Effect of Natural and Polypropylene Fibers on early Age Cracking of Mortars

Throughout time, the use of lignocellulosic resources has been implemented in the development of building materials. Among these resources, natural fibers are used as mineral binders reinforcement due to their specific mechanical properties. This experimental investigation focused on effect of flax and hemp fiber reinforcement on the resistance of pozzolanic-based mortars to cracking due to restrained plastic shrinkage. Results were compared with polypropylene fiber reinforcement and with control mortar without fibers. The quantity of fibers added to the mortar mix were respectively 0.25% - 0.5% by mass of binder for polypropylene fibers and 0.5% - 1% by mass of binder for flax and hemp fibers. All fibers have a similar length of 12 mm. The cracking sensitivity was evaluated based on two different methods: the first consists in casting the mortar in a metal mold with stress risers whose criteria are inspired by the ASTM standards. The second consists in pouring the mortar on a brick support. In order to assess the effect of fibers on cracking due to restrained plastic shrinkage, the number of cracks, total crack area and maximum crack width within the first 6 hours after casting were determined using digital image correlation (DIC). Results showed that the flax and hemp fibers were more effective in controlling restrained plastic shrinkage cracking compared to polypropylene fibers. With a natural fiber of 1% by mass of binder, maximum crack width was reduced by at least 70% relative to control mortar based specimens. Natural fibers show great ability to propensity for cracking due to restrained plastic shrinkage; so that, they could be an alternative and ecological solution for polypropylene fibers.

Investigation of the Efficiency of Manufacturing Polymer Molds by FDM-Printing

The results of experimental studies of the efficiency of manufacturing polymer foundry models by the FDM method are presented. Rational consumables for 3D-printing are revealed. The optimal values of the shrinkage value of the 3D-model during printing and the parameters of the 3D-printer operation mode are revealed. It has been established that polymer casting molds are rationally manufactured by FDM printing, using ABS-plastic as a consumable, while making a correction to linear dimensions at the stage of creating a 3D-model to eliminate plastic shrinkage.