2.1 Gypsum-based lightweight insulation material
The construction industry includes residential, industrial and commercial buildings and consumes huge amounts of energy. Therefore, it is very meaningful to reduce its energy consumption through appropriate and effective thermal insulation strategies. Reasonable use of insulation materials can not only consume less energy for space cooling in summer, but also consume less heat to maintain the temperature of the house in winter. In this way, the purpose of saving energy and controlling indoor temperature can be achieved.
Gypsum-based light-weight thermal insulation material uses industrial by-product gypsum desulphurization gypsum as the main raw material, supplemented by a small amount of additives, lightweight aggregates or foaming agents through a special preparation process to obtain gypsum-based products. It has the characteristics of light weight, excellent thermal insulation performance, fire resistance, dimensional stability and adjustable humidity. New building materials that are energy-saving, environmentally friendly, and waste-reducing are the focus of the development of building materials in the future. Gypsum-based light-weight thermal insulation materials use coal-burning solid waste flue gas desulfurization gypsum as the main raw material, turning waste into treasure, opening up a new way for the comprehensive utilization of solid waste, and having good economic, social and environmental benefits.
2.2 Common lightweight aggregates in gypsum-based insulation materials
Widely used in wall thermal insulation projects, but due to differences in process conditions and raw materials, vitrified microspheres are not completely sealed during the production process, and their brittleness is large, and they are easy to crack or even break during production, transportation and use. As a result, there are more open holes on the surface of the vitrified microbeads actually used, which leads to an increase in water absorption and a decrease in intrinsic strength, which affects the thermal insulation performance and strength of the vitrified microbead mortar.
Expanded perlite has strong hydrophilicity, which causes cracks in its products and affects its thermal insulation effect. At present, the modification of expanded perlite mainly includes organic acid, surfactant modification, coupling agent modification and polymer coating modification to achieve the purpose of reducing the water absorption rate of its products.
Polystyrene particles have excellent thermal insulation properties, low density, low water absorption, and good stability. However, due to their low density, they are prone to segregation during the mixing process of the mortar, and the bonding force with the mortar interface is weak. Defects such as easy rebound and easy combustion to produce harmful gases during construction restrict the application of polyphenylene particles. At present, surface modification technologies, such as epoxy resin, dispersible rubber powder or water-soluble ethylene propionate, have been used, but this greatly increases the cost.
2.3 Preparation method of gypsum-based insulation material
At present, in addition to blending lightweight aggregates with low thermal conductivity to prepare thermal insulation materials with good performance, the project can also be prepared by foaming methods. The foaming method is generally divided into physical foaming and chemical foaming. The chemical foaming method is to introduce the foaming agent (H2O2, aluminum powder, CaH2, etc.) into the slurry; the physical foaming method is to introduce the prefabricated foam into the gelling material. Since the introduction of bubbles in the gypsum slurry increases the phase interface and the surface free enthalpy increases, it presents a thermodynamically unstable state, and when two bubbles of different sizes are in contact, according to the Laplace principle, a large bubble will eventually form Therefore, the stability of air bubbles is difficult to control, and the construction process is easily disturbed by changes in the external environment, which makes it difficult to control the construction quality.
New type gypsum-based insulation material
In addition, due to the increasing calls for the reuse of green resources worldwide, in addition to the preparation methods of the above-mentioned common gypsum-based insulation materials, researchers have also begun to use natural resources as fillers to prepare gypsum-based insulation materials, such as onion skins and peanuts. Shell fibers and date palm fibers are used as fillers. The preparation of gypsum-based lightweight materials can be used as thermal insulation materials, which helps reduce energy consumption and CO2 emissions, and has a great impact on the environment.
2.4 The performance of gypsum-based lightweight thermal insulation materials
Gypsum-based lightweight insulation materials need to have good working performance to meet construction requirements. For example, the workability of adding lightweight aggregates to prepare gypsum-based insulation materials is affected by the lightweight aggregate itself, and high water absorption and non-spherical aggregates will reduce its work. The water absorption rate of the aggregate is affected by the proportion of interconnected holes in the aggregate itself and the pore volume. Usually mixed with rubber powder, cellulose ether, superfine mineral admixtures, etc. to adjust the viscosity of the gypsum slurry to inhibit the floating of light aggregates, reduce the adverse effect on workability, and prepare a gypsum-based thermal insulation material with good workability .
The gypsum-based insulation material prepared by the foaming method has a smaller porosity in the range of 100μm, and the larger the porosity in the range of 100μm-400μm, the higher the compressive strength. Adding water reducing agent, cellulose ether, sepiolite, EVA emulsion, etc. can improve its strength. For the gypsum-based thermal insulation material prepared by adding lightweight aggregate, its mechanical properties mainly depend on the strength of the lightweight aggregate itself.
2.5 Application of gypsum-based lightweight thermal insulation materials
Due to the water resistance of gypsum-based materials, gypsum light-weight thermal insulation materials are mainly suitable for the internal thermal insulation of walls, floors and ceilings. According to actual needs, the bulk density can be prepared from 800kg/m 3 to 300kg/m 3 , and the thermal conductivity can reach 0.01W/ m 2 ·K.
Research progress of gypsum-based phase change energy storage materials
3.1 Phase change energy storage materials and classification
Phase Change Materials (PCMs) can be combined with building materials to form new building materials with heat storage and temperature adjustment functions. It uses gas-solid, gas-liquid, and solid-liquid changes to achieve heat storage and temperature regulation Left and right, to achieve the purpose of living comfort and energy saving. Using phase change materials to store solar energy can play an important role in regulating indoor temperature and reducing energy consumption for space heating and air conditioning.
Classified by chemical composition:
1. Organic phase change materials such as paraffin, fatty acids and polyols have high latent heat of phase change, a wide range of phase change temperature, and are not prone to overcooling and phase separation;
2. Inorganic phase change materials include inorganic hydrated salts, molten salts, etc., which have the advantages of high latent heat of phase change, non-flammability and low cost.
3.2 Preparation technology and performance of phase change energy storage materials
Adsorption type composite phase change material
Use the adsorptivity of porous media as a carrier to absorb phase change materials. Commonly used adsorption materials include inorganic porous minerals and expanded graphite. Porous expansion has a rich pore structure and excellent adsorption performance, and has good thermal conductivity.
Nanocomposite phase change energy storage materials
The principle of nanocomposite phase change energy storage materials is to combine phase change energy storage materials with nanomaterials. In the phase change process, nanoparticles can act as thermal conductivity enhancers, thickeners and nucleating agents, thereby improving inorganic hydration Salt thermal conductivity, to solve the problems of phase separation and supercooling.
Microcapsule composite phase change material
Through the encapsulation of the core material by the wall material, the phase change material is isolated from the outside during the formation of the microcapsule to form a microcapsule phase change material with a core-shell structure. At the same time, the confinement effect of the microcapsule can limit the phase change material to a certain level. In the region, the purpose of improving the dispersion performance of phase change materials is achieved. Macromolecule polymers are commonly used as microcapsule wall materials, and the main researches are melamine-formaldehyde resin, urea-formaldehyde resin, acrylic resin and so on.
3.3 Gypsum-based phase change energy storage materials
Gypsum-based phase change energy storage material is a new type of building material prepared by introducing phase change energy storage materials into gypsum-based materials, which has both excellent thermal insulation properties of gypsum materials and energy storage and heat storage functions.
The preparation method of phase change gypsum building materials includes:
(1) Adsorption impregnation method: After the phase change material is melted into a liquid state, the gypsum board is impregnated to adsorb the liquid phase change material to prepare a phase change energy storage building material.
(2) Direct mixing method: Disperse the phase change material evenly and mix it into the gypsum building materials to prepare the phase change energy storage building material.
3.4 Thermal performance of gypsum-based phase change energy storage materials
When the content of phase change material is 23%, the heat storage capacity of phase change gypsum board is about 11 times higher than that of ordinary gypsum board; research shows that the heat storage capacity of 1.5cm thick phase change gypsum board containing about 45% of the mass of phase change material It is 5 times that of ordinary gypsum board, and its thermal performance is equivalent to that of a 12cm thick brick wall structure.
Related research areas include:
1. The expanded perlite adsorption capric acid-tetradecanol composite phase change material is directly mixed into gypsum;
2. The microcapsule phase change material with paraffin wax as the core material, and the prepared microcapsule phase change material is mixed into the gypsum board;
3. The octadecane and beeswax are encapsulated in a porous material and compounded on the gypsum board to have heat storage and insulation effects;
4. Use expanded graphite to adsorb Na2CO3·10H2O-Na2HPO4·12H2O binary inorganic hydrated salt phase change composite material, and mix different mass fractions of phase change composite material into gypsum.
3.5 Compatibility of gypsum-based phase change energy storage materials
The phase change material is combined with the building material, and the latent heat of the phase change absorbed or released during the phase change of the phase change material is used to increase the heat storage capacity of the building material and improve the thermal inertia of the building material.
The phase-change energy storage building components currently studied use inorganic porous materials or polymer materials to encapsulate the phase-change materials at the macro level. The phase-change materials will inevitably leak during the long-term phase-change cycle, causing the building materials to be corroded and affected. The mechanical properties and durability of the building matrix; the phase change material is encapsulated in the form of microcapsules to be combined with the building components, on the one hand, the dispersion performance, heat transfer area, and heat transfer efficiency of the phase change material are increased, and on the other hand, through the micro The capsule shell material isolates the phase change material from the building matrix, avoids direct contact between the two, and greatly reduces the probability of leakage of the phase change material, which affects the performance of the building matrix.
1. Research on natural vegetation and renewable resources as fillers, such as kapok, wool, etc.
2. The development of multi-functional composite thermal insulation materials requires not only high strength, excellent thermal insulation, etc. 3. Basic performance, but also fire resistance, sound insulation, temperature adjustment, etc., which can be used in more fields.
4. Seek better packaging methods to extend the service life of gypsum-based phase change energy storage wall materials, and further improve the compatibility of phase change materials and gypsum building materials.
5. Develop organic phase change materials with higher thermal conductivity and safety, so that gypsum-based phase change building materials have better mechanical properties and durability.
6. Solve the problems of supercooling and phase separation of inorganic hydrated salt, and efficiently compound with gypsum building materials.
7. Develop the salt microcapsule phase change material with SiO2 as the wall material and use it as a building energy-saving material.
Optimization and performance of gypsum-based thermal insulation mortar mix ratio
experiment procedure
The effect of polystyrene particles and vitrified microbeads on the performance of thermal insulation materials
On the premise that the volume of the lightweight aggregate remains unchanged, the same volume of vitrified microbeads is added instead of polyphenylene particles, and the content of vitrified microbeads is 0, 0.1, 0.2, 0.3, 0.4, and 0.5 of the total aggregate volume.
With the increase in the proportion of vitrified microbeads, the dry and wet density, flexural strength and compressive strength of the composite thermal insulation mortar gradually increase, the moisture absorption rate first decreases and then increases, the thermal conductivity gradually increases, and the rising rate gradually decreases. And when the content of vitrified microbeads accounts for 0.3 of the total light aggregate volume, its dry density, flexural strength, and compressive strength gradually become stable, and the moisture absorption rate reaches the minimum. Because the particle size of polyphenylene aggregate is large and single, the accumulation effect is poor, and there are many large pores between the particles. With the addition of vitrified microbeads, instead of part of the polyphenylene particles, it can be well filled in large particles. Between the pores, thereby reducing the porosity of the mortar.
The effect of the gradation of polystyrene particles and vitrified microbeads on the porosity of thermal insulation materials
In order to study the pore structure of gypsum-based insulation materials, a stereo microscope was used to photograph the pore structure of the sample. In addition, through the use of Image-Pro Plus (IPP) software to effectively test the number and geometry of pore structures in gypsum-based insulation materials.
Microscopic pictures of different gradations of polyphenylene particles and vitrified microbeads
The influence of light aggregate content on various properties of thermal insulation materials
The content of lightweight aggregate was 85.7g, 96.4g, 107.1g, 117.8g, 128.5g, 139.2g, and the content of vitrified microbeads was 0.3 of the total aggregate volume.
As the content of lightweight aggregate increases, the dry and wet densities of thermal insulation materials gradually decrease, and the compressive strength and flexural strength decrease. The rate of decline slows down when the lightweight aggregate exceeds 107.1g, and the moisture absorption rate gradually increases. The thermal conductivity decreases gradually. When the lightweight aggregate content is 117.8g, the dry density of the insulation material is 378.9kg/m3, the flexural strength is 0.67MPa, the compressive strength is 0.84MPa, and the thermal conductivity is 0.0707 W/(m· k).
Combining vitrified microbeads and polystyrene particles to prepare a gypsum-based lightweight ground insulation material can improve the aggregate gradation, thereby increasing the strength of the gypsum insulation mortar. Combining the strength and dry density of the composite thermal insulation mortar, combined with the pore structure, the appropriate amount of vitrified microbeads should account for 0.3 of the total lightweight aggregate volume.
As the content of lightweight aggregate increases, the dry and wet densities of thermal insulation materials gradually decrease, and both compressive strength and flexural strength decrease. When the content of lightweight aggregate exceeds 107.1, the rate of decline slows down, and the rate of moisture absorption increases. When the light weight aggregate content is 117.8g, the dry density of the insulation material is 378.9kg/m3, the flexural strength is 0.67MPa, the compressive strength is 0.84MPa, and the thermal conductivity is 0.0707 W/ (m·k).
