TOPIC OF THE DAY Flexible Pavement Distresses/Failure Of Structure. Causes Of Structure Failure. Repair/Maintenance Of Structure.

Flexible Road Structure PAVEMENT In ‘CIVIL’ terminology “PAVEMENT” described to ‘Road’. Pavement Types: Flexible pavements.  Those which are surfaced with bituminous (or asphalt) materials. Rigid pavements.  Those which are surfaced with Portland cement concrete (PCC).  -------------------------------------- Surface Course (Asphalt wearing course) -------------------------------------- Binder Course -------------------------------------- Base (asphalt base course) -------------------------------------- Sub – Base (Aggregate) -------------------------------------- Capping - - - - - - - - - - - - - - - - Sub - Grade (Earth work-Fill) Flexible Road Structure

DISTRESSES Flexible pavements TYPE of DISTRESSES. CRACKING. DISTORTION. DISINTEGRATION. SKID HAZARD. SURFACE TREATEMENT– SPECIAL PROBLEMS.

CAUSES OF FAILURES Causes of cracking are followed as: Saturated granular bases/ sub-grade. Lower courses of road. Less load-carrying capacity of the structure. Causes of distortion are followed as: Sub grade weakness (compaction occurred). Displacement of surface. Lack of stability. Causes of disintegration are followed as: Too little asphalt. Too thin asphalt surface. The base failure. Poor drainage. Causes of skid hazard are followed as: Wetting. Thin film of water. Thick film of water. Surface contamination (oil spillage/clay types). Causes during surface treatment: Method of construction. Surface treatment. Thin asphalt surface.

Repair & Maintenance of structure

CRACK By filling. In other cases, complete removal of affected area. To make proper repair, then, the necessary steps is followed as: Clean cracked area with brooms/ if necessary, compressed air. Spray asphalt (emulsion/asphalt cement). Usually,0.7/1.1 litre/m² enough for seal coat, if excessive amount loss in cracks, more asphalt should be applied. After spraying asphalt ‘immediately’ apply cover aggregate. Size of agg. For this patch is 6mm (1/4 in.) no. 10 screenings. By rubber-tired machine roll seal coat. If necessary to build up the patched area to the level of the surrounding pavement, a 2nd seal coat can be applied. Allow to cure thoroughly before opening to traffic.

DISTORTION Following steps must be followed: Level the pavement with hot plant-mixed asphalt material. Apply a light tack coat, 0.255-0.7 liter/m² of ss-1, ss-1h, css-1or css-1h asphalt emulsion diluted with equal parts of water. Spread dense-graded asphalt concrete with paver, sure material is feathered at the edges. Compact with a pneumatic-tired roller. If not possible, use a steel-wheeled roller. Place a thin overlay of hot plant-mixed material.

DISINTEGRATION To repair such type of affected pavement follow the steps are: Clean hole of loose material and as much water as possible. Use infra-red heater to heat and soften asphalt surface around hole. Fill hole with asphalt emulsion stockpile mixture and rake smooth. Compact with vibratory plate compactor or roller. Dry compacted patch with infra-red heater.

SKID-HAZARD To repair that type of distress. follow the given steps: Apply specific size slag screening, sand, or rock screening to thee affected area. Aggregate heated and spread product. Immediately after spreading, roll with a rubber-tired roller. When the aggregate has cooled, broom off loose particles. Repeat the process, if necessary.

SPECIAL PROBLEM To cure that type of failure in structure (pavement) then follow the steps of procedure are: hot coarse sand, spread over the affected aras, may be used to replace the lost aggregate. After this, it should be rolled immediately with a pneumatic-tired roller so that it will be seated into the asphalt. On a hot day, spread coarse sand, heated to at least 150ºC over the area that has lost cover aggregate. Follow immediately (before sand has a chance to cool even a few deg.) with pneumatic-roller to seat the aggregate in the asphalt.

CRACKING TYPES OF CRACKING: (flexible pavement). ALLIGATOR CRACKS. EDGE CRACKS. EDGE JOINT CRACKS. LANE JOINT CRACKS. REFLECTION CRACKS. SHRINKAGE CRACKS. SLIPPAGE CRACKS. WIDENING CRACKS.

2. DISTORTION TYPES of DISTORTION: CHANNELS(RUTS). CORRUGATION & SHOVING. GRADE DEPRESSIONS. UPHEAVAL. UTILITY CUT DEPRESSIONS.

TYPES of DISINTEGRATION: POTHOLES. RAVELING.

4. SKID HAZARD TYPES of SKID HAZARD: BLEEDING or FLUSHING ASPHALT. POLISHED AGGREGATE.

5. SPECIAL PROBLEMS TYPE OF SPECIAL PROB. : LOSS OF COVER AGGREGATE. LONGITUDINAL STREAKING. TRANSVERSE STREAKING.