Influence of Fiber Shape and Water-Binder Ratio on Blast Resistance of PVA Fiber Reinforced Mortar

Reducing spall damage is a major problem when designing blast-resistant concrete structures. This study was conducted to evaluate the influence of various material factors on the blast resistance of FRCC slabs under contact detonation. The contact detonation tests were carried out on polyvinyl alcohol fiber reinforced mortar (PVAFRM) slabs with four different shapes of PVA fibers and four different water-binder ratios (W/B) of the mortar matrix. Fly ash (type II) was used as admixture and the fluidity of the PVAFRM in its fresh state was varied using a superplasticizer and thickener. As a result, it was obtained that longer fiber is more effective to suppress spall if the fiber diameter is constant, and if the aspect ratio of fiber (lf/df) is constant, finer fibers are more effective to reduce spall. Moreover, the spall-reducing performance is reduced when the W/B value is too high or too low, and it is considered that there is an appropriate value of W/B that depends on the fiber shape. Introduction When designing blast-resistant concrete structures, reducing spall damage is a major problem. Spalling indicates the failure of reinforced concrete (RC) slabs due to contact detonation which caused by the tensile stress waves reflected from the backside of the slab. To preserve human life under such circumstances, the launch of concrete fragments accompanies the spalling needs to be prevented. The authors have verified the good spall-reducing performance of fiber reinforced cementitious composite (FRCC) slabs under contact detonation. However, a designing method for obtaining the required blast-resistant performance of the FRCC members has not been developed yet; one of the reasons for this is that it is difficult to obtain dynamic mechanical properties of FRCCs corresponding to this problem where the dominant strain rate is of the order of 10–10/s. Hence, it may be convenient to consider the spall-reducing performance of FRCC member as a material property of the FRCC. It can be obtained directly based on material factors such as fiber shape, water-binder ratio, and so on. This study was conducted to evaluate the influence of various material factors on the blast resistance of FRCC slabs under contact detonation; therefore, contact detonation tests were carried out on polyvinyl alcohol fiber reinforced mortar (PVAFRM) slabs with four different shapes of PVA fibers and four different water-binder ratios of the mortar matrix. Explosion Shock Waves and High Strain Rate Phenomena Materials Research Forum LLC Materials Research Proceedings 13 (2019) 103-108 https://doi.org/10.21741/9781644900338-18 104 Table 1 Materials used for PVAFRM. Cement Ordinary Portland cement; Density: 3.16 g/cm Admixture Fly ash (Type II); Density: 2.27 g/cm, Specific surface area: 3890 cm/g Fine aggregate Mountain sand; Surface-dried density: 2.56 g/cm, Water absorption: 2.29%, Maximum size: 2.5 mm, Fineness modulus: 2.58 Chemical admixture Superplasticizer (Polycarboxylic-acid type); Thickener (Methylcellulose type) Short fibers PVA fiber (Type I); Density: 1.30 g/cm, Dimension: φ0.1 × 12 mm, Tensile strength: 1200 MPa, Tensile elastic modulus: 28 GPa PVA fiber (Type II); Density: 1.30 g/cm, Dimension: φ0.2 × 12 mm, Tensile strength: 975 MPa, Tensile elastic modulus: 27 GPa PVA fiber (Type III); Density: 1.30 g/cm, Dimension: φ0.2 × 18 mm, Tensile strength: 975 MPa, Tensile elastic modulus: 27 GPa PVA fiber (Type IV); Density: 1.30 g/cm, Dimension: φ0.2 × 24 mm, Tensile strength: 975 MPa, Tensile elastic modulus: 27 GPa Table 2 Mixture proportions and static mechanical properties of PVAFRM. Fiber type Vf [%] W/B [%] FA/B [%] S/B [%] Unit weight [kg/m] Sp/B [%] Flow γ [kN/m] σB [MPa] E [GPa] εco [μ] σf [MPa] b σ