Effects of fluidal fly ash on abrasion resistance of underwater repair concrete

Abstract

The damages of the surfaces of the hydraulic concrete structures are usually caused by abrasive action of the debris carried by the water. The action of the debris leads also to damages of the structural reinforcement. Therefore, selection of the repair materials is focused not only on the strength requirements, but also the abrasion resistance. On the other hand, there is very important that the majority of the repair works is conducted under water, at great depths. Therefore, the underwater concretes are increasingly used for the repairs. These concretes make possible repairing in the contact with water, with substantially limited wash-out losses of the cement paste. In this context, the important problem is utilization of the pozzolanic materials from recycling for the production of the underwater repair concretes, which allows for the limitation of the cement use. In this paper, the results of the testing of the abrasion resistance of the underwater repair concretes were presented. The concretes under investigation have contained 20%, 30%, 40% and 50% (of the cement mass) of the fly ashes from the fluidal beds. The fluidal fly ashes are the by-products of burning the coal in the energetic plants with the fluidal beds. Abrasion of the underwater concretes was tested using two methods. First method consists in the use of Boehme abrasion tester, which is used in EU countries for determination of the abrasion resistance of concrete. The second method is so-called underwater method according to the US Standard ASTM C1138. The method according to ASTM C1138 appeared to be more reliable in the evaluation of the abrasion resistance of the underwater concretes. The highest abrasion resistance showed the concrete with 30% (in relation to the cement mass) of the fluidal fly ashes. Due to the strong pozzolanic properties of the fluidal fly ashes, the substitution of the 30% of cement with the fluidal fly ash enables obtaining of the concrete with improved compressive strength and abrasion resistance as well as the workability which makes possible the proper conducting of the repair works under water.