Fracture Energy of Steel Fiber-Reinforced Concrete
Steel fiber-reinforced concrete (SFRC) is a cementitious material reinforced with discrete fibers. The energy absorption capacity is the main material property benefited by fiber reinforcement. Closed-loop servo-controlled equipment should be used to evaluate this property. The tests should be carried out using displacement control in order to obtain the postpeak force- displacement relationship (tensile strain-softening branch). To assess the fracture energy of SFRC, three-point bending tests were carried out using displacement control. Series of notched beams reinforced with 30, 60, and 90 kg/m3 of hooked-end steel fibers were tested. Besides the energy dissipated in fracturing the concrete, the energy determined from the force-displacement relationship can also include the energy absorbed during nonlinear behavior of concrete in compression. Ductile materials, such as concrete reinforced with a high content of fibers, develop large deflections before exhausting their energy absorption capacity. In these cases, the "fixed" points of the bar supporting the displacement transducer may not remain fixed, adding an extra deflection into the control displacement transducer and thus leading to incorrect evaluation of the fracture energy. These factors are analyzed in the present work in order to assess the suitability of the specimen dimensions and the test procedures for evaluating the fracture energy of SFRC.
CONCRETE BEAMS REINFORCED WITH CARBON LAMINATE STRIPS BONDED INTO SLITS
Resumen: A strengthening technique based on carbon laminate (CFRP) strips applied into slits cut on the concrete cover, and bonded to concrete by epoxy adhesive, was used for increasing the load bearing capacity of concrete beams failed by bending. This technique avoids the occurrence of the peeling phenomenon, mobilizes high percentage of the full strengthening capacity of the CFRP used, and provides higher protection against fire and vandalism. The adopted strengthening technique is briefly described and the main results obtained are presented and discussed. Using a numerical model developed for non-linear analysis of reinforced concrete structures, the response of the beams tested was predicted. The applicability of this kind of models in such type of reinforced concrete structures is commented.
Thorium in monazite sand; separation and determination by precipitation from homogeneous solution
A new method is described which consists of three steps: (1) decomposition of the monazite sand with perchloric acid; (2) separation of thorium and the rare earths by hydrolysis of methyl-oxalate in acid solution; and (3) separation of thorium from the rare earths by hydrolysis of urea in the presence of formic acid. The authors consider the method to be accurate and rapid.