Title: Macro- Versus Micro-Mechanical Behavior of Plain and Steel Fiber Concrete Subjected to Internal Deformations
Author(s): P. Stroeven, D. H. Dalhuisen, and A. T. Moczko
Publication: Symposium Paper
Appears on pages(s): 871-886
Keywords: corrosion; deformation; reaction (alkali-silicate); reinforcement bar
Inhomogeneous stress situations are prevailing in some engineering problems, such as around corroding steel bars or around aggregate particles expanding due to alkali-silica reaction. Micro-mechanics and macromechanics will significantly differ in those cases. The present article focuses on experiments simulating the effect of steel bar corrosion on four cementitious composites. For that purpose, prismatic specimens containing an excentrically located slightly tapered cylindrical hole, where subjected to controlled push-through of a metal cone of similar shape. Behaviour in the pre-peak range was reflected by strain gauges, and in the post-peak region by clip gauges. Simulateneously, acoustic emission measurements were performed. Various aspects of the tests have been highlighted before in publication to which is referred when relevant. This paper merely presents illustrative data, evidencing typical micro- and macro-mechanical processes taking place under the given conditions. Successively, on macro-level, the elastic range terminates at Discontinuity Point (DP), at ultimate (BOP) a stage of quasi-plastic yielding is obtained, and a mechanism is formed at Crack Opening Point (COP), after which energy due to bar expansion is stored in opening up of only the leading crack. On micro-level, dispersed crack initiation and coalescence in radial direction starts at the interface. this process gradually concentrates in one of the two ‘weakest’ sections of the covercrete. This process slows down, whereupon cracks are initiated at the exterior of the second weakest section. Here they propagate to coalesce with the interor microcracks to form the major crack.