Thermal Conductivity Of Mortar Research Articles

The Effect of Thermal Contact Conductance (TCC) Between Aggregate Inclusion and Matrix on Thermal Conductivity of Cement-Based Material

The effect of Thermal Contact Conductance (TCC)onthermal conductivity of mortar has been studied at the interface between the limestone and cement paste. A novel methodology, which involves the use of Scanning Electron Microscope (SEM) to scan the image of the interface in mortar, the software PlotDigitizer to create a set of points of the interface, and the FE software Abaqus/CAE to perform heat transfer simulation, is proposed in this study. Moreover, several hypotheses at the interface such as the gaps, flaws, and Interfacial Transition Zone (ITZ) are also highlighted. Temperature drop, thermal conductivity, and the TCC coefficient has been calculated for each model in order to understand the effect of TCC on cement-based materials thermal properties. The results show that the temperature drops at the interface are very low and the TCC coefficients are very high so that it can be ignored in heat transfer simulation except for a large air gap at the interface. Thus, it can be concluded that the TCC has no influence on the thermal conductivity of mortar.

The Effect of the Calcined Dam’s Mud as Supplementary Cementitious Materials on Thermal Insulation

In Algeria, the calcined dam's mud is a local renewable waste that proved its use as a supplementary cementitious material (SCMs) with similar mechanical performances and better resistance to several physical and chemical attacks than Portland cement. In the same context, the main objective of the work is to evaluate the effect of this calcined mud on thermal conductivity, which was never tested. To concretize this goal, one mortar based on control cement (CEMI) and three others based on modified cement by replacing CEMI by 10% to 30% Wt rates with the calcined mud of Chorfa dam have been prepared and cured before being put to the test procedure. Compressive strength, apparent density, water absorption after immersion, and thermal conductivity at three degrees of saturation state (saturated, outdoors, and dried state) were tested. The results show that using 10% to 20% replacement rate is characterized by good free lime and calcium hydroxide consumption that produces C-S-H gel, fills pores, decreases porosity, and increases density. The thermal conductivity of mortars based on the calcined mud in all states was lower compared than the control mortar, at saturated state by 16.28%, 17.83%, and 18.60% for the mortars 10%, 20%, and 30% (of cement replacement) respectively, at outdoors state by 5.5%, 4%, and 17.5% and dry state with 8.39%, 20.65%, and 38.07%. 10% to 20% mud replacement is beneficial for use in masonry and plastering wall applications of a building's envelope. 30% replacement rate can be developed and used in environments with minimal class expositions.

PHYSICAL AND THERMAL CHARACTERIZATION OF CEMENTITIOUS COMPOSITES BASED ON PLANT-BIOMASS

This paper presents the results of an experimental study on the evaluation ofphysical and thermal properties of cementitious composites based on plant biomass (rice husks and palm tree fibers). Composites produced are cement mortars with total replacement of sand by aggregates of rice husks (B) or palm tree fibers (F). Three cement content (D1, D2 and D3) and two granulometries of biomass (coarse mixture and fine mixture) were used for the manufacturing of studied samples. After 28 days of curing, dry density, water absorption by capillarity and thermal conductivity of mortars were measured. The results show that dry density and thermal conductivity of composites increase with cement content while water absorption by capillarity decreases with an increase of cement content regardless of biomass size particle. In addition, thermal conductivity increases with dry density and decreases with water absorption by capillary. For all studied mixtures, composites based on palm tree fibers give better results (high dry density, low water absorption coefficient and low thermal conductivity) than those based on rice husks. The results also indicate that the replacement of sand by aggregates of rice husks or palm tree fibers in mortars is an interesting option to be considered to produce new materials with low thermal conductivities (less than 0.50 W/mK).

A thermal cracking pattern-based multiscale homogenization method for effective thermal conductivity of steel fiber reinforced concrete after high temperature

The mesoscopic thermal cracking behavior in steel fiber reinforced concrete (SFRC) caused by high-temperature load can result in a substantial reduction of effective thermal conductivity (ETC) at macroscale level. In this study, a multiscale homogenization method for identifying the ETC of thermally damaged SFRC is proposed. This new method is characterized by the consideration of crack thermal resistance effect rather than using temperature-dependent thermal conductivities of components in cementitious composite. A series of experiments on thermal conductivity of mortar, plain concrete, and SFRC heated at various temperatures is performed. The method predictions satisfy the experimental results extremely well when the interfacial thermal resistance (ITR) coefficient is assumed to increase linearly with temperature. The numerical and experimental results show that the ITR effect makes approximately 50%, 36%, and 7%–12% contributions to the overall thermal conductivity reductions in the mortar, plain concrete, and SFRC heated up to 600 ∘C, respectively. Moreover, it is found that the trend and magnitude of ETC reduction caused by heating increase with the increase in particle content and particle-matrix thermal conductivity ratio due to the synergistic effect of heat bridge and ITR.

Investigation on preparation and multifunctionality of reduced graphene oxide cement mortar

For modern concrete materials and structures, how to realize the multifunctional application is still a challenge. The introduction of functional components into concrete materials is the most effective method. The present study successfully develops a new avenue to prepare rGO suspension with excellent dispersibility and stability through the combination of dispersant and ultrasonic pre-dispersion. This rGO suspension is added to the cement-based material, resulting in the improvement of mechanical and functional properties. The compressive and flexural strength of mortar are increased by 45% and 50% at 3 days, respectively. Meanwhile the hydration heat and pore structure are improved up to doping 2.00 wt% rGO. Moreover, the resistivity and thermal conductivity of mortar are decreased by 45% and increased by 23%, while the electromagnetic shielding effectiveness of cement paste is increased by 45%. In addition, the pressure-sensitive property of mortar increases first and then decreases with the increases of rGO content, wherein the largest stress and strain sensitivity coefficient can reach up to 1.28%/MPa and 147.80 with 2.00 wt% rGO. These results demonstrate that doping rGO is a promising approach to the improvement of the functionality of cement-based materials resulting from the doping rGO is attributed to, the formation of a conductive network structure with the continuous phase in the cement matrix when rGO content reached percolation threshold.

Thermal performance of Rice Husk Ash mixed mortar in concrete and masonry buildings

Rice Husk (RH) is an agricultural waste which is produced in huge amounts from the milling process of paddy rice. Rice Husk Ash (RHA) is a by-product material obtained from the combustion of rice husk. The amorphous silica-rich RHA (84-90 wt%) has a wide range of applications. This research focused on the possibility of utilizing RHA in the process of developing a mortar with low thermal conductivity to enhance the thermal comfort in concrete and masonry buildings. The thermal conductivity of mortar was determined by Lee’s Disc method, and the results were compared to the data for conventional mortar as well as commercial thermal insulation materials. The results indicate a significant reduction in thermal conductivity in the mortar developed with RHA

Properties of cement mortar containing pulverized biochar pyrolyzed at different temperatures

Cement manufacturing is a significant source of global carbon dioxide emissions, which can be curtailed if a portion of cement is replaced by biochar (BC). Although there are positive outcomes of application in BC-cement composites, the effects of pulverized BC pyrolyzed at different temperatures on the properties of cement mortar is remain unknown. Here we studied the fluidity, setting time, water absorption, mechanical strength, albedo, and thermal conductivity of four types of mortar samples that were mixed with a portion of cement replaced by pulverized BC pyrolyzed at 400 °C, 500 °C, 600 °C, and 700 °C, respectively. The replacement ratio of BC to cement, in weight, was set as 0%, 1%, 3%, 5%, and 10%, respectively. The results suggested that 1–3% was the optimal BC addition (irrespective of its pyrolysis temperature) to improve the strength of the mortar without compromising the other mechanical properties of BC-contained mortar composites. Addition of 1.0% of BC under 400 °C minimized the fluidity and the water absorption by 3.0% and 9.0%, respectively. Besides, both the albedo and thermal conductivity of mortars containing BC pyrolyzed at different temperatures decreased linearly with the rise of BC contents. These new findings offer a new win-win outlet for locking BC in inert cementitious materials and reducing the cement consumption.

The utilization of walnut shells as a partial replacement of sand in mortar mixes

AbstractThe effect of walnut shells on different properties of mortar was investigated through several experimental tests. The investigated properties include dry density, thermal conductivity, compressive and flexural strengths. Percentage replacements of the walnut shells to sand ratio were 5, 10, and 15%. The walnut shells used in this study were treated by soaking in boiling water for two periods: 1/2 hr and 1 hr. All mortar mixes have same proportion of 1:3:0.7 by weight for cement, sand, and water, respectively. The test results showed that the use of 15% walnut shells treated for 1/2 hr lead to decrease of the density and thermal conductivity of mortar by 15 and 31%, respectively. On the contrary, the compressive and flexural strengths of mortar were decreased by 17 and 25%, respectively, in comparison to the control mortar after 28 days of moist curing. This study leads to a conclusion that by soaking the walnut shells in boiling water for 1/2 hr enhanced the behavior of mortar compared to the un‐soaked ones. This results in achieving an acceptable strength, good thermal insulator, and environmentally friendly mortar.

Study on EPS thermal insulation mortar prepared by magnesium oxychloride cement

In this paper, a composite thermal insulation mortar was prepared with magnesium oxychloride cement and polystyrene (EPS) particles. The influence of EPS particles content on the mechanical strength, density and thermal conductivity of composite thermal insulation mortar was studied. Also, the effect of fly ash on the density and thermal conductivity of the mortar was researched. It was shown that: (1) Generally, EPS particles could reduce the compressive strength, flexural strength, density and thermal conductivity of the mortar. The 28 days compressive strength and 28 days flexural strength decreased by 93.3 % and 81.3 % respectively, with the content of EPS particles from 0 % to 0.486 %. Also the density of the mortar was reduced from 2043 g/dm3 to 805 g/dm3, and the thermal conductivity was fell from 0.4093 W/(m·K) to 0.2191 W/(m·K). (2) Small amounts (less than 5.487 %) of fly ash could increase the density and thermal conductivity. However, when the content of fly ash was more than 5.487 %, the density and thermal conductivity of thermal insulation mortar were significantly reduced.

Effect of Silicone Rubber of a Waste Composite Insulator on Cement Mortar Properties.

Due to the rapid growth of the electric power system, the silicone rubber composite insulator is so widely employed around the world. However, the aging damage and decommission of it inevitably generates plenty of waste silicone rubber. It takes up large amounts of land for non-degradation, which is becoming a serious environmental issue. In this paper, the effort has been made to reuse the silicone rubber of composite insulator by peeling, breaking and adding it into the cement mortar to partly replace river sand by 5%, 10%, 15%, 20% and 30% in volume. Moreover, the surface modification of silicone rubber particles with H2O2 and KOH is explored to improve hydrophilicity. The mechanical strength of silicone rubber mortar and modified silicone rubber mortar are measured in detail, and the effects of particle size, content and modification of silicone rubber on the properties of mortar are investigated. This study shows that at least a 5% addition of silicone rubber can reduce the strengths, while the 15% addition is obviously favorable for increasing the toughness. Furthermore, the mortar strength gets promoted due to the surface modification. Lastly, the superior thermal insulation and noise reduction of the mortar are obtained as the addition of silicone rubber particles, and an equation between dry apparent density and thermal conductivity of mortar has been developed.

Thermal enhanced cement-lime mortars with phase change materials (PCM), lightweight aggregate and cellulose fibers

The influence of a microencapsulated phase change material (PCM), a lightweight aggregate (LWA) and cellulose fibers on the behavior of cement-lime mortar was investigated. Lightweight aggregates and cellulose fibers were added in order to reduce thermal conductivity. PCM in two different amounts, 10% and 20%, was included to increase thermal inertia of mortars, taking advantage of its heat storage capacity. An experimental program was carried out to assess the effect on physical, mechanical and thermal properties of the different additions and combinations. Thermal conductivity of mortars with PCM at solid and liquid states were measured and Differential Scanning Calorimetry (DSC) was used to evaluate mortars’ enthalpy.Twelve cement-lime mortars designed for rendering applications, were studied and the experimental results were compared. It was observed that the type and amount of component affected physical, mechanical and thermal mortar properties. Lightweight aggregates increased porosity while reduced strength and thermal conductivity. Cellulose fibers did not modify significantly mortar properties. PCM increased mortar enthalpy while acted as a filler, reducing porosity and strength. However, enthalpy was not linearly related only to the amount of PCM and also depended on mortar composition. LWA increased the enthalpy of PCM cement-lime mortars.

Lightweight Mortars Based on Expanded Perlite

Lightweight mortars composed from a lime-metakaolin binder or lime-cement binder and expanded perlite filler were prepared and tested. Mortar test samples were firstly cured in a humid atmosphere and subsequently in laboratory ambient conditions. Development of hardening processes was studied by X-ray diffraction and thermal analysis. Morphology and microstructure of mortars was observed by SEM. Compressive strength, bulk density, porosity, capillary water absorption and thermal conductivity of mortars were determined in predetermined time periods.

Electrical and thermal characterisation of cement-based mortars containing recycled metallic waste

The management and disposal of solid waste from industrial sources is a problem around the world. In recent years, several studies have been carried out to develop advanced construction materials based on the waste valorisation. As a result, building materials with self-healing and self-monitoring properties have been developed using electrically conductive metallic waste. Nevertheless, the addition of metallic waste may influence the electrical and thermal performance of the new building materials. This paper aims to evaluate the effect of the type and content of metallic waste (steel fibres and steel shavings) on the volumetric, electrical, and thermal properties of cement-based mortars designed with self-monitoring purposes. Physical, electrical, and thermal properties of cement-based mortars with four different contents of metallic waste were evaluated by measuring their bulk density, porosity, electrical resistivity, and thermal conductivity. In addition, metallic waste distribution inside the mortar specimens was measured by ultrasonic tests. All the properties were measured on specimens at two curing ages, 7 and 28 days. The main results showed that the addition of metallic waste produced a reduction of the bulk density and an increase of the porosity of cement-based mortars. Furthermore, it was proven that it is possible to evaluate the metallic waste distribution inside the mortars by ultrasound, and that this evaluation is more effective in specimens with fibres than in those with shavings. Likewise, it was proven that metallic waste can modify the electrical resistivity and the thermal conductivity of mortars, regardless of the type and amount of metallic waste. Finally, it was concluded that both the type and amount of metallic waste, and the curing time used in this research did not present a significant influence on the variation of the electrical resistivity and thermal conductivity of the evaluated cement-based mortars.

Physical and mechanical properties of randomly oriented coir fiber–cementitious composites

In this study; important mechanical and physical properties of cement composites prepared with fine aggregate and coir fibers were investigated. In addition to control mortar mixtures without fiber addition, coir fiber incorporated composites were prepared by adding 0.4%, 0.6% and 0.75% coir fiber by weight of total mixtures, respectively. The effect of coir fibers on the mechanical properties of composites under compressive and flexural loads, water absorption capacity and thermal conductivity of mortars were investigated. Moreover, similar mixtures were prepared with alkali treated coir fibers having same ratios and the findings were discussed. As a result, fiber incorporation affects water absorption capacity of mortars, enhances their mechanical and thermal properties and decreases their unit weight. These effects become more significant by increasing amount of fibers and when alkali treated coir fibers are replaced with untreated ones.

USE OF CRUMB RUBBER TO IMPROVE THERMAL EFFICIENCY OF CEMENT-BASED MATERIALS

Motivated by the tremendous trend toward green environment and to reduce the effect of scrap tires on the environment and human health, this research is an attempt to find a practical and environmentally sound solution of the problem of scrap tires by developing a light weight with low thermal conductivity composite construction materials using waste tires. A few literatures may be found about the effect of crumb rubber on thermal conductivity of mortar. Thus, in this research project, an experimental program was established to investigate the effect of the amount and size of crumb rubber (rubber obtained from recycling scrap tires) on the thermal properties of mortar. Four levels of crumb rubber addition: 10, 20, 30 and 40% and three sizes of crumb rubber (#30, #10_20 and a combination of both sizes) were considered to make twelve different mixtures of the rubberized mortar. Specially designed and constructed heat transfer measurement device was used to measure thermal conductivity of the specimens. Results were used to determine the optimal amount of crumb rubber that gives the least thermal conductivity, which directly related to the improvement in thermal resistance of concrete mixtures. It was found that the size and the amount of crumb rubber had an effect on thermal properties of the specimens investigated. The thermal conductivity of rubberized mortar was decreased by 28% when crumb rubber #10_20 was used. It was also found that #10_20 crumb rubber had more effect on the thermal conductivity reduction than #30 crumb rubbers. An empirical equation is proposed to predict thermal conductivity of rubberized mortar.

Mechanical Behaviour and Thermal Conductivity of Mortars with Waste Plastic Particles

In the present paper an investigation of mechanical behaviour and thermal conductivity of a lightweight building material containing either styrene butadiene rubber (SBR) or polyurethane (PU) waste particles is presented. Several mortar mixtures were prepared by replacing quartz sand with 0, 10 and 30% of either SBR or PU post-consumer plastics particles. The influence of rubber particle addition on fresh mortar behaviour, compressive and flexural strength of mortar as well as on mortar thermal conductivity was investigated. An optimization of mortar mixture proportions was carried out by adding a limestone powder as filler. The experimental investigation showed that the addition of rubber particles reduces both the material unit weight and the thermal conductivity. The thermal insulating effect of rubber particles indicates a promising potential for future developments. On the other hand, the addition of limestone powder produced higher thermal conductivity as well as higher compressive and flexural strength.

Mechanical behaviour and thermal conductivity of mortars containing waste rubber particles

In the present paper an investigation of mechanical behaviour and thermal conductivity of a lightened building material containing either styrene butadiene rubber (SBR) or polyurethane (PU) waste particles or scraps coming from wasted rubber-shoe outsoles (SR, acronym of ‘sole rubber’) is presented. Several mortar mixtures were prepared by replacing quartz sand with 0%, 10%, and 30% of either SBR or PU or SR waste particles. The influence of rubber particle addition on fresh mortar behaviour, compressive and flexural strength of mortar as well as on mortar thermal conductivity was detected. An optimization of mortar mixture proportions was carried out by adding a limestone powder as filler. The experimental investigation showed that the addition of rubber particles reduces both the material unit weight and the thermal conductivity. The thermal insulating effect of rubber particles indicates a high and promising potential for future developments. On the other hand, the addition of limestone powder produced higher thermal conductivity as well as higher compressive and flexural strength.

A model for predicting thermal conductivity of concrete

This study investigates the thermal conductivity of fly ash concrete. Experiments were conducted to obtain the thermal conductivity of fly ash–cement pastes and mortars. Pastes were prepared to investigate the effect of fly ash, and mortar specimens were prepared for studying the effect of aggregates. It was found from the test that the replacement of cement by fly ash resulted in lower thermal conductivity. Thermal conductivity of mortar was higher than that of the cement paste. A simple parallel model for predicting thermal conductivity of fly ash concrete was proposed as a time-, material- and mix-proportion-dependent function. Thermal conductivity of concrete was computed based on the volumetric fractions and respective thermal conductivity values of each ingredient including the hydrated and pozzolanic products. Thermal conductivity of all ingredients in concrete are obtained from other studies except for the fly ash powder and hydrated products. In this study, thermal conductivity of hydrated product was obtained by the use of regression analysis together with the test results of cement paste, and thermal conductivity of fly ash powder was derived from the test results of cement–fly ash paste. The model was satisfactorily verified with various experimental results for pastes, mortars and concretes.

Factors affecting the thermal properties of concrete and applicability of its prediction models

In this paper an investigation on thermal conductivity of mortar, concrete and its major constituent aggregate is presented. Four different types of rocks were tested for their conductivities at dry and fully saturated states, which were further crushed and used as coarse aggregates in concrete. Thermal conductivity of mortar and concrete have been measured at various moisture contents. The applicability of Campbell-Allen and Thorne's model in assessing the influence of aggregate type has been investigated. Using a few advanced models for thermal conductivity of porous material, it has been demonstrated that there exists a possibility to gain insight into the nature of the pore that is likely to be encountered in the concrete. The relationship between concrete conductivity and aggregate conductivity at various degrees of saturation including at dry and fully saturated conditions have been developed. Further, equivalent conductivity of solid, which is a necessary input parameter for porous material models, has been evaluated for all the types of concrete under consideration.

The thermal conductivity of fibre-reinforced concrete

The effect of copper and steel fibre inclusions on the thermal conductivity of mortar and concrete is investigated. The experimental technique is based on the conventional steady-state method using desiccated specimens. The results indicate that copper fibres significantly increase thermal conductivity while steel fibres have a lesser effect. Vibration of the fresh concrete, during specimen manufacture, produces some fibre alignment. As a result, it is found that theoretical methods based on the assumption of a random fibre distribution under-estimate the experimental values.