S. Eve

Microstructural and mechanical behaviour of polyamide fibre-reinforced plaster composites

Different concentrations of polyamide fibres with given aspect ratios were associated to a commercial plaster in a view to investigate the mechanical behaviour. The presence of these water-absorbent fibres perturbs the hydration of the plaster and causes changes in the plaster microstructure. All the mechanical parameters decrease monotonically as the concentration of fibres is increased, except the fracture toughness which shows a different trend. The ability of the composites to retain strength at the onset of matrix cracking has been forecast and analysed on a phenomenological basis in terms of a fibre efficiency factor which is a useful supplement to the usual mechanical characterisation of such materials.

Changes in plaster microstructure by pre-stressing or by adding gypsum grains: microstructural and mechanical investigations

Abstract The setting and the mechanical behaviour of a coarse-grained plaster were investigated by means of different techniques: adiabatic calorimetry and measurements of swelling pressure and dimensional variations during the setting, fracture strengths and toughness evaluation, and scanning electron microscopy (SEM) observations. Subsequently the microstructure of the plaster was modified by seeding with gypsum grains of controlled size and concentration, or by applying a compressive stress (pre-stressing) during the setting. The correlation of the microstructural features and the mechanical properties confirms the interest in these methods for mastering the characteristics of a number of widely produced plaster-based materials.

Effects of the hygrothermal environment on the mechanical properties of flax fibres

Since flax is the most promising plant for the reinforcement of polymer-based composites in structural applications, we have chosen to investigate its hygrothermal characteristics which can be useful for the understanding of the behaviour of other plant fibres. The flax fibres were exposed to different hygrothermal conditions: in an oven at various controlled temperatures (–40 to 140℃) and measured relative humidity, in a climate chamber at 50% relative humidity for define temperatures between 25℃ and 85℃, or different determined aging conditions. The correlation of these hygrothermal conditions to the evolution of the mechanical properties gives evidence of the prominent influence of water over temperature on the microstructural changes of flax fibres. The mechanical parameters drastically decrease in usually prescribed hygrothermal aging conditions for organic matrix composite materials, the strength being particularly sensitive to the presence of water. These evolutions were correlated to the fibre microstructure modifications induced by water absorption as revealed by electron microscopy analyses. These findings could be useful for understanding the behaviour of polymer matrix biocomposites in severe hygrothermal conditions.

Effects of Polyamide and Polypropylene Fibres on the Setting and the Mechanical Properties of Plaster

Abstract. We have investigated the setting and the mechanical behaviour of a commercial plaster reinforced with polyamide and polypropylene fibres or plasma-modified polypropylene fibres. The influences of the morphology (diameter, length), the concentration and the nature of the fibres were analysed in terms of the setting time, the dimensional variations and the mechanical properties of the blends. The fibres ability to prevent the composite failure in two distinct pieces depends on their elastic properties and their hydrophilic nature.

Microstructural and Mechanical Characterisation of Polyamide Fibre-Reinforced Latex-Filled Plaster Composite Materials

We have investigated the setting and the mechanical behaviour of latex-filled plaster (binary blends) and latex-filled plaster reinforced with polyamide fibres (ternary blends). The influences of the latex (nature and concentration) and the fibres (concentration, length and diameter) have been analysed in terms of the improvement of the mechanical properties of the plaster (flexural and compressive strengths, first matrix cracking strain, fracture toughness and fibre efficiency factor) and compared to previous results obtained on polyamide fibre-reinforced plaster materials. Introduction Due to its availability, relatively low cost and easiness of use, plaster has been widely used for a long time as a building material (staff, coating, decoration). The recent loss of interest for plaster is essentially due to its low impact resistance, a pronounced brittleness and water-related degradation sensitivity. A number of studies have reported noticeable amelioration of the mechanical properties of plaster by association of natural (sisal, waste paper) or synthetic (glass, polyamide) fibres [1-3] or by inducing changes in the plaster microstructure [4]. Another way for increasing the mechanical properties of plaster while retarding moisture penetration may consist in the addition of polymer latexes [5]. Since their commercial introduction in the early 1950s, epoxy resins in particular, and polymer latexes in general, are mixed with mortars and concrete in order to increase their mechanical parameters. The reinforcement mechanisms invoked include strengthening of the ceramic matrix and improved load transfer upon drying as the polymer had partially filled up the pores of the ceramic. A minimum amount of latex is required for the formation of a continious film within the blend [6]. In this paper we report on the setting, the resulting microstructure and the mechanical behaviour of binary and ternary blends obtained by adding different amounts of different latexes to a commercial plaster and reinforcing with polyamide fibres. Emphasis is put on the role of the polymeric phase in promoting the ability of the fibres to stabilise the first damage created upon loading, and its influence on the fracture toughness. Experimental Materials. A standard commercial plaster (Lutèce 75 from BPB Placo Lambert, Paris), made of 50 to 70% of β-hemihydrate (i.e 50 to 30% of CaSO4), was used for this study. The latexes were powders of vinyl acetate homopolymer (PA050) or vinyl acetate / vinyl versatate copolymers (PAV22P and PAV30, with a higher amount of versatate for the PAV30), polymeric dispersions in water (50 wt.% of solid phase) of a styrene acrylate copolymer (DS931) or an acrylate ester copolymer (DEC27). Different concentrations of each latex (1, 2, 3, 4, 5, 7, 8 and 10 wt.%) were first dispersed in water and then the plaster powder was poured and mixed to obtain a binary blend Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 1479-1482 doi:10.4028/www.scientific.net/KEM.264-268.1479