Thermal Conductivity Of Concrete Research Articles

Comparing heat flow models for interpretation of precast quadratic pile heat exchanger thermal response tests

This paper investigates the applicability of currently available analytical, empirical and numerical heat flow models for interpreting thermal response tests (TRT) of quadratic cross section precast pile heat exchangers. A 3D finite element model (FEM) is utilised for interpreting five TRTs by inverse modelling. The calibrated estimates of soil and concrete thermal conductivity are consistent with independent laboratory measurements. Due to the computational cost of inverting the 3D model, simpler models are utilised in additional calibrations. Interpretations based on semi-empirical pile G-functions yield soil thermal conductivity estimates statistically similar to those obtained from the 3D FEM inverse modelling, given minimum testing times of 60 h. Reliable estimates of pile thermal resistance can only be obtained from type curves computed with 3D FEM models. This study highlights the potential of applying TRTs for sizing quadratic, precast pile heat exchanger foundations.

Experimental study on heat-removal performance in accordance with mesh size of screen installed at opening of inlets and outlets of concrete storage cask

Spent nuclear fuel generated at nuclear power plants must be safely stored during interim storage periods. A concrete storage cask developed for this purpose should be able to adequately emit the decay heat from the spent nuclear fuel; it should also maintain the temperatures of the spent nuclear fuel assemblies within allowable values under normal and off-normal conditions and during an accident. However, since the thermal conductivity of concrete is low and the allowable temperature of concrete is lower than that of steel, the concrete storage cask must be designed to have heat-removal capability with appropriate reliability. A passive heat-removal system was designed to maintain the temperatures of the fuel assembly cladding material and concrete storage cask components within the allowable limits; it consists of four air inlets and four air outlets with openings that are covered by mesh screens to prevent debris or wildlife from entering the ventilation ducts. Thermal tests were performed to evaluate the effect of the mesh size of each screen on heat-removal performance of the concrete storage cask. The screen mesh size was estimated to have an insignificant effect on the temperature rise of the canister surface and the over-pack surface, but it had a considerable effect on the temperature rise of the components of the over-pack body. As the screen mesh size decreased, the heat-removal by natural convection cooling through the passive heat-removal system was reduced, and the temperature of the concrete storage cask rose.

Use the Polymer Concrete as a Substitute for Ordinary Concrete by Improving of Acoustic and Thermal Insulation With Suitable Cost

The purpose of this study is to examine the effect of adding novolac resin by different volumetric percentages to concert as a light weight aggregate In addition to the economic feasibility of the use of these concrete in the field of build and construction .they investigated tht the compression strength, thermal conductivity, acoustic insulation and densities. The results showed ultimate compression strength and acoustic insulation by melting novolac and added to the cement and sand as a polymer concrete in the hot state (by melting novoac >90c).However added novolac resin as aggregate in the cold state to the concrete increase thermal conductivity and increasing compression strength and acoustic insulation .This results gained by chemical interaction of novolac and cement.

Evaluation of Fire-Performance by Cone-Calorimeter Tests and Thermal Conductivity of Polymer-Modified Mortars and Various Concretes

Evaluation of Fire-Performance by Cone-Calorimeter Tests and Thermal Conductivity of Polymer-Modified Mortars and Various Concretes

Experimental thermal characterization of concrete to be used in CP5.2 packaging system

This work deals with the experimental evaluation of the thermal conductivity of a concrete matrix to be used for embedding LILW bituminised Wastes into the packaging system. Such a type of packaging, identified with the acronym CP5.2, has been also qualified by executing at the Lab. Scalbatraio of Dep. of Civil and Industrial Engineering of the University of Pisa, an experimental test campaign accordingly to the IAEA regulations.In particular, the knowledge of the thermal conductivity is important because of the fire or furnace test to carry out in oven at 800 °C for 30 minutes. These data allowed to simulate pre-test conditions and to set up safety and operational fire test procedures.The concrete thermal conductivity was obtained by performing hot wire tests on cylindrical concrete samples for temperatures ranging from 100° to about 800°C.Thermal conductivity is determined at steady state condition. Results indicate a monotonically reduction of the thermal conductivity as the temperature increases. The comparison with concrete thermal conductivity data available in literature indicates a quite good agreement. Finally, visual and X-ray inspection of sample did not highlight the presence of micro/macro damages that would have affected the thermal performance of the concrete under study.

Experimental Study on Temperature Response in Damaged Concrete under Atmospheric Environment

The temperature field in concrete has a significant influence on durability of concrete structures. Meanwhile, there is always damage caused by loads in concrete of a real structure, which affects heat transfer and temperature field. In this paper, the tests on temperature response to heating and cooling as well as moisture transport in concrete with different damage levels were carried out. Five concrete specimens were compressed under uniaxial load to 25%, 40%, 55%, 70% or 85% of the compressive strength, corresponding to different damage levels. One concrete specimen was not subjected to any load, as a comparison specimen. The internal temperature in concrete specimens during heating or cooling process was measured by an embedded humidity and temperature sensor. Thermal conductivity of concrete is the key parameter in denoting the ability of concrete to transfer heat and decreases with the increasing damage level. When the temperature gradient exists in both sides of concrete, the moisture transport will occur in the heat transfer direction. Regardless of heating or cooling process, there is always a hysteresis effect and the temperature response rate changes quickly in the initial stage and decreases gradually with time in damaged concrete. The greater the initial temperature difference is, the greater the initial temperature response rate is. In the same initial temperature difference, the temperature response rate decreases slightly with the increasing damage level, while the moisture transport mass increases evidently.

Thermal conductivity of structural lightweight aggregate concrete

This paper characterises the thermal conductivity of structural lightweight aggregate concrete with strength classes ranging from LC12/13 to LC55/60 and density classes from D1·6 to D2·0. The thermal conductivity of concrete is assessed by a transient test method, taking into account different types of lightweight aggregate and binder, as well as different water/binder ratios. The influence of the concrete constituents on its thermal conductivity is analysed and relations between this thermal property and both the density and water content of concrete are established. It is shown that the thermal conductivity of structural lightweight aggregate concrete can be half that of normal weight concrete of similar composition. A high exponential correlation between thermal conductivity and density of concrete is achieved. On average, thermal conductivity decreases about 0·6% per each 1% increment in aggregate porosity, 8·3% per each 50 l/m3 increment in coarse aggregate volume and 3–9% per each reduction of 1% by weight in water content.

Study of Effective Thermal Conductivity of Glazed Hollow Bead Concrete

Based on analyzing the mechanism of thermal conductivity of glazed hollow bead concrete, this paper divides the channels of thermal conductivity in concrete, constructs the model of thermal conductivity coefficient based on the Theory of Minimum Thermal Resistance, and confirms the model by using the data of other related literatures and the data of our own experiment. The consequence indicates that this model can calculate the thermal conductivity coefficient under arid state exactly. In order to improve the accuracy of this model, we should take the shape of framework, the interface thermal resistance between concrete and framework into consideration

Comparative Measurements of the Thermal Properties of Solid Materials on a New Device and Using a New Non-Stationary Method

The aim of the publication is the comparative measurements of changes in temperature of the significant material coefficient - thermal conductivity for newly developed construction materials (lightweight concrete). The aim is met by using a newly proposed method and a newly developed device by the approximation modelling of the temperature dependence of the thermal conductivity coefficient of the new composites and also the interpretation of measurement results in the context of optimally desired characteristics of thermal insulation concrete. Construction materials for residential buildings should have good thermal insulation properties, i.e. relatively low coefficients of thermal conductivity. With regard to the relatively most important property of concrete – strength, however, the reduction in thermal conductivity of concrete is limited. Thermal conductivity of concrete can be reduced very effectively by increasing its porosity; on the other hand, by increasing the porosity, the strength of concrete is significantly reduced. The publication, therefore, compares the results of temperature dependences of thermal conductivity for three newly designed concretes, namely in the context of their compressive strength.

Thermal Conductivity and Impact Resistance of Concrete Using Partial Replacement of Coarse Aggregate with Rubber

A large number of studies, experiments and practical test projects have been undertaken throughout the world to assess the modifications in the properties of concrete after addition of rubber aggregates. These rubber aggregates are used to replace fine or coarse aggregates in various proportions. This experimental investigation attempts to study the strength properties and non-destructive evaluation of rubberized concrete with coarse aggregates being partially replaced with rubber aggregates from recycled tyres, in order to assess its suitability for use in structural and non-structural components. Effort was also made to determine the change in thermal properties. It was learnt that the inclusion of rubber in concrete makes the material a better thermal insulator, having a lower coefficient of thermal conductivity. This lower thermal conductivity is a property which could be very useful for meeting energy conservation requirements. Attempt was also made to assess the impact resistance of rubberized concrete. A marked improvement in this property was also observed.

Effect of Additive of Expanded Polystyrene and Perlite on Some Mechanical Properties and Thermal Conductivity for Mass Concrete

In this research, the major problem of mass concrete (Differences in Temperature) was studied. Expanded polystyrene and perlite were added in different percentages to investigate the effects on some mechanical properties and thermal conductivity of concrete. Two stages of work were performed.In first stage, reference mix was designed at proportion (1cement: 1.41sand: 2.72gravel) with (0.4) water cement ratio. Four tests were conducted, these tests including density, compressive strength, flexural strength and thermal conductivity through exponential equation depending on dry density. In the second stage, polystyrene beads and perlite were added as volumetric ratio with (10, 15, 20, 25, and 30) percentages to the original size of reference mix and conducted the tests and study their effects .The results showed a significant improvement in thermal insulation and reduced thermal conductivity (40 , 22) % by using (30) % of polystyrene and perlite respectively. The decreasing in some mechanical properties can be seen and this decreasing did not have serious effects on the design efficiency of the structure which conformed with the specifications.

Effect of Additive of Expanded Polystyrene and Perlite on Some Mechanical Properties and Thermal Conductivity for Mass Concrete

In this research, the major problem of mass concrete (Differences in Temperature) was studied. Expanded polystyrene and perlite were added in different percentages to investigate the effects on some mechanical properties and thermal conductivity of concrete. Two stages of work were performed.In first stage, reference mix was designed at proportion (1cement: 1.41sand: 2.72gravel) with (0.4) water cement ratio. Four tests were conducted, these tests including density, compressive strength, flexural strength and thermal conductivity through exponential equation depending on dry density. In the second stage, polystyrene beads and perlite were added as volumetric ratio with (10, 15, 20, 25, and 30) percentages to the original size of reference mix and conducted the tests and study their effects. The results showed a significant improvement in thermal insulation and reduced thermal conductivity (40 , 22) % by using (30) % of polystyrene and perlite respectively. The decreasing in some mechanical properties can be seen and this decreasing did not have serious effects on the design efficiency of the structure which conformed with the specifications.

Thermal Properties and Modeling of Fiber Reinforced Concretes

The aim of the paper is to define the thermal properties (thermal conductivity, density and specific heat capacity) of steel, plastic and glass fiber reinforced concretes that are widely used for industrial floors, and to determine equivalent concrete thermal conductivity values for numerical thermal modelling of steel fibre reinforced concretes. In conclusion with the measurements, simulations and correlations, in the field of building physics and energy design we are able to calculate the fibre reinforced concrete's thermal behaviour accurately.

PHYSICAL AND MECHANICAL PROPERTIES OF CONCRETE INCORPORATING INDUSTRIAL AND AGRICULTURAL TEXTILE WASTES

To reduce the impact on the environment, industrial and agricultural waste products such as carpet waste, sisal and flax have been added to the concrete. Usage of these materials in concrete does not only improve the strength of concrete but also leads to the proper disposal of these materials that leads to reduce the impact on environment. Fiber admixture can effectively improve the mechanical and physical properties of concrete. Utilization of recycled fibers from post-consumer, industrial waste and agricultural waste offer some benefits such as waste reduction, resource conservation, also low-cost materials and reduced need for land filling. Concrete is a tension weak building material, which is often cracked not ridden in plastic and hardened states, drying shrinkage and so on, low tensile strength limited ductility and resistance to cracking. In order to improve attempt has been made to study the effect of these materials on ordinary Portland cement concrete. In the experimental work, glass fibers, sisal, flax and waste carpet waste in different percentage (0.5%, 1% and 2 %) has been added by volume of concrete volume. The hardened concrete properties compressive strength, dry Shrinkage, Impact stress, The effect of temperature and Thermal conductivity of Concrete) were carried out. A total of Thirteen concrete mixtures were performed with cement content of 350 Kg/m 3 at water cement ratio = 0.525 , The amount of water was adjusted according to cement content, The super plasticizer dosage varied from 0.8% to 2.5% of cement content to achieve the required level of workability defined by a slump value of 10± 2cm.

Experimental Study on Thermal Conductivity of Self-Compacting Concrete with Recycled Aggregate.

The research focuses on the use of recycled aggregate (RA), from waste pieces generated during production in precast plants for self-compacting concrete (SCC) manufactured with a double sustainable goal: recycle manufacturing waste (consumption) and improvement of the thermal properties of the manufactured product (energy efficiency). For this purpose, a mechanical study to ensure technical feasibility of the concrete obtained has been conducted, as well as a thermal analysis of recycled SCC specimens of 50 N/mm2 resistance, with different RA doses (0%, 20%, 50% and 100%). The main parameters that characterize a SCC in both states, fresh (slump-flow) and hard (compressive strength), have been tested; also, a qualitative analysis of the thermal conductivity using infrared thermography (IRT) and quantitative analysis with heat flow meter at three temperatures 20 °C, 25 °C and 30 °C have been performed. The results suggest the existence of two different thermal behaviors: concretes with 0% and 20% of RA, and on the other hand concretes with 50% and 100% of RA. It has also demonstrated the validity of the IRT as sampling technique in estimating the thermal behavior of materials having reduced range of variation in parameters.

Experimental investigation of heat removal performance of a concrete storage cask

Spent nuclear fuel generated at nuclear power plants must be safely stored during interim storage periods. A concrete storage cask to safely store spent nuclear fuel should be able to adequately emit the decay heat from the spent nuclear fuel. Moreover, the concrete storage cask must ensure that the temperatures of the spent nuclear fuel assemblies are maintained within the allowable values for normal, off-normal, and accident conditions. Therefore, the concrete storage cask must be designed to have heat removal capabilities with appropriate reliability. However, the thermal conductivity of concrete is not good and the allowable temperature of concrete is lower than that of steel. In this study, a thermal test was performed to evaluate the heat removal performance of the concrete storage cask under development by KORAD (Korea Radioactive Waste Agency), under normal and off-normal conditions. In addition, a thermal test was performed to evaluate the thermal integrity of the concrete under accident conditions. The heat transfer rate to the ambient atmosphere by convective airflow through the passive heat removal system of the concrete storage cask was found to reach 93.5% under normal conditions. Thus, it was confirmed that the passive heat removal system was well designed and worked adequately. In addition, the heat transfer rate to the ambient atmosphere by convective airflow through the passive heat removal system under off-normal conditions was estimated to reach 87.4%. Therefore, it was deduced that the half-blockage of the inlet openings has a relatively small effect on the maximum temperatures and temperature distributions. Moreover, no significant temperature differences were detected with respect to the location of the half-blockage of the inlet openings. This indicated that, the influence of the direction of the half-blockage of the inlet openings on the heat removal performance was minimal. Finally, the maximum temperature of the over-pack inner surface under accident conditions was measured as 103°C, thus verifying that the thermal integrity of the concrete is adequately maintained under accident conditions.

An experimental study to evaluate the effects of adding glazed hollow beads on the mechanical properties and thermal conductivity of concrete

This paper discusses the effects of glazed hollow bead particles on the mechanical properties and thermal conductivity of concrete and the micro appearances of the specimens through the scanning electron microscope. In the experiments, glazed hollow bead was added to the concrete to substitute sands. The amount of glazed hollow bead was kept at 5, 10, 15 and 20% by weight. The results show that the higher the glazed hollow bead amount, the higher will be the percentage of broken glazed hollow bead particles during the mixing process of concrete and that the addition of glazed hollow bead particles reduces the density, compressive strength, elasticity modulus and thermal conductivity coefficient of concrete. When the glazed hollow bead amount reaches 20%, the density, thermal conductivity coefficient, 56-day compressive strength and elasticity modulus of concrete decrease by 14, 69·5, 18·7 and 21·4%, respectively, compared with normal concrete.

Numerical Study on the Surface Convective Heat Transfer of Mass Concrete Structure

The surface convective heat transfer of mass concrete is an important element of concrete structure temperature effect analysis. Based on coupled Thermal Fluid governing differential equation and finite element method, the paper calculated and analyzed the dependence of the concrete surface convective heat transfer on the air flow velocity and the concrete thermal conductivity coefficient. Results show that the surface convective heat transfer coefficient of concrete is a quadratic polynomial function of the air flow velocity, but influenced much less by the air flow velocity when temperature gradient is dominating in heat transfer. The concrete surface convective heat transfer coefficient increases linearly with the thermal conductivity of concrete increases.

A Study of the Thermal Conductivity of New Refractory Concretes with Porous Fillers

An experimental plant for quick comparison of the thermal conductivity of new refractory lining and other materials is proposed. It is found that whitened waste slurry generated in the production of aluminum oxide and distinguished by elevated porosity may be used as the fillers of refractory thermal insulating materials.

Thermal conductivity of hemp concretes: Variation with formulation, density and water content

This study investigates the effect of formulation, density and water content on the thermal conductivity of hemp concretes. The investigations are based on experimental measurements and on self-consistent scheme modelling. The thermal conductivity of studied materials ranges from 90 to 160mW/(mK) at (23°C; 50%RH). The impact of density on thermal conductivity is much more important than the impact of moisture content. It is shown that the thermal conductivity increases by about 54% when the density increases by 2/3 while it increases by less than 15–20% from dry state to 90%RH.