After concrete pouring is completed, it should be cured in time, and curing agent can be sprayed or covered with moisture. Wet maintenance methods such as moisturizing film, geotextile, sack, straw bag and straw curtain can be used in rainy days or when there is sufficient water for maintenance, and water enclosure maintenance is not suitable; For concrete slabs constructed in areas where the temperature difference between day and night is greater than 10℃ or the daily average temperature is lower than 5℃, thermal insulation and maintenance measures should be taken. The curing time should be determined according to the growth of concrete flexural strength, which should not be less than 80% of the design flexural strength, and should generally be L4 ~ 21d. Pay special attention to the moisturizing (warm) curing for the first 7 days.

Technical points of paving asphalt pavement in urban road overhaul and maintenance construction

1. Preventive measures for horizontal deformation reflection cracks on surface layer

(1) The reason of horizontal deformation reflection cracks is that there are joints and cracks in the old cement concrete pavement. If asphalt concrete is paved directly, cement concrete pavement will expand and contract along joints and cracks under the action of temperature change and traffic load. When the expansion and contraction deformation of asphalt concrete pavement is inconsistent with them, cracks will occur in these parts, which is the mechanism of reflection cracks.

(2) Setting a stress reducing layer between asphalt concrete overlay and old cement concrete pavement can delay and restrain reflection cracks.

2. Preventive measures for vertical deformation and damage of surface layer

(1) Local damaged parts have been repaired before overhaul, so these damaged parts should be completely eliminated and repaired again; There is no need to chisel off the whole board and pour it again, only local repair can be adopted.

(2) Use asphalt sealant to treat joints of old cement concrete slabs. Asphalt sealant has good cohesive force and ability to resist horizontal and vertical deformation, which can effectively prevent rain from penetrating into the structure and causing frost heaving.

3. Requirements for substrate treatment

(1) The vertical uneven deformation of the basement leads to the local void of the original cement concrete pavement slab, and the pavement slab in the serious void part is partially broken or broken. In order to ensure the overall stiffness of the cement concrete pavement slab, before paving the asphalt mixture surface, it is necessary to deal with the base at the void and local cracks of the pavement slab and repair the damaged pavement slab. There are two methods to treat the substrate: one is to replace the substrate material, and the other is to fill the cavity in the gap by grouting.

(2) Foundation excavation treatment. For the local fracture or fragmentation of the original cement concrete pavement, chisel out the damaged part, replace the base and compact it, and then pour the concrete again. This conventional treatment method has simple process and thorough repair, but it has great influence on traffic and is suitable for sections with low traffic volume.

(3) Trenchless basement treatment. For the cavity in the cavity, the basement is treated by drilling and grouting from the ground. This method is widely used and successful in urban road overhaul projects. Before the treatment, the ground penetrating radar should be used for detailed exploration to detect the looseness, gap and settlement area near the existing pipeline under the pavement slab.