The causes and solutions of poor pumpability of concrete leading to bottom scratching or hardening

1. Causes of occurrence

(1) The mix proportion selection does not meet the requirements of the pumping process for the workability of concrete.

(2) The amount of cement used is relatively low.

(3) The gradation of sand and stone is unreasonable, and the void ratio is large.

(4) If the sand ratio in the mix proportion is too small and the slump is too large, the concrete is prone to segregation.

(5) Concrete with severe bleeding is prone to scratching the bottom or hardening (sticking to the pot).

(6) Concrete with a large amount of cement is prone to the phenomenon of scratching the bottom.

(7) Concrete with a large amount of admixtures is prone to the phenomenon of scratching the bottom.

(8) A low sand content makes concrete prone to hardening.

(9) Concrete with admixtures that have a high water reduction rate, high bleeding rate, and poor water retention, thickening and air-entraining effects is prone to bottom grasping or hardening.

2. Solutions

(1) Reduce water consumption per unit.

(2) Increase the sand ratio.

(3) Add an appropriate amount of admixtures such as fly ash to reduce the cement usage.

(4) Reduce the dosage of concrete admixtures.

(5) Enhance the air-entraining, thickening and water retention functions of concrete admixtures.