Surface finish and quality control of work [Tolerance of horizontal alignment (edge tolerance), surface level tolerance (Tolerance in Reduced level), surface regularities and irregularities, rectification (sub grade, GSB, WMM, DBM/BC, DLC, PQC) and riding quality of pavement ]

Surface finish and quality control of work:-

This article includes
Tolerance of horizontal alignment (edge tolerance), surface level tolerance (Tolerance in Reduced level), surface regularities and irregularities, rectification (sub grade, GSB, WMM, DBM/BC, DLC, PQC) and riding quality of pavement

A- Horizontally alignments

Horizontally alignments shall be reckoned w.r.t. the center line of the carriageway as shown on the drawings. The edge of the carriage way as constructed shall be correct within a tolerance of ±10 mm there from. The corresponding tolerance for edges of the roadway and lower layer of pavements shall be ±25 mm.


B- Surface Level 
The levels of the subgrade and different pavements courses as constructed, shall not vary from those calculated with reference to the longitudinal and cross-profile of the road shown on the drawing or as directed by the engineer beyond the tolerance mentioned in table below(table 900-1).
Provided, however, that the negative tolerance for wearing course shall not be permitted in conjunction with the positive tolerance for base course, if the thickness of the former is thereby reduced by more than the following limits-

4mm for bituminous wearing course of thickness 40 mm or more
3mm for bituminous wearing course of thickness less than 40 mm
5mm for concrete pavement slab.

For checking compliance with the above requirements for subgrade, sub-base and base course. Measurements of the surface levels shall be taken on a grid of points placed at 6.25 m longitudinally and 3.5 m transversely. For any 10 consecutive measurements taken longitudinally or transversely, not more than one measurement shall be permitted to exceed the tolerance as above, this one measurements being not excess of 5mm above the permitted tolerance.
For checking the compliance with the above requirements for bituminous wearing course and concrete pavements, Measurements of the surface levels shall be taken on a grid of points spaced at 6.25 m along the length and at 0.5 m from the edge and at the centre of the pavement. In any length of the pavement, compliance shall be deemed to be met for the final road surface, only if the tolerance given above is satisfied for any point on the surface.


C - Surface Regularity of pavement courses

The longitudinal profile shall be checked with a 3 metre long straight edge/moving straight- edge as directed by the engineer at the middle of each traffic lane along a line parallel to the centre line of the road.

The max. allowable difference b/w the road surface and underside of a 3 met.

Straight-edge when placed parallel with or right angles to the centre line of the road at points decided by the engineer shall be:-

For pavements surface (bituminous and cement concrete)                            3mm

For bituminous base course                                                                                   6mm

For GSB/base courses                             
                                                                                                                                      8mm

For sub-bases under concrete pavement.                                                          10mm

For subgrade                                                                                                            15mm

D - Rectification

Where the surface regularity of subgrade and the various pavements course fall outside the specified tolerance. The contractor shall be liable to rectify these in manner described below -

1-subgrade – it shall be rectify as constructed a new subgrade.

2- Granular sub-base - it shall be rectify as constructed a new sub-base.

3-WBM/WMM sub-base/base: it shall be rectify as constructed a new WBM/WMM. Only top 75mm shall be scarified and done. The area treated shall not be less than 5m long and 2m wide. In no case shall depressions be filled up  with  unmixed and ungraded material or fines. 

4- Bituminous construction: For bituminous construction other than wearing course, where the surface is low, the deficiency shall be corrected by adding fresh material over a suitable tack coat, if needed, and re-compacting as per specifications.

For wearing course, where the surface is high or low, the full depth of layer shall be removed and replaced with fresh material and compacted. In all cases where the removal and replacement of a bituminous layer is involved, the area treated shall not be less than 5m in length and not less than 3.5 m in width.

5-Dry lean concrete sub-base:  it shall be rectify as constructed a new DLC sub-base.the area treated shall be at least 3m long, not less than 1 lane width and extend to the full depth.

6-Cement concrete pavement: it may rectified by scrabbling or grinding using approved equipment. The areas which have been reduced in level shall be retextured in an approved manner either by cutting grooves (5mm deep) or roughening the surface by hacking the surface. If high areas in excess 6mm or low areas in excess of 3mm occur, and if the contractor cannot rectify, the slab shall be demolished and reconstructed at the contractor’s expense and in no case the area removed shall be less than the full width of the lane in which the irregularity occurs and full length of the slab.

E -Riding Quality:

The riding quality of bituminous concrete wearing surface, as measured  by a standard towed fifth wheel bump integrator(TFWBI- It is also known as Roughometer or Automatic Road Unevenness Recorder gives quantitative integrated evaluation of surface irregularities on an digital counter I LCD screen. It comprises of a single wheeled trailer, with a pneumatic tyre mounted on a chassis, on which an integrating device is fitted ), shall not more than 2000mm per Km.

Thanks a lot
Mukesh Kumar
Gyan of engineering