How to reduce cracks in foam concrete

Foam concrete is a new class A thermal insulation material developed in recent years, which has the advantages of non-toxic, non-combustible, good thermal insulation performance, etc., and has been widely used in the thermal insulation of internal and external walls of buildings and roof insulation

Fire insulation on the outer floors of buildings and buildings. The production methods of foam concrete mainly include physical foaming and chemical foaming. The chemical foaming process is easy to operate and is mostly used in the production of foamed concrete products. However, the existing production process often makes the foaming process non-uniform, and cracks often appear.

Measures to reduce cracks in foam concrete

(1) Using wood to make a mold for pouring foam concrete

A mold for pouring foam concrete is made of wood, and the inner wall of the mold is evenly covered with plastic film. The flat plastic film can reduce the resistance of the side of the mold to the expansion of the slurry, so that the height of the middle of the slurry and the edge are similar, and the uniformity is improved.

(2) Adding a wooden mold upper pressure plate

The addition of a wooden mold upper pressure plate can make the entire mold have a better thermal insulation effect, thereby reducing the temperature difference of each part of the slurry. Normally, when the foam concrete slurry expands by gas, the upper surface is exposed, and the surface temperature of the slurry is lower than the internal temperature, which is easy to produce temperature difference cracks. The upper pressure plate is made of 10-30mm thick plywood. Its thermal conductivity is similar to that of other parts of the mold, and it has a certain thermal insulation effect. At the same time, it can make the temperature of the slurry more uniform, thereby reducing the temperature difference of the slurry. On the other hand, after adding a wooden upper pressure plate, when the foam concrete slurry is poured into the mold, the slurry expands beyond the height of the mold within a few minutes, it will be hindered by the pressure plate, and a certain pressure will be generated on the surface of the slurry, so that the foam concrete The force of the slurry is more uniform during the foaming, setting and hardening process, which ultimately greatly reduces the chance of cracks after hardening.

(3) Balanced pressure plate method

The balanced pressure plate method is to apply a pressure plate (plywood) with a thickness of more than 10 mm and a side length not less than the casting mold on the surface of the foam concrete slurry. By evenly arranging sandbags or blocks on the pressure plate as a load

Load, sandbags or blocks and the weight of the pressure plate will exert pressure on the upper surface of the foam concrete slurry, as shown in Figure 5. The surface pressure should be controlled at 0.2 ~ 0.8 kN / m2. After 10 ~ 200 min of slurry condensation, the pressure plate and the load on it are removed, the mold is removed after curing, and the finished drawing of the foamed concrete board is prepared after cutting and packaging. A certain pressure is given to the top surface of the unhardened foam concrete blank to balance the slurry foaming. The stress in the process can reduce the horizontal cracks located 100 to 150 mm below the top surface of the foamed concrete, and can basically eliminate the pouring. The surface presents the phenomenon of high material in the middle and low material in the edge, reducing the amount of waste after cutting.