Discussion. Results of a Thermo-Couple Study in Mass Concrete in the Upper Tamar Dam.

Abstract

The Paper is concerned with large pours in mass concrete dams, ways and means of preventing cracking, speeding up construction and reducing costs, and possible future improvement in concrete dam construction.93. Since 1945 our firm and its predecessors have been responsible for the design and construction of over 30 dams in the UK, of which about half were earth or rockfill and half concrete, and certain trends have been noticeable in recent years. The proportion of earth and rockfill embankments to concrete dams is increasing. One reason is that the sites now being developed are often less favourable to concrete dams, and another that the cost of earth and rockfill has not increased as rapidly as the cost of concrete, mainly because of the availability of larger and more efficient earthmoving and compacting plant. 94.Although some years ago we were able to get low-heat cement for the Lamaload buttress dam at Macclesfield, it is now difficult to obtain moderate heat cement in the UK and this fact, together with the traditional methods of construction has led to more cracking than in the past.95. There seems to be a tendency to think that the British clinlate is so bad that there is no need to worry about cooling aggregates and curing concrete, but the results of this study indicate that more attention should be given to it.96. The technology of mass concrete construction has not kept pace with that of earthmoving; it seems strange that there has not been any real change in the bucket-bybucket method of moving mass concrete into place. Concrete dams are still constructed by the traditional methods of lifts and blocks, with numerous construction and contraction joints, which are expensive and slow down the rate of construction. In these days of inflation, with high labour costs and high interest rates, financial considerations are very important. If a dam can be built in three years instead of four one can probably save at least 150/, in cost.97. Ofhers have suggested treating concrete in gravity dams as a fill material placed in continuous layers across the valley, using earthmoving and compaction plant. Gentile has described the Alpe Cera Dam in Italy where concrete was placed in layers 0.8 n1 thick, being brought to the site in large dump trucks, spread by angledozers and vibrated by batteries of vibrators fixed on tractors. Each layer was cleaned by machines fitted with brushes and air and water jets, and the ccmtraction joints were cut afterwards by special sawing machines. Such methods could be used on medium sized dams in the UK. Mr DunstanThe modified specification detailed in the Paper will make a reasonable saving but I feel that a total change in the constructional procedure of dams could make an even greater saving. Various suggestions have been made in the past to reduce the cost of concrete dams. Some suggest the use of precast panels as in situ shutters and others the use of dry lean concrete.23 Precast panels have the advantage of reducing the shuttering problems and providing excellent insulation...