Mechanical Properties Of Cement Mortar Research Articles

Investigation of gradient properties for cement mortar interfacial transition zones and their effects on mechanical characteristics using micro-CT

The interfacial transition zone (ITZ) in cement-based composites with aggregates is widely recognized as the most vulnerable component, greatly affecting their physical and mechanical properties. In this study, the effect of the ITZ characteristics on the mechanical behavior of cement mortar using its actual microstructure was investigated with image-based numerical approaches in this study. The volumetric information of the ITZ of the mortar sample was obtained and characterized from high-resolution synchrotron micro-computed tomography (micro-CT) images. The mechanical properties of the mortar were evaluated using the finite element method, based on the components characteristics represented by grayscale information of the micro-CT images. It was found that the adhesion between the aggregates and binder was well replicated in the simulation with the multiple-phase model, based on the gradient characteristics and properties of the ITZ. Considering the ITZ thickness according to the aggregates size, a more realistic crack propagation trend can be observed. The obtained results confirmed the significant influence of the ITZ thickness and phase distribution characteristics on the mechanical properties of cement mortars, emphasizing the importance of considering ITZ phases for accurate material analysis.

Evaluation of mechanical properties of cement mortars containing pond ash as partial replacement of river sand and prediction of properties by regression models

Despite vast research on the utilisation of coal ashes in cement mortars, many studies lack a comprehensive evaluation of properties related to mortar for masonry and plaster work. This study investigate properties like workability, compressive strength, drying shrinkage, tensile bond strength and adhesive strength through a systematic replacement of river sand by pond ash in cement mortars. Volumetric mix proportions of 1:3, 1:4, 1:5 and 1:6 (cement: sand) were considered, where river sand was replaced in the range of 20–100% by pond ash. At 30% pond ash content, properties like the compressive strength, tensile bond strength and adhesive strength improved in the range of 21–30%, 13–20% and 14–24%, respectively, for all mix proportions. At 60% pond ash content, these strength properties were comparable with those of control mixes and found suitable for mortars for masonry works. However, the drying shrinkage increased with an increase in pond ash content. At 30% pond ash content, drying shrinkage increased in the range of 26–40% for all mix proportions. The thermogravimetric analysis (TGA) showed that mixes with pond ash demonstrated reduced portlandite content compared to the control mixes, resulting in the formation of secondary C-S-H gel. Simple regression models were developed based on experimental results to establish the relationships between different properties. Based on coefficient of determination (R 2), variance inflation factor (VIF) and Durbin–Watson statistics, relationships between the strength and shrinkage properties were very well quantified to be used by researchers and practitioners. Utilisation of pond ash as partial replacement of river sand in mortars proved to be a useful step towards achieving circular economy at the same time reducing threat to depletion of limited natural resources.

Gelatin‐based air‐entraining agents for ordinary portland cement: Chelate Ca2+ and reduce surface tension

AbstractIntroducing uniform, stable, and small pores by adding air‐entraining agents (AEAs) is an effective strategy for improving the freeze–thaw resistance and workability of cement concrete materials. In this study, the gelatin with hydrophobic and hydrophilic functional groups was used as an AEA for cement concrete materials and systematically studied its effect on the performance of cement mortar specimens. The results showed that gelatin has a surfactant‐like function and can effectively reduce the surface tension of the gas–liquid interface. In an alkaline environment, Ca2+ ions in cement pore solution chelate with carboxylate ions formed by carboxyl ionization, further enhancing the performance of gelatin‐based AEAs. Thanks to the reduction in surface activity and carboxyl ionization, introducing gelatin increased the porosity of cement mortar specimens from 0.53% to 2.69%. Furthermore, introducing an appropriate amount (>0.1 wt%) of gelatin does not significantly impact the workability or mechanical properties of cement mortar. Based on these characteristics, gelatin has potential as an AEA for cement concrete materials.

Thermal activation and mechanical properties of high alumina coal gangue as auxiliary cementitious admixture

In order to use high alumina coal gangue as auxiliary cementitious admixture via a simple and convenient thermal activation technique, the thermal transformation, mineral phase transformation and structure changes of coal gangue at calcining temperatures of 500–1000 °C were analyzed using x-ray diffraction (XRD), differential thermal Analysis (DTA), thermogravimetry (TG), infrared analysis (IR) and scanning electron microscope (SEM). The mechanical properties of cement mortar with 30% coal gangue auxiliary cementitious admixture were also measured to determine the optimal calcining temperature. As calcining temperature was increased, the coal gangue experienced the following transformations: carbon combustion, dehydroxylation, metakaolin transformation and mullite transformation. The cement mortar with coal gangue auxiliary cementitious admixture calcined at 700 °C presented the highest 28-d flexural and compressive strength, increasing by 8.27% and 11.85% respectively as compared with the benchmark cement mortar. The maximum dosage of coal gangue auxiliary cementitious admixture in cement mortar was further identified to be less than 30% by mechanical properties testing. The activity of high alumina coal gangues at different calcining temperatures was explained from the view points of hydration degree and products. The present investigation can provide a useful reference to utilize high alumina coal gangue as auxiliary cementitious admixture by means of a simple thermal activation at 700 °C.

The Effects of Replacing Sand with Glass Fiber-Reinforced Polymer (GFRP) Waste on the Mechanical Properties of Cement Mortars

The aim of this study is to examine the effect of the partial replacement of sand by Glass Fiber-Reinforced Polymer (GFRP) waste on the mechanical properties of cement mortars. Compressive and flexural tests were carried out on mortars containing 0, 3, 5, 10, and 15% (by volume) of GFRP waste. It appears that the incorporation of 3% GFRP waste did not significantly affect the mechanical strength. However, further increasing the GFRP waste content led to a reduction in the mechanical strength. The flexural strength seemed less affected than the compressive strength, since the decrease in flexural strength at a 10% replacement was only 37%, while it was 54% for the compressive strength. However, an improvement in the toughness of the mortar with an increase in the substitution rate was observed. The reference sample displayed a flexural toughness of 0.351 N·m, while the mortar incorporating 15% of GFRP exhibited a flexural toughness of 0.642 N·m. The reuse of GFRP waste in cementitious materials, therefore, constitutes an interesting recycling solution.

Effect of waste plastic fibers on the printability and mechanical properties of 3D-printed cement mortar

Extensive use and disposal of waste plastic bags have caused significant environmental issues. However, waste plastic bags can be used as fibers to enforce the mechanical properties of cementitious materials. Therefore, the effect of waste plastic fibers on the printability and mechanical properties of 3D-printed cement mortar was investigated in this work. The experiment mainly studied how the parameters of waste-plastic-fiber contents, fiber widths, and printing spacing affected the flowability, buildability, compressive strength, and flexural strength of 3D-printed cement mortar. Additionally, the microstructure of the printed specimens was analyzed by X-ray computed tomography (CT) and scanning electron microscope (SEM). Results showed that the addition of waste plastic fibers improved the flexural strength of 3D-printed mortar to a certain extent, with the maximum value achieved at the fiber content of 0.3%, for the same fiber width and printing spacing. However, as the fiber content increased, the X-CT scan showed that the porosity of the cement mortar gradually increased, resulting in a decrease in its compressive strength. Varying fiber widths had little effect on the mechanical properties of the printed specimens, whereas the spacing between the printing filaments had a significant influence on it. Larger printing spacing lowered the bonding performance between the printing filaments, thereby weakening the mechanical properties of the cement mortar. SEM images revealed that more pores were generated in the printed mortar than in the cast, resulting in the compressive strength of the cast higher than that of the printed. However, the extrusion of the mortar through the nozzle during printing improved the bond strength between the filaments, so the flexural strength of the printed specimens was significantly higher than that of the cast. This study may provide knowledge on recycling waste plastic bags as building materials to alleviate environmental pollution and also reserve resources.

Assessing the effect of adding TiO2 and calcined montmorillonite clay nanoparticles on the mechanical properties of cement mortar

The study analyses the influence on the mechanical strength of titanium dioxide TiO2 and calcined montmorillonite (CMMT) particles added individually and combined to cement mortar mixes. Having both similar and complementary properties, the combined solution of TiO2 and CMMT nanoparticles can induce positive effects on the overall properties of cementitious composites. However, this combination has been tackled only in a couple of studies, with different approaches regarding the design mix, but without comparing the results with the individual-nanomaterial mixes. In this study, the bulk density, flexural strength, compressive strength, and material microstructure were analyzed at 28 days of curing, for an addition of 0.5 wt% and 0.75 wt% TiO2, of 1 wt%, 1.5 wt% and 2 wt% calcined montmorillonite (CMMT), and of nanomaterial combinations. From the flexural strength point of view, the CMMT-modified cement mortar mix registered the highest value of all modified mixes for a cement replacement of 1.5 wt%, reaching a 10.27% improvement compared to the reference mix. The highest compressive strength was recorded for the mix comprised of 1 wt% CMMT and 0.75 wt% TiO2, with an increment of 3.19% compared to the reference mix. The obtained results were confirmed by means of Scanning Electron Microscopy (SEM) investigations showing that the highest amount of CSH was observed for 1% wt% CMMT and 0.75% wt% TiO2, corresponding to the highest compressive strength value.

Influence of Chopped Carbon Fibers Addition with Different Curing Methods on the Mechanical Properties of Cement Mortar Performance

Sustainability is very important to keep industrial growth and human development going. Concrete is the largest manufacturing material in the world and includes cement as a key bonding agent for developing strength. This paper shows that the use of chopped carbon fiber to reinforce cementitious materials improved the mechanical properties characteristics of the mortar. also proposes appropriate curing conditions for the chosen mortar. The experimental investigation was carried out to evaluate the mechanical properties of cement mortar, The study plan consists of four cement mortar mixtures with ratios include 0%, 0.25%, 0.5% and 1% of chopped carbon fiber volume fraction by weight % of cement using normal water for curing. The effects of four different methods of curing on the mechanical properties of cement mortar that have the best properties from adding chopped carbon fiber were investigated including the convectional curing. 1% carbon fibers showed the best improvement in the mortar strength.

Influence of Carbon Nanotubes Concentration on the Mechanical Properties of Cement Mortars

In recent decades, mechanical properties of composite materials containing carbon nanoparticles, in particular single-walled or multi-walled carbon nanotubes (SWCNTs or MWCNTs), have been researched, taking into account their excellent physical and mechanical characteristics. In this work, the influence of the concentration of MWCNTs (0.1, 0.2, 0.3, 0.35 wt.%) on compressive and flexural strengths of the cement mortar was investigated. The results of the research show that the compressive and flexural strengths of the 7 and 28-day curing period samples reach their maximum value at 0.3% of nanotube concentration. In comparison to the control sample, the compressive strength increased by 10.93% within 7 days and by 32.0% within 28 days. And in the case of flexure, the strength of the test samples increased by 33.67% within 7 and by 36.50% within 28 days. It can be concluded that in the case of the selected carbon nanotubes and the material composition at 0.3% of MWCNTs, the compressive and flexural strength reach their maximum values.

Mechanical properties of cement mortar with gamma-irradiated recycled plastic powder, pellet, and fiber

This study aimed to investigate the impact of gamma irradiated recycled polyethylene terephthalate (PET) pellets, powder, and fibers on the mechanical performance and ductility of cementitious mortar. The sensitivity to gamma irradiation was explored by varying the irradiation rate and total dose. The recycled PET additives employed in this experiment consisted of pellets and their different application forms: powder and fiber, containing 30 % recycled raw materials polymerized through a chemically recycled method. For comparison, plain mortar composite and virgin PET mortar composite were used as controls. When PET pellets partially replaced the aggregate, the compressive strength of the composite decreased significantly as the volume fraction of pellets increased. Conversely, specimens partially replaced by PET powder showed an overall increase in compressive strength compared to the control specimens, regardless of the volume fraction of powder, gamma irradiation rate, or total dose, with no change in ductility. To assess changes in tensile strength and ductility of the recycled PET fibers under different gamma irradiation rates and total doses, direct fiber tensile tests were conducted. The gamma-irradiated fiber specimens exhibited a slight increase in strength and ductility. This information allowed for the calibration of the tensile material constitutive relationship of PET fibers, which was subsequently used in nonlinear finite element analysis. The study also investigated the variation in direct tensile, compressive, and flexural strengths with different volume fractions of fiber. The results indicated that the strength enhancement was minimal, but the direct tensile and flexural tensile analyses predicted an enhancement.

Influence of Utilizing Prosopis Juliflora Ash as Cement on Mechanical Properties of Cement Mortar and Concrete

<p>The infrastructure of the country heavily depends on the construction material concrete. The primary ingredient in conventional concrete is cement, fly ash, or another cementitious substance. The need to explore alternative sources is driven by the challenges posed by global environmental warming, which stems from widespread factors, and the escalating costs associated with the extraction of cement from quarries. To replace cement, sand, and aggregate, numerous research investigations have been conducted. The Prosopis Juliflora Ash (PJA) as an additional cementitious component in cement mortar and concrete are examined in this experimental study. The amount of cement produced in the nation will decrease if Prosopis Juliflora (PJ) ash is used as an additional substitute. It will also encourage the use of sustainable materials for concrete and mortar. The objective of this research is to investigate the impact of incorporating PJA as a binding agent on the compressive strength, split tensile strength, and flexural strength of both concrete and cement mortar. In this research, Prosopis Juliflora Ash (commonly known as Seemaikaruvelam) was employed to substitute cement in both cement mortar and concrete, with varying proportions of 10%, 20%, 30%, 40%, and 50%.According to the results of this experiment, 30% of PJA has the requisite strength qualities. This experimental investigation provides valuable insights into the mechanical characteristics of concrete and mortar incorporating PJ ash and emphasizes its potential as a sustainable alternative in the construction industry.</p>

First-principles study on the mechanical properties of cement mortar modified with functionalized graphene oxide.

In this paper, first-principle calculations reveal that the shear strength of the graphene-cementitious interface (G/C-S-H) (12MPa) is lower than that of the epoxy, hydroxyl and carboxyl graphene-cementitious interfaces (G-O/C-S-H, G-OH/C-S-H and G-COOH/C-S-H) (21MPa, 29MPa and 14MPa). This indicates that the introduction of functional groups helps to improve the mechanical properties of the graphene-cementitious contact interface. Electrical analysis of the interface reveals that functional groups adsorbed on graphene change the electron distribution on the graphene surface. The formation of a contact interface between graphene and cementitious not only promotes the interaction between the two, but also serves as a bridge connecting the graphene and the cementitious, exacerbating the charge transfer between the two and promoting the generation of solid chemical bonds. All calculations were performed by the CASTEP module in Materials Studio software, using the GGA-PBE functional for structural optimization. The convergence criteria for the geometry optimization are set to a self-consistent field iteration convergence criterion of 2.0 × 10-6eV and a structural optimization convergence criterion of 0.02eV/Å.

Agglomeration behavior of colloidal nano-silica and its effect on pore structure, mechanical properties and shrinkage of cement mortar

The pozzolanic activity of colloidal nano-silica (CNS) can promote cement hydration, thereby improving the performance of the cement-based materials. However, the CNS itself presents highly electronegative, upon contact with cementitious materials, the electrostatic repulsion between CNS particles is lost due to the high ionic strength and the presence of multivalent cations in cement paste, which could lead to the destabilization of CNS and the formation of CNS aggregate (CNSA). Furthermore, similar to CNS, the chemical composition of CNSA is still amorphous silica because no chemical reaction occurs during the CNS agglomeration process. In theory, CNSA has similar nano effect and chemical activity effect to CNS and it can obviously accelerate the hydration rate of cement, improve the mechanical properties and pore structure of cement-based materials. This study aims to investigate the agglomeration behavior of CNS in cement pore solution (i.e. particle size distribution, zeta potential, residue Ca2+, microstructure) and its impact on the workability, pore structure and mechanical properties of cement mortar. It is proved that CNSA was formed by the complex of CNS and Ca2+ by electrostatic adsorption. And CNS content played a significant role on obtaining stable and narrow dispersion of CNSA in cement pore solution and the optimal content was found out to be 0.4 wt% where the particle size of the CNSA was still in the nanometer scale and stable at 200 nm. Cement mortar properties were also significantly improved through addition of 0.4 wt% CNS. While the basic workability was maintained, the 28-day compressive strength and flexural strength of cement mortar were improved by 8.94 % and 8.75 % respectively, the 28-day porosity was reduced by 8.76 %.

Influence of Incorporating PVC Waste on the Mechanical Properties of Cement Mortar

Currently, recycling of industrial wastes to reduce the environmental impact is the major concerns of researchers. Polyvinyl chloride (PVC) is one of the  waste materials worldwide, with considerable impacts on environmental. Recycling PVC wastes in the concrete or mortar industry is one of the adopted ways to decrease such impact. The purpose of this paper is the reuse of PVC waste deriving from the workshops manufactured doors and windows which made of PVC material. The waste of polyvinyl chloride was collected from one of the factories located in AL-Khoms, then the waste was sieved, the sample that passed through Sieve No.4  and  retained on sieve No.10 was taken. The PVC waste  proportions of (0.06 ˛ 0.08 ˛ 0.1) by weight of cement was added to the mix mortar. The tests carried out during this study were; air content of fresh cement mortar, flow table, dry density of hardened cement mortar, flexural and compression, free shrinkage and finally ultrasound pulse velocity. The results obtained showed a significant improvement in the sound insulation and a decrease in the dry density of the mortar. While the compressive and flexural strength results were slightly lower compared to the standard mortar. In addition, a decrease in the values of flow, free shrinkage and air content was observed with an increase in the PVC content. Nevertheless, the mortar obtained contributes to the conservation of natural resources and maintains the mechanical properties of the cement mortar in structural applications.

Estimation of compressive strength of cement mortars using impulse excitation technique and a genetic algorithm

Compressive strength, a crucial mechanical property of cement mortars, is typically measured destructively. However, there is a need to evaluate the strength of unique cement-based samples at various ages without causing damage. In this paper, a predictive framework using a genetic algorithm (GA) is proposed for estimating the compressive strength of ordinary cement-based mortars based on their dynamic elastic modulus, measured non-destructively using the impulse excitation technique. By combining the Popovics model (PM) and the Lydon–Balendran model (LBM), the static elastic modulus of samples was calculated using constant coefficients, representing an equivalent compressive strength. A GA was then employed to determine optimal values for these coefficients. The results showed that the LBM-based strength was dominant in the middle range of the dynamic Young's modulus while the PM-based strength was dominant for higher and lower values of the dynamic Young's modulus. The model was found to have a small root mean square error (3.1%). The findings suggest that this non-destructive model has potential for predicting the mechanical properties of cement mortars. It allows efficient evaluation of compressive strength without destructive testing, offering advantages for reliable assessments of cement-based materials.

Research on the Effect of Fire Thermal Energy on the Microstructure and Properties Mechanical of Fiber-Reinforced Cement Mortars

Cement mortar is made of a combination of cement, sand, and water, mixed in the right proportions. It is ideal for erecting walls and masonry structures, including those that must bear heavy loads. In addition, it is used in places that are exposed to higher humidity and in facilities located below ground level. The potential uses of a mortar are determined by material modification. The aim of the experimental studies was to evaluate the effect of high temperature on the microstructure and mechanical properties of cement mortars modified with polypropylene fiber. The novelty of this study is an attempt to compare the use of different types of polypropylene fibers in mortars heated at different temperatures. Cement mortars based on Portland cement CEM I 42.5 R with a constant content of three types of fibers in the amount of 0.9 kg/m3 were designed. The samples were cured and then heated in an oven at 300, 500 and 700 °C. The functional properties of cement mortars, i.e., density, flexural and compressive strength after 28 and 56 days of maturation, as well as flexural and compressive strength at elevated temperature, were determined using samples of 40 × 40 × 160 mm. By modifying cement mortars with fibers, it is possible to obtain a cement composite with good strength parameters which is, at the same time, resistant to high temperature.

Microstructural and mechanical properties of photocatalytic cement mortar with g-C3N4/CoAl-LDH nanoflowers

The g-C3N4/CoAl-LDH nanoflowers with a strong photocatalytic activity under UV–visible light irradiation was synthesized and applied with different dosages to prepare photocatalytic cement mortars (PCM). Besides the photocatalytic assessment by NOx degradation, the effect of g-C3N4/CoAl-LDH on the microstructural and mechanical properties of cement mortars were investigated by means of X-ray diffraction (XRD), X-ray computed tomography (X-CT), mercury intrusion porosimetry (MIP), capillary water absorption and strength tests. The results show that in addition to the unique air self-purification characteristics, g-C3N4/CoAl-LDH can promote cement hydration with filling effect and further improve the microstructural and mechanical properties of mortar. Moreover, the ability of g-C3N4/CoAl-LDH to capture CO32− can alleviate the influence of carbonation on photocatalytic performance. Therefore, g-C3N4/CoAl-LDH exhibits lasting photocatalytic performance in cement-based materials. This work is expected to contribute to the effort of searching for new multifunctional nano-additives for improved sustainability of building materials.

Quantitative characterization of the interfacial transition zone around lightweight and normal aggregates in cement mortars at different water-to-binder ratios

The interfacial transition zone (ITZ) between aggregates and cement binders has long been known as the most vulnerable to crack resistance among the three phases in heterogeneous concretes [i.e., aggregate, ITZ, cement binders] owing to its porous microstructure. The characteristics of the ITZ are determined by the aggregate types, water-to-binder (W/B) ratios, and supplementary cementitious materials. Furthermore, the correlations between the physicochemical properties of the interface in the vicinity of saturated lightweight aggregates (LWAs) and the mechanical properties of cement concretes are still controversial because of the rough surface and ambiguous water desorption behavior of LWAs. To clarify such correlations, in this study we systemically investigated the effect of different water desorption behaviors of LWAs in cement mortars for various W/B ratios ranging from 0.2 to 0.5 on the mechanical properties of cement mortars via isothermal calorimetry tests, scanning electron microscopy, and nanoindentation grid tests. In addition, the experimental results were compared to those of mortars containing fine normal-weight aggregates (NWAs). These investigations clarified the effect of mechanical properties and porosity of the ITZ on the inherent strength of cement mortars with different aggregate types and W/B ratios. An improvement in the ITZ morphology around the LWAs was observed in relation to that around the NWAs for W/B > 0.3. Conversely, the porosity increased significantly on the LWA surface with respect to that on the NWA surface for W/B = 0.2. Nanoindentation tests revealed the deterioration of the elastic moduli and hardness of mortars containing LWAs at all investigated W/B ratios.

The Influence of GGBFS as an Additive Replacement on the Kinetics of Cement Hydration and the Mechanical Properties of Cement Mortars

Granulated blast furnace slag (GBFS) is a byproduct of the iron production process. The objective of this study is to determine the effects of ground granulated blast furnace slag (GGBFS), used as a replacement admixture (0–40 wt.%) for ordinary Portland cement (OPC), on the setting time, the heat of hydration, and the mechanical properties of cement mortar. The influence of GGBFS as a replacement additive on the setting time shows that it has an accelerating effect on cement hydration. Calorimetric measurements were performed on the cement paste system to determine the effects of GGBFS on the hydration of OPC. Calorimetric measurements carried out show that the replacement of GGBFS in an amount up to 40 wt.% reduces the total heat of hydration by up to 26.36% compared to the reference specimen. The kinetic analysis performed on the calorimetric data confirms the role of GGBFS as an accelerator by shortening the time during which the process of nucleation and growth (NG), as the most active part of hydration, is reduced up to 2.5 h. The value of the Avrami–Erofee constant indicates polydispersity and heterogeneous crystallization. Mechanical tests of cement mortars were performed after 3, 7, 14, 28, 70, and 90 days of hydration and showed that replacement addition of GGBFS slightly reduced the mechanical properties in the early phase of hydration, while in the later phase of hydration it contributed to an increase in the mechanical properties.

Study on the impermeability and microstructure of cement mortar blended with silicon carbide nanowhiskers

Silicon carbide (SiC) nanowhiskers have many application prospects owing to their excellent mechanical properties, thermal conductivity, and good chemical stability. Herein, we examined the effect of enhancing the mechanical properties and impermeability of cement mortar (CM) by improving the microstructural compactness and reducing the porosity after mixing CM using SiC nanowhiskers. Macroscopic and microscopic tests and analyses of CM blended with different amounts of SiC nanowhiskers were performed using an electro-hydraulic flexural and compressive testing machine, cement mortar penetration tester, field-emission scanning electron microscopy, energy-dispersive spectrometry, X-ray diffraction, and three-dimensional X-ray microscopy. Results demonstrated that the incorporation of SiC nanowhiskers can lead to the following: (1) enhance the mechanical properties of CM, especially in the early stage; (2) fulfill the role of crystal nucleation and promote the hydration reaction; (3) fill the pores, play the role of micro-aggregate filling, improve the compactness, and reduce the porosity and relative permeability coefficient; and (4) play a bridging role and connect internal structures. Our results provide a valuable reference for developing nanowhisker-blended CM.