Introduction: Crack Distribution and Durability of SHCC: Fid-Bau Portal

Introduction: Crack Distribution and Durability of SHCC

Zijl, Gideon P. A. G. / Boshoff, William P. / Wagner, Christian / Slowik, Volker

Abstract Inherent crack control to fine widths in strain-hardening cement-based composites (SHCC) suggests that structural elements produced from SHCC or steel-reinforced SHCC (R/SHCC) may be rendered durable by limiting the ingress rates of potentially deleterious substances. Recently, it has been reported that, while the average crack width in SHCC is maintained up to large tensile strains in excess of 3%, the maximum crack width may equal or exceed those are considered to be limiting in terms of durability. Also, the typical range in SHCC average crack width, from 50 to 100 μm, has been shown to be a threshold in water permeability, at which width permeability is restricted to several orders lower than that expected for crack widths ranging from 0.2 to 0.3 mm — a typical reinforced concrete crack width limit in durability standards. However, it has recently been shown that capillary absorption in dry, pre-cracked SHCC is a quick process, with water penetrating into fine cracks within minutes of exposure. In addition to describing these findings, this chapter sets the scene for later chapters on improved ingress rate characterisation and the actual deterioration of cracked SHCC or R/SHCC. Guidelines for the pre-cracking of SHCC towards durability testing are derived, based on the results of recent comparative testing. These include the specimen shape, size, test set-up, crack measurement to sufficient resolution, and crack width distribution presentation. Finally, the field performance of repairs, structures and structural elements produced from SHCC and R/SHCC in the past decade is reported.