Cement Mortar Specimens Research Articles

Study on the Activity of Aeolian Sand Powder and Alkali Excitation Modification

Aeolian sand powder samples were made from aeolian sand which was obtained from the Kubuqi Desert of Inner Mongolia, China. With the method of boiling, the effects of different mass fraction sodium sulfate and sodium hydroxide on the dissolution of active substances of aeolian sand powder were studied. Meanwhile, based on the “alkali activation” theory, the type of activator, the quality fraction and the pre-curing temperature were shown to be variable, and the effect of aeolian sand powder modification is discussed through the test of the strength of aeolian sand powder–cement mortar. Micro-methods such as the total spectral semi-quantitative analysis, x-ray diffraction, field emission scanning electron microscopy, and nuclear magnetic resonance technology were used to study the mineral composition, microstructure and pore characteristics, and then to discuss the feasibility of aeolian sand powder as an alkali-activated material. The results showed that sodium sulfate had a better activation effect on the aeolian sand powder compared with that of sodium hydroxide. The activation rate of aeolian sand powder increases with the increase of the mass fraction of the activator, and, with the increase of the alkalinity of the solution, the dissolution of SiO2 and other active substances in the aeolian sand powder increases gradually. The effect of sodium sulfate on the aeolian sand powder is better than that of sodium hydroxide, and when the mass fraction of sodium sulfate is 2%, the volume of the aeolian sand powder is 15%. When the pre-curing temperature is 35°C, the modification effect of aeolian sand powder is better and the activity index reaches 108.2%. Under the effects of the sodium sulfate, 2.2% and 2.6% active SiO2 and CaO were, respectively, dissolved from the aeolian sand powder. Then, a polymerization reaction occurred under the combined action of the temperature, which generated the needle-shaped hydration product ettringite with a good development state. Meanwhile, the ratio of the inner 20-nm hole of the aeolian sand powder–cement mortar specimen reached 85.69%, and there were many disconnected capillary pores, the irreducible fluid saturation was as high as 94.311%, and the gelling property was good.

FABRICATION OF ADVANCED MORTAR FOR BUILDING APPLICATION

In this research, cement mortar specimens were prepared with sand to cement(1:2.75) and (1, 2, and 3 wt%) of ceramic oxides (MgO, ZnO and Al2O3) at different particlesizes (11.8, 38.8, 109.8 nm), respectively. At curing time (7days), the (structural, thermaland physical) characteristics of the mortar specimens were investigated.The dry density and porosity results show that the values of density increased by(23.4, 15.6, and 9.5%), and the values of porosity decreased by (76.2, 63.8, and 56.2%) for(MgO, ZnO, and Al2O3), respectively with respect to the reference mortar specimen. Thethermal conductivity results show that the values of thermal conductivity decreased by(47.27, 40.66, and 51.16%) for (MgO, ZnO and Al2O3) respectively, with respect to thereference mortar specimen . Results of characterizations tests (XRD and optical microscope)showed that the reference mortar specimen has high roughness with large number ofCa(OH)2 crystals, as well as the presence of pores, while after adding the nanopowders, itshowed a decrease or disappearance of Ca(OH)2 and produced homogeneous structure ofcalcium silicate hydrate compound (C-S-H), in addition to a large decrease in the pores andsurface roughness. This explains the significant improvement in the properties of cementmortar mixed with nanopowders, hence these mortars were very appropriate for coveringwalls, buildings and other outdoor building applications.

A facile approach of developing micro crystalline cellulose reinforced cementitious composites with improved microstructure and mechanical performance

In the present study, microcrystalline cellulose (MCC) reinforced cementitious composites have been developed using a short and less energy intensive physical dispersion technique. MCC–cement mortar specimens were prepared through addition of aqueous MCC suspensions to the cement-sand mixture. Aqueous MCC suspensions (0.4%, 0.8%, 1.2%, 1.6% and 2% MCC, by weight) were prepared through magnetic stirring of pre-soaked MCC powder for only 45 min. The flow behaviour of freshly prepared MCC-mortar paste as well as bulk density, mechanical performance, microstructure, porosity, water uptake and hydration products of developed cementitious composites were characterized. It was noted that with the increase of MCC content, the flow of mortar paste decreased significantly. Maximum improvements of 20.5% in flexural strength, 19.8% in compressive strength, 100% in flexural modulus and 27.2% in fracture energy were achieved after 28 days of hydration. Mechanical performance was found to be better at lower MCC concentrations and at early hydration days. The addition of MCC significantly reduced the pore size of cementitious matrix, leading to increased dry bulk density and reduced water uptake as compared to the plain mortar specimens.

Utilization of rice husk ash and waste glass in the production of ternary blended cement mortar composites

The purpose of this study is the recycling or reuse of waste materials in the production of ternary blended cement mortars (TBCMs) by a partial substitution of ordinary Portland cement (OPC) with a ratio of 20% waste glass powder (WG) to obtain a blended cement (80% OPC: 20% WG). Three different ratios of rice husk ash namely 2.5%, 5%, and 10% are added to obtain three TBCMs as well as conventional cement mortar CM (zero % of rice husk ash). The specimens of all mortars are cured under tap water for different periods of time namely 3, 7, 28, 60, and 90 days. The influence of amorphous silica present in both waste glass and rice husk ash on the performance of TBCMs is studied. The results emphasized that both the waste glass and rice husk ash has a positive effect in the improvement of the compressive strength values of all mortar specimens with increasing hydration time. While the physical parameters such as total porosity and water absorption percentages decreased. The results also indicated that for any given hydration time, the compressive strength values of TBCMs are higher than those of CM. The noticeable improvement in the compressive strength is for TBCM2 specimens (5% rice husk ash). On the other hand, the influence of gamma-irradiation doses on physico-mechanical properties of unsaturated polyester (UP)/impregnated blended cement mortar composite specimens (TBCMs) is studied. The obtained data showed an enhancement in the mechanical properties of the irradiated specimens as compared to unirradiated ones. Furthermore, the thermal stability of TBCMs is studied by using thermo gravimetric analysis (TGA). The results are also confirmed by XRD analysis.

Ureolytic/Non-Ureolytic Bacteria Co-Cultured Self-Healing Agent for Cementitious Materials Crack Repair.

The present study investigated the CaCO3 precipitation performance of ureolytic and non-ureolytic bacteria co-cultured as a self-healing agent for cementitious materials crack repair. Three different inoculum ratios of ureolytic Sporosarcina pasteurii and non-ureolytic Bacillus thuringiensis (10:0, 8:2, or 5:5) were used. The effect of coculturing ureolytic and non-ureolytic bacteria on microbial metabolism was investigated by measuring the rate of growth in urea-containing medium and the rate of NH4+ and CaCO3 production in urea–calcium lactate medium. The self-healing efficiency of co-cultured bacteria was examined by exposing cement mortar specimens with predefined cracks to media containing single urease-producing or co-cultured bacteria. The obtained results provide new findings, where CaCO3 precipitation is improved by co-culturing ureolytic and non-ureolytic bacteria, owing to the relatively faster growth rate of non-ureolytic bacteria. The crack filling rate correlated with the width of crack, in particular, specimens with a smaller crack width showed the faster filling effect, indicating that the crack width can be a dominant factor influencing the CaCO3 precipitation capacity of co-cultured bacteria.

Quantitative study of electromagnetic wave characteristic values for mortar’s crack

Horizontal 4mm-thickness cracks with various depth in different cement mortar specimens simulate respectively various inner micro-defects. GPR antenna of 1.0GHz and 2.3GHz central frequency scans respectively the inner-cracked specimens and non-crack one. Electromagnetic waveform characteristic, travel time and correlation of encoded ground penetrating radar reflection signals are quantitatively evaluated. The electromagnetic waveform and its travel time from 2.3GHz antenna appear distinct reflection characteristic at the interface of inner crack; while only transmission of electromagnetic wave is observed when 1.0GHz antenna employed. The correlation coefficient of encoded signals, is an available parameter to depict quantitatively inner crack, based on which a brief method to visualize inner crack is promoted within average erroneous percentage of 6% in shallow crack when scanned by 2.3GHz antenna.

Effects of sulfate on cement mortar with hybrid pozzolan substitution

Sulfate is one of the most important chemical risks which affect the durability of concrete and reinforced concrete structures. Therefore, this study investigates the effects of sulfate on blended cement mortars. In this paper, cement mortar specimens were prepared with the substitution of CEM I 42.5 R cement with Fly ash + Bottom ash + Blast-furnace Slag at the ratios of 5%, 10%, 15%, and 20% along with a control specimen without additives. These prepared cement mortar specimens were then cured for 2, 7, 28, 90, 180, and 360 days either in potable water or 10% sodium sulfate (Na2SO4) solution. Cement paste specimens were subjected to the initial setting, final setting, and volumetric expansion tests in accordance with the TS EN 196-3 standard. Cured for 2, 7, 28, 90, 180, and 360 days, cement mortars were subjected to compressive strength tests as per the TS EN 196-1 standard while length change tests were conducted as per the ASTM C 1012 standard.It was found that the compressive strength of cement mortars blended with 5% Fly ash + Bottom ash + Blast-furnace Slag cured in sodium sulfate for 360 days was approximately 2% higher than that of the cement mortar without additives. The length change of specimens obtained from cured in sodium sulfate solution shows best results in higher additive ratio. These all length changes ratio are greater than 0.087% ratio which is maximum length change expansion in potable water. This study suggests that 15% and 20% additive ratios are effective in reducing unfavorable effects of sulfate.

Investigation of the capillary rise in cement-based materials by using electrical resistivity measurement

In order to explain the nonlinear relationship between uptake water and time0.5 during early stage of capillary rise in cement-based materials (CBMs), a batch of well-designed specimens of cement mortar with nine embedded electrodes were introduced. Water distribution in specimens and process of capillary rise in CBMs were investigated by testing the electrical resistivity. Based on the results of experiments, an improved Terzaghi capillary rise model was established by considering the variation of saturation degree of CBMs above the wetting front. Results show that (1) the nonlinear relationship between uptake water and time0.5 was caused by the increase of saturation degree in CBMs above the wetting front, which caused the decrease of capillary pressure, (2) there was an unsaturated transitional region between the wetting front and saturated region during the capillary rise, the height of this region increased with the rise of wetting front, (3) the improved Terzaghi capillary rise model fitted experimental data well.

The Propagation Behavior of Collinear Cracks under Compression

In this paper, brittle materials with three collinear discrete cracks under compression have been studied, and a corresponding fracture condition has been proposed. In order to exam the effectiveness of the fracture condition and investigate the factors that control crack initiation and propagation, experiment study by using cement mortar and sandstone specimens with three collinear cracks has been implemented, and the effects of crack orientations, the distance between two cracks and the confining stresses have been investigated. The test results agree well with the fracture condition proposed in this paper.

Evaluating Corrosion Damage Evolution of Cement Mortar in Acid Environment via Relative Elasticity Modulus Method

In order to study the damage variation along thickness from surface, a relative method combined with impulse excitation test was studied in this work to evaluate the elastic modulus of cement mortar corrosion damage layer, by simulating the damage layer as a coating. The damage layer with different damage degree is treated as multilayer coatings in which each layer has different properties. The elastic modulus of each layer is determined by using the relative method step by step. Single face of Portland cement mortar specimens was exposed in an aggressive environment, with 0%, 5%, 7.5% and 10% HCl content, respectively. The corrosion damage degree and evolution law of the mortar were investigated by measuring the elastic modulus of surface damage layer. With the increase of HCl concentration, thickness of corrosion damage layer increased and the modulus of the damage layer decreased greatly. The elastic modulus of each corrosion layer was obtained at different depths. By this way, damage depth and damage evolution were evaluated effectively.

Using photocatalytic coating to maintain solar reflectance and lower cooling energy consumption of buildings

Solar reflectance is one of the main parameters that affect the heat transfer through opaque building envelope and cooling energy consumption. Deposition of airborne black carbon (BC) darkens the building surfaces and increases the cooling energy consumption. The objective of this study is to experimentally demonstrate that photocatalytic coating with TiO2 is able to maintain solar reflectance of opaque building envelope and lower the cooling energy consumption. Portland cement mortar specimens were coated with transparent silicate coating (TSC), white silicate coating (WSC), and white silicate coating incorporating photocatalyst (PWSC). The solar reflectance, color, heat gain, and surface temperatures of the specimens exposed to a sun simulator for 9 h were determined at three different time points: 1) before BC deposition; 2) after BC deposition; and 3) after 300 h exposure to simulated solar irradiation in an accelerated weathering chamber. The BC deposition reduces the solar reflectance of the specimens by 51 - 56% and increases the heat transfer through the specimens exposed to the sun simulator by 27% - 123%, depending on the solar reflectance before BC deposition. The photocatalytic TiO2 is able to remove black carbon and restore the solar reflectance and color of the PWSC specimen after 300 h of exposure to simulated solar irradiation in a weathering chamber. With the removal of black carbon, the heat gain and inner surface temperature of the PWSC specimen exposed to the sun simulator for 9 h are comparable to those before the BC deposition but 53% and 7.2 °C lower than those after the BC deposition, respectively. The results indicate that photocatalytic coating with TiO2 is able to maintain the solar reflectance of opaque building envelope and lower cooling energy consumption of buildings.

Experimental work on mechanical, electromagnetic and microwave shielding effectiveness properties of mortar containing electric arc furnace slag

It is well known that one of the widely used structural materials is ordinary cement mortar. Whereas the mechanical properties are sufficient as structural materials, its shielding effectiveness and prevention properties of microwave signal is insufficient due to the lack of electromagnetically conductive components. Electric Arc Furnace Slag (EAFS) is a by-product which is produced after the melting and the primary acid refining of liquid steel. It has potential to improve both mechanical and electrical properties of cement. In this study, ordinary cement mortar specimens with Electric Arc Furnace Slag are investigated. The EAFS used in this study takes part in the mortar specimens as aggregate. Electrical properties are measured by a vector network analyzer in the frequency range of 3–18 GHz. Both the reflection and transmission of the proposed specimens exposed to EM wave are evaluated by free space measurement techniques at the same frequency range. The compressive strength, flexural tensile strength and shielding effectiveness of mortars are also tested, respectively. The real part of permittivity increases with the increased EAFS content of the mortars up to dielectric constant of 40. Nearly constant and frequency independent characteristics of specimens have potential applications. Furthermore, the effective dielectric constant of permeability of the mortars is explicitly improved in the related frequency ranges with the addition of the EAF slags. The transmission prevention of the EAF slag mortars tend to increase significantly with the increasing ratio of EAF slag content. The minimum transmission is around −70 dB and the transmission below −10 dB for 40% EAF aggregate ratio in mortar which has the best mechanical properties in the entire frequency range and averagely and it is −10 dB lower than that of the cement without EAF aggregates. The shielding effectiveness is in excellent level for 80% and 100% EAFS aggregate levels and that of 40% aggregate ratio is still in a good level with a value varying between 15 dB and 20 dB. Besides, the mortars with 40% EAF slag content exhibit approximately 7 MPa higher compressive strength value and 0.9 MPa higher flexural tensile strength.

Theoretical Analysis and Experimental Verification of Crack Initiation Characteristics of Compression-Shear Plane Crack with Hydraulic Pressure

In this paper, the crack initiation characteristics of compression-shear plane crack with hydraulic pressure were studied by using theoretical analysis and experimental verification methods. The formula derivation process of stress intensity factor of crack tip and open-type crack initiation angle and initiation strength was expounded in detail. Cement mortar specimens prefabricated with open-type crack were made for biaxial compression test. The results show that the mode I stress intensity factor is inversely proportional to the dip angle of pre-exciting crack, water pressure and crack width. The fracture toughness is most easily achieved when the dip angle of pre-exciting crack is 60°. The mode II stress intensity factor is symmetrically distributed with the dip angle and independent of the water pressure and crack width. For open-type crack, the crack initiation angle decreases with the increase of the dip angle of pre-exciting crack, water pressure and crack width; the crack initiation strength is inversely proportional to the water pressure and proportional to the lateral pressure. The research results can provide ideas for the study of crack initiation under the coupling of ground stress and osmotic pressure in tunnel engineering.

Sensitivity and uncertainty analysis of interfacial effect in SHPB tests for concrete-like materials

The Split Hopkinson Pressure Bar (SHPB) equipment has been widely used to measure the dynamic properties of concrete-like materials at high strain rate between 10s-1 and 103s-1. As we know, a crucial factor that influences the accuracy of SHPB tests is the interfacial effect between specimen and bars. In our work, interfacial effect was investigated and summarized into three types of parameters, i.e., interfacial friction coefficient, specimen diameter and specimen non-parallelism. A series of concrete-like (cement mortar) specimens with two different strengths were tested at three different strain rates on SHPB equipment, and the uncertainty of the interfacial effect was transformed into intervals of these three types of parameters. A numerical model was established in ABAQUS and verified to study the interfacial effect, then the sensitivity analysis of three types of parameters was undertaken to figure out a sensitivity ranking using the full factorial design method. The sensitivity analysis provides an effective measure to promote the experimental accuracy and it is meaningful for understanding the interfacial effect in SHPB tests. Moreover, uncertainty analysis was conducted to give an interval of dynamic response of SHPB tests based on a non-probabilistic interval analysis method. The uncertainty analysis can provide an effective estimation of SHPB experimental results considering the uncertainty of interfacial effect.

Utilization of Electrolytic Manganese Dioxide (E.M.D.) waste in concrete exposed to salt crystallization

In the present study, the physico-mechanical properties and corrosion resistance of reinforced concrete containing Electrolytic Manganese Dioxide (E.M.D.) waste were investigated. Concrete samples prepared in the lab with and without the use of EMD waste were exposed to sulfate and chloride salt solutions. In particular, the test samples were placed in 5% w/w Na2SO4 solution, while chloride penetration resistance was studied in 3.5% w/w NaCl solution. The concrete mixtures were prepared with 0%, 5% and 10% w/w replacement of Ordinary Portland Cement (OPC) with the aforementioned waste additive. For testing, specimens of varying shapes and dimensions were cast; cylindrical reinforced cement mortar specimens were also prepared. Tests for estimating the physico-mechanical properties (compressive strength, modulus of elasticity, porosity and sorptivity), mass loss of steel and thermal response of concrete (DTA/TG) were performed; the carbonation depth of mortars exposed to atmospheric conditions was also estimated. The experimental results generally suggest that the EMD waste additive does not affect negatively the properties of concrete partially immersed in chloride salt solution; in addition, the anticorrosive effect of EMD waste on steel rebars embedded in cement mortars was also observed. On the other hand, the composite concretes immersed in sulfate salt solution exhibited inferior values for all measured properties.

Prediction of chloride diffusion in cement mortar using Multi-Gene Genetic Programming and Multivariate Adaptive Regression Splines

Chloride-induced damage of coastal concrete structure leads to serious structural deterioration. Thus, chloride content in concrete is a crucial parameter for determining the corrosion state. This study aims at establishing machine learning models for chloride diffusion prediction with the utilizations of the Multi-Gene Genetic Programming (MGGP) and Multivariate Adaptive Regression Splines (MARS). MGGP and MARS are well-established methods to construct predictive modeling equations from experimental data. These modeling equations can be used to express the relationship between the chloride ion diffusion in concrete and its influencing factors. Moreover, a data set, which contains 132 cement mortar specimens, has been collected for this study to train and verify the machine learning approaches. The prediction results of MGGP and MARS are compared with those of the Artificial Neural Network and Least Squares Support Vector Regression. Notably, MARS demonstrates the best prediction performance with the Root Mean Squared Error (RMSE)=0.70 and the coefficient of determination (R2)=0.91.

Effects of CO2 surface treatment on strength and permeability of one-day-aged cement mortar

Many of the degradation problems of concrete can be attributed to the weak surface layer. Surface treatment of concrete has been proven a simple and effective method to enhance the durability of concrete. In the present study, two series of portland cement mortar specimens with w/c ratios of 0.4 and 0.3 were prepared. CO2 treatment was applied to he mortars 24h after casting. The results indicated that CO2 treatment resulted a carbonated a layer of less than 1.6mm in thickness, slightly increased compressive strength, but significantly reduced the water permeability, water-vapor transmission and chloride migration of the mortars. Environmental Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FT-IR) Spectroscopy and thermogravimetric analysis (TGA) results indicated that calcium silicate hydrate with low Ca/Si ratio and CaCO3 were the products in the carbonated surface layer.

Phase-field simulation of interactive mixed-mode fracture tests on cement mortar with full-field displacement boundary conditions

Phase-field modeling is an elegant approach to simulate complicated fracture processes, including crack initiation, propagation, merging and branching in a unified framework without the need for ad-hoc criteria and on a fixed mesh. These capabilities can only be fully validated through the comparison with experiments featuring crack development histories and patterns of sufficient complexity. As opposed to conventional mixed-mode fracture tests with predefined loading, interactive tests with multiaxial loading which are controlled during the propagation of the cracks can create more complex and stable crack propagation patterns. Moreover, the development of measurement techniques such as digital image correlation (DIC) provides the possibility to quantitatively characterize the full-field kinematics during the tests. In this work, full-field displacements measured by DIC during interactive mixed-mode fracture tests on cement mortar specimens are adopted as boundary conditions for phase-field numerical simulations. Qualitative and quantitative comparisons are illustrated, demonstrating the capability of the phase-field approach to predict complex mixed-mode fracture phenomena in cement mortar and suggesting possible further developments.

Enhanced properties of cement mortars with multilayer graphene nanoparticles

The present work aims to combine multilayer graphene (MLG) nanoparticles with Ordinary Portland Cement (OPC) mortar specimens, evaluating possible improvements on their mechanical properties and ultimately coming up with an ideal and effective concentration for future applications. Mortars with water/cement ratio of 0.4, MLG dosage varying from 0.015 to 0.033% by weight of cement and sand at a proportion of 3× the weight of cement were prepared. 50×100mm cylindrical specimens were shaped and subjected to compressive and splitting tensile strength tests at the ages of 3, 7 and 28days. In addition, SEM micrographs and metallographic images were collected and analyzed in order to better characterize the sample’s morphology and also in attempt of explaining the MLG influence on cement paste. The optimal tensile strength was achieved with samples designed with MLG dosage of 0.033%, for which the corresponding increases were 100.0, 144.4 and 131.6%, after 3, 7 and 28days, respectively, compared with samples without MLG. On the other hand, the optimal compressive strength increases were obtained with samples designed with MLG dosage of 0.021%, with improvements of 63.6, 94.1 and 95.7% after 3, 7 and 28days, respectively, compared with samples without MLG. The addition of MLG is believed to accelerate cement hydration reactions, reduce the pore volume and harden cement properties. An improvement in thermal conductivity is also associated to MLG incorporation, and this favorable heat transfer in OPC-based mortars probably promoted the observed changes in the composite chemical structure and mechanical properties herein analyzed.

Effects of nano-particles on improvement in wear resistance and drying shrinkage of road fly ash concrete

Nano-materials have been widely applied in cement-based materials due to its excellent performance. Two types of nano-particles, namely nano-SiO2 (NS) and nano-SiC (NC), were employed to prepare nano-modified fly ash cement mortar and road fly ash concrete specimens respectively, and the effects of the nano-particles content on wear resistance and drying shrinkage were studied on the basis of strength test, the mechanisms were then analyzed theoretically. The results indicated that nano-particles could improve the wear resistance of road fly ash concrete, but increase thedrying shrinkage. The optimum added dosage of NS for single-doping NS concrete was 2%, and that for NC was 3%. The superior wear resistance of nano double-doped concrete could be found with 2% NS and 2% NC, and meanwhile, the wear loss was only 0.64kg/m2, with a decrease by 75%; the drying shrinkage rate of the concrete containing 2% NS and 2% NC at 28d was increased by 124.8% and 85.8%, respectively, compared to the reference concrete. Therefore, it is concluded that due to its surface effect, pozzolanic reaction and microscopic aggregate filling effect, nano-particles have larger surface energy, to change the orientation degree of calcium hydroxide crystals in the interface transition zone and fill pores among cementitious materials, thereby improving the wear resistance and drying shrinkage of fly ash concrete. These results would provide guidance on the design of the high wear resistance and low drying shrinkage fly ash concrete.