Cement Mortar Samples Research Articles

Strength and permeation characteristics of cement mortar with Reclaimed Asphalt Pavement Aggregates

In order to assess the effect of fine fraction of Reclaimed Asphalt Pavement (RAP) aggregates as an alternative to natural fine aggregates (NA), cement mortar samples were prepared with 25%, 50%, 75% and 100% replacement of natural aggregates. The influence of grading of fine aggregates was also studied. Even though the compressive strength, flexural strength and splitting tensile strength were decreasing with increase in RAP content, the mortar mixes possessed minimum strength requirement providing the potential of fine RAP aggregate as an alternative. The trend of sorptivity characteristics of RAP cement mortar were in contradiction to the porosity nature of the same which suggests that the conventional methodology to determine the former will not cater for concrete or mortar mixes with RAP aggregates.

Changes in color and thermal properties of fly ash cement mortar after heat treatment

Fly ash (FA) is a powdery substance discharged by power plants after burning coal or other fossil raw materials. The storage and reuse of FA have been under debate since the release of FA into the atmosphere could be detrimental to human health. Fortunately, FA has been mostly collected by plants, and these large amounts of collected FA have led to its reuse, which not only reduces pollution, but FA can be also used in lieu of other materials, such as cement, for environmentally friendly building materials. However, the properties of building materials will undergo deterioration at high temperatures. Therefore, in this study, the influence of heat treatment at high temperatures on FA cement mortar is examined in relation to the color and thermal conductivity changes. Color changes are an apparent indicator, for example, of the variation in moisture content. Thermal conductivity (λ) is an important parameter for evaluating the heat transport properties of materials. Mass loss and density also affect thermal conductivity. In this study, 15 FA cement mortar samples are made from mixtures that contain 3 different FA replacement percentages: 10%, 20% and 40%, for a total of 45 samples. The samples undergo heat treatment at temperatures that range from room temperature to 800 °C before testing is carried out. A color meter and a thermal conductivity tester are used to obtain the color parameters L∗, a∗, b∗ and thermal conductivity, respectively. The samples are also sprayed with a phenolphthalein reagent after treatment to qualitatively observe the changes in pH. It is found that a temperature range of 400–600 °C is critical in which the pH of the mortar decreases due to carbonization and the decomposition of calcium hydroxide, which lead reduced lifespan of the FA cement mortar. The thermal conductivity also decreases at higher temperatures, and is linearly correlated with the density ratio. The experimental results show that the FA percentage has a considerable influence and therefore, there could be an optimum FA percentage.

Effect of nano-SiO2 on physical and electrical properties of PPC cement using complex impedance spectroscopy

The aim of this study was to investigate the effect of nano-SiO2 incorporated in cement blended with 30% class F fly ash on consistency, setting times, compressive strength, chloride penetration, complex impedance spectra and conductivity at 10 kHz. The composite cement was composed of nano-SiO2 in 0, 1, 2 and 3% by weight of cement. The consistency was found to be increasing with the increase in nano-SiO2 content whereas retarding effect was observed for setting time. The compressive strength of cement mortar cube sample was found to be less than the control samples. Depth of chloride penetration was also found decreasing with the increasing dosage of nano-SiO2. Complex impedance spectra are found in semicircle shape in later hours due to the formation of hydration products. Conductivity of all samples found to be decreasing because of the dissolution of ions and formation of hydration products. A good correlation between conductivity and setting time was observed with the help of complex impedance spectroscopy.

Experimental Study on Physicochemical and Mechanical Properties of Mortar Subjected to Acid Corrosion

The 28 days cured cement mortar samples were soaked in HCl (pH = 1 and 2) and H2O (pH = 7) solutions for 90 days. By monitoring the ion concentration of H+ and Ca2+ and measuring the changes in weight loss, longitudinal wave velocity, and uniaxial compressive strength values of the corroded mortar, the physicochemical and mechanical properties of the mortar specimens were studied. Experimental results indicate that the process of the mortar sample subjected to HCL erosion has apparent stage characteristics. In the initial stage of corrosion, the chemical reaction increased the porosity of the specimen, which leads to the decrease of longitudinal wave velocity of the samples. At the same time, the corrosion solution continuously penetrates into the mortar pore system, which leads to the increase of the mass, and it is considered that the diffusion process plays a leading role during this period. Moreover, the colloidal compounds generated by the chemical reaction can not only fill the pore space but also block the continuous reaction, which led to the increase of the longitudinal wave velocity of the specimen. With the prolonging of corrosion time and infiltration path, the pH value and the concentration of Ca2+ tend to be stable, the diffusion action is weakened, and the chemical reaction is continuous, which led to the decrease of the mass and wave velocity gradually. It is considered that the chemical reaction plays a leading role in this process. Based on the induction and analysis of the test results, a generalized porosity model regarding the increase of the porosity and the decrease of effective bearing area of the mortar sample was proposed. The relation between the uniaxial compressive strength and the corrosion time of the corroded mortar is deduced, and the unknown parameters are determined based on the regression analysis of the test data.

Effect of high temperature and type of cooling on some mechanical properties of cement mortar

Mortar of cement as construction materials subjected sometimes to high temperature. Some of properties of this mortar being studied after this effect. The effect of high temperature 100, 200, 400 and 700°C (exposed for two hrs.) on some mechanical properties (compressive and flexural strength) of two groups of cement mortar samples (with and without the addition of crushed bricks and superplasticizer as modifying materials) has been studied. Two methods of cooling samples by air and by water for 1/2 hr. was used, then tested after 3, 7 and 28 days. The results showed that the compressive and flexural strength for reference mix exposed to 700°C and water cooling decreased by 65.3 % and 64.7%, respectively, compared with their reference mix tested at 20°C in 28 days. While mixes containing 100% of crushed brick as an additive and air cooling decreases by 12.3% and 9% of their compressive and flexural strength, respectively compared with the mixes tested at 20°C in 28 days. Also showed that the decreases in flexural strength for no sand mixes containing 100% of crushed brick and 4% of superplasticizer exposed to 700°C and then water cooling was 28.2% compared to those for reference mixes tested at 20°C.

The influence of type of cement on the degradation of microstructure and transport properties of cement mortars exposed to frost induced damage

The purpose of the study is to understand how the cyclic water freezing (0, 25, 50, 75, 100 and 150 freeze-thaw cycles) impacts microstructure and transport properties of cement-based materials. Tests were conducted on cement mortars with different water/cement ratios (w/c=0.45 and 0.40) and on two types of cement (CEM I and CEM III) without air-entraining admixtures. The changes of pore size distribution and open porosity were investigated by means of mercury intrusion porosimetry. Additionally, the relationship between intrinsic permeability and the water absorption coefficient of cement mortar samples was analysed. The water absorption coefficient and gas permeability were determined using capillary absorption test and the modified RILEMCembureau method. The evolution of transport coefficients with growing number of freeze-thaw cycles were determined on the same sample. It was also established that change of pore structure (a decrease of small pore volume <100nm and increase of larger pores >100nm) induces an increase of water transport parameters such as permeability and water absorption coefficient. The higher gas permeability corresponds to the higher internal damage. In particular, it is associated with the change of cement mortar microstructure, which indicates damage of narrow channels in the pore structure of cement mortars.

Effect of Graphene Oxide (GO) on the Morphology and Microstructure of Cement Hydration Products.

In this study, the effects of graphene oxide (GO) on the microstructure of cement mortars were studied using scanning electron microscopy (SEM), thermogravimetric (TG), and X-ray diffraction (XRD) techniques. Cement mortar samples with different proportions of GO (0.02, 0.04, 0.06, and 0.08 wt % based on the weight of cement) were prepared. The test results showed that GO affected the crystallization of cement hydration products, C–S–H (calcium silicate hydrate is the main hydrate product) and CH (calcium hydroxide). The morphology of hydration products changed with the increase of GO content. Furthermore, the results of XRD analyses showed that the diffraction peak intensity and the crystal grain size of CH (001), (100), (101), and (102) for GO samples increased considerably compared with the control sample. Based on the results, it can be understood that GO can modify the crystal surface of CH, leading to the formation of larger crystals.

Study of crack propagation in concrete under multiple loading rates by acoustic emission

It is of great importance to investigate the effect of multiple loading rates on the crack propagation of brittle material such as concrete using acoustic emission because engineering structures are subjected to multiple loading conditions. Although material behaviour under single loading mode has been extensively studied, very limited research has been conducted to investigate the performance of brittle materials subjected to varying loading conditions. This paper presents an experimental study of the effects of single and multiple strain rates on cement mortar samples using acoustic emission. A total number of 81 concrete specimens were tested, in this 28 samples were tested in constant strain rate, whereas rest 53 samples were tested in multiple loading rates. Axial strain, lateral strain and acoustic emission counts were recorded continuously until the specimens had failed. The results showed that concrete behaves differently under multiple loading rates. Acoustic emission was in close agreement with the crack propagation and damage of concrete samples.

The transformation of waste Bakelite to replace natural fine aggregate in cement mortar

Bakelite material has been used to produce the various components for cars and consumer goods industry in Thailand. The growth of Bakelite consumption increases Bakelite waste. Bakelite waste is prohibited from disposing of direct landfilling and open burning because of the improper disposal and emission reasons. A large amount of this waste needs the large safe space of warehouse area for keeping which becomes a waste management problem. Size reduction by milling machine is helpful for waste handling and storing, however, the post-milling waste Bakelite plastic utilization shall be studied to maintain the waste storing capacity. There are some studies of the milling machine used for waste plastic size reduction. However, the particular study of milling machine application for waste size reduction and its milling waste utilization is still insufficient in Thailand. The purpose of this research is the use of waste Bakelite aggregate milling machine for Bakelite waste size reduction and use of the post-milling waste Bakelite as a fine aggregate to replace natural sand material in cement mortar. The waste Bakelite fine aggregate (WBFA) was mixed in cement mortar mixture with the proportion 0% 20% 40% 60% 80% and 100% by volume for cement mortar sample preparation. The mortar sample was tested for compressive strength follow ASTM standard. The compressive test result of mortar samples will be compared between conventional mortar (0% WBFA) and waste Bakelite mortar (WBM) as well as comparing with the mortar standard. From an analysis of the sample test data found that the WBFA content in cement mortar mixture can predict the strength of WBM. The compressive strength of WBM at 28days age with the fraction of WBFA is not exceeded 11.03%, and 23.08% respectively can be met the mortar standard according to the equation. The utilization of WBM to develop mortar non-structural mortar product can be usable from a technical point of view.

Study of the evolution of properties of mortar under sulfate attack at different concentrations

In this study, the samples of ordinary Portland cement mortar were fully immersed in sodium sulfate solutions of different concentrations (0%, 5% and 15%) for up to 270 d. The evolution of the properties of the samples (compressive strength, static modulus of elasticity, stress–strain behaviour, hardened density, water permeability coefficient and length change) was monitored. The surface deterioration of the samples was also observed and the morphological features of the products were investigated using scanning electron microscopy. Water immersion was found to improve for the properties of the samples and reduce the water permeability coefficient. Moreover, at the initial stage of sodium sulfate attack, the presence of sulfate ions had a positive effect on the evolution of the properties due to the formation of ettringite and gypsum. Afterwards, the samples immersed in sodium sulfate solution showed a degradation in the properties, induced by the expansion of expansive products and the generation of micro-cracks. Furthermore, the mortar immersed in sodium sulfate solution showed higher expansion and a larger hardened density than the mortar immersed in water. An increase in the concentration of the sodium sulfate solution was found to reduce the time needed to reach peak properties and to accelerate deterioration of the properties at the late stage.

Performance of cement mortars with waste-material addition in microbiological sulphate environment

Bio-corrosion refers to the corrosion influenced by the presence of microorganisms on the surface of different concrete structures. Sulphate-reducing bacteria (SRB) and sulphur-oxidizing bacteria (SOB) belong to the best studied microorganisms causing bio-corrosion. Concrete sewer pipes, waste water collection systems and treatment plants ensure a suitable environment for the growth and activity of these microorganisms. Sulphur-oxidizing bacteria produce the biogenic sulphuric acid which may cause a significant structural damage to the sewage infrastructure by inducing the deterioration of concrete sewer pipes. This paper discusses the effects of SOB bacterial activity represented by Acidithiobacillus thiooxidans on parameters affecting the durability of cement mortar composites. Two mortar mixtures were used in the experiment: samples with a share of ground granulated blast furnace slag (65 % cement replacement) and the reference samples without any waste addition. The composites were exposed to an aggressive sulphate environment with sulphur-oxidizing bacteria for 60 days. Parameters such as the pH of liquid media and the leachability of the basic inorganic compounds from the cementitious matrix due to the aggressive environment were studied. The better durability of cement mortar samples, based on furnace slag addition, against the biogenic sulphate attack was not confirmed.DOI: http://dx.doi.org/10.5755/j01.ct.67.1.15002

Thermal conductivity of cementitious composites containing microencapsulated phase change materials

This paper investigates the effects of adding microencapsulated phase change materials (PCM) on the thermal conductivity of cement paste and cement mortar composites. Embedding cementitious composites with microencapsulated PCM has been considered a promising method for increasing the thermal mass of buildings to achieve greater energy efficiency and for reducing the risks of thermal cracking in pavements. Cement paste and cement mortar samples were synthesized with a constant water to cement ratio of 0.45. Both contained microencapsulated PCM with diameter ranging from 17–20μm, volume fraction up to 30%, and a melting temperature around 24°C. The cement mortar also contained quartz grains 150–600μm in diameter such that the sum of the volume fractions of quartz and microencapsulated PCM was fixed at 55%. All samples were aged for more than 28days. Their effective density and free moisture content were systematically measured. A guarded hot plate apparatus was designed, assembled, and validated according to the ASTM C177-13 to measure the effective thermal conductivity of the aged specimens of cement paste and cement mortar without and with microencapsulated PCM. Measurements were performed between 10 and 40°C, encompassing the entire PCM phase change temperature window. The effective thermal conductivity of both the cement paste and the cement mortar composites was found to be nearly independent of temperature in the range considered. It also decreased as the volume fraction of microencapsulated PCM increased. Finally, excellent agreement was obtained between experimental data and the effective medium approximation derived by Felske (2004) for core–shell–matrix composites. These results can be used to design cementitious composite materials containing microencapsulated PCMs for energy efficient buildings and crack-resistant pavements.

Role of sodium hexametaphosphate in MgO/SiO2 cement pastes

The extent of reaction between magnesium oxide (MgO) and silica fume (SiO2) is normally limited and mixes require high water contents to give suitable rheology. The use of considerably lower water contents and the formation of magnesium silicate hydrate (M-S-H) gel as a binding phase is made possible by adding sodium hexametaphosphate (Na-HMP) to the mix water prior to the addition of MgO and SiO2. This results in the formation of extensive reaction products and cured samples with high compressive strength and low porosity. In this work, the effect of Na-HMP on the hydration of MgO/SiO2 mixes is investigated using high water to solids ratio samples to allow monitoring of pH and the solution chemistry during hydration. It is shown that a relatively small amount of Na-HMP inhibits the formation of Mg(OH)2 when MgO is hydrolyzed. It is proposed that this is due to adsorption of phosphate species on the MgO which inhibits the nucleation of the Mg(OH)2. This gives rise to high Mg2+ species in solution and elevated pH (>12) conditions relative to when Mg(OH)2 forms. In contrast, the phosphate does not suppress formation of M-S-H gel. In combination with the enhanced dissolution rate of SiO2 at high pH, M-S-H gel can form quickly without competition for Mg2+ ions by Mg(OH)2 precipitation. Incorporating the optimum concentration of Na-HMP into the mix water therefore transforms the properties of cement paste and mortar samples formed by reacting MgO and SiO2.

Chloride penetration in cracked mortar and the influence of autogenous crack healing

Cracks in cementitious materials have a negative influence on the durability in aggressive environments, especially in marine environments since chlorides and sulphates are able to penetrate faster. Since constructions in marine environments mostly have an important social function with a high economic impact, repair of the cracks is of utmost importance.In this paper, the ability of the material to heal 100μm and 300μm cracks autogenously in marine environments is investigated. To do so, some Ordinary Portland Cement mortar samples and Blast-furnace Slag blended mortar samples were permanently immersed in chloride solutions as well as in combined chloride and sulphate solutions. Another part of the samples were exposed to wet-dry cycles in water and in chloride solutions. Autogenous crack healing was evaluated by means of microscopic measurements. The resistance against chloride penetration was measured by means of colorimetric measurements and chloride profiles.It was shown that cementitious materials, exposed to a simulated marine environment, are able to heal or seal crack widths up to 100μm. Autogenous healing is obtained by ongoing hydration, calcium carbonate precipitation as well as by formation of a layer of magnesium and sulphate reaction products (brucite) at the surface. Furthermore, the resistance against chloride penetration improves due to the healing process. However, the efficiency depends on the initial crack width.

Studies on optimization of silica nanoparticles dosage in cementitious system

Optimization of silica nanoparticles (SNPs) dosage in cementitious system was carried out analytically as well as experimentally by understanding the early stage hydration reaction of tricalcium silicate (C3S). XRD and TGA results show the maximum nucleation effect of SNPs at 8 h, when the rate of product formation was higher than the control (∼66% additional CSH and ∼61% more CH with 10% SNPs addition). While at 24 h of hydration, ∼25% additional CSH was formed and CH content reduced by ∼32% with 10% addition showing the pozzolanic effect of SNPs. Further, FTIR results reveal that SNPs accelerate the polymerization in silicate chain and with 10% SNPs addition more crystalline (probably tobermorite like) structure is formed. This is responsible for the formation of highly compact and dense microstructure at 24 h as observed in electron micrographs, which may be responsible for the slow hydration rate at later age. XRD, FTIR and TGA studies on C3S revealed that up to 5% addition of SNPs is beneficial, whereas higher dosages do not contribute significantly. Based on these investigations, studies were performed on cement paste, mortar and concrete samples, which revealed that 2–3% addition of SNPs is the optimum quantity for significant contribution in strength properties.

Effect of Chlorides on Conductivity and Dielectric Constant in Hardened Cement Mortar: NDT for Durability Evaluation

Dielectric constant and conductivity, the so-called EM properties (electromagnetic), are widely adopted for NDT (Nondestructive Technique) in order to detect damage or evaluate performance of concrete without damage to existing RC (reinforced concrete). Among deteriorating agents, chloride ion is considered as one of the most critical threats due to rapid penetration and direct effect on steel corrosion. In the work, cement mortar samples with 3 w/c (water-to-cement) ratios and 4 levels of chloride addition are considered. Conductivity and dielectric constant are measured in the normal frequency range. They increase with strength of mortar and more chloride ions due to denser pore formation. Furthermore, the behaviors of measured EM property are investigated with carbonation velocity and strength, which shows an attempt of application to durability evaluation through EM measurement.

Effects of biodeterioration on the mechanical properties of concrete

Concrete biodeterioration in sewers and structures subjected to environments rich in hydrogen sulfide has been related to the activity of sulfur oxidizing bacteria (SOB). In previous studies, the effect of the activity of SOB on concrete structures has been linked mainly to weight loss. In our work we have investigated, in addition to the weight loss, the variations in porosity and compressive strength. The main objective of this paper is to explore, under controlled conditions, the effect of biodegradation of non-submerged samples, on both the physical properties and the mechanical performance. Towards this aim, cement mortar samples inoculated with pure cultures of Acidithiobacillus thiooxidans, Halothiobacillus neapolitanus, and a consortium containing both strains, were exposed to an H2S-rich environment. Changes in physical properties, including weight and porosity, and compressive strength were measured over 300 days. The results showed that the greatest reduction of weight and compressive strength was observed in samples inoculated with the consortium (7 and 52 %, respectively); while the largest variation in porosity was observed in samples inoculated with A. thiooxidans (27 %). These results were used to obtain relationships between the amount of sulfur available over time with specific physical and mechanical properties; i.e., compressive strength, porosity, weight loss, and physical appearance.

Hydrogen-rich water revealed benefits in controlling the physical and mechanical performances of cement mortar

The present investigation deals with the effectiveness of hydrogen-rich water in controlling the physical and mechanical performances of cement mortar. In this study, the different concentrations of hydrogen-rich water (0.2, 0.3, 0.4, and 0.5ppm) were used to fabricate the mortar samples. The impact of the hydrogen-rich water was evaluated analyzing the setting time, flow table value, bulk density, water absorption, apparent porosity, compressive strength and flexural strength of the cement mortar samples. Analyzing the results, the final setting time of the control, as well as 0.5ppm hydrogen-rich water based cement, is measured to be 257±3min and 14±3min, respectively. Additionally, the compressive as well as flexural strength of 7days cured 0.5ppm hydrogen-rich water based cement mortar is found to be 59% and 30% higher, respectively, as compared to that of the control mortar. This could be primarily governed by the formation of the greater extent of hydrated cement product in the presence of hydrogen-rich water. Therefore, it is demonstrated that the hydrogen-rich water behaves like a cement set accelerator admixture. Finally, a model has been proposed to explain the overall performances of hydrogen water based cement mortar.

Tungsten tailing powders activated for use as cementitious material

Tungsten tailing powders were activated by mechanical and chemical methods for use as cementitious material in mortar. The composition, microstructure and properties of tungsten tailing were characterized with X-ray fluorescence, X-ray diffraction, scanning electron microscopy, Fourier transformation infrared spectroscopy, differential scanning calorimetry and thermogravimetry. The results showed that garnet was the major mineral in the tailing, which possessed excellent chemical and structural stability but poor cementitious property. Mechanical milling and chemical activator were used to activate the tailing. The activation effects and structural evolution of activated tungsten tailing were assessed, and the possible mechanism was discussed. A series of cement mortar samples was prepared to evaluate the cementitious property of the activated tailing. Effects of activation condition and mixture proportion on mechanical strength of cement mortar were investigated. The mechanical and chemical activations could synergistically improve the cementitious property. The properties of cement mixed with 20% of the activated tailing were well comparable with those of 42.5 ordinary Portland cement. The activated tailing as cementitious material could be used to solve the tailings pollution and reduce cost in cement industry.

IMPROVEMENT SOME OF CEMENT MORTAR PROPERTIES CONTAINING NANO METAKAOLINE OR RICE HUSKS ASH

The research aim is to know the improvement extent of some mortar properties like compressive,tensile and flexural strength for the partial substitution of mortar cement by the natural pozzolanic materials of high activity as Nano metakaoline or rice husks ash at ratios of 2%, 3%, 4%, 5% and 6% of its cement weight. Research requirement are (205) samples, (25) samples for reference cement paste standard consistency with initial & final setting time and reference mortar compressive , tensile and flexural strength. (180) Samples are the mixed cement mortar samples for compressive , tensile and flexural strength as per the above substitution ratios for ages of (3) and (7) days. Results showed that the best substitution ratio by Nano metakaolineis(3%) of cement weight for the compressive strength was increased by (110.11%), tensile by (90.49%) and flexural strength by (85.59%) more than their reference mortar strength and the best substitution ratio by rice husks ash is(4%) of cement weight for the compressive strength was increasing by (83.34%) , tensile by (75.67%) and flexural strength by (66.53%) more than their reference mortar strength and the mortar has its good workability during the work.