Abstract
The stress-strain response of the basic concrete making material, i.e. the mortar and aggregates, are well known. In general, the aggregate behaves linearly up till failure, possessing a very high ultimate compression strength and stiffness. The behavior of mortar is non-linear, even at low loading levels. The resulting composite material, the concrete, exhibits a less stiff response, in combination with degradation in strength. This study looked into the influence of the inclusion-to-specimen volume ratio of a 100x100x50 mm mortar specimen. Two inclusion configurations were considered, parallel and diagonal to the line of loading, while the ratio varied from zero to 0.66. It was shown that the inclusion-to-specimen volume ratio strongly influenced the strength, the stiffness, and failure mode. The strength behavior had a minimum and a maximum bifurcation point, while the stiffness response increased, as a function of an increase in the inclusion-to-specimen volume ratio. Visual observation of the cracking pattern revealed that the initial cracking was always situated at the interface between the aggregate and mortar in tension and propagated through the mortar matrix. It was also perceived that the crack propagation path of the very dense, diagonally arranged inclusions deviated from the columnar configuration observed from the parallel inclusion formation. These densely diagonally arranged aggregates also resulted in spalling in the lateral direction.
Highlights
The behavior of concrete is a contribution of the mechanical properties of basic materials
The qualitative data are the visual observation to the crack pattern and the examination of the differences in failure mode for each group of test specimens
The loaddisplacement pattern followed a quadratic function for all specimens, with a very mild deviation in stiffness at every increment of the loading stages. This quadratic tendency of the load-displacement behavior became more pronounced as a function of increase in inclusion-to-specimen volume ratio
Summary
The behavior of concrete is a contribution of the mechanical properties of basic materials. Its ultimate compression strength is approximately one-fifth of the aggregates while the initial stiffness modulus measured only one-seventh to the aggregates These disparities in mechanical properties create stress concentrations and generate strain discrepancies in the boundaries between the inclusions and the mortar that will, in turn, promote premature micro crack initiation in the ITZ [1]. Both studies concluded that the compression strength as a function of an increase in inclusion-tospecimen volume ratio followed a quadratic, convex path where at some point a minimum is reached This pattern was similar in both studies, regardless of the fact that in the experiments conducted by Suarjana [4], the number of inclusions was gradually increased, and in the experiments carried out by Han [3] the diameter of cylindrical inclusion was enhanced. Since it was shown that the configuration of aggregates impacted the behavior of the specimen [6], the study was expanded to analyze the influences of inclusion formation on the strength, stiffness and crack pattern
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