Flexural Strength Of Cement Mortar Research Articles

Effect of nano-metakaolin on the chloride diffusion resistance of cement mortar with addition of fly ash

This study examines the improvement of nano-metakaolin (NMK) on the chloride ion diffusion resistance (CDR) of fly ash (FA) cement-based materials. The rapid chloride diffusion (RCM) method was employed to compare the effects of nano Al2O3, nano CaCO3, nano SiO2, nano attapulgite clay, and NMK on the CDR of cement mortar, and a suitable nanomaterial was identified. Subsequently, the influence of NMK on the CDR, flexural and compressive strengths of FA cement mortar was examined. The chloride ion concentration of NMK/FA cement paste under simulated salt environment were measured. The action mechanism of NMK on the CDR of FA cement mortar was explored through mercury intrusion porosimetry and scanning electron microscopy tests. The results reveal that among these nanomaterials, NMK exhibited the highest cost-effectiveness in enhancing CDR of cement mortar, with a suitable content of 5 wt%. NMK demonstrated a significant improvement in the CDR of FA cement mortar, particularly at a hydration age of 7d. Incorporating 5 wt% NMK into the cement mortar with addition of 30 wt% FA resulted in a 73% reduction in chloride ion diffusion coefficient (Dcl) compared to the cement mortar with the addition of 30 wt% FA at 7d. NMK enhances both flexural and compressive strengths of FA cement mortar at various hydration ages (3, 7, 14, 28 d). The addition of 5 wt% NMK makes a increment of about 10% for the flexural strength of cement mortar with 30 wt% FA at 7d. Moreover, NMK results in a denser internal structure of FA cement mortar, facilitates the generation of C–S–H gel, and reduces the more-harmful pores and harmful pores while increasing harmless and of less-harmful pores cement paste. Additionally, NMK exhibited the most substantial reduction in chloride ion concentration within FA cement paste at 7d. In general, NMK significantly enhances CDR, flexural and compressive strengths of FA cement mortar, especially at a hydration age of 7d.

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 %.

Studying the Effects of Varied Dosages and Grinding Times on the Mechanical Properties of Mortar

With the rapid development of construction and the construction industry, the demand for mortar as a building material is also increasing. With the development of economic society, glass products have been widely used, and glass manufacturing enterprises have produced hundreds of tons of glass fragments and slag. The main component of glass is silica, which has the potential to be used as an auxiliary cementing material. Therefore, waste glass is expected to be recycled in buildings to achieve sustainability. However, due to the chemical properties of the silica tetrahedral structure stabilized by the waste glass, its pozzolanic activity is potent and needs to be stimulated. Glass powders with different degrees of fineness were obtained by physical grinding of waste glass powder (WGP). The standard consistency water consumption, compressive strength, and flexural strength of waste glass powder cement mortar were studied. The grinding times of waste glass powder are 5 min, 10 min, and 15 min, respectively, and the dosages are 5%, 10%, 15%, and 20%, respectively. The experimental results show that the average particle sizes of the grinding times of 5 min, 10 min, and 15 min are 1670.0 μm, 243.0 μm, and 13.2 μm, respectively. The waste glass powder with a grinding time of 15 min has a specific surface area of 670 m2/kg, which has high pozzolanic activity. The compressive and flexural strength of cement mortar specimens with 5% waste glass powder is the best, and the later strength is improved to a certain extent. The consistency of the cement mortar increased after adding waste glass powder. Compared with the 28 d compressive strength activity index of pure cement mortar specimens, the waste glass powder with 5–10% content reached more than 70%.

Experimental and machine learning approaches to investigate the effect of waste glass powder on the flexural strength of cement mortar.

Using solid waste in building materials is an efficient approach to achieving sustainability goals. Also, the application of modern methods like artificial intelligence is gaining attention. In this regard, the flexural strength (FS) of cementitious composites (CCs) incorporating waste glass powder (WGP) was evaluated via both experimental and machine learning (ML) methods. WGP was utilized to partially substitute cement and fine aggregate separately at replacement levels of 0%, 2.5%, 5%, 7.5%, 10%, 12.5%, and 15%. At first, the FS of WGP-based CCs was determined experimentally. The generated data, which included six inputs, was then used to run ML techniques to forecast the FS. For FS estimation, two ML approaches were used, including a support vector machine and a bagging regressor. The effectiveness of ML models was assessed by the coefficient of determination (R2), k-fold techniques, statistical tests, and examining the variation amongst experimental and forecasted FS. The use of WGP improved the FS of CCs, as determined by the experimental results. The highest FS was obtained when 10% and 15% WGP was utilized as a cement and fine aggregate replacement, respectively. The modeling approaches' results revealed that the support vector machine method had a fair level of accuracy, but the bagging regressor method had a greater level of accuracy in estimating the FS. Using ML strategies will benefit the building industry by expediting cost-effective and rapid solutions for analyzing material characteristics.

Experimental Investigation on the Mechanical Properties of Cement Mortar Incorporated With Graphene and C&D Waste

Concrete is one among the essential materials utilized in engineering works.The two main properties which attribute to the reliability of concrete as a universal choice are strength and durability. Despite its remarkable properties, it has few shortcomings, namely, low tensile strength, low ductility, and unavoidable cracks. All of these inadequacies are the result of the relatively porous microstructure of concrete. The use of nanomaterials is the most influential and powerful alternative to overcome these limitations. In this paper, a comparative study of the mechanical properties of normal strength mortar over the mortar reinforced with graphene has been presented. Making use of the construction demolition waste in different proportions, namely, 25% and 50% as the partial replacement for fine aggregate, graphene was incorporated in the cement mortar of 1:3 grade in the proportion of 0.1%, 0.4%, 0.7%, and 1% by weight of cement respectively. The proportion of construction demolition waste and graphene were consequently varied and the corresponding change in mechanical properties, namely, compressive strength, tensile strength, and flexural strength of cement mortar was observed on the 7th day, 14th day, 21st day, and 28th day respectively and the same was compared with the result of normal mortar. It was observed that these mechanical properties increased with an increase in the proportion of graphene up to a certain limit after which it decreased. However, the optimum percentage of graphene varied along with the variation in the percentage of C&D waste.

Reinforcement of ultra-low dosage of polycarboxylate ether (PCE) grafted nano-silica sol to the mechanical and durable properties of cement mortar

How good dispersion of nano-SiO2 (NS) plays a great influence on how strong reinforcing efficiency to cement-based materials. In this study, a novel nanohybrid of polycarboxylate ether (PCE) grafted nano-silica sol (PCE@NSS) was prepared by sol–gel methods to chemically adsorb PCE onto NSS. The developed nanohybrid showed a higher ultraviolet–visible (UV–Vis) absorbance and slower sedimentation in alkaline solutions, indicating the better dispersion and stability of PCE@NSS than that of untreated NSS. By this way, only 0.05 wt.% addition of PCE@NSS was helpful to refine the capillary pore size and reduce the total porosity of cement mortar, which in turn improved the compressive and flexural strength of cement mortar by 18.34% and 10.5% at 28 days, respectively. In addition, a reinforcing index (R index) with the ratio of strength enhancement % to dosage % was proposed, indicating that the R index of PCE@NSS showed 10 times higher than that of other NS-based nanomaterials reported in literatures, addressing the highly reinforcing efficiency of PCE@NSS to cement mortar. Furthermore, water absorption coefficient of cement mortar was therefore reduced by 12.7% with 0.2 wt.% addition of PCE@NSS. In conclusion, such an ultra-low dosage of PCE@NSS with better dispersion and stability exhibited great potential to reinforce cement-based materials with highly efficiency, lower cost and reduced carbon emissions.

The ITZ microstructure, thickness, porosity and its relation with compressive and flexural strength of cement mortar; influence of cement fineness and water/cement ratio

The ITZ microstructure, thickness, porosity and its relation with compressive and flexural strength of cement mortar; influence of cement fineness and water/cement ratio

Effect of cement partial substitution by waste-based biochar in mortars properties

Incorporation of biochar in cementitious materials is a promising solution in the mitigation of environmental pollutants by partially cutting off the consumed ordinary Portland cement and reducing the amount of waste disposal in landfills. This work studied the partial replacement of cement by biochars having a different chemical composition and its effect on the performance of cement mortars. The feedstocks for biochar production were selected from biomass wastes produced in agro-industrial and forestry sectors in Portugal. They included olive stone, rice husk and wood chips from residual forest biomass. Biochars were produced at 500 ℃ using a slow pyrolysis process. The biochars were added at different cement replacement rates; 0.5, 1, 2 and 4 wt% of cement weight. XRD and TGA were used to elaborate the effect of biochar on the hydration products. Effect of biochar addition on the capillary water absorption, compressive and flexural strength of cement mortar was analyzed. The results suggested that the biochars contributed to the promotion of hydration products. Cement replacement with 4 wt% olive stone and rice husk biochars was associated with a slight increase of 28-days compressive strength. Rice husk biochar showed the best long-term mechanical performance due to its pozzolanic reaction in the matrix. No significant changes were observed in the water absorption of cement mortar after the addition of 4 wt% biochar as cement replacement. The research outcomes suggested the beneficial effect of cement replacement with biochars from olive stone and rice husk up to 4 wt% with comparable properties.

Effect of Recycled Powder on Properties of Cement Morta

The effects of two types of recycled micro-powder (concrete powder and brick powder) replacing part of cement on the mechanical properties of cement mortar were studied. The results show that the contribution of recycled concrete powder to concrete strength is slightly stronger than that of brick powder. In a certain range of dosage, the performance of recycled concrete powder is close to that of pure cement. When the content of recycled concrete powder is less than 10 %, the compressive strength and flexural strength of cement mortar will not be greatly affected: over 20% cement mortar strength will decrease significantly. When the grinding content of recycled concrete is 5 %, the strength of cement mortar is even increased by 4.5 %. The relationship between recycled brick powder content and cement mortar strength is almost linear to 20% limit. The more recycled brick powder content is, the more obvious the cement mortar strength decreases. The particle size of regenerated powder has a certain influence on its activity. After a certain time of ball milling, the activity of regenerated powder can be effectively increased, but the ball milling time is too long, resulting in very fine particles. The activity of regenerated powder increases slightly with the increase of ball milling time, but the effect gradually decreases after more than 1 h.

Influence of wetting–drying cycles on compressive and flexural strength of cement mortar and CFRP-mortar bond strength

When mortar is exposed to the marine environment, its mechanical properties can degrade due to weathering by seawater spray and capillary rise. This paper investigates the compressive, flexural, and pull-out bond strengths of a commercially available M3 type mortar. Mortar cube and beam specimens were used for the compressive and flexural strength tests and UPV test. Mortar beams were also retrofitted with carbon fibre polymer (CFRP) and their flexural and pull-out bond strengths were investigated. All the specimens, except the control group, were subjected to accelerated wetting and drying cycles (WDC) over a period of nine weeks, where each cycle consisted of four days of wetting in tapwater and seawater at room temperature and three days of drying at 60 °C. A notable decrease in the compressive, flexural, and pull-out strengths of the mortar specimens, along with physical degradation of the mortar, CFRP and epoxy were observed following the WDC. Correlations between flexural and compressive strengths, and pull-out and compressive strengths is proposed, which can be useful in assessing the material properties of mortar during its service life.

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.

Genetic programming based formulation for compressive and flexural strength of cement mortar containing nano and micro silica after freeze and thaw cycles

Replacing cement with supplementary cementitious materials such as nano and micro-silica would improve the mechanical properties including compressive strength (Fc) and flexural strength (Ff). Also, the frost resistance of the cement mortar as adding micro and nano-silica reduces its porosity. The purpose of this investigation is to evaluating the capability of Genetic Expression Programming (GEP) to predict and formulate the hardened characteristics of cement mortar with the simultaneous addition of nano and micro-silica by considering the freeze-thaw (F-T) cycles based on experimental data. 32 mix designs were prepared with 0.4 and 0.5 water/binder ratios, 990–1200 gr of cement content, 2.667–3.222 of sand/cement ratio, 0 to 0.051 of nano-silica/cement ratio, and 0–0.157 of micro-silica/cement ratio. The parameters modeled by GEP were porosity, Fc, and Ff by considering the F-T cycles. The results obtained from the experimental program of this study were used as input dataset for the proposed GEP models. The correlation between GEP and the experimental results was evaluated and a small dispersion was observed. The results showed the power and robustness of the GEP tool for modeling the hardened characteristics of the cement mortar comprising nano and micro-silica. It also produced a formulation to predict these properties as a function of the mixture components. Finally, a sensitivity analysis was performed and the contribution of the predictor variables on the variation of the Fc and Ff was evaluated.

Effect of porosity on predicting compressive and flexural strength of cement mortar containing micro and nano-silica by ANN and GEP

The aim of this study is to evaluate the effect of porosity on mechanical properties of cement mortar containing micro and nano silica in two aspects of experimentation and modeling of prediction. For this purpose, 32 mix designs were considered with various replacement percentages of nano silica (Ns) and micro silica (Ms) in forms of alone and together. The microstructure effect of Ns and Ms on the mechanical properties of cement mortar was investigated by Field Emission Scanning Electron Microscopy (FE-SEM) analysis. Moreover, Artificial Neural Network (ANN) and Genetic Expression Program (GEP) models are presented to predict the compressive and flexural strengths of cement mortar by focusing on the effect of porosity in models. So, a comparative probe was carried out on two statuses. Once, porosity wasn't considered as input parameter, and, in the next step, it was considered as input parameter in developing ANN-I or GEP-I and ANN-II or GEP-II models, respectively, in order to specify the sensitivity of the models to select the proper input parameters for accurate prediction. The results showed that the use of simultaneous Ns and Ms led to a decrease in the porosity and an increase in the flexural and compressive strengths. This is due to the synergistic effect on the microstructure of cement paste. The current modeling results showed that the ANN-II and GEP-II models have higher accuracy in the prediction of mechanical properties considering porosity as an influential input parameter. Moreover, the validation of proposed models was evaluated with the help of a collection of previous literature.

Effect of porosity on predicting compressive and flexural strength of cement mortar containing micro and nano-silica by multi-objective ANN modeling

Abstract This study describes the effect of various porosity values on the compressive and flexural strength of cement mortar hardened specimens containing micro silica (Ms) and nano silica (Ns) in the two phases of experiment and the prediction modeling. For this purpose, an extensive experimental program containing 32 different mix designs with 960 specimens, two different water to binder ratios (0.50 and 0.40) and various percentages of Ms and Ns contents (1.4, 2.8 and 4.2 wt%) by weight of cement has been performed. In order to investigate the effects of Ms and Ns contents on the microstructure of hardened cement mortar specimens and, consequently, on the mechanical properties of cement mortar, a Field Emission Scanning Electron Microscopy (FE-SEM) analysis was employed. Furthermore, proposing a multi-objective ANN model (MOANN model) along with the correct selecting of the input parameter are the two essential factors for achieving the mixture with the desired properties. In order to determine the sensitivity of the models in selecting the effective and correct input parameter for reliable and accurate predictions, a parallel examination was performed on the status of ANN and MOANN models, both with and without the presence of the porosity values as the input parameter. The experimental results indicated that the simultaneous presence of Ns and Ms contents in the cement mixture increases the compressive and flexural strength in addition to the decreasing the porosity values. The modeling results show that the MOANN-II model has a higher accuracy in prediction due to the simultaneous prediction of the compressive and flexural strength of cement mortar where the presence of the porosity as an effective and proper input parameter was considered. Finally, the proposed model was validated with the help of the collections' dataset of previous studies.

Design methodology and mechanical properties of Superabsorbent Polymer (SAP) cement-based materials

Superabsorbent Polymer (SAP) is attracting great concerns in cement-based materials. However, the design of SAP cement-based materials is lack of theoretical basis. This study proposed a design methodology of cement-based materials containing SAP based on the criterion of flowability similarity. The workability and mechanical properties of SAP cement-based materials with W/C of 0.30 and 0.35 were studied. The standard extra water diversion rates under different SAP contents were determined. With the increase of SAP content, the standard extra water diversion rates increased. The influence of curing conditions on the strength growth of SAP cement-based materials was also investigated. Under water curing condition, SAP played a negative effect on the compressive strength of cement mortar and concrete; while SAP enhanced the compressive strength at the later age under air curing condition. Different from the compressive strength, SAP helped enhance the flexural strength of cement mortar under both water curing and air curing conditions. The criterion of optimal effect of internal curing was employed to analyze the mechanical properties of cement mortars with 0.5% SAP.

Bond strength evaluation between textiles reinforced mortar with carbon nanotubes and concrete substrate

Abstract The influence of using carbon nanotubes to improve bond strength between textiles reinforced mortar and concrete was investigated. Forty-two specimens were tested using double-shear test to evaluate the effect of various parameters such as CNTs addition, type of textile material, bond length and width, and number of TRM layers on the bond behavior. Two types of textile: carbon and basalt fibers were used. Various bond length and width including 50 mm, 100 mm, and 150 mm were considered. Three different percentages of CNTs; 0.05%, 0.1%, and 0.2% by weight of cement, were used. The effect of CNTs addition on the mechanical strength of cement mortar and pull-off strength of TRM were also investigated. Test results showed that adding small amount of CNTs enhanced the tensile and flexural strength of cement mortar, the pull-off strength of the TRM, and the ultimate bond load between the TRM and concrete substrate. The ultimate bond load was highly dependent on the amount of added CNTs, type of textile material, geometry of the bonded area, and number of TRM layers. The SEM images showed the role of the CNTs to enhance the adhesion at the fiber-matrix interface.

Laboratory Investigation on Mechanical Properties of Cementitious Composites with a Low Brittleness

In this study, laboratory tests were conducted to investigate the mechanical behaviors of cement mortars incorporated with different admixtures, such as polypropylene fiber (PP), slag, silica fume and fly ash. Orthogonal tests were designed to evaluate the effects of the admixtures on the brittleness. The flexural strengths and the compressive-flexural ratios were selected to evaluate the brittleness. The optimal proportion can be obtained when PP content was 1.6 kg/m3, and the content of fly ash, slag and silica fume was 10%, 20% and 3% of the cement content respectively. Using the optimal proportion, the 3d flexural strength of cement mortar was 5.65 MPa, which was 19% larger than the specimens without the addition of admixtures; the compressive-flexural ratio was 4.1, which was reduced by 19% in contrast to the control group. The flexural strength at 28d was 9.04 MPa, which was 13% higher than the control group; and the compressive-flexural ratio was 4.21, decreasing 24% compared to the control group. SEM technology was utilized to characterize the evolution of the microstructure induced by the addition of mineral admixtures and PP fiber. Results showed that mineral admixtures made the mortars denser, and the PP fiber formed a cross-linking structure, improving the brittle-resistance. The test results provided some guidance for the mixture design of pavement concrete with a high flexural strength and a low brittleness.

Effect of cement strength class on the generalization of Abrams' law

Abrams' law is used to predict the compressive strength of cementitious materials based on water/cement ratio (W/C). While compressive strength does not only depend on W/C, but also there are many factors that influence the strength of mortar, such as cement strength class and sand/cement ratio (S/C). Novelty of this study, the effect of three types of cement strength classes in 54 cement mortar mix designs on generalization of modified Abrams' law and Bolomey's formula are investigated. Modified equations base on cement strength class and S/C were proposed for the compressive and flexural strength of cement mortar in the range between a very low W/C and a very high W/C. The results showed that the modified equations additional to W/C are strongly influenced by the cement strength class and S/C. Moreover, to show sensitivity of above parameters microstructural characteristics were also studied by the scanning electron microscope (SEM) and an energy dispersive spectrometer analysis (EDS).

ANN and GEP prediction for simultaneous effect of nano and micro silica on the compressive and flexural strength of cement mortar

Artificial neural networks (ANNs) and genetic expression programming (GEP) have recently been used to model the properties of cement mortar containing nano silica (NS) or micro silica (MS) to minimize the experimental work. Appropriate ANN and GEP models were proposed in this paper to predict the simultaneous effect of NS and MS on cement mortar properties because available models are not suitable to predict simultaneous effect of NS and MS. For this purpose, ANN and GEP models were trained on 640 different mixture proportions considered from literature and the prediction results were compared to available models. Moreover, in order to validate the proposed ANN and GEP models, a total of 480 compressive (50 × 50 × 50 mm) as well as 96 flexural (40 × 40 × 160 mm) specimens were constructed while considering cement strength class of 42.5 MPa and also, mechanical properties were tested.The higher accuracy results observed when in proposed models for predicting of compressive strength of cement mortar used normalized input parameters. Moreover, flexural strength of cement mortar estimated by the new ANN and GEP models is validated by experimental effort and the results show high accuracy compared to previous models. Finally, a comparative evaluation was also performed on two conditions of with and without considering porosity as an input parameter in the new suggested ANN and GEP models.

Mechanical Behavior of Cement Mortar with Different Polymer Type

Mechanical property of cement mortar is closely related to polymer modifier type. Four kinds of polymer latex including Chloroprene Rubber (CR), Styrene Butadiene (SBR), Styrene Acrylic (SA) and Polyvinyl Acetate (PVAc) were selected to prepare the modified cement mortar in this study. Mechanical behavior of modified cement mortar was evaluated by flexural strength, Compressive Strength and Tensile Strength, respectively. The micro-morphology of modified cement mortar was observed by scanning electron microscope (SEM), which was useful to analyze the modification mechanism. The results show that the SBR and PVAc latex can effectively improve the flexural strength of cement mortar, while the compressive strength is reduced slightly. Tensile strength of modified cement mortar was increased, especially the PVAc latex modified cement mortar.