Thermal Conductivity Of Concrete Research Articles

High thermal conductivity concrete for energy piles

Research is increasingly focusing on thermal properties of concrete with the aim of reducing the heat exchange between buildings and environment. On the other hand, concretes with high thermal conductivity could have interesting applications in the field of thermo-active ground structures as Geothermal Energy Piles (GEPs). This kind of foundations represent an environmentally friendly technology that allows exploiting the heat of the shallow earth surface to supply renewable energy for the air conditioning of buildings. GEPs are needed for structural and geotechnical reasons and allow recovering the installation costs connected to vertical boreholes. Concrete drilled or driven piles are equipped with a Primary Circuit (PC) of high-density polyethylene plastic pipes attached to the reinforcement cages. Thermal energy is extracted from or injected into the ground thought a carrier fluid that flows into the pipes of the PC. To improve the heat exchange between the pile and soil the thermal properties of the concrete should be considered as design parameters. Concrete thermal conductivity, contrary to what happens for the buildings, should be increased to optimise the thermal performance of the GEPs. Different solutions that modify the mix design of concrete are proposed to the aim of increasing the thermal performance of GEPs.

Effect of polyethylene powder and heating treatment on the microstructure and hardened properties of foam concrete

To tackle the energy consumption issue and meet the energy-efficiency building requirement, this study proposes a method by incorporating polyethylene (PE) powder as a multi-function and low-cost construction material in the foam concrete to enhance the thermal insulation. The effects of heating treatment and dosages of PE powder on the dry density, compressive strength, water absorption, thermal conductivity and microstructure of foam concrete were investigated. The pore structure and morphology were examined using Image-Pro-Plus software, electron microscope and SEM-EDS. Results indicate that the dry density and compressive strength of foam concrete generally decreased, while the water absorption overall increased with higher dosage of PE powder. Thermal conductivity of foam concrete containing PE powder without heating treatment exhibited a rising trend with the increase of dosage, while that of foam concrete prepared with the PE powder was greatly inhibited by heating treatment. Both the average roundness of pores and the porosity of foam concrete increased with the incorporation of PE powder, but the smaller effective pore size in the foam concrete with heating treatment was significant. The PE membrane coated on the pore wall and clogged the pore structure, which was verified by SEM-EDS analysis on the microstructure of foam concrete after heating treatment.

Test and Calculation Model of Thermal Conductivity of Concrete

In order to study the influence of water content and hydration degree on the thermal conductivity of concrete, based on the steady-state plate method, the influence of water content, temperature, hydration degree and other factors on the thermal conductivity of early concrete was studied, and the calculation model of thermal conductivity of early concrete was established according to the test results and influence rules. The results show that there is a linear relationship between the thermal conductivity and water content at 28d, the higher the hydration degree is, the lower the thermal conductivity of concrete is; the difference between the measured value and the calculated model value is small, and the calculation formula can meet the requirements of engineering calculation.

Relationship between Thermal Conductivity and Compressive Strength of Concrete: A Review

Relationship between Thermal Conductivity and Compressive Strength of Concrete: A Review

Thermal conductivity evolution of early-age concrete under variable curing temperature: Effect mechanism and prediction model

The thermal conductivity and microevolution mechansim of early-age concrete (EAC) under variable curing temperature environments significantly influence the temperature cracks in massive concrete. An experiment was carried out to compare thermal conductivity evolution differences of EAC under variable curing temperature (VCT) and standard curing temperature (SCT) conditions. The concrete specimens of moisture and dry states were used to consider the effect of moisture content on thermal conductivity. Results showed that the moisture concrete thermal conductivity under VCT condition decreases with curing ages and is higher than SCT condition. For the dry samples, the thermal conductivity of VCT condition increases with curing ages and is lower than the SCT condition. The difference in thermal conductivity between VCT and SCT increases from zero to seven days and decreases after seven days. The scanning electron microscope (SEM) tests showed that the VCT leads to slower growth of pore structure and larger porosity of EAC due to the slower hydration rate under VCT condition. The thermal conductivity difference between VCT and SCT is mainly caused by the differences in water content, chemical components in solid phase, and porosity (solid-phase volume fraction). Meanwhile, the relation among thermal conductivity, porosity and most probable pore size shows that curing temperature has a great effect on hydration degree and controls the thermal conductivity evolution. Besides, a prediction model of EAC thermal conductivity under VCT condition was built based on hydration kinetics.

A Comparative Study on the Thermal Conductivity of Concrete with Coal Bottom Ash under Different Drying Conditions

The utilization of coal bottom ash (CBA) and fly ash in concrete has become more common. For CBA concrete, curing conditions would influence the thermal properties of the concrete due to the high water absorption capacity of the CBA aggregate. In addition, CBA and fly ash contents in concrete affect the thermal properties of the concrete. Therefore, the effects of the drying conditions and the CBA and fly ash contents on the thermal conductivity of CBA concrete were investigated in this study. The thermal conductivity of concrete was measured under two different curing and drying conditions: oven-dried conditions and saturated surface-dry (SSD) conditions, with curing times of 28 and 91 days. The concrete mixtures also contained different levels of CBA and fly ash. Crushed sand in the concrete mixtures was replaced by CBA with replacement ratios of 25%, 50%, 75%, and 100% by volume. In addition, cement in the concrete mixture was substituted by fly ash with replacement ratios of 20 and 40% by volume. The thermal conductivity of concrete under the oven-dried conditions was much lower than that under the SSD conditions. Moreover, the thermal conductivity of the concrete decreased as the CBA content increased under both the oven-dried and SSD conditions. The material properties of the concrete, including unit weight, compressive strength, and ultrasonic velocity, were also measured in the study. Compared with the SSD conditions, the compressive strength, unit weight, and ultrasonic velocity of CBA concrete were considerably lower under the oven-dried conditions. Moreover, the relationships between the thermal conductivity and unit weight, compressive strength, and ultrasonic velocity were suggested.

Research on influencing factors and time-varying model of thermal conductivity of concrete at early age

The thermal conductivity of concrete was investigated under the unsaturated condition during early curing. Based on the improved steady-state method, the thermal conductivity of unsaturated concrete at different ages under curing at the constant temperature of 20 ℃, 5 ℃, and −5 ℃ was tested. The influences of the water-binder ratio, initial air content, fly ash content, curing age, and curing temperature on the thermal conductivity of concrete were analyzed. The water-binder ratio, initial air content, fly ash content, curing age, and curing temperature are inversely proportional to the thermal conductivity of early age concrete. Through the analysis of the correlation between these factors and the thermal conductivity, the correlation between various factors and the thermal conductivity of concrete from large to small is as follows: curing temperature, initial air content, curing age, water-binder ratio, fly ash content. A multiple regression prediction time-varying model with acceptable accuracy is proposed to ensure the accuracy of the effective thermal conductivity prediction.

Comprehensive review study for the effect of utilizing waste ma-terials on the thermal conductivity of concretes

Since concrete is one of the most popularly utilized building mixtures in construction, a high demand of natural resources is significantly emerged. Therefore, a skyrocketed attention has been paid to create new opportunities for the use of recycle materials to develop a new construc-tion substance with more satisfactory properties. The use of waste products in concrete is not only economical, but it helps in solid waste management as well. Among various properties of concrete, thermal conductivity is a crucial factor that plays an important role in in building insu-lation by evaluating a material's capacity to transfer heat. This paper aims to review the potential application of waste materials in concrete as additive ingredients and investigate the effect of this waste material on thermal conductivity of concrete. The review of literature revealed that the application of most of the waste materials exhibited an obvious potential as thermal insulator. However, further investigated work is needed to highlight the advantages of utilizing waste mate-rials in concrete containing various type of waste materials

Influence of Partial Replacement of Cement by Various Percentage of Scoria in Self-Compacting Concrete on Thermal Conductivity in the Jordan Building Construction for Energy Saving

The objective of this study has been to investigate the effect partial percentages of Scoria on Self-Compacting Concrete (SCC) in order to evaluate thermal conductivity in the Jordan building construction. The mechanical properties slump flow test, the compressive strength, the thermal conductivity (k-value) values, and the expected model for energy performance have been assessed. The slump flow test has revealed that the workability of fresh concrete has increased with increased partial replacement of scoria and vice versa. The compressive strength result has indicated that the maximum compressive strength obtained at 25% replacement has been 49.78 MPa. The thermal conductivity (k-value) result has showed that inversely proportional to the connection between scoria ratio and concrete thermal conductivity, indicating increases an insulating effect by reducing the thermal conductivity from 6.2 to 3.3 W/m K. as well as influence of scoria in the SCC is a suitable option for energy performance in the construction of buildings.

A Comparative Study on Plastic Concrete and Partially Replaced Plastic Concrete using Plastic Aggregate with Conventional Concrete

Solid waste management is one of the major environmental concerns in our country now a day. The present study covers the use or recycled plastics as replacement of coarse aggregates in concrete. The main aim of the study is to investigate the change in mechanical properties of concrete with the addition of plastics in concrete. Along with the mechanical properties, thermal characteristics of the resultant concrete are also studied. It is found that the use of plastic aggregates results in the formation of lightweight concrete. The compressive, as well as tensile strength of concrete reduces with the introduction of plastics. The most important change brought about by the use of plastics is that the thermal conductivity of concrete is reduced by using plastics in concrete. Therefore, it can be said that recycled plastics can be used for thermal insulation of buildings.

Experimental Study on Freeze-Thaw Properties and Thermal Conductivity of Green and Environment-Friendly Three-Admixture Concrete

Using straw powder (rice husk ash), fly ash, silicon powder and other three admixtures to prepare concrete can improve the ecological environment and promote the reuse of agricultural and industrial wastes. In this paper, 9 groups of freeze-thaw specimens and 9 groups of thermal conductivity specimens of green and environment-friendly three admixture-blended concrete were prepared with corn, wheat and rice husk powder, replacing cement with straw powder by 6% and 8% respectively and replacing cement with fly ash by 20% and silica fume by 10%. The test results show that the mass loss rate of the concrete ranges from 0.8% to 1.4% and from 3.5% to 4.4% after 25 and 50 freeze-thaw cycles, respectively. The thermal conductivity of the concrete falls within the range of 0.2901 w/(m· K)-0.5834 w/(m·K), which is suitable for the existing building reconstruction and new construction projects in cold and severe cold areas.

Thermal conductivity and shrinkage properties of slag-based cement concretes

The thermal conductivity, specific heat, and total drying shrinkage test of slag blended OPC cement is conducted by using a Hotdisk-2500S thermal conductivity, and non-contact shrinkage deformation measurement apparatus based on ISO 22007-2 and GB/T50082-2009 test standards, respectively. The influence of replacement rates of slag cement (0, 30, 50, and 70%) and high-temperature exposure (21, 200, 400, 600, and 800 °C) on the thermal properties of concrete is analysed. The results show that for all three concretes, the thermal conductivity initially decreases with increasing temperature up to 400 °C, then after it remains almost constant between 400 and 600 °C, and gradually begins to decrease again up to 800 °C. Furthermore, thermal diffusivity of concrete group G-70, shows 21.4, 21.6, and 37.6% increment in 21, 200, and 600 °C temperature exposure respectively compared to concrete group G-0. Though, as the exposure temperature keeps rise to 800 °C, its value starts to decrease. Furthermore, the results indicated that high volume slag cement content in the concrete mix lessen the drying shrinkage of the concrete at later age. Test data is used as a function of temperature and slag replacement to establish high temperature relations for thermal properties. The proposed thermal property relationships can be used as input data for validation in computer programs and to evaluate the response of OPC and slag blended Portland cement concrete structures subjected to fire.

Characteristics of hemp fibre reinforced foam concretes with fly ash and Taguchi optimization

This study presents investigation on microstructural, mechanical, durability and thermal characteristics of hemp fibers (HFs) reinforced foam concrete with fly ash (FA) and Taguchi optimization approach. Three series of foam concretes mixtures were produced with foam contents of 50, 75 and 100 kg/m3. There is a reference mixture without HFs and FA. Thus, mixtures contain FA as cement replacement at the concentrations of 0%, 10%, 20%, 30%, 40% and 50%. HFs with varying fiber length were introduced into mixes at concentrations of 0.75%, 1.5% and 3% by weight of cement. Slump test was done to see workability. Compression and flexural properties were determined at 7, 28 and 91 days. Durability was investigated by high temperature, freeze–thaw and sulphate exposures. Thermal conductivity, drying shrinkage, porosity, water absorption and dry unit weight properties of foam concretes were also investigated. Experimental results were analyzed using Taguchi optimization approach. Addition of HFs provides very large compressive and flexural strength enhancements. FA addition reduces the drying shrinkage and thermal conductivity while it increases the high temperature resistance of foam concretes.

Effect of waste marble powder and rice husk ash on the microstructural, physico-mechanical and transport properties of foam concretes exposed to high temperatures and freeze–thaw cycles

An experimental program was performed to evaluate the impact of rice husk ash (RHA) as cement replacement and waste marble powder (WMP) as sand replacement on the microstructural, mechanical and transport properties of foamed concrete exposed to high temperature and freeze–thaw cycles. For this, Portland Cement (PC) was replaced by RHA at 10% and 20%wt of binder and silica sand was replaced by WMP at 25% and 50%wt of fine aggregates to cast foamed concrete mixtures. Two different foam contents of 40 kg/m3 and 80 kg/m3 were used in the production of foamed concretes with water/binder (w/b) ratio of 0.70. Two reference mixtures were produced from silica sand and without RHA at each foam content. Other foam concretes were fabricated from 25% and 50% WMP instead of silica sand and 10% and 20% RHA instead of cement. Fresh properties of mixtures were evaluated by performing slump test. Transport properties of foam concretes were investigated, including porosity, sorptivity and water absorption after 90 days curing. Mechanical properties of foam concretes were investigated, including compressive and flexural strength ultrasonic pulse velocity (UPV) after 7, 28 and 90 days. Drying shrinkage and thermal conductivity of concretes were also studied after 90 days. Durability of concretes were also investigated after exposure to the temperature of 200, 400, 600 and 800 °C and freeze–thaw (F-T) cycles of 100 and 200 in addition to microstructure investigations. Results show that 10% RHA as cement substitute and 50% WMP as sand substitute give optimum percentage especially at late-age of 90 days at foam content of 40 kg/m3. The lowest drying shrinkage and sorptivity were obtained by using 10%RHA and 25%WMP. The results also indicate that water cooled specimens showed more strength loss than air cooled specimens after 200 °C. The worst F-T performance was obtained for the mixture containing 10% RHA and without WMP by 43.8 and 59.8% strength reductions.

Experimental study on the frost resistance and thermal conductivity of Environmental fair-faced concrete

For fair-faced concrete buildings and structures, the secondary recycling of agricultural and industrial wastes can achieve both green energy saving and heat preservation, save costs, and protect and promote ecological and resource environments. In this paper, to fully recycle agricultural waste and industrial waste, the new type of fair-faced concrete was prepared by triple doping of fly ash, slag and rice husk ash, and three sets of concrete thermal conductivity test blocks and two sets of freeze-thaw test blocks were prepared and tested for thermal conductivity and mass loss rate. The test results showed that the thermal conductivity of the new fair-faced concrete is 0.9644 W/(m⋅K) on average, and the mass loss rate was 1.825 and 2.575 after 25 and 50 freeze-thaw cycles respectively, which meet the requirement of less than 5%. The new type of fair-facedr concrete has good energy saving and durability, and can be applied in construction projects in cold regions.

Experimental study on freeze-thaw performance and thermal conductivity of green ecological concrete

For the existing and new buildings in cold areas, this paper makes full use of the agricultural waste of finely ground rice husk and the recycled coarse aggregate of the concrete of the construction industry waste to form green ecological concrete by compounding, which can promote the ecological environment and the secondary recycling of agricultural and industrial waste; compounding finely ground rice husk and recycled coarse aggregate can save cost, improve the later strength of concrete, and green energy saving and heat preservation, and protect Ecological resources and environment. After mixing the two to replace cement and natural coarse bone by the same amount, we prepared two sets of concrete thermal conductivity test blocks, four sets of frozen and thawed test blocks, and tested the thermal conductivity of concrete, mass loss rate. The test results showed that the thermal conductivity value of the green concrete was 1.17 W/(m-K), and the mass loss rate was 3.85% and 4.08% after 25 and 50 freeze-thaw cycles respectively, and the green ecological concrete had excellent energy saving and durability.

Model for Predicting the Thermal Conductivity of Concrete

Thermal conductivity of concrete greatly influences the heat transfer of buildings and affected by many factors. This paper presents a prediction model for thermal conductivity of concrete by adopting the theory of Wiener bounds and considering concrete to have four components (water, air, aggregate, and cement mortar). The proposed model considers the combined effects of porosity, water saturation, and the volume fraction of aggregate on the thermal conductivity of concrete by weighting parameters of $${\eta }_{1}$$ , $${\eta }_{2}$$ , $${\eta }_{3}$$ , respectively. By adjusting the weighting parameters of each component, the model can consider the influence of various factors on the thermal conductivity of concrete more comprehensively. Thermal conductivity of each component and expression of weighting parameters are determined by literature and experiments. The proposed model has been verified by the measured thermal conductivity of concrete under different porosities, water content, and volume fractions of aggregate with the prediction accuracy of $$\pm 12\mathrm{\%}$$ . Finally, the regularity of the change in the thermal conductivity of concrete with porosity, water saturation, the volume fraction of aggregate, and temperature is analyzed.

Thermal conductivity of geopolymer concrete with different types of aggregate

In this article the influence of aggregate of geopolymer concrete used in concrete printing of buildings and structures, architectural elements on its thermal conductivity is studied. All tests were conducted on device for measuring thermal conductivity called PIT-2 designed to measure the thermal conductivity of building and heat-insulating materials under stationary thermal conditions in accordance with ISO 7345:1987* and ISO 9251:1987. As the fine aggregate most commonly used river sand, quartz sand, ceramic foam, as well as one new coniferous shavings were taken. The results of 4 tests to determine the thermal conductivity of geopolymer concrete with various aggregates are listed in the summary table in the study. According to the test results, the lowest coefficient of thermal conductivity has geopolymer concrete on ceramic foam. In this study geopolymer concrete is considered as the main material for concrete printing of the houses and architectural forms. This material reduces CO2 emissions in the atmosphere.

Heat-Insulating Properties Of Effective Light Weight Concretes For Three-Layer Protecting Coverings Of Buildings

Аt present, an intensive change in the structure and materials of building envelopes is taking place in order to increase the energy efficiency of buildings, as well as to improve their appearance and extending the period of maintenance-free operation. The paper presents the results of studies of the physical-mechanical properties of light polystyrene concrete and effective heat-insulation of three-layer structures based on heat-insulating light and structural heavy concrete. To obtain the concrete mixture, Portland cement, granular foam polystyrene, polycarboxylate super-plasticizer, quartz sand and limestone crushed stone were used. All raw materials were of local origin (Vietnam). The composition of the heavy and light concrete mixture was calculated using the absolute volume method according to the standard of Vietnam, the thermal conductivity of concrete was measured with an appropriate device. It has been established that using local surface components it is possible to obtain structural concrete, as well as polystyrene concrete, which has sufficient tensile and tensile strength during bending and heat conduction in the dry state. From the calculations made with the use of the computer program, it follows that the three-layer reinforced concrete coating slab, consisting of heavy and polystyrene concrete, has better thermal insulation properties compared to a coating of the same thickness of solid and perforated structural concrete, as well as with a panel with foam polystyrene blocks.

Effects on the Compressive Strength and Thermal Conductivity of Mass Concrete by the Replacement of Fine Aggregate by Mussel Shell Particulate

The behaviour of mussel shell particulate as fine aggregate for mass concrete has been analysed. The shells were washed and mechanically crushed to obtain a particle size similar to that of the natural aggregate (fine) to be replaced, which was dried at 140 °C. The Faury-Joisel method was used to design the H-35(95)-20-6 structural mass concrete sample, with 0%, 10%, 30% and 60% replacements of fine aggregate by mussel shell particulates, performing compressive strength and thermal conductivity analyses at 7 and 28 days. The results indicate that in order to maintain the compressive strength of H-35(95)-20-6 structural mass concrete, the replacement percentage should not exceed 40%. On the other hand, as the mussel shell particulates in the concrete increase, the thermal conductivity decreases, turning into a material with a tendency to increase thermal insulation, which would help to improve the new demands on energy saving and efficiency in households, if used as coating. Hence, it can be concluded that it is feasible to replace fine aggregate with mussel shell particulate matter, which would be useful in increasing the recycling of this residue and in reducing its natural exploitation.