Durability of coating mortars containing acai fibers

Mortars with external coating are often subjected to situations of sudden degradation, such as heat stroke, salt attack in coastal environments, or rain. Therefore, the objective of this work was to evaluate the results of durability of mortars with external coating in the proportion 1: 1: 6: 1.5 (cement: hydrated lime: sand: water), containing incorporation of 0, 1.5, 3.0 and 5% of fiber of acai treated with NaOH solution. The main importance of this work is to improve the understanding of the durability of cementitious mortars containing natural fibers, especially acai fiber. After characterizing the fibers using SEM-EDS, 50 x 100 m cylindrical specimens were cured at room temperature for 28 days and tests were carried out on compressive strength and mass loss in mortars subjected to degradation by wetting cycles and drying, salt spray exposure and thermal shock. It was proven that mortars containing up to 3.0 % of acai fiber underwent reinforcement with the incorporation, presenting an increase in compressive strength from 6.23 to 8.41 MPa, but that mortars containing 5.0 % suffered a drop in resistance due to the excess of fibers, which compromised the wetness of the cementitious matrix. In addition, the durability results proved that the presence of fibers in a percentage of up to 3.0 % created an adhesion and stress transfer bridge that reduced the drop in strength and the loss of mass of the material when subjected to durability in tests wetting and drying and thermal shock tests. This fact is proven by comparing the compressive strength of mortars after the wetting and drying cycle in which the reference composition showed resistance of only 4.37 MPa against 6.65 MPa for the composition with 3%. The same is observed in mortars after thermal shock tests, with a resistance of only 5.82 MPa for the reference composition and 7.02 MPa for the composition with 3% acai fiber. The exception occurred in salt spray tests, where mortars performed very poorly due to the rotting of the acai fibers, which because they are organic deteriorated in the presence of salts. Even so, it was found that mortars with 1.5 % fiber show a better behavior than the reference mortar in all situations, including in salt spray attack. (C) 2020 The Authors. Published by Elsevier Ltd.