DRY LEAN CONCRETE FOR ROADS

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.
Rolling & Spreading of DLC
·   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.          
·    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.

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