SPECIALIST EQUIPMENT
Spraying of test panels
TABLE 1. Types of PP fibres
GRAPH 1. Performance of flat fibre at 6 kg/m³ in square panel test
GRAPH 2. Performance of embossed fibre at 6 kg/m³ in square panel test
words, the fibres should only start to be pulled out as the maximum breaking load of the concrete lining is approached.
FLAT VERSUS EMBOSSED To compare the performance of flat and embossed fibres in different strengths and ages of concrete, tests were carried out on square panels at 7, 28 and 90 days. (Round test panels are often used in mining but results from square panels can be converted to those obtained from round panels by dividing the EA obtained by 2.5).
Te performance of the flat fibres can be seen in Graph 1. With increasing age and strength of the concrete, the performance of the system improves. Te embossed fibres show a different behaviour (see Graph 2). Te performance in the lower deformation range is very similar. In the higher deformation range and with increasing concrete strength and age the performance decreases.
After the tests, the fibres in the cracks
were counted and classified into snapped and pulled out fibres. Te percentage of snapped fibres increases with strength/ age for both fibre types, but the increase of broken embossed fibres is significantly higher.
WHAT DO THE TEST RESULTS TELL US?
A number of conclusions can be drawn from these results. Firstly, that modern sprayed concrete tends to develop significant strength with age. Secondly, it is important to consider at what age the sprayed concrete will be loaded and how big the deformations will be. Te results also show that flat fibres can take higher loads and deformations, as long as the loads are applied when the concrete has reached a higher age/ strength. Meanwhile, embossed fibres can be better for lower age/strength concrete (up to 14 days). Also, they provide greater
stiffness with lower overall levels of deformation. Master Builders Solutions provides
various types of structural PP fibres in its MasterFiber range. Te firm’s knowledge of concrete technology and chemistry allows it to design the concrete mix and select the fibres for a maximum structural response, depending on the geology of the mine. For reinforced sprayed concrete, the
main requirement is to maintain a certain level of ductility under high deformation conditions. Te strength and age of the concrete matrix, as well as the fibre type, must be considered to achieve the desired performance.
Roland Mayr is global technical manager sprayed concrete at Master Builders Solutions.
www.master-builders-solutions.com
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