Experimental Investigation On Early-age Shrinkage And Cracking-resistance Property In Polypropylene Fiber-reinforced Concrete

This paper studies the early-age shrinkage and cracking-resistance property of polypropylene fiber reinforced concrete. we discussed it from three aspects including formation mechanics, experimental investigation, and theoretical research.A new type of apparatus for measuring early-age shrinkage is presented on the basis of advantages and disadvantages of the follow apparatus in or aborad. Sufficient tests indicate manifestly the apparatus has the characters of high accuracy, convenience. We also improved the ring-shaped restrained apparatus , so that we can quantitatively test the strain-stess relationship of concrete when it was restrained. The main research results were expressed as the follows.First, we studied on the effects of different additions polypropylene fibers on the early-age plastic shrinkage and workability of concrete under two different test conditions. The results showed that: polypropylene fibers can both reduce the early-age shrinkage of concrete by a certain range under two conditions; however, the addition of polypropylene fibers bring an obvious slump loss to fresh concrete ,Compared with under the test condition of the same water-cement ratio, the shrinkage-reduced of polypropylene has a little drop under the same slump condition.Second, conventional ring-shaped testing system was developed, and the development of self-induced tensile of concrete under partially restrained condition was investigated. The results showed that the time of cracks appeared delayed, and the length, width and number of fiber reinforced concrete are all lower than reference without fiber. Combined with the research results of early-age free shrinkage and restrained shrinkage, we also analyzed the mechanism of shrinkage-reduced and crack-resistant of polypropylene fibers; the results mentioned above are the coefficient results of shrinkage and creep.Finally, early-age shrinkage of Concrete containing polypropylene fiber,shrinkage-reducing agent and expanding agent solely or coherently are studied . The results show that, shrinkage-reducing agent can decrease early-shrinkage of concrete by an obvious rate; polypropylene fiber and expanding agent which were double-doped can increase effectively the shrinkage-reducing rate of the two materials which was single-doped. Combined with the results of cracking-resistance experiments, we found out an effective material measures to solve early-age cracking of concrete structure.