METHODOLOGY FOR DRY LEAN CONCRETE
(Acceptance Criteria: Ref. Sec 600 of MORT&H)
Scope
The work shall consist of construction of Dry Lean Concrete (DLC) Sub-base for Cement Concrete Pavement in accordance with the requirement of technical specifications and in conformity with approved lines, grades and cross-sections.
Equipment/Machinery Requirement:
- Batching & mixing plant
- Tipper
- Sensor paver
- Tandem roller
MATERIALS
- Test certificates from manufacturer shall be presented for each lot of cement or cement testing shall be carried out in our site laboratory and result will be submitted. Joint test shall be carried out for the approval obtained from the Engineer’s Representative for every 200cum of material. Water shall be tested as per requirement of IS: 456 and approval obtained in advance.
- Cement shall be procured in polyethylene Bags and loaded manually in to hopper of cement pump. From hopper of pump it will be pumped to the Silo of the Batching Plant.
- Combined grading of aggregates (Coarse & Fine) will be carried out at laboratory attached with the plant, at least once daily and adjustments in Mix proportions will be made for aggregates components, accordingly.
- All approved aggregate shall be stacked separately at plant site in stack 5.00 Meter clear Distance apart and shall be identified by placards marked ‘APPROVED’ placed on top of the heap.
MIX DESIGN
The mix shall be proportioned with a maximum aggregate cement ratio 15:1. The right amount of water will be decided so as to ensure full compaction under rolling and will be assessed at the time of rolling the trial length. As the too much water will cause the lean concrete to be heaving up before the wheels and picked up on the wheels of the roller and too little will lead to inadequate compaction, a low in-situ strength and open textured surface, the optimum moisture content and degree of compaction shall be determined during the trial length. These parameters can be decided during the trial length and be approved by the Engineer.
The minimum cement content in the lean concrete shall not be less then 150 kg/cum of concrete. If the minimum cement content is not sufficient to produce concrete of the specified strength, it will be increased as necessary. The average compressive strength of each consecutive group of 5 cubes made in accordance with clause 903.5.1.1 will not be less than 10 Mpa at 7 days. The design mix meeting these requirements will be got approved from the Engineer and demonstrated in the trial length construction.
Construction Process
Preparation of Surface:
Loose patches on the drainage layer shall be watered and compacted to achieve a firm surface. Prior approval of length of every days’ paving shall be obtained in advance. As for as possible the construction traffic shall be avoided on the prepared surface. A day before placing of the lean concrete, the sub surface shall be given a fine spray of water and rolled with one or two passes of a smooth wheeled roller after a lapse of 2-3 hours in order to stabilize the loose surface.
Concrete Production: Concrete shall be produced in the Batching Plant, which is capable of proportioning the material, by weight, with each type of material being weighed separately. The batching and mixing shall be carried out in a forced action central batching and mixing plant, which has automatic control. The controls are fully computerized so as to ensure accurate proportioning and mixing. The accuracy of weighing scales of the batching plant will be within +/- 2 percent in the case of the aggregates and +/- 1 percent in the case of cement and water. Additives will be introduced into the mixture in diluted form. Loaders will be used to load aggregates from stacks of approved material into bins. Batch plant bins will have a storage capacity of 35 cum each. Water will be obtained from the bore wells at the plant site. Water will be stored in the water tank of 120 kl capacity. Mixing time shall be established to the satisfaction of the Engineer’s Representative. Concrete will not be produced when ambient temperature fall below 5 deg centigrade of exceeds 35 deg cent. Following measures to control temperature within 30 deg cent will be adopted.
Mechanically water will be sprinkled to cool the aggregate.
Cover will be provided for aggregate to be used in next 24 hours.
Chilled water will be used for preparation of concrete. For this purpose water chilling plant of capacity 15000 lt/hour capacity and storage of 50000 It will be used.
Transportation: 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. The concrete will be transported by tippers/ dumpers of 6 cum capacity and sufficient in number. The number of the tippers beadequate in number so as to feed the Paver to work at a uniform speed and in an uninterrupted manner.
PLACING:
a) The work will be carried out with sensor Paver for laying of main carriageway in one pass..
b) Surveyor will fix the alignment for every day’s work, one day in advance, and get it approved from Engineer’s Representative.
c) Prior to start of paving, string line will be set, approx. 200mm above DLC top levels on each side, on longitudinal profile, on stakes placed 10 met apart.
d) Air and concrete temperature shall be measured and recorded in the concrete docket, at the plant site as well as laying site. No concrete will be done when the concrete temperature cannot be maintained below 30 deg cent & and when ambient temperature is more than 35 deg cent. Plant operation will be stopped based on feedback from laying site.
e) Tracability of concrete received from the batching plant will be maintained by recording data as shown on Tracibility form.
Compaction:
a) Rolling shall be done by double drum vibratory roller of 80 KN static weight and shall commence immediately after laying by Paver. First pass of the roller shall be given in static mode and there after roller shall be operated in the vibratory mode. Sufficient number of passes would be given till the density of compacted layer reaches more than 97% of Dry density achieved in Trial length construction. Areas inaccessible for the roller will be compacted by plate vibrators. Static roller will be used as stand by in the event of breakdown of vibratory roller but further work will not be carried out till the vibratory roller is available in working condition at-site.
b) Honey-combed surfaces shall be corrected by scarifying and repairing with concrete prepared with aggregate of 10 mm size before start of rolling operations.
c) Surface regularity during the course of laying will be checked with a 3 meter straight edge. High points of the surface will be corrected by scarifying & rerolling and the low areas shall be corrected by filling with fresh materials and rolling. The spreading, compacting and finishing of the lean concrete shall be carried out as rapidly as possible and the operation shall be so arranged as to ensure that the time between the mixing of the first batch of concrete in any transverse section of the layer and the final finishing of the same shall not exceed 90 minutes when the concrete temperature is above 25 and below 30 degrees Celsius and 120 minutes if less than 25 degree Celsius. However, these parameters will be decided in the trial length.
CURING: As soon as the lean concrete surface is compacted curing shall commence. Hessian shall be used and will be kept moist for 7 days by regular sprinkling of water from flexible pipe attached with a water tanker. Water tankers will be deployed round the clock for providing water for curing. Water will be available from the bore wells along the length of the road.
TRIAL PAVE
a) Trial paving will be conducted at outside the road alignment and at our campsite
b) Length of laboratory Pave shall be kept as 60-70 meter.
c) Target level for the Trial shall be fixed prior to paving.
d) Suitability of moisture content of Mix shall be examined during the trial length construction to ensure that maximum density and compressive strength related to corresponding water content are achieved.
e) Density of compacted materials of trial length will be determined as per IRC SP-46. Specified and taken as reference density. Approval of trial length shall be obtained from the Engineer.
f) 3-meter wide portion of hardened concrete of trial length shall be cut and reversed for inspection of bottom surface. The entire process of mix design & trial length shall be repeated if segregation of mix is observed.
g) Achieve levels will be compared with the target levels.
h) Approval of Engineer’s representative will be obtained before proceeding with the main work.
TESTING:
Testing will be carried out as per table enclosed (Encl-III). Level conformance of finished DLC will be ensured by taking levels at specified grids and compared with the target levels. Concrete testing record will be maintained as per format enclosed (Encl- IV).
Tolerances: The tolerances for surface regularity, level, thickness,
density and strength shall conform to the requirements given in clause 903.5. Control of quality of material and work shall conform to the specification as laid down in Section 900 of MORT&H Specifications.
TRAFFIC:
No heavy commercial vehicles like trucks and buses shall be permitted on the lean concrete sub-base after its construction. Light vehicles shall be allowed after 7 days of its construction.
MACHINARY AND MANPOWER: Machinery and manpower will be deployed as detailed in encl-V.
Is representative will be obtained before proceeding with the main work.
Environmental Safety
1.Water will be obtained from the bore wells situated at our Camp Sites so that it will not affect nearby localities.
II. The Batching Plants are situated at our Camp Sites at Km15.700 and water sprinklers will be installed to minimize Dust & Cement in the localities.
Ⅲ. Fuel Storage and Refuelling at Site are in the Camp Sites and Strict Supervision will be maintained to stop Spillage or leakage to any nearby water bodies.
IV. Our Mechanical Staff will maintain Batching plant & other related equipment’s regularly to reduce Noise & Atmospheric Pollution.
V. The constructions Vehicles, Machineries and Equipment’s will move in our designated area so it prevents compaction of any type of vegetation and plants.
VI. All workers will be suitably provided with safety guards at the site.
VII. Safety Signals & Sign boards will be provided at every 200 m at the Construction Site.