During the period of concrete curing, we should focus on strengthening the humidity and temperature control of concrete, minimize the exposure time of surface concrete, and cover the exposed surface of concrete closely (tarpaulin, plastic sheeting, etc.) in time. Can be used to cover) to prevent evaporation of surface moisture. Before the initial setting of the exposed surface protective layer concrete, the covering should be rolled up and rubbed with a trowel at least twice to make it smooth, and then covered. At this point, attention should be paid to the fact that the covering should not directly contact the concrete surface before the final setting of the concrete. Steam curing of concrete can be divided into four stages: static stop, heating, constant temperature and cooling. Steam curing of concrete shall meet the following requirements respectively:
(1) During the static stop, the ambient temperature should be kept not lower than 5℃, and the temperature of concrete can only be raised after the pouring is completed for 4 ~ 6h.
(2) The heating rate should not be greater than 65438 00℃/h. ..
(3) At constant temperature, the internal temperature of concrete should not exceed 60℃, and the maximum temperature should not exceed 65℃. Constant temperature curing time should be determined by experiments according to the demoulding strength requirements of components, concrete mixture ratio and environmental conditions.
(4) The cooling rate should not be greater than 65438±00℃/h-00℃/h ... After concrete pouring, the beam is sealed with a curing cover, and steam is input to control the humidity and temperature around the beam.
When the temperature is low, input steam to raise the temperature, and after the initial setting of concrete, the bridge deck and the box are stored with water to keep moisture. The heating rate shall not exceed10℃/h; The constant temperature shall not exceed 45℃, the concrete core temperature shall not exceed 60℃, and the individual maximum temperature shall not exceed 65℃. When cooling, the cooling speed shall not exceed10℃/h; When the temperature decreases to a point where the difference between the beam temperature and the ambient temperature does not exceed 15℃, remove the curing cover. The cooling of box girder cavity is slow, so ventilation measures can be taken appropriately. The temperature of all parts in the hood is consistent, and the temperature difference is not more than 65438 00℃.
During steam curing, the temperature should be measured regularly and recorded. The pressure thermometer is arranged in the inner box span, 4m near the beam end and outside the side formwork. Measure the temperature every 2 hours at constant temperature, and every 1 hour at temperature rise and fall to prevent concrete cracks.
After steam curing, water must be sprayed immediately for curing, and the time shall not be less than 7 days. For concrete poured in winter construction, covering curing should be adopted. When the average temperature is lower than 5℃, the maintenance should be carried out according to the winter construction method. When curing formwork concrete by spraying curing agent on the surface of box girder, measures such as covering formwork, watering and sprinkling water should be taken to keep it moist and moist, so as to ensure that formwork joints are not dehydrated and dry. In order to ensure the smooth form removal, the formwork can be loosened slightly after 24 ~ 48h of concrete pouring, and water conservation can be continued until the form removal, and then the moisture can be kept to the specified age.
After the concrete surface protective layer is removed or the formwork is removed, measures such as storing water, watering or covering with water should be taken to wet cure the concrete. When the concrete surface is wet, bare concrete can be quickly covered or wrapped with linen, straw curtains and other materials, and then wrapped with plastic sheets or canvas with linen, straw curtains and other moisturizing materials. When painting, the coatings should be intact and completely overlapped with each other, and there should be condensed water droplets on the inner surface. Conditional areas should try to extend the concrete coating and moisture curing time. Spray film curing liquid is suitable for special-shaped or large-area concrete structures that are not easy to spray curing. In this method, the solution of perchloroethylene resin is sprayed on the concrete surface with a spray gun, and a plastic film is formed on the concrete surface after the solution volatilizes, so that the concrete is isolated from the air, the water in it is prevented from evaporating, and the normal hydration is ensured. Some films will age and fall off after curing, otherwise they are not suitable for spraying on the concrete surface to be painted in the future. In summer, the film should be protected from the sun after forming, otherwise it will crack easily. When curing concrete with spraying curing liquid, no leakage shall be ensured.
Gray curing agent or transparent material is usually used to cure the long-term exposed concrete surface. The color of gray curing agent is close to the color of concrete, and it can also paint and add color to the surface. By the end of weathering, its appearance is much better than that of white curing agent. Transparent curing agent is a kind of transparent material, which can't paint concrete, but can only keep its original appearance. In the process of cast-in-place concrete slab, nine splint strips with thickness greater than 12mm (width 100mm) are spread along the periphery of cast-in-place concrete slab, and fixed with two nails with a length of 35mm per meter; Stair treads and cast-in-place slabs are also planking, which requires the stair treads to be flat and the step height difference is less than 3 mm; When the concrete slab is large, it should be cured in blocks according to the concrete pouring time and plane size, and the boundary is also paved with 9 plywood strips with a width of100 mm; Slate laying should be smooth and close to the edge; After the concrete is cast, it should be leveled with coarse wooden crabs in time and maintained in time, especially before the initial setting at high temperature in summer, the coarse crabs should be leveled for the second time. Before the final set, it should be cured by full water method (that is, spread three plywood and other flat plates on the board surface, and then the water will flow to the concrete surface through the board surface until the slats overflow) for 3 ~ 7 days, and the curing time should be extended if conditions permit; Avoid moving concrete during curing; Stair treads shall be cancelled after the concrete strength reaches 100%.
This kind of curing method can well ensure the curing of concrete under the condition of constant temperature and humidity, greatly reduce the plastic shrinkage cracks caused by temperature and humidity changes and water loss, well control the thickness and flatness of the board, well ensure the surface strength of concrete, avoid the hollowing of the floor, well ensure the appearance quality of concrete, and reduce the costs of leveling, roughening and corner protection in the decoration stage. The water-saving and moisture-retaining curing film of concrete is made of a new controllable polymer material as the core and a plastic film as the carrier. Polymer material can absorb 200 times its own weight of water, which becomes a transparent lens after water absorption and expansion, turns liquid water into solid water, and then continuously penetrates into the curing surface through capillary action, and at the same time continuously absorbs the evaporated water of the curing body during the hydration heat of concrete. Therefore, in a curing period, the cured film can keep the cured surface moist, and the relative humidity is greater than or equal to 90%, which can effectively inhibit micro-cracks and ensure the engineering quality.
As a new type of material, concrete moisturizing and curing film is widely used in various fields of highway, railway, water conservancy and other engineering construction, and plays an increasingly important role in preventing concrete quality problems.
A, highway cement concrete pavement health
1. When the concrete reaches the initial setting and the expansion joint is cut, the residue such as sawdust on the expansion joint and panel shall be removed by high-pressure water gun;
2. Arrange the cured films on the road surface layer by layer, and the overlapping width of two adjacent films shall not be less than 50mm (as shown in figure 1);
3. Take the distance of about 10m as the laying stage of the solidified film, and repeat the following procedures: firstly, sprinkle water until the free water thickness of the road surface is 3 mm ~ 4 mm, and roll the arranged solidified film forward on the road surface to make the polymer water-absorbing material in the film fully absorb water to the thickness of 5 mm ~10mm;
4. During the whole laying process, the overlapping width of two adjacent films should always be kept above 50 mm (as shown in Figure 2);
5. Both sides of the film have overlapping glue, which can realize overlapping adhesion between films; In order to prevent the gap caused by insufficient adhesive adhesion from forming a wind tunnel and affecting the quality of health care, a transparent adhesive with a width of 50mm can be used to stick the film lap;
6. In order to prevent the cured film from being blown away by the wind or washed away by heavy rain during the whole curing period, a small amount of cement blocks or aggregates should be pressed in. In particular, the membrane laid at the central isolation belt and the shoulder must be compacted (as shown in Figure 3 and Figure 4);
7. The film shall cover the side wall edges on both sides of the concrete slab, and 100 mm ~ 200 mm shall be reserved for crushed stone (as shown in Figure 5);
8. After the curing period expires, the uncovered curing film can be retained as the initial curing cover after concrete paving and before the cutting of expansion joints, and the old film can be used to reduce the curing cost and improve the curing quality.
Second, highway cement stabilized base and base maintenance
1. Lay curing film on the pavement step by step. During the whole laying process, the overlapping width of two adjacent films should always be greater than 50mm (as shown in figure 1);
2. There is no need to sprinkle water immediately after rolling. If the time exceeds 4 hours, spray water once until the road surface is wet, and roll the arranged cured film forward on the road surface (as shown in Figure 2);
3. There is overlapping glue on the edge of the film, which can realize overlapping adhesion between films; In order to prevent the gap caused by insufficient bonding from forming a wind tunnel and affecting the sanitary quality, a small amount of cement blocks or aggregates can be pressed.
4. The membrane shall cover the side wall edges on both sides of the concrete slab, and 100 mm ~ 200 mm shall be reserved for sand pressure (as shown in Figure 5).
Matters needing attention and solutions:
1, and the lap width of two adjacent films should not be less than 50mm；;
2, highway cement concrete pavement health sprinkler, pavement free water thickness is 3 mm ~ 4 mm; When the stable base and base of highway need water, the pavement must be wet (the water consumption is about 2 kg/m&; sup2);
3. During the maintenance period, vehicles should be relatively prohibited from rolling on it (especially in the first four days), otherwise the maintenance film will be damaged due to rolling and the maintenance quality will be reduced;
4. It is relatively forbidden to drag, grind and kick the curing film on the pavement artificially, so as not to damage the curing film and reduce the quality of health care;
5, to patrol at any time, if discover a breach or hole, should be timely with transparent adhesive paste repair;
6. After the curing period, the curing film should be removed in time to avoid being blown by the wind and affecting the project image and environmental protection.