Experimental Mechanical Characterization of Silica Fume-based No-fines Concrete Reinforced by Steel or Nylon Fibers

Aims: In this study, the mechanical characterization of no-fines concrete solutions is addressed experimentally, with the purpose of possibly increasing their strength by using silica fume and embedded fibers (steel and nylon fibers) as possible efficient reinforcement. Background: Due to competition between developed and advanced countries, the contemporary construction sector is currently experiencing a shortage of fundamental building materials. In this regard, no-fines concrete is becoming increasingly popular, and it has been proven in the literature that it can offer some advantages as an economic and lightweight solution compared to conventional concrete. However, experiments and investigations are still needed to investigate the potential mechanical advantages for its efficient use in buildings, given that the major limitation compared to normal concrete is represented by limited strength. Objective: The primary objective of the present study is to assess the mechanical strength of no-fines concrete samples in which steel fibers, nylon fibers, and partial cement replacement with silica fume are used. For this purpose, no-fines concrete specimens are produced with fixed mix proportions of 1:6 cement-aggregate (c-a) ratio, various coarse aggregate gradations ((20-10) mm and (10-5) mm), and fixed w/c ratio (0.42). Methods: The experiments are carried out on cubes, cylinders and prisms of concrete samples with various aggregate solutions. The nominal length of both types of fibers is fixed at 20 mm. Steel fibers with 1 mm in diameter and nylon fibers with 0.3 mm, 0.4 mm, 0.5 mm, or 0.6 mm diameters, respectively, are taken into account to explore their effects on compressive strength, split tensile strength, and flexural strength. Results: The presented experimental results showed various mechanical advantages, such as increased compressive, splitting tensile and flexural strength parameters, for most of the examined samples. Nylon fibers, in particular, proved to significantly increase compressive, splitting tensile, and flexural strength values, compared to normal concrete, with additional benefits compared to steel fibers (for the examined arrangements and configurations). Conclusion: Overall, the examined compositions and mixtures of silica fume-based no-fines concrete samples encourage further investigations for the optimization of these solutions. In this regard, in addition to mechanical capacities, further key parameters (such as weight, cost, impact on concrete microstructure, etc.) will be taken into account.