The main reasons are as follows:

(1) The surface of the formwork is not smooth, and there are dry and hard cement paste blocks and other impurities.

(2) The wood formwork is not fully wet before the concrete is put into the formwork.

(3) The release agent of steel formwork is not evenly applied.

(4) The joint of the formwork is not tight, and the pouring concrete runs away.

(5) The thickness, spacing and position of cushion block of steel bar protection layer are improper.

(6) The slump and workability of concrete are not good.

(7) Improper vibration during concrete pouring.

(8) The concrete pouring height exceeds the specified requirements and no measures are taken, resulting in concrete segregation.

(9) The concrete formwork is removed too early.

The prevention and control measures are as follows:

(1) The pockmarked parts shall be washed with clean water, and then plastered with cement slurry or 1:2 cement mortar after being fully wetted.

(2) Clean the concrete and rust on the exposed reinforcement, and then use 1:2 cement mortar to smooth. If the exposed reinforcement is deep, the weak concrete shall be removed, cleaned up, compacted with a higher grade of pea stone concrete, and carefully maintained.

(3) Small honeycomb can be washed with water and repaired with 1:2 cement mortar; for large honeycomb, loose stones and protruding particles shall be removed first, and rounded into bell mouth, and then cleaned and soaked with water, and then compacted with a higher grade of pea stone concrete, and then carefully maintained.

(4) The hole treatment needs to study and formulate the reinforcement scheme together with the design unit, and then deal with it according to the approved scheme. When dealing with the hole in the beam, the support shall be used at the bottom of the beam, and then the uncompacted concrete at the hole shall be chiseled out to form an inclined shape (with the outer opening upward) for pouring concrete. Wash it with clean water and keep it moist for 72h, then pour and tamp the slightly expanded pea stone concrete with a higher grade, and then maintain it carefully. Sometimes, due to the large hole, it is necessary to support the formwork before pouring concrete.