M. L. L. OLIVEIRA, P. J. P. GLEIZE and H. R. ROMAN Universidade Federal de Santa Catarina Departemento de Engenharia Civil – Caixa Postal 476 CEP 88040 – 970 – Florianópolis – SC – Brazil
This research is part of a project with the objective to show that the presence of polypropylene fibres in hydraulic binder based materials can lead to an improvement of their physical and mechanical characteristics. The benefits of the use of polypropylene fibres in the concrete are well known (for example, it leads to a shrinkage decrease). On the other hand, the use in masonry mortars (at least in Brazil) is very scarce. The use of polypropylene fibres in masonry mortars can play a significant role in the improvement of the quality of the masonry mortars. This work is divided in two parts. In the first part, the influence of the addition of 1 and 2% of two types (monofilament and multifibrilated) and two lengths (12 and 18mm) of polypropylene fibres on compressive strength of a cement-lime mortar and, masonry prisms was studied. Mortars volume proportions were 1:1:6, the water proportion being adjusted to reach the required consistency. Surprisingly, results showed that the addition of fibres, even if the water/binder is higher, increased the mortar compressive strength principally in the case of the 18mm length multifibrilated fibres. In the same way, the fibres contribute to increase the masonry prisms’ compressive strength. An increase of the efficiency ratio (ratio between the block compressive strength and the prism compressive strength) can be very useful for the dimensioning of structural masonry walls. In the second part of this work, the influence of the addition of low quantities of polypropylene fibres (0.05%, 0.15% and 0.30%) was studied on the main physical and mechanical characteristics of a cement-sand mortar (1:3 by volume) and two cement-lime-sand mortars (1:0.5:4.5 and 1:2:9 by volume). Results showed that the addition of fibres reduces the consistency but improves the cohesion of mortars. The fibres improve appreciably the water retention but only for mortars without lime. As expected, the fibres improve the dimensional stability of the mortars. From the mechanical point of view, statistically the fibres have no effect on the compressive and flexural strength of the cement mortars or cement-rich mortars; on the other hand, for the low-cement mortars, there were decreases in both compressive and flexural strengths. The addition of fibres improves the mortar’s ductility especially for cement-rich mortars.