The early strength growth of foamed concrete is slow, generally reaching 30% of design strength in 3 days, 50% of design strength in 7 days, and 70% of design strength in 15 days. Therefore, early maintenance of foamed concrete is particularly essential. Usually, after the pouring of the foamed concrete, the curing with the mold is mainly used, and the watering curing is supplemented to keep the surface of the foamed concrete moist. The curing time is not less than 14d. Do not use water directly on the exposed surface of newly poured foam concrete. For convenience, the entire curing process of foamed concrete is divided into two stages, initial curing and wet curing. The initial curing should start immediately after the freshly mixed foamed concrete is poured, and the damp curing starts after the concrete is finally set.
1 Routine maintenance
Foam concrete maintenance should pay attention to two aspects of humidity and temperature. Conservation is not only watering and moisturizing but also to control the temperature change of concrete. While wet curing, it should be ensured that there is no excessive difference between the surface temperature of the foamed concrete and the internal temperature and the atmospheric temperature. Taking comprehensive measures of heat preservation and heat dissipation can prevent the temperature drop and temperature difference from being too large.
Foam concrete is usually cured by spraying water or retaining water or covered with wet sand and wet sacks. Foamed concrete poured in cold weather is generally kept moist using steam delivery in a sealed enclosure. Moisturizing foamed concrete under sun and sun protection conditions are often more effective than sprinkling water onto the exposed surface of the foamed concrete. Sealing film curing (impermeable plastic film or film formed by curing agent) is an excellent thermal insulation curing method when the water source is insufficient. Still, it should be noted that the surface of the foamed concrete must be in a saturated state before the film is sealed.
After removing the formwork or removing the insulation protection, if the surface temperature drops suddenly, the foamed concrete may generate cracks. Only when the temperature of any part of the foamed concrete is gradually decreasing, can the protection be removed. Large-volume foamed concrete cannot be cooled too quickly, because when there is a temperature difference between the inside and outside of the foamed concrete, there is a high possibility that the foamed concrete on the surface of the quenched surface will crack. When the foam concrete adopts dry heat insulation, sufficient water must be added.
2 Maintenance in a hot environment
Compared with ordinary concrete, the strength of foamed concrete is prolonged. But in the later period, it is not ideal for maintaining foamed concrete with high temperature. According to the size of the component, cement content, water-binder ratio, environmental conditions, and hot conditions, it is necessary to take the following measures to control the temperature of the foamed concrete during the curing period: (1) reduce the pouring temperature of the foamed concrete; (2) cover Materials with excellent thermal insulation performance; (3) foamed concrete should be poured at low temperature; (4) the exposed surface of newly poured foamed concrete should be covered.
3. Low temperature (negative temperature) environment maintenance
Natural curing of foamed concrete at low temperatures should be covered with opaque plastic film or sprayed with curing fluid. When curing under adverse temperature conditions, watering is not allowed. After pouring the foamed concrete, it should be covered with plastic film and insulation materials such as straw or hay for insulation to prevent the concrete from freezing. Insulation blankets made of glass fiber, sponge rubber, cellulose, mineral wool, vinyl foam, and polyurethane foam are more effective. In cold weather conditions, additional heat is required to maintain the temperature of 10 ℃ ~ 15 ℃, so that the temperature is conservative, you can use heating coils, portable circulating heaters or steam to provide the required heat.
To sum up the maintenance in all the situations mentioned above, the loss of moisture in the foamed concrete should be avoided. To ensure the loss of water in the process of hydration heat of foamed concrete cement, cracks were caused by uneven heating of the adhesive's hydration heat.