Example 5: Repeated pipe blockage caused by failure of 01315mm sand particles
Machine-made sandstone powder (referred to as powder below 75μm), reaching 3312%. In order to meet the particle grading requirements, the crushed stone plant will wash the machine-made sand with water, and the powder will be washed away by water to make the fine particles 01315mm sieve pass the sieve residual value 5%. At first, we did not pay enough attention to this situation. The average particle size of the sand increased by 2%, but the pumpability did not improve, and the phenomenon of pipe plugging increased under the same conditions. By testing sand with a high content of stone powder, the strength has not decreased, but has been improved.
The effect of fine aggregate on the pumpability of concrete is greater than that of coarse aggregate, and it flows smoothly in the concrete transportation pipe, because the mortar lubricates the pipe wall. Coarse aggregates are always suspended in the mortar, so fine aggregates are required to have a good particle gradation. After washing with water, 300μm and 150μm, up to 75μm and the fine particles at the bottom of the sieve, most of the fine particles of 01315mm are removed, while The gradation becomes coarser, and it is not the soil but the fine particles that are removed. The content is too low, and the lubricating pipe wall slurry is reduced. When the material passes through the bent pipe, the coarse aggregate changes from the position suspended in the slurry to the slurry that is close to the wall of the pipe. It first blocks when passing through the elbow or the variable pipe, and the pumpability is not good. The 01315mm stone powder in pumpability is very important in fine aggregate.
By adjusting the gap between the crushers, the crushed raw river pebbles were washed into the crusher after being washed with water. The mud content was calibrated with methylene blue to be 1104, and the residual amount of 01315 sieved particles reached 2115%.
Example 6: PH value of admixture affects pumping
When the concrete slump is at the same grade and the same admixture, sometimes the pumping effect is poor, and sometimes the pumping effect is good. For example, on the second floor of a commercial residential building, the No. 1 warehouse 3215 cement is used up, and the No. 2 warehouse is used. The same day, the same location, the same grade of cement label, W / C, and the mix ratio have not changed, but the cement is not in the same batch. In the plant, the slump immediately becomes smaller, making pumping difficult.
After investigation, the C3A of the cement is basically the same, except that the pH value of the admixture changes from partial alkali to acid, and the temperature of the concrete rises by 215 ℃. Our analysis is that the high alkaline cement meets the acid admixture. Thermal acceleration accelerates slump loss.
Therefore, the admixture should be tested by the PH value to determine the admixture: ①Cement C3A is below 8, mixed according to the normal recommended amount. ②Cement C3A increased from 011 to 015 in 8-9. ③ If the C3A of the cement is higher than 9, it will increase by 013%. This greatly reduces slump fluctuations and reduces the number of deployments on site. The total amount of admixture should not exceed 3%, and concrete condensation will occur abnormally if it exceeds 3%. The use of standard sand mortar fluidity to control the admixture quality is more in line with the actual concrete. The mortar fluidity is controlled between 170-210mm, and the clean slurry fluidity is controlled above 220mm.