ABSTRACT
The basic characteristic of mass concrete canal linings is perhaps their great rigidity, which makes them highly vulnerable to cracking caused by differential settling of the underlying ground or due to heat stress. On the other hand, there are some types of canal linings that can be
considered as being somewhat flexible because they posses a certain capacity to deform without cracking. Prefabricated and brick linings are sometimes known as “semi-flexible” because their numerous construction joints adapt to the ground better than linings that are constructed onsite. Typical flexible linings are the so-called bituminous or asphalt ones and
in their most widely used form consist of a thin layer of a mixture of bitumen, gravel, sand and powder, also called filler, all of which are duly compacted. This mixture is also known as “asphalt agglomerate” and even “asphalt concrete” because it has a composition that is similar to concrete, however the binder in this case is bitumen in place of cement. It is also different in the fact it does not include any water and the much smaller aggregate. In this text, bitumen is a product obtained from asphalt through a pro-
cess of fractional distillation, which has certain penetration powers (see Section 4.4). Bitumen can also be obtained from petroleum. Another basic characteristic differentiating between flexible asphalt and
rigid concrete linings is that the former possesses great capacity to withstand deformation and thus adapts well to variations of temperature, lengthening or shortening as necessary with very small compression or traction stress, which means that these types of canals do not require joints. Nevertheless, they do have significant disadvantages. If there is excessive
heat from sunlight when the canal is empty, there is a danger that the lining could soften sufficiently to tend to flow to the bottom and the lower parts of the slopes. These linings are softer than those of cement concrete and do not with-
they drink from the canal.
