Search

Sediment-laden hydrodynamic action can result in significant abrasion of concrete in hydraulic structures such as coastal defences, spillways, navigation locks, etc. Current guidance for designers of such structures in regard to abrasion resistance is often lacking in detail and does not account for the emergence of new and more sustainable concrete constituents. Further, field studies in which concrete abrasion in the coastal environment has been thoroughly measured for defined exposure conditions and concrete mixtures are non-existent in published literature. The objective of this research is to investigate the resistance of concrete to abrasion damage by waterborne sediments through an extensive experimental campaign and a field study. The ASTM C1138 (underwater) test method was used to evaluate the effect of coarse aggregate type and quantity, replacement of a proportion of natural coarse aggregates (NCA) with recycled waste glass particles (RWG) and addition of basalt micro-fibres on the resistance of concrete to abrasion by waterborne solids. Thereafter, relations of the basic mechanical properties of concrete (compressive strength, tensile splitting strength and modulus of elasticity) with abrasion loss in the underwater test were comparatively examined. Finally, and for the first time, a detailed field investigation supported by terrestrial laser scanning (TLS) was conducted on stepped concrete coastal defence elements at Cleveleys on the Fylde Peninsula in Lancashire, UK. It was found that the replacement of 25% fine aggregates with NCA did not significantly impact on the abrasion performance. However, depending on the test duration, replacement of 25% NCA with recycled tyre rubber aggregates having aspect ratios of approximately 4 enhanced abrasion resistance by up to 64%. Based on the tests conducted on concrete mixtures in which 0, 12.5, 25, 50 and 100% of NCA was replaced with RWG, Kruskal-Wallis tests at 95% confidence revealed that use of up 25% RWG as coarse aggregate was not significantly deleterious to abrasion resistance. Also, concrete produced with 100% RWG as coarse aggregates exhibited comparable performance to a similar mixture produced with limestone coarse aggregates. Further, experimental test results also revealed that use of basalt micro-fibres (17 microns diameter x 25.4 mm) in dosages of 0, 1, 1.5 and 3 kg/m3 neither enhanced abrasion resistance nor basic mechanical properties of the resultant concrete. Regression analyses and F-tests respectively indicated that there was a stronger and significant relation between abrasion losses at all test durations and tensile splitting strength of concrete with the exception of basalt fibre reinforced concretes which only followed this trend at 24-hour test duration. Field investigations showed that the concrete revetment armour units at Cleveleys are exposed to a macro-tidal environment with significant wave heights and peak periods of 0.42 to 1.92 m and 3.7 to 6.5 s respectively. Based on the abrasion damage observed, the units experience intense interaction with shingle of 26 mm (mean diameter) in the zone between Mean High Water Springs and Mean High Water Neaps thus yielding peak concrete abrasion rates of 3.5 to 4.5 mm/year. The polished abraded surface texture and absence of craters suggest that the main concrete loss mechanism was polishing/grinding.