A, concrete bridge deck pavement diseases and causes
1. 1 is poorly designed. In order to reduce the dead load, designers try to reduce the thickness of bridge deck by increasing the amount of steel bars or adopting high-strength steel bars (such as box girder structures with thin roofs). This kind of bridge deck is not rigid enough, and it deforms greatly under heavy load. With the continuous impact and vibration of vehicles, fatigue cracks are prone to appear on the bridge deck and pavement and develop rapidly. Continuous beam bridge, arch bridge and cantilever beam bridge produce negative bending moment due to load, and the upper part is pulled, which makes the bridge deck pavement suffer from tensile stress and cracks, thus causing bridge deck pavement diseases.
The thickness of 1.2 is not enough. Due to the prefabrication of beam yard, cast-in-place support, hanging blue suspension casting of bridge hollow slab and superstructure of box girder, it is impossible to accurately predict the pre-camber of beam and slab, support settlement and prestressed anti-arch. If the construction control is not in place, it is difficult for the elevation of the top surface of the main girder to reach the design value during construction. Moreover, when designing the springing height of prestressed beams, the influence on the thickness of bridge deck is not considered, especially when the springing height of long-span beams increases, the thickness of bridge deck pavement will decrease accordingly. Moreover, because the designed bridge deck pavement thickness is generally small, generally 8 ~ 12 cm, the cumulative positive error of substructure elevation and the positive error of beam slab construction will inevitably reduce the thickness of bridge deck pavement. In the process of beam and slab construction, if the acceptance of each link is not strict, the size of the beam and slab will be too high; Support elevation control is lax, higher than the design elevation; Excessive inclination of beam and slab, or adjustment of longitudinal and transverse slopes of bridge deck, etc., may lead to the elevation of the top surface of beam and slab being higher than the design value, making the thickness of bridge deck pavement locally too thin and weakening the rigidity and bearing capacity of bridge deck pavement.
1.3 is not strong enough. Improper mix design or lax construction control, incorrect height position of steel mesh pad, failure to play the anti-crack role of steel mesh, resulting in insufficient strength; When new concrete is poured, there is water on the bridge deck, which is wet by rain, and the surface laitance is not treated, which affects the performance of concrete or causes insufficient strength due to insufficient thickness; The concrete bridge deck pavement is thin, and the poor maintenance causes the vibration to be not dense or the strength is not enough; In winter construction, improper use of antifreeze and freezing of concrete lead to insufficient strength. Under the action of vehicle load, diseases such as flooding, cracking, looseness, fracture and so on will soon appear on the bridge deck pavement.
1.4 is not firmly bonded. Before the bridge deck pavement construction, the loose sand, mud and dirt on the top surface of the beam were not cleaned, and the surface of the main beam was not cut or the density and depth of the cut hair were not enough. Some of the top surfaces of the main girder are polluted because they are used as storage yards or temporarily opened to traffic, and the cleaning work during construction is invalid. They are only washed with high-pressure water, not brushed with steel wire brush, which can't guarantee thorough cleaning. In addition, the rough cutting effect is poor, the top of the beam is not watered before pouring, and empty drum appears after pouring, which greatly reduces the adhesion between the bridge deck pavement and the beam surface and destroys the integrity of the cement concrete layer. After opening to traffic, the severe impact of wheels and loads caused the deck to peel off.
Second, the bridge deck pavement damage disease analysis
Due to excessive pursuit of flatness and neglect of compactness, the pavement strength is low and water seepage causes early damage. At the same time, the difference of pre-camber of three-layer asphalt pavement on subgrade and improper adjustment of paving thickness may make the pavement thickness of this layer insufficient, resulting in early damage of bridge deck pavement. Poor adhesion between layers makes bridge deck pavement unable to play an integral role. Poor adhesion will be caused by the pollution of the lower layer, the poor quality of the adhesive layer materials used, uneven distribution, and the driving effect after distribution. The rainwater on the bridge deck can't be discharged horizontally because of the guardrail, but can only be discharged to the drainage hole along the longitudinal direction of the guardrail wall. Under the action of high temperature and high pressure, some rainwater infiltrated into the pavement is easy to peel off the asphalt film, causing early damage to the pavement.
Iii. Countermeasures to deal with diseases
3. 1 Improve the structural design of bridge deck system. The top layer of the beam should be designed with reserved reinforcement firmly combined with the bridge deck; The influence on the thickness of bridge deck should be fully considered when designing the camber height of prestressed beam, and it is generally controlled according to the design height of pier and bearing during construction. Appropriately increase the thickness of bridge deck concrete and the density of steel mesh, and improve the diameter and grade standard of steel bars; The asphalt pavement is damaged at the expansion joint, and pits and grooves may appear. Therefore, in the design of expansion joints, steel fiber concrete with C40 grade or above should be designed in addition to sufficient anchoring reinforcement at the beam ends. In order to ensure its smoothness, expansion joint construction should be carried out after the completion of asphalt concrete pavement; The elevation of the bottom of the outlet of the drainage hole is designed to be at least 1cm lower than the top of the cement concrete bridge deck, and a slope is made around the outlet to ensure that the water infiltrated into the asphalt concrete pavement can be discharged through the drainage hole; The bridge deck should be designed with two layers of asphalt concrete, which not only improves the smoothness, but also ensures its durability.
3.2 Ensure the thickness of bridge deck concrete. 1) Before the construction of bridge deck pavement, the elevation of the top surface of beam and slab should be carefully checked to avoid the inconsistent thickness of bridge deck pavement, which will cause the thin or thick joint to become a weak section, and the concrete will be unable to bear tensile stress and crack when it shrinks; Special attention should be paid to the height of the tooth block concrete, which cannot affect the thickness of the bridge deck concrete. The elevation of the top surface of beam and slab must meet the requirements of the thickness of bridge deck pavement, and the extra concrete and loose concrete and negative bending moment tensioning teeth must be chiseled away in advance. The flatness of the top surface of the beam must be strictly controlled. When plastering, scaffolding should be placed on the slideways on both sides. The number and rigidity of plates should be sufficient. Workers stand on the board to plaster, and use a 3m ruler to check the flatness vertically and horizontally, so as to ensure the smoothness of good cushion for bridge deck pavement. No potholes and water accumulation. Prevent the uneven top surface of the beam from increasing the friction resistance between the beam and the concrete interface, leading to cracking of the weak bridge deck. 2) Strictly control the construction quality of concrete and the geometric dimensions of beam and slab, especially the beam height. It is necessary to ensure that the camber of the same span beam slab is basically the same, so as to ensure that the thickness of bridge deck pavement is basically the same.
3.3 Ensure the strength of bridge deck concrete. 1) Strictly control the mix proportion of concrete, use sand and gravel materials with good gradation and qualified quality indicators, and strictly pass the cement inspection to ensure the qualified strength of concrete. There should be corresponding quality assurance measures for bridge deck concrete construction in winter and summer. If there is water on the bridge deck, it should be removed before pouring concrete. Concrete should have good workability, slump should be controlled in 3-5 cm. When pumping concrete is used, water reducing agent should be added, and the slump should be reduced to the lower limit as far as possible while meeting the requirements of construction machinery and specifications. The concrete shall be vibrated and compacted, and the bridge shall be leveled with a three-roll slurry lifting unit, a vibrating rod and a flat vibrator, and try to cooperate with a vacuum suction plastering machine. Small and medium-sized bridges can be vibrated by vibrating beams and leveled by rolling bars. When low-lying places are found during vibrating, they should be leveled with concrete in time. It is forbidden to use cement mortar to make up afterwards. 2) The correct positioning of steel mesh can enhance the crack resistance of bridge deck and improve the overall strength of concrete. In the past, the steel mesh of bridge deck pavement was often positioned with concrete pads, which caused quality hidden trouble because of the low strength of the pads. This shortcoming can be overcome by using short steel bar support positioning method. The reinforcement length is about 80% of the pavement thickness, and the two-way spacing is about 50cm. One end of the positioning rod is welded with the steel mesh, and the other end is vertically supported on the beam surface, and the steel mesh is supported at multiple points. After the steel bar binding is completed and passed the inspection, the bridge deck concrete should be poured as soon as possible. Before pouring concrete, it is forbidden for all vehicles and other personnel to pass on the tied steel bars to avoid deformation and displacement of the steel bars.
3.4 Improve the bonding ability between bridge deck concrete and beam top concrete. Brush the top surface of the precast beam body to expose stones; If twisted joint concrete is designed between beams, the combination of bridge deck concrete and beams should be strengthened when pouring; Before the steel bars on the bridge deck are bound, the top of the beam must be thoroughly cleaned, and scum should be chiseled, and washed with air pump or high-pressure water when necessary. Sprinkle water to wet the top of the beam before pouring concrete, but there can be no water; The full-width construction of bridge deck should be completed at one time. When the bridge deck is too wide and divided into two parts, the lower cross slope should be poured first to avoid the secondary pollution of curing water. In the second picture, dust and sundries, especially the joints, must be removed before pouring concrete.
Four. Conclusion:
The construction quality of highway bridge deck is the premise to ensure the safety and stability of bridge. Although the deck pavement is not large in the whole bridge project, it has a great influence on traffic. The quality of bridge deck pavement is one of the keys to ensure the operation quality of expressway. Construction must be carried out in strict accordance with the design requirements, and comprehensive measures should be taken from the aspects of design, construction and maintenance to improve the construction quality of bridge deck engineering.
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