Mechanical Properties Of Cement Composites Research Articles

The effects of apricot kernel shell nanobiochar on mechanical properties of cement composites

Valorization of agricultural wastes is important both economically and environmentally. This study aimed to investigate the use of biochar as a filler to improve the mechanical properties of mortar and to help sequestrate CO2. The biochar was produced by pyrolysis of apricot kernel shell at 500 °C. Nanobiochar particles with dimensions less than 500 nm were obtained by high-energy ball milling process. Scanning electron microscope was used for determining the morphology of nanobiochar. The nanobiochar at different volume percentages [0.00-0.04-0.06-0.08-0.12-0.15%] was added to mortar. The mortar was casted into 40x40x160 mm molds. After water curing at 20°C for 28 days, compressive strength and flexural strength tests were performed. The mixture containing 0.04% nanobiochar by volume had an increase in flexural and compressive strengths by 5% and 15% respectively, while its fracture energies for flexure and compression increased by 98% and 38% respectively compared to the reference mortar. Furthermore, the mixture having 0.12% volume had an increase in flexural and compressive strengths by 32% and 11%, respectively, while the increase in fracture energies for flexure and compression was 52% and 25%, respectively, compared to the reference mortar. The mechanisms of nanobiochar effect on flow, strength, and fracture energy were enlightened. The nanobiochars bridge the cracks, divert the cracks, act as hydration nucleation sites, enhance the matrix by its porous structure, and developed internal curing that led to increase in strength and fracture energy. This study suggests that the biochar produced from the apricot kernel shell has the potential to be used as a carbon sequestering mixture to improve performance of mortar and thereby utilizing waste as a construction material, contributing to the economy and environment.

Multifunctional properties of carbon fiber integrated cement composite – A review and insights

This article examines the strength characteristics of carbon fiber-reinforced cement composite (CFRCC). The research explores the residual mechanical characteristics and microstructure of concrete reinforced with carbon fiber. The review also focused on the determination of the effect of CFRCC on the improvement of strength, microstructure, crystalline phase shift, and hydration products of the cement composites. The review indicates that the inclusion of carbon fibers can intensify the flexural and splitting strengths of CFRCC, but the compressive strength is magnified to a lesser extent. In addition to the initial elastic modulus and peak stress of carbon fiber-reinforced cement composite, a discernible strain-rate hardening effect was also observed. This indicates that carbon fiber-reinforced cement composite has a promising future as cement composite reinforcements. The review of the characteristics of the composites also suggests their applicability in tunnel building in the cement composite. It is determined that carbon fiber-reinforced cement composite has a stronger capacity to withstand impact loads, and further information about its features will be supplied. The scanning electron microscopy (SEM) result demonstrates that the single and most significant failure mode under stress is carbon fiber breaking and the pull-out of carbon fibers. Thus, the review reveals that carbon fibers have a limited but positive act on enhancing the mechanical properties of cement composites.

Carbon nanotubes-coated cement particles for cement-based sensors with excellent piezoresistivity

Typically, self-sensing cement composites are prepared by directly mixing cement particles with conductive additives, such as carbon black, carbon nanotubes (CNT), and graphene. This study proposes a novel approach to directly coat cement particles with CNT as the conductive filler (CNT@cement) before contact with water, aiming to develop a high-performance self-sensing cement-based sensor. CNT@cement nano/micro hybrid fabrication relies on a simple and efficient method that enables the uniform absorption of CNT on the surface of cement particles without any surfactants, thereby not diminishing the workability and mechanical properties of cement composites. This cement composite exhibits improved microstructure, bending strength, and electrical conductivity. Remarkably, the formulation with the addition of 0.1 wt% CNT@cement hybrid increases the bending strength by about 23% and improves the electrical conductivity by approximately two orders of magnitude, outperforming previously reported cement composites with similar CNT content. Additionally, outstanding piezoresistivity with a fractional change in resistivity of 1.26 is achieved for our cement-based sensor. These findings represent a major step toward the practical application of CNT in structural health monitoring.

Flexural creep of multi-wall carbon nanotube reinforced cement based composites under high stress level

Different concentrations (0–0.2 wt.%) of multiwall carbon nanotubes (MWCNT) was used to improve the mechanical properties of cementitious composites. The first part of the work showed that adding 0.05 wt.% of MWCNT produced a maximum reinforcement in terms of flexural and compressive strength. The second, the role of MWCNT on mechanical strength improvement was investigated. MWCNTs can absorb water to weaken the cement hydration at the beginning, and then, release water to promote the hydration of cement. The third part focused on using a home-made four-point bending testing device to study the flexural creep behavior under high stress levels (70, 80 and 90% of the flexural strength) and the results are discussed in terms of creep strain and Poisson ratio difference. The data obtained were also compared with the empirical creep models and the creep coefficients obtained were agreement with that from the AASHTO model. Finally, a regression analysis was used to fit the creep compliance of MWCNTs reinforced cementitious composites for the range of conditions studied. The results showed that the creep compliance can be fitted by a power-law for a stress level below 0.85, while a linear function was obtained above.

Modeling and Optimization of Date Palm Fiber Reinforced Concrete Modified with Powdered Activated Carbon under Elevated Temperature

Date palm fiber (DPF) is one of the abundant solid waste materials in the agriculture sector in Saudi Arabia, and it is gaining great attraction due to its advantages compared to synthetic and other natural fibers. For proper utilization of DPF in cementitious composites, its performance under high temperatures needs to be understood. This is because DPF is a cellulose-based agricultural fiber material and is expected to degrade when subjected to high temperatures. This will cause a significant loss in strength and structural integrity of the composites. The use of Pozzolanic materials has been reported to reduce the loss in mechanical properties of cementitious composites under high temperatures. With powdered activated carbon (PAC) being a low-cost material compared to other Pozzolanic materials, this study utilized PAC as an additive to the DPF-reinforced concrete to mitigate its loss in mechanical strength when exposed to elevated temperature. The experiment was designed using response surface methodology (RSM), which was used to construct mathematical models for estimating the strengths of the concrete exposed to high temperatures. The DPF was added at proportions of 1%, 2%, and 3% by weight of cement. Similarly, the PAC was added at 1%, 2%, and 3% by weight of cement to the concrete. The concrete was subjected to elevated temperatures of 300 °C, 600 °C, and 900 °C for a 2 h exposure period. The degradation of the concrete in terms of mass loss and the compressive strength of the concrete after heating were measured. DPF in the concrete led to an escalation in weight loss and reduction in strength, which was more pronounced at a temperature of 600 °C and above. The addition of PAC resulted in an enhancement in the strengths of the concrete containing up to 2% DPF at 300 °C, while at 600 °C the improvement was minimal. The models developed for predicting the mass loss and strengths of the DPF-reinforced concrete under high temperatures were statistically significant with a high correlation degree. Based on the optimization results, DPF-reinforced concrete produced with 1% DPF, and 2.27% PAC as additives and subjected to a temperature of 300 °C for 2 h yielded the lowest mass loss of 2.05%, highest residual compressive strength and relative strength of 45.85 MPa and 106.7% respectively.

Date and doum palm natural fibers as renewable resource for improving interface damage of cement composites materials

BackgroundVarious recent studies have investigated the use of traditional fibers (metallic or synthetic) as reinforcement in mortar. In recent times, there has been growing interest in using natural fibers as reinforcement in cement composites. This study was conducted to assess the impact of date palm, doum palm, and sisal fibers on the mechanical properties of cement composites. Genetic modeling was chosen to find the shear damage at the fiber-matrix interface of the three cement composites using genetic crossing operator, which allows us to calculate the damage at the interface using two damages of the matrix and the fibers, respectively.ResultsOur objective is to examine and evaluate the interface damage of date palm/mortar, doum palm/mortar and sisal/mortar under different mechanical tensile stresses ranging from 25 to 37 MPa with fiber volume fraction from 1 to 5%. It was found that the interface damage of date palm/mortar and doum palm/mortar cement composites was minimal compared to that of sisal/mortar. However, several researchers found that an increase in fiber volume fraction leads to decrease in mechanical properties and density in cement composites what we confirmed in this study that interface damage increases when the volume fraction increases.ConclusionsThe results are in line with the findings of a recent experimental study on the use of other plant fibers. Their results showed that incorporating ramie fibers resulted in a 27% increase in compressive strength, whereas the use of synthetic fibers resulted in 4% decrease in tensile strength in compression. It is recommended the use of doum and date palm natural fibers in the composition of mortars with a fiber volume fraction of 1 to 5% in order to reduce and avoid interface damage and limit the negative impact of synthetic fibers on the environment.

Evaluation of the Microstructure and Mechanical Properties of Biopolymer-Based Cementitious Composites with Silver Nanoparticles

This study investigated the effects of using silver nanoparticles (Ag NPs) on the microstructure and mechanical properties of cementitious composites. Ag NPs were synthesized with an ultrasonic irradiation method using konjac gum–polyethylene glycol (KG/PEG) and locust gum–polyethylene glycol (LG/PEG) and characterized using scanning electron microscopy (SEM), energy dispersive X-ray (EDX), high-resolution transmission electron microscopy (TEM), and Fourier-transform infrared (FTIR) analyses. To identify the effect of the Ag NPs on the mechanical properties of mortar, four different cement mortar mixtures were prepared with varying percentages of Ag NPs (0%, 0.5%, 1%, 2%, 3%, 4%, and 5% by weight). Clear improvements were observed in the 7- and 28-day compressive and flexural strengths of nanocomposites with Ag NPs. A thorough microstructure investigation using SEM, EDS, XRD, and thermogravimetric analysis (TGA) was presented, and the relationship between microstructure and the mechanical properties of cementitious composites including Ag NPs was discussed.

Interface Microstructure–Based Mechanical Property Evaluation of C-S-H

The grain–grain interface of cement, which is composed of the complex needle-shaped microstructure of calcium silicate hydrate (C-S-H), is crucial in the development of the mechanical properties of cementitious composites. These C-S-H needles grow radially outward from the grain surface. This work proposes a combined experimental and modeling approach to incorporate the finer details of these needle geometries and the distribution of mechanical properties in an interface-based multiscale mechanical model for hydrating tricalcium silicate (C3S). At micrometer and sub-micrometer length scales (<5 μm), electron microscopy images revealed that the geometrical nature of these needles at the grain interface varies with days of hydration. The mechanical properties of C-S-H at the nanoscale were observed to be higher at the inner core and reduced toward the outer product. The model developed can incorporate the details of these needle microstructures and their mechanical properties at the microscale and can predict the bulk properties of hydrated C3S at higher scales.

Rheological and Mechanical Properties of Kenaf and Jute Fiber-Reinforced Cement Composites

This study investigated the rheological and mechanical properties of cement composites with kenaf and jute fibers for use in shotcrete. The length and volume fractions of the fiber were varied; the rheological properties were analyzed in terms of air content, compression and flexural tests were conducted, and the degree of fiber dispersion was assessed using fluorescence microscopy. The rougher surfaces of the jute fibers led to a higher yield stress and viscosity of the composite compared to the kenaf fibers. The use of 10-mm-long jute fibers at 2.0% volume fraction led to optimal rheological properties while 30-mm-long jute fibers at 1.0% resulted in the worst properties. The yield stress and plastic viscosity exhibited positive and negative correlations with the fiber volume fraction, respectively. This was likely because of the bridging and fluid actions of the bubbles at higher fiber content. For a given fiber content, only the yield stress increases with an increase in fiber length. Although all the mechanical properties deteriorated (compressive strength decreased from 27.5 to 6 MPa, and flexural strength deteriorated from 6.2 to 1.8 MPa), the mixtures failed in a ductile manner. Using 10-mm-long kenaf fibers at 2.0% induced optimal fiber dispersion, whereas the minimum dispersion-coefficient value was found for 5-mm-long kenaf fibers at 0.5%.

The Effect of Magnetized Water on the Fresh and Hardened Properties of Slag/Fly Ash-Based Cementitious Composites

The physicochemical structure of the mixing water used in concrete has a significant effect on the physical and mechanical properties of cementitious composites. The studies on the effect of magnetized water (MW) on the properties of FA/BFS-based cementitious composites are still in their infancy. This study explores the effect of MW on the fresh and hardened properties of fly ash (FA)/blast furnace slag (BFS)-based cementitious composites. A total of 22 different mixture groups having FA/BFS (0, 5, 10, 15, 20, and 25%) by weight of cement were produced using tap water (TW) and MW. The fresh-state properties (the initial and final setting times and the consistency) and hardened-state properties (the compressive strength, water absorption properties, and rapid chloride ion permeability test) of produced cementitious composites were investigated. The development of hydration products was analyzed using scanning electron microscopy (SEM) and the mercury intrusion porosimetry (MIP) test. The results reveal that the fresh- and hardened-state properties of cementitious composite samples produced with MW are significantly improved. The properties of the samples utilizing MW showed that FA and BFS could be used at a higher rate for the same target properties in cementitious composites by using MW as mixing water. Using up to 25% FA/BFS in cementitious composites prepared with MW is recommended.

Experimental study of the durability of high-performance cementitious composites with amorphous metallic fibers

Amorphous metal fibers (AMF) can significantly enhance the mechanical properties of cementitious composites, however, research on the durability properties of cementitious composites containing AMF is still incomplete. In this study,(AMF)were strategically utilized to enhance the durability of cementitious composite. The long-term performance of amorphous metal fibers reinforced cementitious composites (AMFRCC) with four fiber contents (0.4%, 0.8%, 1.2%, 1.6%) was systematically evaluated under chloride corrosion, sulfate cycling, and free-thaw cycling conditions, using conventional Steel fibers reinforced cementitious composites (SFRCC) as a control group, and the reliability life of AMFRCC under freeze–thaw conditions was predicted. The results showed that SF and AMF volume fractions above 1.2% are detrimental to cementitious materials' chloride ion penetration resistance. After dry and wet sulfate cycles, AMF is not corroded, while the uniformly dispersed AMF can fully exploit the crack arresting effect and reduce internal defects in cementitious materials. However, in long-term sulfate environments and freeze–thaw environments, corrosion of SF causes severe degradation of SFRCC performance. Furthermore, the Wiener model can more accurately predict the lifetime of AMFRCC and SFRCC in freeze–thaw environments when the relative dynamic modulus of elasticity is used as an indicator of degradation.

Influence of Laboratory Synthesized Graphene Oxide on the Morphology and Properties of Cement Mortar.

The introduction of Graphene Oxide (GO), a nanomaterial, has shown considerable promise in improving the mechanical properties of cement composites. However, the reasons for this improvement are not yet fully understood and demand further research. This study aims to understand the effect of laboratory-produced GO, using Tour's method, on the mechanical properties and morphology of cement mortar containing GO. The GO was characterized using Fourier-transform infrared spectroscopy, X-ray Photoelectron Spectroscopy (XRD), X-ray powder diffraction, and Raman spectroscopy alongside Scanning electron microscopy (SEM). This study adopted a cement mortar with GO percentages of 0.02, 0.025, 0.03, 0.035, and 0.04 with respect to the weight of the cement. The presence of GO in cement mortar increased the density and decreased the consistency and setting times. At the optimum of 0.03% GO viscous suspension, the mechanical properties such as the 28-day compressive strength, splitting tensile strength, and flexural strength were enhanced by 41%, 83%, and 43%, respectively. In addition, Brunauer-Emmett-Teller analysis indicates an increase in surface area and volume of micropores of GO cement mortar, resulting in a decreased volume of mesopores. The improvement in properties was due to increased nucleation sites, calcium silicate hydrate (CSH) density, and a decreased volume of mesopores.

Graphene-oxide-reinforced cement composites mechanical and microstructural characteristics at elevated temperatures

Abstract The focus of this research was to investigate the effects of graphene oxide (GO) on the microscopic composition, structure, pore size, and mechanical properties of GO-reinforced cement composites. Furthermore, the research explored the thermal behavior of GO-reinforced cement mortar at different elevated temperatures (250, 500, 750, and 1,000°C). This study considered three sets of GO-reinforced cement composites with 0.1, 0.2, and 0.3 wt% of GO (by weight of cement); the water–cement ratio in all the mixtures was 0.5. To characterize the chemical composition, microstructure, and hydration degree resulting from GO addition, X-ray diffraction, thermogravimetry, derivative thermogravimetry, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and micro-computed tomography (Micro-CT) were used. The experimental results revealed that GO addition changed the microstructural composition and pore diameter distribution of the cement composite. The optimal amount of GO required for improving the mechanical properties of the cement composite under both unheated and heated conditions was identified to be 0.1 wt%. GO improves the cement matrices’ ability to bind with GO nanosheets, leading to compressive strength retention and decreased micro-cracking (computed by material and defected volume changes by Micro-CT analysis). This is primarily due to the hydration products. However, the optimal amount of GO can result in nanomaterial agglomeration, thus lowering the thermal resistance of the cement composite. Overall, the study identified GO as a nano-additive with the potential to improve the strength and toughness of the cement composites. Moreover, the effect of elastic modulus was also evaluated. As a result, the GO microstructure analysis revealed that it has a porous structure with a visible crack pattern.

Mechanical Properties of Polyvinyl Alcohol Fiber-Reinforced Cementitious Composites after High-Temperature Exposure.

The mechanical properties of cementitious composites before and after exposure to high temperature are affected by calcium–silicate–hydrate (C–S–H) gels. To evaluate the effects of high temperature, plyvinyl alcohol (PVA) fiber content, and the cooling method on properties of cementitious composites, physical, mechanical, and microscopic tests were performed in this study. The target temperatures were 25, 100, 200, 300, 400, 600, and 800 °C. The PVA fiber contents were 0.0, 0.3, 0.6, 0.9, 1.2, and 1.5 vol%. The high-temperature resistance of PVA fiber-reinforced cementitious composite (PVA-FRCC) specimens was investigated through changes in their appearance, mass loss, compressive strength, splitting tensile strength, flexural strength, and microstructure. The results showed that PVA fibers reduced the probability of explosion spalling in the PVA-FRCC specimens exposed to high temperatures. The mass loss rate of samples exposed to temperatures below 200 °C was small and lower than 5%, whereas a significant mass loss was observed at 200 °C to 800 °C. A small rise in the cubic compressive and splitting tensile strengths of samples was found at 400 °C and 300 °C, respectively. Below 400 °C, the fibers were beneficial to the mechanical strength of the PVA-FRCC specimens. Nevertheless, when the temperature was heated above 400 °C, melted fibers created many pores and channels, which caused a decrease in the strength of the specimens. The method of cooling with water could aggravate the damage to the cementitious composites exposed to temperatures above 200 °C. High temperature could lead to the decomposition of the C–S–H gels of the PVA-FRCC samples, which makes C–S–H gels lose their bonding ability. From the perspective of the microstructure, the structure of PVA-FRCC samples exposed to 600 °C and 800 °C became loose and the number of microcracks increased, which confirmed the reduction in macro-mechanical properties.

Synergistic strengthening mechanism of Portland cement paste reinforced by a triple hybrid of graphene oxide, functionalized carbon nanotube, and nano-silica

• Triple hybrid of GO, f-CNT, and NS as a cement composite reinforcement was studied. • Amount of GO was selected as a variable in the triple hybrid. • Optimal ratio of GO for the triple hybrid was found to be 0.04 wt% (of cement) • Dispersion of the triple hybrid depends on the bonds between the nanomaterials. • Hydration and mechanical properties of cement composites are affected by dispersion of the triple hybrid. This study investigates the synergistic strengthening mechanism of graphene oxide (GO), functionalized carbon nanotubes (f-CNT), and nano-silica (NS) triple hybrid-reinforced Portland cement composite. GO was selected as the variable owing to the synergistic effect of GO with both f-CNTs and NS upon dispersion by forming bonds with both nanomaterials. At a low GO dosage (∼0.03 wt% of cement), the bond between GO and NS deteriorated the dispersion in Ca 2+ -rich solution due to the overly attached NS on the GO surface. The highest GO fraction (0.05 wt%) also led to poor dispersion as the excess GO was agglomerated by Ca 2+ ions. However, an optimal amount of GO (0.04 wt%) significantly improved the dispersion quality. The enhanced dispersion of the triple hybrid positively influenced the hydration degree and mechanical performance of the cement paste (133 % and 156 % for compressive and tensile splitting strength compared to OPC) and the pozzolanic reactivity of NS.

Synergistic Effect of PVA Fiber and PTB Emulsion on Mechanical Properties of Cementitious Composites for Damage Repair in Operating Tunnels

Operating tunnels are often located in complex geological conditions and are prone to various types of damage. Even after structural repair, the repaired material may be vulnerable to secondary damage. It is difficult to effectively repair operating tunnel damage. Hence, developing high-performance repair materials for tunnel structures is critical. This study aimed to develop repair materials by studying the synergistic effects of fiber and polymers. The effect of polyvinyl alcohol (PVA) fiber and PTB (COMPAKTUNA.PRO) emulsion on the compressive strength (40 × 40 × 40 mm, GB/T 17671-2020), flexural strength (40 × 40 × 160 mm, GB/T 17671-2020), uniaxial tensile properties (330 × 60 × 13 mm, JC/T 2461-2018), bond strength (40 × 40 × 160 mm, JC/T 2537-2019), rapid chloride migration coefficient (ϕ100 × 50 mm, GB/T 50082-2009), porosity (40 × 40 × 40 mm, SY/T 6490-2014), and scanning electron microscopy (less than 1 cm3, GB/T 27788-2020) was analysed. The test was completed in the laboratory of our school, and the average value of three specimens per mix ratio was taken. The results indicate that both PVA fiber and PTB emulsion addition reduce the compressive strength but significantly increase the flexural strength, tensile strength, and ultimate tensile strain of cementitious composite. The compressive-to-flexural strength ratio decreases, and the uniaxial compression toughness index increases. The cementitious composites exhibit good integrity after damage. The influence of the PVA fiber is more potent than that of the PTB emulsion. The PTB emulsion increases the impermeability and bonding strength of the cementitious composite and can improve the disadvantages caused by adding the PVA fibers. The bridging effect of the PVA fiber and the membrane-forming effect of the PTB emulsion together influence the performance and cause a synergistic effect to achieve superposition and complementation of advantages. The optimal content of the PVA fiber and PTB emulsion under the synergistic effect can be obtained. The findings can provide a theoretical basis for the optimal design and practical application of restoration materials.

Investigation on Mechanical Properties of Cementitious Composites cured in colloidal Nanosilica SiO2 solution.

Nano technology is one of the most widely searched techniques in the world nowadays. Several studies reported with nanoparticles are based on the nano-silica (nano-SiO2) addition to the fresh mix to improve the performance of concrete. Nano-SiO2 is highly reactive with calcium hydroxide and is able to act not only as a filler, blocking the concrete pores, but also as an activator to promote pozzolanic reaction. In this study, the effect of different concentration of nano silica solution on concrete compressive strength when using it in curing instead of water. Samples were made by adding fly ash (FA/PC= 1.2 and 2.2) and some were immersed in water and others in a suspension containing water with Nano SiO2 with different concentrations (0.5, 1, 2 and 3) %. Then submit the samples to compression test after 3, 7 and 28 days to notice the impact of using Nano silica solution in curing stage. Fly ash has been used in this experiment for several reasons. 1. Development of the mechanical properties of the cement-bonded composites. 2. Reduces the percentage of cement use and therefore we will keep the environment clean because the cement reaction produces CO2 which cause polluting to the environment.

Investigation of mechanical properties of PVA fiber-reinforced cementitious composites under the coupling effect of wet-thermal and chloride salt environment

In this study, the mechanical properties of polyvinyl alcohol fiber-reinforced cementitious composites (PVA-FRCC) under the coupling effect of wet thermal and chloride salt environment were investigated through a series of experiments, including compressive strength, flexural performance, elastic modulus, three-point bending fracture, and scanning electron microscope (SEM) tests. An environmental simulation test chamber was used to simulate the wet-thermal and chloride salt environment, in which the parameters of temperature, relative humidity (RH), mass fraction of the NaCl solution, and action time were determined to be 50 °C, 100%, 5%, and 30 d, respectively. The volume contents of the PVA fibers incorporated in the cementitious composites were 0, 0.3%, 0.6%, 0.9%, 1.2%, and 1.5%. The results indicated that the mechanical properties of the cementitious composites decreased after being subjected to the coupling effect of the wet-thermal and chloride salt environment. The incorporation of the PVA fibers improved the mechanical properties of the cementitious composites under the coupling effect of the wet-thermal and chloride salt environment. When the addition content of PVA fiber was approximately 0.6–0.9%, the mechanical performance of PVA-FRCC was the best. Compared with the cementitious composite without fibers, the maximum growth rates of the cube, axial and residual compressive strength, elastic modulus, and flexural strength of the PVA-FRCC under the coupling effect of the wet-thermal and chloride salt environment owing to the addition of PVA fiber reached 29.96%, 46.92%, 29.71%, 46.15%, and 67.06%, respectively. In particular, the 1.5% PVA fiber dosage increased the initiation and unstable fracture toughness, and fracture energy by 145.57%, 333.01%, and 2656.38%, respectively.

Unfolding behavior of self-folded boron nitride nanosheets inducing ductility of cementitious composites

A classical molecular dynamics simulation is adopted to study unfolding behavior of self-folded boron nitride nanosheets (BNNSs) in the cementitious composite. The simulation results show that unfoldings of the self-folded BNNSs initiate at the interface between the interlayers of the self-folded BNNSs because this interface is weaker than the BNNS-tobermorite interface under individual tensile and shear deformation. The interfacial microstructure shows that the ends of the self-folded BNNSs are embedded into the rugged surfaces of tobermorite, which exhibits a mechanical interlocking effect on the BNNSs-tobermorite interface. Furthermore, the existence of the hydrogen bonds at the BNNS-tobermorite interface yield a robust interfacial interaction between BNNSs and tobermorite. The critical peeling forces required to peel the adhesion between BNNS and tobermorite and between interlayers of self-folded BNNSs are obtained from a continuum model, which gives insights into the unfolding initiation of the self-folded BNNSs. The progressive peeling at the BNNS-tobermorite interface allows the self-folded BNNSs to maintain mechanical reinforcement in tobermorite under a large deformation at the atomistic scale. The atomistic scale reinforcement of the self-folded BNNSs in the deformation capacity and mechanical properties of cementitious composites significantly improves the ductility of cementitious composites.

Loading-rate-dependent effects of colloidal nanosilica on the mechanical properties of cement composites

Colloidal nanosilica (CNS) has shown great potential in the fabrication of high-performance cement composites by improving their quasi-static mechanical properties. However, the effects of CNS under higher strain rates (i.e. dynamic loads) have been seldom explored. In this study, we thoroughly investigated the loading-rate-dependent effects of CNS on the mechanical performance of Portland cement paste. A Split Hopkinson Pressure Bar (SHPB) equipped with a high-speed camera was utilised to conduct dynamic testing under two different strain rates, namely ≈40 (1/s) and ≈120 (1/s), to analyse dynamic compressive strength, modulus of elasticity, failure strain, energy absorption, and fragment size distribution of the composites. Although CNS significantly improved the quasi-static mechanical properties, it had detrimental effects on the dynamic strength, stiffness, energy absorption, and fragmentation behaviour of the cement composites. These negative effects were attributed to the rapid flocculation of CNS upon mixing with the alkaline environment of cement, which led to the formation of a weak and porous hydration phase in the hardened cement paste, as corroborated by microscopy analysis. These findings demonstrate the importance of dynamic characterisations to fully understand the mechanical effects of nanomaterials because quasi-static investigations might not reveal their potential side effects.