Cracks in the leveling layer of bridges under construction in expressway are very common, especially in the bridge deck pavement and the construction of extra-large bridges, which have not attracted enough attention from quality supervision departments to some extent. On the one hand, it may be tiny cracks, on the other hand, it may be tiny cracks, which are difficult to completely eliminate. This may be the reason why the management department or the construction unit did not pay attention to it.

If the cracks are not treated in time or eliminated, they will be refracted to the asphalt concrete surface with repeated rolling by heavy vehicles, and then cracks will be formed on the oil surface. Once they are soaked in water, they will crack and even seriously damage the oil surface, greatly reducing the service life of the oil surface. The analysis of pavement cracks mainly starts from the following aspects.

Uneven top surface of beam and slab leads to uneven thickness of leveling layer, which leads to different shrinkage degree of concrete with different thickness during solidification, and cracks are formed by itself. If the paving thickness is uniform, the flatness of beam-slab roof should be controlled first, which involves the overall construction level of a construction unit. Not only are the top plates of beams and slabs even and flat, but the tensioning sequence is consistent, the Zhang Lala force is standardized, and the length of pre-storage period is strictly controllable—that is, the pre-storage period cannot be too long after grouting, otherwise the arching of beams and slabs will be too sluggish and the camber of adjacent beams and slabs will be too large, resulting in uneven thickness of bridge deck pavement.

The paving thickness of leveling layer is too thin. Due to the poor flatness of beam-slab roof, different pre-camber, the overall flatness is poor, but in the process of paving concrete, only the average thickness can be guaranteed-generally the paving thickness is 80mm (less than 90mm), and in order to consider the overall construction, the minimum thickness should not be less than 60 mm-if it is less than this thickness, the beam-slab roof will be damaged by heavy load.

Maintenance is not standardized. The irregular maintenance after paving mainly reflects that the geotextile for maintenance is not covered in time, or the geotextile is not evenly distributed in time, which makes the early strength lack of water and causes cracks. If the general construction unit pays attention to this point, this problem can be overcome. Generally speaking, the regimen is 7 days, at least 3 x 24 hours (influenced by climate and temperature).

The concrete gradation is unreasonable. Concrete gradation is mainly due to less coarse aggregate and more fine aggregate, and unreasonable aggregate gradation does not bend, which is also related to the uniformity of feeding, feeding and mixing time in the mixing station. This can only be overcome by close cooperation between mixer operators in the foreground and background and testers and inspectors.

Connect the heavy car too early. Due to the urgent construction period, after the completion of construction, when the strength is not equal to 3x24h or the curing strength is less than 70%, the construction vehicles will pass from above. It is particularly important to note that heavy vehicles will suddenly brake or even turn around on the leveling layer, causing damage to the pavement with insufficient strength-causing cracks. This is a problem of construction organization.

The protective layer of steel bar is too large. Generally, the qualified rate of reinforced protective layer on pavement can exceed 30%, which is a good construction level. It is difficult to really standardize the protective layer (design protective layer), which has a lot to do with the construction arrangement. Because half of the bridge deck requires paving and molding at one time, and there can be no joints in the middle, it is inevitable that heavy vehicles pulling concrete in front will be crushed on the paved steel mesh, and then concrete will be laid-it is difficult to make the steel mesh with good support support support again. It is often that the steel mesh sticks to the top plate of the beam and slab, especially the mesh in the middle lane, which leads to too large a protective layer, which is not even a protective layer. If the concrete is laid in other ways-concrete pump truck, ground pump, trolley, etc. , limited by slump and laying time. Reinforced protective layer is a subject worthy of study, and interested construction unit enthusiasts can further study it.

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