基于NMR技术的玄武岩纤维喷射混凝土韧性演化规律

随着煤矿开采深度的增加,普通喷射混凝土支护结构易开裂脱落。玄武岩纤维(BF)的加入可以有效地提升喷射混凝土韧性与抑制围岩变形的能力。通过弯曲韧性试验研究了BF对玄武岩纤维喷射混凝土(BFRS)韧性的影响规律,通过核磁共振试验(NMR)研究了孔隙分布对BFRS韧性的影响,并进行了井下现场支护试验。结果表明:BF掺入后,BFRS 7 d与28 d试块抗弯强度分别提高了9.8%,6.8%,且BF对早龄期抗弯强度提升效果更为明显;分别采用DBV与JSCE标准对BFRS韧性进行评价,实验发现最优纤维掺量为4.5 kg/m~3,此时D■和D■分别为29.5 N·m和57.9 N·m,试件弯曲韧性比同时达到最大值0.875;对比可知,DBV多值韧性标准更适合评价BFRS抗弯韧性。通过NMR试验发现纤维掺量对BFRS孔隙结构影响较大,纤维掺量达到3 kg/m~3时,BFRS大孔径孔隙占比仅为0.25%,当纤维掺量超过临界掺量4.5 kg/m~3,BFRS大孔径孔隙占比增加,喷射混凝土基体内部缺陷增多,韧性降低。进行井下支护试验发现BFRS抑制变形能力优于普通喷射混凝土,其中纤维掺量为4.5 kg/m~3时,支护段巷道35 d收敛位移最小,仅为0.21 mm,此时支护效果最好。分布在BFRS基体内部的纤维可以形成稳定的三维承力结构,有效改善BFRS基体内部孔隙结构,增加BFRS韧性,提高被支护巷道抗变形能力。高韧性BFRS可以有效地满足深部大变形巷道支护要求,达到"变形不开裂,开裂不掉落"的效果。

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 surrounding rock deformation.The influence of BF content on the basalt fiber reinforced shotcrete (BFRS) toughness was studied 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 enhance 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/m3,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 standard is more suitable for evaluating BFRS flexural toughness.The NMR results show that the fiber dosage can greatly influence 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 toughness property decreases.The BFRS performance is better than that of traditional shotcrete in restraining deformation from the underground roadway supporting test.The 35 d convergence of roadway is only 0.21 mm at the fiber dosage 4.5 kg/m3,which achieves an acceptable result.The fibers distributed in the BFRS matrix can form a stable three dimensional structure,improving pore structure,increasing flexural toughness,and enhancing the anti deformation property 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”.