Concrete is characterized in terms of its engineering properties, mainly strength and stiffness, which are subsequently used in structural design. However, the apparent (i.e., measured) concrete properties are not intrinsic but dependent on the conditions under which the measurement is performed. Herein a combined experimental and numerical study is performed to clarify the effects of hygral gradients and resulting eigen-stresses in self-restrained concrete on its apparent strength. Compressive strength, splitting tensile strength and Young's modulus are tested. Three mixes of varying strength grades are studied: normal strength, high strength, and ultra-high performance fibre reinforced concrete. Samples are subjected to two different curing conditions. To investigate the effect of size on the apparent properties, 50 mm, 100 mm and 150 mm cubes are tested. Depending on the size of the specimen there can be an underestimation or overestimation of up to 25% of the real concrete (e.g., splitting, direct tensile) strength.

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Hybrid application of conventional concrete and Strain Hardening Cementitious Composite (SHCC) is recently shown to be promising for crack width control. In this paper, a combined experimental and numerical study is performed to validate the concept and to study the effect of interface treatment on crack width control. The interface is varied between smooth, profiled, partially debonded and completely debonded surfaces. The beams are tested under a four-point bending configuration. The crack development is monitored using digital image correlation throughout the loading, and maximum crack width of 0.3 mm at the surface is taken as the limiting criterion for analyses. The hybrid and control beams are simulated using the lattice model. Both experimentally and numerically, it is observed that stronger interfaces enable the composite action in the hybrid beams and provide better crack width control compared to the artificially weakened interfaces.@en