be inferred that the addition of superplasticizer in cement slurry reduces the amount of CO32- ions and Ca2+ ions during carbonation process of cement hydration products, which are strongly related to the pH level in pore solution. These ions play a significant roles in determining the mechanical properties of cement slurry.

The adaptability of polycarboxylate superplasticizer in alkaline electrolyzed water (AEW)-based cement composites containing clay: Workability and mechanical properties

Improving the adaptability of polycarboxylate superplasticizers (PCE) in high-clay content mortar is of great significance in enhancing the workability and mechanical properties of mortar containing clay. In this study, the potassium-based alkaline electrolyzed water (AEW) was used as mixing water for cement mortar. The excellent properties of AEW enabled PCE to be more compatible in cement mortar containing montmorillonite (MT) or kaolin (GL), improving the performance of mortar containing clay. The results showed that compared with ordinary tap water (OTW), the adsorption rate of clay minerals on PCE decreased in the AEW environment, and the clay interlayer spacing of MT was also reduced. AEW can inhibit the intercalation and adsorption of PCE molecular side chains by clay minerals to some extent. However, due to its unique crystal structure, the adsorption of MT on PCE was still significantly higher than that of GL. At the same time, increasing the content of clay mineral led to a decrease in mortar performance. Compared with the GL series, the MT series had a more significant negative impact on mortar fluidity and strengths. AEW also can promote hydration reactions, release more hydration heat, and produce more hydration products to encapsulate clay particles, thereby improving the workability and mechanical properties of cement paste containing clay. Furthermore, the high-activity AEW is rich in positively charged metal ions that can interact with clay minerals preferentially over cement particles, which enables the clay interlayer structure to be quickly saturated by AEW water molecules, effectively hindering the adsorption of PCE by clay minerals. However, in both the OTW and AEW environments, the intercalation effect of GL on PCE molecular side chains was not significant. Therefore, AEW has great potential in improving the adaptability of PCE in muddy cement pastes, which can help to enhance the workability and mechanical properties of muddy cement composites. This study provides theoretical references for preparing high-performance anti-clay concrete.

The influence of graphene oxide on the hydration and mechanical properties of cement-based materials with low water-binder ratio

Graphene oxide (GO) has been used as a functional material in cement-based materials. Most of current research suggests that GO effectively enhance the mechanical properties of cement paste with high water-to-binder (w/b) ratios (0.30–0.50). However, due to the high cost of GO, its use in ordinary concrete materials with high w/b ratios is limited. It has shown promising potential for reinforcement in ultra-high performance cement-based materials with low w/b ratios, such as UHPC. Nevertheless, existing studies have paid limited attention to the effects of GO in cement-based materials with low w/b ratio. This study selected cement-based materials with a w/b ratio of 0.17 as a representative example to investigate the changes in the mechanical properties of hardened cement paste after the addition of GO under different curing conditions. Additionally, by combining the results of microstructural analysis of hydration products, the study explored the mechanism by which GO affects the mechanical properties of cement-based materials with low w/b ratios. The research findings indicate that though an appropriate dosage of GO enhances the compressive strength of cement-based materials with low w/b ratios, it significantly reduces their flexural strength. In addition, GO accelerates the dissolution process of Ca2+ in the early stages, enhancing the degree of cement hydration and increasing the thickness of inner hydration products (IP). This action leads to an increase in the calcium-to-silicate (Ca/Si) ratio and a weakening of the microstructure in outer hydration products (OP). Resultantly, these changes lead to the refinement of small pores and the coarsening of large pores within the hardened cement-based material, collectively manifesting as an improvement in compressive strength and a reduction in flexural strength of the cement paste.

Development of a universal atomistic cement model incorporating nanomaterials: From laboratory investigation to molecular simulation

Hydrated cement is considered one of the most complex binder systems. The development of models that suitably represent hydrated cement is still far from established due to the complexity of the hydration process, as well as the multiscale phase and different morphological properties. Therefore, this study attempts to develop a hydrated cement model using molecular-level simulation and laboratory testing. This model aimed to predict the mechanical properties of cement paste between 0.25 and 0.65 w/c ratios. In this regard, five cement paste mixtures with various w/c ratios were prepared and tested to evaluate their mechanical properties and micro-structures. Then, a novel modeling methodology using molecular dynamics (MD) simulation was carried out to develop an ingredient-based atomistic cement model. In this regard, the Dreiding force field (DFF) was used in all the simulation processes, starting from the cement clinker phases to the hydrated cement. The experimental results of cement paste mixtures revealed some useful data that was supportive of the simulations. Radial distribution function (RDF) and fractional free volume (FFV) were utilized to investigate the local atomic structure of the cement paste models. The calcium-silicate-hydrated (C–S–H) of the developed model was characterized through RDF and benchmarked to a well-known mineral analog, namely tobermorite. The developed model was computationally tested under different w/c ratios, and reliable results in terms of micro-structural matrix as well as mechanical properties were obtained. Then, the cement models incorporating different ratios of nano-silica were developed, and a good estimation of the mechanical properties was obtained. Because of the universal nature of the reported model in this research, it could be utilized to further predict the mechanical behavior and durability performance of the cement paste.

The influence of multi-scale tough liquid fiber toughening agent on the mechanical properties of oil well cement-based composite materials

Cementing is a key process in drilling engineering, and the cement sheath in cementing can sometime have problems such as significant brittleness, low toughness, and low resistance to impact damage, especially in perforation and fracturing environments where the cement sheath is more susceptible to damage. In response to the above issues, three types of inorganic carbon fibers, including 1 mm carbon fiber, 2 mm carbon fiber, and nanocarbon fiber, were studied indoors to investigate the influence of their ratios on the mechanical properties of cement paste. The optimal mixture of 1 mm carbon fiber, 2 mm carbon fiber, and nanocarbon fiber in a ratio of 3:2:1 was selected, and a multi-scale liquid fiber toughening agent BS-54 was obtained through special liquefaction process treatment. The liquid fiber toughening agent BS-54 has good water dispersibility and can evenly disperse in the slurry water, effectively improving the dispersion and addition of multi-scale fibers in cement slurry. The cement slurry prepared with multi-scale dispersed liquid fiber toughening agent has good rheological properties, water loss, and thickening properties. The addition of multi-scale dispersed liquid fiber toughening agent to cement slurry significantly increases the tensile strength, impact strength, and compressive strength of cement paste, effectively reduces the elastic modulus of cement paste, improves the strength of cement paste, and achieves toughening effect. Microscopic analysis shows that the active nanoparticles dispersed by multi-scale dispersed liquid fiber toughening agents can interweave between gaps, and the dense cross-linked structure formed by their multi-scale micro nano structure improves the toughness and strength of cement slurry. Moreover, the multi-scale dispersed liquid fiber toughening agent cement slurry ensures that the cement stone sample has good integrity under external impact, which is conducive to improving the impact resistance of the cement stone.

Circular Economy Approach: Recycling Toner Waste in Cement-Based Construction Materials

Based on a waste generated survey by companies in the area of the city of Bahia Blanca (Argentina), the possibility of incorporating part of them in a Portland cement matrix was examined. Among the waste is toner (TW), which is obtained from cartridges used in photocopiers, laser printers, and faxes. This paper aims to analyze the physical and mechanical properties of cement pastes and mortars using toner as a Portland cement replacement compared to a reference sample without toner. The mixes were made with 2.5, 5, 10, and 15 wt.% replacement of cement by toner, and it was measured the flow, normal consistency, setting time, calorimetry, and Frattini test in pastes and mechanical strengths in mortars employing standardized tests. Also, an analysis of the leachate in the curing water was carried out after 56 days to look for contaminating materials. The replacement of up to 5% cement with toner did not produce substantial alterations in the final setting time or mechanical properties. No heavy metals were found in the leachate, so TW can be immobilized in a cementitious matrix as it does not cause leaching above the established limits. Therefore, TW from a local industry can be used in construction materials and could contribute to a reduction of up to 14% of CO2 emissions with a cement replacement of 15% in cement-based materials.

Mechanical properties of cement pastes containing plasma-treated silicon-based materials

The study delves into the impact of waste silicon-based materials on the mechanical characteristics of the resulting cement pastes. The investigation uses Portland cement CEM I 42.5R in conjunction with silicon-based waste materials sourced from the packaging industry, specifically from Recifa, a.s. Variations between the sample groups arise from differences in the concentration of silicon-based materials and the method of surface treatment. The inquiry seeks to assess the effects of two distinct levels of Si-based material incorporation, namely 10 wt. % and 20 wt. %, along with plasma treatment involving two different gases: oxygen (O2) and hydrogen (H2). The mechanical attributes under scrutiny encompass compressive and flexural strengths. The evaluation of mechanical properties is carried out on samples aged 28 days, with dimensions measuring 20 × 20 × 100 mm.

Nondestructive testing on concrete-based treated wastewater

Recycled wastewater in construction presents an opportunity to ease freshwater scarcity while advancing sustainability. This study investigated the influences of cement-type and treated wastewater source on setting time and mechanical properties of cement paste and mortar. Three cement types: ordinary Portland cement (CEM I), CEM III/A, and CEM IV/A-P, were encountered. Four plants treated wastewater versus potable water as control were included. Fifteen mixes were encountered; every 5 mixes addressed certain cement types along with specified treated water types. Two phases were designed: Phase I for pastes toe value setting time and Phase II for the mortar to evaluate the flexural and compressive strengths of tool 90 specimens, 6 at 2 and 28 days of age. The significant impact of both variables was observed. CEM III/A displayed the fastest setting among the other mixes, while CEM I was the slowest. Wastewater accelerated setting versus distilled water. The mechanical performance also varied based on the cement–wastewater combination. CEM IV/A-P provided optimal strength enhancement up to 50% in flexural and 35% in compressive strength with wastewater compared to CEM I control. Results were attributed to cement–water interactions influencing hydration and microstructure, while CEM I underperformed with wastewater, CEM III/A, and CEM IV/A-P benefits, especially at early ages. Considerable variability highlights the complex interplay of factors governing performance. Coupled chemical-microstructural analysis was recommended to elucidate underlying mechanisms. Overall, tailored cement–wastewater selection shows promise for sustainable concrete, pending further optimization and durability testing. The study provides a platform for context-specific development of eco-efficient construction materials utilizing locally available resources.

Volume Stability and Mechanical Properties of Cement Paste Containing Natural Fibers from Phragmites-Australis Plant at Elevated Temperature

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.

Exploring the different stages of treated wastewater on various cement types

Recycled wastewater in construction presents an opportunity to ease freshwater scarcity while advancing sustainability. This study investigated the influences of cement type and treated wastewater source on setting time and mechanical properties of cement paste and mortar. Three cement types, ordinary Portland cement (CEM I), CEM III/A, and CEM IV/A-P, were encountered. Four plants treated wastewater versus potable water as control. Fifteen mixes were encountered; every 5 mixes addressed certain cement types along with specified treated water types. Two phases were designed; Phase I evaluated setting time in pastes and Phase II evaluated the flexural and compressive strengths of mortar specimens at 2 and 28 days of age. The significant impact of both variables was observed. CEM III/A displayed the fastest setting among the other mixes, while CEM I was the slowest. Wastewater accelerated setting versus distilled water. The mechanical performance also varied based on the cement–wastewater combination. CEM IV/A-P provided optimal strength enhancement up to 50% in flexural and 35% in compressive strength with wastewater compared to CEM I control. Results were attributed to cement–water interactions influencing hydration and microstructure. While CEM I achieved low mechanical strength with wastewater; CEM III/A, and CEM IV/A-P benefits, especially at early ages. Considerable variability highlights the complex interplay of factors governing performance. Coupled chemical-microstructural analysis was recommended to elucidate underlying mechanisms. Overall, tailored cement–wastewater selection shows promise for sustainable concrete, pending further optimization and durability testing. The study provides a platform for context-specific development of eco-efficient construction materials utilizing locally available resources.

Dielectric and mechanical properties of cement pastes incorporated with magnetically aligned reduced graphene oxide

Magnetic nanocomposites were fabricated by attaching surface-modified magnetite nanoparticles to the surface of reduced graphene oxide (rGO) in this study. By applying an external magnetic field, the rGO were highly aligned in the cement paste. The orientation factor of aligned rGO was found to be 0.71 by analyzing the polarized Raman scattering spectra. The alignment of the rGO contributed to both the mechanical and dielectric properties of the cement paste. The flexural strength of the specimen with aligned rGO improved by 48% compared with that of the cement pastes with randomly distributed rGO. The dielectric constant at 100 Hz of the specimen with aligned rGO was increased by 271% compared with that of cement pastes with randomly distributed rGO. A modified rule of mixtures was proposed to predict their mechanical and dielectric properties. This study offers insight on the development of nanofiller-incorporated cement-based materials with enhanced mechanical and dielectric properties.

Effect of plant-based natural fibers on the mechanical properties and volume change of cement paste

PurposeThe purpose of this paper is to check the feasibility of using biomaterial such as of Phragmites-Australis (PA) in cement paste to achieve sustainable building materials.Design/methodology/approachIn this study, cement pastes were prepared by adding locally produced PA fibers in four different volumes: 0%, 0.5%, 1% and 2% for a duration of 180 days. Bottles and prisms were subjected to chemical shrinkage (CS), drying shrinkage (DS), autogenous shrinkage (AS) and expansion tests. Besides, prism specimens were tested for flexural strength and compressive strength. Furthermore, a mathematical model was proposed to determine the variation length change as function of time.FindingsThe experimental findings showed that the mechanical properties of cement paste were significantly improved by the addition of 1% PA fiber compared to other PA mixes. The effect of increasing the % of PA fibers reduces the CS, AS, DS and expansion of cement paste. For example, the addition of 2% PA fibers reduces the CS, expansion, AS and DS at 180 days by 36%, 20%, 13% and 10%, respectively compared to the control mix. The proposed nonlinear model fit to the experimental data is appropriate with R2 values above 0.92. There seems to be a strong positive linear correlation between CS and AS/DS with R2 above 0.95. However, there exists a negative linear correlation between CS and expansion.Research limitations/implicationsThe PA used in this study was obtained from one specific location. This can exhibit a limitation as soil type may affect PA properties. Also, one method was used to treat the PA fibers.Practical implicationsThe utilization of PA fibers in paste may well reduce the formation of cracks and limit its propagation, thus using a biomaterial such as PA in cementitious systems can be an environmentally friendly option as it will make good use of the waste generated and enhance local employment, thereby contributing toward sustainable development.Originality/valueTo the authors best knowledge, there is hardly any research on the effect of PA on the volume stability of cement paste. Therefore, the research outputs are considered to be original.

Converting sintering red mud to valuable calcium carbonate whiskers via an innovative magnesium-modified wet carbonation

Sintering red mud (SRM) is an industrial alkaline waste residue generated from the sintering process in alumina production, which is often directly discarded and causes environmental issues. In this study, an innovative magnesium-modified wet carbonation method was proposed to convert sintering red mud to valuable calcium carbonate whiskers using CO2-containing flue gas. The effects of carbonation conditions including temperature, MgCl2 concentration, and duration on the composition, microstructure, and morphology of carbonated products were systematically investigated. It was found that a high whisker content of 60% with an aspect ratio of ∼6 could be obtained under the optimal conditions of 80 °C, 0.4 M MgCl2, and 2 h reaction time. Besides the formation of whiskers, amorphous aluminosilicate gel was also generated during SRM carbonation. The effects of the as-prepared whisker-rich materials as partial cement replacement on the mechanical properties of cement paste were evaluated with 5 wt% replacement, the 28 d compressive strength was significantly improved by 20.5% compared to the control specimen. The effective reinforcement was ascribed to the fibrous whiskers and enhanced interfacial bonding. This method enables high-value utilization of SRM waste and CO2 fixation, providing a green and low-cost approach to producing high-performance cementitious materials.

Effect of using heavy chemical additives on the mechanical properties of cement pastes, radiation exposure and the corrosion behavior of reinforced steel upon exposure to sea water

The current study aims to explore the impact of lead oxide and lead phosphate on the attenuation coefficient of concrete used as radiation shielding in nuclear facilities, the physico-mechanical properties of cement pastes, and the corrosion behavior of reinforced steel when exposed to seawater. The mixtures were prepared upon partial replacement of Portland cement with lead oxide and lead phosphate at levels ranging from 0.1% to 0.5%, by mass. The physico-mechanical properties of cement pastes were examined. Gamma transmission parameters were measured, as was the effective removal-cross-section (ΣR) of fast neutron spectra, while the corrosion behavior of embedded steel reinforcement upon exposure to sea water was measured. Results indicated that In comparison to the reference OPC sample at early ages, the compressive strength value of the hardened cement pastes decreases with increasing lead oxide and lead phosphate content. but at 28 and 90 days, the hardened cement paste's compressive strength values increase as lead oxide and lead phosphate levels rise by up to 0.2% and are on par with or higher than those of the OPC control. Results demonstrated that the acceptable amount of lead oxide and lead phosphate in cement pastes is 0.2% wt. of the total cement content without affecting the mechanical properties of cement pastes. The initial and final setting times of cement pastes increase with increasing lead oxide and lead phosphate content. The concrete mixes containing 0.2% of lead oxide and lead phosphate enhances the attenuation properties for gamma rays and fast neutrons than the control mix. It has been observed that lead phosphates have dual effect on reinforced concrete represented in improving the compressive strength, besides, acting as anodic passivation supporting the passivation of steel reinforcement and suppressing the corrosion that could ensue due to penetrating aggressive ions.

Thermal performance and mechanical properties of phase change cement paste with Nano-SiO2 grafted straw-paraffin

In paraffin-based phase change concrete, rice straw can be used as the carrier for paraffin, however, the compatibility between rice straw and cement matrix is poor. In this study, Nano-SiO2 was grafted on straw-paraffin to improve the interfacial compatibility, and its influences on thermal performance and mechanical properties of phase change cement paste were investigated. Firstly, the phase change potential heat and tensile property of Nano-SiO2 grafted straw-paraffin were tested. Then, the thermal performance and mechanical properties of cement paste with Nano-SiO2 grafted straw-paraffin were tested. The results indicate that: (1) The melting temperature of Nano-SiO2 grafted straw-paraffin (PRS-1%) is 51.15℃, 0.39% lower than paraffin-straw without Nano-SiO2(PR), the enthalpy value is 85.64 J/g, 8.74% higher than PR. (2) The tensile strength of PRS-1% is 38.63 MPa, which is 18.63% higher than PR. After 100 phase change cycles, its tensile strength is 23.98% higher than PR. (3) The Nano-SiO2 grafting can reduce the volume of pores and cracks at straw-paste interface, decrease the content of Ca(OH)2 and increase the content of C-S-H gel at the interface. (4) Compared with cement paste with PR, the compressive strength and flexural strength of cement paste with PRS-1% increase by 21.05% and 16.55%, respectively. (5) The Nano-SiO2 grafting (1%) can increase the specific heat capacity and thermal conductivity of straw-paraffin based phase change cement paste by 2.24% and 9.64%, respectively.

Research on the strength prediction for pervious concrete based on design porosity and water-to-cement ratio

Abstract The strength prediction of pervious concrete is hard to implement for the mix design due to the porous structure. This work studied the influence of the water-to-cement ratio on the fluidity, viscosity, and mechanical properties of cement paste. Then, the porosity, permeability, and compressive strength of the pervious concrete with various porosities were investigated, and the test results were fitted and analyzed. The result indicates that as the water-to-cement ratio increases, the viscosity of the cement paste reduces and the fluidity increases. The water-to-cement ratio has a negative linear relationship with net slurry strength. The porosity and permeability of pervious concrete fluctuate in accordance with the same rule as the water-to-cement ratio changes. The compressive strength of pervious concrete with varying design porosities increases initially, then declines as the water-to-cement ratio rises. According to the linear fitting analysis, when the water-to-cement ratio is constant, the permeability and compressive strength of pervious concrete have a positive and negative linear relationship with the design porosity, respectively. By analyzing the fitting results and combining the volume method of pervious concrete, a calculation method for mix proportion design is proposed to predict the strength of pervious concrete.

Synergistic enhancement of the mechanical properties of cement-based materials by using microcrystalline cellulose and nano-silica composites

The flexural strength and compressive strength are the two most important parameters that characterize the mechanical properties of cement-based materials, but the two are usually mutually exclusive or negatively correlated. The flexural strength of cement-based materials cannot be effectively improved by a single nanomaterial without reducing their compressive properties. Therefore, compounding various micro–nano materials, fully utilizing their respective advantages, and developing composite materials with new properties and application characteristics are important techniques for enhancing the mechanical properties of cement-based materials. This study aimed to investigate the synergistic enhancement of the mechanical properties of concrete by using microcrystalline cellulose (MCC) and nano-silica (NS) composites. MCC and NS were mixed and modified to synthesize MCCNS materials, which were added to cement slurry for experiments. Results indicated that the flexural strength and compressive strength of the cement paste with MCCNS materials were significantly increased compared with those of the cement pastes without MCCNS or with only NS. The flexural strength of the cement paste with MCCNS-1 was increased by 47%, 20%, 6.3%, and 6.8% after curing for 1, 7, 28, and 56 days, respectively. Meanwhile, compressive strength was also increased by 14.4%, 6.3%, 6.8% and 6.5%, respectively. In addition, the reaction mechanism was speculated through a variety of test results. The addition of MCCNS material facilitated the formation of additional C-S-H, which also contributed to enhancing the mechanical properties of cement paste.

Investigation on the compositional and performance evolution of cement paste subjected to Xenon radiation

This study addresses the critical question of how Xenon radiation, simulating natural solar radiation, affects the compositional, structural, and mechanical properties of cement paste. This aim is to understand the micro-to macro-scale changes in cement paste subjected to such radiation, a key concern for the durability of construction materials in solar-intensive environments. Employing a comprehensive suite of analytical techniques, including XRD, TG, 29Si NMR, 1H NMR, CT, SEM, and Vickers hardness testing, we systematically analyze the changes in phase composition, bound water content, silicate chain length in C–S–H, microstructure, and micro-mechanical behavior before and after radiation exposure. Our research uncovers a substantial decomposition of ettringite and a discernible reduction in the bound water content within the cement paste post-radiation exposure. Crucially, we detected a significant elongation in the C–S–H chain length, with a peak increase observed at 6%. This elongation is coupled with an increase in pore coarseness and a proliferation of internal defects. These alterations collectively lead to a marked decrease in the material's mechanical strengths: we noted a reduction in flexural strength by up to 18% and in compressive strength by as much as 25% at the macroscopic level. This research thus provides essential insights into the design and development of high-durability cementitious materials for solar radiation-intensive environments, contributing to the advancement of sustainable and resilient infrastructure.