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< prev - next > Energy Hydro power Layout_and_construction_of_canals (Printable PDF)
If a tin is used as a measuring unit then the mix should consist of 1 tin of
cement, 2 tins of sand and 4 tins of split stones. However, the water varies
depending on its equivalence.
For lining canals using the wooden frame method, the concrete used is f'c = 175
kg/cm2 2 inches thick, equivalent to 5 cm. Therefore the crushed stone is
1 : 2 : 3,
The wheelbarrow used for the works must be calibrated to find out how many
cubic feet it can hold.
A wheelbarrow usually holds 1 level cubic foot. For f'c = 2.10 kg/cm2, for
example, the following should be used:
1 bag of cement, 2 wheelbarrows of sand and 2 wheelbarrows of crushed
stones. Bear in mind that the material in the wheelbarrow must be level.
So that it reaches the f'c design resilience, good concrete not only depends on
the dosage but also on other factors that should not be neglected, such as:
- The water/cement ratio, by weight
- Mixing
- Transport
- Laying
- Consolidation
- Curing
The water/cement ratios w/c for each of these doses are:
Table 2
f’c w/c
140 0.66
175 0.59
210 0.51
If the w/c ratio is altered, that is if more water than necessary is added, the
concrete will be less resilient and the structure could fail as it may not be strong
enough to support the compression stress.
A mixer should preferably be used for the concrete mix, as the mixing time - no
more than 1.5 minutes - and the order in which the aggregates, cement and
water are added, are both important.
When a mixer is not used and the mix is prepared manually, it is recommended
that the correct proportions of dry aggregates and dry cement are mixed at least