DLC or Dry Lean Concrete is cement concrete
with low slump value to be laid for rigid pavement over sub-base and rolled
& compacted by mechanical means.
· Ordinary Portland cement, Portland PozzolanaCement or Portland Slag Cement be used for DLC.
· Coarse aggregate shall consist of Clean, hard, strong,
dense, non-porous and durable pieces of crushed stone or crushed gravel and
shall be devoid of pieces of disintegrated stone, soft, flaky, elongated, very
angular or splintery pieces. The maximum size of the coarse aggregate shall be
25 mm.
· The fine aggregate shall consist of clean, natural sand or
crushed stone sand or a combination of the two and shall conform to IS : 383.
Fine aggregate shall be free from soft particles, clay, shale, loam, cemented
particles, mica, organic and other foreign matter.
· The coarse and fine aggregates may be obtained in either of
the following manner:
(i) In
separate nominal sizes of coarse and fine aggregates and mixed together
intimately before use.
(ii) Separately as 25 mm nominal single size,
12.5 mm nominal size graded aggregates - and Fine
Aggregate of crushed stone dust or sand or a
combination of these two.
AGGREGATE GRADATION FOR
DRY LEAN CONCRETE:-
Sl No
|
Sieve Sizes
|
Percentage passing the
sieve by weight
|
1
|
26.50 mm
|
100%
|
2
|
19.00 mm
|
80-100%
|
3
|
9.50 mm
|
55-75%
|
4
|
4.75 mm
|
35-60%
|
5
|
600.00 micron
|
10-35%
|
6
|
75.00 micron
|
0-8%
|
· Water for mixing and curing of concrete shall be clean
and free from injurious amounts of oil, salt, acid, vegetable matter or other
substances harmful to the finished concrete.
· The
mix shall be proportioned with a maximum aggregate cement ratio of 15 : 1.
· The
minimum cement content is 150 kg/cu.m. of concrete.
· The
average compressive strength of each consecutive group of 5 cubes made shall
not be less than 10 MPa at 7 days. In addition, the minimum compressive
strength of any individual cube shall not be less than 7.5 MPa at 7 days.
· The
batching plant shall be capable of proportioning the materials by weight, each
type of material being weighed separately. The cement from the bulk stock shall
be weighed separately from the aggregates. The batching and mixing shall be
carried out preferably in a forced action central batching and mixing plant
having necessary automatic controls to ensure accurate proportioning and
mixing. Other types of mixers shall be permitted subject to demonstration of
their satisfactory performance during the trial length. The type and capacity
of the plant shall be got approved by the Engineer before commencement of the
trial length. The (weighing balances shall be calibrated by weighing the
aggregates, cement, water and admixtures physically either by weighing with large
weighing machine or in a weigh bridge. The accuracy of weighing scales of the
batching plant shall be within ± 2 per cent in the case of aggregates and ±1
per cent in the case of cement and water.
· Plant
mix lean concrete shall be discharged immediately from the mixer, transported
directly to the point where it is to be laid and protected from the weather by
covering the tippers/ dumpers with tarpaulin during transit. The concrete shall
be transported by tipping trucks, sufficient in number to ensure a continuous
supply of material to feed the laying equipment to work at a uniform speed and
in an uninterrupted manner. The lead of the batching plant to paving site shall
be such that the travel time available from mixing to paving.
· Lean
concrete shall be laid/placed mechanically /manually. The concrete shall be laid in one layer
in an even manner without segregation, so that after compaction the total
thickness is as specified. The laying of the two- lane road sub-base may be
done either in full width or lane by lane. Preferably the lean concrete shall
be placed and compacted across the full width of the road, by constructing it
in one go or in two lanes running forward simultaneously.
· The
compaction shall be carried out immediately after the material is laid and leveled
with 8 -10 Tonne Static Roller. In order to ensure thorough compaction which is
essential, rolling shall be continued on the full width till there is no
further visible movement under the roller and the surface is closed.
 |
| Rolling & Compaction; Spreading of DLC |
· As
soon as the lean concrete surface is compacted, curing shall commence. Curing
shall be done by covering the surface by gunny bags/hessian, which shall be
kept continuously moist for 7 days by sprinkling water.
· The
minimum dry density obtained shall be 97% of the dry density achieved during
trial length construction and the density achieved at the edges (i.e. upto 0.5m
from the edge) shall be not less than 95% of the MDD.
