Before the concrete mix is paved, the level of the base layer, wetting conditions, the position of the reinforcement and the transmission bar device should be checked comprehensively. Poor levelness of the base layer may cause inconsistency in thickness of the road surface, forming a weak section at the junction of too thin or thick and thin, and the concrete is easy to be stretched and cracked when it shrinks. In addition, the grass-roots level should be kept moist, but no waterlogging phenomenon, to prevent the absorption of concrete moisture caused by plastic concrete water loss cracking.
The height of the formwork and the width between the formwork should be checked to see if they meet the requirements, and the formwork should be firmly attached to the surface of the base layer so that it can withstand the vibration of the vibrating beam without losing shape. If there is a gap between the formwork and the base, the gap should be filled to prevent slurry leakage during tamping. In order to dismantle the formwork, apply isolating agent or lay a layer of agricultural plastic film on the inside of the formwork, the film can prevent water leakage and slurry leakage, and ensure the strength and density of the concrete slab edge and corner.
In the process of concrete pouring, the cloth should be scattered to ensure that the concrete mixture is evenly distributed and there is no accumulation. When paving, the concrete should be scattered and leveled with iron palladium. When using dump truck or mixer truck to unload, it is forbidden to focus on several points of cloth to make the concrete pile up, and it is easy to destroy the homogeneity of concrete mix in the process of leveling. When the thickness of concrete slab is more than 220mm, it can be paved in two times, and the thickness of the lower part should be 2/3 of the total thickness; when the thickness of the slab is less than 220mm, it can be paved at one time. The loose concrete should be slightly higher than 5% of the design height of the top of the formwork.
After the concrete is poured, use the vibrating rods to “insert quickly and pull slowly” at an angle of 30°~45° to fully vibrate and evenly vibrate in the shape of “character”, so that no vibration is missed and no vibration is lost. The distance between each vibrating rod is not more than 1.5 times of its radius of action or controlled according to 30cm, and the distance between it and the formwork is less than 0.5 times of the radius of action of the vibrating rod. When vibrating, the slurry overflows on the surface of the concrete mix, the mix fills the formwork and no longer sinks significantly, and the bubbles on the concrete surface no longer overflow significantly.
After the concrete is sufficiently vibrated using vibrating beams, the vibrating beams should be used to follow and walk back and forth 2 or 3 times to achieve a flat and uniform surface with no exposed stones. Vibratory tamping should be supplemented with manual leveling and the formwork should be checked at all times. If there is sinking, deformation or loosening, it should be corrected in time.
After leveling the vibrating beam, use 600mm-700mm long trowel (wood or plastic) to squeeze and compact the surface of the concrete slab, and press out the cement slurry until the slab surface is smooth and the mortar is uniform, generally about 3-5 times.
Finish the surface
Before the concrete first set, when there is no secretion on the surface, rub the surface with a grinding disk, so that the surface is further pulp compaction, eliminate the concrete secretion process of water channel, eliminate small cracks, control the expansion of cracks. Mopping process should be timely and in place to effectively eliminate the purpose of surface cracks, mopping process to do “wipe”, but also to do “pressure”. In summer, when the weather is hot and windy, the evaporation rate is fast, so we should take timely moisturizing measures to prevent the surface from evaporating too fast, which will produce hard shell, and the interior is too soft to form spring pavement.
Before and after the final setting of concrete, the finishing and embossing processes should be completed, and the finishing should be carried out 3 to 4 times to effectively compact the concrete surface and prevent the concrete pavement powder.
About 10min after finishing the smearing, you can use the brown brush, metal comb to gently pull the hair along the transverse direction to make a transverse non-slip groove with the depth of 2~3mm and the interval of 1.5~2cm.
Removal of the mold
The demolition time should be determined according to the temperature and concrete strength growth, and when ordinary Portland cement is used, the general permissible demolition time should be in accordance with the provisions of Table 1.
Note: 1) The allowable demolition time is the interval from the time the concrete is formed to the start of demolition. 2) When using slag cement, it is advisable to extend the demolition time by 50-100%.
2 When slag cement is used, the allowable demolition time should be extended by 50%-100%.
The minimum requirement for demolition is that the sides and corners of the concrete surface layer shall not be damaged, and large-area demolition can be carried out only when the integrity of the concrete pavement corners is guaranteed.
Mold removal first remove the template support, iron brazier, etc., and then use the flat-headed iron crowbar inserted between the template and the concrete, slowly prying outward, do not damage the concrete slab edge, remove the template should be promptly cleaned and maintained and put flat pile to prevent deformation.
Special person should be in charge of the cutting joint, and the cutting joint should be made according to the safety operation regulations and technical requirements of the cutting joint. It is an important measure to grasp the timing of seam cutting, which is an important measure to prevent transverse cracks and broken slabs on concrete pavement, and it should be “rather early than late” and “no shallow seam cutting”, with the earliest timing of seam cutting being that the blade does not bounce up stones and does not tear the edge. Depth of cutting seam: the depth of the cutting seam with power rod shrinkage should be 1/3 to 1/4 of the board thickness, the shallowest shall not be less than 70mm; the depth of the cutting seam without power rod shrinkage should be 1/4 to 1/5 of the board thickness, every 5m interval set up an expansion joint.
Concrete pavement should be taken in a timely manner after receiving light insulation measures, the general priority of water-absorbent cotton felt better, the first three days to ensure that the cotton felt moisture and not wet, 3 days before the maintenance of wet water. The use of plastic film covering the concrete surface maintenance, although it can also prevent water loss when adsorbed on the film of water droplets and concrete contact point powder. Maintenance time of not less than 14d, after the expiration of the maintenance period can be removed before the cover.
Concrete road slab in the initial stage of construction and maintenance, does not produce temperature contraction of the maximum temperature drop value of the broken plate is generally 5 ~ 6 ℃. When the temperature drop value exceeds the temperature drop value, the temperature stress is higher than the strength of the age of the concrete, it is easy to break the slab phenomenon.
When the concrete has reached its design strength, it may be allowed to open to traffic. When special circumstances require an earlier opening to traffic, the concrete slab shall be at least 80 per cent of the design strength and the vehicle load shall not be greater than the design load. The strength of the concrete slab shall be based on the strength of the concrete test block of the same condition.