Estudo do desempenho de um novo ensaio na definição de parâmetros referentes à ligação entre concretos e à recuperação localizada de pilares

Abstract

The research presented in this report proposed to investigate the capability of a new test - the Sleeve Test - to provide data regarding bond (both adhesion and friction) between concrete of an existing reinforced concrete column (old concrete) and concrete that will be used in its recovery (new concrete), as well as information regarding sleeve transverse reinforcement (helical reinforcement/spirals or welded hoop reinforcement/ties) that can guide recovery designs using the reinforced concrete jacketing technique, especially the localized jacketing. The experiments were divided into eight series, distinguished by the nominal concrete compressive strength (20 or 30 MPa); by the size of course aggregate (gravel 00 or gravel 1); by the height of old-new concrete interface (10, 14 or 17.5 cm); as well as the specimen cross-sectional geometry (circular or square) and, finally, by the presence or absence of longitudinal reinforcement in them. For each series, in addition to the Sleeve Tests, tests were performed according to ABNT standards, for the characterization of both old and new concrete mechanical properties (compressive strength, tensile strength and modulus of elasticity). The theoretical tensile rupture loads of the eight series were calculated using formulations recommended by ABNT NBR 6118:1980 for confined columns and compared to the experimental rupture loads. The observed correlations indicate that rupture load values theoretically estimated can be used, with appropriate adaptations, in the design of repaired columns by localized reinforced concrete jacketing. In four series, Slant Shear Tests were also performed on cylindrical test specimens (9,8 cm in diameter and 20 cm in height) inclined at angles of 45º; 52.5º; 60º and 75º. By the test date of each one of the eight series, the age of old concrete ranged between 461 and 573 days and the age of new concrete (grout) was always 7 days. Experimental values for the adhesion and friction between old and new concrete were obtained from the Sleeve Test results, according to a theoretical formulation specifically proposed for them. Regarding the Slant Shear Tests, the theoretical formulation has already been well defined in the literature. Comparison between experimental results obtained from both tests, with appropriate considerations to the specimen rupture modes, showed that, by using a single specimen geometry, the Sleeve Test presents the advantage of providing friction angles ranging from the lowest to the highest (above 75o) values. The high values for the friction angles (74.2º to 78.4º, exceptionally, 82.8º) between old and new concretes obtained by using the Sleeve Test were qualitatively corroborated by the results obtained from the Slant Shear Test because, by using this later method, the rupture of specimens occurred basically, even for a slope angle of 75º, in a monolithic manner, i.e, outside the slip inclined plane, a fact that prevented a reliable definition of values for adhesion and friction by means of this test. Another advantage of the Sleeve Test is that it implicitly takes into account the difference between values for modulus of elasticity and Poisson ratio of old and new concretes. However it should be emphasized that the definition of adhesion and friction by means of the Sleeve Test requires a priori the definition of the new concrete tensile strength. In this research, such resistance was obtained by means of the Splitting Tensile Strength Test (Brazilian Test). One additional and important advantage of the Sleeve Test is to provide support to the definition of sleeve transverse reinforcement (confinement reinforcement) that is capable of rising the specimen rupture stress up to the level required by the column repair design. Based on Sleeve Tests results, the localized recovery design was proposed for two different reinforced concrete column models (15x15 cm and 20x20 cm in cross-sectional dimension) presenting a total loss of resistant capacity in 5 cm in its mid third length. For each model, two columns were tested: one with its original cross section (original column) and another with its original cross section totally damaged and recovered by applying the reinforced concrete jacketing sleeve (recovered column). The tests performed with both recovered columns showed that the rupture occurred outside the jacketing sleeve and no relative displacement between the sleeve and the recovered column was observed. These facts indicate not only that column localized recovery by reinforced concrete sleeve jacketing can be efficiently and safely executed but also that the adopted calculation methodology based on the confinement reinforcement expressions deduced from the Sleeve Test results can be used in this type of design, until further research allows the definition of a more refined methodology. Therefore, based on the results obtained from this experimental research, it can be concluded that the Sleeve Test is capable to provide sufficiently reliable data related to the bond (both adhesion and friction) between old and new concrete, as well as to the confinement reinforcement necessary to guarantee efficient behavior of localized recovery of columns by using reinforced concrete sleeve jacketing.