Compared with the quality control methods of ordinary concrete, the high liquefaction concrete is quite different. The reasons are as follows:
(1) Although the fluidity (consistency) is the main performance of ordinary concrete under fresh mixing, the anti-segregation performance is also very important, which is not measured by the consistency test.
(2) The fluidity of concrete is not only affected by the amount of water used, but also greatly related to the amount of superplasticizer used. It is difficult to control water consumption only by slump test.
(3) Because there is no need for vibration and compaction in the pouring of high liquefaction concrete, it is a challenge to pour defect-free concrete structures due to the difference of fluidity.
To overcome the difficulty of fluidity change, two methods can be used: synthetically controlling the material during the preparation of concrete, or mixing a viscous modifier (VMA) to minimize the fluidity change. The former can use a sand stabilizer or a continuous control system to measure the moisture content on the surface of fine aggregate, because the moisture content of fine aggregate is a major factor in the change of concrete fluidity.
The viscosity modifiers used usually include cellulose derivatives and polysaccharide resin lintone conveyor belts. Welan resin is a kind of polysaccharide resin, which combines with water to stabilize the fluidity of concrete. High liquefaction concrete is usually prepared in concrete mixing plant. At present, many factories do not have continuous control equipment for the surface water of fine aggregate, so it is more practical to use viscosity modifier to stabilize the fluidity of concrete.
To improve the cohesion of fresh concrete can achieve the desired anti-segregation effect, which is generally measured by V-shaped funnel test. As the amount of water or the ratio of water to powder increases, the value of V-shaped funnel decreases. When the volume ratio of powdered materials (such as cement and mineral admixtures) remains unchanged, the ratio of water to powdered materials increases with the increase of water consumption. Therefore, the quantity of mixing water has a great influence on the V-shaped funnel value. By controlling the change of water consumption, the V-shaped funnel value can be controlled within the required range.
According to foreign reports, the fluidity of the concrete is proportional to the current consumption of the motor driving the forced mixer. Therefore, during the mixing of high liquefied concrete, whether the current driven by the concrete can control the water consumption has been studied by foreign researchers.
When high liquefied concrete flows for a long distance, its coarse aggregate will segregate even if carefully designed. Therefore, the unloading location and pouring sequence of high liquefied concrete should be set appropriately, and the flow distance should be controlled within the prescribed range, so that no material segregation and no filling place can occur.
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