Fracture Mechanical Properties of Rocks and Mortar/Rock Interfaces
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MANOUCHEHR HASSANZADEH Division of Building Materials, Lund Institute of Technology, Box 118, S221 00 Lund, Sweden
ABSTRACT This study has determined the fracture mechanical properties of 9 types of rock, namely fine-, medium- and coarse-grained granites, gneiss, quartzite, diabase, gabbro, and fine- and coarse-grained limestones. Test results show among other things that quartzite has the highest compressive strength and fracture energy, while diabase has the highest splitting tensile strength and modulus of elasticity. Furthermore, the strength and fracture energy of the interfacial zone between the rocks and 6 different mortars have been determined. The results showed that, in this investigation, the mortar/rock interfaces are in most cases weaker than both mortars and rocks. INTRODUCTION The introduction of superplasticizers in concrete technology has made it possible to produce concrete with low water/binder ratios. Consequently, it has been possible to produce concrete which has much higher compressive and tensile strength than normal concrete. High strength is not the only advantage of high-performance concrete: the increased impermeability of the concrete, due to low water/binder ratio, has positive effects on its durability. The disadvantage of high-performance concrete in comparison with normal-strength concrete is its increased brittleness [2, 3]. The increase in brittleness is caused by the fact that the ability of the material to store elastic energy has increased due to higher strength, while its ability to consume the stored energy when it is released, during the fracture process, has not increased in the same order. The ratio between the energy which is consumed by the material during fracture and the maximum elastic strain energy which can be stored per unit volume of the material under uniaxial tensile stress condition is proportional to lch= EGF/f 2 , E = modulus of elasticity, GF = fracture energy and ft = tensile strength. lch which has the dimension length is, according to the "Fictitious Crack Model" [1, 4, 6], a material property and is called characteristic length. The lower the lch, the higher the brittleness of the material. In normal-strength concrete GF and ft are primarily governed by the mechanical properties of the cement paste and the shape and the amount of the aggregates, not by the mechanical properties of the aggregates. However, as the cement paste becomes stronger the influence of the mechanical properties of the aggregates on the mechanical properties of concrete increases. Since approximately 75% of the volume of concrete is occupied by aggregates, among which 50% are coarse aggregates, it is important to determine to what extent the mechanical properties of concrete are influenced by the mechanical properties of the aggregates. Furthermore, it is important to determine to what extent it is possible to design concrete composition with the desired mechanical properties by choosing aggregates of 377 Mat. Res. Soc. Symp. Proc. Vol. 370 0 1995 Materials Research Society
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