N.Z. RESOURCES FOR CONCRETING BEING CHECKED

Bay of Plenty Beacon, Volume 14, Issue 84, 11 January 1950, Page 5

N.Z. RESOURCES FOR CONCRETING BEING CHECKED

Utilisation of materials for concrete and cement which are close to the sites of projected large schemes leads to a considerable saving 'in the costs of concrete-dam construction and further examination of material from many areas is now being made. The magnitude of concrete-dam construction in New Zealand has called for extensive research by scientists of the Dominion Laboratory and the Dominion Physical Laboratory of the Department of Scientific and Industrial Research. The chemistry and physics of cemerft and concrete are investigated with special regard to local conditions, and the application of the results of this work may lead to considerable savings. Broadly, the quality of cement is examined under four chartcteristics: Chemical composition, fineness, heat-evolution, and total alkali content. The importance of cementalkalis upon the durability of concrete has only recently been realised, and a close check has, therefore, to be made on the alkali content of all cement used in dam construction, because when present in excessive amounts alkali reacts with certain types of aggregate, causing cracks to develop that may seriously affect the permanence of the structure. In the investigations the high quality of all the cement made in New Zealand has been confirmed.

A programme of mortar-bar tests which will take two years to complete, has been put in hand with aggregates from many areas including quartzite from Cobb River, basalt from Ongoroto, sand from Arapuni, greywacke from Muku and Whitehall, and thyolite from Whakamaru and McLaren Falls. Six bars from each source of aggregate have been made, and cements of both high and low alkali-content have been used. At monthly intervals the bars are removed from storage for examination and measurement. When the mortar-bar tests are completed, the information obtained will be correlated; and since the aggregates from all sources were previously examined chemically in comparison with aggregates of known reactivity, these tests are expected to form a basis whereby aggregates may in future be assessed solely by the more rapid chemical method.

Geologists and chemists of the Department of Scientific and Industrial Research are co-operating in a survey of raw materials for cement making, and samples are taken from various parts of New Zealand. Should expansion of cement production be decided upon, the necessary information will be available, for instance, of the suitability of the material close to the sites of projected dams.