جستجوی مقالات مرتبط با کلیدواژه « high temperature » در نشریات گروه « عمران »

In this paper, the fracture parameters of lightweight geopolymer concrete based on the C - class fly ash (LWFCGC) are presented. The experiments include three-point bending tests on 36 beams with different activator to binder ratios. Compressive and tensile strength tests were also performed on hardened concrete after 24 hours of curing at 80 ° C. In this research, three mix designs with activator to binder ratios of 0.4, 0.5 and 0.6 were considered. The samples showed relatively decent compressive strengths. In each mixture, the fracture parameters were analyzed using size effect method. The results showed that by increasing the activator to binder ratio fracture toughness and fracture energy decreased. Moreover, the ductility, measured by means of the effective length of fracture process zone, increased.The samples showed relatively decent compressive strengths. In each mixture, the fracture parameters were analyzed using size effect method. The results showed that by increasing the activator to binder ratio fracture toughness and fracture energy decreased. Moreover, the ductility, measured by means of the effective length of fracture process zone, increased.

With the advancement of technology in the world, industrial waste has become one of the most important environmental challenges. Deformation and reuse of these wastes is one of the ways to improve the sustainable state of the environment. Glass and rubber are among the most widely used materials in the world, which due to their nature have a lot of wastes. Waste tires cause a lot of environmental pollution due to their non-degradable materials. The use of waste glass and rubber in the construction industry can be a good solution in reusing waste materials. Concrete, on the other hand, is one of the most widely used materials in the construction industry, and the addition of rubber and glass crumb to concrete can improve some of its mechanical and dynamic properties. Of course, heat resistance of materials is one of the features that is effective in the type of application. Adding waste rubber and glass to concrete, of course, depending on their amount and size can increase the heat resistance of concrete to some extent.
In this research, the effect of replacing small and large aggregates with rubber and also glass powder with cement in concrete at ambient temperature and high temperature has been studied. The size of rubber used in concrete in two categories is 1 to 3 mm and 5 to 10 mm, which are replaced by fine-grained and coarse-grained, respectively, with replacement values ​​of 0, 5 and 10%. The size of the glass used is smaller than 75 microns and it can be replaced with cement with 0, 10, 15 and 20% replacement values. Shredded truck tires and powdered construction glass were used. In this study, cubic specimens were made into 15 x 15 x 15 cm specimens and cylindrical specimens with a diameter of 15 cm and a height of 30 cm were made according to the standards and processed for 28 days in optimal conditions. After processing, the number of cubic and cylindrical specimens was subjected to compressive and tensile tests. A number of other samples were placed in an electric furnace and heated to 600 ° C as standard. After removing the samples from the furnace, they were naturally placed at room temperature for 24 hours and then they were tested for the Residual compressive and tensile strength. The microstructure of concrete containing glass and rubber was examined by scanning electron microscope (SEM). The results of this study showed that adding rubber and glass to concrete causes a decreases compressive strength and increases tensile strength. The D10C10 design, which has the highest compressive strength, has a resistance reduction of about 12% compared to the reference design. The highest tensile strength of heated samples is related to D5C15 design, which is about 43% higher than the heated reference design. By comparing the sum of heated and unheated samples, it can be seen that heat at 600 ° C has reduced the compressive strength by an average of about 33%. In general, concrete made with 10% replacement of rubber instead of coarse in unheated samples and 15% glass instead of cement in heated samples showed better properties. Also, in the study of concrete microstructure, adhesion between rubber and concrete was appropriate.

In this laboratory study, Ultrasonic Pulse Velocity (UPV) was investigated in high-temperature slag slag concrete used in pavement at high temperature at 90-day curing age, followed by scanning electron microscopy (SEM) imaging test in concrete. The overlap of the results was analyzed and investigated. In this regard, one mixing design was made of control concrete and three mixing designs were made of low-slag slag concrete containing 0, 4 and 8% nanosilica. Then, the optimal design obtained from the test results was selected from three designs of alkaline slag concrete and 1 and 2% of polyolefin fibers were added to it, and two other designs were made of alkaline slag concrete, new samples under room temperature and High temperatures were subjected to UPV, SEM and analysis. The results showed an 11% improvement (Scheme 3 compared to Scheme 2) in the passage of ultrasonic waves by adding nanosilica to alkaline slag concrete at room temperature, but the presence of polyolefin fibers reduced the UPV by 12% (Scheme 6 compared to Scheme 3). High heat application in concrete had harmful effects on the results of UPV and SEM test, so that the lowest and highest rate of decrease in ultrasonic wave velocity in concrete samples of 37 and 46%, respectively, belong to plan 1 (containing ordinary concrete) and plan 2. (Alkaline slag concrete without nanosilica) was obtained. Microstructural studies of SEM showed the coordination and overlap of the results obtained in this study.

Increasing demands for the use of lightweight concrete as well as blast-induced hazards in all over the world have led to performing extensive studies to achieve a better understanding of the behavior of the impact and heat-resistant lightweight concrete. In fact, the plastic concrete is of high ductility and low permeability whose compressive strength is much lower than that of the ordinary concrete. This type of concrete is obtained by mixing cement, sand, water and bentonite. Bentonite in this mixture is a type of clay that promotes its formation and stability. In this paper, the effect of steel, polypropylene and glass fibers on the post-heat strength (both tensile and compressive) of the plastic lightweight concrete has been investigated. To do so, after the process of heating on the specimens (exposure temperatures of 25, 100, 250, 500 and 700 °C), the compressive and tensile strength tests were conducted on the specimens. Accordingly, the results indicate that the addition of the steel fibers greatly affects the concrete strengths such that in some cases, the post-heat strengths of the concrete was enhanced by more than 40%. However, it was found that in contrast to the steel fibers, polypropylene and glass fibers leave insignificant effects on the post-heat performance, which is attributed to their physical and visual characteristics.

In the present study, the effects of glass and basalt fibers (GF and BF) and temperature on the properties of self-compacting lightweight concrete (SCLC) has been investigated. For this aim, the fresh and hardened properties of 12 SCLC mixes have been investigated that contained monotype and hybrid fibers. The volume of the monotype fibers were 0.25%, 0.5%, 0.75% and 1% of the concrete volume. The hybrid fibers had volume fractions of BF/GF= 0.25%/0.75%, 0.5%/0.5%, and 0.75%/0.25%. The self-compacting properties of SCLC was assessed by means of slump flow, T500, V-funnel and J-ring. After 28 days of curing, the compressive, splitting tensile and flexural strengths tests were performed to characterize the mechanical properties of SCLC at room temperature of 20 °C and high temperatures of 100 and 300 °C. The test results of fresh concrete showed that all the mixes could be defined as SCLC with good flowability, viscosity and passing ability. Hardened test results indicated that the addition of the fibers reduced the compressive strength and increased the tensile strength, flexural strength and fracture energy. Moreover, compared to monotype fibers, the hybrid ones formed effectively enhanced mechanical behaviors of SCLC. The mixes containing 0.75% GF and 0.25% BF was the optimum one and determined acceptable fresh and hardened properties as well as high temperature resistance.

Structures are considered as one of the main sources and resources of each country, due to their long-term and continuous use and the need to preserve human lives; they must always have sufficient stability and safety. Accordingly, the behavior of concrete is subject to the high degree of temperature is very important. The use of high-alumina cement has attracted the attention of researchers because of the considerable weakness of conventional cements at temperatures above 300 ° C. In this study, using the cement of IRC40 Calcium Aluminate instead of conventional cement, the combination of two types of steel fibers and polypropylene fibers was used in the manufacture of concrete. The purpose of this study was to evaluate the effect of high temperatures on the mechanical properties of Calcium Aluminate cement concrete and calculate the energy absorption of concrete samples after depositing them in the vicinity of 600,110 and 800 degrees Celsius. In the same way, four mix composition based on the use of four levels of 0, 0.5, 1, and 1.5% hybrid fibers were used to make a total of 108 samples, including cube compressive specimens of 10 × 10 × 10 cm, cylindrical tensile specimens with a diameter of 10 and a height of 20 cm and flexural beams with dimensions of 6 × 8 × 32 cm. According to laboratory results, the use of 1.5% of the hybrid fiber increased the amount of mechanical properties, including compressive strength, tensile strength and flexural strength, as well as increased energy absorption.

Heat, both in transient and steady state, changes the physical and chemical properties of concrete. In addition, the use of slag with Portland cement is very effective on development of concrete microstructure. The main products of hydration process are cement paste and slag, which plays important role in increasing concrete strength, C-S-H and C-A-Fe-H microstructures. Based on this, this paper has focused on the concrete containing varying degrees of steel slag in order to get a deeper perception of the changing behavior of C-S-H and C-A-Fe-H due to being exposed to high temperature. In this regard, 150 cubic samples of concrete with zero, 5%, 10%, 15% and 20% replacement of steel slag to Portland cement were treated for 28 days in a moisture bath. Then, all samples were exposed for 1 hour to 25 to 800 ºC. The percentage of weight change, compressive strength and cracking behavior of samples were investigated. Furthermore, in order to evaluate the microstructural behavior of test samples in different temperatures, SEM photos and EDS were used. Based on the results, the behavior of concrete samples depends on the variations of C-S-H and C-A-Fe-H microstructures under high temperature. The compressive strength of samples containing 5 to 15% steel slag increased as compared to conventional concrete sample. Based on SEM photos, the reason for this increase is higher density of C-S-H and C-A-Fe-H microstructures and FeO(OH).

One of the major environmental contamination factors is cement production and of major damaging factors of reinforced concrete structures is high temperatures. In this study, the effect of substitution of 10 and 20% of cement weight with zeolite on mechanical and durability properties of concrete structures at high temperatures has been investigated. Mechanical properties including compressive and tensile strength of concrete in the hot condition and the durability characteristics of the concrete after cooling, including surface water absorption, the penetration depth of water, electrical resistance and weight loss have been investigated. This study covers temperatures of 28 to 800 ° C. The results showed that the replacement of cement with zeolite reduced the compressive strength and tensile strength of 28 and 42 days. This assessment at high temperatures showed that although the replacement a portion of cement with zeolite decreased the compressive strength of normal concrete, the normalized compressive strength improved at most test temperatures. In addition, it was observed that by substitution 10 and 20% of cement weight with zeolite, the tensile strength of normal concrete at high temperatures increased by 21 and 13 percent averagely. This improvement for normalized tensile strength was 22 and 14%, respectively for mentioned substitution. Although the increase in the test temperature has had adverse effects on the durability of concrete, the replacement of cement with zeolite has improved the durability specification. The best durability properties of concrete were achieved in samples containing higher percentages of zeolite.

The use of fibers in concrete improves strength, ductility and durability of concrete. Concrete has fireproofing properties, but rebars are the most important concern of reinforced concrete structures in the event of fire outbreak. Therefore, one of the recommendations to reduce these risks is the use of alternative materials like fibers. In this paper, the effects of different temperatures on the mechanical properties of concrete with different cement contents containing steel and polypropylene fibers were studied. Although the samples were placed under temperatures of 25, 100, 250, 500 and 700 °C, the results revealed that the effects of fire on concrete containing steel fiber is more damaging, and also the compressive and bending strengths at 25 °C and tensile strength at 250 °C have the maximum values.

It is assumed that concrete structures are resistant to fire. Past research in this field has shown that in these structures, numerous problems occur during a fire. During the fire in concrete structures, fire fighters mainly use water to put out the fire. Upon contact with water, a great thermal difference occurs in the heated organ which affects most properties. No independent experimental study, to the researcher’s knowledge, has been conducted in order to investigate the effect of increased duration of high temperature on compressive and tensile strength of concrete containing glass fiber exposed to fire. However, the present study aims to investigate the effect of increased duration of high temperature on compressive and tensile strength of concrete containing glass fiber at a rate of 1%, 2%, and 3% exposed to high temperature (600 °C) in three different target times including 30 minutes, one hour, and two hours. Samples were cooled in two ways: slow cooling (exposure to air) and fast cooling (water spray immediately after exposure to heat). A total of 84 cubic samples (size: 150×150×150 mm and cylindrical samples sized 150×300 mm were prepared for studying compressive strength and tensile strength, respectively. After 28 days of processing and gaining the required strength, samples were put in annealing furnace and the experiments were conducted. The results showed that heat reduces the strength considerably. The slowly-cooled samples showed better performance compared to those cooled quickly. Also, heat caused many cracks in concrete samples.

The behavior of light weight concrete at elevated temperature is of significant importance in providing safety of structures in response to certain accidents or particular service conditions. This paper deals with the physical and mechanical properties of light weight concrete “containing leca” such as: compressive strength, water absorption, mass loss and spalling. Specimens with different amount of Nano Silica by applying the Taguchi method for an optimal mix design had been made and after curing for 28 days and being subjected to 200, 400 and 600˚C specimens had been compared with the specimen without Nano silica and cured at room temperature. It was found that by increase temperature to 600˚C physical properties of light weight concrete like water absorption goes bad and in some condition an improvement in mechanical properties like compressive strength had been emerged surprisingly.