جستجوی مقالات مرتبط با کلیدواژه « Portland Cement » در نشریات گروه « عمران »

Application of different stabilizers and additives such as cement, lime, and fly ash is one of the solutions for improving weak and problematic subgrade soils. In this study, a clay soil was stabilized using different percentages of cement and lime (0, 3, 5, 7 and 9%) and with different moisture content (optimum humidity level, wet side and dry side) and unconfined compressive strength (UCS) test was conducted at different curing times (7, 14, 21, 28 and 60 days). Then, the gene expression programming (GEP) method was employed to model the UCS of cement-stabilized and lime-stabilized clay soil. In the developed models, three variables of additive percentage, curing time and moisture content are used as the input variables to predict the UCS. The results of this study showed that the coefficient of determination (R2) for the model developed to predict the UCS of cement-stabilized clay soil is 0.935 and 0.926 for training and testing data, respectively. The R2 value for the model developed to predict the UCS of lime-stabilized clay soil is 0.911 and 0.884 for training and testing data, respectively. The results of the parametric study showed that the UCS increases with the increase in the percentage of cement and lime and the curing time and decreases with the increase in the moisture content.

Three types of chemical additives were used to modify the recycled mixture with emulsion bitumen.   These chemical additives are composite port land cement (CPC), hydrated lime (HL), and a combination of hydrated lime and ballast blast furnace slag (GGBF).   The presence of different additives in the performance of the recycled mixture was investigated by volume and strength tests, humidity sensitivity test, rutting test and bending test at low temperature. The test results show that the performance improvement of emulsion recycled mixture depends on the types and percentages of chemical additives. Several recommendations are given for the selection of chemicals.

Heavy metals are found in high concentrations in industrial wastewater and cause damage to humans and other organisms by entering to water, soil and food chain. Stabilization and solidification is a common process in the treatment of sludge containing heavy metals. In this study, solidification/stabilization of ceramic tile industry sludge was investigated using cement and additives like water, lime, microsilica and ordinary clay.

In this study, by designing the tests by response surface methodology, the effect of different additives on compressive strength and metals concentration after pollution leakage test was investigated. So, hazardousness of wastes after stabilization and solidification and the samples tolerance against the environmental loads was evaluated.

Results showed the highest value compressive strength in high amounts of cement. Decreasing the amount of waste and replacing more lime, clay and microsilica, the compressive strength was increased. In optimal mode, by 5.77% lime, 8.69% clay, 4.35% microsilica and 51.84% cement, the maximum compressive strength was achieved about 116 kg/cm2. The minimum concentration of Cr was 0.0782 mg/L and resulted from 11.23% lime, 21.31% clay, 10.65% microsilica and 27.46% cement. Minimum Pb concentration (0.0043 mg/L) was obtained in 11.23% lime, 21.31% clay, 4.35% microsilica and 33.76% cement.

The more efficiency on compressive strength is related to cement. In addition, applying the lime, clay, microsilica and cement concluded the effective reduction of Cr and Pb concentration in leaching the stabilized samples.

Nowadays unlike decades ago, environment plays decisive role for using materials in construction. For example, one considerable part in a project is exploring environmental aspects as a preparatory topic. Chemicals such as cement have been used for decades in construction projects, however chemicals will lead to health catastrophe for both environment and human consequently. One considerable hitches in human life is waste materials such as sawdust which will jeopardise environment. One solution to alleviate these problems is using wastes in construction projects as substitution for cement. In this research, sawdust and zeolite were used to decrease cement use on sandy soil's improvement. Amount of materials are as follows: 4% cement (base on main soil weight), 0,1,3 and 5 % sawdust with two different sizes include powder and fibers (as supersede by cement) and 0, 10, 30 and 50 % zeolite as a supersede by cement. Results showed that zeolite and sawdust increase OMC but decrease MDD. Zeolite meets its optimum in 30% and powdered and fibrous sawdust in 3 and 1% subsequently. Finally, rupture strain will experience a sharp increase by enhancing amount of sawdust. Overall it can be concluded that longer sawdust is more effective than short one.

Soil properties improvement involves a variety of approaches. Among them, the addition of specific materials to the soil has been widely adopted in the literature. Although cement impact on environment is negative, it has been widely-used in many construction projects. Therefore, the main purpose of this research is to find suitable alternative methods to decrease cement usage, one of which is the addition of polypropylene fibers and zeolite. 126 types of unconfined compression tests with different ingredients were carried out with the aim of decreasing cement usage and improving soil properties. Two types of sandy soil were adopted in this study, i.e., SP and SW soil. They were improved by 4% of cement, 0, 0.25, 0.5, 0.75, and 1% of polypropylene fibers with random distribution, and 0, 10, 30, 50% of zeolite were used during curing periods of 7, 14, 28 days. According to the compaction test results, with the addition of 0.5% polypropylene to the SW soil, and 1% to SP soil, the value of optimum moisture increases, and then decreases. On the other hand, the addition of polypropylene fibers resulted in decrease of the special dry weight of both type of soils. It also revealed the optimum percentage of zeolite and polypropylene fibers to the SW soil are 30% and %0.5, respectively, while this values in the SP soils are 10% and %0.75, respectively. The proper adoption of zeolite and polypropylene in cement led to increase in unconfined compression tests as well as elastic deformation strength.

In the present study, Evolutionary Polynomial Regression (EPR) technique is employed to develop a mathematical model to estimate the USC of Full Depth reclaimed (FDR) materials stabilized with Portland cement. To this end, a dataset containing 62 records from experimental studies related to unconfined compressive strength of full-depth reclaimed (FDR) base stabilized with Portland cement were used. Percentage of cement, percentage of RAP, percent passing of #200 sieve, optimum moisture content, and curing time were considered as independent variables. The results show that EPR has a great capability for prediction of the UCS in case of FDR base stabilized with Portland cement.

In order to mitigate the environmental impact of iron ore tailing (IOT) and also to reduce the use of natural aggregates, these materials can be used as road materials after stabilization with chemical additives. In this research, the feasibility of using Golgohar IOT, stabilized with 4, 6 and 8% of Portland cement as road base materials, has been investigated. To this end, modified Proctor compaction test, unconfined compressive strength (UCS) test and durability against freezing and thawing (F-T) cycles test were conducted on IOT samples stabilized with different percentages of Portland cement. Results of compaction testing on the samples showed that increasing the percentage of cement increases the optimum moisture content (OMC) and decreases the maximum dry density (MDD). In the next stage, IOT were stabilized using 4, 6 and 8% of Portland cement and UCS samples were fabricated with three different compaction moistures (dry side, optimum moisture content and wet side) and cured for 7, 28 and 56 days. The results showed that with increasing the percentage of cement from 4 to 8% for all curing times, the UCS increased between 1.45 to 2.15 times. Also, the 28-day UCS and 56-day UCS are about 1.73 times and 2.34 times the 7-day UCS, respectively. It was also found that the UCS increases with decreasing moisture content. The results of durability tests against (F-T) cycles on the samples showed that with increasing the percentage of cement, the durability of stabilized materials increases, so that in samples with higher percentage of cement, the lowest percentage of weight loss and volume reduction is observed. Finally, it was found that IOT stabilized with at least 4% of Portland cement provides the necessary strength and durability criteria for use as stabilized base layer.

Portland cement is one of the most common materials for improving the mechanical properties of soils; however, it has a lot of detrimental effects on the environment. Cement production releases million tons of carbon dioxide gas (CO2) to the air and uses million tons of raw material such as clay and limestone. For this purpose, geotechnical engineers are looking forward to using a new friendly environment material instead of cement. Geopolymers are new alternative materials that have some advantage such as high resistance, friendly environment, long durability, and low cost. Two materials need to make a geopolymer matrix. First, any materials have silicate and Aluminium oxide and Second Alkaline activators. In this study, a geopolymer based on rice husk ash and iron ore tailings (IOT) are used for sandy soil stabilization. Two types of alkaline activators are used: 1) Type I sodium hydroxide and 2) Type II carbide calcium residue. Various parameters such as type of material consumed, percentage of compound composition, type of alkaline activator, and processing time are considered as influencing factors in the behavior of the stabilized specimens. Unconfined Compressive Strength (UCS) and splitting tensile strength tests (Brazilian test) are the main criteria for a comparison of the specimens to evaluate the effect of a geopolymer on the mechanical behavior of the specimens. X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) analyses are performed to investigate the microstructures of the stabilized soil. The results show that by adding the optimum amount of additives and handling the specimens under ambient conditions, the unconfined compressive strength of the specimens increased. The optimum percentage of selected specimens is a combination of 10% of rice husk ash and 24% of iron ore tailings for activator I and 18% of iron ore tailings for activator II. The use of type I activator indicates that it is highly effective in the formation of aluminosilicate gels in geopolymer compounds.

Cement-based Stabilization/Solidification (S/S) process is one of the best technologies available for the treatment of heavy metal contaminated soils. This method has been very popular among researchers in field application. Two mechanisms of solidification and stabilization in this method include the formation of cementation products (such as C-S-H) and achievement of alkaline condition for development of pozzolanic interactions. The pH variation range directly affects the heavy metal ion precipitation. On the other hand, environmental factors and soil-cement-contaminant interaction affect the cement hydration products and pH range of solidified contaminated soil. Therefore, this interaction process controls the immobilization of metal ions in solidified/stabilized sample. The main objective of this paper is to evaluate the effect of fly ash on the heavy metal retention in cement-based solidification/stabilization in a long-term process. In order to investigate the effect of fly ash on the optimum amount of required cement at different concentrations of contaminants, several mixtures of fly ash and cement were applied to solidified contaminated bentonite. In these series of experiments, 75-25 and 50-50 wt% mixtures of Portland cement and flay-ash (class F) were mixed and were added to contaminated bentonite samples. The bentonite samples were laboratory contaminated with Pb(NO3)2 in the concentration range of 5 to 100 cmol/kg-soil. The prepared samples were kept for 7 to 90 days. Different experiments which include TCLP, XRD, pH measurement, and solubility evaluation in different alkaline and acidic conditions were performed on samples. Furthermore, the trend of pozzolanic reactions of the samples in the short and long terms was evaluated by determining the setting time of solidified/stabilized samples. The results were analyzed based on the effect of pH variation upon concentration of released lead ions from samples. The results indicated that the use of 10% binder, despite common recommendations in geotechnical stabilization, would not be suitable for S/S of contaminated bentonite soil at all studied Pb concentrations. Moreover, the results indicated that in contaminated samples with 50 and 100 cmol/kg-soil lead nitrate, due to the high precipitation of lead hydroxide, a reduction in C-S-H formation and an increase in the setting time occurred. In addition, replacing cement with fly ash in samples reduced the pH and decreased the concentration of released Pb in TCLP test. According to the achieved results due to the precipitated Pb ions in stabilized/solidified contaminated bentonite, an appropriate quantity of the cement-fly ash binder is when the pH of the stabilized/solidified samples is in a safe zone that occurs in the pH range of 8 to 12. According to the results of this paper, the use of fly ash in the S/S process helps achieve this safe range of pHs.

One of the Practical solutions for improving subgrade soil is the utilization of additives for soil stabilization. Generally, the unconfined compressive strength (UCS) and indirect tensile strength (ITS) tests are employed for quality control of stabilized materials. These tests are time- consuming due to the time needs for curing of samples, and can also be costly if the number of samples increases. In this study, we have employed two methods including artificial neural network (ANN) and adaptive neuro-fuzzy inference system (ANFIS) to predict UCS and ITS of clayey subgrade soil stabilized with Portland cement and iron ore mine tailing (IOMT). To this end, cement content, IOMT content, optimum moisture, and curing time were considered as input parameters, and unconfined compressive strength, as well as indirect tensile strength, were considered as output parameters and in each case a dataset consisting of 100 data points were used for developing computational intelligence models. Modeling by means of these three methods confirmsthe superiority of the artificial neural network model over ANFIS model. Also, the sensitivity analysis showed that the Portland cement content and IOMT Content have the greatest and lowest effect on the predicted compressive and tensile strength, respectively.

Collapse refers to sudden decrease in the soil volume upon wetting which is attributed to loss in the strength of the inter-particle bonds. Collapsible soils can be founded at vast areas around the word and subtropical areas of Iran. Collapse characteristics contribute to various problems to infrastructures that are constructed on loess soils. For this reason, collapse behavior of loess soils has been subject of interest. In this study, stabilization of Semnan loess which is composed of fine sand and silt bonded by weak clay bonds has been investigated. The loess was mixed with Portland cement in the order of 0.5%, 1%, and 2.5% for and with nano-clay in order of 0.05%, 0.1%, and 0.25%. The specimens were prepared to achieve dry density of 14 kN/m3 and water content of 5%. Oedeometer tests were performed to determine the collapse potential according to ASTM D5333 after 7, 14, and 28 days. Results showed that both Portland cement and nano-clay can reduce collapse potential. Improvement performance was significantly dependent on the binder content and curing time. The best improvement performance was observed at low nano-clay content and it was reduced by increasing nano-clay content. Unlike the cement stabilization, treatment process with nano-clay was relatively fast that terminated when soil moisture content was evaporated. In addition, in this study micromechanical soil behaviors were investigated by scanning electron microscopy (SEM) image of the treated and untreated specimens.

Due to the limited soil resources and population increase, the use of contaminated or problematic soil is inevitable. There are different methods to improve the geotechnical properties of clay soils. One of the ways is to stabilize the soil with stabilizers such as Portland cement and lime. Investigation of the combined effect of organic pollutants under the influence of stabilizers (Portland cement (I) and lime) on Kaolinite clay using modified Proctor and CBR experiments constitutes the present research framework. The maximum unit weight decreased with an increase in Anthracene content while its variations were strongly dependent to the Glycerol content. The maximum of dry unit weight and a minimum of optimum water content occurred at a glycerol content of 6%. Based on test results, it was found that the increase in strength of clean Kaolinite using 6% of Portland cement is equivalent to that of 30% lime. It was also found that the contaminants decrease the strength of kaolinite; however, both stabilizers increase it. The effect of Portland cement on the strength of the specimens contaminated with Anthracene was better than that of lime and the effect of Portland cement and lime on the improvement of samples contaminated with Glycerol was considerable.

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.

Concrete structures Projects under construction near wetlands cause harmful substances to enter the wetland and thereby escape or death of animals, wetland accumulation from artificial sediments, chemical change of water, etc. Using pozzolans as well as environmentally friendly concrete is a good way to reduce harmful substances.. In this research conducted in Anzali International Wetland, the effect of constructing concrete foundations along the road of Anzali port on the pollution of the wetland was investigated and the amount of chemical changes of the sample prepared in the wetland water by different concrete, one concrete made with Portland cement and another Portland blend concrete and fused micro-silica gel. The results of this study showed that by reducing the concrete content of 8% and adding the same percentage of fused micro-silica gel to the concrete volume of the bridge bridges, while increasing the bridge's resistance, Biodiversity and pollution of the wetland water also occurred in the environmental assessment of the bridges Concrete and metal found that it is more suitable to produce less pollutants in the process of manufacturing metal bridges. Addition of fiber-reinforced silica gel resulted in less change in the chemical quality of water than in cement-based concrete, and only due to the presence of silica, the amount of silicon element was greater than that of cement-based concrete.

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.

Over the recent decades, understanding fundamental aspects of cement chemistry has advanced. Due to the recent developments in the eld of cement for improving and reducing the negative environmental impacts of cement production, it is necessary to model or simulate hydration reactions of the cementitious materials. The process in which the cementitious materials form is of great importance. Hence, employing thermodynamic science properly is important. This knowledge gives a powerful insight into developing links between the mineralogy and engineering properties of hydrated cement paste and, therefore, anticipates improvements in its performance of cement production. The hydration process is dramatically in uenced by cement chemistry and microstructures, as a slight change in cementitious generic ingredients can create great differences in the hydration products. Usage of supplementary cementitious materials has considerable in uence on the amount and kind of hydrates formed and thus volume, porosity and durability of cementitious systems. In this paper, blast furnace slag of Esfahan Steel Company with the replacement percentages of 10 to 80 was used to make several thermodynamical models at constant temperature of 20C. Thermodynamic modeling was based on the method of minimizing Gibbs free energy to calculate the composition of the pore solution and solid phase's developments. It is ideal for better understanding reactions' mechanisms during the hydration process. GEM software was applied for thermodynamical modelling. The formed phases assemblage, concentration of pore solution and chemical shrinkage of models were examined. Thermodynamic calculations indicate that slag consumes portlandite and increases calcium silicate hydrates. It also reduces the pore solution volume that results in higher chemical shrinkage and increases the amount of hydrotalcite. Overall, the ndings of slag replacement in cement are higher volume of hydrates, improvement of mechanical properties and, enhanced durability of concretes with cementitious materials.

Sulfate attack is a series of physico-chemical reactions between hardened cement paste and sulfate ions. Sulfate ion penetration into the cement results in the formation of voluminous and deleterious phases such as gypsum and ettringite which are believed to cause deterioration and expansion of concrete; However, there is no direct relationship between Ettringite or solids formation during the sulfate attack and the amount of expansion. Concrete deterioration due to sulfate attack depends on multiple elements, however, in experimental studies, the implementation of the elements and obtaining the results in a short time are very difficult. Therefore, the significance of theoretical and software modelling along with in experimental studies, reducing the time and cost, increases so much as to achieve reliable results. Thermodynamic simulations, in this research, are employed according to the method of minimizing Gibbs free energy in order to better understand the external sulfate attack and the behaviour of mortar samples made of ordinary Portland cement and blended cements.GEM software helps in studying the microstructure of cement, volume and type of phases formed in sulfate solutions under different conditions. With this software, a virtual laboratory of materials could be created, which simulates natural processes such as hydration, sulfate attack, and factors that affect them with less time and cost. This modeling type could be utilized for cement systems in order to calculate sets of stable phases. A system achieves thermodynamic equilibrium when there is no more spontaneous tendency for change. GEM software which is able to calculate the stable phase as a function of reactants, temperature and pressure is employed. In this software chemical interactions involving solids, solid solutions, metls, gas/fluid mixture, aqueous electrolyte, (non-)electrostatic surface complexation, and ion exchange can be considered simultaneously in the chemical elemental stoichiometry ( electrical charge) of the system, i.e. without any mass balance constraints for ligands or surface sites. GEMS simulates various mass-transfer processes and reaction paths, such as mixing; But this software cannot replace our knowledge of physical chemistry. Type and volume of phases formed during the sulfate attack and factors affecting that such as cement chemistry, rice husk ash and sulfate solution with different concentrations were studied With the help of this method. Simulation of mortar samples was performed in sodium sulfate with concentrations of 4 and 44 g per liter and 10 and 15 percent rice husk ash substitution. Mortar samples at 20 ° C and water-cement ratio of 0.5 is assumed. Rice husk ash substitution has an effective role in microstructures improvement, reduced impermeability, and volume of forming products. Sodium sulfate is more dangerous and destructive compared to other sulfates like calcium sulfate or potassium sulfate and forms phases with higher volumes. The results clearly indicate that rice husk ash, consumed portlandite completely and produced maximum volume of calcium silicate hydrate(C-S-H) by 15 percent replacement and also there is not a simple relationship between the increase of formed phases by the penetration of sulfate ions and the observed expansion. Generally, the results correspond to the studies and in experimental results which have examined micro structure.