Spalling micro

Electric heaters will be used to induce additional thermal stresses that aim to force the rock in the pillar walls to spall. To simulate the effect of confinement from backfill, a water pressure of 1 MPa will be applied in one of the holes. All experimental stages will be monitored by an Acoustic Emission (AE) and micro-seismic system. Convergence and strain measurements will be made to monitor the deformation. 

After milling, and deeper removal where cracking and spalling have occurred, a bridge or car park deck can then patched in the delaminated areas and a dense cementitious overlay of micro silica, polymer modified or low slump, low water/cement ratio concrete or other suitable waterproofing (chloride ingress resistant) deck concrete is put back on. This will slow the corrosion rate and the appearance of further delaminations (Figure 5.10). 

Banthia and Nandakumar (2003) have employed secondary polypropylene micro-fibres to enhance the deformation of steel fibre-reinforced concrete. More recently, Dawood and Ramli (2012) proposed the combination of steel fibres with synthetic and palm fibres as a means of reducing the corrosion problems of fibres and improving the flowing and mechanical properties of concrete. Lee et al. (2012) have shown that the blending of nylon and polypropylene fibres improves the spalling protection of FRC subjected to fire. Azhari and Banthia (2012) have blended carbon fibres and nanotubes in the development of smart stmcture materials, such as strain sensors. 

It is no longer neeessary to demonstrate the influence of oil contamination on Rolling Contact Fatigue (RCF). Previous studies have shown the consequences induced by the travel of solid particles inside the contacts. In fact, when particles enter the contact, they indent the surfaces. The resulting surface defects, called dents, become stress raisers and increase the risk of spalling and consequently of RCF. In order to compare numerical and experimental results, some tests were performed on a two disk machine with artificially dented surfaces. Cross-sections were performed to complete the surface observations, and to analyse the crack initiation sites and the crack propagation directions. This paper proposes an analysis of these cross-sections to identify the cracks that lead to micro and macro spalling. 

For the smooth disk, it was quite difficult to situate the cross-sections in relation with the surface photographs due to the great amount of micro spalls. The micro cracks observed on the surface are less propagated. They induce micro spalling which not exceed 3 up to 4 pm (Figure 7-a.2, a.3 and a.4). As it was mentioned before, the load direction tends to close the cracks and stop the crack growth. 

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