Rheological control in production of engineered cementitious composites

This paper reports on a study of rheological control of fresh properties during processing of engineered cementitious composites (ECC) for the purpose of more effectively realizing mechanical properties optimized through micromechanical design theory. Four factors (Class C fly ash [FA] to Class F FA ratio, water-binder ratio [w/b], amount of high-range water reducer [HRWR], and amount of viscosity-modifying admixture) were investigated to determine their effects on the fresh and hardened properties of ECC. Test results indicated that among the investigated factors, the w/b most strongly affects the plastic viscosity of ECC mortar (without fiber), which in turn have a significant impact on the ECC composite ultimate tensile strength and tensile strain capacity. Marsh cone flow test and mini-slump flow test were demonstrated as simple and practical methods to characterize the rheological properties of ECC mortar. By complying with the recommendations of rheological control for producing ECC summarized in this paper, it is expected that self-consolidating ECC with optimum rheological properties that promote uniform fiber distribution throughout the matrix can be easily produced and optimized tensile properties can be realized for micromechanics-based optimized ECC mixture design.