Strengthen the quality control of the returned concrete treatment to achieve scientific and rational utilization of the returned concrete, reduce waste and increase efficiency. The concrete returned to the station shall be first considered for use with a lower grade. When it is impossible to reduce the grade for use, the reasons should be identified according to the situation, the performance of the concrete should be judged, and then reasonable treatment should be carried out.
Too much or too little slump
If the slump is too large (or segregated), the dry material or thick mortar of the same proportion should be added according to the actual situation, and the rapid stirring should not be less than 90s. After inspection, there is no dry material block, the slump meets the design requirements, and the actual water-to-binder ratio No more than the theoretical water glue ratio can be out of the station. If the slump is too small, the cement should be added appropriately, and then the admixture should be added, and forced stirring until the slump reaches the exit requirements.
Concrete return due to construction reasons
Concrete returned due to various reasons such as transportation, pumping, pouring, etc., is first weighed by the tanker driver. The quality inspector calculates the remaining amount according to the weighing list provided by the tanker driver and the tare weight of the tanker, and then according to the same grade or lower grade. Use the following processing methods:
Use at the same level
If the delay time is within 2 hours, the cement dosage should be increased by 10-15kg/m3 and the admixture should be increased by 0.1% to 0.3%. Or directly reduce a strength level, and appropriately increase the amount of admixtures for adjustment. The delay time is 2 to 4 hours. After treatment, the amount of cement should be increased by 20 to 40 kg/m3 compared with the original mixing ratio, and the admixture should be increased by 0.4% to 0.6%. Or directly reduce the two strength levels, and appropriately increase the amount of admixtures for adjustment.
During the initial setting time of the concrete, the slump loss of the concrete is large due to the high temperature, long transportation distance, and long pressing time. The total amount of the admixture that has been added cannot exceed 20% of the maximum amount of the admixture. It should be added gradually, add less first, and after mixing, the mixer truck rotates quickly for about 2 minutes, and the slump is measured to meet the requirements. The concrete transported to the site cannot be unloaded immediately, and the transporter should be quickly turned for 2 minutes before unloading to ensure slump and quality. Concrete that exceeds the initial setting time should be discarded and cannot be reused. The longer the stagnation time before concrete pouring, the more serious the loss of concrete strength, which should be paid enough attention.
Admixture adjustment
Post time: Jul-18-2022