An Early-age Evaluation of Thermal Cracking Index of Heavy Concrete Applying for Airport Pavement

Industrial waste management has been an integral part of many countries in the world, including in Vietnam. In which, bottom ash (BA) has been used as a pozzolanic additive in compositions of the heavy concrete applying for airport concrete pavement (ACP), which allows reducing the hydration heat, the cost, and the thermal cracking of the concrete during the construction process. The purpose of this study is to summarize the experimental laboratory results of the heavy concrete samples containing 35 % BA sourced from a thermal power plant in Vietnam. The mechanical and thermal properties of the heavy concrete samples were determined at different curing ages. Besides, the heat of cement hydration during the preparation of the heavy concrete in the laboratory was measured using a "TAM AIR" isothermal calorimeter. Moreover, the Midas civil computer software based on the finite element method was used to analyze the temperature field and thermal cracking index of the ACP at the early ages. As the results, the heavy concrete had the respective thermal conductivity and the average of specific heat of 1.1 W/(m.°C) and 878.35 J/(kg.°C). Moreover, the value of thermal cracking index indicates that no cracking occurred on the ACP at the early ages. Furthermore, the results of the present study can be considered as a useful reference source for future projects that are associated with the construction of the ACP

Performance Evaluation of Pre-foamed Ultra-lightweight Composites Incorporating Various Proportions of Slag

This research examines the feasibility of using a mixture of cement, fly ash, ground granulated blast-furnace slag, and river sand to manufacture pre-foamed ultra-lightweight composite (PULC). Four PULC specimens were prepared with the substitution of cement by slag at 0, 10, 20, and 30 % by weight. The engineering properties of PULC samples were evaluated through the tests of compressive strength, dry density, water absorption, drying shrinkage, and thermal conductivity. Besides, numerical simulation of heat transfer through the PULC brick wall and the microstructure observation were performed. The performance of PULC mixtures incorporating slag showed higher effectiveness than merely used cement. The substitution of 20 % cement by slag resulted in the highest compressive strength as well as the lowest value of water absorption of the PULC samples. Also, the efficiency of the thermal conductivity was in inverse proportion with the density of PULC specimens and it was right for water absorption and drying shrinkage. Moreover, numerical simulations showed that the temperature distribution values in the wall made by PULC material were smaller than in the wall made by the normal clay brick in the same position. Besides, the microstructure analysis revealed that the existence of slag generated a more dense structure of PULC samples with the addition of calcium-silicate-hydrate (C-S-H) gel, especially for a mix containing 20 % slag. Thus, the results of this study further demonstrated that a 20 % slag was the optimal content for the good engineering properties of the PULC samples

Temperature distribution in concrete structure under the action of fire using Ansys software

In the last few decades, fires caused serious damage in civil engineering, especially in the high-rise building, factories, offices, etc. Usually the structures are built with fireproof materials such as concrete. It is a complex material, and its properties can change dramatically when exposed to high temperatures. This problem requires engineers to study and evaluate the effect of the fire in the structure. This paper studies the effect of the fire on the temperature distribution in concrete structure using Finite Element Ansys software. The results will be used to provide reference data for concrete structures under the action of fire. The research is an intermediate task to convert the fire activity in a structural model into the real impact in calculating model. It plays significant role in calculating structural model for counteracting the action of fire

Building a nomogram to predict maximum temperature in mass concrete at an early age

During the construction of massive concrete structures, the main factor that affects the structure is temperature. The resulting temperature is the result of hydration of the cement and some other factors, which leads to the formation of thermal cracks at an early age. So, the prediction of temperature history in massive concrete structures has been a very important problem. In this study, with the help of numerical methods, a temperature nomogram was built to quickly determine the maximum temperature in concrete structures with different parameters such as size, cement content, and the initial temperature of the concrete mixture. The obtained temperature nomogram has been compared with the results of the finite element method and the model experiment gives reliable results. It can be used to predict maximum temperature in mass concrete structures to prevent the formation of thermal cracks

Influence factors on the temperature field in a mass concrete

In construction practice of concrete mass needs a large amount of concrete. Due to the small surface area to volume ratio, the concrete mass is often happening thermal cracking caused by the release of heat during the hydration of the cement. The causes of thermal cracking in concrete mass are complex but the main reason is the increase in temperature in the concrete structure. Provide measures to control the maximum temperature concrete mass is very absolutely necessary. A finite element model of the concrete mass was established by the software Midas civil, the temperature field in the concrete mass has been determined and a mathematical model was created that adequately describes the influence factors on the temperature field in a concrete mass such as unit cement content, cement maximum heat released, the placing temperature of concrete and the water temperature in order to determine the optimal parameters

The thermal stress of roller-compacted concrete dams during construction

During the construction of concrete dams from rolled-compacted concrete, the main effect on the structure are the temperature effects. As a result of heat generation during hydration of cement and the influence of many other factors, significant temperature gradients and cracks may occur. In this paper, the optimal maximum temperatures arising in the body of the concrete dam under construction are determined by the method of experiment planning and the method of numerical simulation - the finite element method. The analysis of the influence of the acting factors on the temperature regime and the thermal stressed state at the rock-built concrete dam from rolled concrete is carried out. The dependences are obtained and nomograms are constructed to determine the optimal parameters. With the help of the computer program Midas Civil 2011, calculations of the temperature regime of the constructed dam were carried out and the maximum temperatures were determined. The calculations of thermal stress state of the structure along with an analysis of the possible cracking are conducted

Evaluating the Effectiveness of Continuous Composite Beams for Steel-Concrete Bridges and Control Concrete Cracks of the Supports at an Early Age

This study presents a solution to contextualized span bridges constructed with composite steel girders with reinforced concrete slabs by reinforced concrete. This kind of structure, in comparison with a simple span, has many advantages as overcoming internal forces, reducing large displacements and cutting the number of expansion joints. Also, numerical simulations were conducted to evaluate the effectiveness of continuous composite beams for steel-concrete bridges and control of cracking of concrete at the supports at an early age. The models and conclusions in this paper can provide safety guidance for construct composite steel girder bridge in Vietnam

Mechanical-thermal characteristics of foamed ultra-lightweight composites

Turning waste into construction materials recently gets much attention from the researchers in the world due to the advantages of not only the eco-friendly environment but also the positive enhancement of material characteristics. Thus, this study investigates the feasibility of the use of a ternary mixture consisting of cement, ground granulated blast-furnace slag (GGBFS), and fly ash (FA) for producing foamed ultra-lightweight composites (FULC) with the designed dry density of approximately 700 kg/m(3). The FULC specimens were prepared with various FA/GGBFS ratios (16/24, 20/20, and 24/16) and foaming agent/water ratios (1/60, 1/80, 1/100, and 1/120). The constant water-to-binder ratio of 0.2, cement content of 40 % by mass, and superplasticizer dosage of 0.2 % by mass were applied for all FULC mixtures. Properties of the FULC specimens were evaluated through laboratory tests of compressive strength, dry density, thermal conductivity, water absorption, and thermal behavior following the relevant ASTM standards. Additionally, both the microstructure observation and cost analysis of all FULC mixtures was performed. Test results show that reducing GGBFS content resulted in a reduction in the compressive strength, dry density, thermal conductivity, and cost of the FULC. A similar trend could be observed when reducing the concentration of foam in the FULC mixtures. As the results, the 28-day compressive strength, dry density, thermal conductivity, water absorption, and cost of the FULC were in the ranges of 4.41-5.33 MPa, 716- 729 kg/m(3), 0.163-0.182 W/mK, 41.5-48.5 %, and 15.3-20.9 USD/m(3), respectively. Furthermore, the FULC exhibited excellent performance under fire conditions as the maximum temperature at the internal surface of the FULC and the normal brick walls were 122 degrees C and 318 degrees C after 120 minutes of firing, respectively. Consequently, both GGBFS and FA had enormous potential for the production of FULC.Web of Science986art. no. 980

Performance evaluation of pre-foamed ultra-lightweight composites incorporating various proportions of slag

This research examines the feasibility of using a mixture of cement, fly ash, ground granulated blast-furnace slag, and river sand to manufacture pre-foamed ultra-lightweight composite (PULC). Four PULC specimens were prepared with the substitution of cement by slag at 0, 10, 20, and 30 % by weight. The engineering properties of PULC samples were evaluated through the tests of compressive strength, dry density, water absorption, drying shrinkage, and thermal conductivity. Besides, numerical simulation of heat transfer through the PULC brick wall and the microstructure observation were performed. The performance of PULC mixtures incorporating slag showed higher effectiveness than merely used cement. The substitution of 20 % cement by slag resulted in the highest compressive strength as well as the lowest value of water absorption of the PULC samples. Also, the efficiency of the thermal conductivity was in inverse proportion with the density of PULC specimens and it was right for water absorption and drying shrinkage. Moreover, numerical simulations showed that the temperature distribution values in the wall made by PULC material were smaller than in the wall made by the normal clay brick in the same position. Besides, the microstructure analysis revealed that the existence of slag generated a more dense structure of PULC samples with the addition of calcium-silicate-hydrate (C-S-H) gel, especially for a mix containing 20 % slag. Thus, the results of this study further demonstrated that a 20 % slag was the optimal content for the good engineering properties of the PULC samples.Web of Science65128627

Influence of Size and Construction Schedule of Massive Concrete Structures on Its Temperature Regime

Cracking is an important problem in the process of building a concrete massive structure. The overwhelming majority of cracks occurring in the concrete are usually caused by temperature effects. Because of this, it is essential to control and regulate temperature, it is necessary to prevent cracking. The formation of the temperature regime of a massive structure is affected by a large number of factors: its size; cement consumption and its maximum heat release; temperature of the concrete to be laid; ambient temperature, etc. In this paper, we consider the influence of the size and construction schedule of a massive concrete structure on its temperature regime. Using the computer program Midas civil 2011, the temperature regime was calculated, maximum temperatures were obtained in massive concrete and massive concrete columns with different sizes. The analysis of possible fracture for different values of the factors are considered