Layered SHCC with Crack and Diffusion Control for Improved Durability of Concrete Structures

Strain hardening cementitious composite (SHCC) material used as a repair material on reinforced concrete structures for protection against environmental exposure is considered in this study. By layering different SHCC mixtures, one can create functionally gradient material (FGM) to control crack spacing, localization and opening. Compared to cracks in ordinary RC, formation of micro-cracks increases resistance to moisture, gas and salt penetration, the key to cement-based material durability. As variable functions in this study equivalent diffusivity of carbonation and chloride ions in assumed crack width are used to examine the effect of layer distribution. FGM is then created by layering the SHCC of various material properties and the obtained durability as a function of time for corrosion initiation is studied. From the numerical simulation, it is found that the corrosion initiation time of sound FG-SHCC is extended significantly compared to uniform SHCC and this beneficial behavior is found in cracked FG-SHCC as well. FG-SHCC compared to homogeneous material shows both for chloride attack and carbonation moderate to high increase in durability, based on the crack width. Effect of layering decreases with increasing crack width. Due to the nature of crack width limit of SHCC, beneficial behavior of layering to form FG-SHCC during service load is always present.