Rheological property regulation for Engineered Cementitious Composites (ECC) to achieve desired mechanical properties

Achieving excellent mechanical properties of Engineered Cementitious Composites (ECC) requires not only appropriate mix proportions but also stringent control over the rheological properties. The study regulated the rheological properties of ECC by varying the content of polycarboxylate superplasticizer (SP/B). Then the corresponding mechanical properties including compressive strength, flexural strength, and uniaxial tensile properties were measured, followed by an analysis of their variations based on the strength and energy criteria, fibermatrix interfacial characteristics and fiber dispersion. The test results show that with an increase in the SP/B, there was a minimal change in the compressive strength and flexural strength of the cement matrix in ECC. However, the mechanical properties of ECC first increased and then decreased. The mechanism is as follows: when the yield stress and plastic viscosity of the matrix are too high, most of the mixing energy is consumed by matrix flow rather than fiber dispersion. Due to the limited power of the mixer, the shear stress generated cannot surpass the yield stress, thus resulting in poor mixing of ECC paste. Conversely, if these parameters are too low, centrifugal forces cause fibers to accumulate along the mixer wall. During setting, low-viscosity paste cannot prevent fiber floating, further aggravating accumulation on the surface. All the reasons mentioned above increase the probability of uneven fiber distribution. As a result, the specimen fails rapidly after cracking. Finally, a satisfactory range for the plastic viscosity of ECC - from 15.09 Pa s to 27.11 Pa & sdot;s - was proposed.