Mechanical Properties Of Basalt Fiber Reinforced Polymer (BFRP) Tendon At Varying Strain Rates And Elevated Temperatures

Fiber reinforced plastic/polymer（FRP）is well known for their day-by-day increasing applications in infrastructural engineering due to their excellent mechanical properties and corrosion resistance.With the rapid development of economy and technology,the lightweight,long-span and long-service-life structures in buildings and bridges are needed,and the utilization of FRP will solve the problem encountered.Basalt fiber reinforced plastic/polymer（BFRP）is a new type of FRP materials with environmentally friendly,which has been the focus in recent years.Civil engineering components are always under high risk of earthquake,explosion or any impact/collision situation,and exposing to unpredictable elevated temperature environment.Therefore,it becomes necessary to analyze the mechanical properties of BFRP tendons at varying strain rates and elevated temperatures.This paper investigated the mechanical properties of BFRP tendon by using MTS universal testing machine and INSTRON servo-hydraulic high-speed testing machine.Several analytical methods such as digital image correlation（DIC）technology,scanning electron microscope（SEM）,thermo-gravimetry analysis（TGA）,and differential thermal analysis（DTA）were used to explain the failure process and modes.Combining with the structural reliability theory and reliability design the model of the tensile strength of BFRP tendons was established.The main investigations and results in this paper can be summarized as:（1）The anchorage behaviors of BFRP tendon with different type of anchors（clip-type anchor and bond-type anchor）,different type of bonding materials（reactive powder concrete and epoxy resin glue）,and different anchorage lengths（40 mm,60mm,80 mm,100 mm,150 mm,200 mm and 250 mm）were tested by static pull-out tests using MTS universal testing machine.The results show that,the failu re pattern of specimens with clamp-type anchors is shear failure.When the anchorage length of the BFRP tendon is less than the critical anchorage length,the failure pattern of specimens with bond-type anchors is pull-out failure,the bond strength and critical testing anchorage length between the BFRP tendon and bonding media can be calculated.When the anchorage length of the BFRP tendon is approximate equal to the critical anchorage length,the failure pattern can be described as cracking in the testing section and pullout in the anchored section.When the anchorage length of the BFRP tendon is longer than the critical anchorage length,the failure pattern of specimens with bond-type anchors is blasted failure,and the tensile properties of the BFRP tendons can be analyzed.（2）The tensile properties and shear properties of BFRP tendons were tested by using MTS universal testing machine,and the tensile strength,elastic modulus,ultimate strain,toughness and shear strength were abtained.The effect of bonding media,anchorage lengths（150 mm,200 mm and 250 mm）and testing lengths（100mm,200 mm,300 mm,400 mm and 500 mm）on the tensile properties of BFRP tendons were analyzed.The results show that,comparing to the reactive powder concrete,the tensile strength of BFRP tendon is increased by using epoxy resin glue as the bonding medium.As the anchorage length and testing length increase,the tensile strength,ultimate strain and toughness decrease,and the variation of elastic modulus is slight.（3）The dynamic tensile performance of BFRP tendon was tested by using INSTRON servo-hydraulic high-speed testing machine.The effect of varying strain-rates(1.5×10^-4 s^-1～28.98 s^-1)over damage process was characterized by digital image correlation（DIC）method.The micrographs by scanning electron microscopy（SEM）identified the modes of fracture during the experimental tests.The discreteness of failure strength at various strain-rates was analyzed by Weibull distribution.The experimental investigation proved that the BFRP tendon is highly influenced by strain-rate under tensile loading.As the strain-rate increases,the tensile strength,elastic modulus and toughness of BFRP tendon increase significantly,but the ultimate and maximum strains relatively decrease.Besides,with the increase in strain-rate,the failure area is more dispersed,the relative time of first crack is shorter,and the fracture surface is rougher.It is also estimated that Weibull distribution is one of the best available statistical tools for estimating randomness in BFRP tendon in practical engineering applications.（4）The tensile and shear properties of BFRP tendon after thermal aging was investigated.The effect of elevated temperatures（20℃～500℃）on the failure mode and mechanical properties of BFRP tendon were studied.The thermal performance of BFRP tendon was analyzed by thermo-gravimetric and thermal difference analyzer,which can explain the changes of the thermal decomposition characteristics,failure process and failure mode of BFRP tendon under different elevated temperatures.The results show that,the tensile properties and shear properties of BFRP tendon change significantly with the treat temperatures.As the treat temperature increases,the color of the BFRP tendon changes from light brown to dark brown,and to charcoal black.When the treat temperature performed from room temperature upto 100°C,the tensile properties of BFRP tendon chenge slightly.When the treat temperature of BFRP tendon is higher than 200°C,the tensile strength,elastic modulus and toughness decrease.When the treat temperature of BFRP tendon is lower than 300°C,the shear properties of BFRP tendon have almostly no chenge.When the treat temperatures of BFRP tendon is higher than 400°C,the shear strength decrease significantly,and the failure mode has obviously change.The thermal performance of BFRP tendon can explain the effect of thermal aging on the tensile properties and shear properties.