During the "Eleventh Five-Year Plan" period, the construction project of Tongcun cement road was implemented in our province. Our county seized this historical opportunity and set off a boom in the construction of Tongcun Highway. As the project manager of Tongcun County Office, after several years' practical experience and consulting relevant materials, I have discussed the problems of broken slabs that often appear in the construction of cement concrete pavement of Tongcun Highway and the treatment methods as follows.
First, the reason of broken plate 1. Raw materials are unqualified. The main materials of cement concrete pavement are cement, gravel (crushed stone), medium coarse sand and water. Insufficient cement grade, poor stability and insufficient strength; Harmful substances or silt content in aggregate exceeds the standard. Improper control of concrete mix proportion. In construction, because the aggregate is too dry or too large, the mixing water is absorbed during construction, and the measurement is inaccurate, which affects the initial strength of concrete. All of the above will lead to the appearance of broken boards. In order to ensure the construction quality of concrete pavement, Tongcun Office of our county has made clear the origin and specifications of raw materials such as cement and sand. The cement is road portland cement produced by three enterprises in the county, and the medium and coarse sand is Muma River and Jingyang River in the county. It is required that the maximum particle size of gravel is less than 4 cm, and sand, gravel (crushed) stone, cement and water must pass inspection. Cement factory inspection certificate shall conform to the design label. The silt content of sand should be controlled. When stirring, we must pay attention to the ratio of various materials and must stir mechanically. 2, cement concrete pavement engineering construction technology should be considered in the construction organization design to set up the supply distance of mixing station, generally should not exceed 10km. It is best to use a mixer for long distances. The transportation distance of Tongcun highway construction is generally not more than 5 kilometers. Attention should be paid to vibration, especially on the artificially laid sections. Should strictly follow the requirements of the specification. The vibration duration of the vibrator at each position shall be subject to the cement slurry flooding the concrete, and shall not be over-vibrated. When vibrating with a flat vibrator, it should not be less than 15s, and when vibrating with an internal vibrator, it should not be less than 20s. In the process of concrete pavement construction, the process control is improper, the mixing time is insufficient, and the vibration is not dense; When the temperature of concrete members is too high during mixing, the bending and tensile stress of concrete will increase due to the temperature difference during cooling and hardening, leading to cracking; Improper process control during construction (such as failure to treat construction joints when concrete is discontinuous, untimely joint cutting, leakage during vacuum water absorption, improper installation of dowel bars, and construction in unfavorable seasons). ) affect the flexural tensile strength of concrete itself is insufficient, leading to cracking. The base surface is uneven and the material humidity is not suitable. The uneven surface of the base course results in inconsistent pavement thickness, which increases the friction resistance between the base course and the surface course and causes the weak parts of the pavement to crack under the action of tensile stress. The base material is too dry, which absorbs the moisture of the bottom concrete, thus reducing the flexural strength of the concrete and leading to cracking. Second, the reason for cracking and plate breaking within the service life 1, and the lack of early design experience led to the thin thickness of concrete slab; Plate size division does not meet the specification requirements; Improper selection of raw materials and design mix proportion. 2. Uneven settlement of subgrade Improper handling of wet and soft subgrade, inconsistent compaction standards at the junction of filling and excavation, insufficient compaction near bridges, culverts and structures, and improper handling of subgrade at geological changes of road sections will lead to uneven settlement of subgrade and cracking of concrete slabs. 3. The unstable base construction quality is not good, the surface is uneven, and the strength is uneven, which leads to the increase of bending and tensile stress of the surface concrete slab and the slab breaking; The joint filler at the joint of the surface layer fails. When the plate flexes, the accumulated water at the joint becomes pressure water, which causes pumping mud and gaps at the joint and causes the plate to be broken. Other circumstances, such as poor road drainage, overloaded vehicles increased. Three, the prevention of broken slab of cement concrete pavement is mainly in the process of construction and use, so the prevention of broken slab should be controlled according to its different periods. 1, good structural combination design can effectively prevent cement concrete pavement from breaking due to design and overload factors during use. The influence of design factors is mainly caused by poor consideration of structural combination design and drainage design. In the structural combination design, the influence of pavement base on cement concrete slab should be considered emphatically, that is, pavement base should have good water stability and smoothness besides sufficient strength and stiffness. Good water stability can effectively avoid the generation of pumping mud, thus avoiding the damage of the base and the void at the bottom of the slab, providing good support for the cement concrete panel and avoiding the slab breaking; Good flatness can effectively avoid the stress concentration area of cement concrete slab under load and avoid slab breaking. 2. Prevention of slab breaking during construction: strictly control the mixture ratio of cement concrete mixture to avoid excessive water-cement ratio or segregation of mixture, so as to ensure sufficient strength of concrete mixture. At the same time, strictly control the slotting time, which generally depends on the temperature, so as to avoid breaking the slab due to the shrinkage of concrete, because the changes of temperature, humidity and wind will cause the concrete to dry up greatly. 3. Prevention of slab breakage during use Cement concrete pavement will be broken due to pumping due to overload and various groundwater entering cracks in cement concrete pavement. Therefore, overload should be strictly controlled, all kinds of cracks in cement concrete pavement should be filled in time, all kinds of groundwater should be prevented from entering the cement concrete pavement structure, the source of frost boiling should be eliminated and the slab should be avoided. Four, the treatment method of cement concrete pavement broken plate should be based on the different degrees of broken plate and take corresponding methods for treatment. The shape of broken seam: ① straight broken seam; (2) Small slope fracture; (3) The joint at the corner is broken; (4) Large slope fracture. The first three situations are more common, and the fourth situation is less common. There are many methods to deal with the broken joint (slab) of concrete upper deck. Through the experience of several broken slabs, I think the method of filling expansive concrete with pits is simple and easy to learn, and the treatment effect is good. The main construction technology is: 1. Dig a hole. According to the position of cracks, the cement concrete panel is cut into rectangular grooves, which run through the whole thickness. It is best to cut the groove wall into a slope of 1: 0. 15, so that the repaired concrete and slab can bear the traffic load more fully. The right-angle sides of the groove are parallel to the contraction joint and the longitudinal joint respectively. For straight fractures, the cutting width of both sides of the fracture is not less than 20cm, and the total width is not less than 40cm；; If the crack is slightly inclined or bent, it shall be no less than 10cm from the protruding part or end of the crack, and the total width of trench excavation shall be no less than 40cm. If the fracture is near the contraction joint and the cutting edge is not more than 40cm away from the contraction joint, the original contraction joint should be regarded as an edge of the groove. For the broken joint at the corner, the concrete around the broken joint (broken plate) should be cut and dug according to the requirements of the above cutting size. For the fracture with large dip angle, the concrete around the fracture can be divided into two pieces and dug out. Before digging, according to the broken joints and the size requirements, chalk lines are made on the cement concrete pavement in Kunxi with chalk barrels, and then cut along the line with a cutting machine, and then the concrete pavement to be dug is cut into a mesh with a cutting machine. The smaller the mesh area, the easier it is to dig. Then use a hexagonal drill and a sledgehammer (an eight-pound hammer) to dig out the concrete. After excavation, safety signs should be set around the trench. 2. When the groove is filled with expansive concrete, the pavement we poured is a slab pavement with a higher grade than the original one. The pavement design grade of Tongcun cement road is 30 #, and the broken joints are treated with alumina (that is, aluminum powder sold in the market with a content of 0.3%). Its mixing ratio is cement, concrete, sand, crushed stone, water and alumina =100:158: 275: 62: 0.3. 3. After the curing tank is filled, there should be signs or obstacles around it to avoid driving. When the expansive concrete reaches the final setting time (usually 8 hours), fine soil with a thickness of not less than 15cm can be laid on the concrete for maintenance, and the soil should always be moist. After two weeks of health care, you can remove signs or obstacles and start to pass. V. Conclusion After several years of driving observation, the expansive concrete in the tank is closely combined with the original pavement slab, even without asphalt waterproof material, which shows that it is feasible to use expansive concrete as the filling material for pavement slab treatment, so it has been recognized and popularized in the construction of cement road in Tongcun County.
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