Unreasonable aggregate grading
If there is too much coarse aggregate, there is little fine aggregate, or the grain shape is not good, and the sand rate is small. As a result, the fine aggregate cannot fill the pores of the coarse aggregate and form bubbles. Additives and cement and admixtures
Decrease in cement, increase in water consumption and free water, but if too much admixture will increase the viscosity of concrete, so that bubbles are not easy to discharge.
For the treatment measures of concrete bubbles, select the appropriate vibrating equipment, and determine the appropriate vibrating time, vibrating radius and frequency. At the same time, vibrate according to the method of "fast insertion and slow pumping, up and down drawing", the vibrating rod should be straight up and down, Quickly insert and pull slowly, no leakage is allowed. When vibrating, it should twitch up and down. The duration of each vibration point is based on the appearance of scum on the surface, so as to expel the air bubbles.
Strictly prevent the occurrence of under-vibration, leakage and over-vibration of concrete. Strengthen the cleanup of the template, select the release agent and strictly control its quality, and no oily release agent should be used. During the construction process, apply the release agent evenly, but not too much, so as to avoid the phenomenon of accumulation and flow.
Concrete should be poured in layers, and the layer thickness (referred to as the thickness after tamping) should be determined according to conditions such as mixing and transportation capacity, pouring speed, vibration capacity and structural characteristics. The large paving thickness of pumped concrete should not be greater than 600mm, and the thickness of other concrete paving should not be greater than 400mm.
Strictly choose aggregates, and control the size of aggregates and the content of needle flakes, carefully select when preparing materials, and discard unqualified aggregates. Determine a reasonable gradation to make the ratio of coarse aggregate to fine aggregate moderate. Choose admixtures and cement with uniform and stable distribution and excellent chemical composition.
In actual production, the compatibility test of cement and admixture should also be carried out, and then the materials with better matching should be selected for production. In addition, it should be noted that the workability of concrete should not be blindly pursued to ensure that the admixture is not excessive.