Thermal Conductivity Of Concrete Research Articles

Methodology for the Prediction of the Thermal Conductivity of Concrete by Using Neural Networks

The energy consumption of buildings presents a significant concern, which has led to a demand for materials with better thermal performance. Thermal conductivity (TC), among the most relevant thermal properties, is essential to address this demand. This study introduces a methodology integrating a Multilayer Perceptron (MLP) and a Generative Adversarial Network (GAN) to predict the TC of concrete based on its mass composition and density. Three scenarios using experimental data from published papers and synthetic data are compared and reveal the model’s outstanding performance across training, validation, and test datasets. Notably, the MLP trained on the GAN-augmented dataset outperforms the one with the real dataset, demonstrating remarkable consistency between the model’s predictions and the actual values. Achieving an RMSE of 0.0244 and an R2 of 0.9975, these outcomes can offer precise quantitative information and advance energy-efficient materials.

Optimization of fiber reinforced lightweight rubber concrete mix design for 3D printing

A novel lightweight insulation concrete for 3D concrete printing is developed in this study, which incorporates crumb rubber (R) as a modifier to achieve low density, exceptional thermal insulation properties, and high ductility. The mechanical properties and fiber reinforcement mechanism of lightweight rubber aggregate concrete (CR) are investigated under varying R substitution rates, encompassing compressive strength, flexural strength, tensile strength, and tensile strain of CR. The thermal conductivity test offers insights into the thermal insulation mechanism of CR. The study investigates the compatibility between the material properties of fiber reinforced rubber concrete and the parameter matching of concrete printing equipment, as well as explores the relationship between interlayer bond strength and material composition. The optimal water-binder ratio for 3D printed fiber-reinforced lightweight rubber concrete compatible with printer equipment is determined through fluidity experiments and buildability tests. The findings indicate a statistically significant decrease in CR density by 16.5% when the replacement rate reaches 30%. Although the mechanical strength of CR decrease with the increasing substitution rate of R, the tensile strain showe an increasing trend. The addition of glass fiber reinforcement resulted in a notable enhancement of the mechanical properties and a significant increase in tensile strain for CR. In addition, CR thermal conductivity is reduced by 20.65%, with the excellent thermal insulation performance. This study is of great significance to promote the rational utilization of rubber resources, promote the development of circular economy, and build a conservation-oriented and environment-friendly society.

Heat-insulating foam-silicate materials

Purpose: The aim of this work is to study the density, thermal conductivity and strength of insulating materials and fine-grained concrete based on cement binder with the use of foamed silicates. Vermiculite from Tatarsky deposit (Krasnoyarsk region), perlite from Khasynsky (Magadan region) and Mukhor-Talinsky (Republic of Buryatia) deposits, and tripoli from Potaninsky deposit (Chelyabinsk region) are used to obtain porous fillers.Research findings: It was found that the strength of materials based on cement binder and foamed silicates is determined by the strength of hydrated cement, aggregate, and contact zone of hydrated cement and filler. The coefficient of thermal conductivity of insulating materials based on foamed granules of natural dispersed raw materials (vermiculite, perlite, tripoli) with cement (23.5 vol. %) ranges from 0.112 to 0.181 W/(m·deg), which is 1.5–1.6 times higher than thermal conductivity of the granular layer.Compressive strength of the obtained materials ranges between 2.0 and 4.0 MPa. Compressive strength of lightweight concrete with the silica sand content of 32 vol.% and plasticizer, increases up to 8.5 MPa in compositions with vermiculite and up to 9.4 MPa in compositions with perlite from Mukhor-Talinskoe deposit.Depending on the quartz sand content, the density of concrete with foamed vermiculite and foamed perlite varies from 1100 to 1400 kg/m3 and from 1300 to 1600 kg/m3, respectively. Thermal conductivity of concretes with minimum density is 0.193 W/(m·deg) in the composition with vermiculite and 0.286 W/(m·deg) in the composition with perlite. At the maximum density of fine-grained concrete, the thermal conductivity increases to 0.277 and 0.411 W/(m·deg), respectively.

Towards a more realistic MELCOR model for a dry cask for spent nuclear fuel. Part II: application.

Nowadays, a great deal of attention is devoted to the development of best-estimate models able to produce more realistic outcomes. This is also the case for system codes, such as MELCOR, that are being mostly used in a conservative way especially when dealing with the licensing process. The above-mentioned need for more realistic results is at the core of this two-paper series related to the creation of a more accurate MELCOR model for the HI-STORM 100S dry cask. The findings obtained from the sensitivity studies carried out in the Part I are leveraged to set up an improved MELCOR model, the characteristics of which are consistent with the typical features of Spent Nuclear Fuel (SNF), and with geometrical and material properties of the cask itself. The addition of an axial power profile in the Fuel Assembly (FA), the better characterization of the flow losses in the air gap between internal metallic canister and external concrete-based overpack, and the choice of an appropriate value for the concrete thermal conductivity, are taken into account conjointly in this Part II. The outcomes from the improved MELCOR simulation are reported mainly in terms of the Peak Cladding Temperature (PCT), being the variable under regulatory surveillance. However, in addition to PCT, calculated temperature profiles are displayed and compared against the ones resulting from the previous model.

Mechanical and Thermal Properties of Sustainable Low-Heat High-Performance Concrete

One of the main drawbacks of utilizing mass concrete is the high amount of heat produced during the hydration of cementitious materials. Low-heat high-performance concrete (LHHPC) is a special type of concrete with low Portland cement content and low heat of hydration. The main aim of this research is to experimentally explore the potential use of blast furnace cement (CEM III) and fly ash (FA) in LHHPC. CEM III is a type of cement with low heat of hydration. FA was used at various dosages, namely 10%, 20%, 30%, and 40%, as a partial replacement of CEM III for producing more sustainable LHHPC. The mechanical and micro-structural characteristics of the LHHPC mixes were investigated. In addition, the concrete thermal conductivity and heat of hydration were predicted and compared using ANSYS finite element software. The experimental results showed that 40% FA as a CEM III partial replacement decreased the heat of hydration in LHHPC by 38.7%. In addition, the produced LHHPC showed low thermal conductivity, which indicates a decrease in early-age cracks. The produced LHHPC showed a constant compressive strength of 90 days compared with the corresponding 28-day compressive strength. The experimental results were supported by scanning electron microscope (SEM) analysis and the numerical analysis for the LHHPC. The 3D finite element model provided accurate predictions for temperature distribution. The results of this research indicated that FA and CEM III can successfully produce LHHPC with adequate strength and low heat of hydration.

Comparative study of the effect of silica nanoparticles and polystyrene on the properties of concrete

The current article examined the effect of adding nano silica and polystyrene granules on the compressive strength and thermal conductivity of concrete. Nano silica and polystyrene granules were added in proportions (1%, 2%, 3%) to the concrete mixture, and the compressive strength and thermal conductivity of the concrete mixtures were examined. The results showed when silica nanoparticles were added, the compressive strength increased, however when polystyrene granules were added, the compressive strength decreased. The thermal conductivity of concrete by adding nano silica and polystyrene granules ranged within (0.43–0.45) W/m. oC. The best percentage of silica nanoparticles (SiO2) and polystyrene granules can be added to concrete to obtain the maximum compressive strength values, which amounted to (3%) and (0.8%), respectively.

Application of recycled aggregates generated from waste materials towards improvement in acoustical and thermal conductivity of concrete

The construction sector, in addition to being very important for the economy of several countries, also creates a large amount of construction waste which has a significant impact on the environment. Usage of alternative coarse aggregates (ACA) materials for partial replacement or complete replacement of coarse aggregates can be identified from multiple sustainable sources including solid waste generated on a regular basis. There are limited studies that have explored the utility of waste materials for coarse aggregate (WMCA) in improving concrete qualities like compressive strength, thermal conductivity, and acoustic properties. Previous researchers have conducted several feasibility studies of using construction-and-demolition-waste (CDW) in engineering works, which lead economic and environmental sustainability in the construction sector. Studies show that the thermal transmittance (U-Value) of concrete, which varies between 0.62 to 3.33 W/m2K, is affected by the type of aggregates being used. It has also been demonstrated that concrete to be a good sound insulator due to its high density, but a poor sound absorber with a reflection of up to 99% of sound energy. Opportunities for usage of waste materials like coconut shells, crumb rubber aggregate (CRA) from scrap tyres, glass, plastic wastes. e-waste, construction and demolition waste (CDW), polystyrene, styrofoam and polystyrene as partial replacement of CA need investigation in depth. Some previous studies, that examined the utility of alternate materials like scarp tyres, broken bricks, CDW etc. used as partial replacement of CA, have shown promising results. This article presents a literature review on the production and utilization of waste materials for coarse aggregate in concrete for improving the acoustical and thermal properties. Summarily, this review may help in alleviating concerns of consumers and further promote the use of recycled aggregate on a larger scale in civil engineering.

Impacts of Conifer Leaves and Pine Ashes on Concrete Thermal Properties

Global energy consumption has substantially increased. Although the thermal properties of conventional concrete have been comprehensively researched thus far, considerable research is left to address the impacts of agricultural waste ashes on the thermal characteristics of ternary binders. Conifer leaves and pines are inexhaustible resources, and the effects of their ashes on concrete properties, especially the thermal conductivity, are seldom investigated. In this study, 153 concrete samples containing 5, 10, 15, and 20% replacement levels of conifer leave and pine ashes were cast, and water absorption, compressive strength, and thermal conductivity of specimens were monitored. In addition, a thermal performance test of concrete exposed to a heating source was carried out to evaluate the impacts of conifer ashes on concrete thermal conductivity. The results revealed that regarding compressive strength, the optimum replacement levels for pine and leaves ashes are 15% and 10%, respectively. Compared to reference samples, replacing 20% pine and leaves ashes resulted in an 11.9% and 9.3% reduction in water absorption, respectively. The application of conifer ashes considerably reduced concrete thermal conductivity, which is essential for erecting low-energy buildings. Conifer ashes were found to considerably drop the thermal conductivity of the specimens (1.565 W/m/K) to a lower amount. Concrete specimens containing 20% pine and leaves ashes reduced thermal conductivity by 24.7% and 26%, respectively. Thus, the application of conifer ash enhanced the concrete thermal performance, leading to a lower energy consumption overall in concrete buildings.

Enhancement of conventional concrete mix designs for sensible thermal energy storage applications

The study examines twenty-nine different concrete mix designs with varying constituents to improve thermal performance for energy storage at elevated temperatures up to 420 °C. Effects of variables including the type and volumetric percentage of coarse and fine aggregates, the type and replacement content of supplemental cementitious materials, water-to-cement ratio, the type and quantity of steel fiber reinforcement, and the inclusion of iron oxide powder are experimentally investigated by measuring the mechanical and thermal properties of each mix, with the overall goal of enhancing thermal performance and mitigating mechanical degradation for thermal energy storage (TES) applications. It is found that the use of siliceous aggregate with a high volumetric percentage produces the highest improvement (23 %–37 % at elevated temperatures) of concrete thermal conductivity, while silica fume replacement of Type I cement provides the highest improvement (4 %–8 % at elevated temperatures) of concrete specific heat. To simulate the operation of a TES system, thermal cycling was conducted to examine the change in concrete properties as a function of repetitive heating (during and after 50 total cycles to 420 °C). Based on the results of testing, concrete mix designs with high aggregate percentages (up to 72 % by volume), siliceous coarse aggregate, silica fume replacement of Type I cement (15 % by weight), and steel fiber reinforcement (up to 2 % by volume) facilitate enhanced TES performance by providing consistent thermal conductivity of ~2.2 W/m·K and specific heat of ~3.2 MJ/m3·K under cyclic high temperature exposure.

Multiscale Theoretical Model of Thermal Conductivity of Concrete and the Mesoscale Simulation of Its Temperature Field

Temperature field analysis is the precondition of studying the heat and mass transfer and durability of a concrete building; thermal conductivity is a key parameter that affects the distribution of the temperature field of concrete. Through reasonable assumptions and simplifications, the relationship between the micro-microscopic composition of concrete and its macroscopic thermal conductivity is established, and a multiscale theoretical model of thermal conductivity considering the influence of interface transition zone (ITZ) is proposed. The model can predict the thermal conductivities of concrete and its components at an arbitrary saturation. Subsequently, the influence of saturation, water-cement ratio, volume fraction and type of coarse aggregate, and sand ratio is researched. Moreover, according to the prediction results of the proposed model, a mesoscale simulation of the concrete temperature field is carried out. The results demonstrate that the presence of aggregate and ITZ leads to the isotherm deflection and abruption at the junction of the phases. Meanwhile, the heat flux density at the corners of the polygonal aggregate is significantly higher than at other positions; the phenomenon, first named the “corner effect” in the research, causes the temperature field distribution of concrete containing polygonal aggregates to be more uneven than that of circular and elliptical aggregates, and it is more likely to produce temperature-induced cracks. The research helps explain the influence mechanism of material components on the thermal conductivity of concrete and the distribution of its temperature field and provides a basis for the fine simulation of concrete thermal crack growth and creep at variable temperatures.

Steam structure and thermal conductivity of lightweight concrete aggregate

The article describes the results of theoretical and experimental studies to identify the relationship between the parameters of the steam structure and thermal conductivity of ashclaydite. The correlation dependences of the thermal conductivity coefficient of ash-claydite on its parameters of the stream structure have been established. The analysis of these works shows that the thermal conductivity of lightweight concrete depends on the type of porous aggregate, on the direction of the heat flow in relation to the layering of the concrete, the average temperature at which heat transfer occurs, the average density and moisture content of the concrete. In most works, a significant effect of the steam structure of the aggregate on the thermal conductivity of concrete is noted.

Investigation of compressive strength and thermal properties of corn cob ash cement concrete

Corn cob is an agricultural waste obtained from maize or corn. Previous studies considered the conversion of corn cob into useful materials by incorporating its ash as partial replacement for cement in concrete. However, there is paucity of information on the thermal properties of Corn Cob Ash (CCA) concrete. Therefore, the thermal properties of CCA concrete were examined in this study. The chemical composition of the CCA was determined. A total number of 105 concrete cubes of size 150 mm with varying percentage by weight of CCA to Ordinary Portland Cement (OPC) replacement order of 0, 5, 10, 15 and 20% were cast using mix ratio 1:2:4 with water/cement ratio of 0.55. Slump and compacting factor were carried out for workability test. The concrete cubes were tested for compressive strength at 7, 14, 28, 56 and 90 days and thermal properties at 28 and 90 days. Obtained results were subjected to Analysis of Variance (ANOVA). The CCA possessed combined silica, alumina and ferric oxide of 65.41%. The slump and compacting factors ranged from 87–105 mm and 0.92–0.97, respectively. Compressive strength of CCA concrete at 90 days ranged from 26.50 to 17.00 N/mm2 at 0 to 20% CCA. Thermal conductivity, heat capacity and thermal diffusivity of the CCA concrete at 90 days ranged from 1.283–1.012 W/m·K, 3.927–2.632 mJ/(m3k) to 0.867–0.407 mm2/s, respectively as CCA increased from 0 to 20%. OPC concrete incorporating CCA has insulating property. CCA can be used when compressive strength is required but not more than 10% replacement.

Thermal Conductivity of Coconut Shell-Incorporated Concrete: A Systematic Assessment via Theory and Experiment

To minimize the energy consumption and adverse impact of excessive waste accumulation on the environment, coconut shell (CA) became a potential (partial) replacement agent for fine aggregates in structural concrete production. Thus, systematic experimental and theoretical studies are essential to determine the thermal and structural properties of such concrete containing optimum level of CA. In this view, an artificial neural network (ANN) model, gene expression programming (GEP) model, and response surface method (RS) were used to predict and optimize the desired engineering characteristics of some concrete mixes designed with various levels of CA inclusion. Furthermore, the proposed model’s performance was assessed in terms of different statistical parameters calculated using ANOVA. The results revealed that the proposed concrete mix made using 53% of CA as a partial replacement of fine aggregate achieved an optimum density of 2246 kg/m3 and thermal conductivity of 0.5952 W/mK, which was lower than the control specimen (0.79 W/mK). The p-value of the optimum concrete mix was less than 0.0001 and the F-value was over 147.47, indicating the significance of all models. It is asserted that ANN, GEP, and RSM are accurate and reliable, and can further be used to predict a strong structural–thermal correlation with minimal error. In brief, the specimen composed with 53% of CA as a replacement for fine aggregate may be beneficial to develop environmentally amiable green structural concrete.

Experimental Study of Thermal Conductivity of Concrete with Biosourced Material for Saved Energy in Buildings

Abstract This study aims to improve the thermal efficiency of concrete slabs by introducing a plant material. This can contribute to the improvement of internal thermal comfort for buildings and this by lower energy consumption. For this, several experiments were carried out at the laboratory, to find the thermal properties of a new innovative building material produced by inserting ALFA (STIPA TENACISSIMA) into a concrete slab. Several mass percentages of ALFA relative to the total mass of the concrete slab (0%, 0.4%, 0.8%, 1.2% and 1.6%) were studied to see the effect of the introduced quantity of this plant on the thermal conductivity of concrete. It was concluded that the insertion of ALFA in the concrete, decreases considerably the thermal conductivity. The best results are noticed for 1.2% of ALFA, whose thermal conductivity of the concrete is reduced up to 50.61%. As a result, heat gains and losses, through wall or slab, are significantly reduced, which reduces the energy consumed by cooling and heating of homes. In addition, the degree-day method was used to calculate the costs of cooling and heating energy for 58 regions in Algeria. The lowest total energy cost is noticed in the TENES region, while the highest energy cost is noticed in the BORDJ B. MOKHTAR region.

Residual Strength and Thermal Conductivity of Self-Compacting Concrete with Recycled Expanded Polystyrene Subjected to High Temperatures

One of the most important processes of physical deterioration in concrete is the exposure to high temperatures that influences their durability and stability during life service. In addition, if self-compacting concrete is formed by lightweight aggregates, such as EPS, it is necessary to analyze its behaviour after it has been exposed to high temperature conditions. This research shows research that evaluates the effect EPS on the mechanical properties of self-compacting concrete at high temperatures. This study evaluated physical-mechanical properties, including residual compressive strength and thermal conductivity after exposure at 22oC, 150oC, 350oC, 500oC and ISO834. Experimental results showed that the loss of residual compressive strength of the specimens up to 350oC is almost insignificance, but it will be reduced by 49% and 70% when temperatures increase up to 500oC and 700oC respectively. EPS contributes to lightness, thermal insulation, and commitment to the environment in lightweight SCC.

Effect of Foaming Agent, Binder and Density on the Compressive Strength and Thermal Conductivity of Ultra-Light Foam Concrete

The study is focused on ultra-light foam concrete (FC) aimed as a thermal insulation material. Two important properties of such material were investigated: compressive strength and thermal conductivity. In the conducted tests, the influence of the air-dry density (200–500 kg/m3), type of foaming agent (synthetic and protein) and binder type (ordinary Portland cement—OPC; calcium sulphoaluminate cement—CSA; metakaolin; siliceous fly ash—SFA; calcareous fly ash—CFA) on the mentioned properties were examined. The results confirmed the dependence of compressive strength and thermal conductivity on the FC density but also indicated the important effect of the nature of the foaming agent and the binder type. The best thermo-mechanical properties were obtained for the foam concrete made of protein-based foaming agent, OPC and metakaolin. Simultaneously, the use of CSA mixed with metakaolin and foam based on the synthetic foaming agent also shows satisfactory properties.

Prediction of thermal conductivity ofconcrete under variable temperatures in cold regions using projection pursuit regression

A projection pursuit regression (PPR) model was proposed in this paper to predict the thermal conductivity of concrete (TCC) under variable temperatures in cold regions. The PPR model was established based on experimental data obtained from a single–factor experiment. Unlike the conventional PPR model that selected a random form from an empirical distribution function to describe the ridge functions in advance, the PPR model in this paper can directly apply numerical functions to describe the ridge functions obtained by projection. The comparison study indicated that, for the TCC prediction, the PPR model (R = 0.985) outperformed trained model based on Back–propagation (BP) neural network (R = 0.974). The PPR model simulation results demonstrated that the aggregate volume fraction, sand rate, saturation, water–cement ratio, fly ash content, and slag content all had impacts on the TCC under variable temperatures in cold regions. Especially, in temperature-sensitive zone (0 °C to −10 °C), it was found that the TCC of specimens with high water–cement ratio and high saturation degree increase abruptly but other factors did not cause the similar abrupt change of the TCC during the same temperature range. The correlation between the water-cement ratio and temperature–sensitive zone was explained after an in–depth study of the concrete pore structure.

Fire Resistance of Concrete Structure- A Review

Fire resistance is one of the key factor which aids toward the durability of a structure. Concrete is the most widely used construction material and is also an effective material for structural fire protection. Physical and thermal properties are used to measure the fire resistance of concrete. Three main reasons of concrete fire resistance are: non-combustible, non-toxic, low thermal conductivity (concrete retain slow rate of heat transfer). The lower value of concrete thermal conductivity behaves like a perfect shield to protect the material and adjacent space from fire damage. Fire resistance of concrete depend on a few different factors mainly: aggregate type, moisture content, density, thickness. Aggregate type suitable for fire resistance of concrete are Limestone, dolomite and lime rock. This paper reviews works done by various researches on the effect of aggregates towards the fire resistance of concrete.

Heat transfer performance of energy piles in seasonally frozen soil areas

Energy piles constitute a combination of ground source heat pump and building pile foundation technology. Energy piles can not only exchange heat with soil and extract geothermal energy but can also bear upper loads. However, due to the complex geological and climatic conditions in seasonally frozen soil areas, research on the heat transfer performance of energy piles in these areas is limited. According to the characteristics of the ground temperature distribution in seasonally frozen soil areas, the soil region can be divided into frozen and nonfrozen layers. First, a laboratory model test was carried out to investigate the heat transfer performance in these two layers. Then, a three-dimensional heat transfer model of an energy pile suitable for seasonally frozen soil areas was established. The actual working conditions of the real-scale model were simulated, and parametric analysis was then conducted. The results indicated that in annual energy pile operation, the energy pile maximum heat exchange amount per unit length can reach 125 W/m. In the performed parametric analysis, the pile length, concrete thermal conductivity, fluid volumetric flowrate and pipe type impose the greatest influence on the energy pile heat transfer performance, while the pile diameter and concrete cover thickness impose relatively little influence. Moreover, the influence of the pipe diameter should be further studied.

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.