chapter  0
21 Pages

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Where ft(t) and GF(t) are tensile strength and fracture energy at different ages. They can be determined by tests. The similar Eqs. for bilinear assumption can be obtained in the same way. Table 1 gives the results of our tests [2 ]. There are more than 8 specimen in each age-group. TABLE 1

An expressway and some highways were monitored for long time to summarize characteristics of cracking. Tests were conducted to explore the influence factors such as structures and materials of pavements. An important observed fea­ ture of transverse cracking is it'll form a final regular cracking state giving equivalent crack spacing. A hypothesis of section contraction in overlay is presented and the finite element method is used to calculate the temperature stress field. Results show that stress concentration exists at the free-edge of overlay under low temperature contraction and the good bonding action between subgrade and overlay may reduce the stress concentration. The shear-lag model of two-layer system is used to explain the final regular cracking state and gives good agreement with experimental re­ sults. Study shows that increasing the thickness or the elastic modulus of pavements and decreasing the elastic modulus of base, especially increasing the crack depth in base will decrease the regular transverse crack spacing. Longitudinal cracking in the center of road is also regarded to be caused by the same mechanism of transverse crack­ ing. Its onset depends on the relative magnitude of the width of road and the regular transverse crack spacing. To pre­ vent transverse cracking in rigid pavements, the spacings of joints should be less than the regular transverse crack spa cing.