Mechanical Properties Of Cement Composites Research Articles

Composite grouting mortar based on 3D-NKM - nanocrystalline inoculant

For the waterproofing of tunnels and the uniform distribution of space between the lining of tunnels and rock, composite injection solutions are used. To improve the physical and mechanical properties of cement composites, the nanoconstruction effect is used, which is possible when using nanoparticles with extended geometry. Nano-additives and nanomodifiers consisting of nanoparticles, both natural and artificial and technogenic, can be used for the production of cement-containing solutions and concretes. For example, under certain conditions nanocrystalline powder of oxides and hydroxides of aluminum to nanotechnogenic raw materials can be referred to wastes of technogenic origin. The paper investigated the effect of nano-additives-boehmite, which is a waste of production, to increase the strength and frost resistance of plugging materials made on the basis of cement when administered. It is established that the use of boehmite as an additive in cements leads to an increase in the strength properties of concrete and increase its frost resistance, which is a prerequisite for long-term and reliable operation of the composite solution. Thus, the composite solution modified by boehmite is the basis for the creation of plugging solutions

From Graphene Oxide to Reduced Graphene Oxide: Impact on the Physiochemical and Mechanical Properties of Graphene-Cement Composites.

Graphene materials have been extensively explored and successfully used to improve performances of cement composites. These formulations were mainly optimized based on different dosages of graphene additives, but with lack of understanding of how other parameters such as surface chemistry, size, charge, and defects of graphene structures could impact the physiochemical and mechanical properties of the final material. This paper presents the first experimental study to evaluate the influence of oxygen functional groups of graphene and defectiveness of graphene structures on the axial tension and compression properties of graphene-cement mortar composites. A series of reduced graphene oxide (rGO) samples with different levels of oxygen groups (high, mild, and low) were prepared by the reduction of graphene oxide (GO) using different concentrations of hydrazine (wt %, 0.1, 0.15, 0.2, 0.3, and 0.4%) and different reduction times (5, 10, 15, 30, and 60 min) and were added to cement mortar composites at an optimal dosage of 0.1%. A series of characterization methods including scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, thermogravimetric analysis, and Fourier transform infrared spectroscopy were performed to determine the distribution and mixing of the prepared rGO in the cement matrix and were correlated with the observed mechanical properties of rGO-cement mortar composites. The measurement of the axial tension and compression properties revealed that the oxygen level of rGO additives has a significant influence on the mechanical properties of cement composites. An addition of 0.1% rGO prepared by 15 min reduction and 0.2% (wt %) hydrazine with mild level of oxygen groups resulted in a maximum enhancement of 45.0 and 83.7%, respectively, in the 28-day tensile and compressive strengths in comparison with the plain cement mortar and were higher compared to the composite prepared with GO (37.5 and 77.7%, respectively). These results indicate that there is a strong influence of the level of oxygen groups and crystallinity of graphene structures on the physiochemical and mechanical properties. The influence of these two parameters are interconnected and their careful balancing is required to provide an optimum level of oxygen groups on rGO sheets to ensure that there is sufficient bonding between the calcium silicate hydrate (C-S-H) components in the cement matrix and minimum level of defects and higher crystallinity of graphene structures, which will improve the mechanical properties of the composite. Finding the optimized balance between these two parameters is required to formulate graphene cement composites with the highest performance.

Mechanical properties and reinforcing mechanisms of cementitious composites with different types of multiwalled carbon nanotubes

In this study, reinforcement effect of 12 types of multiwalled carbon nanotubes (MWCNTs) on mechanical properties of cementitious composites was investigated Research results showed that among pristine MWCNTs with different diameters and lengths, the short MWCNTs with large diameter present the best reinforcing effect on strength of composites. Functionalization of MWCNTs is beneficial for enhancing strength of composites. Moreover, hydroxyl-functionalized MWCNTs feature a better reinforcement effect compared to carboxyl-functionalized MWCNTs. The best relative/absolute enhancements of 79%/74 MPa and 64.4%/5.6 MPa in compressive and flexural strength of composites are achieved by incorporating 0.5% of nickel-coated MWCNTs. XRD analyses revealed that the incorporation of MWCNTs decreases the orientation of CH in matrix, which is consistent with SEM observations. TG analyses showed that MWCNTs inhibit hydration of composites due to their absorption effect. However, extensive MWCNT networks improve microstructure of matrix and hinder the crack development under loading through fiber bridging and pull-out.

Voids identification in rubberized mortar digital images using K-Means and Watershed algorithms

In the construction industry, the use of sustainable raw materials has become a challenge. Rubber scrap tires have been investigated by several researchers as an alternative aggregate to conventional because it has become a major environmental problem in all parts of the world. Scanning Electron Microscopy (SEM) images are contributing to the understanding of the influence of this type of aggregate in the main physical and mechanical properties of cementitious composites. Voids derived from the use of rubber as aggregate in mortar can be found by SEM technique; however, that depends on a visual analysis, having a low accuracy of the recognition. To do so, image processing techniques can be used to fill the gap by increasing the reliability of the microstructural analysis. In this work, tire rubber waste is used in 0%, 5%, 10%, 15% and 30%, replacing, in mass, the conventional aggregate. Density, voids index, water absorption and mechanical resistance of the rubberized mortars were evaluated. Microscopic images were collected by scanning electron microscopy and subsequently applied to image processing technique for quantitative identification of voids in each mixture with rubber. Rubberized mortars showed lower mechanical strength compared to conventional sample. However, that is due to the voids increase in matrix mortars rubber, a property that could be calculated by SEM image analysis with the aid of image processing technique, K-Means algorithm and Watershed, which showed an accuracy of 88% identification in relation to the visual analysis. The best characterization of rubberized mortars pathologies is an important tool in the fight against mechanical strength, contributing to the increase of the use of rubber as an aggregate, which reduces the extraction of natural materials and the inadequate disposition of waste tires.

Nanoscaled Mechanical Properties of Cement Composites Reinforced with Carbon Nanofibers.

This paper reports the effects of carbon nanofibers (CNFs) on nanoscaled mechanical properties of cement composites. CNFs were added to cement composites at the filler loading of 0.2 wt % (by wt. of cement). Micrographs based on scanning electron microscopy (SEM) show that CNFs are capable of forming strong interfacial bonding with cement matrices. Experimental results using nanoindentation reveal that the addition of CNFs in cement composites increases the proportions of high-density calcium-silicate-hydrate gel (HD-CSH) compared to low-density CSH gel. It was also found that the inclusion of CNFs increases the compressive strength of cement composites.

Optimum carbon nanotubes’ content for improving flexural and compressive strength of cement paste

This study investigated the effect of multi-walled carbon nanotubes’ (MWCNTs) weight fraction on the setting time and mechanical properties of cementitious composites. Different cement mixes containing CNT-to-cement weight fractions of 0.03, 0.08, 0.15, 0.25, 0.35 and 0.5wt% were prepared in addition to the control mix. The initial and final setting times of the fresh pastes were measured on the cast day and the flexural and compressive strengths of the hardened samples were determined after 28days of moist curing. The fractured surfaces of the samples were then examined using a scanning electron microscope (SEM). The results showed that the 0.25wt% CNTs is the optimum weight fraction in terms of achieving maximum strength at a reasonable cost. Batches with lower CNTs’ contents than 0.25wt% demonstrated lower flexural and compressive strengths, whereas batches with higher CNTs’ contents than 0.25wt% produced similar or slightly higher strengths. Analysis of variance (ANOVA) confirmed that increasing CNTs’ concentration above 0.25wt% will not have a significant effect on the compressive and flexural strengths. Investigations of the microstructure, which was carried out using SEM, showed good dispersions of the nanofilaments within the cement matrix. Spots of agglomerations were noticed in batches containing 0.25, 0.35 and 0.5wt%. SEM images have also indicated that CNTs were embedded within the cement hydration products. The study findings were useful for determining the CNTs’ content required to achieve both optimum dispersion and maximum strength enhancement of cementitious composites.

Carbon nanotubes and superplasticizer reinforcing cementitious composite for aerostatic porous bearing

Cementitious composites are low cost and readily manufactured materials which can be used for specialist applications such as the production of aerostatic porous bearings. A design of experiment was used to identify the effects of superplasticizer additions and carbon nanotube inclusions on the physical and mechanical properties of cementitious composites which can be applied as porous restrictor in aerostatic thrust bearings. The presence of carbon nanotubes was able to increase the bulk density, the compressive strength and the modulus of elasticity, and also decrease the apparent porosity of the composites. The composite made with 0.4 wt.% of superplasticizer and 0.05 wt.% of carbon nanotubes achieved acceptable properties for the use as double-layered porous restrictor in aerostatic thrust bearings.

Improving the mechanical performance of cement composites by carbon nanotubes addition

Abstract: The addition of high performance nano materials like carbon fibers, carbon nanotubes, graphene etc. in the cement and concrete is gaining attention for achieving multifunctional composite materials with enhanced mechanical, physical and electrical properties. The nano-metric size range and the exceptionally high mechanical properties of carbon nanotubes possess very great potential for their utilization in cementitious composites for obtaining remarkable properties. Billions of ton of concrete is used every year in construction industry and its quantity may be reduced to a large extent only by improving the mechanical and durability properties. One way of achieving the enhanced mechanical properties of cement composite is the utilization of thoroughly dispersed carbon nanotubes in the composite matrix. In the present research, small fractions of multiwall carbon nanotube (MWCNTs) i.e. 0.05 and 0.10 wt.% of cement have been incorporated into the cement concrete and their influence on the mechanical properties of the resulting composites have been studied. It is a well-known fact that the uniform dispersion of the MWCNTs in the composite matrix holds the key for the performance improvement. Therefore, special attention was paid to this aspect and uniform dispersion of MWCNTs was achieved through the use of high energy sonication in the presence of modified acrylic based polymer (acting as a surfactant). The concrete specimens were tested in splitting tensile, flexure and compressive strength after 3, 7, 28 and 56 days of immersed water curing. It was observed that the addition of 0.05wt.% MWCNTs increased the splitting tensile strength by 20.58%, flexural strength by 26.29% and compressive strength by 15.60% as compared to the control mix at 28 days of curing. The strength enhancements for the concrete mixes containing MWCNTs may be regarded to the phenomenon of bridging, pinning and branching of the cracks at nano/micro level due to the presence of MWCNTs. Beside strength enhancements, it was also observed that the MWCNTs had tremendously enhanced the fracture energy and breaking strains of the concrete mixes as observed in three-point bending tests. The research concludes that very low amounts of MWCNTs incorporated in the cement concrete mixes improve their mechanical strengths and fracture behavior remarkably but the thorough dispersion of MWCNTs in the matrix have to be insured.

Revealing the dependence of the physiochemical and mechanical properties of cement composites on graphene oxide concentration

This paper presents a comprehensive study to evaluate the influence of graphene oxide (GO) concentration on the physiochemical and mechanical properties of cement mortar composites.

Synergistic effect of graphene-oxide-doping and microwave-curing on mechanical strength of cement

In this communication, efficient reinforcement of cement matrix was obtained by graphene-oxide (GO) doping and curing treatments. The compressive strength of plain cement is 14.3±0.2MPa. When the cement contained 0.5wt% GO, its strength reached 19.4±0.9MPa. The strength can be further enhanced by curing, which follows the sequence: Microwave-cured GO-cement > Microwave and water-cured GO-cement > Water-cured GO-cement > GO-cement without curing. The highest compressive strength (32.4±0.7MPa), which was achieved by combining GO-doping and microwave curing, is 126.6±8.1% higher than that without GO-doping and microwave curing. This demonstrates a synergistic effect of GO doping and microwave-curing on the strength of cement composite materials. Furthermore, X-ray diffraction (XRD), Fourier transform Infrared Spectroscopy (FTIR), and field emission scanning electron microscope (FESEM) characterizations revealed that the combination of GO doping and microwave-curing remarkably accelerated cement hydration, leading to the regular and compact structure and thus a high compressive strength. This work provides a new way to improve the mechanical properties of cement composites.

Mechanical Properties of Cement Composites Reinforced by Carbon Microfibers: Compressive and Bending Strength

The paper deals with comparison of chosen mechanical properties of cement composites reinforced by carbon microfibers. There are tested three mixtures, which are different in their composition. Each sample was tested by destructive methods to determine their mechanical and physical properties. The main object of experiments was verification of an influence of individual components in concrete mixture on mixture cohesion with a surface of carbon fibers. Evaluation of results and use of the best concrete mixture for experimental testing like a change of mechanical and physical properties is the second object of this paper.

Dispersed Reinforcement Based on Natural Fibres Used in Cement Composites

One of the options for improving the mechanical properties of cement composites is the use of fibre reinforcement. Nowadays, steel or polymer fibres are most frequently used for this purpose. However, given the increasingly stricter requirements related to environmental protection, one goal is to find ways of using alternative fibres of natural origin or waste fibres for which it is difficult to find other practical use. This paper focuses on one part of the development of materials which contain natural waste fibres as dispersed reinforcement in thermally insulating cement composites. The authors aimed to observe what influence the fibres have on the material’s final mechanical properties as well as thermal insulation properties. Another important factor, which was investigated, was the quotient of mechanical and thermal insulation properties. The results of this research showed that waste cellulose fibres have a considerable effect. The best compressive strength values were found in mixture M-2-BF which contained waste basalt fibres. The highest flexural strength values were reached by mixture M-3-CF-a containing cellulose fibres.

Promising low cost carbon-based materials to improve strength and toughness in cement composites

The Bio-char, the solid sub-product of pyrolysis process, has several applications in the cement and concrete green technology. In this research, the utilization of Bio-char such as nanoparticles has been analysed. Two types of pyrolyzed agro-food waste, coffee powder and hazelnut shells, have been investigated as carbon nano-aggregates, in different percentages of addition with respect to the weight of the cement. Results have demonstrated that small amount of both pyrolyzed materials improves the mechanical properties of cementitious composites, as they are capable of increasing not only the flexural and compressive strength, but also the fracture energy with a more tortuous crack path which increases the final fracture surface.

Study on the three dimensional mechanism of graphene oxide nanosheets modified cement

This paper has established a 3D mechanism model of graphene oxide (GO) nanosheets modified cement. The GO nanosheets were compounded by the improved Hummers’ method and characterized by Fourier transform infrared spectroscope (FTIR), transmission electron microscope (TEM) and atomic force microscope (AFM). The mechanism of GO nanosheets modified cement was investigated by scanning electron microscope (SEM), differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), FTIR and X-ray photoelectron spectroscope (XPS). Based on these analyses, it was confirmed that the –COOH in the GO nanosheets reacted with the hydration product of cement (Ca(OH)2). The chemical reactions connected the GO nanosheets each other, producing a 3D network structure in the GO nanosheets modified cement. Moreover, the hydration products were also inserted into this 3D network structure. Therefore, the introduction of GO nanosheets improved the mechanical properties of cement composites.

Effect of fiber length and surface characteristics on the mechanical properties of cementitious composites

A disadvantage of conventional concrete is its low flexural strength and ductility in tension. Cracks form when the tensile strength of conventional concrete, which is limited, is exceeded due to various actions (loads, restrained shrinkage, temperature variation, chemical reactivity) accentuating the effects of carbonation and chloride-induced corrosion of concrete and reinforcement, thereby compromising the residual service life and strength of concrete members. Addition of fibers to enhance the flexural capacity of structural materials through crack control is an ancient idea that is now spearheading novel developments in the area of high-performance cementitious materials. Currently, the state of the art is focused on the use of synthetic fibers in self-consolidating, fine-aggregate cementitious mixes that demonstrate strain hardening properties in tension, outstanding crack control and improved durability performance. This paper deals with experimental characterization of the performance of a material of this class, reinforced with PVA fibers (polyvinyl alcohol with original hydrophilic surface properties). Parameter of study is the length of the fibers as well as the fiber surface properties which are chemically modified through pertinent surfactants. The parametric study compares the mechanical response of FRC to that of plain (unreinforced) cementitious material of the same composition, through tests of material samples in uniaxial compression, extension, splitting and flexure.

The influences of soft and stiff inclusions on the mechanical properties of cementitious composites

The embedment of microencapsulated phase change materials (PCMs) is a promising means for improving the thermal inertia of concrete. However the addition of such soft microcapsules degrades the mechanical properties, i.e., the elastic moduli and compressive strength, of cement-based composites. This study experimentally quantifies the effects of stiff quartz inclusions and soft PCM microcapsules, individually, and when added together, on the mechanical properties of cementitious composites. In addition, a variety of effective medium approximations (EMAs) were evaluated for their ability to predict the experimentally measured composite effective moduli. The EMAs proposed by Hobbs and Garboczi and Berryman (G-B) reliably estimate experimental data. The experimental data and the EMAs were applied to develop a design rule for performance equivalence, such that the composite modulus of elasticity can be maintained equivalent to that of the cementitious paste matrix, in spite of the addition of soft PCM microcapsules.

The Influence of Nano-Fe3O4 on the Microstructure and Mechanical Properties of Cementitious Composites.

In the last decade, nanotechnology has been gathering a spectacular amount of attention in the field of building materials. The incorporation of nanosized particles in a small amount to the building materials can influence their properties significantly. And it can contribute to the creation of novel and sustainable structures. In this work, the effect of nano-Fe3O4 as an admixture (from 1 to 5 wt.% in mass of the cement) on the mechanical and microstructural properties of cementitious composites has been characterised. The study showed that Fe3O4 nanoparticles acted as a filler which improved the microstructure of a cementitious composite and reduced its total porosity, thus increasing the density of the composite. The presence of nanomagnetite did not affect the main hydration products and the rate of cement hydration. In addition, the samples containing nanomagnetite exhibited compressive strength improvement (up to 20 %). The study showed that 3 wt.% of nano-Fe3O4 in the cementitious composite was the optimal amount to improve both its mechanical and microstructural properties.

Influence of Recycled Materials on Resulting Mechanical Properties of Cement Composites

This article presents the mechanical properties of composite materials based on recycled materials which differ in their composition – type of recycled materials. Dynamic modulus of elasticity was monitored during the first 28 days since manufacture by use of non-destructive testing (resonance method). Flexural strength and compressive strength were determined for the 28 days old specimens. The aim of this article was to determine the influence of type and amount of recycled material on the resulting mechanical properties. Mixtures with 3 different microground materials (recycled concrete, marble powder and silica sand) were tested. Microground materials were produced in the company Lavaris (Czech Republic) by use of high speed grinding. The results obtained from these materials were compared with reference material – cement mortar.

Physical and mechanical properties of cementitious composites containing recycled glass powder (RGP) and styrene butadiene rubber (SBR)

Substantial amount of glass wastes are being generated all around the world. In most cases, they end up in the landfill without considering recycling option. Since it is an inert material, they occupy the landfill space for considerable amount of time unless there is a potential for recycling. Such glass wastes in the crushed form have a good potential in the infrastructure industry. In this research we investigate the possibility of utilizing recycled glass powder (RGP) in along with supplementary cementitious materials (SCMs), such as fly ash (FA) and silica fume (SF) as partial replacements of cement. The physical and mechanical properties of fresh and hardened cement mortar with such combinations are investigated. In order to improve the physical and mechanical properties of hardened mortar, styrene butadiene rubber (SBR) was also added in the mortar mix. The result shows that the addition of fine RGP, FA and SF significantly improved the bond between the SBR and cement matrix which leads to an increase in the compressive and flexural strengths. Moreover, the addition of RGP, SF and FA considerably reduced the alkali silica reaction (ASR) expansions, percentage of water absorption, and the rate of water absorption than those of the control mix. This study shows that the RGP can be successfully utilized as an effective mineral admixture in cement mortar with 25% optimal replacement of cement.

Role of EG surface modification in shaping the mechanical properties of cement composites

800x600 Cement mortars modified with expanded graphite (EG) subjected to surface treatments in gaseous ozone were investigated. It was shown that the bonding between carbon additive and cement paste strongly depends on the surface modification of EG and the chemical composition of EG surface plays the important role in shaping the mechanical properties of cement composites. The expanded graphite subjected to ozone treatment showed the substantial increase of flexural toughness of cement composite. The above results were confirmed by XPS and SEM analysis. Normal 0 21 false false false PL X-NONE X-NONE MicrosoftInternetExplorer4 DOI: http://dx.doi.org/10.5755/j01.ms.21.2.5860