ABSTRACT
Concrete is a product obtained through the intimate mixture of gravel, fine gravel and sand (in suitable proportions), together with cement and water. Either after or simultaneously with the pouring of the paste into the mould or formwork that provides the shape of the part to be manufactured, it is essential that the mixture is correctly compacted in order to reduce as much as possible any interior cavities. Following this, there is a process called “setting”, during which the mixture hardens, heat is given off and the manufactured part undergoes a reduction in dimensions known as “shrinkage”. Cement concrete is very frequently employed as a canal lining material.
However, the conditions to which it is exposed are extremely difficult and, to a certain extent, are not suited to its characteristics. It must be remembered that the Bureau of Reclamation, in its book on
concrete, considered that concrete employed in canal linings is the one that has to withstand the most arduous of conditions (9). For this reason, it recommends the use of air entraining agents, a study of the water-cement ratio, the use of perfect grain size, very good compaction and that close attention be paid during the concrete pouring operation, etc. Cement concrete is extremely impermeable and only small amounts of
filtration would occur if it were not for the very great danger of cracking involved. This is because, although it is a material with excellent compressive strength, it has, on the other hand, poor tensile strength. It is a highly rigid material that adapts very poorly to ground strain, no matter how small they are because the material is quite unable to withstand them. Significant stress is also produced due to shrinkage and temperature drops, which enormously increase the danger of cracking appearing, which then becomes the cause of serious filtration. Water loss in mass concrete-lined canals does not occur in a uniform
fashion over the entire lining, but instead is localized to the cracks or poorly
