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THE above heading is the title of a recent paper dealing with the prortioning of concrete. The information is of such value that it is proposed to give a summary of the paper arranged so that the main divisions will be similar to thosc of the Bulletin fo facilitate reference.
The subject of the attrition of concrete surfaces exposed to sea action was dealt with by me in a paper read on January 22nd, 1920, before the Concrete Institute, now known as the lnstitutim of Structural Engineers. The object of the present communication is to describe the results of the experiments referred to in that paper. I endeavoured there to analyse the mechanism of attrition, going on from that to investigate the factors governing, and the possible methods for reducing attrition. It was shown that the injury to the concrete surface was primarily due to a fracturing and breaking away of the particles forming that surface, the conditions being exceptionally favourable
for the removal of the broken material by the water. In the latter respect such surfaces as are now considered differ fundamentally from horizontal surfaces upon which the products of disintegration are allowed to collect in the form of dust, forming a protecting layer. It was shown, broadly, that whether or not surface would resist the attack of boulders driven against it by the sea would depend upon two main
factors :-(n) The stress produced on the material by the blows of the boulders.(b) The resistance of such material to disintegration.
Dr. J.S. Owens
Ladies and Gentlemen,
With the example of my illustrious predecessors before me, I feel that I am at a loss in knowing how to give you such an Address as will be a worthy follower to those which have already been delivered to this Institution.
Major James Petrie