Micromechanics theory guidelines and method exploration for surface treatment of PVA fibers used in high-ductility cementitious composites

High-ductility cementitious composites (HDCCs) with multiple cracking and excellent tensile strain behavior have been widely studied. The fiber component plays a pivotal role and its surface state directly determines the mechanical performances of composites. In this work, micromechanics design theory was used to guide polyvinyl alcohol (PVA) fiber surface treatment. Based on the strength criterion, energy criterion and fracture criterion, the frictional bond strength needs to be limited to an appropriate range. In addition, three different modifying agents (i.e., an oil agent, hydrophilic silica, and nanoscale graphite) were applied as coatings to the PVA fiber surface. The results showed that the hydrophilic silica treated PVA fibers (S-PVAF) and nanoscale graphite-treated PVA fibers (G-PVAF) exhibited high hydrophobicity and roughness; consequently, the chemical bonding was greatly reduced. However, the S-PVAF still exhibited breakage and abrasion damage during the pullout process, whereas the G-PVAF were pulled out completely. Finally, the fiber bridging stress versus crack opening sigma(delta) relation was studied by using notched coupon specimens. G-PVA-HDCCs exhibited greater complementary energy. The tensile ductility reached 2.7%, which was higher than that of oiled PVA-HDCC. The results showed the promising advantages of using nanoscale graphite for surface treatment to achieve a higher surface quality. (C) 2018 Elsevier Ltd. All rights reserved.