The physical and chemical performance of artificial reef blocks made using quarry by-products

The cost of construction materials is a major factor determining the economic viability of artificial reefs. The use of by-products is one method of reducing costs, but often, to comply with licensing conditions, chemical and physical stability have to be demonstrated before such materials may be employed. Granite quarrying produces a range of low-value by-products, including an aqueous granite powder suspension. When mixed with other by-products and consolidated using 5% (w/w) cement and 5% (w/w) coal fly-ash, this substance was used to produce concrete blocks with a compressive strength of approximately 14 N mm(-2) after a standard 90-day curing period. The blocks exceeded the strength requirement of commercial building blocks (British Standard 6073) by five times, were cheaper to produce compared with standard construction-grade blocks, and permitted a range of design options to be considered through the inclusion of voids. The chemical stability of the proposed concrete and base granite material was tested, under conditions designed to maximize metal flux, and showed significant but very low leaching of iron, strontium, barium, rubidium, manganese, and uranium. Metal leaching was not necessarily in proportion to the metal concentration in the base material. Quarry by-products can be used in the manufacture of blocks that are physically robust and environmentally safe with a concomitant reduction in production costs. (C) 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd. All rights reserved.