After PROSTAR is poured into holes drilled in rock or concrete the expansive stress gradually increases with time and it becomes more than 30 n/mm2 at room temperature after 16 hours
As PROSTAR generates its expansive stress the object to be cracked undergoes a process of £¨1£© crack initiation £¨2£© crack propagation and £¨3£© the increase of crack width therefore this fracture mechanism is distinguished from a breakage by blasting
The mechanism by the expansive stress of PROSTAR is shown in fig 4 cracks initiate from an inner surface of the holes being caused by tensile stress at a right angle with stress of PROSTAR then as the expansive stress of PROSTAR is kept up even after the appearance of cracks the cracks propagate and also new cracks initiate during the process usually for a free surface exists the crack as shown in fig5 is pushed apart mainly by the bottom of the hole running toward the free surface when multiple number of holes that are properly adjacent to each other, are filled with PROSTAR the cracks from the hole propagate to connect with the neighboring holes as shown in fig6 it is therefore possible to determine the directions of the cracks by appropriately arranging the hole spacing its depth and its inclination
Fig.4:Fracture Mechanism by the Expansive Stress of PROSTAR
Fig.5:Sectional-view of the Crack Formation in the Material with Two Free Surfaces
Fig.6:Crack Propagation
