Fiber-reinforced self-compacting concrete (FRSCC) is a high-performance building material that combines positive aspects of fresh properties of self-compacting concrete (SCC) with improved characteristics of hardened concrete as a result of fiber addition. Considering these properties, the application ranges of both FRSCC and SCC can be covered. To produce SCC, either the constituent materials or the corresponding mix proportions may notably differ from the con-ventional concrete (CC). These modifications besides enhance the concrete fresh properties affect the hardened proper-ties of the concrete including creep and shrinkage. Therefore, it is vital to investigate whether all the assumed hypothe-ses about conventional concrete are also valid for SCC structures. In the present paper, a numerical and experimental study about creep and shrinkage behavior of FRSCC and SCC is performed. Two new creep and shrinkage prediction models based on the comprehensive analysis on the available models of both CC and SCC are proposed for FRSCC and SCC structures. In order to evaluate the predictability of the proposed models, an experimental program was carried out. For this purpose, four SCC mixes - plain SCC, steel, polypropylene, and hybrid FRSCC - are considered in the test pro-gram. Several specimens were loaded and deformation in non-loaded specimens was also measured to assess shrinkage. All specimens were kept under constant stress during at least 364 days in a climatic chamber with temperature and rela-tive humidity of 22°C and 50%, respectively. Results showed that the new models were able to predict deformations with good accuracy, although providing deformations slight overestimated.
This paper demonstrates the application of microfocus X-ray computed tomography (CT) to study solute transport in cracked concrete. Cracks in a cylindrical specimen of ordinary Portland cement (OPC) and fly ash mortar were induced using a splitting tensile test. Cesium Carbonate (Cs2CO3) was then used as a tracer in the in-situ diffusion test with the aid of X-ray CT. Image analysis was also employed to measure the 3D crack geometry and tracer diffusivity from these CT images. The geometric tortuosity of the crack was approximately 1.25 irrespective of the crack opening width and whether fly ash was added or not. On the other hand the constrictivity increased for the fly ash mortar having roughly the equivalent crack opening width. The measured diffusivity in the crack was controlled by both crack opening width and constrictivity. Results obtained from microtomographic images suggest that the entire crack space may not always be filled with the tracer. The diffusive transport of solute in cracks thus can be restricted from microstructure’s point of view. Smaller crack opening would increase such restricted diffusion. Indications also suggest that the addition of fly ash would lead to the reduction of diffusivity through uncracked body of the mortar.
To assess the ecological and mechanical performances of concrete structures, a new holistic approach is herein presented. The embodied energy and the carbon dioxide released by the production of a certain concrete, with preestablished strength and ductility, are both combined to define the so-called eco-mechanical index. Alternatively, the ecological and mechanical indexes can be reported within a non-dimensional diagram, especially when code rules or tender requirements are the benchmarks. In the two cases, a comparison among different structural concretes can be performed in order to select, or tailor, new eco-friendly and high performance cement-based composites. This approach is carried both for compression and for tension in order to investigate all possible situations occurring in concrete structures. As a result, the best concrete can be attained not only by applying ecological strategies for sustainability (e.g., the partial substitution of cement with mineral additives), but also by increasing the work of fracture both in tension and in compression (e.g., by means of steel fibers).
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