The assessment of abrasiveness and hardness of rocks have been extensively covered by previous researchers, with little attention to flints, which were only described as highly abrasive. However, analysis of flints has shown that abrasivity of flints varies. These parameters are important inputs for the prediction of drill bit wear rate and design of various parts of drilling/tunneling/mining equipment. In this paper, a classification of flints (sampled from the English, French and Danish Chalk) which correlates with the abrasivity and hardness of flints is proposed. The results showed lighter/grey flints (with more calcite) have lower potential to cause drill bit wear as indicated by hardness and geotechnical wear indices than dark flints. This tends to suggest that even small variations in the carbonate content results in significant variation in abrasivity and that colour can be used as an indication of the potential of flints to cause tool wear.
In most continents, flints are found either as nodules, sheets or as extensive thick beds (tabular) in chalk. Encountering flints during engineering works usually leads to challenges affecting the entire project execution/costs. These threats are among the major factors affecting engineering projects in chalk. The problems are in the form of abrasive wear of drilling/tunneling tools, which are mostly felt during excavation because they were not envisaged at the preliminary stage of the project. This usually leads to costly changes or redesign of both the project or excavation machinery and associated cutting parts (Hahn 1999, Mortimore 2012 and Varley 1990). Therefore, proper understanding of wear properties of flints will help in predicting their potential to cause drill tool wear, and will also aid in the design of excavation systems before onward mobilisation to the field.
Unfortunately, despite the persistent threats posed by flints, the hardness and abrasiveness of flints are not well understood and attempts to understand these are very limited. Similarly, to date, no attempt has been made to relate the hardness and abrasiveness of flints to their various colours. Thus, this paper looks at the wear properties of flints using Shore Hardness (SH, n= 39), Cerchar Abrasivity Index (CAI, n= 71), X-Ray Diffraction (XRD, n= 14), Vickers Hardness Number of Rock (VHNR, n=14), Rock Abrasivity Index (RAI, n= 108), Scanning Electron Microscopy and Image analysis (ImageJ). These methods were used to determine the abrasive properties of flints and to define which flint has more chance of causing drill wear, when characterized by colour. The aim is to establish a simple classification of flints for prediction of tool wear rate based on colour variation, for use at the preliminary phase of site investigations.
