Avaliação de aderência à tração em argamassas utilizando a técnica de ultrassom

Abstract

It is possible to verify, in Brazil, numerous pathologies involving the constructions made and many of them are related to the mortar coatings. In addition, coatings are very important as they account for 10 to 30% of the total cost of construction and 100% of the seal tightness of ordinary masonry. Given the context presented, the present work aimed to establish a correlation between the results of a non-destructive test, ultrasound, and a destructive test, the pullout, which determines the tensile bond strength, one of the main properties of the mortar. To this end, 10 concrete slabs were built that served as substrate, with dimensions of 25 cm wide, 50 cm long and 4 cm high. The plates were made according to the recommendations of NBR 14081-2. Subsequently, on each slab were applied industrialized mortars of the type Medium Plaster and Thick Plaster, being 5 slabs used as substrate of each type of mortar. The mortar layer was 2 centimeters thick. In each of the 10 plates, in sequence, 8 samples were delimited, according to the instructions of NBR 15630, to perform the experimental procedures. Ultrasound tests were performed according to NBR 15630 and pullout tests according to NBR 13528. Through statistical and graphical analyzes, results considered very discrepant with the others were eliminated and a correlation between the tests was elaborated, using Pearson's correlation coefficient, thus measuring the strength of the interaction between the data pairs. For those in which a strong correlation was found, trend lines and linear regression equations were developed, which resulted in forecasts with more than 60% accuracy for Medium Plaster and over 50% accuracy for Thick Plaster. It was concluded that, although few plates presented a strong correlation between the test results, those that presented such correlation provided the construction of satisfactory equations, whose prediction of pullout resistance through the ultrasound data was very close to the value obtained, mainly for Medium Plaster. It is therefore possible to predict the tensile strength of the mortar using the ultrasound test.