Construction technology of cement concrete pavement

Construction technology of cement concrete pavement

Cement concrete pavement has been widely used at all levels because of its advantages of compression resistance, bending resistance, wear resistance and high stability. There are more and more cement concrete pavements in China's high-grade highways. In recent years, cement pavements have been widely used in rural highway construction, making the scientific and standardized construction of cement concrete pavements a concern of highway builders. Then, I will share with you the construction process of cement concrete pavement. Welcome to read and browse.

1, template installation

Formwork should be made of steel, and non-standard parts such as bends and minor works can also be made of wood. The formwork shall be intact and have sufficient strength. The inner, top and bottom surfaces shall be smooth and straight, and the local deformation shall be no more than 3 mm. The maximum lateral deflection of formwork during vibrating shall be less than 4mm, and the height shall be consistent with the thickness of concrete pavement slab, with an error of no more than? 2mm, longitudinal seam template flat seam tie rod eyelet position should be accurate, tongue-and-groove seam tongue-and-groove length error is steel template? 1mm, wooden template? 2 mm.

2. Install dowel bar

When installing the side formwork, the dowel bar is installed at the position where the dowel bar needs to be installed.

When the concrete slab is continuously poured, the dowel bar can be installed by the reinforcement bracket method. That is, a circular hole is reserved on the caulking plate for dowel bars to pass through, wooden or iron caulking slats are placed on the caulking plate, an inverted U-shaped groove is made at the lower part of the joint template according to the position and spacing of dowel bars, so that dowel bars can pass through, both ends of dowel bars are fixed on the bracket, and the bracket feet are inserted into the base.

When the concrete slab is poured discontinuously, the dowel bar can be installed by the method of fixing the top wooden mold. That is to say, a positioning template is added to the outer side of the end template, and the dowel bar passes through the hole of the end template according to the spacing, rod diameter and drilling hole of the dowel bar on the plate until the hole of the outer positioning template. Two templates can be fixed by a cross bar with half the length of dowel bar. When the concrete of adjacent slabs is continuously poured, the baffle, cross bar and positioning formwork shall be removed, and joint slabs, wooden joint pressing slabs and dowel sleeves shall be set.

3, paving and vibrating

1) Preparation before paving

There are many preparations before concrete paving, mainly emphasizing the unloading process of sprinkling water before paving.

1. 1 Sprinkle water

Sprinkling water before paving is a seemingly simple process, which is often ignored by builders, but if it is not handled properly, it will seriously affect the quality of pavement.

Sprinkler quantity should be determined according to the substrate, temperature, humidity, wind speed and other factors. , that is, to ensure that the base is wet before laying concrete, and try to spread it evenly, especially where the base is uneven. Judging from the current construction site, in most cases, the amount of sprinkling water is insufficient because the base is dry and a large number of small cracks are produced at the bottom of the paved concrete pavement. Some small cracks overlap with the cracks caused by the shrinkage stress of concrete itself, which increases the cracks of the whole concrete pavement.

1.2 discharge

Unloading of dump trucks is also a process that is often neglected. In the construction, it often happens that too many materials are piled up, which brings difficulties to the construction. Sometimes too little cloth will lead to insufficient concrete and the thickness of pavement cannot be guaranteed. This phenomenon of less and less concrete will seriously affect the smoothness of concrete pavement. In the process of construction, most construction workers rigidly unload a car for a certain distance, ignoring the uneven change of the grassroots, which is objectively common.

At present, the construction level of many enterprises is not very high, especially the elevation control of pavement base is not in place, which leads to poor smoothness of base and increases the difficulty of concrete pavement construction. In actual construction, we can determine the concrete unloading amount by measuring the distance between the foundation surface and the elevation line of the base of the surface layer, which will avoid the problem of uneven unloading.

The maximum thickness of semi-hard concrete mixed on site allowed to be paved at one time is 22 ~ 24cm；; The maximum thickness of plastic commercial concrete paving at one time is 26cm. When the maximum paving thickness exceeds one time, it should be paved and vibrated twice. The paving interval between two layers should not exceed 30min. The thickness of the lower layer is about greater than that of the upper layer, and the thickness of the lower layer is 3/5.

Every time concrete is paved, vibrated, leveled and plastered, it shall be continuously constructed. If it is necessary to interrupt, construction joints should be set, and their positions should be at the joint positions specified in the design. When vibrating, flat vibrator or plug-in vibrator can be used.

During construction, vacuum water absorption method can be used for construction. Its characteristics are that the water-cement ratio of concrete mixture is 5% ~ 10% higher than that of common concrete mixture, which is easy to spread and vibrate, reduces labor intensity, speeds up construction progress, shortens concrete plastering process, and improves the shrinkage resistance, impermeability and frost resistance of concrete.

Attention should be paid to the following points during construction:

(1) The vacuum water absorption depth shall not exceed 30cm.

(2) The vacuum water absorption time shall be 1.5 times of the thickness of the concrete pavement slab (the water absorption time is measured in minutes and the thickness is measured in centimeters).

(3) Suction pads should be laid, especially the periphery should be close to each other. Generally, when the pump is started, the water absorption will gradually increase to 400~500mmHg in the vacuum gauge lmin, and the maximum value should not be greater than 650 ~ 700mgHg, so the measured water output meets the requirements. When the pump is turned off, the vacuum gradually decreases, and the four corners of the suction pad are slightly lifted, and the suction 10 ~ 15s is continued to remove the residual water in the working face and pipeline.

(4) After vacuum water absorption, it can be leveled with a rolling pin, vibrating beam and plastering machine to ensure smooth surface and further enhance the uniformity of plate strength.

4. Joint construction

The construction of longitudinal joints shall comply with the provisions of design documents. Longitudinal joints are generally longitudinal construction joints. Pull rod should be installed after template installation and before concrete pouring; The tie rod of the longitudinal construction joint shall be installed through the tie rod hole of the formwork; After the concrete is hardened, transverse joints shall be sawed with a saw; You can also bury the joint plate in the pouring process and pull it out after the initial setting of concrete to form a joint. When sawing, the strength of concrete should reach 5 ~ 10 MPa, which can also be determined by field trial sawing. The transverse contraction joint should be sawed after the concrete hardens, and it can also be formed in the newly poured concrete when the conditions are not met.

Sawing seams must be timely. During construction in summer, it is advisable to saw one board every 3-4 boards first, and then make it up. It is also allowed to press a contraction joint every 3 ~ 4 boards to prevent the concrete board from cracking before sawing. The transverse expansion joint shall be 90 with the road centerline. , seam wall must be vertical, seam width is consistent, seam can not have cement slurry. The lower part of the joint is provided with an expansion joint plate, and the upper part is filled with joint material. Expansion joint plates should be prefabricated in advance, such as oil-immersed fiberboard (or cork board) and sponge rubber foam board. Before the precast expansion joint plate is embedded, the joint wall should be clean and dry, and the expansion joint plate should be closely combined with the upturned wall.

5, surface finishing and anti-skid measures

After concrete is poured on the surface of cement concrete pavement, the concrete surface must be leveled manually or mechanically before final setting. Manual grinding is labor-intensive, which will bring water, cement and fine sand to the concrete surface, so that the surface will shrink more than the lower concrete or mortar, and the strength will be lower. When mechanical polishing is used, a disc is installed on the machine, which can be used for rough polishing; Put on a fine wiper and you can polish it off.

In order to ensure traffic safety, the concrete surface should have a rough and non-slip surface. Regarding the anti-skid standard, according to the recommendation of the Anti-skid Committee of the International Road Congress, when the speed of newly paved concrete pavement is 45km/h, the minimum friction coefficient is 0.45; When the vehicle speed is 50km/h, the minimum friction coefficient is 0.40. During construction, the smooth surface can be lightly brushed along the horizontal direction with a brown brush or combed into a horizontal groove with a depth of 1 ~ 2mm with a steel wire comb; At present, it is often used in hardened pavement, and the pavement is sawed into transverse small grooves with a depth of 5 ~ 6 mm, a width of 2 ~ 3 mm and a spacing of 20 mm

6, maintenance and caulking

After the concrete slab is completed, it should be cured in time, so that the mixture in concrete has good conditions for the development of hydration and hydrolysis strength and prevents shrinkage cracks. The curing time is generally around 14 ~ 2ld. Concrete should meet the design requirements. During the curing period and before joint sealing, vehicles are forbidden to pass, and pedestrians can only pass after reaching 40% of the design strength.

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