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

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