Lightweight concrete is a kind of lightweight porous material which is made by adding chemical foaming agent in cement slurry and using its chemical reaction to produce gas, thus introducing a large number of tiny bubbles into slurry.With the improvement of building energy conservation standards, Lightweight concrete such as foam concrete has high thermal conductivity, although it is fireproof, which leads to the gradual increase of insulation board design thickness, easy to produce empty drum cracking, serious insulation layer will fall off, external insulation cracking, seepage, fall off and other quality problems.
As the lightest solid material, aerogel has a thermal conductivity of less than 0.013 W/(m•K), which is one of the materials with the lowest thermal conductivity in the field of high temperature insulation. Aerogel itself is non-combustible and has excellent fire resistance.
The preparation process of lightweight concrete is as follows: 1. Add water, and aerogel, fiber, water reducer, etc. Disperse evenly, then add cement, stir 2 min~3 min to uniform, finally add coagulant, foaming agent, stir 20 s~30 s, make paste;(3) step 2 made of paste into the mold, stop 4 h~6 h to remove the mold, 24 h after cutting.
1. Influence of aerogel content on apparent density of lightweight concrete
The stacking density of aerogel is very low, and the addition of direct admixture will significantly reduce the apparent density of inorganic foaming insulation board, leading to a significant decline in compressive strength and other properties.Through adjusting the dosage of foaming agent, foam height reaches 1 m3 or slightly higher than 1 m3, as the dosage of aerogel increase gradually, gradually reduce the dosage of foaming agent, guarantee the foam height consistent, so the apparent density changes very little preparation of lightweight concrete, with the increase of the dosage of aerogel outside, per cubic meter of lightweight concrete increases slightly, the weight of the powder preparation of lightweight concrete apparent density also increases slightly.
2.Effect of aerogel content on thermal conductivity of lightweight concrete
With the increase of aerogel content, the thermal conductivity of lightweight concrete first decreases and then increases. When the aerogel content is 120 L/ m3, the thermal conductivity reaches 0.056 W/(m•K) at the minimum.With the gradual increase of aerogel content, the stacking density of aerogel is very low. In order to ensure the basically consistent foaming height, the content of foaming agent gradually decreases, and the porosity of lightweight concrete gradually decreases.When the content of aerogel is low, the reduction of the content of foaming agent reduces the number of pores introduced into lightweight concrete, improves the porosity stability of lightweight concrete, and increases its closed porosity rate. At the same time, the addition of aerogel reduces the density of pore wall material, improves its thermal insulation performance, and further reduces the thermal conductivity.As the content of aerogel continues to increase, the number of pores in lightweight concrete significantly decreases and the thickness of pore wall increases. When the improvement of aerogel's thermal insulation performance on pore wall is not better than the increase of thermal conductivity caused by the decrease of the number of pores, the thermal conductivity changes from reduction to increase.
3. Influence of aerogel content on water absorption of inorganic foam insulation board
With the increase of aerogel content, the water absorption rate of lightweight concrete decreases gradually. The water absorption rate of lightweight concrete without aerogel is 9.5%, while that of lightweight concrete with aerogel content of 200 L/m3 is 7.4%, which decreases by more than 20%.Analysis of its reasons include the following three aspects: (1) aerogel has a strong hydrophobicity, reduce the water absorption of materials;(2) after the addition of aerogel, the content of foaming agent decreases, which improves the porosity stability of lightweight concrete and increases its obturation rate.(3) with the increase of aerogel content, the number of lightweight concrete pores decreased, the thickness of the hole wall increased, can better prevent moisture into the lightweight concrete internal pores.
4. Influence of aerogel content on compressive strength of inorganic foaming insulation board
With the increase of aerogel content, the compressive strength of lightweight concrete first increases and then decreases. When the aerogel content is 80 L/ m3, the compressive strength reaches a maximum of 0.60 MPa. The variation trend of compressive strength is basically opposite to that of thermal conductivity.The favorable factors of compressive strength include: (1) after adding aerogel, the content of foaming agent decreases, improving the stomatal stability of lightweight concrete, increasing its obturation rate, and decreasing the proportion of hole breaking and penetrating.(2) with the increase of aerogel content, the number of pores of lightweight concrete decreases and the thickness of pore wall increases.Adverse factors of compressive strength include: (1) aerogel incorporation reduces the density of pore wall materials, resulting in decreased bearing capacity of pore wall materials, and (2) aerogel incorporation leads to an increase in water consumption.When the content of aerogel was low, favorable factors played a dominant role and the compressive strength increased. However, with the increase of the content of aerogel, the influence of unfavorable factors was greater than that of favorable factors and the strength gradually decreased.