Face slab concrete suffers from serious frost damage in cold regions in China, how to improve the frost resistance of face slab concrete in cold regions is one of the important issues in concrete faced rockfill dam (CFRD) design and construction. The results in this paper indicate that the frost resistance of concrete can be improved by adding fly ash, fiber, MgO and shrinkage-reducing admixtures (SRA), and the efficiency is in the sequence: (fly ash + fiber) > fiber > fly ash > MgO > SRA. The incorporation of 0.8 kg/m 3 PVA fiber and 20 wt% fly ash together enhances the compressive strength and tensile capacity of concrete by 6-7 % at late age, whereas the addition of 6 wt% MgO or 1 wt% SRA reduces the compressive strength and tensile capacity by about 4-10 % at various ages. The Ds of concrete added with fly ash, fiber, MgO and SRA is within the range of 2.619-2.796. The frost resistance of concrete correlates linearly with the air void parameters, pore structures and Ds. The utilization of fly ash and/or PVA fiber refines and optimizes the pore structure, thus increasing Ds and improving the frost resistance. On the contrary, MgO and SRA in this study are less effective in refining the pores than PVA fiber and fly ash, thereby producing smaller Ds and relatively weaker frost resistance.

Dam concrete suffers from serious abrasion damages in southwestern China, the abrasion resistance of concrete is therefore one of the most important factors determining the reliability even the safety of the dams. In the present work, the effects of fly and/or silica fume on the mechanical properties, drying shrinkage, as well the cracking and abrasion resistance of concrete were investigated, then the pore structures of concrete added with fly ash and silica fume and the pore surface fractal dimensions (Ds) were determined by the mercury intrusion porosimetry (MIP) method and a fractal model, respectively. Finally, the relationships between the abrasion resistance of concrete and the porosity as well as the Ds were revealed and discussed. The results indicate that silica fume significantly increases the drying shrinkage especially at early age, while the incorporation of fly ash and silica fume together can decease the early plastic shrinkage-induced cracking risk and the final shrinkage to some degrees. Besides, the utilization of 5 wt% silica fume and 20 wt% fly ash together increases the abrasion resistance and mechanical property by about 4-9 % at various ages. In addition, the compressive strength and the abrasion resistance of concrete are linearly correlated with the concrete porosity and the Ds. Both the fly ash and silica fume could decrease the porosity of concrete and increase the Ds, therefore the concrete containing fly ash

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Cement-based materials, including cement and concrete, are the most widely used construction materials in the world. In recent years, the investigation and application of fractal theory in cement-based materials have attracted a large amount of attention worldwide. The microstructures of cement-based materials, such as the pore structures, the mesostructures, such as air voids, and the morphological features of powders, as well as the fracture surfaces and cracks, commonly present extremely complex and irregular characteristics that are difficult to describe in terms of geometry but that can be studied by fractal theory. This paper summarizes the latest progress in the investigation and application of fractal theory in cement-based materials. Firstly, this paper summarizes the principles and classification of the seven fractal dimensions commonly used in cement-based materials. These fractal dimensions have different physical meanings since they are obtained from various testing techniques and fractal models. Then, the testing techniques and fractal models for testing and calculating these fractal dimensions are introduced and analyzed individually, such as the mercury intrusion porosimeter (MIP), nitrogen adsorption/desorption (NAD), and Zhang’s model, Neimark’s model, etc. Finally, the applications of these fractal dimensions in investigating the macroproperties of cement-based materials are summarized and discussed. These properties mainly include the mechanical properties, volumetric stability, durability (e.g., permeability, frost and corrosion resistance), fracture mechanics, as well as the evaluation of the pozzolanic reactivity of the mineral materials and the dispersion state of the powders.