Flexural toughness evolution of basalt fiber reinforced shotcrete based on NMR technology

With the coal mining depth going deeper,the traditional shotcrete support structure is easy to crack and fall off. The basalt fiber (BF) can improve the flexural toughness of shotcrete,which can effectively restrain the surround- ing rock deformation. The influence of BF content on the basalt fiber reinforced shotcrete (BFRS) toughness was stud- ied by Bending Toughness Test. The effect of pore distribution on the toughness of BFRS was studied by Nuclear Magnetic Resonance (NMR) Test,and the underground roadway support test was carried out. The results show that the flexural strength of BFRS at 7 d and 28 d curing ages increase by 9. 8% ,6. 8% respectively,and BF can obviously en- hance the early age flexural strength. The flexural toughness of BFRS specimens are evaluated by Standards of DBV and JSCE. At the optimum fiber dosage 4. 5 kg / m3 ,the flexural index Df1 ,Df2 are 29. 5,57. 9 N·m,respectively,the bending toughness ratio reaches the maximum value 0. 875,which indicates that the DBV multi value toughness stand- ard is more suitable for evaluating BFRS flexural toughness. The NMR results show that the fiber dosage can greatly in- fluence on the pore structure. At the fiber dosage 3 kg / m3 ,the large pore size ratio is only 0. 25% . The proportion of large pore size increases once the fiber dosage beyond 4. 5 kg / m3 ,the shotcrete matrix defects increase,and the tough- ness property decreases. The BFRS performance is better than that of traditional shotcrete in restraining deformation from the u3nderground roadway supporting test. The 35 d convergence of roadway is only 0. 21 mm at the fiber dosage 4. 5 kg / m ,which achieves an acceptable result. The fibers distributed in the BFRS matrix can form a stable three-di- mensional structure,improving pore structure,increasing flexural toughness,and enhancing the anti-deformation prop- erty of the roadway supporting structure. High toughness BFRS is the considerable material for the large deformation roadway supporting in deep mine,which can achieve the performance of “deformation but no crack,cracking but no fall”.