Abstract The literature indicates that it is difficult or even impossible to associate with strong statistical confidence the bond strength of a mortar coating with the properties of the ceramic block, such as roughness and water absorption. In this work, it is assumed that the variability in capillary water absorption and roughness, and the use of methods that provide differences in sampling area are key factors that make it difficult to model and obtain a proper correlation between these properties and the tensile bond strength of the render. Blocks with different porosities and roughness were used in the experimental program, and an original methodology was defined. Substrate properties showed high variability between blocks in the same batch, and in different regions of the same block. The proposed methodology allowed to obtain a significant correlation between substrate properties and the render’s tensile bond strength.

Resumo O emprego de agregado reciclado de concreto (ARC) para a produção de novos concretos é uma alternativa interessante para mitigar impactos ambientais. O ARC pode aumentar a porosidade e impactar negativamente as propriedades do concreto. A cinza de casca de arroz (CCA), empregada como material cimentício suplementar, pode mitigar estes efeitos. Este estudo investiga a retração em concretos produzidos com ARC e CCA, propondo um modelo matemático para explicar os comportamentos observados. Foram elaborados concretos com 25 e 50% de ARC graúdo, e 10 e 20% de CCA em substituição ao cimento, com uma única relação água-aglomerante (0,64). A absorção e água capilar e total, bem como a porosidade, foram avaliadas aos 28 dias. A retração foi medida em 1, 4, 7, 14, 28, 63, 91 e 112 dias. Os resultados indicam um efeito significativo da interação entre ARC e CCA.

Abstract The admixture of recycled concrete aggregates (RCA) in new concretes is an interesting alternative in the efforts to mitigate environmental impacts. RCA may increase porosity and change properties of concretes. Rice husk ash (RHA) is employed as supplementary cementitious material may improve concrete properties. The present study investigated the shrinkage of concrete prepared with RCA and RHA, proposing a mathematical model to explain the phenomenon. Concretes were produced with 25% and 50% of coarse recycled aggregate as replacement of natural aggregate, 0%, 10%, and 20% of RHA as replacement of cement, and a water-to-binder ratio of 0.64. Water absorption and capillary and total porosities were analyzed on day 28. Shrinkage tests were conducted on days 1, 4, 7, 14, 28, 63, 91, and 112. The results point to a significant interaction between RHA and RCA.