Porous concrete will shrink, so it is necessary to deal with its shrinkage character firstly when studying the problems of joint location and reflection crack of porous concrete base.

Character: high breaking tenacity, high modulus, low shrinkage, good creep-resistance and dimensional stability, one of the best reinfocement materials for semi-steel radial tire.

Mutual relation on molding shrinkage between central character and restriction character is studied, and connection formula is established.