The fracture of pavement concrete slab mainly occurs in longitudinal continuous pouring, and the cracks are generally parallel to the transverse contraction joints and are corrugated. The main causes of steel plate fracture are:
A) when continuous casting, the kerf is not timely, and the concrete shrinks and breaks in the process of condensation and hardening;
B) Construction is interrupted for a long time after concrete pouring, which leads to uneven contraction and fracture of joints;
C) Uneven shrinkage cracks caused by large difference in water-cement ratio of the same section during casting;
D) Reflective cracks during the construction of "covering layer" of old pavement;
E) Pavement base is rigid or semi-rigid, and cracks have appeared due to foundation settlement or temperature difference. In addition, the construction surface of the base is uneven and unsmooth, which limits the free expansion and contraction of the concrete slab, and the concrete laid on this base is easy to break at the cracks of the base;
F) When pouring "filling the warehouse", the temperature stress will cause the concrete at the position where the false joint of the embedded concrete slab has been broken to shrink and displace, which will cause tensile stress to the newly poured concrete, thus causing the newly poured concrete to break at this position.
Preventive measures for steel plate fracture
The fracture of airport cement concrete pavement slab directly affects the appearance, performance and economy of pavement, so it is particularly important to prevent the fracture of concrete pavement slab. The following preventive measures can be taken during construction:
A) timely sewing. For the concrete poured in the morning, when the construction temperature is high, the false joints should be cut off before the lowest temperature comes that night. If it is too late to cut them all off, a seam should be cut every 10 ~ 15m to reduce the shrinkage spacing of concrete.
B) In hot season, night construction measures can be adopted, especially the "covering" construction of old pavement. Construction measures at night combined with sprinkling water on the old pavement can effectively avoid the occurrence of reflection cracks.
C) The old pavement shall be directly covered, and the new and old pavements shall be welded in strict accordance with the design requirements; Before "covering", apply appropriate pre-covering repair technology to repair any kind of damage that can be found in the original old pavement, then pour concrete and do a good job of heat preservation and maintenance.
D) During pouring and filling, isolate the previously laid concrete false joints with two layers of linoleum, or set up construction joints in this part.
E) When the concrete pouring is interrupted for a long time due to unexpected reasons, construction joints should be set at the joints, and it is not allowed to continue pouring at other positions of the slab.
F) Strictly check the quality of grass-roots construction. Those who fail to pass the acceptance shall not carry out surface construction, and lime is strictly prohibited at the lime-soil base.
G) Before paving concrete at semi-rigid base, pave leveling layer at base. Only after passing the inspection can concrete be paved.
H) Strictly control the water-cement ratio to ensure that the mixture is evenly stirred.