Mechanical Properties Of Cement-based Composites Research Articles

Impact of chitosan extracted from shrimp shells on the shrinkage and mechanical properties of cement-based composites using dendritic fibrous nanosilica

Dendritic fibrous nanosilica (DFNS) was functionalized using microcrystalline chitosan, derived from shrimp exoskeletons, to act as a robust anchor, resulting in DFNS@Chitosan. In order to prevent the restacking of chitosan sheets, the supramolecular polymerized chitosan not only served as a spacer but was also incorporated into cement-based composites. The physical-chemical characteristics of DFNS@Chitosan were assessed through various analytical techniques such as TEM, SEM, TGA, FTIR, AFM, XPS, and EDX. The potency and auto-induced contraction of Cement-based composite materials fortified with DFNS@Chitosan were probed. The incorporation of DFNS@Chitosan resulted in an increase in both compressive and interfacial stretching potency of the cement-based composites. Furthermore, the presence of DFNS@Chitosan effectively inhibited the occurrence of auto-induced contraction in the cement-based paste. This research endeavor is anticipated to promote an alternative utilization of DFNS and shrimp waste shells in the development of sustainable building materials.

Effect of CTBN and Nano-SiO2 modified epoxy resin powder on the mechanical properties of cement-based composites

The high brittleness of oil well cement seriously affects the cementing quality. In order to maintain the safe and effective production of oil and gas wells, it is crucial to employ solid flexible fillers to reduce the brittleness of cement. In this study, a new type of flexible resin material (C-ER) was prepared by modifying epoxy resin with liquid nitrile butadiene rubber (CTBN) and nano-SiO2. The chemical composition, hydrophilicity, dispersibility, microstructure, and mechanical properties of C-ER were studied by FT-IR, XPS, contact angle, UV spectroscopy, SEM, DMA, and uniaxial compression. The results show that CTBN reacted with the epoxy group successfully. Due to the presence of SiO2, C-ER has good hydrophilicity and dispersion properties. The introduction of flexible segments makes C-ER have a lower modulus and crosslinking density, and its compressive elastic modulus is reduced by 47.4 % compared with pure resin. In addition, the effect of C-ER on the performance of oil well cement was tested. The results show that the addition of C-ER does not affect the fluidity of cement slurry and can improve the strain capacity of cement stone under load. Compared with blank cement and unmodified resin cement, the flexural strength of cement sample containing 4 % C-ER particles increased by 9.0 % and 25.1 %, respectively, and the elastic modulus of cement stone decreased by 31.2 % and 25.0 %, respectively. SEM images show that C-ER maintains good dispersion and bonding properties in cement matrix. C-ER can reduce the brittleness of cement effectively through its own elastic deformation and debonding to the cement matrix.

Synergistic Effect of Carbon-Based Reinforcements on the Mechanical Properties of Cement-Based Composites

Carbon reinforcements are used to improve the mechanical properties of cement, allowing the preparation of a strengthened and toughened composite. Functionalization through a reaction with acid is necessary to guarantee both a good dispersion in water and a strong interaction with cement. Different functionalized reinforcements improve the mechanical properties of the composites in comparison with pristine cement. The use of a combination of carbon fibers, carbon nanotubes, and graphene nanoplatelets were analyzed in order to verify their synergistic effect. The use of functionalized carbon nanotubes and carbon fibers demonstrates an improvement of 71% in flexural strength and 540% in fracture energy.

Influences of silicon carbide fineness on thermal and mechanical properties of cement-based composites

Cement-based composites with high thermal conductivity have important application potential in building engineering, such as ground source heat pump and high-efficiency floor heating system. In order to study the influences of silicon carbide (SiC) fineness on the thermal and mechanical properties of cement-based composites, SiC with different fineness was used to prepare cement-based composite materials (CCMs). A series of tests, including microstructure analysis, compressive and flexural strength, thermal conductivity, thermogravimetric analysis and heating simulation test were performed to investigate the thermal and mechanical properties of CCMs. The results reveal that SiC was wrapped by hydration system evenly and could keep its good structural integrity. Reducing SiC fineness could enhance the air-entraining effect, which could produce more weak interfacial areas and pores in hydration system. The degree of cement hydration reduced as the fineness of SiC reduced. Finer SiC usually led to higher thermal conductivity of CCMs, and the thermal conductivity of CCMs could be increased by 125.34% compared with the control group. The compressive and flexural strength increased first and then decreased as the fineness of SiC reduced. The heating simulation test indicates that the thermal performance of CCMs increased with reducing SiC fineness. Specially, the heating efficiency of CCM-3 increased by 21.6% compared with the control group. The results could be helpful in improving the thermal performance of heating system and reducing carbon dioxide emissions.

The reuse potential of spent ZIF-8@GO-COOH nano adsorption materials: Study on their impact on the hydration mechanism and mechanical properties of cement-based composites

Spent adsorbents often contain harmful substances, which may have an impact on the ecological environment if these substances enter the environment. This study mainly introduces a safe treatment method for solid waste formed after heavy metal ions are adsorbed by an efficient adsorbent, ZIF-8@GO-COOH. This work mainly discusses the impact of solidifying the spent adsorbent in the cement system on the cement mechanical properties and hydration process. The experimental results showed that when the dosage of the spent adsorbent was 0.01%, 0.02%, 0.03%, and 0.04%, respectively, the compressive strength of 28 d was increased by 4.24%, 6.16%, 7.19%, and 8.87%, respectively, compared with the cement without spent adsorbent. Introducing spent ZIF-8@GO-COOH in the cement production process does not have a negative impact on the cement mechanical properties, and can refine the cement pore structure and dense microstructure, thereby improving the compressive strength. The Toxicity Characteristic Leaching Procedure (TCLP) results showed that solidifying the spent adsorbent with cement can effectively reduce the leaching of heavy metal ions in the spent adsorbent. This study solidifies the spent ZIF-8@GO-COOH nanoadsorbent material into the cement system as a sustainable alternative to landfilling. This treatment method has certain economic benefits and safety, and has some reference significance for promoting the development and improvement of spent adsorbents and improving their safe treatment and reuse.

Enhancement of the piezoresistive and mechanical properties of cement-based composites filled with CNTs/GO and nano-SiO2 sprayed steel fibers

Steel fibers (SFs) are one of the most suitable functional fillers for the preparation of large-volume self-sensing concrete due to their good dispersion and toughness, whereas it has poor sensing performance. In this paper, a CNTs/GO-sprayed method was proposed to modify the surface of SFs as well as nano-SiO2 was used to enhance the interface between SFs and matrix, in which the content of carbon-based materials could be precisely quantified. Then, self-sensing performance, pull-out test, and macro stable mechanical performance were carried out. The results revealed that the specimens filled with straight smooth (SS) SFs sprayed with GO and nano-SiO2 had the highest self-sensing ability. Compared to unmodified SFs, the degree of improvement reached 225% and 270% within 0 ∼ 60 kN and 0 ∼ 90 kN, respectively, and the addition of nano-SiO2 increased the pull-out energy. In addition, the macro mechanical properties of the specimens filled with the modified SS SFs were better than that of the hooked end (HE) SFs.

Multi-scale synergistic modification and mechanical properties of cement-based composites based on in-situ polymerization

For the multi-scale and multiphase composite structure, modifying cement-based material at different scales to improve structural and mechanical performance is necessary. This paper developed a continuous multi-scale synergistic modified cement-based material with excellent properties by polymers, whiskers, and fibers. Notably, the polymer network is formed by in-situ polymerization in the hydration process of cement and works in concert with different scales modified substances. Specifically, the effect of in-situ polymerization of acrylamide monomers (IPAM), calcium carbonate whiskers (CW), and polyvinyl alcohol (PVA) fibers on mechanical strength is analyzed by response surface methodology, and the optimal mix ratio design is obtained. With the optimized mix ratio, the flexural strength of multi-scale modification samples is increased by more than 135% compared to the neat paste, while the 28d compressive strength is maintained essentially the same, with only a 2.9% reduction. And multi-scale samples' properties are significantly improved compared to single-scale samples. In addition, multi-scale composites' mechanical properties and microstructure are characterized in detail to investigate the incredible performance and the modification mechanism. Three modified materials form a continuous micro-meso-macro multi-scale structure in the cement matrix. Moreover, the interaction between IPAM, CW, and PVA fibers is confirmed. The IPAM can in-situ modify the interfacial structure of fibers and whiskers, strengthen the interrelation between different scales, resulting in exciting enhancements of the cement-based composite's structure and performance. This multi-scale modification strategy provides new ideas and promising applications for preparing high-performance cement-based materials.

Improving the Performance of Lightweight Crumb Rubber Mortar Using Synthetic, Natural, and Hybrid Fiber Reinforcements

The global market for tires is ever-growing, and partially replacing sand with crumb rubber (CR) as fine aggregates in concrete could reduce environmental pollution. However, the main barrier to the complete usage of recycled tire crumbs in construction is the deterioration effect of CR on the mechanical properties of cement-based composites. Therefore, this paper attempts to improve the fresh and hardened properties of crumb rubber mortar (CRM) by incorporating polypropylene-polyethylene synthetic fibers with coconut and kenaf natural fibers as reinforcements. A total of 18 mix designs were developed with varying fiber combinations and rubber crumb replacement. Subsequently, parametric studies with chemical admixture were conducted at 3, 7, and 28 days to improve the flowability and resulting mechanical properties of the fiber-reinforced CRM. According to the results, the single and hybrid fibers positively improved the mechanical properties of cement mortar at 5–15% CR replacement. It can be concluded that adding single and hybrid fibers enhanced the performance of cement mortar modified with tire crumb rubber aggregates by providing varying degrees of improvement.

Characteristic of Fresh and Harden Properties of Polyvinyl Alcohol Fibre Reinforced Alkali Activated Composite

Fibre can enhance the mechanical properties of cement-based composites, but fibre also degrades their workability. However, the quantitative effects of fiber content and length-diameter ratio on alkali-activated materials are still unclear. Various aspect ratio, volume fraction of polyvinyl alcohol fibre (PVAF), and various water-binder ratio were employed to prepare a total of 26 groups of fibre reinforced alkali-activated composite (FRAAC). The influence of PVAF fibre factor (product of fiber volume fraction and length-diameter ratio) on flowability, compactness, strength, and crack fractal dimension of FRAAC was researched. The influence of water-binder ratio on the plastic viscosity of FRAAC was more significant than that on the yield stress. When fibre factor was lower than critical value of 150, the influence of fibres could be overlooked. The reason was that the space between fibres was distant, so the flowability of FRAAC was not impacted by PVAF. At this time, fibres were challenging to restrict the cracks in matrix and increase their mechanical properties. When fibre factor was higher than critical value 150 and lower than density packing value 450, the flexural strength, compressive strength and crack fractal dimension of FRAAC were considerably enhanced, and the FRAAC could still flow easily under dead weight. When fibre factor were above 450, noteworthy fibre balling considerably decreased the flowability, leading to poor solidity and reduced compressive strength. Hence, the ideal content of PVAF in alkali activated composite is between 150/(l/d) and 450/(l/d).

Microstructural investigation of mortars incorporating cockle shell and waste fishing net

Large amounts of cement and natural aggregates are used annually to produce concrete, and the high energy consumption required for the production of these materials is considered to be a major environmental concern globally. This study investigates the effect of marine wastes, such as cockle shells and waste fishing nets, on the microstructural characteristics of cement-based materials. Crushed cockle shells were used as a substitute for fine aggregates, and ground waste fishing nets were utilized as a fiber replacement to enhance the flexural performance of cementitious materials. Varying amounts of cockle shell and waste fishing net were washed and then used as substitutes for fine aggregates and fibers, respectively, in cement mortar specimens. 10, 20, and 30 wt% of cockle shells were substituted for fine aggregates, and the waste fishing net of 1.0 % of the total volume was also considered in the mixtures. The compressive and flexural strength of the specimens were measured to examine the effect of marine waste replacement on the mechanical properties of cement-based composites. Scanning electron microscopy, X-ray diffraction, and micro-computed tomography were utilized to investigate the microstructural characteristics of the materials with different substitution ratios of cockle shells and waste fishing nets. The obtained results confirm that properly washed and processed cockle shell powder can be used as an alternative to fine aggregates for conventional cement-based composites, and waste fishing nets can be utilized as a reinforcement for improving the flexural performance of cement mortar.

The influence of biochar shape on cement-based materials

Biochar-containing cement composites have attracted increasing interest in recent years due to the possibility of reducing the environmental impact linked to cement. They can also improve the mechanical properties and the electrical conductivity of cement-based materials. One parameter that can affect the mechanical performance of biochar-containing cement composites is the morphology of the biochar. While it is reasonable to expect a different behaviour for different shapes (sheet-, sphere- or rod-shaped), a full understanding is yet to be achieved of the competing effects of aspect ratio, morphology and composition linked to the specific biochar source. This study shows that biochar can improve the mechanical properties of cement-based composites: 1 wt% of biochar improves compressive strength and flexural strength by 7% and 15%, respectively. The results presented in this study confirm that biochar has a positive effect on both the mechanical and environmental behaviour of cement-based materials.

Carbon dots as a superior building nanomaterial for enhancing the mechanical properties of cement-based composites

Carbon nanomaterials, such as graphene and its derivatives can act as a significant building nanomaterial for ameliorating the various properties of cement-based composites, but their poor water solubility lead to unevenly dispersed in the cement pore solution, and limits their effective application in cement-based materials. Moreover, the high price of these nanomaterials restricts the practical use in industry. Herein, in this study, the carbon dots (CDs), which was prepared by the improved microwave pyrolysis method, is demonstrated to own the superior performance in the enhancement of the cement-based composites mechanical properties for the first time. The X-ray powder diffraction (XRD), High-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS) and related structural characterizations are performed to prove the successful synthesis of CDs, and the compressive strength of cement-based composites increased by 16.8% after curing 28 days at the 0.08 wt% CDs dosage in comparison to the blank samples. Through thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and mercury intrusion porosimeter (MIP) and XRD, it is proved that: i) the small nanometer size and good water solubility of carbon dots promote them easily filling into the pores of cement as a result of increasing its compactness; ii) the carbon dots act as much more nucleation sites to make the hydration products superimposed in a more dense room; iii) the surface of carbon dots possess many hydrophilic groups, including carboxyl and amide, these groups produce a strong adsorption on the cement particles and then affect the formation of hydration products. These joint effects effectively enhance the compressive mechanical strength for cement-based composites. Besides, the simple preparation of CDs with a low price is suitable for the industrial application. The CDs as the superior alternative nanomaterial for heightening the properties of cement-based composites show a great potential, and is significant for the exploitation of building nanomaterial with outstanding performances for cement.

Basic tensile creep of concrete with and without superabsorbent polymers at early ages

Internal curing with superabsorbent polymers (SAP) significantly affects both deformational and mechanical properties of cement-based composites at early ages. Despite substantial previous research, the impact of SAP on the basic tensile creep of early-age concrete is hardly investigated. In this paper, through direct tensile testing, the basic tensile creep of concrete with a water-to-binder ratio of 0.35 and containing 0.3% SAP (by mass of binder) loaded at early ages was studied. Concrete with SAP exhibited higher basic tensile creep than the reference concrete without SAP when first being loaded at 1 day, 6 days, and 14 days. The higher basic tensile creep of early-age concrete with SAP may be due mainly to the formation of large air voids, delayed cement hydration, and also higher internal relative humidity. The applicability of using the B3 model and the MC2010 model to predict the basic tensile creep of early-age concrete was examined. A modified MC2010 model was then proposed to more realistically reflect short-term tensile creep characteristics of early-age concrete with and without SAP. The model parameters were first determined through best-fitting with the measured creep data for reference specimens loaded at 1 day. Subsequently, the model, with parameters so determined, was used to predict the specific basic tensile creep for specimens loaded at 6 days and 14 days. The good agreement between the model predictions and test results suggests an acceptable predictive capability of the modified model. Besides, the autogenous shrinkage, compressive strength, and elastic modulus of the two types of concrete, with and without SAP, were also investigated and highlighted.

Compatibility between Rice Straw Fibers with Different Pretreatments and Ordinary Portland Cement.

The compatibility between crop straw and Portland cement greatly restrict the application of crop straw in cement-based materials. In this study, rice straw fibers with different pretreatments were added to ordinary Portland cement (OPC), and the influence of different rice straw fiber (RF) content on the hydration process of OPC was measured using calorimeter tests. Additionally, compatibility between RF and OPC was evaluated using the inhibitory index. As a result, steam explosion treatment of rice straw removed most hemicellulose and post-treatment bleaching was used for delignification. As compared with the pure OPC, addition of RF inhibited the hydration of OPC, and the inhibition degree reduced with the increase in pretreatment degree of RF. The inhibitory index grade of different RF filled OPC (RF-OPC) samples is directly related to hemicellulose and lignin content. Compared with lignin, hemicellulose has a greater influence on cement hydration. Without considering the influence of other components, the RF-OPC samples with hemicellulose content of 1.54 wt.% reached the inhibitory index extreme grade, and the hemicellulose content of 2.05 wt.% led to the cessation of cement hydration. The inhibitory index of the samples with 2.05 and 0.85 wt.% lignin content is moderate and low grade, respectively. In addition, the results of XRD patterns and SEM images are consistent with those of heat of hydration. In terms of mechanical properties of cement-based composites with 10 wt.% rice straw fibers, pretreatment of fibers is beneficial to improving the fracture toughness of the samples.

Effect of CNFs on the mechanical properties and microstructure of early strength seawater sea-sand engineered cementitious composites

Carbon nanofibres (CNFs) are a promising material for improving the mechanical properties of cementitious composites. Thus, it is necessary to disperse CNFs for use in materials. In this study, three types of surfactants used in distilled water and seawater were investigated. To obtain the optimal dispersion conditions, the effects of different types and concentrations of surfactants and ultrasonic treatment times on the dispersion of CNFs were investigated quantitatively. The CNF suspensions were studied via visual examination, Transmission electron microscopy (TEM), and Ultraviolet–Visible (UV–Vis) spectroscopy. The compressive strength, tensile strength, and porosity were examined to evaluate the mechanical properties of CNF-modified early strength seawater sea-sand engineered cementitious composites (SS-ECCs). Moreover, field-emission electron Scanning microscopy (SEM) was used to study their microstructures. After dispersion with surfactants and ultrasonication, individual fibres were found in the suspension. Seawater adversely affected the stability of the suspensions. Well-dispersed CNFs improved the mechanical properties of the cementitious composites, with an increase in compressive and tensile strengths of 21–24% and 16–20%, respectively. The tensile strain capacity increased by approximately twofold. The porosity was reduced and the pores structure was refined. Microscopic examination proved that CNFs were also well dispersed in cement matrix. The results showed that the addition of CNFs could significantly improve the mechanical properties of cement-based composites.

Surface Modification of Glass Textile for the Reinforcement of a Cement-Based Composite: A Review

The mechanical properties of cement-based composites reinforced with glass textile are strongly affected by the low ability of the inorganic matrix to penetrate within the single filaments, and by the low durability of the fibers in an alkaline environment. Over the last decades, different studies have investigated the possibility to improve the mechanical properties and the durability of this class of composites by modifying the surface of the reinforcement, mainly using different types of organic or inorganic coatings. Although different solutions have been proposed, the feasibility of applying these techniques strictly depend on the final application of the composite. This review aims to give an overview of the different methods that have been proposed in the literature and to highlight advantages and drawbacks.

Effects of nano-SiO2 coated multi-walled carbon nanotubes on mechanical properties of cement-based composites

Interfacial microstructure and interactions largely affect the mechanical properties of multi-walled carbon nanotubes (MWCNTs) reinforced cement-based composites. To improve the interfacial adhesion of MWCNTs-cement composites, a simple and effective method for preparation of SiO2/MWCNTs nano-composites were put forward using polyvinyl pyrrolidone (PVP) as a surfactant without any oxidation treatment on MWCNTs. The morphology, microstructure and chemical composition of SiO2/MWCNTs nano-composites were characterized by electron microscopy, Fourier transform infrared spectroscopy (FTIR), Raman spectrum, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). It was found that amorphous nano-SiO2 uniformly and densely grown on the surface of MWCNTs, forming a rougher film. The chemical reactivity of the nano-SiO2 film was detected by immersion tests in Ca(OH)2 solution, where EDS and FTIR analysis confirmed the formation of hydrated calcium silicate gel (C-S-H). The effects of SiO2/MWCNTs on mechanical properties of cement mortars were investigated and compared with that of cement-based composites incorporating pristine MWCNTs. When 0.25 wt% and 0.50 wt% SiO2/MWCNTs were added, the flexural strengths of cement mortars were increased by 11.9% and 25.4%, respectively, which were more significant than the enhancement effects on compressive strengths (8.5% and 19.0%). The fracture surfaces of different samples were observed by SEM, and the Ca(OH)2 content was quantitatively determined by TG analysis, indicating that the chemical reaction of nano-SiO2 film with Ca(OH)2 generated from cement hydration process can effectively increase the C-S-H gel content at the interface between MWCNTs and cement matrix, which is the prime reason for the increase of mechanical properties.

Overview of Workability and Mechanical Performance of Cement-Based Composites Incorporating Nanomaterials

The need to enhance the mechanical performance of cement-based composites such as concrete and mortar has led to the development of various innovative ways to meet the current and future performance demand. The recent trend in cement-based composites technology has shown the viability of further enhancement of the mechanical performance of cement-based composites by the incorporation of nanomaterials. As the proportions of components in cement-based composites, it is paramount for the stakeholders in the construction industry to understand how nanomaterials affect the mechanical performance of these composites. Therefore, this overview was undertaken to investigates the effect of nanomaterials on the mechanical properties of cement-based composites. Results from various studies showed that the mechanical properties of cement-based composites can be improved with the incorporation of nanomaterials. The enhancement in the mechanical properties of the cement-based composites with the incorporation of nanomaterials was attributed to the pore filling effect of the nanomaterials coupled with the ability to accelerate hydration reaction which results in the formation of more products. It was also observed that the optimum dosage of nanomaterial varies with types. Therefore, it was recommended to determine the optimum dosage of these materials before its large-scale application.

Relationship between oxygen content of graphene and mechanical properties of cement-based composites

Cement composites were realized containing graphene-based materials having different oxygen content (from 0 to 45%). It was found that the polarity of the reinforcement influences both the dispersion in water and the chemical interaction with the hydrated cement matrix, and thus the mechanical performance of the composites. In particular, the reinforcements with the highest oxygen content result aggregated while the cement with the highest strength is obtained with functionalized graphene, containing 5% oxygen, where the surface has sufficient polar groups to guarantee proper dispersion and interaction with the hydrated cement.

Effects of different kinds of carbon black nanoparticles on the piezoresistive and mechanical properties of cement-based composites

Carbon black nanoparticles (CBN) of different sizes, morphologies, microstructures and surface areas can be used to develop cement-based materials for strain monitoring and damage detection of concrete structures. There is a lack of systematic comparisons between mechanical and electrical properties of smart mortars fabricated with CBN of different characteristics. In this study, (4 × 4 x 7.5) cm prismatic composites containing CBN of distinct dibutyl phthalate (DBP) absorption number, conductivity and surface area were produced and subjected to direct current (DC), biphasic DC, piezoresistive and compression tests. Results show that CBN aggregates with the lowest structure (DBP of 125 cm³/100 g) and the highest resistivity provided high values of gauge factor, stress sensitivity and compressive strength, while CBN aggregates with very high structure (174 cm³/100 g) and low resistivity provided low internal capacitance and high electrical conductivity. The experimental data indicated that increases in structure and surface area improved the conductive network and reduced the internal capacitance, but decreased both compressive strength and piezoresistive response, due to reductions of variations of tunneling resistance between nanofillers.