Hourglass-shaped specimen: compressive strength of concrete and mortar (numerical and experimental analyses)

Abstract

Cylindrical specimens whose diameter is equal to half its height have been used worldwide. The statistical scattering in experimental testing of cementitious materials is a phenomenon known in literature and one reason is linked to the geometry of the specimens, which implies the possibility of different failure modes. This paper shows the evaluation of an hourglass-shaped sample , in which the highest stress occurs at the centre of the specimen, with negligible influence of stress distribuition from its ends. An amount of 260 cylindrical and hourglass samples were tested, with varying water/cement ratio and age. FEM analyses showed that stress in the central part of the hourglass specimens is 2.25 higher than that present at its ends. Modes of failure occured in differente ways in cylindrical specimens, whereas only one mode of failure was verified in hourglass specimens. The cylindrical samples showed bimodal frequency distribution, demonstrating the influence of the central part (material properties) and of its ends (boundary conditions), while the hourglass displayed a Gaussian distribution.

High Temperature Compression Tests of A Commercial Isotropic Ultrafine Grain Graphite

“…For this reason, hourglass geometry has been considered suitable for compressive tests on graphite. Similar conclusions were suggested by Bezerra et al [22] .…”

“…Moreover, failure due to contact and friction stresses arose during testing the cylindrical geometries, both at room temperature and at 1000 °C. Similar behaviour of cylindrical samples have been encountered by Bezerra et al [22] in his study on mortar and concrete compressive mechanical tests. For this reason, no further tests have been performed with this geometry.…”

“…Bezerra et al [22] carried out numerical studies and experimental tests on concrete and mortar in order to assess the most suitable geometry for compression tests. The results demonstrated an apparently higher compressive strength of hourglass specimens than cylindrical ones, due to a reduced influence of the contact effects between sample and punch.…”

Influence of the molding process and different surface regularization methods on the compressive strength of concrete specimens

“…The choice of specimen size depends on the dimension of the aggregates, considering a diameter at least three times larger than the nominal maximum dimension of the coarse aggregate. The use of cylindrical specimens may be justified by the absence of edges, favoring consolidation, but Bezerra, Alves, Barbosa, & Torres (2016) evaluated an hourglass-shaped specimen, in which the distribution of stress at the edges is irrelevant, with the greatest stress occurring in the middle of the specimen. Tam, Daneti & Li (2017) mentioned that the cylinder shape is favorable, considering the material consumption to specimencast.…”