hesam madani

Calcium aluminate cement is one of the special cements that performs much better than Portland cement in severe environmental conditions. Engineers, on the other hand, have been critical of this unique cement due to the loss of long-term strength and durability caused by the conversion phenomena. The goal of this study is to improve the durability of calcium aluminate mortar by replacing the cement with pumice powder. In this study, pumice was used as cement substitutes in proportions of 0, 5,15,25, 40, and 60%, and a total of 6 mortar mixes were developed and it was examined in terms of durability properties. The results showed that the plain mixture reached a compressive strength of 33 MPa at the age of 1 day, and 44MPa at the age of 28 days but at 90 days, due to the conversion phenomenon, its strength had decreased by 45%. Pumice had a considerable effect on the strength and, more significantly, the durability properties of mixtures by influencing the conversion phenomena. At the age of 90days, Compressive strength, chloride ion migration coefficient, and electrical resistance, for example, have improved 47%, 78%, and 400% in the ideal mixture (P40) compared to the plain mix. According to the review of the literature, the effect of replacing pumice with CAC cement has not been considered significantly and the effect of pumice on the durability of this type of cement has not been investigated, which can be considered an innovation of this study.

Calcium aluminate cement (CAC) is considered as a specific cement due to its special properties and maybe have improved performances compared to the Portland cement under some severe conditions. Although alumina cement has many advantages, it is not widely used in the construction industry because it obtains reduced strength in the long term and has not been adequately investigated. In this study, an attempt is made to improve the durability and mechanical properties of mortars with this type of cement using supplementary cementitious materials (SCMs) such as pumice, zeolite and limestone powder in high cement replacement levels. In this study, porosity, rapid chloride migration and acid resistance tests were employed to investigate the durability properties. In addition, the microstructure of the mixtures was investigated using scanning electron microscopy (SEM). The SCMs were used as cement substitution in proportions of 25, 40, and 60 % and a total of 10 mortar mixes were investigated. The results indicated that the pumice and zeolite significantly improved the mechanical strength and durability properties of the mixes. The microstructural studies revealed one of the most important reasons for the reduction of the compressive strength of the plain mixture. The results of this study show that the use of pumice and zeolite mitigates the conversion process, resulting in better performance of the mixes compared to the plain mixture.

The present study investigates the mechanical properties and durability of geopolymer mixtures produced based on pumice natural pozzolan, ground granulated blast furnace slag (GGBFS) and waste soil of aggregate production plants. The aforementioned materials were used in the hybrid form to produce geopolymer. For this purpose, waste soil and pozzolans have been replaced with slag at the levels of 25%, 50% and 75%. The characteristics which have been studied were, compressive strength, flexural strength, sorptivity, rapid chloride ion migration (RCM) coefficient and water absorption content. In addition, different curing conditions were investigated for different mixtures and the results have been compared with each other. The present results indicate that due to the lower reactivity of the natural pozzolan and the waste soil compared to GGBFS, partial replacement of these materials with slag enhanced the mechanical and durability properties, so that the best mixture in terms of durability properties was P25S75. This mix outperformed the S100 mixture in several characteristics. The combined use of GGBFS and the waste soil has also improved the characteristics compared to the mixture with 100% waste soil, which was significantly higher than the promoting effect of GGBFS on the natural pozzolan.

Various tests are carried out in order to control the concrete quality. One of the most important of these is the concrete compressive strength test. So as to do this test, concrete samples are taken by the quality-control laboratories of the concrete production companies. Different metal, composite and plastic molds exist for sampling concrete that each, of which has unique advantages and disadvantages. In this study, we investigate the effect of concrete sampling molds’ quality and material on the compressive strength and distortion of concrete samples. Finally, based on the accomplished studies, it is found that samples with metal molds compared with other samples have highest compressive strength and lowest distortion. It also observed that the lowest value of compressive strength and the highest value of distortion are related to the samples with composite molds.

This study investigates the effect of steel fibers and its hybrid form with glass fiber on the properties of cement composites. The studied mechanical properties included compressive strength and flexural strength, and the energy absorption rate of the specimens was determined by the flexural toughness. In the mixtures, Portland cement and calcium aluminate have been used as bonding agents the mixes containing 2% steel fiber (% of total volume of the mixture), 2% AR Glass fiber, and hybrid of these fibers were made of glass fiber (2% steel fibers and 2% glass fiber), the length of these fibers was 25 mm. The compressive strength test was performed at the age of 1, 7, 28 and 90 days. Speciments made with calcium aluminate cement had higher compressive strength due to quick formation of microstructure compared to Portland cement mixtures, so that 90-day compressive strength of Portland cement mix was lower compared to the 1-day compressive strength of Calcium aluminate concrete. Incorporating 2% steel fibers also had a slightly enhancing effect on compressive strength. Flexural strength test was carried out at 28 and 90 days. The steel fibers create appropriate mechanical bond with the cementitious matrix, and the ultimate flexural strength was about 2 times higher than non-fibers specimen, due to the congrated geometry of the steel fibers. Substituting glass fiber also increased the ultimate flexural strength due to the high aspect ratio glass fibers and the well formed Interfacial transition zone (ITZ). The hybridization of the aforementioned fibers with steel fibers increases the bending strength due to the synergistic effect. The energy absorption content of the cementitious mix measured by flexural toughness index shows that this energy absorption content increases with the hybridization of the glass and steel fibers, so that the hybrid specimen made with Portland cement had a flexural toughness of 34.4 Nm. The glass fiber increased the toughness due to its excellent energy absorption. The steel fibers in the mixed increased the area under the flexural loading cureve and prevent the mixture from being destroyed by the first crack. In the shrinkage test results the control specimen with the two types of cements did not differ significantly, but the addition of 2% of the fibers (steel fiber and glass fiber) reduced shrinkage by their limiting effect on length change and propagation of micro cracks. When the percentage of glass fiber become higher, similar to the hybrid mix, the shrinkage was reduced further. This experiment was performed uo to 270 days and it was observed that the shrinkage of the hybrid specimen made with Calcium aluminate cement reduced by 65.5% compared to the plain concrete. In this study, the RCMT was carried out at 90 days. The results indicate that the penetration rate of the hybrid specimens and the glass fiber mixtures were lower than those of the steel fibers incorporated mixed. Also, in comparing two types of calcium aluminate cement and Portland cement, specimen made with calcium aluminate cement, the chloride ion penetration was lower than those made with Portland cement due to the improved Interfacial transition zone (ITZ) and less porosity of this type of cement.

In this research, a comparison has been made between the mechanical properties of cement based mixtures containing glass fiber. For this purpose, a type II portland cement and a calcium aluminate cement have been used. In order to investigate the mechanical characteristics, the tests including compressive strength, flexural strength, toughness, ultimate tensile strength, impact resistance and drying shrinkage of the mixtures were evaluated at ages from 28 days to 270 days. Glass fiber was incorporated in the mixes at replacement levels of 2 and 4 percent (percent of the total volume of the mixture). Based on the tests, the results indicate that the mixtures made with calcium aluminate had improved properties compared to the mixtures made with Portland cement. Furthermore, by adding glass fiber to the mixes, the flexural strength was increased by about 32% in 28 days compared to the plain mixture. Adding glass fibers in both types of cement also improved tensile strength, flexural toughness and impact resistance, as well as drying shrinkage.

In this experimental study the effects of two types of polymers including ethylene vinyl acetate and styrene acrylic on the properties of cement mixtures have been investigated. Polymer contents of the mixtures were 5, 10, 15 and 20% by weight of cement and the ratio of water to cement was 0.33. In order to investigate and evaluate the effect of polymer materials on the properties mixtures, the compressive, flexural and tensile strengths, impact resistance, shrinkage, rapid chloride migration coefficient and the capillary water absorption contents were investigated. The specimens were cured under wet conditions at early ages (7 days) and dry periods at later ages (After 7 days). The results indicate an improvement in several mechanical characteristics such as flexural strength, tensile strength, impact resistance and a significant influence on reducing the permeability of cement mixtures in the rapid chloride migration and water absorption tests by use of polymers.

Abstract One of the important issues concerning the cement mixtures is the durability against several destructive factors such as chloride induced corrosion and sulfate attack, which can in some way result in concrete deterioration. In the current experimental study, the effects of polyethylene vinyl acetate and polyvinyl acetate on the durability of clacium aluminum cement based mixtures have been investigated and evaluated. In this study, the test results including compressive strength, permeable pores, rapid chloride migration coefficient and the compressive strength of sulfuric acid-treated mixtures have been reported. The results suggest that the polymers of ethylene vinyl acetate and polyvinylacetate can reduce the penetration rate of water and chloride ion migration in cement based mixtures and ethylene vinyl acetate outperformed the polyvinyl acetate in enhancing these properties. The polymers reduced compresssive strength noticeably at early ages, however at later ages the differences between the compressive strengths of the polymer modified and plain mixure were reduced, even at high percentages of incorporation (25%).

Nowadays, the utilization of polymer modified cement base materials in waterproofing coatings and mortars is spreading. However, the influence of polymers on some types of special cements has not been investigates appropriately. In the current study due to the characteristics of calcium aluminate cement such as fast hardening and accelerating, the effects of some types of polymer materials on the properties of polymeric modified mixtures have been investigated. To this purpose the incorporation levels were 5, 15 and 25 percent by weight of cement. The water to cement ratio in all the mixtures was also 0.38. In order to keep the water content of the mixtures in a constant level, the water content of superplasticizer and the latexes (vinyl acetate and ethylene vinyl acetate) was considered as a part of the mix water. It should be mentioned that the polymers were replaced with sand. In this experimental study, a combination of dry and wet curing conditions was utilized. For this aim, after demolding of the specimens, they were cured in water for 6days, and after this period the specimens were cured in dry conditions at temperature of 25 degree of Celsius. The mechanical properties which studied in this research were compressive strength, flexural strength and flexural toughness. The shrinkage of the specimens has also been measured. It should be noted that in this study, the rapid chloride migration test was used to evaluate the durability properties of the cement base mixtures against diffusion of chloride ions. The results indicate that use of the polymers could improve the mechanical characteristics such as flexural strength and durability in regards of chloride ion diffusion as well as length change due to shrinkage. The polymer materials in calcium aluminate cement based mixtures have deceleration effect on cement hydration which results in lower compressive strengths compared to the plain mixture, which this effect is more evident at higher replacement levels. Despite the considerable reduction in compressive strength results at early ages especially for the mixtures with high contents of polymers, the differences at later ages were significantly lower. For instance, at 5% incorporation level, similar results with the plain mixture were obtained. In contrast to the compressive strength test results, high levels of polymer materials increased the flexural as well as flexural toughness in comparison with the plain mortar. It is noteworthy that incorporation of ethylene vinyl acetate in the mixtures could provide improved characteristics compared to the mixes with vinyl acetate at replacement levels of 5% and 25%. However, at 15% replacement level, similar results were obtained for the aforementioned polymers. The rapid chloride migration coefficient in the plain mix increased with age. However, using the polymers compensated for this effect and lower permeability values were obtained at later ages. It should be mentioned that the Rapid Chloride Migration Test coefficients were so low that the mixtures could be considered as relatively impermeable mortars. The shrinkage was also influenced by content of the polymer materials and those with higher contents have reduced length change.

One of the disadvantages of ultra-high performance concrete (UHPC) is high content ‎consumption of cement which leads to high level of material cost compared to ordinary ‎concrete. Therefore, finding appropriate supplementary cementitious materials could reduce the environmental CO2 ‎emission due to the reduction of cement consumption and may enhance the mechanical properties ‎of ultra-high performance concrete. In this study, the pozzolanic activity of five ‎industrial waste materials including silica fume, glass powder, copper slag, coal waste and silica floor has been investigated.‎ It is expected that these materials in concrete can react with calcium hydroxide from ‎cement hydration and produce C-S-H compounds. The pozzolanic, mechanical and diffusivity properties of ultra-high performance concrete ‎made from the aforementioned materials ‎as well as the pozzolanic properties were studied under standard and thermal treatment from 3 days up to 120 days.‎ The results showed that the temperature and time are two significant factors on the ‎performnce and pozzolanic activity of materials and use of higher curing temperatures led to improved mechanical properties for the mixtures containing silica fume. However, higher curing temperatures led to weaker durability and mechanical characteristics of UHPC with the other supplementary cementitious materials.

Some of the nanoparticles such as zinc oxide have a significant antibacterial activity that can be used in removal of pathogenic organisms in certain water resources application. This study was specifically undertaken to investigate the use of cement matrix modified with Zinc oxide nanoparticles to prevent the growth of Pseudomonas aeruginosa and Bacillus cereus. The results showed that ZnO nanoparticles with the size lower than 20 nm were dispersed well in the cement matrix. Results also showed that inhibitory effect against gram-negative bacterium of Pseudomonas aeruginosa was higher than gram-positive bacterium of Bacillus cereus. Also, confinement of ZnO nanoparticles by cement materials reduced the photocatalytic activity slightly. Based on the preparation of antibacterial formulation of cement matrix containing ZnO nanoparticles, concrete surfaces with ZnO nanoparticles can be used in a wide range of aquatic environments for prevention of pathogenic bacterial growth.

In recent years, several researches have been carried out to investigate the applications of nano science in the concrete technology. It appears that by combination of nano science and concrete technology, new scientific horizons could be opened and high quality construction and building materials may be produced. . As a matter of fact, some types of nano materials have photocatalytic characteristics and could disintegrate the pollutants and various types of organic substances. Hence, utilizing nano technology, multi-purpose materials with enhanced characteristics and new applications such as self- cleaning surfaces could be produced.
Several types of nano materials have photocatalytic characteristics, which among them nano ZnO and TiO2 have found higher attention. The influence of TiO2 on the cement based materials has been the subject of several researches. However, nano ZnO was not considered appreciably. Thus, in the present study, the performance of different percentages of Nano ZnO on the mechanical and microstructural properties of concrete has been investigated. The studied properties were setting times, compressive strength, hydration degree, reaction with calcium hydroxide and microstructural analysis by scanning electron microscopy images (SEM). Moreover, with regards to the photocatalytical properties of this material, the influence of nano ZnO on the removal of a type of algae was scrutinized. The results indicate that nano-ZnO could significantly increase the initial and final setting times, leading to the slow formation of microstructure at very early ages.Furthermore, the photocatalytic investigation showed that the mortar surfaces containing these nanoparticles could prevent the growth of the blue-green algae.

In the current study, the response surface methodology has been used for designing of the experiments. Considering the conventional soil-compaction method, the main factors investigated include cement and w/c contents. The upper and lower levels of the factors of cement and w/c content were 308-392 kg/m3 and 0.34-0.39, respectively. The dry specific weighs, compressive strengths, permeable voids, and capillary absorption coefficients were determined according to the ASTM D 1557, ASTM C39, ASTM C642 and ASTM C1585 at ages up to 180 days, respectively.
Using the statistical analyses, the prediction models and contours of the durability characteristic and 28 day compressive strength were derived. The analysis of variance (ANOVA) was also performed on the results to estimate the significance of the factors. It could be concluded that the terms of the cement content, w/c and their interaction significantly influenced the responses of the compressive strength, dry specific weight, water absorption and permeable voids. The results also indicated that by obtaining an optimum level of dry density one could reach the lowest level of permeable voids and water absorption into the concrete. This is achieved by adjusting the interaction of cement content and w/c content. However, no meaningful correlation was found between the dry density and capillary absorption coefficient. This indicates that the tortuously and continuously of microstructure may be independent from the dry density. However, similar contour trends were obtained for the dry density and capillary absorption coefficient.

This paper aims at investigating the influence of partial replacement of Portland cement with ultrafine fillers compared to limestone powder on the durability and mechanical characteristics of concrete. For this purpose, ultrafine calcium carbonate materials with different specific surface areas of 9.7 and 15.1 m2/g and limestone powder (0.72 m2/g) were used. The results indicate that the ultrafine fillers enhanced the durability properties compared to the mixtures containing limestone. For instance, ultrafine fillers provided up to 20% higher concrete surface resistivity and 20% lower rapid chloride migration test (RCMT) coefficient, while limestone mixes showed equal or even lower durability levels compared to the plain mixture with 0% supplementary cementitious materials. The influence of filler materials on the compressive strength was not significant. However, regardless of the surface area, incorporating filler materials at levels up to 5% led to somewhat higher compressive strengths compared to the plain mixture. Generally, it seems that using finer fillers may lead to more durable concrete mixes.

Nowadays, pozzolans are used as cement replacement materials. In recent decades, a large number of studies have investigated the effect of nano silica on the properties of cement based materials. In many cases it has been shown that the use of nano silica as a pozzolan could improve the properties such as mechanical properties and durability of concrete and it has caused to increase service life of structures. Due to the large variety of nano-silica, some of them such as nano silica gel have been studied scarcely. Nano silica gel could have widespread applications, especially in dry mortars. The aim of this study is to provide a method for the production of nano-silica gels and their effects on the properties of cement mortars. The results indicate the good performance of nano silica gel in the process of compressive strength development at early ages. Furthermore, the microstructure was improved considering the results of water permeability and Rapid chloride Migration Test (RCMT) at 28days. By increasing the percent of substitution, strength properties and microstructure were improved.