Experimental Investigation On Shrinkage And Cracking Property In Polypropylene Fiber-mortar

The shrinkage and crack resistance properties of polypropylene fiber reinforced mortar are investigated, from the aspects of function mechanism, experimental investigation and engineering application. The crack resistance mechanism of polypropylene fiber is explored, moreover, parameters such as the respective contents of fly ash and polypropylene fiber is determined. The effects of fly ash and polypropylene fiber on cement mortar mechanical properties as well as the influences of polypropylene fiber on cement mortar properties, such as anti-plastic cracking and dry shrinkage are systemically analyzed; thereby the optimum polypropylene fiber content in cement mortar is obtained. Making an especially useful attempt to quantitative evaluate the cracking-resistance property of polypropylene fibers cement mortar, the best evaluation method of cracking-resistance is discovered.Research in this paper shows that, cement mortar with C/S of 1:3,W/C of 0.65, and fly ash amount of 10% displays the best performance; With the increase of polypropylene fiber content, cement mortar's rupture strength and compressive strength during each age all firstly decline and then increase, while the ratio of rupture strength to compressive strength varies very small, its anti-plastic cracking and shrinkage cracking resistant properties increases significantly. The mix of fiber into cement mortar can reduce its dry-shrinkage ratio in free shrinkage conditions at the same age, while under the restrained shrinkage conditions the dry-shrinkage ratio firstly increases, and then decreases.As the results of mortar plastic shrinkage cracking experiment tested by slab type method shows, the cracks firstly appears in mortar without polypropylene fiber. With the augment of polypropylene fiber content, occurrence time of the first crack delay, the number of large crack descends or the width of crack decreases. Weather resisting property experiment showed that the special plaster mortar is basically no cracking if the content of polypropylene fiber becomes more than 0.3%. Based on overall experimental study and theoretical analysis, the optimum content of polypropylene fiber in cement mortar can be determined, that is 0.3%.Finally, using self-designed constraint experimental device, the dry-shrinkage ratio of mortar with different polypropylene fiber content is tested, fiber mortar shrinkage stress during all ages are calculated, the effects of age and fiber content on mortar shrinkage stress are analyzed. The elastic modulus formula of mortar with different polypropylene fiber content has been derived, a kind of quantitative evaluation method of mortars crack resistant has been put forward, and an evaluation index of mortar crack resistance is established.