Previous workers have noted variations in skid resistance value of aggregates of similar trade-group categorization and of similar petrographical grouping, due to detailed mineralogical and petrographical changes. Some further examples are noted and, with particular reference to limestone aggregates the cause of these variations is discussed, together with the question of blending aggregates of different polishing characteristics with the aim of achieving certain desired levels of skid resistance.

The topographical characteristics of aggregates of various type, natural and artificial and at various states of polish, have been studied by means of the Stereoscan electron microscope and related to petrographical detail, and to geological, crushing and polishing history.

The effect of different states of polish of a particular roadstone surface on the wet skidding resistance of rubber compounds is shown to be of the same order of magnitude as that encountered in testing a surface of a given state of polish with rubber compounds of poor and good wet-grip properties.

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