1、英文原文： The effect of fibre type and dosage rateon the performance of Fibre Reinforced ShotcreteJM Denny & PC HaganThe University of New South Wales (UNSW), SydneyA study was undertaken to optimise the performance and reduce the cost of Fibre Reinforced Shotcrete (FRS) in an underground mine by varyin
2、g fibre type and dosage rates.The effect of two steel and two plastic type fibres were assessed in terms of strength and postcrack toughness of the FRS. Samples were subjected to the ASTM C1550 round panel test and uniaxial compressive strength test. A cost model was developed to assess differences
3、in the cost of each fibre type and addition rate. Significant differences were observed across the range of fibre types investigated. One mix was found to be more cost effective than the others while achieving a better level of performance.INTRODUCTIONFibre Reinforced Shotcrete (FRS) is extensively
4、used throughout the underground operations of the Cannington Mine, Queensland, as an integral part of the ground support system.A study to assess alternate FRS mixes was jointly undertaken between BHP Billiton, the mine owners, and Jetcrete (Australia) Pty Ltd, the principal con tractors for the sup
5、ply and application of FRS at the mine. The objective was to determine which of the mixes would deliver the same or better levels of performance at a lower cost.At the commencement of the program, performance of FRS at the mine was measured in terms of uniaxial compressive strength (UCS). Bernard (1
6、999) had argued that this property is inappropriate as a measure of performance, proposing instead a measure of the materials flexural toughness or its resistance to crack propagation. Jetcrete (Australia) Pty Ltd, as the spraying contractor for the mine, also expressed an interest in a toughness me
7、asure of a mix as a replacement to reliance solely on UCS as the performance measure. The contact at the mine required the supply of a mix with a minimum UCS of 40 MPa. At the time there was little knowledge of what level of toughness was required at the mine.With regard to the FRS mix, the test pro
8、gram considered two factors fibre type and addition or dosage rate of fibres. A cost model was developed to assess any differences in cost.The study also considered the substitution of silica fume with kaolite which could be supplied at a lower unit cost. The silica fume is used as a cement substitu
9、te in the FRS mix principally to increase strength and reduce porosity.TEST PROGRAMThe variables in the test program included: fibre type,dosage rate: mass of fibre (kg) per unit volume (m3) of FRS, replacement of silica fume by kaolite. The performance of each variable was compared against the “Sta
10、ndard” mixatCannington which used EE256 slitsheet steel fibres.The types and dosage rate of the various fibres were selected by the mine owners and contractors and are summarised in Table 1. Three levels of kaolite were tested against the Standard mix 40, 60 & 80 kg/m3. The Mining Department at the
11、mine authorised the testing of each fibrecrete mix.TABLE 1 Range of fibre types examinedFibretype ManufacturerFibreLength Dosage RateEE256 BHP25mm60kg/m3RC65/35 Bekaert35mm30&35kg/m3HPPSyntheticIndust50mm6 &7 kg/m3BarchipHT48 HagiharaIndust.48mm9kg/m3change in the environmental variables. Each sampl
12、ehad a nominal diameter and thickness of 800 mm and 75 mm, respectively. The samples were cured for a minimum of 28 days prior to testing.The round panel test was carried out in accordance with ASTM C1550 using facilities in the School of Civil Engineering and Environment at the University of Wester
13、n Sydney. An MTS 250 kN servohydraulic actuator was used to apply a load at the centre of the sample at a controlled rate so as to achieve a constantrate of displacement of 4.0 mm/s. The sample was symmetrically supported at three points some375 mm radius from the centre and restrained to prevent an
14、y lateral movement.The peak load was measured for each sampleand the energy calculated to cause displacements of 5, 10, 20& 40 mm. As the peak load precedes crack formation, it represents the strength of the concrete matrix. With further loading beyond the peak load, the incremental energy absorbed
15、in the FRS is measured by integrating the load/displacement curve from the peak load to the various levels of displacement.The peak load was measured for each sample and the energy calculated to cause displacements of 5, 10, 20& 40 mm. As the peak load precedes crack formation, it represents the str
16、ength of the concrete matrix. With further loading beyond the peak load, the incremental energy absorbed in the FRS is measured by integrating the load/displacement curve from the peak load to the various levels of displacement.Graphs for the other fibre mixes are shown in Figures2 to 4. The graphs indicate some difference in behaviour between the dif
