Chapter: Civil : Construction Materials: Lime, Cement, Aggregates, Mortar
Briquette Method
Briquette Method
Briquette Method: A mixture
of cement and sand is gauged in the proportion of 1:3 by weight. The percentage
of water to be used is calculated from the formula (P/5) + 2.5, where P =
percentage of water required to produce a paste of standard consistency. The
temperature of the water and the test room should be 27 o ± 2 o C. The mix is
filled in the moulds of the shape shown in Fig. 5.11.
After
filling the mould, an additional heap of mix is placed on the mould and is
pushed down with the standard spatula, until the mixture is level with the top
of the mould. This operation is repeated on the other side of the mould also.
The briquettes in the mould are finished by smoothing the surface with the
blade of a trowel. They are then kept for 24 hours at a temperature of 27 o ±
2 o C and in an atmosphere having 90 per cent humidity. The briquettes are then
kept in clean fresh water and are taken out before testing. Six briquettes are
tested and the average tensile strength is calculated. Load is applied steadily
and uniformly, starting from zero and increasing at the rate of 0.7 N/sq mm of
section in 12 seconds.
Ordinary Portland cement should
have a tensile strength of not less than 2.0 N/mm2 after 3 days and
not less than 2.5 N/mm2 after 7 days.
Notes: (i) In the tension test of cement the load
on the briquette should be applied centrally. Since briquettes become brittle
with age, the effect of slight eccentricity or any torsional strain is
pronounced in long-time tests.
(ii) The strength increases when the loading rate
is increased from that specified.
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