CDW recycled aggregate renderings: Part I – Analysis of the effect of materials finer than 75 μm on mortar properties

Experience shows that renderings produced with natural sands or construction and demolition waste (CDW) recycled aggregates could have a tendency to poor performance, due primarily to the variable quality of the sands, the absence of a well established mix design method for mortars, and other factors such as façade design, substrate quality and the placement technique. This paper focuses some of those factors, particularly the effectiveness of a mix design method for the control and analysis of the influence of the recycled aggregate composition on the properties of mortars and renderings performance. The leveling time of renderings was also studied. The mix ratio of Portland cement, natural fine sand and laboratory recycled sands – from ceramic blocks, concrete bricks and milled mortar – was defined by a mix design method previously studied. The method takes into account two parameters for the mix design of mortars: the “aggregates and plasticizing materials to cement ratio” and “the total materials finer than 75 μm” in the dry mortar. This study analyzes the effectiveness of the second parameter for the control of the performance of mortars and renderings. In Part I, results show how the geology of the river and CDW recycled sands and the “total material finer than 75 μm” parameter can be correlated in order to explain the properties of mortars, as the cement content is kept constant. The variations in water requirement and physical and mechanical properties of mortars were analyzed, namely drying shrinkage, compressive strength, tensile strength and compressive elastic modulus. The performance of the renderings will be discussed in Part II of this paper.