Experimental Study On Flexural Performance Of Short-Cut Basalt Fiber Reinforced Concrete Beams

It is known that normal concrete generally has low tensile strength,poor toughness,easy to cracking and poor durability.Thus,there are many members or structures that cannot meet the expected function due to the poor behavior of normal concrete,causing serious economic losses.In order to improve the mechanical properties and the durability of concrete,it is advisable that adding fibers with various types into the normal concrete,which is also regarded as one of the most important research fields of the concrete modification recently.The fibers with uniform and disorderly distribution inside concrete matrix,can not only restrain the cracks induced by both the shrinkage and temperature,especially during the curing period,but also increase the crack-control ability and bearing capacity.These improvements thank to the fibers playing the important role of enhancing the cracking resistance and toughness.Compared to other types of fiber,the short-cut basalt fiber has attracted wide attention because the fiber contains potential advantages,such as good mechanical properties and durability,environmental-friendly,convenience in getting raw materials.Therefore,in this thesis,the material tests regarding mechanics for the short-cut basalt fiber reinforced concrete(BFRC)are first carried out.Then a series of BFRC beams are prepared and conducted through the four-point bending tests.The improved calculated formulas used for predicting the BFRC beam’s cracking moment and short-term stiffness,are finally proposed and also are validated by some collected test data.The main conclusions are as follows:(1)When compared to normal concrete,the basalt fiber concrete shows more micro-cracks under compression,so that the phenomenon of concrete crushing is alleviated.While the fracture surfaces with coarser and more tortuous are observed for those failure in tension.Showing that the basalt fibers inside the concrete blocks are distributed randomly and evenly,which effectively improve the integrity of concrete and the brittle failure.(2)The strength of basalt fiber concrete is generally higher than that of normal concrete.Moreover,the increment ratios climb first and then drop with increasing fiber content,and the strength of basalt fiber concrete reaches the peak point when the fiber volume ratio is equal to 0.10%.Therefore,in terms of the basalt fiber concrete,the fiber volume ratio of0.10% is taken as the optimal fiber content.(3)The BFRC beams are similar to those of ordinary concrete beams regarding the failure modes.They all basically meet the plane assumption and behave good deformation as balanced-reinforced beams.During the loading process,basalt fibers do play a role of enhancing crack-resistance but mainly before the yielding of main reinforcement.It means that the ability in the cracking control,the capacity corresponding to the first crack occurred as well as the flexural stiffness is improved due to the existence of basalt fibers,while the positive influence on the ultimate capacity is ignored.(4)The strengthening effect of short-cut basalt fibers on concrete beams is closely related to the aspect ratios,main reinforcement ratios and the depth of fiber layer.As the fiber length or main reinforcement ratio increases,the increment ratios for both the cracking and yielding capacity show a downward trend.In addition,when the depth of fiber layer is greater than 1/3 of that beam,the beams’ mechanical properties in service gradually increase with the fiber layer depth,but once the fiber layer depth is up to 1/2 of the beam depth,the mechanical behavior of this composite beam is almost the same as that of the full-section BFRC beam.(5)Based on the existing design theories,the improved calculation formulas in terms of the compute of the cracking moment and the short-term stiffness are proposed using regression analysis with test data from this thesis,which takes the fiber parameters,the main reinforcement ratios and the depth of fiber layer into consideration.The variation is also checked by collecting other relevant test results in the meantime.