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

Abstract 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.

摘要 本研究依据NBR 15575-4（ABNT，2013）标准开展热循环试验（thermal cycling tests），对掺加再生细骨料（recycled fine aggregate）的抹灰砂浆（rendering mortars）的性能衰减情况进行评估。本次试验所用抹灰砂浆按体积比1:1:6（水泥、石灰、砂）配制，原材料采用巴西产CP II F-32型水泥、CH-I型石灰膏、河砂以及再生混凝土制备的细骨料，再生细骨料的掺量分别为砂质量的2%、4.5%、7%和9.5%。将抹灰砂浆涂抹于陶瓷基底后，待其养护至28天龄期时，分别开展粘结抗拉强度（bond tensile strength，依据NBR 13528（ABNT，2010）标准）、采用D型邵氏硬度计（Shore durometer type D）测定的表面硬度（依据ASTM D 2240-5（美国材料与试验协会，2005））以及超声波传播速度（velocity of ultrasound waves）三项性能测试。将涂抹有抹灰砂浆的陶瓷基底试样进行热循环加速老化处理以实现砂浆性能劣化。所有受试抹灰砂浆均出现表面硬度下降（降幅约10%）、超声波传播速度降低（降幅约25%）以及粘结抗拉强度下降（降幅约15%）的现象。对抹灰砂浆的断裂破坏情况进行评估后发现，掺加2%与4.5%再生细骨料的砂浆试样劣化程度最为显著。