20 BULLETIN 1077, U. S. DEPARTMENT OF AGRICULTURE. 



JOINTS. 



Concrete contracts or expands with changes in temperature and 

 differences in moisture content. It also shrinks materially during the 

 period of setting and initial drying out. In practically all early 

 concrete pavements transverse expansion joints were constructed 25 

 to 30 feet apart, with the idea of relieving the pavement slabs of all 

 stresses due to expansion and contraction, thereby preventing trans- 

 verse cracking due to tensile stresses or failures due to compressive 



Dcy = Coordinates of Point opposite PC. 



DC|U| = Coordinates of PC, 



F= Offset from Tangent to Circular Curve. 



£,= Length of Transition Curve. 



F= Central Angle of Transition Curve. 



= Central Angle of Circular Curve from PC. to PC.,. 

 "U/= Amount of Pavement Widening. 



Fig. 5. — Method of widening curve.s using transition curves. 



stresses. In these pavements it was found, however, that a majority 

 of the slabs cracked transversely, that it was very difficult to secure 

 a pavement Avith good riding qualities in the neighborhood of the 

 joints, and that if the expansion joints were not constructed so as to 

 be perpendicular to the surface of the pavement the end of one slab 

 was very likely to rise above the end of the adjacent slab. Not in- 

 frequently this relative movement amounted to 2 or 3 inches and in- 

 convenienced traffic very materially. If the joint varied from the 



