Lightweight pozzolanic materials used in mortars: Evaluation of their influence on density, mechanical strength and water absorption

Lightweight aggregates are widely used in renders to obtain low densities and better workability. This type of aggregate requires higher than normal water:cement ratios, especially in renders involving the addition of alkyl celluloses or modified starches. This paper reports the effect of some lightweight materials (expanded perlite, expanded glass, hollow micro-spheres and expanded polystyrene) on density, fluency, sorptivity, water absorption and mechanical strength, all of which play an important role in renders and coatings. The percentages of the lightweight materials are: 0%, 0.58% and 1.74% w/w on the whole composition. The experiments show that mechanical strength, sorptivity and water absorption are affected in different ways, depending on the lightweight material and the dose used. Expanded glass and hollow micro-spheres showed some pozzolanic activity, which was corroborated, by short-term compressive strength tests, in specimens of lime and cement that were tested after seven days. Finally, conductivity tests were carried out using lime suspensions in the presence of such pozzolanic materials.