Discussão sobre métodos acelerados para a avaliação do envelhecimento de revestimentos de argamassas submetidos a ciclos térmicos: aplicação em argamassa com fíler de concreto

Abstract

Construction industry has shown a significant growth this past decade. With it, grows the demand for raw materials and there is a generation of waste at construction sites and in industries linked to the sector. According to the Ministery of Mines and Energy (MME) in 2008, sand production reached an estimated 279 million tonnes and it is estimated that in 2030 its production can reach 1.276 billion tons. The use of construction and demolition waste for the production of coating mortars can bring economic and environmental benefits, but its use is only possible if the coating is durable, supporting environmental actions. This study is the development, application and comparison between two thermal cycling test methods. The first method is based on the NBR 15575-4:2013 standard, uses radiant boxes and consists in unilateral exposure of masonry coated to simultaneous cycles of heating and cooling under wetting. This method were also underwent to thermal exposure 3 prisms of each mortar, in the dimensions of 40x40x160 mm. In the second method, the coated system is fully exposed to temperature variations and remains in a climatic chamber that performs repeated heating and cooling cycles. The mortars used and applied to ceramic substrates have been produced in a proportion of 1: 1: 6 by volume (cement, lime and sand) using Brazilian cement CP II F-32, CH-I lime putty, river sand and filler produced from recycled concrete aggregate (RCA), in compositions with varying content (2, 4.5; 7 and 9.5%) relative to the mass of sand. The first activity of the experimental program was the development of the methods for performing thermal cycling and in their assessment. Mortars and coatings were produced, and then was performed thermal cycling. The method using a climatic chamber for thermal cycling has showed lower efficiency for the degradation of mortar; the method that uses radiant thermal boxes has demonstrated greater efficiency in the accelerated aging of the coatings. The thermal cycling exposure resulted in a significant loss of properties of the prisms, in all addition levels of ARC’s filler. The thermal cycling in mortar applied on the ceramic substrate showed less degradation than the prisms, and the two coatings with a low content of filler (2% and 4.5%) showed higher degradation in mortars while other coatings (with 7 and 9.5% of filler) had the lowest coating bond strength.