Mechanical Properties Of Cement Mortar Research Articles

Mesoscopic numerical simulation of fracture process and failure mechanism of cement mortar

AbstractCement mortar is an important part of building material and a typical cement matrix composite material. In current work, the mechanical properties and failure mechanism of cement mortar under static compression are studied by using the Base Force Element Method (BFEM). The static compression damage program of cement mortar is compiled grounded on the BFEM of the potential energy principle. An elastic polyline damage constitutive model is put forward to express the meso‐damage and evolution process of cement mortar. A 2D random circular aggregate model of cement mortar was established. The numerical simulation of the uniaxial static compression is carried out, the stress–strain curve, damage process, and damage model are obtained. The strength of the interfacial transition zone and the failure process of hardened cement mortar were discussed. A mesoscopic equivalent model is proposed to analyze the mechanical properties of cement mortar by considering the effect of initial porosity.

Effect of particle characteristics stress on the mechanical properties of cement mortar with coral sand

The coral sand is widely used as a construction material in the world. The mechanical behavior of cement mortar made by coral sand would be quite different from that made by the Leighton Buzzard sand (LBS) due to the inherent properties of coral sand, such as large void ratio, irregular shape and particle breakage. The effect of particle size on the particle crushing stress and influence on the mechanical behavior of cement mortar are examined in this study. A series of single particle compression tests of coral sand particles were carried out. The results revealed that the characteristic stress of single particle for both coral sand and LBS decreased with the increasing of particle sizes. The exponent relationship between the average crushing characteristic stress and particle size was proposed. The crushing stresses of single particles were in a wide range which varied from 0.99 MPa to 38.25 MPa and 10.98 MPa to 89.41 MPa for coral sand and LBS, respectively. The uncertainly of the crushing stress for single particles was analyzed and considered as Gaussian distribution. A probability density function of characteristic crushing strengths for both coral sand and LBS particles were derived and further verified with experimental results. Finally, the cement mortar specimens with five different types of particle size distributions of coral sands were prepared and tested to investigate the effects of the particle characteristic stress on the compressive strength of the cement specimen. An exponent relationship between the compressive strength and the particle crushing strength was derived and proposed which could helpful for the concrete mix proportion design with coral sands.

The Role of Polypropylene Microfibers in Thermal Properties and Post-Heating Behavior of Cementitious Composites.

This paper experimentally studied the effect of polypropylene (PP) microfibers on thermal and post-heating mechanical behaviors of cementitious composites. Cement mortars with small dosage of polypropylene fibers were prepared, heated at various temperatures (150 °C, 200 °C, 450 °C, and 600 °C), and then tested. The investigated parameters include residual compressive and flexural strengths, elastic modulus, fracture energy, stress intensity factors, failure modes, microstructure (scanning electron microscopy (SEM) imaging), thermal conductivity, heat flow (differential scanning calorimetry (DSC) test), mass loss (thermogravimetric analysis (TGA) test), and chemical composition (XRD analysis). The results showed the efficiency of PP fibers to enhance the post-heating behavior and the residual mechanical properties of cement mortar after heating. The presence of PP fibers did not affect the heat flow and the mass loss of cement mortar at room temperature. However, heating cement mortar at temperature beyond the melting point of the fibers negatively affected its thermal behavior. The presence of PP fibers played a major role in bridging the cracks and mitigating their propagation. Once the melting point of the polypropylene fibers is exceeded, the fibers melted and created extra voids in the microstructure of concrete.

Influence of Phosphorus Slag on Physical and Mechanical Properties of Cement Mortars.

Influences of phosphorus slag from 10% to 50% (by mass) on the setting time and the water requirement of the normal consistency of cement pastes, flowability, resistance to carbonation, and the compressive strength of cement mortars were investigated. The physical activation by improving fineness and the chemical activation by adding the chemical activator were evaluated by the compressive strength of cement mortars with 30% by mass of phosphorus slag. Hydration heat, X-ray diffraction, and scanning electron microscopy were used to study the microstructure of cement pastes and mortars with 30% by mass of phosphorus slag and the chemical activator. Results showed that the setting time of cement pastes was delayed by phosphorus slag from 10% to 50%. Phosphorus slag had nearly no effects on the water requirement of the normal consistency of cement pastes and the flowability of cement mortars. The resistance to carbonation of cement mortars was decreased by phosphorus slag from 10% to 50% according to the acceleration carbonation. The compressive strength of cement mortars was also decreased by phosphorus slag from 10% to 50% and the low activity of phosphorus slag was concluded based on compressive strength of cement mortars. The effect of the chemical activator on the compressive strength of cement mortars with 30% by mass of phosphorus slag was better than improving fineness of phosphorus slag from 300 m2/kg to 450 m2/kg. Both hydration heat and cement hydrates were inhibited by phosphorus slag and could be partly compensated by the chemical activator. Loose morphology and propagations of microcracks were found in cement pastes and mortars with 30% by mass of phosphorus slag.

Mechanical Properties of Cement Mortar after Dry–Wet Cycles and High Temperature

The dry–wet cycle and high temperature exposure are important factors affecting the normal use and durability of concrete structures. The objective of this work is to investigate the mechanical properties of cement mortar specimens after combinations of dry–wet cycles and high temperature exposures, uniaxial compressive tests on cement mortar specimens were carried out under the following two sets of conditions: (1) high temperature treatment followed by a dry–wet cycle and (2) a dry–wet cycle followed by high temperature treatment. The results show that the compressive strength of specimens increases with the number of dry–wet cycles. After a dry–wet cycle and then a high temperature treatment procedure, the compressive strength of a specimen will first decrease and then increase with the number of dry–wet cycles. The strain at the peak stress of cement mortar decreases as the number of dry–wet cycles increases. At present, there are few research results about the mechanical properties of concrete first after combinations of dry–wet cycles and high temperature exposures. The work in this paper can enrich the results in this area.

Mechanical characterization of cement-based materials containing biochar from gasification

This study focuses on the influence of biochar – a solid, porous, carbonaceous material product resulting from biomass gasification of wood waste – on mechanical properties of cement mortars. In order to investigate its effectiveness for structural purposes, biochar is added in cement mortar in increasing percentages, up to 2.5% by weight of cement. Experimental findings show that, by including a proper biochar percentage, compressive and flexural strengths comparable to those of control specimens are obtained, with a slight increase in fracture energy. The use of biochar in building materials as carbon sink is also part of a strategy for the development of more sustainable materials within the construction industry, since the dual aim of storing carbon in a stable form in buildings and promoting waste reutilization by increasing the recycling rate could be achieved.

Statistical variations and new correlation models to predict the mechanical behaviour of the cement mortar modified with silica fume

ABSTRACT Despite many of the research studies on the effect of the silica fume content on the mechanical properties of the cement mortar, there has not been a comprehensive study investigating the effect of silica fume content, curing time and water to cement ratio on the compressive, tensile and flexural strengths of cement mortar. In this study investigates the subject which could be beneficial for building and construction field. More than 1000 data on the mechanical properties of the cement mortar modified with different percentages of silica fume varied from 5% to 55% (by dry weight of the cement) collected from the literature. The statistical analysis, modelling and non-linear regression analysis were performed on the collected data. The water to cement ratio (w/c) ranged between 0.20% and 1% and the compressive strength, tensile strength and flexural strength of cement mortar modified with silica fume up to 90 days of curing were ranged between 2.5MPa and 87 MPa; 2 MPa and 6.8 MPa; and 1.2 MPa and 9.2 MPa, respectively. Vipulanandan correlation model was used and compared with the Hoek-Brown model to correlate the mechanical properties of cement mortar modified with silica fume. The Vipulanandan correlation model has a lower root mean square error (RMSE) compared to the Hoek-Brown model. The results of the present study showed that there is a good relationship between the compressive strength with flexural strength and tensile strength for cement mortar modified with silica fume. Based on the data analysis the per cent of silica fume up to 55% had the lowest effect on increasing the compressive strength compared with w/c and curing time.

COMPARING THE RESULTS OBTAINED FROM IN-SITU METHODS FOR DETERMINING THE STRENGTH OF THE CEMENT MORTARS

Nowadays, the in-situ evaluation of the cement masonry strength is inevitable. The in-situ methods of determining the strength are usually applied for evaluating the status quo and identification of the reason(s) of the masonry and materials’ failure. This article makes use of two in-situ methods, namely twist-off and friction-transfer, as well as standard laboratory methods to evaluate the mechanical properties of cement mortars, including compressive, flexural and tensile strength, in different ages and under various curing methods. Considering the differences in the performance of the above-mentioned in-situ methods, the results obtained from the two methods will be compared so that their differences can be figured out. Moreover, the correlation between the results obtained from the in-situ methods and the laboratory methods has been made clear and calibration curves have been offered for use in determining the mechanical properties of the mortars. The obtained results are expressive of a difference by about 30% between the readings obtained in in-situ twist-off and friction-transfer methods. Furthermore, there is a linear correlation found with a high intensity of 90% between the standard laboratory methods and the aforesaid in-situ methods.

Effects of selected chemical admixtures on physical and mechanical properties of cement mortar

This study was aimed to determination of appropriate dosage of selected chemical admixtures to reduce water cement ratio for mortar mix also to determine its effects on physical and mechanical properties of cement mortar. Amount of water used in concrete is very important for the physical and mechanical properties. Less amount of water increase the strength but reduce the workability. Water retarding admixture can reduce the water cement ratio with desired workability. In this experiment plasticizer (master pel 707) and super plasticizer (master polyheed 8632) was used. The used dosages of admixture were 0.5%, 1% and 1.5% according to cement weight. The test was done at 3 days, 7 days, 28 days and 91 days. 2.76″ cube mold was used for the work. The experiment was done to find the difference between with and without admixture used in mortar. Water used reduced with add of plasticizer and super plasticizer. In the experiment the workability of normal mortar and admixture used mortar remain same. The compressive strength is high for 1.5% super plasticizer used sample. So 1.5% super plasticizer is recommended for high strength.
 Progressive Agriculture 30 (3): 305-310, 2019

Application of bacterial nanocellulose fibers as reinforcement in cement composites

In this study, the potential effect of bacterial nano-cellulose on mechanical properties of cement mortar was evaluated. For this purpose, bacterial nano-cellulose (BNC) directly as powder and gel (0.1, 0.3, and 0.5 wt%), and indirectly as coated onto the polypropylene fibers were used in the preparation of cement paste in order to investigate the effect of each method on the flexural strength, compressive strength and water absorption of specimens. Results indicated that samples containing BNC gel and powder enhanced mechanical properties. However, BNC-gel indicated inferior properties compared to powder. The maximum increase in flexural strength between all samples was observed in the specimens containing 0.5% of BNC powder, which was 104%, compared to the control sample. In addition, utilizing nanofibers decreased the water absorption of cement mortar. The water absorption of specimens containing 0.1% of the gel fibers and 0.3% of powder was decreased by 26% and 37%, respectively. According to scanning electron microscopy (SEM) analysis, the roughness and specific surface of polypropylene fibers coated with BNC were increased. This can improve the interaction of these fibers with the cement matrix. The results show clearly that the application of BNC nanofibers improves the mechanical properties of cement paste and workability of polypropylene fibers.

Effect of Graphene Oxide/Graphene Hybrid on Mechanical Properties of Cement Mortar and Mechanism Investigation

This paper evaluated the effect of graphene oxide/graphene (GO/GR) hybrid on mechanical properties of cement mortar. The underlying mechanism was also investigated. In the GO/GR hybrid, GO was expected to act as a dispersant for GR while GR was used as reinforcement in mortar due to its excellent mechanical properties. For the mortar specimen, flexural and compressive strength were measured at varied GO to GR ratios of 1:0, 3:1, 1:1, 1:3, and 0:1 by keeping the total amount of GO and GR constant. The underlying mechanism was investigated through the dispersibility of GR, heat releasing characteristics during hydration, and porosity of mortar. The results showed that GO/GR hybrid significantly enhanced the flexural and compressive strength of cement mortars. The flexural strength reached maximum at GO:GR = 1:1, where the enhancement level was up to 23.04% (28 days) when compared to mortar prepared with only GO, and up to 15.63% (7 days) when compared to mortar prepared with only GR. In terms of compressive strength, the enhancement level for GO:GR = 3:1 was up to 21.10% (3 days) when compared with that of mortar incorporating GO only. The enhancement in compressive strength with mortar at GO:GR = 1:1 was up to 14.69% (7-day) when compared with mortar incorporating GR only. In addition to dispersibility, the compressive strength was also influenced by other factors, such as the degree of hydration, porosity, and pore size distribution of mortar, which made the mortars perform best at different ages.

Impact of elevated temperature on the mechanical properties of cement mortar reinforced with rope waste fibres

The exposure of concrete or cement mortars to fire or other elevated temperatures negatively affects the mechanical properties, and a change may also occur in the pore structures, leading to cracking and spalling. In order to hinder or reduce the negative impact of elevated temperature on cement mortar, as well as to promote reuse of waste in the concrete industry to improve the environment, this study aims to investigate the effect of elevated temperature on the mechanical properties of cement mortar reinforced with rope waste fibres (RWF). The fibres were obtained by cutting a used polymeric rope (0.034 mm in diameter) into small fibres with average lengths of 12 mm. Four mortar mixtures, including one reference mixture (without fibres) and three mixtures containing RWF in proportions of 0.25%, 0.5% and 0.75% (by mortar weight), were cast. After 28 days of curing, the hardened specimens were air dried for at least two weeks, and some specimens were exposed to a controlled temperatures of 300 and 600 °C for two hours, while the others were placed at ambient temperature. All specimens were then examined via compressive strength, flexural strength, mass loss, ultrasonic pulse velocity and visual inspection tests. The results indicated that RWF can prevent cracks appearing at 600 °C; however, the RWF had a negative impact on the compressive strength of the mortar under elevated temperatures, despite the flexural strength and UPV properties being improved significantly.

Effect of Particle Size Distribution of Sand on Mechanical Properties of Cement Mortar Modified with Microsilica

Effect of Particle Size Distribution of Sand on Mechanical Properties of Cement Mortar Modified with Microsilica

Nano CaCO3 particles in cement mortars towards developing a circular economy in the cement industry

This paper calls into question the effects of incorporating nano calcium carbonate (CaCO3) particles in cement mortars, as they are interesting additive materials already successfully tested as cement nanofiller. These nanoparticles could potentially be prepared through the carbonation route using CO2 from combustion gases from the cement industry. This could enable a circular-economy approach for carbon capture and its re-use within the cement industry, in a sustainable and synergistic manner. In this study, part of the cement content was substituted with commercial nano CaCO3 particles to investigate their effects on the flexural and compressive strength of the resulting cement mortars, after curing for 7 and 28 days. Decreasing the cement content could lead to a reduction in the carbon footprint of cement, which is responsible for approximately 8% of global carbon dioxide emissions. Preliminary results using synthesized CaCO3 particles as nanofillers showed that, after 7 days of curing, mechanical properties of cement mortars improved. This indicates that hydration reaction was accelerated since CaCO3 acts as seeding for this reaction. By contrast, after 28 days of curing, no major improvement was observed. A higher content of calcium carbonate nanoparticles may have reduced the filler effect of these particles due to aggregation phenomena. In the present work, the effects of commercial nano CaCO3 particles on cement hydration were investigated. Mechanical tests showed promising results both after 7 and 28 days of curing. This could lead to the reduction of the carbon footprint of cement manufacturing and produce increasingly better performing building materials. Thus, the development of a circular economy in the cement industry could be achieved.

The effect of water to cement ratio and age on the mechanical properties of cement mortar and concrete made of micro‐nano bubbles without adding any admixtures

AbstractThe effect of using water containing micro‐nano bubbles (WMNB) without adding any admixtures and normal water (NW) on the mechanical properties of cement mortar and concrete samples were investigated. Four various water to cement ratios equal to 0.6, 0.5, 0.4, and 0.35 (ranging from conventional concrete to high strength concrete), and three different curing ages of 7, 28, and 90 days were considered. The experimental results showed that the initial and final setting time of cement paste, the flow of hydraulic cement mortar and the slump of concrete samples made with WMNB were lower than that of made with NW. However, the compressive strength of cement mortar in using WMNB indicated an increase up to 16 and 7% in at 7 and 28 days, respectively. We also concluded that the optimum percentage of water to cement ratio was 0.35, which in that ratio the compressive strength enhancement of concrete made of WMNB reached the peak of 6, 18.3, and 16.3% at 7, 28, and 90 days age, respectively. Whereas increasing water to cement ratio, resulted in reducing the compressive strength of concrete. Besides, the high‐resolution scanning electron microscopy images with Energy Dispersive X‐Ray analysis were briefly conducted to explore the morphological change.

Influence of Granulometry on Thermal and Mechanical Properties of Cement Mortars Containing Expanded Perlite as a Lightweight Aggregate.

This research aims at clarifying the influence of the granulometry of expanded perlite, on the thermal conductivity, structural strength, density, and water absorption of lightweight mortars. Three original perlite gradations have been obtained and three pairs of twin test mortars have been tested with those gradations. SEM tests have also been run to clarify the interaction, at a microscopic level, between the expanded perlite and the cement grouting. The results indicate that the mere manipulation of the granulometry may have a considerable and very beneficial effect on the mixture’s properties, such as thermal conductivity and water absorption.

Effect of Dispersion Method for Nano-Materials on Some Mechanical Properties of Cement Mortar

This study was involving the dispersion method of nano-materials replacement and the interaction with cement mortar behavior for many mortar samples under variable curing time ,with constant water to cement ratio (W/C=0.45) .Some mechanical properties such as (compressive, flexural strength and hardness tests) was studied. The main parameters are depending on the small amount replacement ratio of nano-particle (ZrO2) with respect to the mass of the cement (OPC) type (I). The addition of nano-material by replacement on the mixture of mortar includes (1, 2, 3,4and 5%) with constant W/C ratio and also the amount of the fine aggregate use is 2.75 from the amount of cement. The results show that, the strength of the mortar that consist from colloidal nano materials give better properties than from both mortar with dry nano-materials replacement and without nano-materials in all test, But the nano-Zirconia materials give good properties up to 2% in all tests compared with control cement mortar.

Effect of Graphene Oxide on Mechanical Properties of Cement Mortar and its Strengthening Mechanism.

The effects of the water–binder ratio and different graphene oxide (GO) sizes on the mechanical properties of GO-cement composites were systematically studied by preparing GO-cement mortars. The scanning electron microscopy observation (SEM) of the surface and fracture surface of cement pastes was carried out to study the morphology of cement hydration crystals in GO-cement systems under different space conditions. It was found that GO nanosheets significantly improved the compressive, flexural, and tensile strengths of cement mortars. When the dosage of GO nanosheets was 0.03% by weight of cement, the compressive, flexural, and tensile strengths at 28 days increased by 21.37%, 39.62%, and 53.77%, respectively, but GO was not found to be able to regulate the formation of flower-like cement hydration crystals. It was only shown that the growth space had an important influence on the morphology of hydrates. A possible working mechanism was proposed by which GO nanosheets prevented the expansion of microcracks in the cement pastes via a shield effect, thus enhancing the strength and toughness of the cement composites.

Comparative Analysis of Static and Dynamic Mechanical Behavior for Dry and Saturated Cement Mortar.

Deformational and breakage behaviors of concrete and cement mortar greatly influence various engineering structures, such as dams, river bridges, ports, tunnels, and offshore rig platforms. The mechanical and petrophysical properties are very sensitive to water content and are controlled by the liquid part in pore spaces to a large extent. The objective of this paper is to investigate the water saturation effect on the strength characteristics and deformability of cement mortar under two loading conditions, static and dynamic compression. A set of cement mortar samples was prepared and tested to study the mechanical behavior in dry and saturated states. The first part of the research incorporates the study of static mechanical properties for dry and brine-saturated cement mortar through uniaxial compressive strength tests (UCS). Second, drop-weight impact experiments were carried out to study the dynamic mechanical properties (impact resistance, deformation pattern, and fracture geometry) for dry and saturated cases. The comparative analysis revealed that water saturation caused substantial changes in compressive strength and other mechanical characteristics. Under static loading, water saturation caused a reduction in strength of 36%, and cement mortar tended to behave in a more ductile manner as compared to dry samples. On the contrary, under dynamic loading conditions, water saturation resulted in higher impact resistance and fracture toughness as compared to dry conditions. In addition, fractures could propagate to smaller depths as compared to dry case. The study will help resolve many civil, mining, and petroleum engineering problems where cement structures undergo static as well as dynamic compression, especially in a hydraulic environment where these structures interact with the water frequently. To the best of our knowledge, the effect of water saturation on the dynamic mechanical properties of cement mortar has not been well understood and reported in the literature.

Effect of graphenene nanoplatelets on microstructure and properties of cement mortar under simulated acid rain

The mortar loses strength under acid rain conditions, causing cracking, weight loss and damage to the structure. This paper studies the effects of graphenene nanoplatelets(GNP) mortar under simulated acid rain conditions. A control sample without GNP and the addition of GNP were ranging from 0.2% to 0.6% by weight of ordinary Portland cement were prepared. In different corrosion days, the mechanical properties of the GNP cement mortar were measured, scanning electron microscopy also applied. Results showed that the mechanical properties of cement mortar added with graphene are improved. Compared with the control sample, the compressive strength and flexural strength of specimens containing 0.2wt% GNP are increased by 10% and 8%, respectively. Adding GNP can improve the acid resistance and durability of cement mortar.