Experimental investigation of fiber content and length on curing time‐dependent mode‐I fracture behavior and properties of cemented paste backfill and implication to engineering design

Abstract

The inclusion of fiber in cemented paste backfill (CPB) can significantly alter the mechanical response of the CPB body. The intrinsic defects in CPB and the potential dynamic loading condition make it necessary to investigate the fracture properties of fiber-reinforced CPB (FR-CPB). The mode-I fracture behavior and properties are crucial to the successful engineering application of FR-CPB technology used in underground mines. The contribution of fiber length and content to the evolutive mode-I fracture behavior and properties of FR-CPB was examined in this study. The results show that the addition of fiber reduces the prepeak stiffness but improves the mode I fracture toughness (K Ic ), and the improvement in K Ic increases with fiber length. In contrast, the initial increase in fiber content (from 0% to 0.5%) benefits the K Ic acquisition, while a further increase in fiber content from 0.5% to 0.75% poses a negative influence on the K Ic development. Moreover, with the adoption of the cement hydration model, four predictive functions are proposed to describe the contribution of fiber length and content to the development of fracture properties. In addition, K Ic is identified as a more reliable fracture property for assessing the immediate ground support role played by the FR-CPB structure. The findings are helpful when it comes to the determination of the fiber length and content in FR-CPB design. K E Y W O R D Scemented paste backfill, fiber reinforcement, fracture toughness, tailings, underground mine List of abbreviations/symbols: CB, chevron bend; CCNBD, cracked chevron-notched Brazilian disc; FRCC, fiber-reinforced cementitious composites; FR-CPB, fiber-reinforced cemented paste backfill; K IC , mode I fracture toughness; LPD, load-point displacement; NT, natural tailings; PSD, particle size distribution; SCB, semicircular bending test; SR, short rod; ST, silicate tailings; TSF, tailings storage facilities; UCS, uniaxial compressive strength; w /c, water to cement ratio; T, thickness of sample; F l , fiber length; F c , fiber content; F lr , reference fiber length; a, notch length; D, diameter of sample; FM-ITZ, fiber-matrix interfacial transition zone; P, normal force; S, half of the distance between the two supporting rollers; R, radius of sample; k s , stiffness; E i , fracture initiation energy; E m , critical fracture energy; P m , peak force; Y I , stress intensity factor; u, displacement; i, stage number; E p , postpeak fracture energy; ξ f , final degree of cement hydration; ξ, degree of cement hydration; τ, curing time constant; β, shape constant; t e , curing time; T r , reference curing temperature; T c , actual curing temperature; E a , energy activating cement hydration; R', natural gas constant; a i , b i , c i , d i , fitting constants.