Abstract
Fiber cement, similarly to all cementitious materials, undergoes dimensional and volumetric changes when it is exposed to dry and wet environments. When exposed to natural weathering, cement-based materials absorbs and may also release water to their surroundings via a very complex inherent pore structure. In this work initialized a few years ago, some properties of asbestos-free fiber cement composites were studied, such as density, porosity and loss or absorption of water. For the understanding of the behavior of this material, modifiers were employed in the cement matrix such as styrene- acrylic, styrene-butadiene and vinyl acetate-versatic vinylester copolymers to verify their influence on the variables described above. All composites were analyzed by mercury intrusion porosimetry (MIP). For monitoring the expansion/shrinkage movements, the specimens were exposed inside a controlled environmental chamber with constant temperature and relative humidity (RH) during the test time. The results showed no interference on hygral behavior because particular casting process of these composites but, as showed by literature, increase of toughness. Also, it was possible to verify that moisture movement within the asbestos-free fiber cement can be very complex and the variables density and porosity (pore structure) play a very important role in the expansion/shrinkage properties of these composites.
Highlights
Cement-based composites exposed to natural weathering absorb water and may release water to the surroundings via a very complex inherent pore structure
In Brazil, frequently failures have been observed in joints of asbestos-free fiber cement sheets because the excessive moisture movements of these composites
Various forms of shrinkage are associated with cementitious materials and since drying shrinkage is among the most troublesome, it is a useful tool for the performance evaluation in the development of improved materials
Summary
Cement-based composites exposed to natural weathering absorb water and may release water to the surroundings via a very complex inherent pore structure. Various forms of shrinkage are associated with cementitious materials and since drying shrinkage is among the most troublesome, it is a useful tool for the performance evaluation in the development of improved materials It is evident from the factors mentioned above that it would be an extremely difficult task to describe the exchange of water in the pores of cement-based fiber composite during exposure to natural weathering. The transportation of pore water in fiber cement composites is complex, it is important to describe in general terms the behavior of the material under certain climatic conditions as the exchange of water in the pores results in dimensional changes (expansion or shrinkage) within the product. This paper shows the influence of density, porosity (pore structure) and sorption of water in the moisture movements of asbestos-free fiber cement where exchanges in these variables were made by the use of different copolymers
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