Effects of fiber properties on flexural and fracture characteristics of manufactured sand concrete based on acoustic emission

Fiber-reinforced concrete (FRC) with natural sand (NS) as fine aggregate has been regarded as an favorable cementitious composites in engineering application due to its superior mechanical and fracture properties, etc. As a promising substitution for NS in conventional concrete, manufactured sand (MS) presents great potential in minimizing environmental impacts and increasing economic benefits. This paper presents the effects of fiber type (steel fiber, basalt fiber, glass fiber), fiber content (0 %, 1 %, 2 %) and fiber length (6 mm, 13 mm, 20 mm) on mechanical and fracture characteristics of manufactured sand concretes (MSCs) with 100 % replacement ratio of NS with MS. The entire fracture processes of MSCs were monitored using acoustic emissions (AE) in real time. The results showed that flexural strength of MSC increases with the addition of three different fibers, and steel fiber exhibits the best reinforcement effect. MSC with 1 % steel fiber content exhibits the highest flexural strength. Meanwhile, the longer the fiber length is, the smaller the flexural strength presents. The effects of fiber properties on AE parameters (count, b- value, information entropy) revealed that the addition of fibers reduces the fluctuation of counts and information entropy. The MSC with 2 % steel fiber content exhibits more dramatic fluctuations of b-value and information entropy after post-peak, which reveals greater internal damage in specimen. The longer the steel fiber is, the more dramatic the AE signal fluctuations and the more severe the damage inside the specimen emerge. Parametric analysis of rise angle (RA) and average frequency (AF) for classifying fracture modes (tensile and shear cracks) show that the incorporation of fibers can reduce the tensile cracks of MSC specimen under four-point bending. With the increase of fiber content, the tensile cracks first decrease and then increase. The longer fiber length is, the more tensile cracks generate during the fracture process.