Fiber durability

The service life of strain-hardening cement-based composite materials (SHCC) is based on the service life of all the system components: fiber, matrix, and fiber–matrix interface. This chapter describes SHCC durability from the fiber perspective, distinguishing between different fiber types commonly used in SHCC: polyvinyl alcohol (PVA), polyethylene (PE), polypropylene (PP), and natural, steel and glass. Their relative strengths should be considered during any design process, especially when determining the long-term durability of the composite material. PVA is considered a chemically stable fiber, resistant to acid solutions, organic solvents, and alkaline environments. It has proven long-term durability, based on its high strength retention after accelerated aging cycles. The fibers are also hydrophilic as the cement matrix, leading to strong bonding between the two. PE and PP, both olefin type fibers, are also known for their high durability performance in the cement matrix. However, these fibers are hydrophobic and therefore do not have any chemical affinity to the hydrophilic cement matrix, resulting in low bonding between these fibers and the cement matrix. Glass fibers are relatively sensitive to the alkaline environment of the cement matrix. Consequently, special glass fibers (known as AR or alkali-resistant fibers) have been developed with improved alkali resistance. Steel fibers have a good affinity with the cement matrix but, depending on the environmental conditions, can undergo corrosion. The new trend of natural fibers in SHCC design offers a major advantage: combining low cost with local availability. However, they are susceptible to weathering, alkaline environments, biological attack, and mineralization.