Initiation and development of cracking in ECC materials: Experimental observations and modeling

Applications of fiber reinforced engineered cementitious composites (ECC) and other strain hardening cementitious composites (SHCC) require information on their material properties for structural purposes as well as for durability. The distinctive material properties of ECC and other SHCC materials are the tensile stress-strain relationship and the cracking characteristics including crack width and spacing prior to localization of cracking. The investigations presented in this paper will focus on these distinctive features and aim at developing tools to predict and design for specific composite behavior. The initiation and development of cracking are principal mechanisms in the tensile deformation behavior of ECC and other SHCC materials. In this paper, the parameters affecting the initiation and propagation of cracking and the fiber bridging stress-crack opening relationship are investigated. Furthermore, the observations will form the basis for calibration of a plasticity based damage mechanics model for ECC. It is found that the size and distribution of flaws in the cementitious matrix and the range of fiber bridgingcrack opening characteristics throughout the composite material are the governing parameters for the tensile stressstrain response. Particularly important for the durability of structures containing ECC is the evolution of crack widths under increasing tensile loads up to the tensile strength of the material. The experimental data and analytical tools presented in this paper will provide detailed information on this particular feature of ECC materials.