More than 1/3 of the total energy consumption of the whole society comes from building energy consumption. In the current situation of resource shortage, it is imperative to reduce the energy consumption of new buildings.The traditional way to reduce the energy consumption of buildings is to use rock wool, foam materials, polystyrene board, polyurethane board, etc. These materials are either of high thermal conductivity, not good energy saving effect;Or poor fire protection, creating other risks for the building.The invention of silica aerogel material opens a new way for building energy conservation.
Silica aerogel is a new kind of nanomaterial with porous network framework structure and large specific surface area. Inside the material, there is more than 90% volume of air with very low density.Aerogel material has very low thermal conductivity, and it is used as a building material, which has the advantages of light weight and good energy saving effect.
1. Advantages of silica aerogel energy saving materials
The reason why silica aerogel energy-saving materials are able to develop rapidly and attract the general attention of scholars from different countries has its outstanding advantages, which are mainly reflected in the following:
First, good insulation effect. Silica aerogel materials have high porosity.There are three types of heat transfer in silica aerogel materials: (1) Low conductivity. Silica aerogel has low density and high porosity, and its structural characteristics extend the heat propagation path in the material, greatly reducing the heat transmission efficiency, and its heat conductivity is 0.2% of that of solid homogeneous materials.(2) Convection.The colloidal particle size of silica aerogel materials is less than 20 nm, less than 1/3 of the average free path of air molecules (about 70 nm), which greatly restricts the free movement of air molecules inside silica aerogel materials, and greatly reduces the convective thermal conductivity of air.(3) Radiation.The thermal radiation of silica aerogel is repeated with the wavelength of infrared light, which can hedge most of the infrared radiation, shielding the thermal radiation, and the thermal conductivity of radiation is very low.Therefore, the overall thermal conductivity of silica aerogel is very low, which is usually between 0.01 and 0.03w /(m•K) at room temperature under atmospheric pressure. It is the lowest among known solid materials and has a good thermal insulation effect.
Second, silica aerogel has low density.The density of silica aerogel materials is between 0. 16 and 4.0 kg /m3, while the density of air is 1.29 kg /m3, wood is 0.5 ×103 kg /m3, and steel is 7.9×103 kg /m3.
Third, high transparency. Silica aerogel is a nanoscale porous colloid material, with a long average free path of light and almost zero thermal reflection. It can penetrate sunlight and reduce infrared radiation at low temperature. It can be used in solar energy collection system to significantly improve heating efficiency and reduce heat loss.
In addition, silica aerogel also has significant advantages in acoustic insulation, fire prevention, corrosion resistance and aging resistance. It is a new type of building energy-saving material with safety, energy saving and environmental protection.
2. The role of silica aerogel in mortar and concrete
Traditional mortar and concrete are basic building materials with bonding ability formed by adding cement, fine aggregate or aggregate and water, with high density and almost no thermal insulation performance. Adding silica aerogel with low thermal conductivity into traditional mortar and concrete can make up for this defect.
How to apply silica aerogel in mortar and concrete？
Make gels with Portland cement, adding SiO2 aerogel and glass beads, made silica aerogel insulation mortar, glass beads is greater than the size of the silica aerogel particles size, the larger the size of the glass beads filling in mortar matrix, the small size of the silica aerogel particles further fill the space of glass beads, effectively reduce the thermal insulation mortar of porosity, the significant increase in the path of heat through the heat preservation mortar, sharp decline in coefficient of thermal conductivity, heat preservation performance improved significantly.Apply insulation mortar on the exterior wall surface of the building, and use analysis software to simulate the insulation performance. When the outdoor temperature is 38 ℃ in summer, the indoor temperature is only 23 ℃.When the outdoor temperature is -16 ℃ in winter, and the indoor temperature is 15 ℃, the greater the thickness of the insulation mortar, the greater the temperature difference between indoor and outdoor, it can be seen that the silica aerogel insulation mortar hinders the diffusion of heat, and the insulation energy saving effect is obvious.According to the analysis of its economic and social benefits, for a 24-story building, the use of insulation mortar with a thickness of 30 mm can save 50% of energy consumption a year, save the heating and cooling cost of 594 yuan, and reduce CO2 emissions by nearly 4 t, thus protecting the atmospheric environment.
When silica aerogel is added to concrete, it can not only reduce the quality of concrete, but also reduce the thermal conductivity. However, the addition of silica aerogel will damage the mechanical strength of concrete, so silica aerogel concrete is usually used on non-load-bearing walls.
Silica aerogel material has unique physical and chemical properties due to its special microstructure, especially its very low thermal conductivity, which makes it have a great application prospect in the construction industry. Silica aerogel is added to mortar and concrete to improve the effect of energy conservation and heat preservation from the basic skeleton structure of buildings.The organic or inorganic composite modification of pure silica aerogel can improve the comprehensive properties of composite materials and yield higher economic and social values.
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