Evaluation of early age cracking in rendering mortars with polypropylene fibers

The incorporation of fibers in concrete produces an improvement in the characteristics of the material as observed in different studies. In order to obtain the same good results, fibers are added to rendering mortars to reduce some of their drawbacks. However, this type of mortar has some specific characteristics, such as hydrated-lime utilization or higher air, which is not usual in concrete. Thus, this study aims to evaluate the potential of polypropylene fibers to reduce early age cracking caused by restrained shrinkage in rendering mortars. Two types of mortars were used to verify possible differences in the way they responded to the introduction of fiber. The influence of the fiber content was also investigated. Mortars were evaluated in fresh state, and mechanical behaviors were measured at several ages. The restrained shrinkage cracking was followed for 21 days using the ring test method. The use of polypropylene fibers leads a smaller value of total crack width and a delay of the first crack. Also, the elastic modulus shows a higher correlation with the mortars crack width. Both parameters were successfully used to predict the mortars crack width. The ring test method may be a suitable test method to evaluate the capacity of fibers to control the crack formation in rendering mortars.