The common type of cracks and prevention measures
1. Common types of cracks
(1) transverse cracks. The cross seam is the most common kind of crack in the asphalt pavement of expressway. Most of the transverse joints are part of the semi-rigid base cracking caused by cracks in the road cracks, but also includes the temperature cracks, when the rain along these cracks into the pavement structure within the layer, will shorten the road life.
(2) longitudinal cracks. Divided into top-down surface cracks and bottom-up fatigue cracks. This kind of crack is mainly caused by the non-settlement of the roadbed. When the compaction is not uniform during the construction of the roadbed, there will be a phenomenon of insufficient compaction. After the opening, the roadbed will be further compacted Knot, resulting in the formation of longitudinal cracks.
(3) net crack. When the grass-roots local strength is insufficient, such as less binder material, aggregate segregation, lack of compaction, etc., as well as the lack of subgrade and surface strength, such as deformation, sinking, porosity is too large, once the role of heavy vehicles The surface layer will be pulled into a crack, deformation into a crack.
2. Causes of cracks in expressway pavement
The occurrence of expressway pavement cracks is mainly affected by the following factors: the performance of pavement materials and roadbed packing, construction technology, climatic conditions, vehicle load and so on.
(1) road materials and roadbed packing. Expressway pavement base is usually used "cement stabilized gravel layer + lime fly ash + lime soil base layer" structure, this inorganic binder is composed of solid, liquid and gas phase, solid-liquid three-phase in the cooling process Interactions allow the inorganic binder to stabilize the material to produce volume shrinkage. The water is the main influencing factor of the temperature contraction of this kind of material. The effect of water on the inorganic binder is mainly through the capillary tension, the expansion effect and the freezing effect. When the capillary water is evaporated, the adsorbed water of the semi-rigid base material will begin to evaporate, and the water film on the surface of the particle will become thinner, so that the particle spacing becomes smaller and the molecular force increases, resulting in further shrinkage of the pavement layer Of the amount of shrinkage than the impact of capillary effect is much greater, when the adsorption of water film to a certain extent, it will stop the contraction. As the density of cement after compaction is insufficient, the soil is not uniform, and the evaporation of water in the cement stabilizes the water content of the base of the cement. The base layer shrinks to form the shrinkage cracks at the base layer and causes the stress concentration at the top of the crack, Reach the road surface, the formation of reflective cracks.
(2) climate temperature conditions. The non-load cracks on the asphalt surface of the expressway are mainly temperature cracks, and the number and distribution density of the cracks are closely related to the decrease of the temperature. With the increase of the low temperature duration, the cracks will increase and increase, and the same crack width will be Will gradually widen. When the temperature is high, the good stress relaxation property of the asphalt material makes the deformation caused by the temperature rise and fall not produce excessive temperature stress, but when the temperature drops, the asphalt material will gradually hard and begin to shrink, asphalt surface layer If the tensile stress produced exceeds the tensile strength of the asphalt mixture, the asphalt layer will crack. Especially in the large temperature difference between day and night, in the asphalt surface will have a greater temperature stress, long-term repeated temperature rise and fall will lead to asphalt surface temperature stress fatigue, reduce the asphalt mixture limit tensile strain, plus asphalt Aging to reduce the stress relaxation performance of asphalt, and ultimately to the ultimate tensile strength, so that cracks in the road.
(3) vehicle load. In the investigation of the distribution of the sub-lanes of expressway pavement cracks, the distribution of the pulp and the crack is mainly in the traffic lane, and the horizontal and vertical cracks are staggered or even cracked, which fully explains the influence of the heavy-duty vehicle on the road cracks Very large, and even the structural damage to the road. The investigation shows that the asphalt pavement destruction is often concentrated in the rainy season, when the asphalt pavement is highly permeable or poor drainage, the rain through the asphalt surface gap or gap, soaking the structure layer material and even subgrade soil, to increase the deformation, , Reduced bearing capacity, shortened service life. Especially in the role of traffic load, into the gap between the pavement structure layer of water, will become a high pore water pressure and high flow rate of water, scouring the surface material, to promote the asphalt surface peeling, loose and other diseases, and then damage The performance of the entire pavement structure.
3. Common crack prevention and control measures.
(1) sewing seam with sewing method. First remove the cracks in the dirt, and then according to the size of the crack, cutting the size of the paste seam, usually 2cm wide, but also pay attention to avoid sticking with veneer contaminated. With a spray gun baking sewing belt, when the sewing surface of the oil point and paste the paste with the paste surface becomes slippery, the seam can be attached to the seam surface. In the end of sewing seam, baking time should be slightly longer.
(2) mechanical irrigation joints. Mainly used slotting machine, filling machine, air compressor and other irrigation joints. Including slotting, clear seam, irrigation joints, cooling and other processes. Is currently using more of a kind of perfusion processing methods.
(3) ordinary irrigation method. That is, the use of artificial in the field of asphalt heating, with iron pots or special equipment for irrigation joints, generally need to irrigate 2-3 times, asphalt can be cooled. This method is simple, low cost, but the treatment effect is poor, need to repeat the construction every year, do not advocate the use.