Tolerances and Price Impacts

Presented by:- Er. Bhagawan Shrestha

Tolerances

• Construction Control Testing/Process Control Testing

Unless otherwise directed, values given in these Specifications are minimum values for the properties of materials and the workmanship. They shall be considered satisfactory, if all results of the tests, taken at the frequencies specified, are at least equal to the values given in the relevant Section of these Specifications

Tolerances (contd.)

• In the Specifications, minimum numbers of tests to be conducted for checking the construction tolerances (Surface levels, thickness, width, smoothness, compaction etc) have been provided in relevant section of the Specifications.

Tolerances (contd.)

• Where any tolerances are exceeded, the Contractor shall assess the full extent of the area which is out of tolerances and shall make good the surface of the pavement course, earthworks or formation in the manner described in Section 1100.

Tolerances (contd.) (a) Horizontal Alignments: Horizontal alignments shall be determined from the centreline of the pavement

surface as shown or calculated from the Drawing. The centreline of the pavement surface as constructed, and all other parallel alignments, shall be correct within a tolerance of 13 mm there from.

(b) Thickness of Pavement Layers

The average thickness of any pavement layer measured at five conjugative points at every 20m in any Section shall not be less than the thickness specified nor more than 120% of the thickness specified or ordered by the Engineer. The thickness of the pavement layer measured at any point shall have tolerance of + 25 % and - 2 % of the thickness specified.

Tolerances (contd.)(c) Surface Levels of Pavement Layers and Formation

The level measured at any point on the surface of a pavement layer to the formation level shall not deviate from the corresponding level calculated from the Drawing by more than the tolerances shown in Table 11.1.

For checking compliance with Table 11.1 measurements of surface levels shall be taken at points selected by the Engineer at 12.5m centres longitudinally and at 2m centres transversely.

(d) Surface Regularity

The surface regularity of pavement layers and the formation shall be tested at points decided by the Engineer with a rigid, steel straight-edge of 3 m length placed parallel to or at right angles to the centreline of the road. The maximum allowable deviation of the surface below the straight-edge shall not deviate from that shown on the Drawing by more than the tolerances shown in Table 11.1.

Tolerances

Description Tolerances

Horizontal Alignments ± 13 mm

Thickness of pavement layers Avg. thickness measured at 5 conjugative pts at every 20m in any section – 0.00 and +20% of thickness specified

Measured at any pt. -2% and +25% of thickness specified

Cutting & embankment slopes -0.00 and +0.25

Width of cuttings and embankments

±200mm for cutting-0.00 and +50mm for embankment

Depth of side drains ±25mm

Tolerances (contd.)

Layer

Level

mm

Straight edge

mm

Slope or Crossfall %

Bituminous Wearing Course 10 6* 0.25

Bituminous Binder Course 10 6 0.25

Base 10 6 0.25

Subbase 15 10 0.50

Gravel Wearing Course 15 15 0.50

Formation (subgrade) +0

-25

20 0.50

Table11.1:Tolerances for Level And Surface Regularity

Tolerances (contd.)

• * In case of asphalt concrete surface it shall be 4mm.

• The tolerances for level and surface regularity as given in above table shall be applicable only for New construction, Re-construction and Rehabilitation works and not applicable in case of resealing by surface dressing / sand seal / slurry seal in existing paved surfaces.

Tolerances (contd.)Description Tolerances for spray

rates of Bit. binderTolerances for application rates of Agg/chips

width

Prime coat and tack coatAcross width of each spray runFor each single run of spray

± 5% of rate ordered ± 0.03l/sq. m. of specified rate

Surface dressingAcross width of each spray runFor each single run of spray

± 5% of rate ordered ± 0.03l/sq.m. of rate ordered

± 5% of rate orderedAvg. overall width measured at six equidistant pts over a length of 100m at least equal to width specified or instructed.At no point distance between c/l and edge of surface dressing be narrower than that instructed/ specified by more than 13mm.

Tolerances (contd.)Penetration Macadam- Semi-groutAcross width of each spray runFor each single run of spray

± 5% of rate ordered

± 0.03l/sq.m. of rate

± 5% of rate ordered

Sand sealAcross width of each spray runFor each single run of spray

± 5% of rate ordered

± 0.03l/sq.m. of rate

± 5% of rate ordered

Slurry sealAcross width of each spray runFor each single run of spray

± 5% of rate ordered

Not less than rate ordered

Tolerances (contd.)• For Asphalt Concrete, Sand Asphalt, Emulsion Aggregate Mix and Cold

Asphalt, the composition of the mixture as determined from the laboratory and site trials should be maintained within the following tolerances, per single test:-

(a) Bitumen content : 0.3% of

(Total weight of bitumen in total mix) (b) Aggregates (i) Passing through 10 mm sieve and larger sieves : 6%of X

(ii) Passing through 10 mm sieve and retained on 1mm sieve : 4% of X

(iii) Passing through 1 mm sieve and retained on 0.075 mm sieve : 3% of X

(iv) Passing through 0.075 mm sieve : 2% of X Where X: Total wt of dry aggregates including mineral filler

Tolerances (contd.)

Number of batches Maximum coefficient of variationOrdinary concrete High quality concrete

After 20 tested batches 18% 15%After 50 tested batches 15% 12%

Section 2000- Concrete for structure provides the tolerances for the concrete works which are as follows:• In the case of Early works test cubes, no single result (average of 3 cubes)

should be less than the characteristic strength (fck) and the avg. of 3 consecutive results should not be less than characteristic strength (fck) + 4 (N/mm2).

• When at least 20 consecutive results on tested batches are available for any class of concrete mixed in any one plant, no single result should be less than characteristic strength (fck) – 4 and the average of any group of three consecutive results should not be less than characteristic strength (fck) + 4 (N/mm2).

• In addition the Coefficient of Variation shall be less than the figure given below:

results theofValueAverageresults theofDeviationStandardVariationoftCoefficien theWhere

Mechanically Stable Sub base (Example)

Tests One test in every Min. no of tests per section

Materials:GradationPlasticity IndexMaximum Dry Density and Optimum Moisture Content

Workmanship:Field Density and Moisture Content

200 m3 or part of it and change in source" " " "1000 m3 " " "

500 m2

222

2

Construction Tolerances:Surface LevelsThicknessWidth

10 m25 m200 m

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Table 12 .2 : Minimum Testing Frequency

Tolerances (contd.)

• The work is considered conforming to the requirements of the Contract if the entire quality assurance tests are performed with the frequency as stipulated in the Technical Specifications and the results fall within the tolerances stipulated in the Technical Specifications.

Price Impacts

Sub – Standard Payment

• The Standard Specifications for Road and Bridge Works stipulates the Sub – Standard Payment for the Cement Masonry works and Cement Concrete works only.

Sub – Standard Payment• Concrete and Cement masonry works not meeting the

requirements of the relevant Specifications (termed as substandard concrete) shall be paid as substandard work provided it is accepted by the Engineer as substandard work.

• For the acceptance of such work the Engineer may require further investigation and/or tests which the Contractor shall conduct at his own cost.

• Acceptance or rejection of such work is the sole responsibility of the Engineer and his decision in this respect shall be the final and binding upon the Contractor.

Sub – Standard Payment

• If accepted as substandard work the payment for such work shall be made at the contract unit rate reduced by the formula given below

Design strength - Observed strengthPercent of reduction, P = X

100 Design strength

Sub – Standard Payment

• But the limit of non compliance is not specified and solely given the authority to the Engineer for decision.

• The Engineer may conduct the Non destructive tests for the conformation of the strength, homogeneity and durability at the cost of the Contractor to accept the work as sub standard.

Sub – Standard Payment

• If tolerances exceed the limits specified in the Contract/Standard Specifications for road and Bridge works in all other works except the cement concrete and cement masonry works, then the work should be rejected and rectified and /or reconstructed as per the instruction of the Engineer and no adjustment for contract price should be done.

THE END

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