Assessment By Law of Mixtures Approach of Interfacial Adhesion Strength in Cellulose-Cement Composites

Cellulosic-pulp-reinforced cement sheets are produced in large scale for more than 25 years. This followed studies that had focused on the fibre and matrix characteristics, and on their composite behaviour, solving to a limited extent the problems arising from fibre-matrix incompatibility and deterioration due to alkali attack. In spite of that, much has yet to be done in terms of providing a material with properties competitive with those of asbestos cement, mainly considering their long term performances. Current research on cellulose-pulp reinforced cement composites concentrates on evaluating the deterioration mechanisms, the treatment methods and the modelling of the effects of these mechanisms on the physical, mechanical and micro-structural aspects of the material. Interfacial adhesion governs the mechanical behaviour and many physical properties of composites. Therefore, it is a key issue when focusing on durability, since the deterioration mechanisms and the treatment methods exert direct influences on the fibre-matrix interface. Direct assessment of adhesion strength by pull-out tests on fibres generally shorter than 2 mm in cellulose-cement composites presents practical difficulties. Also, direct application of the equations derived from the composite's micromechanics to this type of cement composites, as produced by the vacuum-dewatering process, and containing high volume fractions of curly fibres would be problematic. Fortunately, a significant amount of data is available in the literature regarding the physical and mechanical behaviour of cellulose-cement composites of a variety of compositions and produced under similar conditions. This allows establishing mutual correlations. This is used as reference framework for the design of the cellulose-cement compositions tested by the authors. The outcomes reveal this approach a valuable tool in comparative studies on the mechanical behaviour of cellulose-cement composites dealing with effects of treatment methods, deterioration mechanisms and processing parameters.