Interfaces in Fibre Reinforced Cements
- PDF / 4,593,914 Bytes
- 12 Pages / 420.48 x 639 pts Page_size
- 21 Downloads / 207 Views
INTERFACES IN FIBRE REINFORCED CEMENTS
A. BENTUR Building Research Station, Department of Civil Engineering, Institute of Technology, Haifa, Israel
Technion,
Israel
ABSTRACT The microstructure of the matrix in the vicinity of the fibre surface is quite different from the microstructure of the bulk paste matrix. This can have an important effect on the processes that take place at the interThe present paper face, such as crack-fibre interaction and debonding. describes the special structure of this zone, in monofilament and bundled fibre reinforced cements, and discusses its effects on some characteristics of the mechanical performance of the composites, which cannot be predicted by analytical models assuming a uniform matrix up to the fibre surface. The modification of the microstructure at the interface as a means for improving properties in some composites is described.
INTRODUCTION Fibre reinforced cements, as well as other cement composites, are characterized by a transition zone in the vicinity of the fibre surface, in which the microstructure of the paste matrix is considerably different from the microstructure of the bulk paste, away from the interface. The nature and size of this transition zone depends on the type of fibre, the production technology and, in some systems, it can change considerably with time. The nature of the transition zone plays a major role in controlling some of the properties of fibre reinforced cements, since it is in its vicinity that the critical processes during loading take place: (a) interaction of a propagating crack, initiated in the brittle matrix, with the fibre that should be arresting its advance; and (b) debonding and pull out of fibres bridging over the crack. In the present paper the microstructure of the transition zone will be reviewed and discussed in terms of the types of fibres and production technology of the composite. Special attention will be given to the inhomogeneous and porous nature of this zone. Several aspects of the performance of fibrous composites will be evaluated in terms of the structure of the transition zone: the interaction of cracks with fibres, crack arrest mechanisms induced by fibres and pull out processes of fibres. The effect of changes in the transition zone with time on the aging of some fibrous cement composites will be discussed. Several means to change the performance of fibre-cement composites through the control of the structure of the transition zone will be presented.
MICROSTRUCTURE OF THE FIBRE-MATRIX TRANSITION ZONE The special microstructure of the transition zone in cement composites is closely related to the particulate nature of the matrix. It consists of discrete cement particles ranging in diameter from -1 to -100 4m (average size of -10 pm) in the fresh mix, which on hydration react to form a matrix made up mainly of colloidal CSH particles and larger crystals of CH. The particulate nature of the fresh mix exerts an important influence on the
Mat. Res. Soc. Symp. Proc. Vol. 114.
1988 Materials Research Society
Dow
Data Loading...
