Development and Implementation of a Performance-Related Specification for SR 9a, Florida: Final Report
Appendix B: Technical Special Provisions for Performance-Related Specifications for Rigid Pavement (Financial Project ID 209600-1-52-01-SR 9A, Duval CO.)
This Technical Special Provision applies to 12.5-in mainline pavement on FPID 209600-1-52-01, from Station 127+00 to Station 149+17.52, as shown on the plans.
The Department will pilot a Performance-Related Specification for Portland cement concrete (PCC) pavement on this project. The Composite Pay Adjustment Factor is based on the difference between the estimated Life-Cycle Cost (LCC) of the as-designed pavement and the estimated LCC of the as-constructed pavement, as determined by the PaveSpec 3.0 software as defined in FHWA-RD-98-155, Guide to Developing Performance-Related Specifications. The Composite Pay Adjustment Factor will apply to pay item 350-1-19 (12.5-in mainline pavement only). The Composite Pay Adjustment Factor is based on the individual pay factors for the concrete strength, slab thickness, and initial smoothness. The minimum value of the Composite Pay Adjustment Factor shall be limited to 90 percent and the maximum value shall be limited to 110 percent.
The main objective of these performance-related specifications (PRS) is to provide the agency with a methodology to assure that the design assumptions are being fulfilled, promote high quality construction, and to protect the agency from poor workmanship. At the same time, it allows the contractor the maximum freedom in deciding how to perform the construction. PRS provide rational methods for contract price adjustment based on the difference between the as-designed and as-constructed life cycle costs of the pavements.
The proposed PRS were developed using Level 1 of the FHWA methodology, as defined in FHWA-RD-98-155, Guide to Developing Performance-Related Specifications for PCC Pavements, and implemented in the PaveSpec 3.0 software. PRS employ distress prediction models to relate the acceptance quality characteristics (AQCs) to future pavement performance and associated LCC. Figure 1 illustrates how the PRS methodology works. The FHWA website (www.tfhrc.gov/pavement/pccp/pavespec/pavespec.htm) provides additional information about PRS and the PaveSpec 3.0 software.
The pay adjustment factor (PF) is defined as the percentage of the bid price that the contractor is paid for the construction of a concrete pavement lot and is computed based on the difference between the as-constructed and as-designed LCC (in present-worth dollars) as follows:
PF* = 100*(BID + [LCCdes - LCCcon]) / BID (1)
- BID = Contractor's bid price, $.
- LCCdes = As-designed life cycle cost, $.
- LCCcon = As-constructed life cycle cost, $.
* The pay adjustment factor (PF) will be applied to pay item 350-1-19 only.
Figure 1. Basic concepts of LCC-based PRS.
The LCC is computed using prediction models for slab cracking, joint spalling, joint faulting, and pavement smoothness. A key aspect of using LCC to define the PFs is that the LCC of the as-constructed lot is the overall measure of quality, providing a rational way to develop an overall pay adjustment factor for the lot.
3. ACCEPTANCE QUALITY CHARACTERISTICS
Pay adjustment in these specifications is based on the following key quality characteristics only:
- Concrete strength.
- Slab thickness.
- Initial smoothness.
Several other quality characteristics (e.g., air content, slump, dowel placement, tie bar placement) are very important, but are not directly considered in these PRS. These quality characteristics and construction requirements are considered as described in FDOT's existing construction specifications. Also, contractors shall provide a concrete mix design according to FDOT's existing specifications.
3.1 Target Quality Levels
If the FDOT mean and standard deviation targets for each of the AQCs used for pay adjustment are met, the agency will pay 100 percent of the bid price. Table 1 shows target quality levels (mean and standard deviations) at which FDOT will pay 100 percent of the bid price.
|AQC||Lot Target Values|
|Slab thickness, in||12.5||0.5(1)|
|Concrete 28-day Compressive Strength, psi||4,500||610(2)|
|Initial Profile Index, in/mi||3.0||1.0(3)|
(1) Thickness: mean and standard deviation computed from independent cores (2 cores per sublot)
(2) Strength: mean and standard deviation computed from averages of 2 cylinders per sublot
(3) Smoothness: mean and standard deviation computed from averages of inside and outside wheel paths of the lane per lot
3.2 Rejectable Quality Levels
Rejectable quality level (RQL) is the level of quality below which (for thickness and strength) or above which (for smoothness) the pavement is deficient enough that a corrective action or "remove and replace" is warranted. Table 2 shows the RQLs (lot mean values) for each of the AQCs used for pay adjustment in these PRS.
If the quality of the as-constructed lot (as measured by the acceptance test results) of any of the AQCs is below the RQL, the Engineer will determine the appropriate corrective actions.
If the individual sublot value does not meet Table 2, the Engineer will determine the appropriate correction action or remove and replace. If the material is left in place, the pay factor will be based on the actual value and not the RQL.
|AQC||RQL (Lot Mean)|
|Slab Thickness, in||12.0|
|Concrete 28-day Compressive Strength, lbf/in2||2,700|
|Initial Profile Index, in/mi||Centerline radius ≥ 2000 ft: 5.0
Centerline radius < 2000 ft: 7.0
3.3 Maximum Quality Levels
Maximum quality level (MQL) is the level of quality at which the pavement is unnecessarily more conservative than the design so that no further pay increase will be applied. Table 3 shows the MQLs (lot mean values) for each of the AQCs used for pay adjustment in these PRS.
If the quality of the as-constructed lot (as measured by the acceptance test results) of any of the AQCs is higher (for thickness and strength) or lower (for smoothness) than the MQL, the pay factor at the MQL will be used for computing the composite PF and adjusting the payment. The actual values will be used to compute the standard deviation.
|AQC||MQL (Lot Mean)|
|Slab Thickness, in||13.5|
|Concrete 28-day Compressive Strength, lbf/in2||5,500|
|Initial Profile Index, in/mi||0.0|
3.4 Testing Methods
Table 4 shows the testing methods for slab thickness, concrete strength, and initial smoothness. The testing methods for these AQCs are discussed further in the following sections.
|Slab Thickness, in||Cores (See below under "Slab Thickness")|
|Concrete 28-day Compressive Strength, psi||Cylinders (ASTM C-31 and C-39)
Cores (ASTM C-42), for partial lots
|Initial Profile Index, in/mi||Electronic Model of California Profilograph with 0.2-in blanking band (ASTM E-1274)|
(1) All AQCs must be measured within the same sublot limits
3.4.1 Concrete Strength
The required strength cylinders shall be cast from a randomly selected truck within the sublot. The cylindrical specimens shall be molded and cured in accordance with ASTM C-31 and tested in accordance with ASTM C-39 standard test methods.
3.4.2 Slab Thickness
The thickness of cores will be used for determining slab thickness. The thickness core borings shall be taken from randomly selected locations within the sublot. If corrective work that may affect thickness (such as grinding to meet the ride requirements) is performed, the thickness core borings shall be taken after the completion of these actions.
The core shall be a minimum of 4 in in diameter. The slab thickness at a cored location shall be recorded to the nearest 0.1 in, as the average of three caliper measurements of the core length. The three measurements shall be obtained and marked at locations spaced at approximately equal distances around the circumference of the core.
3.4.3 Initial Smoothness
The pavement surface smoothness shall be tested using an electronic model of the California Profilograph with 0.2-in blanking band. The smoothness testing shall be conducted after the concrete cures and all curing materials (except for the impervious coating) are removed.
Pavement profiles shall be taken at the traffic wheel paths (3 ft from and parallel to each edge of pavement placed at 12 ft width, or less) after all grinding operations have been completed. When pavement is placed at a greater width than 12 ft, the profile will be taken 3 ft from and parallel to each edge and each side of the planned longitudinal joint. When the pavement being constructed is contiguous with an existing parallel pavement that was not constructed as a part of this contract, the profile parallel with the edge of pavement contiguous with the existing pavement shall not be taken. In this case, the sublot shall be represented by one profile. The profile shall be started and terminated 15 ft from each bridge approach or existing pavement that is being joined.
4. Specification Changes
The provisions of Sections 346, 350, and 352 as it relates to the construction and acceptance of the 12.5-in concrete pavement are modified as follows:
Sub-article 350-3.13 (page 354) is deleted.
Sub-article 350-12.1 (page 358) is deleted and replaced with the following:
350-12.1 Finishing: As the water sheen disappears from the surface of the pavement and just before the concrete achieves its initial set, drag a seamless length of damp burlap that extends the full width of the strip of constructed pavement, longitudinally along the surface to produce a uniform gritty texture.
Use a burlap drag that consists of two layers of medium weight burlap with the trailing edge of the lower layer extending approximately 2 in [50 mm] behind the upper layer. Support the burlap so that a length of at least 3 ft [1 m] of burlap is in contact with the pavement.
Except in areas where using hand methods to construct the pavement, support the lead end of the burlap drag by a traveling bridge. Maintain the drag clean and free of incrusted mortar. Replace the burlap with new material as necessary.
Sub-article 352-4 (pages 370-372) is modified by the following:
The Department will perform all California Profilograph (FM 5-558) testing used for acceptance and pay.
5. SAMPLING PLAN FOR PAY ADJUSTMENT
A vital assumption upon which the statistical acceptance procedures are based is randomness of sampling. Random sampling is defined as a manner of sampling that allows every member of the population (lot) to have an equal opportunity of appearing in the sample. The PRS AQCs are measured for each sublot, and pay adjustment is made on a lot-by-lot basis. Thus, the sublot boundaries must be marked and maintained until finalizing the payment computation. The lot shall be divided into three sublots for sampling and testing purposes. Markers shall be placed every 0.05 mile along the mainline traffic lanes to help determine the lot and sublot limits.
The definitions of lot, sublot, and sampling frequency for compressive strength, thickness, and initial smoothness are presented below.
5.1 Pavement Lot
A pavement lot is defined as the amount of material or construction produced by the same process, so that each AQC is likely to be from the same distribution. Each lot is one lane in width and ranges between 0.1 and 1.0 mi in length. The maximum lot size is defined as a 1-day production of one lane, or 1.0 lane-mi, whichever is less. If the 1-day production is longer than 1.0 mile, the Engineer shall divide the 1-day production into multiple lots. If concrete placement includes two or more lanes in one pass, this production is still divided into lots consisting of one lane each. The Engineer may terminate the lot if there is any reason to believe that a special cause affected the process and resulted in a significant shift in the mean or standard deviation of any of the AQCs. Changes in the concrete mix design do not necessarily terminate the lot. This determination is made by the Engineer.
To meet the sampling frequency requirements (as discussed in the "Pavement Sublot" and "Sampling Frequency" sections of these specifications), the minimum lot length is 0.10 mi (528 ft). If the lot length is less than 0.10 mi, it shall be grouped with the next lot. If the last lot in the paving project is less than 0.10 mi long, it shall be grouped with the previous lot. In summary, the lot is 1-lane wide and ranges between 0.10 and 1.0 mi in length.
A partial lot is defined as a lot for which concrete strength testing was conducted on none or only one of the planned sublots due to premature stoppage of paving. Premature stoppage of paving is defined as the stoppage of pavement construction operations due to unexpected conditions such as weather or equipment problems. A partial lot shall be re-divided into sublots similar to a new lot.
If the concrete strength of a sublot of a partial lot has not been tested using cylinders, two drilled cores shall be taken from the sublot to measure the 28-day compressive strength of the in-place concrete. These cores shall be tested according to ASTM C-42. The Engineer may allow the thickness cores to be tested for strength. The core and cylinder test results shall be combined to determine the mean and standard deviation of the 28-day compressive strength for the partial lot.
5.2 Pavement Sublot
The application of this PRS requires that the lot be divided into discrete sublots and that sampling be conducted in each sublot for all AQCs. This means that strength, thickness, and smoothness shall be measured within each sublot boundary. The minimum sublot length is established so that at least one Profile Index (PI) measurement can be taken for each sublot. If the minimum pavement length for measuring PI is 0.05 mi, the minimum sublot length shall be 0.05 mi. If the lot is less than 0.15 mi long, it shall be divided into two sublots of approximately equal length. If the lot is 0.15 mi or longer, it shall be divided into three sublots of approximately equal length.
5.3 Sampling Frequency
The sampling frequencies for concrete strength, slab thickness, and smoothness are described below.
5.3.1 Concrete Strength
A strength test for each sublot is determined as the average of the 28-day compressive strength of two cylinders cast from a sample of concrete from the sublot. In the case of partial lots, the strength cylinders will be supplemented by cores. Thus, the strength sample size is one per sublot and the number of replicates per sample is two.
5.3.2 Slab Thickness
A thickness measurement for each sublot is determined by taking two core borings at two random locations in the sublot. Thus, the thickness sample size is two per sublot and the number of replicates per sample is one.
5.3.3 Initial Smoothness
A longitudinal profile trace shall be taken at each wheel path (inside and outside) within each sublot. The Engineer will compute the PI for discrete sections within each sublot. The Engineer will set these sections to be of approximately equal length and be practical to measure. The PI values that constitute the smoothness sample are computed as the average of both wheel path traces. Thus, the number of PI sections along the lot represents the sample size, and the number of wheel paths (i.e., 2) represents the replicates per sample.
5.3.4 Slump, Air, and Temperature
Plastic properties will be determined at a frequency of one per sublot coinciding with the compressive strength sample.
6. PAY ADJUSTMENT
PRS recognize that marginal products still have some value and advocate payment adjustment schedules instead of requiring complete removal unless the pavement is so deficient that replacement or correction action is warranted (i.e., at the RQL). It shall be noted that the Department will provide the software that implements the pay adjustment computation procedure.
6.1 Individual Pay Adjustment Curves
Individual pay adjustment factors for concrete strength, slab thickness, and initial smoothness shall be determined using the pay factor curves shown in figures 2, 3, and 4 or tables 5, 6, and 7.
Figure 2. Concrete strength pay adjustment curve.
|Lot Mean Strength, psi||Lot Standard Deviation (computed using means of 2 cylinders), psi|
Figure 3. Slab thickness pay adjustment curve.
|Lot Mean Slab Thickness, in||Lot Standard Deviation (computed from independent cores), in.|
Figure 4. Initial smoothness pay adjustment curve.
|Lot Mean PI, in/mi||Lot Standard Deviation (computed using means of 2 wheelpath profiles), in/mi|
These curves and tables were developed using the PaveSpec 3.0 PRS software and account for the mean and standard deviation of the AQCs. Linear interpolation or extrapolation shall be used between the values shown in these tables, if needed.
The determination of individual pay factors from figures 2, 3, and 4 or tables 5, 6, and 7 requires computing the mean and standard deviation of the concrete strength, slab thickness, and initial smoothness for the as-constructed lot based on the field testing results. These statistics shall be calculated as follows:
- = Mean of n random samples of the AQC under consideration for the lot.
- Xi = Sample measurement (for smoothness and strength, Xi is a mean of multiple replicates, and for thickness the mean of all cores).
- n = Sample size per lot, n for each AQC is as follows:
- Strength: 1 sample per sublot (each is a mean of two cylinder measurements, or core measurements for partial lots).
- Thickness: 2 samples (cores) per sublot.
- Smoothness: number of required profile sections per lot (each is represented by the mean profile passes in the wheel paths).
The thickness lot standard deviation (where number of replicates = 1) is computed as follows:
The strength and smoothness unbiased lot standard deviation (where more than one replicate per sample are used) is computed as follows:
- m = Number of replicates per sample, m for strength and smoothness are as follows:
- Strength: 2 replicates (i.e., 2 cylinders per sample, or cores for partial lots).
- Smoothness: 2 replicates (i.e., wheel paths per lane).
- CSD = Correction factor (based on the total sample size, n) used to obtain unbiased estimates of the actual lot sample standard deviation. Appropriate CSD values are determined using table 8.
|Number of Samples, n||Correction Factor, CSD|
6.2 Computation of Pay Adjustment
The lot composite (overall) pay factor is computed as follows:
PFcomposite = (PFsmoothness * PFstrength * PFthickness) / 10000 (5)
- PFcomposite = Composite (overall) pay factor, percent.
- PFstrength = Strength pay factor (obtain from table 5), percent.
- PFthickness = Slab thickness pay factor (obtain from table 6), percent.
- PFsmoothness = Initial smoothness pay factor (obtain from table 7), percent.
The actual pay adjustment for the as-constructed lot is computed using the lot composite pay factor as follows:
PAYADJLot = BID * AREALot * (PFcomposite - 100) / 100 (6)
- PAYADJLot = Pay increase (+) or decrease (-), $.
- BID = Contractor bid price for pay item 350-1-19, $/yd2.
- AREALot = Measured actual area of the as-constructed lot, yd2.
- PFcomposite = Composite pay factor (from equation 5), percent (e.g., 101 percent is expressed as 101.0).
PAYLot = BID * AREALot + PAYADJLot (7)
- PAYLot = Adjusted payment for the as-constructed lot, $.