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Write short notes on: Rollers & compactors.
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Rollers can be classified as :

  • Static smooth wheeled roller : These are rollers used with or without ballast and may be 3 wheeled or tandem type. These are conventional rollers used for almost all types of rolling. It is not effective on uniformly graded sand, gravel or silt. Nowadays Diesel powered rollers have replaced traditional steam rollers. The units of 8 to 10 tonnes imparting pressure of 20 to 40 kg per linear cm are generally used.

  • Sheep-foot or Pad-foot rollers:These may be self driven or tractor driven and are suitable on cohesive soils specially when water content is on higher side. The inherent dynamic beat developed by these tamping pads can in many cases produce a high degree of compaction at higher rate.

  • Pneumatic-Tyred rollers: These are used for compaction both in earthwork and bituminous road construction. On bituminous wear courses, it can eliminate surface cracking and material crushing caused by steel rolls. These rollers are available in weights ranging from 6 to 30 tonnes with 500 to 4000 kg per tyre and tyre pressure from 2 to 8 kg/sq.m.

  • Vibratory Rollers: Different types and sizes of vibratory rollers to suit specific conditions are available like. i) Rollers with large vibrating drum in front with 2 steel or pneumatic tyred rear driving wheels. ii) Roller with tandem smooth wheels, either one wheel vibrating and driven or both wheel vibrating and driven. iii) The small duplex roller with twin vibrating rolls weighing 1 to 1.5 tons for trench reinstatement.

Compactors can be divided into the following groups:

  • Towed static smooth compactors: Smooth rolls were the first type of rolling compaction equipment used. These were pulled by men or horses and were first used by Roman to roll and smoothen their roads and paths.

  • Static Sheepfoot or Padfoot compactors:

    There are several types of feet or legs of different shapes available. When compacting earth fills, the feet penetrate deep into the loose material during the first passes and compact the soil from the bottom up. The kneading effect of the sheepfoot compactors is used to break up the earth lumps and reduce the air voids in the cohesive granular soils.

  • Static three wheel self propelled compactors:

    These have three rolls, a small usually split steering roll in the front and two large drive rolls mounted on rear axle at the both ends. Split principle in front provides a differential action steering manoeuvres.

  • Static tandem compactors: Tandem rollers have two equal sized rolls and are centred line-tandem. These are used for compaction of bituminous layers as they leave a smooth surface. The contractors prefer larger size tandem vibratory compactors.

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