Research on the design application and effect of lightweight concrete materials in improving the thermal insulation performance of housing buildings
Publié en ligne: 21 mars 2025
Reçu: 10 nov. 2024
Accepté: 11 févr. 2025
DOI: https://doi.org/10.2478/amns-2025-0682
Mots clés
© 2025 Shuo Shi, published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.
Lightweight concrete, also known as foamed cement, foam concrete, etc., is a new type of building energy-saving material that is wasteful, environmentally friendly, energy-saving, inexpensive and non-combustible. Lightweight concrete is formed by introducing air or gases such as nitrogen, carbon dioxide and oxygen into the concrete paste through chemical or physical means according to the application needs, and formed with a large number of fine closed pores after reasonable curing and molding [1-4]. It has the advantages of light weight, good thermal insulation, easy construction, etc., different from the traditional sound insulation materials, inorganic, non-combustible, and thus has good fire resistance, can improve the safety and fire performance of the building, so it has been widely used in construction [5-8]. The production of lightweight concrete is usually a mechanical method of foam agent aqueous solution prepared into foam, and then the foam is added to the slurry containing siliceous materials, calcium materials, water and a variety of admixtures, etc., after mixing and stirring, casting molding, maintenance and become a porous material [9-12].
The application effect of lightweight concrete in building insulation is very significant. First of all, it can effectively insulate the heat, reduce the energy consumption of the building, and improve the energy utilization efficiency of the building [13-14]. Secondly, the light weight of lightweight concrete can reduce the self-weight of the building structure, reduce the pressure of the building on the foundation, which is conducive to the structural safety of the building. In addition, the high strength of lightweight concrete can meet the requirements of various skeleton structures and improve the overall performance of the building [15-18].
Literature [19] evaluated the effect of two types of EPS beads and untreated Vietnamese FA on the properties of lightweight concrete. The mix proportions of lightweight concrete were calculated by the absolute volume method. The results pointed out that the dry density and mechanical properties of lightweight concrete were inversely proportional to the EPS microspheres and FA content. Literature [20] investigated the thermal properties of lightweight concrete with different vermiculite mixing percentages based on experimental studies. An analytical simulation was also carried out for various fuels and different climatic zones to assess the energy consumption in building applications, and a comparative analysis revealed that energy efficient materials can save more cost due to the higher cost of fuel. Literature [21] aims to compare the performance of lightweight concrete produced with different lightweight aggregates. Not only the properties of concrete containing pumice and expanded polystyrene beads were examined, but also the properties of expanded perlite concrete and autoclaved aerated concrete were comparatively analyzed. The results indicated a significant relationship between the modulus of elasticity and the unit weight of concrete. Literature [22] used several types of plastic wastes in the design of concrete mixes to replace natural aggregates and determined the physical, mechanical, thermal and hygienic properties of this concrete and verified its effective thermal insulation capacity by comparative evaluation. It is emphasized that the design of lightweight concrete containing plastic waste aggregates has a high potential for development. Literature [23] applied TGA to investigate the thermal stability of natural fiber RC. The thermal conductivity results indicate that increasing the percentage of natural fibers in concrete improves the thermal insulation properties and reduces the compressive strength. Whereas, TGA results pointed out that the thermal stability of jute fibers etc. is relatively better than that of veg concrete and sisal fibers etc. are less thermally stable. Literature [24] developed green high performance lightweight concrete with good thermal insulation for energy saving. It consists of lightweight microspheres and sustainable ultra-high performance concrete and is discussed in detail. Its promising applications in energy efficient buildings and large span lightweight structures are emphasized. Literature [25] reviewed the effect that the parameters of lightweight concrete have on the FC compressive strength and thermal conductivity, especially LC made with calcium sulfate binder. The results of the study showed that calcium sulfate lightweight materials have good thermodynamic properties. Literature [26] used expanded perlite and fine-grained waste glass sand as the main aggregates for concrete mixes. By producing a variety of foam concrete, the material composition and ratio were described and their properties were analyzed. The results showed that the glass sand improved its physico-mechanical properties and durability, while expanded perlite enhanced its insulating properties. The practicality of using waste glass sand to produce sustainable insulating foam concrete is emphasized. Literature [27] reveals the wide range of applications of foamed concrete, describes the use of its raw materials, characteristics, production process and its application in foamed lightweight concrete with densities between 300 kg/m3 and 1800 kg/m3, and discusses the factors affecting the advantages and disadvantages of foamed concrete based on previous studies. Literature [28] examined the latent heat and energy storage properties of lightweight concrete with high PCM content. By conducting experiments on the compressive strength and thermal conductivity of the samples. It was concluded that “PCM aggregates have different degrees of influence on the mechanical and thermal properties of concrete”.
In this paper, a high specific strength ESP lightweight concrete was designed to address the problems of low apparent density and high strength of EPS lightweight concrete, and the incompatibility of low thermal conductivity and high strength. The surface of EPS particles was modified to enhance the bonding force in the transition zone of the concrete interface. The effect of lightweight concrete with high specific strength on the thermal insulation performance (thermal conductivity) of residential buildings was also investigated. The thermofluid meter type thermal conductivity meter was used to examine thermal conductivity, and the thermal conductivity coefficient was used to analyze the relationship between concrete and thermal insulation performance. Data fluctuations of thermal conductivity of concrete were observed for different matrix materials, ESP types, ESP particle size and grade pairing, ESP admixture, and PVA fiber admixture.
Concrete is the most important building material for civil engineering since the introduction of cement and the subsequent birth of concrete and reinforced concrete have been many years in the past. In the past century, concrete technology has continued to develop and progress. Concrete materials are now lightweight, high-strength, high-performance, and multi-functional. In the process of production and practice in order to solve the shortcomings of ordinary concrete quality, and gradually developed a new variety of concrete - lightweight concrete.
Lightweight concrete refers to light coarse aggregate, light sand or ordinary sand, cement and water formulated from the dry apparent density of not more than 1950kg/m³ of concrete. With the advancement of lightweight production technology and the emergence of high-performance lightweight accompanied by the development of high-performance concrete, lightweight concrete has been further developed, the emergence of high-performance lightweight concrete, which refers to the porous lightweight aggregates formulated with a high specific strength, high workability, good volumetric stability and excellent durability of the new type of concrete for structures.
Concrete, as a commonly used construction material, plays an important role in construction projects. Thermal conductivity is a physical quantity that characterizes the nature of heat conduction of a material, it refers to the energy transferred through an area of 1m2 in 1h under steady state conditions in a 1m-thick object with a temperature difference of 1℃ between the two surfaces, numerically equal to the density of heat flow divided by the negative temperature gradient. Concrete thermal insulation performance depends mainly on the material, shape, the content of the connecting holes at the same time and also by the solid phase of the material’s own properties as well as the influence of the bulk weight, heat transfer in the gas phase including gas conduction transfer, convection transfer of gases, surrounded by gas between the solid surface of the heat transfer by radiation. The average temperature, density and nature of the material, open and closed porosity, the composition of the gas in the closed pore, and moisture content are all factors that affect the thermal conductivity:
The effect of temperature, with the increase in temperature thermal conductivity increases. the effect of humidity, due to the insulation of most of the material contains many independent small holes, when the humidity is large, moisture instead of gas in the pores, and the moisture of the thermal conductivity is relatively fast, which makes the coefficient of thermal conductivity is greatly increased, which is why the humidity of the thermal conductivity of the coefficient of thermal conductivity plays a vital role in the determination of the coefficient of thermal conductivity of the adiabatic material of the method has a steady state method and the method of the non-steady state of the two major types of methods. The effect of porosity, with the increase of the material’s pore thermal conductivity decreases, thermal insulation performance; the impact of material density, material density reduction leads to a reduction in thermal conductivity, thermal insulation performance enhancement, but when the density is reduced to a certain extent, the density reduction will make the thermal conductivity increase (reason: the increase in the pore space of the material, the formation of a number of closed interconnected holes can reduce the thermal conductivity can be improved thermal performance, but when the density is reduced to a certain extent, the pore space becomes connected to the groove or When the pore becomes large, the convection of the air inside the pore is enhanced, and at the same time, the radiation effect between the pores is also improved, which will cause even if the density is reduced but the thermal conductivity increases instead).
Based on the mathematical equations used to characterize the physicochemical changes in multiphase systems studied by previous researchers, a mathematical model for the hydration of each major component in lightweight cement paste was derived. In the hydration model of each component of lightweight cement paste, the hydration process of cement is further investigated and a mathematical model is constructed to describe the relationship between the degree of hydration and the hydration rate, which leads to the relationship between the degree of hydration and time.
The effective thermal conductivity of concrete is an ideal theoretical calculation, because after the complete hardening of the cement internal in addition to the fully hydrated slurry, there is part of the unhydrated slurry, belonging to a large number of cement solid phase, part of the liquid phase, as well as the formation of the gas phase of the tiny pores exist at the same time. According to the EMPT model theory: if the two-phase material components are uniformly distributed, any one of which is not obviously continuous or dispersed, both have the possibility of forming an independent heat conduction, then the EMPT equation is applied to describe. The formula is given in (1):
Where,
Where,
Where,
The emphasis on energy-saving technical standards in building structures has been increasing by researchers and construction technicians. Thermal insulation material is an important part of building energy saving, which is related to the safety and durability of the entire building. Therefore, it is very important to study the factors that affect the performance of thermal insulation materials. To summarize, the influencing factors are porosity, apparent density, thermal conductivity, mechanical strength, and moisture absorption. And porosity will have a certain degree of influence on the apparent density, strength, and thermal insulation performance of heat preservation and thermal insulation materials.
The test method of thermal conductivity is shown in Fig. 1, because the thermal conductivity is related to the performance index of heat preservation and thermal insulation materials, so the test method of thermal conductivity has been a research hotspot. The steady state method and the non-steady state method are two commonly used methods. The protective hot plate (box) method, the thermofluid meter method and the circular tube method are the main contents of the steady state method, while the laser flash method and the hot wire (tape) method form the main contents of the non-steady state method.
Test method of thermal conductivity
Based on the above comparative analysis of various test methods, this test uses the PDR300 thermal conductivity tester produced by Beijing Hongou Cheng Yun Technology Co., Ltd, the standard is based on GB1029-2008 “insulation material steady-state thermal resistance and related characteristics of the determination of the protection of the hot plate method”, the test part of the double-plate structure. When using PDR300 Thermal Conductivity Tester, it is necessary to put two concrete slabs (with exactly the same ratio) into the instrument and clamp them. The instrument controls the technical parameters of the test through its own microcomputer setup system. The operator can adjust the I/O and D/A information to control the internal parameters of the instrument (including temperature control, specimen surface temperature collection, print test data, display process change curve). After putting in the source concrete plate can be controlled by controlling the instrument indicated “left clamping” and “right clamping” button to control the panel tightly attached to the specimen surface.
The operating principle of the system is described below. A metering area is provided in the central region of the instrument’s protective heat shield, and a one-dimensional steady heat flow is constructed over the two specimens with parallel surfaces used (the model is similar to a pair of parallel homogeneous plates bounded by an infinite flat plate). When the test device is activated, the entire system generates a certain amount of heat Q to pass through the specimens.
Based on the relevant test experience and theoretical research, the thermal conductivity calculation formula is shown in equation (6):
In Eq:
Instrument selection for thermal conductivity test, when starting the test device, the whole system will create a certain amount of heat Q to pass through the specimen, and the formula for calculating the conductivity coefficient is shown in equation (7):
Eq:
PDR300 instrument for recording the heating of the unit, which is composed of heating panel (C) + protection plate (D) + measurement plate (H), heating panel made of the wrong material, because the metal lead is the amount of heat conductor and lighter, so that the specimen can be heated uniformly and to obtain a smaller thermal inertia, improve the test accuracy. And the cold plate (O) + protection plate (E) + cooling water together constitute the cold plate unit, by the instrument inside the constant temperature water tank to regulate the temperature of the two cold plate, the cold plate temperature is set by the operator through the computer system. There are also two protection plates H and D, whose materials are the same as those of the instrument’s heating components, so that the temperature difference between the two sides of the partition can be precisely adjusted, which is conducive to the improvement of precision. In order to stabilize the test environment, the instrument’s outer protective components made of cork, but also to improve the accuracy of favorable. Developed by the United States Dallas 18b20 information technology temperature sensors and high-precision DC power sensors together constitute the measurement system, can also improve the accuracy of the measurement. The system is equipped with a cylinder that uses pneumatic principles to automatically fix the test piece. This can be convenient to clamp the test piece and thus save manpower and material resources. The refrigeration mechanism of the instrument can quickly cool down the cold plate, which can be quickly realized when the average temperature of the test specimen is lower than room temperature, and the detection range is greatly expanded and less affected by the ambient temperature.
The introduction of EPS particles into the cement cementitious material matrix, can be produced lightweight thermal insulation EPS concrete, its apparent density is small, low thermal conductivity, used as a building envelope components have thermal insulation, temperature regulation and environmental protection efficacy, building energy efficiency and maintenance of indoor temperature comfort is beneficial, and its components thermal insulation schematic shown in Figure 2. EPS particle size and admixture are the main parameters affecting the thermal properties of EPS concrete.
Insulation
The expanded polystyrene (EPS) particles used in this study are low-density particles made by suspension polymerization of styrene and addition of a blowing agent. The air contained in the particles is separated into countless closed cell pores, and it is their presence that gives polymer foams many valuable properties. The EPS particles are generally spherical in shape, and the particle size and apparent density can be adjusted within a certain range. The diameter of 5mm 160 times the foam multiplication of ultra-light round EPS particles, apparent density can be as low as 7.4kg/m³, the bulk density of only 4.8kg/m³. In addition to the original EPS, can also be used to formulate the concrete recycled EPS particles. Recycled EPS is made from waste electrical packaging and other EPS products after the crushing of small particles. EPS lightweight concrete is equivalent to the introduction of EPS particles in ordinary concrete or mortar constitutes a hole. Existing EPS concrete generally has low apparent density and high strength. Low thermal conductivity and high strength are not compatible, among other bottlenecks. Therefore, it is urgent to carry out research on lightweight and high specific strength, low thermal conductivity, green and energy-saving EPS lightweight concrete.
In order to eliminate the problem of “weak connection” in the interfacial transition zone between the EPS light aggregate phase and the cement stone phase in EPS concrete, and to improve the adhesion in the interfacial transition zone of the concrete, it is necessary to modify the surface of EPS particles. The test is based on the “slurry shelling principle”, spraying modifier solution on the surface of EPS particles to pre-treat the EPS particles, so as to realize the compatibility between the inorganic cementitious materials and organic particles, and to improve the interfacial bonding force between the organic particles and the inorganic cementitious materials. By reviewing the literature and combining the laboratory conditions, homemade HPMC solution modifier was used. Due to the electrostatic attraction between the EPS particles, in the water is easy to produce “accumulation” phenomenon, can be used to spray the modifier solution on the surface modification of EPS particles. The specific process is as follows:
A measuring cylinder was used to measure the EPS particles used in the test, and the prepared HPMC modifier solution was uniformly sprayed onto the surface of the constantly turned EPS particles. When the surface of the EPS particles is completely wetted, an appropriate amount of high-flow early-strength cementitious material is slowly added to wrap a certain amount of cementitious material to form a “core-shell structure”, that is, a layer of hydrophilic silicate “shell” is formed on the surface of the EPS particles.
The relationship between thermal conductivity of stone-type primary EPS concrete and bulk density is shown in Fig. 3. In the case of the same bulk density, the thermal conductivity of stone-type EPS lightweight concrete is higher than that of stone-free EPS lightweight concrete, which is caused by the fact that the thermal conductivity of concrete is larger than that of mortar. As the bulk density of stone type EPS lightweight concrete decreases, the stone content decreases, and the difference between the thermal conductivity of stone type EPS lightweight concrete and stone-free EPS lightweight concrete with the same bulk density becomes smaller. At low bulk density below 1400kg/m³, the thermal conductivity of stone-type EPS lightweight concrete is close to that of stone-free EPS lightweight concrete of the same density. Due to the use of EPS to replace the higher thermal conductivity of the stone method of preparation, with the increase of EPS mixing, its matrix part of the stone proportion becomes less, the thermal conductivity of the matrix material itself decreases. Under the double effect of the decrease of thermal conductivity of matrix material and the rise of porosity (EPS content), the thermal conductivity of primary EPS concrete with stone type decreases more rapidly with the decrease of bulk density than that of stone-free type.
The effect of matrix material type on the thermal conductivity of concrete
The thermal conductivity-bulk density relationship of stone-type recycled EPS concrete is shown in Fig. 4. The thermal conductivity of recycled EPS concrete is similar to that of primary EPS with the same bulk density, and the thermal conductivity-bulk density relationship of the two coefficients of concrete almost curves overlap. The thermal conductivity of virgin and recycled EPS lightweight concretes with similar mixing ratios and bulk densities of 1811 kg/m3 and 1779 kg/m3 were 0.88 W/(m·K) and 0.874 W/(m·K), respectively. This test shows that the effects of recycled EPS and virgin EPS on the thermal conductivity of concrete are similar.
Effect of eps type on thermal conductivity of concrete
At a certain amount of EPS admixture, the EPS particle size presents a different situation on the thermal conductivity of concrete, and the average thermal conductivity of each specimen of EPS concrete with different particle sizes was measured by Root. Thermal conductivity test results are shown in Table 1. From the table, it can be seen that the thermal conductivity of EPS concrete decreases with the particle size, the reason may be that the small particle size particles and the matrix occupy a large interfacial area, and its interface disperses the thermal conductivity, making the thermal conductivity decrease, but the magnitude of its change is small. In the EPS dosage of 40%, the particle size of 3mm, 3 ~ 5mm, 5mm particle size EPS concrete thermal conductivity were 0.320W/m·K, 0.325W/m·K, 0.341W/m·K, check the specification can be seen in the construction of the thermal conductivity of thermal insulation mortar Requirements are not higher than 0.29W/m·K, indicating that in order to make EPS concrete to achieve better thermal insulation performance, need to further study the effect of large dosage of EPS on its thermal insulation properties of the law.
Effect of EPS article size and graded concrete performance
| 40% | |||
|---|---|---|---|
| EPS size/mm | 3 | 3~5 | 5 |
| Heat conductivity/(w/m.k) | 0.320 | 0.325 | 0.341 |
| 70% | |||
| EPS size/mm | 3 | 3~5 | 5 |
| Heat conductivity/(w/m.k) | 0.202 | 0.217 | 0.222 |
Concrete components should have excellent thermal insulation performance to improve the indoor thermal comfort of the building and to achieve the purpose of energy saving and consumption reduction in the building, generally using raw materials with low thermal conductivity as aggregate, such as EPS particles, perlite, etc., or increase the internal pore structure of the EPS concrete to increase the porosity, such as the use of blowing agent, etc. In this experiment, large dosage of EPS was used to enhance the thermal insulation performance of concrete. In this experiment, large dosage of EPS is used to enhance the thermal insulation performance of concrete. The effect of EPS dosage on concrete properties is shown in Fig. 5. The thermal conductivity of EPS concrete decreases with the increase of EPS dosage, and increases with the increase of its dry density. The main reason is that the mass of EPS particles is small, low thermal conductivity, when the EPS dosage increases, it will make the dry density of EPS concrete decrease, at the same time, the porosity of EPS concrete increases, which will make the thermal conductivity of EPS concrete decrease, and the specimen shows good thermal insulation performance. When the EPS dosage is 70%, the thermal conductivity of EPS concrete is only 0.223W/m·K, while the thermal conductivity of building thermal insulation mortar is only 0.213W/m·K, and the dry density of concrete is 800kg/m³. It shows that when the EPS dosage is 70%, EPS concrete can be used as a potential building thermal insulation material to meet the lightweight, high strength basis, as well as good thermal insulation properties.
The effect of EPS content on concrete properties
The effect of PVA fiber dosage on the performance of EPS concrete is shown in Figure 6, the thermal conductivity of EPS concrete with the increase in the dosage of PVA fibers showed a trend of decreasing and then increasing, the main reason is that the addition of PVA fibers makes the internal porosity of the concrete increase, and the thermal conductivity is then reduced. When the PVA dosage of 0.7, the lowest thermal conductivity of concrete, only 0.023W/m·K, lower than the thermal conductivity of unadulterated PVA fiber. The reason is that the fiber is uniformly divided in the concrete interior, the pores between the fiber and the fiber is filled with hydrated gel, PVA fiber and hydrated gel interface bonding is better, and can refine the concrete inside the pore, reducing the fiber and the fiber contact with each other, so as to avoid thermal bridging effect due to the fiber and the fiber contact to reduce the fiber’s solid-phase heat conduction, improve the specimen’s thermal insulation properties. At the same time, the addition of the appropriate amount of PVA fiber makes EPS concrete pore wall and pore space in the number of voids, cracks and other defects to reduce the number of internal holes to increase the number of average pore size becomes smaller, the pore structure has been improved, which in turn improves the porosity, then the coefficient of thermal conductivity is reduced. However, when the PVA fiber doping is too high, the fiber is difficult to disperse and agglomerates, lap each other, increasing the solid-phase heat conduction of the fiber, so that the thermal conductivity increases, and the thermal insulation performance is reduced.
The effect of PVA content on the thermal conductivity of concrete
This paper utilizes the recycling of waste polystyrene foam EPS particles and the improvement of recycled EPS particles to enhance the bond in the interfacial transition zone of concrete, thus achieving both high strength and thermal insulation performance. The relationship between different matrix materials, ESP types, ESP particle sizes, and grade pairing, etc. The thermal insulation performance of concrete was determined by measuring its thermal conductivity. The results show that:
The thermal insulation performance of stone-free EPS lightweight concrete is better than that of stone-based EPS lightweight concrete under the same bulk density. At the same bulk density, the thermal insulation performance of recycled EPS concrete is similar to that of virgin EPS. The smaller the particle size of EPS and the higher the EPS admixture, the lower the thermal conductivity of concrete and the better the thermal insulation performance. When the PVA admixture is 0.7, the concrete has the lowest thermal conductivity and the best performance.