Factors affecting the strength of cast-in-place foam concrete

The introduction of voids in the lightweight of cast-in-place foam is intended to impart lightness, sound insulation, thermal insulation and high flow. However, from the point of view of structure and mechanics, a large number of defects have also been introduced, resulting in a greatly reduced strength of the hardened foam concrete. Since the porosity of foam concrete is usually as high as 50-70%, the strength of foam concrete is much lower than that of ordinary concrete.

Like ordinary concrete, the strength of foam concrete is not a fixed value. Different types of cementitious materials, cement content, concrete mix ratio, water to cement ratio, foam amount, foaming agent, curing system and other admixtures are used, all these things affect the strength of foam concrete.

1. The effect of the mix ratio. If cement is used alone to prepare foam concrete, the strength of the foamed concrete increases with the increase in the strength grade of the cement used. However, in actual construction, it is often necessary to add admixtures such as fly ash, silica fume, slag, and sand. The addition of the mixed materials leads to a decrease in the early strength of the foamed concrete, but has little effect on the late strength. If an activator is simultaneously introduced, the loss of early strength can be alleviated to some extent. When sand is used as a fine aggregate, it generally does not cause a decrease in the strength of the foamed concrete, but is rather advantageous for volume stability and shrinkage reduction.

2. The effect of water to cement ratio. If only the internal structural changes of the foam concrete are analyzed, an increase in the water-cement ratio will inevitably lead to a decrease in strength. However, a large number of experiments have shown that when the water-cement ratio increases within a certain range, the strength does not decrease, but increases. This is because the preparation of foam concrete has a process of mixing the foam.

If the foam is evenly distributed in the system, the slurry needs to have good fluidity and a higher water to cement ratio is required to ensure good fluidity. However, in the case of a low water to cement ratio, appropriate measures can be taken to ensure good fluidity of the cast-in-place foamed concrete, thereby producing a high-strength bubble-mixed foam concrete.