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.