Degradation of rendering mortars made with fine concrete aggregates by thermal cycles

This study evaluates the loss of the properties of rendering mortars with recycled fine aggregate submitted to thermal cycling tests based on the NBR 15575-4 (ABNT, 2013) standard. The mortars were produced at a mix-proportion of 1:1:6 in volume (cement, lime and sand) using Brazilian cement CP II F-32, CH-I lime putty, river sand and fine aggregate produced from recycled concrete, in compositions with 2, 4.5, 7 and 9.5% relatively to the mass of sand. The rendering mortars were applied on ceramic substrate and evaluated, at 28 days of age, for bond tensile strength (NBR 13528 (ABNT, 2010)), surface hardness determined by Shore durometer type D (ASTM D 2240-5 (AMERICAN..., 2005)) and the velocity of ultrasound waves. The systems formed by the rendering mortars applied on the ceramic substrate were subjected to accelerated ageing by exposure to thermal cycling, which degraded the mortars. All rendering mortars presented superficial hardness decline (in the order of 10%), lowered velocity of ultrasound waves (about 25%) and lowered bond tensile strength by about 15%. The evaluation of the rupture of the rendering mortars showed that those with 2 e 4.5% fine aggregate content suffered the greater degradation.

Keywords:
Accelerated ageing; Recycled fine aggregate; Rendering mortar; Thermal cycle