One of the important issues in the production of concrete is environmental variability that affects the concrete and elements constructed from this material. Due to the importance of different characteristics of concrete in short- and long-term conditions, this article aims to investigate the influence of Initial temperature conditions of self-compacting concrete on its long-term characteristics and determine the Initial optimal temperature of concrete. For these purposes, several experiments under three temperature conditions of 5, 20, and 40 degree-of-Celsius were conducted to evaluate the rheology and mechanical properties of fresh concrete in the range of 7 and 28 days. In these experiments, alternative mineral admixtures of cement such as micro-silica, fly ash, and zeolite were used to build the concrete specimens. Results demonstrate that the mechanical properties of the specimens increase with increasing Initial temperature in the short term, while such properties significantly decrease in the long term compared to the specimens constructed under lower Initial temperature. Moreover, the fluidity of self-compacting concrete increases with increasing Initial temperature.

Structural fire safety capacity of concrete is very complicated because concrete materials have considerable variations. In this paper, constitutive models and relationships for concrete subjected to fire are developed, which are intended to provide efficient modeling and to specific fire-performance criteria of the behavior of concrete structures exposed to fire. They are developed for unconfined concrete specimens that include residual compressive and tensile strengths, compressive elastic modulus, compressive and tensile stress-strain relationships at elevated temperatures. In this paper, the proposed relationships at elevated temperatures are compared with experimental result tests and pervious existing models. It affords to find several advantages and drawbacks of present stress-strain relationships and using these results to establish more accurate and general compressive and tensile stress-strain relationships. Additional experimental test results are needed in tension and the other main parameters at elevated temperatures to establish well-founded models and to improve the proposed relationships. The developed models and relationships are general, rational, and have good agreement with experimental data.

Li-ion battery temperature affects its performance, significantly, and keeping its temperature in proper operational temperature is obligatory; so, this guarantees the performance, safety, and life span of the battery. In this study, the performance of the planar Li-ion battery temperature management system with 6 cells in cold weather (Initial temperature -20oC) is investigated. The maximum temperature difference and the average temperature of the battery cells are the two main performance criteria of the temperature management system. Effects of mass flow rate, number of heating plates, and flow arrangement consisting of parallel, counter, and zig-zag flow arrangements on the performance criterion and also on the warm-up time are studied. Results show that by increasing the fluid mass flow rate batteries reach the proper temperature (20 oC) faster and the temperature difference decreases. At a constant mass rate, the addition of heating plates decreases the warm-up time. The zig-zag flow arrangement has better performance in terms of temperature difference criteria up to 8 times and reaches 2.1 degrees at the maximum value, but parallel-flow warms up the batteries faster than the other flow arrangements.

In recent years, the use of processed mineral resources in the science of civil engineering has gained a wide scope. Some of these materials, such as slag-furnace-slag, can improve adhesion and filling in the structure of concrete due to the presence of abundant silica-aluminate materials in them. In this laboratory research, a mixing design was made of ordinary concrete with a cement grade of 450 kg/m3. A mixing design was also made of activated alkali concrete based on blast furnace slag to compare and evaluate the tensile strength of concrete under ambient temperature and heat of 500 degrees Celsius, at the age of 90 days. Next, X-ray diffraction (XRD) and scanning electron microscope (SEM) images at the processing age of 90 days at ambient temperature and under heat of 500 ℃, in order to further investigate and verify the results of the resistance test. Tensile testing was done on concrete samples. The obtained results indicate that the tensile strength at ambient temperature is 5.048 MPa for ordinary concrete and 4.41 MPa for activated alkali concrete, which had a difference of 12.63%. By applying high heat to the concrete samples, the amount of tensile strength drop in normal concrete reached 51% and in alkali activated concrete 21%. The results of the XRD and SEM tests were in agreement with each other and overlapped with the results of the tensile strength test.

The behavior of concrete structures that are exposed to extreme thermo-mechanical loading is an issue of great importance in nuclear engineering. The structural re-safety capacity of concrete is very complicated because concrete materials have considerable variations. Constitutive models and relationships for preloaded Normal and High Strength concrete (NSC and HSC) subjected to fire are needed, which are intended to provide efficient modeling and to specify the fire-performance criteria of the behavior of preloaded concrete structures exposed to fire. In this paper, formulations for estimating the parameters aecting the behavior of uncon ned preloaded concrete at high temperatures are proposed. These formulations include residual compression strength, Initial modulus of elasticity, peak strain, thermal strain, transient creep strain and the compressive stress-strain relationship at elevated temperatures. The proposed constitutive models and relationships are veri ed with available experimental data and existing models. The proposed models and relationships are general and rational, and have good agreement with the experimental data. More tests are needed to further verify and improve the proposed constitutive models and relationships.

The fire phenomenon can cause the loss of structural materials resistance which may end to damage or even structural total collapse. Physical and chemical changes in concrete due to firing also make serious structural defects in concrete structures. Therefore, prevention of reduction of concrete resistance is attended in this research. The primary idea is based on decreasing concrete thermal conductivity to increase chemical and physical resistance. Because of low density and porosity light weight aggregate concrete has low thermal conductivity which can postpone the resistant loss due to high temperature. A set of tests performed to achieve an optimum light weight aggregate concrete mix design in room normal temperature by changing the amount of sensitive mix components and controlling compressive strength and density. In next step some effective additives were implemented to make the optimum mix design against high temperature. For this purpose, 9 different mix designs obtained from the Taguchi method were prepared. For each mix design, 9 test specimens were made. At each, ambient temperature, 400 ͦC and 800 ͦC, three samples of each design are tested. The experiments conducted in this research include testing of compressive strength, ultrasonic pulse, and weight loss and heat effect on the appearance of lightweight concrete. It was seen that the effect of temperature above 400 ͦC is more significant on concrete compressive strength and in temperatures below 400 ͦC density loss is more considerable. The results of tests indicate that reducing the water to cement ratio and using super plasticizer has a desirable effect on the physical and mechanical properties of lightweight concrete at higher temperatures. However, test results showed that the presence of silica fume up to 15 percent of weight of cement can’t improve the strength of lightweight concrete neither in ambient nor in elevated temperature. Optimum mix design lost about 49 percent of compressive strength in 800 ͦC. Also it was observed that loss of density and compressive strength due to elevated temperature are in direct relation.

Rheological parameters of concrete, including yield stress and plastic viscosity, have a major impact on its pumpability. In the present study, the effect of temperature of mixtures with and without superplasticizer on their pumpability, has been studied through laboratory examination of yield stress and plastic viscosity of mixtures at three temperatures of 10, 20 and 30 ° C. In addition to investigating the effect of mixture temperature immediately after production, changes in these parameters over time, at the three temperatures mentioned, were also investigated.The results show that for mixtures without superplasticizer, increasing the temperature, results in increased yield stress. Additionally, the rate of yield stress increase at higher temperatures, was higher compared to that at lower temperatures. In terms of plastic viscosity, the mixture with lower temperature, had the highest amount of plastic viscosity and the rate of plastic viscosity increase over time, was greater for mixtures with higher temperatures. Calculation of the pumping pressure based on the rheological parameters, indicates that shortly after production, higher temperatures do not have a significant effect on pumpability. However, over time, the pumpability of the higher temperature mixtures will decrease, resulting in higher pumping pressure.The results indicate that for mixtures containing superplasticizers, higher concrete temperature, results in a decrease in the pumping pressure during Initial times after production. However, over time, it loses this advantage and will have poorer performance compared to the lower-temperature mixtures.

Rheological parameters of concrete, including yield stress and plastic viscosity, have a major impact on its pumpability. In the present study, the effect of temperature of mixtures with and without superplasticizer on their pumpability, has been studied through laboratory examination of yield stress and plastic viscosity of mixtures at three temperatures of 10, 20 and 30 ° C. In addition to investigating the effect of mixture temperature immediately after production, changes in these parameters over time, at the three temperatures mentioned, were also investigated.The results show that for mixtures without superplasticizer, increasing the temperature, results in increased yield stress. Additionally, the rate of yield stress increase at higher temperatures, was higher compared to that at lower temperatures. In terms of plastic viscosity, the mixture with lower temperature, had the highest amount of plastic viscosity and the rate of plastic viscosity increase over time, was greater for mixtures with higher temperatures. Calculation of the pumping pressure based on the rheological parameters, indicates that shortly after production, higher temperatures do not have a significant effect on pumpability. However, over time, the pumpability of the higher temperature mixtures will decrease, resulting in higher pumping pressure.The results indicate that for mixtures containing superplasticizers, higher concrete temperature, results in a decrease in the pumping pressure during Initial times after production. However, over time, it loses this advantage and will have poorer performance compared to the lower-temperature mixtures.