Mechanical Properties Of Cement Paste Research Articles

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.

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.

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.

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.

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.

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.

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.

The Effect of Different Biochar on the Mechanical Properties of Cement-Pastes and Mortars

In recent years, there has been a concerning surge in CO2 emissions, with the construction and materials production sectors standing out as significant contributors to greenhouse gas pollution. To tackle this pressing environmental challenge, architectural design and civil engineering are actively pursuing strategies to mitigate their carbon footprint. These initiatives include adopting eco-friendly construction materials with reduced toxicity, rigorous energy management practices across the entire life cycle of structures, and incorporating innovative materials like biochar. Biochar is a carbon-rich byproduct generated through controlled thermochemical processes, such as pyrolysis or gasification, that stands out for its remarkable capacity to extract energy from processed biomass while delivering substantial environmental advantages. This study examines the use of biochar as a filler in cement-paste and mortar, as well as its influence on mechanical properties. In the case of cementitious pastes, results show that small amounts of biochar (1-2-5% by weight of cement) can improve the compressive and flexural strength, as well as fracture energy, thus generating a more tortuous crack path that increases the final surface area. In mortar specimens, the biochar influence does not show similar patterns or characteristics as the cement-paste in flexural and compressive strengths; nevertheless, biochar particles improve the toughness.

Effect of CO2 Curing on Mechanical Properties of Cement PastesEffect of CO2 Curing on Mechanical Properties of Cement Pastes

Erken yaşta CO2 kürü, çimento hidratasyon ürünlerinin oluşumunu etkileyerek çimento bağlayıcılı malzemelerin mekanik özeliklerini değiştirebilmektedir. Farklı su/çimento (s/ç) oranlarında (%28 ve %32) çimento hamurları hazırlandıktan sonra 4 farklı şekilde CO2 kürü uygulanmıştır. Çimento hamurlarının karıştırma işlemi bittikten 15 dk sonra numunelere 15, 30 ve 60 dk CO2 kürü (1, 3, 5, 8 ve 10 bar) uygulanmıştır. Aynı zamanda numunelerin bir kısmına da priz başladıktan sonra (117 dk) 30 dk CO2 kürü (1, 3, 5, 8, 10 ve 50 bar) uygulanmıştır. Çimento hamurlarının 7 günlük basınç dayanımları incelenmiştir. En yüksek basınç dayanımı (112.73 MPa) 15 dk ön bekleme yapılmış ve 60 dk süresince 3 bar CO2 kürü uygulanmış KK %28 kodlu numunede elde edilmiştir. Kontrol numunelerinde s/ç oranı arttığında basınç dayanımındaki azalma %27 iken, 15 dk ön beklemeden sonra 60 dk CO2 kürü uygulanan numunelerdeki bu azalma oranı %53’dür. Dayanım artışı açısından genel olarak çimento hamuruna uygulanan en uygun kür işlemi 15 dk ön bekleme sonunda 60 dk 3 bar CO2 kürüdür.Erken yaşta CO2 kürü, çimento hidratasyon ürünlerinin oluşumunu etkileyerek çimento bağlayıcılı 
 malzemelerin mekanik özeliklerini değiştirebilmektedir. Farklı su/çimento (s/ç) oranlarında (%28 ve 
 %32) çimento hamurları hazırlandıktan sonra 4 farklı şekilde CO2 kürü uygulanmıştır. Çimento 
 hamurlarının karıştırma işlemi bittikten 15 dk sonra numunelere 15, 30 ve 60 dk CO2 kürü (1, 3, 5, 8 ve 
 10 bar) uygulanmıştır. Aynı zamanda numunelerin bir kısmına da priz başladıktan sonra (117 dk) 30 dk 
 CO2 kürü (1, 3, 5, 8, 10 ve 50 bar) uygulanmıştır. Çimento hamurlarının 7 günlük basınç dayanımları 
 incelenmiştir. En yüksek basınç dayanımı (112.73 MPa) 15 dk ön bekleme yapılmış ve 60 dk süresince 3 
 bar CO2 kürü uygulanmış KK %28 kodlu numunede elde edilmiştir. Kontrol numunelerinde s/ç oranı 
 arttığında basınç dayanımındaki azalma %27 iken, 15 dk ön beklemeden sonra 60 dk CO2 kürü uygulanan 
 numunelerdeki bu azalma oranı %53’dür. Dayanım artışı açısından genel olarak çimento hamuruna 
 uygulanan en uygun kür işlemi 15 dk ön bekleme sonunda 60 dk 3 bar CO2 kürüdür.

An alkali-responsive mineral self-healing agent with mechanical property enhancement for cementitious composites

Self-healing cementitious materials are regarded as an effective choice to increase the sustainability of the resource and environment. In this study, an alkali-responsive mineral self-healing agent (AMS) was prepared inspired by bone repair. The healing component, phosphate, was loaded into the halloysite nanotubes (HNTs) and encapsulated by the layer-by-layer (LbL) self-assembly method. The structure and alkali-responsive behavior of AMS, the effect of AMS on the mechanical properties of cement pastes, the stability of AMS before cement cracking, and its effect on the self-healing efficiency of the cement pastes were investigated with a range of analytical techniques. Results showed that AMS was successfully encapsulated and endowed with excellent alkali responsiveness. The incorporation of AMS was effective in reinforcing the mechanical performances of cement pastes. XRD analysis showed that the phosphate encapsulated in AMS can be mostly retained until cracks appear. When cracks occurred, the B-type carbonated calcium-deficient hydroxyapatite was found as the main product in the crack environment. The surface crack around 130 μm in the damaged specimens containing 5% AMS was fully sealed and healed, and its damaged compressive strength was almost completely recovered after curing for 28 days. The synergistic effect of autonomous healing triggered by AMS and autogenous healing behavior promotes the self-healing process and improves the self-healing efficiency of the hardened cement pastes.

The Early Age Hydration Products and Mechanical Properties of Cement Paste with Steel Slag Powder as Additive under Steam Curing Conditions

To explore the feasibility of the application of steel slag powder (SSP) in steam-cured precast concrete, 0% and 20% SSP were used to replace cement and prepare cement paste, and the early age performance of steam-cured (80 °C for 7 h and 7 d) SSP-blended cement paste, including different types and amounts of hydrates, the microstructure and mechanical properties were investigated and compared with those of 28 d standard-cured SSP sample. The results show that SSP addition promotes the generation of laminar C-S-H gels and granular C-S-H gels after an initial 7 h steam curing. Further extending the lasting time of 80 °C steam curing to 7 days favors the production of hydrogarnet and crystalline C-S-H, of which the amount of formation of hydrogarnet in SSP composite cement paste is less and the particle size is smaller than those in the control sample. However, steam curing increases the gap between the number of hydrates formed in SSP-blended cement paste and the control paste. The delayed hydration effect of SSP on cement offsets the promoting effect of steam curing on the hydration of cement; in consequence, the incorporation of SSP seems to be detrimental to the hydration of steam-cured cement paste.

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

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

Nanoindentation and nano-scratch testing on cement paste

Carbon nanotubes are an attractive reinforcement material for several composites. This is due to their inherently high tensile strength and high modulus of elasticity. This study focused on the nanomechanical characteristics of cement paste with and without short multi-walled carbon nanotubes (MWCNTs). The objective behind studying the nanomechanical properties of cement paste is to better understand the fundamental behaviour of cement at the nanoscale level. Cement paste is a complex material that consists of various phases, including cement hydrates, unhydrated cement particles and porosity. By studying the mechanical properties of cement paste at the nanoscale, researchers can gain insights into the mechanisms that govern the behaviour of this material. Following earlier tests, the amount of MWCNTs was kept constant (0.30% by weight of cement). The nanomechanical parameters explored included the localised Young's modulus and hardness. According to the test results, short MWCNTs increased the proportion of high-density calcium silicate hydrate in the cement paste. The nanomechanical properties (localised Young's modulus and hardness) of cement paste with short MWCNTs were found to be greater than those of cement paste without MWCNTs. According to nano-scratching experiments, the cement matrix with short MWCNTs was substantially more durable than the matrix without them.

Phase separation of recycled concrete powder during grinding and consequent influences on its hydration behaviors in cement paste

Recycled concrete powder (RCP) collected from waste concrete recycling presents significant variation in both composition and hydration behavior, while available literatures were mainly carried out on RCPs derived from target concrete, mortar, or cement paste, RCPs collected from actual waste concrete is totally different from RCPs reported, their roles has not been clarified yet due to its complexity in components, leading to substantial deviation in understanding the roles of RCP in cement-based materials. In this study, RCP collected from a waste concrete reutilization plant was classified into five fractions, then effects of RCP fractions on heat evolution and mechanical properties of cement pastes were investigated. The results showed that hydration products and un-hydrated clinker were predominantly concentrated in fine RCP fraction, while higher proportion of aggregate grains (mainly quartz, anorthite, and dolomite) in coarse RCP fraction, indicating that cement paste was pulverized or milled into finer particles prior to fine and coarse aggregates due to its diminished elastic modulus. Compared with coarse RCP fraction, fine RCP fraction showed significant acceleration of cement hydration and higher strength contribution, which can be attributed to the remarkable pore refinement of fine particle and conspicuous seeding effect of C–S–H in RCP. Furthermore, increased dissolution of Si4+ and Al3+ from the fine RCP fraction was observed, then more hydration products were generated to densify the microstructure of cement paste. The results provided a deeper insight into the roles of RCP in cement-based materials, and then facilitate the efficient utilization of RCP to achieve resource-conservation development.

Influence of MgAl-LDHs/TiO2 composites on the mechanical and photocatalytic properties of cement pastes and recycled aggregates

To study the effects of MgAl-LDHs/TiO2 on the properties of cement paste and recycled aggregates, MgAl-LDO (MgAl-LDHs calcined products) and TiO2 were mixed during the reconstruction of MgAl-LDHs laminates based on the memory effects of layered double hydroxides (LDHs), and then MgAl-LDHs/TiO2 was synthesized. The performance changes were characterized with hydration heat tests, the microscopic morphologies of the hydration products, and the physical and mechanical properties of the cement paste. The effect of the MgAl-LDHs/TiO2 on the multi-interfacial transition zone (ITZ, the interface between the old paste and new paste) of the recycled aggregates was characterised with the micromorphology, meso-mechanical properties, and element diffusion behaviour. The photocatalytic activity of MgAl-LDHs/TiO2 loaded on recycled aggregate was evaluated with the degradation of methylene blue under sunlight. The results showed that the addition of MgAl-LDHs/TiO2 promoted the initial hydration of ordinary Portland cement (OPC) and induced and promoted the growth and formation of crystalline cement hydration products. The initial setting time and final setting time were shortened, and the compressive strength of the hardened paste was improved when MgAl-LDHs/TiO2 was added to the cement paste. The MgAl-LDHs/TiO2 compacted the recycled aggregates and improved the structural properties of the ITZ. The MgAl-LDHs/TiO2 altered diffusion within the ITZ. The total efficiency for the degradation of methylene blue by the 5–10 mm MgAl-LDHs/TiO2 loaded on recycled aggregate reached 82.2% after 80 min under simulated sunlight.