Comprehensive Study of the Properties of Engineered Cementitious Composites Incorporating Synthetic Wollastonite Microfibers

In this study, synthetic wollastonite microfibers (SWMs) with a dense acicular particle structure and a very high aspect ratio were developed by using a three-stage production method consisting of the mechanochemical, hydrothermal autoclave and sintering processes. The maximum aspect ratio of SWMs was 44∶1, which is a needle-like particle with the highest aspect ratio. The effects of SWMs on the workability and rheological, mechanical, durable, and dimensionally stable properties of engineered cementitious composites (ECCs) were investigated using many tests for each property. For this purpose, SWMs were substituted with cement-fly ash (C-FA) at 3%, 6%, and 9%. The study found that replacing C-FA with 6% SWMs can significantly enhance the compressive strength, modulus of elasticity, flexural strength, and ductility of ECCs. Substituting 6% C-FA with SWMs not only enhanced the mechanical properties but also led to improved durability and dimensional stability. In particular, in the freeze-thaw test, which is a long-term durability test (300 freeze-thaw cycles), SWMs provided significant performance improvement in terms of % mass loss, ultrasonic pulse velocity, relative dynamic modulus of elasticity, durability factor, and residual flexural performance. In addition, the 180-day drying shrinkage and 30-day average crack width of ECC were reduced approximately 105 με and 16 μm, respectively. Moreover, the test results were supported by microstructural analysis. This comprehensive study indicates that SWMs have the ability to be used in ECCs to improve their properties.