To strengthen the quality control of returned concrete treatment, in order to achieve a scientific and reasonable use of returned concrete, reduce waste and increase efficiency.
The concrete returned to the station should first consider the use of reduced grade.
When cannot reduce the grade to use, should distinguish the reason according to the situation, judge the performance of concrete, and then carry on the reasonable treatment.
Slump too large or too small
If the slump is too large (or segregation), dry material or thick mortar with the same ratio should be added according to the actual situation, and the quick stirring should be no less than 90s.
After checking that there is no dry material block, the slump meets the design requirements, and the actual water-binder ratio is not greater than the theoretical water-binder ratio, which can be discharged from the station.
If the slump is too small, cement should be appropriately added, then admixture added, and forced mixing until the slump reaches the outbound requirements.
The concrete is discharged due to construction reasons
For the returned concrete caused by transportation, pumping, pouring and other reasons, the tank truck driver should weigh the concrete first, and the quality inspector should calculate the remaining square amount according to the weighing sheet provided by the tank truck driver and the tare weight of the tank truck.
Then, according to the same grade or lower grade, the following treatment methods should be adopted:
Use of the same grade
Delay time within 2H, after treatment should ensure that the amount of cement than the original mixing ratio increased by 10 ~ 15kg/m3, admixture increased by 0.1% to 0.3%. Or directly reduce a strength grade, appropriate increase admixture amount to adjust.
Delay time in 2 ~ 4h, after treatment should ensure that the amount of cement than the original mixing ratio increased by 20 ~ 40kg/m3, admixture increased by 0.4% to 0.6%. Or directly reduce the two strength levels, appropriate increase the amount of admixture to adjust.
In the initial setting time of concrete, due to the higher temperature, longer transport distance, longer time caused by concrete slump loss, can be added through the test of the same model
