Cementitious Composite Specimens Research Articles

Production of Agro-waste cement Composites: Influence of nutshells on mechanical and hardened properties

Different countries have been encountering significant obstacles in the disposal of agro-wastes in landfills, with a recent increase in landfill sites receiving inadequate or no treatment. Moreover, in addition to high disposal costs, several factors related to landfills pose a significant threat to human health and ecosystems – examples include leachates, toxins, and greenhouse gases, which constitute environmental problems. Nutshells are an example of agro-waste materials that can be utilized in different industrial and engineering applications to help save the environment. This study aims to evaluate and investigate the utilization of nutshells (from pistachios, walnuts, and hazelnuts) as a replacement material to produce an agro-waste cement composite. Different nutshell contents (0.5, 1, 1.5, 2, and 2.5% by weight of cement) were used in the preparation of the cement composite mixtures. The nutshells were characterized by X-ray diffraction and energy-dispersive X-ray spectroscopy, and scanning electron microscopy (SEM) was also implemented to observe the prepared cement mortar composites. The compressive strength, hardness, thermal conductivity, and water absorption of cementitious composites were investigated, highlighting that the addition of nutshells significantly enhances the compressive strength. Agro-waste cement composite specimens with a nutshell content of 2.5% exhibited the highest compressive strength. Other properties of the cement composites, such as the thermal insulation properties, were also enhanced by the inclusion of nutshells. For instance, thermal conductivity of all mortar composite samples reduced by 57, 48, and 45% for the addition of 2.5% walnut, pistachio, and hazelnut shells, respectively. This eco-friendly material represents a potential way to address the generation of waste products from agricultural activities and nature; suggested uses of such composites include their application in lightweight panels, thermal insulators, and sustainable building blocks, among several other materials.

Designing of passive cooling silicon oxynitride composite cement

Si2N2O, which shows high radiative cooling ability, was mixed and hardened with ordinary Portland cement to prepare cement specimens having radiative cooling abilities. The bulk cement specimens were prepared with diameters of 50 mm and two different thicknesses of 3 and 10 mm, and Si2N2O powder were mixed with 2 and 10 wt%. The temperatures of the blank specimen (without radiative cooling Si2N2O powder) and the cement composite specimens were measured in a thermostatic chamber maintained at ambient temperature, and the radiative cooling abilities of the specimens were evaluated. The obtained specimens showed a radiative cooling ability in the range 0.077–0.92 W/m2; thus, the results of this study suggested the possibility of a cement composite with passive cooling property.

Effect of core and veneer porcelain thickness and resin cement on opalescence property of glass-ceramic veneers.

This study aimed to analyze the effect of core and veneer porcelain thickness and resin cement on the opalescence property (OP) of glass-ceramic veneers, which were used to restore discolored teeth. IPS e.max CAD LT A3 ceramic specimens were fabricated by computer aided design and computer aided manufacturing (CAD/CAM). The thickness values of core porcelain groups were 0.25 and 0.50 mm, and those of the core/veneer porcelain groups were 0.25 mm core/0.25 mm dentin, 0.50 mm core/0.25 mm dentin, 0.50 mm core/0.50 mm dentin, and 0.50 mm core/0.25 mm dentin/0.25 mm incisal. To simulate the clinical bonding procedure of porcelain veneer, resin cement Variolink N Bleach XL was coated at the bottom of CAD/CAM porcelain veneer specimens to make composite specimens of CAD/CAM porcelain veneer and resin cement. The L*a*b* values of specimens in the reflection and transmission pattern were measured by a spectrophotometer. Then, the OP was calculated. The OP values of 0.25 and 0.50 mm core porcelain groups, and 0.25 mm core/0.25 mm dentin, 0.50 mm core/0.25 mm dentin, 0.50 mm core/0.50 mm dentin, and 0.50 mm core/0.25 mm dentin/0.25 mm incisal core/veneer porcelain groups were 6.10±0.50, 7.00±0.24, 6.40±0.24, 7.08±0.28, 7.16±0.21, and 7.86±0.11 respectively. With increasing thickness of core porcelain, the OP values increased significantly (P<0.05). When 0.25 mm-thick dentin porcelain was added, no significant difference was found in the OP values of specimens with the same core porcelain thickness (P>0.05). For the 0.50 mm core porcelain group, no significant difference was found between 0.25 and 0.50 mm-thick dentin porcelain groups (P>0.05), but the OP values increased significantly after increasing the 0.25 mm incisal porcelain (P<0.05). The OP values of 0.25 mm core/0.25 mm dentin, 0.50 mm core/0.25 mm dentin, 0.50 mm core/0.50 mm dentin, and 0.50 mm core/0.25 mm dentin/0.25 mm incisal CAD/CAM porcelain veneer-resin cement composite specimens were 6.29±0.31, 7.56±0.36, 7.67±0.30, and 8.65±0.53. The OP values increased with increasing thickness of the porcelain layer (P<0.05), but no statistically signi-ficant difference was found between the groups of 0.50 mm core/0.25 mm dentin and 0.50 mm core/0.50 mm dentin (P=0.733). The influence of porcelain layer thickness and resin cement on the OP value was statistically different (P<0.05), and no interaction was found between the total thickness and the presence of resin cement (P>0.05). When using glass-ceramic veneers for discolored teeth, the following are recommended to improve the OP and obtain a natural and realistic effect: adopt the design of direct sintering incisal porcelain with core porcelain; appropriately increase the thickness of core porcelain; and select resin cement with opaque effect.

Complete stress–strain curves of reactive powder concrete reinforced with basalt fibres

The compressive stress–strain curves of reactive powder concrete (RPC) reinforced with basalt fibres (BFs) were experimentally studied. The length and volume content of BFs were considered as the influencing parameters. A total of 15 groups of cementitious composite specimens were investigated. The workability, failure mode, peak stress, corresponding strain at peak stress, elastic modulus, toughness index and stress–strain curve of the cement-based composites were carefully explained. The results indicated that an increase in fibre volume content gradually decreased the workability of the specimen. Specimens reinforced with 6 mm and 12 mm long BFs showed different failure modes from those reinforced with 18 mm BFs. The former had better integrity, while the latter had poor integrity. The shorter BFs (6 mm and 12 mm) improved the performance under peak stress and the compressive toughness of the RPC. For the 18 mm long BFs, with increasing fibre content, the peak stress and the corresponding strain decreased and the toughness index also decreased gradually. The fibre length/content had a small effect on the elastic modulus of the RPC but, with increasing fibre volume content, the peak secant modulus of the specimens decreased gradually. Considering the results of four groups of models, a group of predictive models was selected to express the complete stress–strain curves of RPCs reinforced with BFs.

Mechanical strength and water penetration depth of palmyra fibre reinforced concrete

Natural fibre reinforced composites are replacing the conventional fibre reinforced composites for several applications due to natural fibre availability, variety and lesser raw material cost. Using natural fibres in composites also reduces the issue of agricultural residue disposals, which are in abundance. Different natural fibres exhibit unique properties when it is used in composites and hence there is a need to study the behaviour of scarcely used natural fibres. Indian palmyra trees (Borassus flabellifer) are fast growing commonly found trees in Southern India. From the base of these palm tree leaves, palmyra fibres are taken out. Though these fibres are locally available in huge quantities, these are very rarely used as reinforcing material in concrete compared to other natural fibres like coir, sisal, jute etc. Palmyra fibre reinforced cement composite specimens were prepared by varying the fibre content (0.5%, 1% and 2% by weight of cement) and length of fibre (25 mm and 50 mm). Plain concrete and palmyra fibre reinforced concrete specimens of identical size were tested for mechanical strength and also for its depth of water penetration. The work carried out revealed that the water penetration of palmyra fibre reinforced concrete increased with fibre content increase. The compressive strength of palmyra fibre reinforced concrete improved up to 1% of fibre content and further increase in fibre content upto 2% resulted in compressive strength reduction for both the fibre lengths. However, split tensile strength, flexure strength and shear strength increased with fibre content increase in the mix. Based on the mechanical strength properties investigated, increase in shear strength was found to be more significant with the inclusion of palmyra fibres in concrete.

Enhanced transport properties of graphene oxide based cement composite material

This study is aimed to evaluate the transport properties of a cement composite incorporated with graphene oxide (GO). GO is a 2-dimensional nano material, enriched with reactive oxygen functional groups which made it as a suitable reactive material with cementitious materials. The GO-cement composite was prepared by adding GO in four different proportions such as 0.01%, 0.02%, 0.03%, and 0.04% by weight of cement. In the durability aspect water absorption, water sorptivity, resistance to acid attack, mechanical properties, thermal analysis, chloride migration coefficient, and chloride penetration depth were examined experimentally for GO-cement composite specimens and compared with plane cement composite specimens. Experimental results indicated that 14.5%, 30%, and 40.47% degradation in water absorption capacity, chloride migration coefficient, and chloride penetration depth of cement composite specimens with 0.03% addition of graphene oxide than normal cement composite specimens at 28 days of curing. Additionally, significant decrement in the sorptivity coefficient of cement composite was also achieved at 0.03% of GO addition. Mechanical properties were enhanced by 77.70% in flexural strength at 0.03% of GO addition and 47.61% in compressive strength at 0.04% of GO addition in cement composite at 28 days of curing. SEM analysis of the test samples exhibited the pore filled structure of the cement composites with GO addition. In addition, all GO-cement composite specimens exhibited greater resistance to an acidic environment and negligible loss in strength and weight was observed than normal cement composite specimens at 28 days immersion in 2% and 5% concentrations of both H2SO4 and HCl acidic solutions. Thermal resistance was increased in the terms of compressive strength in all GO-cement composite mixes gradually by increasing the concentration of GO content from 0.01% to 0.04% by weight of cement. It can be concluded that an effective improvement in transport properties of cement composite was achieved by the incorporation of graphene oxide nano material.

Using scanned images to estimate salt formation on the surface of cement composites

Introduction. An engineering method is proposed for assessing salt formation on the surface of cement composites exposed to adverse operating conditions. The technique is based on the histogram method used to determine the dominant brightness of the half-tone image of scanned cement composites. The criterion for ranking composites is a relative dimensionless value –– a metric obtained by comparing the brightness of a grayscale image with the brightness level of white.&#x0D; Materials and methods. We selected three types of compositions of composites in the amount of 21 items; each of them contains three samples –– a control sample and samples exposed to high humidity and positive temperatures for 15 and 45 days. Each composition is represented by a scanned raster image of the sample surface. The images are further subjected to digital processing using a software program written in the C++ programming language and the OpenCV technical vision library. This allows you to use the available methods and classes to develop algorithms to solve the problem in question and to convert a full-color RGB image to a grayscale image. Such images are used to analyze histograms, which determine the dominant level of brightness to determine the numerical metric for quantifying the salt formation on the surface of cement composite samples on the basis of their scanned images.&#x0D; Results. A description of the software algorithm, used to detect salt formation on the surface of cement composite specimens that have passed performance tests under high humidity conditions at positive temperatures, is presented. The method of ranking cement composite samples using the values of their dominant brightness relative to the brightness of control samples is shown. The comparative analysis of the study is presented in the form of numerical data and explanatory diagrams.&#x0D; Conclusions. Software modeling is employed to demonstrate the expediency of the methodology for the assessment of salt formation on the surface of cement composites and other building materials prone to salt formation.

Effect of Single-walled Carbon Nanotubes on Strength Properties of Cement Composites.

This study aimed to investigate the effects of single-walled carbon nanotubes (SWCNTs) on strength the properties of cement composites when surfactant (SAA) was applied as the dispersion method. TritonX-100 (TX10) was used as the SAA to pretreat SWCNTs, which has been proved to perform well in dispersing the agglomerates of SWCNTs. In this study, four different concentration of SWCNTs, namely 0.00 wt%, 0.02 wt%, 0.04 wt%, and 0.06 wt% by the mass of cement, were used to prepare cement composite specimens. The compressive strength and flexural strength of specimens were tested and recorded. The results show that the compressive and flexural strengths of cement composites decreased with the increase in the concentration of SWCNTs without the addition of TX10. However, when SWCNT suspensions were pretreated with TX10, the strength variation pattern changed; the compressive and flexural strengths of cement composites increased as a function of the concentration of SWCNTs, although there were reductions compared to non-TX10-treated specimens at all concentrations of SWCNTs. Furthermore, the relationship between the strength of cement composites and bulk density of specimens was considered.

Enhancement of Energy Absorption Capacity of Polyethylene Fiber-Reinforced Cementitious Composites According to Admixtures and Curing Conditions

This study aims to enhance the energy absorption capacity of cementitious composites with 2 vol.% of polyethylene fibers, by adjusting mixing ingredients and curing conditions. Ground blast furnace slag, cement kiln dust, limestone powder, and silica fume were incorporated, and two different curing conditions were applied: 72 h of curing at 90 ℃ and 120 h of curing at 40 ℃. Compressive strength test and direct tensile test were performed on 6 mixtures and the test results were compared with those of ultra-high-performance concrete and engineered cementitious composite specimens. The maximum compressive strength of the 6 mixtures was measured to be approximately 117 MPa. The higher cement replacement ratio of the other components resulted in a decrease in the compressive strength of the specimens cured at 90 ℃. In the direct tensile test, the specimens cured at 40 ℃ exhibited lower tensile strength than those cured at 90 ℃, but the strain capacity was increased by approximately 305% and reached 7.7%. This also resulted in an enhancement of the energy absorption capacity from 80%–292% because of the differences in micro-cracking and fracturing behaviors, such as an increase inthe number of micro-cracks and decrease in crack width.

Workability, microstructure, strength properties and durability properties of graphene oxide reinforced cement paste

ABSTRACTGraphene oxide (GO) is one of the prominent nanomaterial, this has been utilised in the cement composite materials. Graphene oxide represents unprecedented range of properties with a potential to enhance the strength and toughness of cement-based composites. In this study, the influence of graphene oxide was evaluated on the workability, microstructure, strength and durability properties of the fresh and hardened cement composites. Different percentages of graphene oxide were added at 0wt%, 0.01wt%, 0.02wt%, 0.03wt% and 0.04wt% by weight of cement. Workability in terms of fluidity, setting time and viscosity tests were conducted to the fresh GO-cement paste samples. Compressive and flexural strength tests were conducted to the hardened GO-cement paste samples at 28 days. Through scanning electron microscopy (SEM), morphology and microstructure of hardened cement paste were investigated and XRD technique was assisted in identifying the crystalline materials and studying the phase composition of cement composites. Results exhibited that, graphene oxide addition increases the viscosity, decreases the fluidity and shortens the setting time of the cement paste. Increased compressive and flexural strength results were appeared due to the addition of graphene oxide at different dosages. At 0.04wt% of graphene oxide dosage, the compressive strength was increased by 46.6% and flexural strength was increased by 75% than normal cement paste at 28 days. Water permeability of the cement composite specimens was highly reduced due to the graphene oxide reinforced infiltration barrier, which leads to the improvement in durability.

Enhanced mechanical and heating performance of multi-walled carbon nanotube-cement composites fabricated using different mixing methods

To improve the mechanical strength of cement materials used in infrastructure, this study investigates cementitious composites containing multi walled carbon nanotubes (MWCNTs), fabricated using different mixing methods and MWCNT concentrations. A total of 30 MWCNT cementitious composite specimens were fabricated, and the compressive strengths and heating performances of the MWCNT cementitious composites were tested. Mercury intrusion porosimetry tests were conducted to assess porosity decreases in the MWCNT cementitious specimens, and field emission scanning electron microscopy images were obtained to elucidate the internal structures of the composites.

High Strain Rate Compressive Behavior of Micro-Fibre Reinforced Fine Grained Cementitious Composite

This paper presents an experimental study on the high strain rate compressive behavior of micro-fibre reinforced ultrahigh performance cementitious composite, which is intended to be used as a matrix for slurry infiltrated fibre concrete (SIFCON). Cementitious composite specimens with 5 different types of microfibres, namely aramid, carbon, wollastonite, polypropylene and glass in amounts of 1.5-2.0% by volume were prepared and investigated. Split Hopkinson pressure bar (SHPB) equipment was used to determine the cementitious composite behavior at strain rates up to 1600 s-1. Quasistatic tests were performed, as well and ratios of these properties at high strain rates to their counterparts at static loading were compared. The dynamic increase factors were calculated. Strain rate sensitivity was observed - compressive strength was found to be increased with strain rate for all tested specimens. Peak stress values, critical compressive strain and post peak behaviour varies for specimens with different micro-fibre reinforcement, which allows to find the optimal reinforcement for high strain rate impacted structures.

Self-healing performance of aged cementitious composites

This study investigates the autogenous self-healing capability of one-year-old engineered cementitious composites (ECC) with different mineral admixtures to understand whether self-healing performance in late ages is similar to that of early ages. Sound and severely pre-cracked specimens were subjected to different environmental conditions including water, air, “CO2-water,” and “CO2-air” for one year plus 90 days of initial curing. Self-healing performance of ECC mixtures was assessed in terms of crack characteristics, electrical impedance testing, rapid chloride permeability testing and microstructural analysis. Laboratory findings showed that the presence of water is crucial for enhanced autogenous self-healing effectiveness, regardless of mixture composition. “CO2-water” curing resulted in the best self-healing performance of all curing conditions, which was confirmed with results from different performance tests throughout the experimental study. By further curing specimens under “CO2-water” (depending on the ECC mixture composition), cracks as wide as half a millimeter (458 μm) were easily closed by autogenous self-healing within only 30 days of further curing, and all cracks closed completely after 90 days. Because high levels of CO2 emission are a global problem, the effectiveness of “CO2-water” curing in closing microcracks of aged cementitious composites specimens through autogenous self-healing can help reduce the increasing pace of CO2 release. The results of this study clearly suggest that late-age autogenous self-healing rates of ECC specimens can be significantly enhanced with proper further environmental conditioning and mixture design.

Effects of silica fume on mechanical strength and microstructure of basalt fiber reinforced cementitious composites (BFRCC)

In this study, the effect of different silica fume contents (0%, 5%, 10%, 15% by binder mass) as a replacement for cement on the mechanical strength and microstructure of cementitious composites containing chopped basalt fibers (0%, 1% and 1.5% by volume) has been evaluated. Flowability, compressive strength, flexural strength, toughness, water absorption and specific electrical resistivity of cementitious composites specimens have been investigated. The quality of fiber bonding in microstructure of cementitious matrix at 28-day age have been also analyzed and evaluated by the scanning electron microscope images (SEM). The results showed that clumping occurred at high amounts of fibers (1.5%) and silica fume (15%) which caused mixing and casting problems. Adding basalt fibers increased the flexural strength and toughness 2 and 6 times, respectively; however, it caused 47% decrease in compressive strength. Including silica fume had positive effects on fiber-matrix transition zone structure while increasing mechanical strength and specific electrical resistivity up to 20 times due to production of pozzolanic reactions and decreased portlandite so that it raised uniformity and density as well as bond quality.

Influence of Basalt Mesh Induced Increase of Heterogeneity of Cement Composites with Dispersed Fibers on Its Resistance under Near-Field Blast

This paper describes the influence of multiple basalt meshes in the cement composite specimens on the damage induced by near-field blast. Experimental measurements performed in the Boletice military area in 2014 and 2015 are evaluated by numerical simulations. The evaluation of the results is mainly focused on the stress propagation in the cement composite with dispersed fibers, the propagation of the overpressure caused by the blast and velocity of the ejected parts from the specimen. The influence of the presence and position of the basalt meshes in the specimen on its damage induced by delamination is also examined.

Moisture-dependent piezoresistive responses of CNT-embedded cementitious composites

This study experimentally investigated the effect of moisture content on the piezoresistive responses of carbon nanotube (CNT)-embedded cementitious composites. In an experiment, changes in electrical resistance were measured under repeated application of sinusoidal compressive forces to the CNT-embedded cementitious composite specimens with different moisture contents. Experimental results revealed that as the internal relative humidity (IRH) of the specimens decreased, the piezoresistive responses, such as initial electrical resistivity, amplitude of electrical resistivity change, and piezoresistive sensitivity, increased significantly. The rate of change in piezoresistive sensitivity resulting from IRH variation increased nonlinearly with IRH drop, and rapid increase was observed when IRH drop was more than 35%, which was related to evaporation of surface multilayer adsorbed water in the specimens. The results of this study can be used for improving quantitative evaluation of the piezoresistive responses of CNT-embedded cementitious composites with variable moisture content, in the long term.

Thermo-mechanical toner transfer for high-quality digital image correlation speckle patterns

The accuracy and spatial resolution of full-field deformation measurements performed through digital image correlation are greatly affected by the frequency content of the speckle pattern, which can be effectively controlled using particles with well-defined and consistent shape, size and spacing. This paper introduces a novel toner-transfer technique to impress a well-defined and repeatable speckle pattern on plane and curved surfaces of metallic and cement composite specimens. The speckle pattern is numerically designed, printed on paper using a standard laser printer, and transferred onto the measurement surface via a thermo-mechanical process. The tuning procedure to compensate for the difference between designed and toner-transferred actual speckle size is presented. Based on this evidence, the applicability of the technique is discussed with respect to surface material, dimensions and geometry. Proof of concept of the proposed toner-transfer technique is then demonstrated for the case of a quenched and partitioned welded steel plate subjected to uniaxial tensile loading, and for an aluminum plate exposed to temperatures up to 70% of the melting point of aluminum and past the melting point of typical printer toner powder.

On the Fresh/Hardened Properties of Cement Composites Incorporating Rubber Particles from Recycled Tires

This study investigates the ameliorative effects on some properties of cement-based materials which can be obtained by incorporating rubber particles as part of the fine aggregates. The aim is to find out optimal cement composite/mortar mixtures, containing recycled-tyre rubber particles, suitable for specific engineering applications. Different percentages of rubber particles, from 0% to 75%, were used and, for each percentage, the suitable amount of sand was investigated in order to achieve the best fresh/hardened performances. In particular the following characteristics were examined: density, compressive strength, modulus of elasticity, shrinkage, weight loss, flexural behaviour, thermal conductivity, rapid freezing and thawing durability, and chloride permeability. The experimental results were compared with the ones of cement composite specimens without rubber aggregates. Test results show that the proposed rubberized mortar mixes are particularly suitable for some industrial and architectural applications, such as under-rail bearings, road constructions, paving slabs, false facades, and stone backing.

Toughness evaluation of ultra-high toughness cementitious composite specimens with different depths

Ultra-high toughness cementitious composite (UHTCC), which is a kind of high-performance fibre-reinforced cementitious composite, is characterised by tensile strain hardening behaviour and remarkable toughness capacity. The current study presents a toughness estimation of UHTCC beams of different depths under four-point bending. An improved method, based on ASTM C 1609 and JCI-SF 4, is used to evaluate the toughness capacity. In this method, an equivalent deflection transformation relationship between different depths of samples is introduced to ensure that toughness comparison is conducted at similar deformation states. Two toughness evaluation indices at equivalent controlling deflection are adopted. One is the new proposed toughness index Tv, which represents the energy dissipation per unit volume in the plastic hinge region, and the other is the traditional flexural strength parameter. Theoretical analysis and experimental results both indicate that the proposed toughness index Tv is independent of depth for strain hardening cementitious composite, which can be considered as an intrinsic material property.

Application of low modulus polymeric fibers in engineered cementitious composites

Nowadays, the advantages of staple fibers applied as reinforcement in cementitious composites are well known. The fiber to cement interfacial interactions influences mechanical properties of composites. Engineered cementitious composites are cement-based composites which are made of cement binder, small size sands, fillers, high modulus fibers, and supplementary cementing materials. They have improved tensile and flexural properties in comparison to normal concretes. To achieve these properties, high modulus fibers such as carbon, steel, and polyvinyl alcohol fibers have been used in engineered cementitious composites. In this research, low modulus polymeric fibers such as nylon 66, acrylic, and polypropylene were used as substitute of high modulus reinforcing fibers in engineered cementitious composite. The low modulus fibers were characterized carefully for physical–mechanical properties. The flexural behavior (flexural strength and flexural toughness) of the engineered cementitious composite specimens from this article was studied using a three-point bending test method. The results were compared to engineered cementitious composite containing polyvinyl alcohol. It was found that low modulus fibers caused considerable improvement in flexural behavior but results were lower than composites containing polyvinyl alcohol fiber. It was also found that these fibers are suitable choices for producing low price, acceptable performance engineered cementitious composites for usual applications in construction industry.