The Influence of the Matrix-Aggregate Bond on the Strength and Brittleness of Concrete
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THE INFLUENCE OF THE MATRIX-AGGREGATE OF CONCRETE
BOND ON THE STRENGTH AND BRITTLENESS
WU KERU* and ZHOU JIANHUA** *Professor, Department of Materials Science University, Shanghai, China **Research Assistant, Department of Materials University, Shanghai, China
and
Engineering,
Tongji
and
Engineering,
Tongji
ABSTRACT In this paper, the influence of the matrix-aggregate bond on the strength and brittleness of concrete is studied. Six different matrixaggregate interfaces are used to evaluate the interfacial bond capability. The results obtained on the strength and brittleness index of concrete show that strengthening and toughening of concrete can be obtained simultaneously, if the interfacial bonds are changes so that they conform to a rational distribution according to aggregate size. These results are discussed in terms of the energy dissipation and crack propagation during failure of concrete.
INTRODUCTION In research on the mechanical behaviour of concrete, the bond between the aggregate and the matrix is a matter of general interest. Hsu et al. [1] observed cracking of plain concrete in compression directly with microscopic and x-ray techniques. Even prior to loading, cracks were observed at the aggregate-matrix interface. Up to about 30% of ultimate strength f', there was very little extension of these cracks. Beyond 0.30 f', the cracks began to grow under increasing load. After 0.50 fc, the bond cracks also began to extend through the matrix, bridging between the coarse aggregate particles. Finally, beyond about 0.75 f'. the matrix cracks began to form a much more extensive network. This indicates that the aggregatematrix interface is the weakest region of concrete. Other researchers have thoroughly investigated the interfacial bond in concrete with the help of advanced modern measuring techniques [2,3,4]. They found a transition zone existing between aggregate and matrix and also concluded that according to the composition, structure, the formation mechanism and the mechanical properties, this zone is the weakest link in the internal structure of concrete. The purpose of this paper is to investigate the effect of bond on the strength and especially on the brittleness of concrete so that the possibility of improving the mechanical properties of concrete by changing the interfacial bond can be explored.
EXPERIMENTAL EXAMINATION OF THE BOND CAPABILITY In order to represent the effects of the bond between aggregate and matrix on the mechanical behaviour of concrete, six interfacial cases were designed (Table I). The splitting strength and fracture energy of the above interfaces were measured, respectively, on cube specimens of 2 x 2 x 2 cm (Fig. 1) and notched beam specimens of 2.5 x 2.5 x 20 cm (Fig. 2). These specimens were maintained in water for 40 days before testing.
Mat. Res. Soc. Symp. Proc. Vol. 114. e1988 Materials Research Society
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