search.noResults

search.searching

saml.title
dataCollection.invalidEmail
note.createNoteMessage

search.noResults

search.searching

orderForm.title

orderForm.productCode
orderForm.description
orderForm.quantity
orderForm.itemPrice
orderForm.price
orderForm.totalPrice
orderForm.deliveryDetails.billingAddress
orderForm.deliveryDetails.deliveryAddress
orderForm.noItems
SPECIALIST EQUIPMENT


FIBRE THE RIGHT


Roland Mayr explains how selecting the right structural synthetic fibres for sprayed concrete depends on when and how the concrete will be loaded


safely, fast and in a highly mechanised way. Te use of synthetic fibres, generally


F


polypropylene (PP), allows the concrete structure to behave in a ductile way, enabling significant deformation before failure. Structural synthetic fibres form an internal network and add superior tensile properties to the sprayed concrete. Tey have advantages over steel fibres in that they do not corrode and have a far smaller carbon footprint. Effective surface support and protection against the weathering of rock and strata are critical to the safety, efficiency and longevity of any mining operation. Different types of synthetic fibre cause the reinforced sprayed concrete to behave differently. Making the right choice of fibre depends on how much loading the


28 www.engineerlive.com


ibre-reinforced sprayed concrete is widely used for rock support, with fibres replacing conventional mesh reinforcement. It can be applied


concrete must take and how quickly that loading will be applied – and that depends on the ground and on planned mining operations. As shown in Table 1, there are three main shapes of structural PP fibres available: flat, embossed and crimped. To compare the performance of different fibers, energy absorption (EA) tests on panels of sprayed concrete containing the fibres can be used. EA is a measure of the toughness of sprayed concrete, with a load applied to the centre of a panel to mimic deformations. Typically, fibre testing panels are prepared


by spraying the concrete in the same way it would be applied underground, but with less accelerator. Sometimes the panels are also cast under lab conditions, but this can give misleading results, depending on the types of fibres used. Embossed fibres typically show a better performance under cast conditions because the liquid cement paste penetrates all the fine indentations in


the fibre to form a good bond. However, under spraying conditions, the cement paste stiffens immediately due to the addition of the accelerator and hence does not penetrate the indentations as well. Te performance of PP fibres depends on the fibre strength and the properties of the interface between the fibre and the concrete matrix. Tis is influenced by both the surface structure of the fibre (flat, embossed) and the strength (age) of the matrix.


Te age at which energy absorption


panels are tested varies from country to country, from 7 to 28 days. Te testing can be done either when a certain strength is reached or at a certain age. It should be noted that, if a shotcrete shell is loaded a long time after it is applied, the strength and performance can be quite different than if it is loaded immediately Ideally, a fibre would not be pulled out easily or break as a load is applied. In other


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52