Expansion joints are set to prevent cement concrete from being crushed or arched at the edge of contraction joints when the temperature rises. Shrinkage joint is to prevent concrete from producing irregular cracks when the temperature drops. Expansion joint is to prevent the extrusion joint between plates from being too wide, and it needs to be filled with asbestos and asphalt, while contraction joint is not needed. Technical Requirements When there is no requirement in the design, the spacing between contraction joints and expansion joints shall meet the following requirements: 1. The longitudinal contraction joint spacing is generally 3 ~ 6 meters, and 3 meters should be used when the construction temperature is high; Second, the transverse contraction joint spacing is generally 6 ~ 12 meters, and 6 meters should be used for outdoor ground or high temperature season construction; Three, the gap between expansion joints is generally 30 meters. Longitudinal seam? Joints on cement concrete pavement slab parallel to the road centerline.

Longitudinal seam has the form of flat seam and tongue-and-groove seam. Generally, the form of flat seam and pull rod is adopted. The tie rod is made of threaded steel bars, and its position is located in the center of the plate thickness. There are many forms of longitudinal seam, which can be summarized as: (1) vertical longitudinal seam, (2) staggered seam and (3) oblique seam. Vertical and longitudinal joints are the most widely used method for pouring concrete dams. Generally, keyways must be left on the longitudinal joint surface, and a grouting system should be arranged, and the dam should be sealed after the dam is cooled to a stable temperature. From the structural point of view, the longitudinal joint will cut the complete section into several pieces, which will cause significant stress redistribution. Therefore, in general, longitudinal joints must be grouted. Because these costs are huge and require strong cooling capacity, the dam can not be stored immediately after pouring, which has an impact on the overall progress of the project construction.

Expansion joint refers to the expansion joint set on the cement concrete pavement slab. Its function is to make the cement concrete slab expand and contract freely when the temperature rises, and the real joint should be adopted.

? The purpose of setting expansion joints is to eliminate temperature stress caused by temperature change. In principle, there should be few or no expansion joints. The author thinks that the following points should be considered when setting expansion joints.

(1) In winter construction season, expansion joints are generally set every 100~ 150m; In summer construction, if the thickness is more than 20cm, expansion joints are not needed. In other cases, a joint is generally set every100 ~ 200m during construction.

(2) Expansion joints shall be set at all tangents of urban road intersections.

(3) The expansion joint should be set at the joint with the fixed structure.

(4) In general, the turning radius r

(5) When connecting with flexible pavement, it can be set as shown in Figure 2 if it is a high-grade highway, and as shown in Figure 3 if it is a general-grade highway.

(6) The vertical curve can be provided with tenon-less expansion joints at the slope change point, but the concave vertical curve can be provided with no expansion joints, because the tensile force generated by temperature is equivalent to a relatively stable prestress applied to the concrete slab, which is a stress beneficial to the slab.

(7) For urban roads with small longitudinal slopes, it is generally unnecessary to add expansion joints on convex curves.

(8) The temperature difference in the tunnel is not large, so it is not necessary to set expansion joints. Generally, expansion joints are only set at entrances and exits.