Quality Assurance Handbook for Rural Roads Volume-I - pmgsy

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Quality Assurance Handbook for Rural Roads
(iv) Take about 100 gm of cement and mix it with water to make a stiff paste. Make a cake with sharp
edges. Put it on a glass plate and slowly take it under water in a bucket, without disturbing the
shape of cake. After 24 hours, the cake should retain its original shape and gain some strength.
(v) Setting time: Make a stiff paste of neat cement and water, and form it into a pat of about 75 mm
dia and 12 to 25 mm thick. The pat should commence to set in 30 to 60 minutes. The commencement
of setting can be roughly estimated by pressing the uncut end of a lead pencil into mass. The
resistance to piercing increases suddenly when setting commences. In 18 to 24 hours, the pat
should have hardened sufficiently so that a scratch can be made with a thumb nail.
(vi) Soundness: Boil the set pat (as above) in water for about 5 hours. The pat should remain sound
and hard and should not swell, crack or disintegrate, but may show only hair cracks. Reject
cement if pat shows radial cracks or curl or crumble.
(vii) Fineness: In the sieve test, 100 gm cement is correctly weighed and placed on 90 micron sieve. Air
set lumps, if any, are broken down with fingers. The sample is sieved for 15 minutes and the
residue left on the sieve is weighed. The amount of residue should not exceed 10% for OPC.
800.3 Sand or Fine Aggregate
The sand should be sharp, clean, chemically inert, coarse and gritty to the touch and free from silt/clay
and organic impurities. The general quality of sand can be assessed as below:
(i) Presence of Silt or Clay: Rub a sample of sand between damp hands and note the discolouration
caused on the palm. If the sand is clear, the palm would be stained slightly. If the hands stay dirty
after sand has been thrown away, it indicates too much of silt or clay.
(ii) Sedimentation: Place, without drying, a sample of sand in a 200 ml measuring cylinder upto 100
ml mark. Add clean water upto 150 ml mark. Shake the contents vigorously and allow it to settle
for 3 hours. The height of the silt visible as a layer above the sand is expressed as a percentage of
the sand below.
(iii) Organic impurities: Shake the sample with an equal volume of 3% solution of NaOH (Caustic
soda) and allow it to settle for 24 hours. Examine the colour of the liquid above the sand. Clear or
pale yellow colour shows that the sample is tolerably free from organic impurities. Dark yellow or
brown tinge shows that the sand should be washed and tested again. If on retesting, dark yellow
colour persists, the sand should be rejected.
800.4 Cement-Mortar
(i) The cement mortar if unused for more than 30 minutes after addition of water shall be rejected
and removed from site.
(ii) The mix proportion of cement: sand can be checked as follows:
Take about 200 gm of green cement mortar and add 100 ml of water in a measuring jar and shake
the contents well and allow the contents to settle. While the sand gets deposited at the bottom,
cement shall settle above. From the volumes of each, the approximate proportion of cement and
sand can be determined.
(iii) Consistency: Mortar consistency can be checked by the following:
(a) If a small quantity of mortar is dropped from a trowel, the trowel ought to be left perfectly
clean.