EFL Accceptance parameters for VDOT Approved Mixes.pdf

This document is discussion of the differences of VDOT acceptance parameters and adapting these parameters to the Special Contract Requirements of sub section 106.05 (a) General –the VDOT acceptance parameters will be subject to statistical evaluation to determine the value of work. The Variability-Unknown/ Standard Deviation Method will used to determine the estimated percentage of the lot that is within the specification limits as per EFLHD’s standard practice.

Most of VDOT acceptance parameters are based on mean values with a range tolerance, or value ranges. The following are adaptations of VDOT acceptance criteria for a Percent Within Limits (PWL) based acceptance criteria.

The following items are acceptance items for VDOT:

% AC

Specific sieve sizes – depends on NMSA of JMF

VTM (Air Voids)

VFA (Voids filled with Asphalt)

Density

Lift thickness (for base courses only)

Comments on specific acceptance items

% AC: VDOT’s acceptance is based on a ± tolerance of 0.30 of the MEAN (average) from the target value for a 4-sample lot and a ± tolerance of 0.21 of the MEAN (average) from the target value for an 8-sample lot. See VDOT table II-15 Process Tolerance. This acceptance parameter as enforced by VDOT does not reward good process control. You can run low %AC from the Target Value and then compensate with running high %AC to get your average within the tolerances. So this type of spec does not curtail wide variations in process control.

After reviewing what would be fair for the contractor in terms of process control – EFL proposes to adopt our ± 0.4 spec limit form the contractor’s JMF target value. Reasonable process control will achieve a 1.0. Since this is a Level II Quality Characteristic.

To summarize with an example the following mix design has a 4.4% Target AC content.

Number of samples (lot size) VDOT EFL administered

4 Average of 4 tests between 4.1- 4.7

4.4 ± 0.4 Spec limits 4.0 - 4.8

8 Average of 8 tests between 4.19- 4.61

4.4 ± 0.4 Spec limits 4.0 - 4.8

Lot size does not change spec limits for EFL method of acceptance – variability of a limited number of samples is accounted for by number of samples using PWL method. That is, a lot size of 4 for the same PWL value will have a higher pay factor than a lot of 8 samples.

Specific sieve sizes – VDOT’s acceptance is based on a ± tolerance of MEAN (average) from the target value. Tolerance is dependent on number in samples in lot size and the sieve size.

After review of the VDOT specification - it was determined that EFL would utilize the lot size of 4 from VDOT table II-15 Process Tolerance to apply as a ± deviation from the target value.

So allowable deviations would be TV ± the following values for upper and lower spec limits

Sieve 1” ¾” ½” 3/8” #4 #8 #30 #50 #200

Deviation

4.0 4.0 4.0 4.0 4.0 4.0 3.0 2.5 1.0

% VTM (Air Voids) VDOT acceptance for air voids during production has a lower and upper spec limit of 2.0% - 5.0% respectively for mixes that are being utilized on this project. So acceptance for VTM would be 3.5% ± 1.5% for all HMA.

% VFA (Voids Filled with Asphalt) VDOT acceptance lower and upper specification limits is a function of NMSA size. Target value and ± deviation for upper and lower spec limits are listed below.

NMSA 1” (25.0 mm) ¾” (19.0) ½” (12.5mm) 3/8 (9.5 mm)

Target Value 73.5 72.5 74.0 76.0

± deviation 10.5 8.5 9.0 8.0

Lower Spec Limit 62 64 65 68

Upper Spec Limit 83 81 83 84

Density - VDOT utilizes stratified random sampling using a nuclear density gauge for acceptance. Lot size is 5000 linear feet of a paving pass. Each lot is divided into five 1000 foot sublots. Density requirements are based on a range of 98 percent to 102 percent of the target nuclear gauge control strip density value. The control strip density is based on the average of 10 nuclear determinations at stratified random locations within the control strip. Length of control strip is 300 feet. So there is an upper and lower spec limit of ± 2% (98 % to 102%) of the density value – NOT ± 2% of target density. No cores are cut to measure % density of the compacted mat directly.

If the quantity is not sufficient nuclear density pattern and control then Table III-5 is applied where the following densities are required:

Mix Type BM-25.0 IM-19.0D IM-19.0A SM - 9.5D,12.5D

SM

9.5E,12.5E

SM- 9.5A,

12.5A

% of MTD 91.5 92.0 92.2 92.2 92.2 92.5

EFL proposes for simplicity that the lower spec limit of 91.5 be utilized for BM-25.0 mixes and that a lower spec limit of 92.0 be utilized for all 19mm, 12.5mm, and 9.5 mm mixes. No upper specification limit would be applied for density. % Density would be measured for acceptance by coring the compacted mat at the same frequency as loose mix sampling for %AC, Gradation, VTM, VFA. Nuclear gauge density readings would be for contractor process control during paving.

Lift thickness: VDOT uses lift thickness as an acceptance parameter for the base course. A lot size is the same quantity as used for acceptance of other mix properties except the maximum lot size is 1 mile of 24 foot width base course.

Thickness allowances are as follows:

Single test 2 test: mean 3 test: mean 4 test: mean

±0.60 ± 0.45 ± 0.35 ± 0.30

If an individual test is more than 0.60 greater than the specified lift thickness the contractor will not be paid for the excess. There will be a deduction based on excess material If the core is 0.60 deficient or greater and less than 1.5 inches the contractor will put enough material from a finer graded mix to bring up to the proper depth. Greater than 1.5 inches then add more base to bring it up to the plan elevation.

Propose to follow VDOT method. No change. Cores would come from stratified random sampling of a sublot for density.

Lot Size: VDOT sublots are 500 tons. Lot size is 2000 tons if production for the day from the same source is less than 2000 tons. Lot size of 4000 tons may be used if production exceeds 2000 tons on a daily basis. So the number of samples in a lot will vary from 2 to maximum of 8 based on the above criteria.

EFLHD proposes to not limit lot size and use VDOT’s 500 ton sublot for random stratified sampling purposes. Lot size would be determined by change of asphalt plant, end of season, gap in paving of a significant duration, or contract schedule or option.

Sampling: Loose mix samples per VDOT are taken from the middle of truckload of HMA.

Truck determined by random number * 500 tons.

EFLHD proposes to sample from the mat behind the paver and splitting and quartering the sample to have on portion go to the contractor (or QAM) and one to EFLHD. Sampling would be stratified random relying on random number *500 tons factoring in paving width and mat thickness to locate correct location to sample.

Table 1 outlines the conversion of VDOT acceptance parameters to EFLHD statistical evaluation to determine the value of work.

Table 2 outlines VDOT lot size and sampling locations and the conversion to EFLHD lot size and sampling practices.

Table 1 – Conversion of VDOT acceptance parameters to EFLHD statistical evaluation to determine the value of work.

Acceptance Parameter VDOT EFLHD (contract) Comments % AC Mean (average) value with tolerance from mix design target value (TV) depending on lot size

TV ± tolerance of 0.30 of the MEAN lot size = 4

TV ± tolerance of 0.21 of the MEAN lot size = 8 mix design target value (TV) ± allowable deviation

%AC (Mix Target Value) ± 0.4

EFLHD spec rewards best practices of process control.

Asphalt producer following industry good practices can easily achieve a PF =1.00

Sample size is accounted for in PWL calculation

Sieve Size % passing Tolerances

Mean (average) value with tolerance from mix design target value (TV) for a sieve size depending on lot size mix design target value (TV) for a sieve size ± allowable deviation

% Passing TV (of sieve) ± 4%

EFLHD spec rewards best practices of process control.

Asphalt producer following industry good practices can easily achieve a PF =1.00

Sample size is accounted for in PWL calculation

% VTM (Air Voids) Control within Range

Range from 2.0% to 5.0% during production

Midpoint of range with ± deviation for upper and lower spec limit

3.5% ± 1.5% Lower Spec Limit = 2% Upper Spec Limit = 5%

EFLHD spec rewards best practices of process control

Sample size is accounted for in PWL calculation.

Table 1 continued - Conversion of VDOT acceptance parameters to EFLHD statistical evaluation to determine the value of work.

Acceptance Parameter

VDOT EFLHD (contract) Comments

% VFA (Voids Filled with Asphalt)

Control within Range

Range Varies based on NMSA

25.0 62-83

19.0 64- 81

12.5 65- 83

9.5 68 - 84

Midpoint of range as Target Value with ± deviation for upper and lower spec limit

NMSA TV ± deviation

25.0 73.5 ± 10.5

19.0 72.5 ± 8.5

12.5 74.0 ± 9.0

9.5 76.0 ± 8.0

EFLHD spec rewards best practices of process control

Sample size is accounted for in PWL calculation.

Density VDOT utilizes stratified random sampling using a nuclear density gauge for acceptance. Lot size is 5000 linear feet of a paving pass. Each lot is divided into five 1000 foot sublots.

Density requirements are based on a range of 98 percent to 102 percent of the target nuclear gauge control strip density value.

The control strip density is based on the average of 10 nuclear determinations at stratified random locations within the control strip.

Length of control strip is 300 feet.

Lower spec limit for density

Lower spec limit of 91.5 be utilized for BM-25.0 mixes

Lower spec limit of 92.0 be utilized for all 19mm, 12.5mm, and 9.5 mm mixes.

Density evaluated per each sublot by coring compacted pavement mat

Measure per AASHTO T166 if core absorption is less than equal to 2.0%. Use AASHTO T331 if core absorption greater than 2%

Coring of mat for each sublot will provide for in place density of the completed mat

Lot size would not be limited

Sample size is accounted for in PWL calculation.

Thickness measurements of Base course

Mean of core deviations from plan thickness. Per VDOT 315.07 (c) Pavement Tolerances - Thickness Tolerance - deduct and remedial work spelled out in 315.07 (c)

Same procedure – except cores would be taken and measured as part of density evaluation – one per 500 ton sublot With lot size greater than 4 the tolerance would be plan thickness ± 0.30 inches

Table 2 - VDOT lot size and sampling locations and the conversion to EFLHD lot size and sampling practices.

Item VDOT EFLHD (contract) Comments LOT Size VDOT sublot is 500 tons. Stratified random sampling within sublot.

A lot is either 2000 tons for production of 2000 tons or less or 4000 tons for more than 2000 tons in a day.

So total samples in Lot would range from 1 to 8 samples.

Lots do not cross into next day.

EFLHD will use a sublot of 500 tons.

Stratified random sampling within sublot.

Lot size would be determined by change of asphalt plant, approved change in mix design by producer, end of season, gap in paving of a significant duration, or contract schedule or option.

Lot size would not be limited except by the above list of circumstances.

Overall material quality evaluated over whole project - since JMF being produced should be consistent during a short period of time that paving typically occurs.

Sample size is accounted for in PWL calculation.

Sampling (For Loose Mix)

VDOT samples from midload of trucks.

Truck is selected by stratified random sampling.

Sample is used to determine %AC, % Passing of control sieves, VTM, VFA

EFLHD samples from mat behind paver.

Location is selected by stratified random sampling.

Sample is used to determine %AC, % Passing of control sieves, VTM, VFA.

VMA is reported for information only.

Sample is spilt and quartered with 2 quarters to contractor and the other 2 quarters to

EFLHD

Best represents what is in place on the road / finished product.