Mechanical Properties Of Cement Composites Research Articles

Improvement of the mechanical properties of cementitious composites by the novel synthesized borophene nanosheets

This study is the first investigation focused on the preparation of novel synthesized borophene nanosheets and their use in cementitious composites. The two-dimensional β borophene was prepared by a facile and low-cost sonication process including ultrasonic cavitations. To understand the effect of the novel synthesized borophene nanosheets, varying ratios of 0, 0.5, 1, 2, 3, and 5 wt% of cement were incorporated in cement composites and improvements on the mechanical strength, workability, and toughness were identified. Also, for the microstructure evaluation, several advanced characterization techniques including SEM, EDS, XRD, and TGA were presented and the relationship between the microstructure and mechanical properties of cementitious composites modified with borophene nanosheets was discussed. As a result of this study, with the incorporation of the borophene nanosheets, clear improvements were achieved for the 28 day compressive and flexural strengths of the specimens within a range of 5–19% and 4–13%, respectively. The findings also indicated that borophene nanosheets contributed to the formation of a denser microstructure of the corresponding cement composites. Thus, within this study, the utility of as-prepared borophene nanosheets in cementitious composites is proved and proposed as a two-dimensional potential nanomaterial candidate to be used in cementitious composites.

Potential of Using Amazon Natural Fibers to Reinforce Cementitious Composites: A Review.

The engineering application of natural lignocellulosic fibers (NLFs) has been intensifying all over the world due to their low cost and abundance, as well as their being eco-friendly and presenting favorable technological properties in polymeric and cementitious composites. Brazil, especially the Amazon region, owing to its climate and geographic position, has an abundant variety of NLFs that are still unexplored with great potential for use in various composite materials and applications such as civil construction, automobile parts and armor. Therefore, this review aims to establish a parallel between the technological properties of cementitious composites reinforced with Amazon NLFs, both in fresh and hardened states, and to analyze, compare results and contribute to a better understanding of the similarities and differences between the types of reinforcements. A relevant contribution of this review is the possibility of improving knowledge about Amazon NLFs, showing their potential for application in eco-friendly materials, in addition to contributing to studies with new NLFs not yet applied in composite. For this, it was necessary to carry out a literature survey on the physical, chemical and mechanical properties of cementitious composites reinforced with NLFs, in addition to analyzing case studies involving fibers such as curaua, açai, bamboo, jute and sisal. It can be concluded that the physical and chemical characteristics of the Amazon NLFs directly influence the technological properties of cementitious compounds, such as mechanical strength and water absorption. However, there might be a need for surface treatment aimed at improving adhesion and durability of the cementitious composite. Finally, some suggestions for future research work are highlighted in order to show the need to continue investigations on the application of Amazon NLFs in cementitious composites.

Electrical Conductivity and Compressive Strength of Cement Paste with Multiwalled Carbon Nanotubes and Graphene Nanoplatelets

Many studies have been conducted using carbon-based nanomaterials (CBNs) for improving the electrical conductivity and mechanical properties of cementitious composites, but their practical use is yet to be achieved. Several methods have been attempted to secure the dispersibility in the cementitious composite matrix of CBNs, such as multiwalled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs). In this study, MWCNTs and GNPs were noncovalently functionalized using melamine, a low-cost chemical, and ball milling, a simple process commonly used in industrial fields. Additionally, MWCNTs and GNPs having one- and two-dimensional shapes were mixed with the cement paste to examine their effect on electrical conductivity and compressive strength. Following the experiment, it was shown that the electrical conductivity was improved via the noncovalent functionalization of MWCNT and GNP. The compressive strength increased up to approximately 0.30–0.60% of the CBNs content; however, for CBN content higher than 0.60%, the compressive strength decreased. The hybrid MWCNT and GNP mixture had a negligible effect on the electrical conductivity and compressive strength.

Cementitious composites incorporating Multi-Walled Carbon Nanotubes (MWCNTs): effects of annealing and other dispersion methods on the electrical and mechanical properties

This study focuses on different techniques for dispersing Multi-Walled Carbon Nanotubes (MWCNTs) in cementitious materials. The impact of dispersion is observed through electrical resistivity and mechanical properties of cementitious composites. Two contents (0.5 and 1% by mass of cement) of MWCNTs are investigated and three different techniques were used to disperse CNTs in water by sonication: (i) pristine, P-CNT, (ii) functionalized carbon nanotubes by classical approach (dispersive agent, D-CNT), and (iii) by an innovative approach (annealing, A-CNT). Self-sensing response of the material under cyclic compressive loading is measured with Wheatstone Bridge (WSB) circuit. Results showed a detrimental effect of dispersive agent on the resistivity and mechanical properties of cementitious composites irrespective of the content of CNTs. However, the impact of P-CNT and A-CNT on the reduction of mechanical properties is slight. With the use of 1% content of A-CNTs, a stable resistivity response of the material is observed irrespective of the saturation degree. This indicates that content higher than 1% of A-CNTs is not required for the development of smart cementitious composites for structural health monitoring (SHM). The test results of self sensing measurements indicate a poor repeatability of the electrical response for plain mortar under each loading cycle while, stable response is noticed with specimens incorporating 1% of A-CNTs. The maximum variation in fractional change in voltage (FCV) shown by plain mortar is 6.3% indicating high electrical resistance of plain mortar, while in case of mortar containing 1% A-CNTs, variation in FCV is 35% indicating lower electrical resistance and better sensitivity of the material.

Synergistic effects of CNTs/SiO2 composite fillers on mechanical properties of cement composites.

This paper investigated the hybridization use of carbon nanotubes (CNTs) with nano-SiO2 in cement composites. The (CNTs)/SiO2 composite fillers were designed and prepared by electrostatic self-assembly technology to reinforce cement composites. The mechanical properties, microstructure and hydration characteristics of cement composites incorporating CNTs/SiO2 fillers were systematically researched. The morphology and optical microscopy results show that the CNTs inside CNTs/SiO2 fillers tended to unwind due to the mechanical separation and steric hindrance of nano-SiO2 particles with certain size, and its agglomeration degree in the suspension greatly alleviated over time. With the appropriate incorporation of CNTs/SiO2 fillers (containing 0.10 wt% CNTs and 0.50 wt% nano-SiO2), the flexural strength, compressive strength and flexural toughness of the cement mortar matrix were sharply increased by 33.5%, 36.5% and 56.0% after curing for 28 days compared to the plain sample, respectively. Microscopic observations show that appropriate nano-additives can densify and refine the hydrated microstructure, and the crack-bridging, debonding and pull-out behaviors of CNTs were all observed. Hydration analysis quantitatively reveals that CNTs/SiO2 fillers significantly accelerated the cement hydration process by virtue of the nano-nucleating action. The reinforcing mechanisms of CNTs/SiO2 fillers can be attributed to the proposed synergistic effects of CNTs/SiO2 fillers, which mainly include the better dispersion stability of CNTs, the nucleating effect of nano-additives and the pozzolanic reaction by nano-SiO2, thus positively leading to increased mechanical properties.

A study on effectiveness of inorganic and organic corrosion inhibitors on rebar corrosion in concrete: A review

Reinforced concrete is the most extensively used building material in the construction industry. Generally, well-made concrete provides good physical and chemical protection to the embedded steel bar against an aggressive environment. The highly alkaline concrete pore solution protects the steel reinforcement from aggressive ions by forming a passive oxide layer over the steel surface. However, the passive film can be destroyed, and corrosion of steel reinforcement can be initiated either due to carbonation or due to the presence of a sufficient amount of chloride ions at the rebar level. Chloride induced corrosion of steel reinforcement affects the durability and decreases the service life of reinforced concrete structures exposed to aggressive environments, which results in huge repair and maintenance costs. By keeping in view, the substantial economic loss incurred due to corrosion of steel reinforcement in reinforced concrete structures, it is necessary to adopt adequate measures to minimize the corrosion of steel reinforcement in concrete. The most common corrosion prevention technique is the use of corrosion inhibitors in concrete. Several research works have been reported in the literature to evaluate the efficiency of corrosion inhibitors against chloride-induced corrosion of steel reinforcement in concrete. Corrosion inhibitors are typically introduced either as an admixture during the preparation of fresh concrete mixes or as a surface application on the hardened concrete to prevent the onset of corrosion of steel reinforcement or extend the corrosion initiation time in reinforced concrete structures. This review article summarizes the reported research works on inhibiting the behaviour of organic and inorganic corrosion inhibitors against chloride-induced corrosion of steel reinforcement in simulated concrete pore solution such as saturated calcium hydroxide solution containing varying concentrations of chloride ions as well as in cementitious composites. Further, the reported research works on the effect of corrosion inhibitors on the mechanical properties of cementitious composites are also are reviewed and discussed.

Influence of fibers on the mechanical properties of cementitious composites - a review

Concrete is one of the major construction materials and it will possess sufficient compressive strength if properly designed and prepared. However, due to lower tensile strength and brittle nature, plain cement concrete tends to show sudden failure. Under this context, the different methods to improve the tensile strength of concrete have gained importance. The addition of fibers to concrete is considered to be an effective method to prevent brittle failure and improve the desirable characteristics of concrete such as tensile strength, impact resistance, abrasion resistance, shatter resistance, post-cracking ductility and strain capacity. Some types of fibers are also used in concrete for the repair, rehabilitation and retrofitting of structural members. The amount of fibers added to a concrete mix is based on volume fraction and aspect ratio. The past studies carried out on Fiber Reinforced Concrete (FRC) led to the development of more effective fiber mixing methods and performance-enhancing strategies. Among the various fibers, steel fiber is the conventional and most popular material. Several other natural and synthetic fibers also have been subjected to extensive research across the globe. In addition to all these, the effectiveness of recycled fiber reinforced concrete (RFRC) and fiber reinforced geopolymer concrete have been checked by several researchers and advancements in these materials are considered to be crucial steps towards the achievement of sustainable construction. This paper reviews the performance of various natural and synthetic fibers such as steel fiber, glass fiber, basalt fiber, jute fiber, and polymer fiber as a reinforcing material in concrete. The study is based on various fresh and hardened properties of FRC and parameters such as relative fiber matrix stiffness, volume of fibers, aspect ratio of fibers, orientation of fibers, workability and compaction of concrete, size of coarse aggregate and mixing.

Mechanical Properties of Cement Composites Using Modified Plastics by Gamma Irradiation

Recently, pollution caused by an increasing amount of worldwide plastic waste has become a global problem. However, these concerns can be alleviated by the use of gamma-ray technology. Using radiation technology, plastic wastes can be converted into a variety of useful purposes presenting powerful opportunities for environmental sustainability and material innovations. Plastics are strong, durable, waterproof, lightweight, easy to mold, and recyclable. In this study, plastic aggregate modified by gamma irradiation was mixed into cement composites, and mechanical property evaluation experiments were conducted. As a result, it was confirmed that the physical performance of cement composites was improved by up to 70% in the case of using the modified plastic aggregates compared to the general plastic aggregate.

The mechanical performance of recycled cardboard kraft fibres within cement and concrete composites

Global population growth around the world requires significant infrastructure and building developments. The building and construction industry uses excessive quantities of virgin resources for those developments as well as contributing to the waste generated from the residential and commercial sectors. A contemporary solution is required to reduce these negative environmental impacts. In this study, the mechanical properties of cement composites containing kraft fibres (KFs) derived from waste cardboard was experimentally investigated. KFs and metakaolin (MK) were integrated within concrete samples as a cement substitute material. The compressive, flexural, and tensile strength was determined on three mix designs containing 5% raw KFs, 5% surface modified KFs, and matrix modified concrete specimens. Silica fume (SF) was applied to the fibre walls as fibre modification to lower the alkaline zone around the fibre within the cementitious matrix. 5% MK was used as a partial cement substitute to lower the alkaline level of concrete samples. All KF concrete specimens exhibited lower compressive strength properties. However, MK modified samples exhibited the highest tensile strength of 11 MPa. Fibre modified samples had stronger compressive and tensile strength of 20 and 9 MPa, compared to raw KFs. However, raw KFs exhibited a higher flexural strength of 2.5 MPa. The compressive, tensile, and flexural strength of the control were 25, 10 and 2.6 MPa, respectively. Scanning electron microscopy (SEM) observations demonstrated sufficient SF adhesion on the fibre walls, while the energy dispersive x-ray spectroscopy (EDS) observations showed efficient dispersion of all composite materials.

Influence of nanosilica and binary oxide systems on the selected physical and mechanical properties of cement composites

Influence of nanosilica and binary oxide systems on the selected physical and mechanical properties of cement composites

Behavior and design of nano/micro-scale carbon modified multifunctional cementitious composites

This work proposes a design concept of nano/micro-scale carbon modified multifunctional cementitious composites based on the original fabrication method of combined graphene/PVA nanofluid additive, in which nano carbon material graphene was produced from low-cost graphite raw material and surface functionalized by PVA in water in a one-step preparation process, which can directly substitute water in the cement casting. Incorporating the complementary advantages of the bridging three-dimensional micron-scale carbon fiber and the pore-filling and lubricating two-dimensional nano-material graphene, the composite modification can not only improve the mechanical properties of cementitious composites but also gift them with high electrical conductivity, whose electrical resistivity dropped to 0.72 kΩ·cm compared to 13.12 kΩ·cm of the blank. In particular, under such low resistivity, the mechanical strengths were not reduced as with the addition of other single carbon materials but were improved compared with the blank. The results of this work provide a novel approach for designing and developing multifunctional cementitious composites, which would be a promising building material for structural health monitoring.

Nano-Silicon Dioxide-Optimized Cementitious Composite Material in the Restoration of Concrete Cracks in House Building

This study aimed to investigate the restoration performance of nanocomposite materials used in house building. The ethyl orthosilicate was used as raw material, the sol–gel method was adopted to synthesize nano-silicon dioxide (SiO2), and the doped nano-SiO2 cementitious composite material was prepared. Then, the mechanical properties of the cementitious composite material based on different nano-SiO2 content was analysed through the characterization and performance test. The results showed that the nano-SiO2 prepared this time had regular crystal phases, small particle size, and certain thermal stability, with fully developed crystal grains. By analysing the mechanical properties of nano-SiO2 doped cementitious composites, it was found that the initial setting time and final setting time both showed an upward trend when the doped content of nano-SiO2 was less than 3%. Besides, the initial setting time and final setting time of cementitious composites decreased when the content was 3%–5%. The fluidity analysis indicated that the fluidity of cementified composites gradually dropped with the growth of nano-SiO2 content. The test results of mechanical properties of cementitious composites doped with nano-SiO2 revealed that the flexural strength and compressive strength of cementitious composites presented a trend of first rising and then falling, as the nano-SiO2 content rose. Shrinkage test results showed that the shrinkage rate of the gel composites increased with the growth of duration. The specific surface area and pore ratio measurement results indicated that the specific surface area of the cementitious composite doped with nano-SiO2 was 33.42 m2/g, and the porosity was small. In conclusion, the nano-SiO2-doped cementitious composite material synthesized in this study had good mechanical properties and could be applied in the repair of concrete cracks in house building.

An Experimental Study on the Mechanical Properties of Cement Composites Based on Curing Methods and Plastic Aggregate Types

An Experimental Study on the Mechanical Properties of Cement Composites Based on Curing Methods and Plastic Aggregate Types

Effects of post-fire curing on the mechanical properties of cement composites containing carbon black nanoparticles and multi-walled carbon nanotubes

Concrete elements exposed to fire can partially recover strength and stiffness if recured in water or in a moist environment. This paper reports a pioneering investigation of the influence of post-fire curing on residual mechanical properties and microstructure of cement mortars containing different concentrations of carbon-black nanoparticles (CBN) or multi-walled carbon nanotubes (MWCNT). A total of 84 specimens were subjected to various maximum exposure temperatures (200, 400, or 600 °C) and post-fire curing (water-recuring for 1 day followed by air-recuring for 27 days). X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectrometry (EDS) were used to investigate the microstructure of different types of specimens. Experimental tests were carried out to determine the compressive strength, static modulus of elasticity, and dynamic modulus of elasticity of rehydrated specimens. Nanofillers enhanced the strength recovery of composites exposed to temperatures up to 400 °C, since they improved rehydration reactions. In this case, the rehydration process provided values of relative residual strength and elastic modulus factors higher than 85%. Composites containing 0.4% MWCNT and 3% CBN presented the best strength and stiffness recovery. Therefore, small contents of carbon nanomaterials provided additional nucleation sites for dehydration products to sediment and being rehydrated. Moreover, water adsorbed by the nanomaterials during the water-recuring process was used later to provide greater rehydration. Composites containing 1.2% MWCNT and 9% CBN presented lower mechanical properties recovery, as high contents of nanomaterials made it harder for water to reach decomposed C-S-H gel, hindering the development of rehydration reactions. After 600 °C, lower relative residual factors were obtained, but always higher than 40%. It happened because nanofillers were not able to provide those rehydration improvements, since their thermal decomposition started at about 500 °C.

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.

Mechanical properties of graphene nanoplatelets-reinforced concrete prepared with different dispersion techniques

In this paper, an experimental investigation is carried out to study the effects of graphene nanoplatelets (GNPs) on the mechanical properties of cementitious composites with coarse aggregates. The concrete mixtures with GNPs concentrations ranging from 0.025% to 0.10% by weight of the cement are prepared, where a wet dispersion technique that employs high shear mixing and polycarboxylate-based superplasticizer to disperse GNPs in water. The effects of various dispersion parameters including different high shear mixing durations as well as the use of ultrasonication together with high shear mixing on the dispersion of GNPs are studied. The dispersion quality of GNPs is assessed through optical microscopy, Raman spectroscopy, and Scanning Electron Microscopy tests. Compressive strength and flexural strength tests are conducted to assess the effects of GNPs on mechanical properties of the fabricated GNP-reinforced concrete specimens. Results show that all the dispersion procedures considered in this study can disperse GNPs in water without causing any basal or vacancy defects in graphene sheets and reduce the size of graphene flakes. The use of ultrasonication together with high shear mixing leads to the smallest size graphene sheets. When the GNPs are added to the concrete mixture at a dosage of 0.025%, a maximum increase of 17% in compressive strength is observed, while no significant effect of GNPs on the flexural strength is noticed.

Investigating the compatibility of nickel coated carbon nanotubes and cementitious composites through experimental evidence and theoretical calculations

Nickel coated multi-walled carbon nanotubes (NiMCNTs) are favorable reinforcing nanofillers for modifying cementitious composites due to their preeminent mechanical properties, electrical conductivity, thermal properties and dispersibility. This paper investigates the mechanical properties and compatibility of NiMCNTs filled cementitious composites, having two different types of cement, two water to cement ratios, and two dosages of five types of NiMCNTs. The results show that 0.06 vol% NiMCNTs with small aspect ratios can significantly enhance the mechanical properties of cementitious composites, while NiMCNTs with large aspect ratios play a better strengthening effect at 0.03 vol%. The flexural strength/toughness of cementitious composites containing 0.06 vol% NiMCNTs with an aspect ratio of 200 can be increased by 19.65%/116.78%. Adding 0.03 vol% NiMCNTs with an aspect ratio of 1000 enhances the compressive strength/toughness of composites by 18.61%/47.44%. Besides, NiMCNTs have preferable compatibility to cementitious composites prepared by P·O 42.5R cement with a water to cement ratio of 0.3. The enhancement mechanism is related to the denser microstructure and effective suppression of microcracks in the cementitious matrix by NiMCNTs with filling, bridging and pull-out effects, as well as the high interface bond strength between NiMCNTs and matrix. A strength prediction model for NiMCNTs reinforced cementitious composites is also established to estimate the mechanical strength of cementitious composites containing NiMCNTs with different aspect ratios/contents, showing a small relative error within ±6%/±13% for predicted flexural/compressive strength values in comparison with the experimental results.

Elastic properties of cement-based composites reinforced by nano-tailored hybrid fiber

The elastic properties of cementitious composites reinforced by nano-tailored hybrid fibers are analyzed using a micromechanical method. The microstructural feature of the hybrid fiber is that uniformly aligned carbon nanotubes (CNTs) are grown radially on the circumferential surface of carbon fibers (CFs). The CNT waviness and CNT/cement interfacial region are considered. The predictions are compared with experiments, which guarantee the validity of the model. The mechanical properties of cementitious composites, especially in transverse direction, are enhanced due to the radial growth of CNTs on the CFs. The CNT/cement interfacial zone may have a significant effect on the elastic behavior of the nano-tailored hybrid fiber-cement composites. As the mechanical properties of interphase are higher than those of the cement matrix, increasing the interphase thickness causes an improvement in the elastic and shear moduli. The CNT non-straight shape decreases the transverse elastic modulus.

Synthesis of Highly-Dispersed Graphene Oxide Nanoribbons-Functionalized Carbon Nanotubes-Graphene Oxide (GNFG) Complex and Its Application in Enhancing the Mechanical Properties of Cementitious Composites.

In this study, a graphene oxide nanoribbons–functionalized carbon nanotubes–graphene oxide (GNFG) complex was hydrothermally synthesized as a nanomaterial for reinforcing cementitious composites, using a modified Hummers’ method. Three types of components existed in the GNFG: Type I, the functionalized carbon nanotubes–graphene oxide nanoribbons (FCNTs–GNR); and types II and III are graphene oxide (GO) and functionalized carbon nanotubes (FCNTs), respectively, which exist independently. The dispersivity of GNFG and its effects on the mechanical properties, hydration process, and microstructures of cement pastes were evaluated, and the results were compared with those using cement pastes incorporating other typical carbon nanomaterials. The results demonstrated that dispersion of GNFG in aqueous solutions was superior to that of the CNTs, FCNTs, and GO/FCNTs mixture. Furthermore, the highly-dispersed GNFG (0.05 wt.%) improved the mechanical properties of the cement paste after 28 days of hydration and promoted the hydration of cement compared to CNTs, GO, and GO/FCNTs mixture (0.05 wt.%). The results in this study validated the feasibility of using GNFG with enhanced dispersion as a new nano-reinforcing agent for various cementitious systems.

Data-driven machine learning approach for exploring and assessing mechanical properties of carbon nanotube-reinforced cement composites

Traditional experimental investigation on the mechanical properties of cement composites is deprecated due to the intensive time and labor involved. Existing predictive models can hardly map the complicated relationships among mechanical attributes and behavior. This study first adopts machine learning to predict the mechanical properties of carbon nanotube (CNT)-reinforced cement composites. For this purpose, predictive models are trained on the previously published experimental data and results demonstrate that machine learning models present better generalization ability and predictive performance than the traditional response surface methodology. A sensitivity analysis indicates that the factor having the maximum influence on compressive strength is the length of CNTs, whereas that having the maximum influence on flexural strength is the curing temperature. Thus, it can be concluded that compared with the traditional experimental investigation and regression methods, machine learning can efficiently and accurately predict the mechanical properties of CNT-reinforced cement composites.