8.10     ACCEPTANCE AND TESTING

8.11     FIELD TESTS AND CERTIFICATION OF MATERIALS

Sampling and testing are required to determine whether quality of materials and construction are in reasonably close conformance with plans and specifications.

Project inspectors shall identify and inspect all materials received on a project before they are incorporated into work.  Inspectors shall determine that proper inspection reports or certifications are on hand, and that no unusual alterations in characteristics of materials due to handling or other causes occurred.

Guide schedules attached to Materials I.M. 204 contain various field tests and sampling frequencies on asphalt materials and mixtures.

The Quality Management - Asphalt (QM-A) program was started in 1992 with the goal of improving the overall quality of asphalt mixtures produced and giving the contractor the responsibility for mix design, sampling, testing, and making mix adjustments.  In other words, contractors assumed start-to-finish responsibility for the product they produce and place.  QM-A is the implementation of contractor process control for asphalt mix production and placement.  Most administrative questions involving QM-A projects can be answered by referring to Materials I.M. 511 and the current specifications for Flexible Pavement.

Nearly all Primary and Interstate asphalt mix tonnage is constructed under QM-A specifications.  It is intended that QM-A be applied to all interstate asphalt mixtures placed in a travel lane and other mixture bid items with a plan quantity greater than 1000 tons.  State park, institution, maintenance and other projects utilizing small asphalt mix quantities will not typically be QM-A.   “Quality Control for Small HMA Paving Quantities” (Specification 2303.03, E) is applied to asphalt mixture bid items with plan quantities of 1000 tons or less and asphalt patching bid items.  For items bid in square yards, convert the plan quantity to weight basis, using an estimated unit weight of 145 lbs/ft³, to determine if item meets the 1000 tons threshold.  

Asphalt Materials

Acceptance of asphalt materials will be on the basis of certification from an approved refinery or distribution terminal source.  Formal approval of a source is to be issued by the Construction and Materials Bureau.  Refer to Materials I.M. 437 for additional information.

Each shipment invoice covering certified materials delivered to a project shall have a signed certification statement as to type and grade, specific gravity, load quantity, batch number or other identification, project number, and compliance with appropriate Iowa DOT specifications.  Copy of this invoice shall be furnished to project engineer or project inspector for review and filing.

Aggregates

Aggregate production and inspection are covered in detail by Materials I.M.'s 204 and 209.  Acceptance for quality will be based on source monitoring and test results on assurance or project samples.  Acceptance of mixture gradation is outlined in Construction Manual 2.53 and 3.22.

8.12     RESPONSIBILITY AND DOCUMENTING ASPHALT MIXTURE PROPORTIONING CHANGES

Specification 2303 and Materials I.M.’s 510 and 511 give explicit guidelines that shall be followed for controlling asphalt mixtures.  They establish job mix criteria and corrective procedures to be followed when mixture characteristics are changed from the job mix formula during mix production.

On QM-A projects, contractor has sole responsibility for making mix changes; however, District Materials Engineer and project engineer must be kept informed and involved in these changes.   Mix change decisions must be an interactive process between contractor and agency.

The project engineer must also insure that required changes are implemented as soon as possible when mixture characteristics fall outside Specification 2303 and Materials I.M. 510 Appendix A limits.  On each working day, project engineer shall determine if work for previous working day was within Specification and I.M. guidelines.  If not, immediately consult with District Materials and the contractor to assure corrective action is taken.

Adjusting Asphalt Binder Contents

For determining whether asphalt binder content is within required guidelines, refer to Specification 2303.  Limits are given for the air voids that are determined daily according to Materials I.M.’s 321 and 501, based on the Rice Procedure as per Materials I.M. 350.  Work using asphalt mixtures with air voids outside the specified limits shall be avoided. 

On QM-A projects, job mix control by the contractor involves sampling, testing, reporting results, and making appropriate mix changes.  Asphalt mix sampling and testing is performed up to five times per day at the asphalt plant site so immediate results are available.  The contractor is responsible for making meaningful mix changes before the lab voids go out of compliance.  The project engineer should coordinate closely with the contractor and District Materials Engineer for a resolution when lab voids are noncomplying. 

When test results for lab voids are outside the limits given in Specification 2303, the contractor needs to initiate appropriate changes in asphalt mixture.  When asphalt binder content changes are considered to adjust lab voids, caution must be used to assure that adequate binder film thickness required in Materials I.M. 510 Appendix A, Table 1 is maintained.  When the resulting film thickness is outside the specified range, procedures given in Specification 2303.05, A, 3, c. should be used to determine the appropriate price adjustment or alternate course of action.  Reductions in asphalt binder content must not reduce the target below the calculated minimum allowable asphalt binder content.  Documentation of changes should be on "Asphalt Paving Daily Plant Report".

Documenting Corrective Action for Noncomplying Air Voids Test on Specimens Taken from Constructed Pavement

Materials I.M. 204 also requires project engineers to report tests for field air voids on mix samples from compacted roadway on "Asphalt Paving Daily Plant Report."  Specification 2303 stipulates the required range for these tests.

Range given for these voids is the average of all tests for each day's construction calculated by plant inspector.

When tests for these air voids are outside required range, density results shall first be reviewed.  Example:  If density results are on lower end of range but still passing, perhaps air voids will fall within range specified by increasing density.  After review of density and testing procedures, Materials forces shall be notified to consider changes in mix proportions.  If conflicts develop between lab and field voids, concentrate on achieving proper lab voids.  Generally, there won't be a problem keeping field voids within specification if lab voids are on target.

When noncomplying tests for air voids in specimens taken from constructed pavement occur, project engineer will notify District Materials.  Plant inspector will document noncompliance on "Asphalt Paving Daily Plant Report" containing the noncomplying test results.

Adjusting Aggregate Proportions

Contractor must occasionally adjust aggregate proportions to consistently comply with job mix target gradation tolerance and to correct calibration errors.

For QM-A projects, the contractor shall initiate and make appropriate changes to ensure compliance under guidelines set forth by Specification 2303 and Materials IM’s 510 and 511.  Although this must be done as an interactive procedure with project engineer, approval of the project engineer for these changes is not necessary as long as results are within the constraints of specifications and Materials I.M.'s.

Specification 2303 and I.M.’s 510 and 511 provide many of the guidelines needed for making mix change decisions.  Project engineers are expected to reference these documents and communicate closely with the contractor and District Materials prior to, during, and after the need for decisions concerning mix proportion changes so problems can be avoided.

Proportion changes shall be documented on "Asphalt Paving Daily Plant Report."

8.13     DENSITY CONTROLS FOR ASPHALT CONSTRUCTION

            Uncompacted Asphalt Mixture Samples

Specifications for asphalt paving require each layer to be compacted to a prescribed density (field voids) related to the laboratory density (voids) representing that particular lot.

On QM-A projects, up to five paired hot box samples per day will be obtained by the contractor, as directed and witnessed by the certified agency personnel (HMA Level I or HMA Sampler).  One of each paired sample is then transported to the field lab for quality control testing.  The hot box samples must be taken from behind the paver as prescribed by I.M. 322, by a technician with either HMA Level I or HMA Sampler certification.  The grade inspector or plant monitor shall direct and witness contractor sampling to ensure it is properly done by appropriately certified personnel and shall document the GPS coordinate location of uncompacted mixture samples taken.  The contractor will also transport the verification portion of the paired hot box samples, the split cold feed verification samples, and asphalt binder verification samples to the District Materials Lab on a daily basis.  The inspector or plant monitor must properly identify and secure all verification samples with tamper proof devices prior to transport by contractor personnel.  No security measures are required if custody of samples is maintained by contracting authority personnel.

An average of all laboratory compacted specimens from the daily hot box samples will be used to determine the degree of field density (voids).  For Percent-Within-Limits (PWL) analysis of laboratory voids, no less than 8 and no more than 15 sequential tests (sublots) will constitute a lot.  The specification for Asphalt Mixtures describes how to combine daily sublots when less than eight samples would otherwise be obtained for the lot.

            Compacted Asphalt Mixture Samples

Density (field voids) of pavement is determined from core samples cut by contractor, normally on the next working day following construction.

Eight samples shall be cut from each daily lot of (mat) construction.  The contractor may request to have a quality control plan with a higher testing frequency, at no additional cost to Contracting Authority, if pre-approved at the preconstruction conference.

The contract documents may also require additional samples be taken on the resulting longitudinal joint between adjacent lanes.  These longitudinal joint cores, when required, shall be evaluated separately from the eight mat cores (above).  The sampling procedure, frequency and lot size for longitudinal joint cores shall be as specified in the contract documents.

Specifications also describe a statistical procedure for field density (voids) evaluation together with a schedule and corresponding formulas for determining payment adjustments for the lot.  Project inspection personnel shall observe the following when using the statistical procedure. These procedures are valid for all asphalt paving projects.

n Contractor is required to take prescribed number of samples at locations selected and marked out by project inspector.  Project inspector or monitor (HMA Level I or HMA Sampler certified) will direct and witness the core sampling, as well as document the GPS coordinate location of core samples taken.  A circle approximately 16" in diameter is adequate for identification of sampling location.  The core should be taken from within the area identified.  It is not appropriate for contractor to use a nuclear device to "hunt" for a particular spot to sample; coring locations are no longer random when a nuclear device is used in this fashion.

n Sample locations should be selected randomly within areas designated by specifications.  The length laid in each lot is divided into approximately equal sublots.  Obtain one sample at a random location within each sublot.  This should be accomplished using a spreadsheet or other computerized program specifically designed for this purpose.  A mat core will not be taken less than 1 foot from the edge of a given pass of the finishing machine.  Procedure for identifying random locations should provide for the potential to obtain a mat core sample at any distance 1 foot or greater from the edge.  Similarly, random cores are not to be taken within 1 foot of runouts, day’s work joints or structures.  For pavement sections with a paved (or partially paved) shoulder placed concurrently with mainline lane, the random location should be based on a distance 1 foot or greater from the lane line (painted edgeline location).  In other words, the paved shoulder area is excluded from the random core sampling area (lot) for the mainline lane.  Similarly, paved ramp shoulders are excluded from sampling area for the ramp’s driving lane.  The latest version of “Random Core Location Program”, a spreadsheet for determining random core sample locations, is available from the Construction and Materials Bureau website.

n If layer being sampled adheres to a lower layer, it may be necessary to sample through two or more layers or full depth.  Contractor will need to remove the extra depth by sawing the sample with a masonry saw.  It may be necessary to cool sample by refrigeration or ice to prevent damage during sawing.  It is important that core bits be kept sharp.

n Each sample shall be inspected carefully by the contractor and inspector prior to testing (preferably at the time of core drilling).  Be sure core sample is representative of density of mixture placed.  If damage is noticeable or if sample is thinner or thicker than specifications allow, discard without testing and take another to replace it.

n The project inspector or plant monitor is responsible for performing tests required to determine density (field voids) of core samples.  This typically involves measuring, placing in water bath, drying, and weighing of cores.  For most efficient use of time, other plant monitor duties may be performed while the core samples are drying.  To be qualified to perform core density testing, the inspector or plant monitor must have obtained either HMA Level I or HMA Sampler certification.

n If test result is outside the specified range, sample shall be retested to insure accuracy.  However, after a sample is tested, resampling of individual locations shall not be done.

n Tests on density (field voids) samples give inaccurate results if samples are damaged during handling.  Contractors and project inspectors are advised to use extreme care when taking, transporting, and preparing cores for testing.

n Samples should be transported on hard flat surfaces to avoid loss of density by distortion.  Core samples must be identified and secured by the inspector in a tamper-proof container prior to transport by contractor personnel.  No security measures are required if custody of samples is maintained by contracting authority personnel.  If necessary to store samples, storage should be in a cool place and on a hard flat surface.

n Specifications also require contractor to take density samples as promptly as practical.  Samples should be taken no later than the next working day following construction.  If contractors are unable to comply with this timing, project inspectors shall stop construction until contractors are able to do so.

n Refer to Materials I.M.’s 501 and 508 and Specifications for determination of "outlier" field density (voids) values. 

n Project inspector shall report lot failures to project engineer and contractor on the same day tests are performed.

Procedures for Construction of Test Strips

Test strips are used to evaluate properties of asphalt mixture and identify an effective rolling pattern.  The specification entitled "Test Strip Construction for Class 1 Compaction" requires the contractor to construct a test strip of the surface course mixture before its placement on Interstate highways, Primary highways, and ramps connecting Interstate and Primary highways.  Specifications further require test strip construction of the intermediate mixture at the start of placement on Interstate highways and Interstate-to-Interstate ramps.  Test strips for base mixtures are optional for the contractor, except for evaluation of base mixture to be placed as a surface course.

Proper construction and documentation of test strip is the responsibility of the contractor.  Documentation of test strip development and final rolling pattern should be provided by contractor to inspector. 

The specifications outline several steps that must be followed to construct a test strip.  Documentation of this procedure is required.  If properly performed, compacting a control test strip using a nuclear gauge will establish a rolling pattern that achieves required density (field voids).  Personnel participating in tests may include roller operators, nuclear gauge operator, paving supervisor, project inspector, and District Materials personnel.  The following procedure describes steps to be taken by the contractor to effectively construct a test strip.

n Pre‑size roller train

It is extremely important to properly balance roller capacity with paver speed.  The paver speed is generally controlled by asphalt plant production rate in tons per hour.  This assumes adequate trucks are available for continuous production.  Determine paver speed by considering tons delivered to paver and mat thickness and width.  Assume paver operates 50 minutes each hour.

Vibratory rollers are typically used for breakdown rolling.  Determine frequency (vibrations per minute) of roller which establishes maximum permissible rolling speed in feet per minute to assure 10 impacts per foot.  Contractor should provide this roller information.  It can be checked with a reed tachometer.

Estimate number of coverages of each roller to achieve required density (field voids).  Determine number of passes necessary to accomplish estimated coverages considering width of roller.  A coverage requires sufficient side‑by‑side passes to cover entire mat width once.  Include the catch‑up pass.

Knowing maximum roller speed and number of coverages estimated to achieve density (field voids), determine total feet per minute (ft/min) of full width mat that roller can effectively compact.  Assume 80% roller efficiency.

                          ft/min (completed) =                        roller speed (ft/min)                           .

                                                          number of passes for estimated coverages required  

Compare ft/min completed of roller to paver speed.  If ft/min completed is greater than paver speed in ft/min, roller is adequate.  If ft/min completed is less than paver speed, additional rollers must be provided or paver speed must be reduced to equal or less than roller capacity.

Example:

                  Mat width = 11.5 feet

                  Compacted thickness = 2 inches

                  Production rate = 150 tons/hour

                  Roller width = 6 feet

                  Frequency = 2400 VPM

                  Assumptions:

                  Paver will operate 50 minutes per hour.

                  Roller efficiency is 80%.

                  Compacted density equals 146.7 pcf.

                  Density will be achieved with 3 coverages.

A.    Determine paver speed to match production

150 tons/hour = 2.5 tons/min.

60 mins./hour

2.5 tons/min. = 34.08 cubic ft./min.

146.7 pcf

34.08 cubic ft./min.                                   = 18 ft./min.

11.5 ft. (mat width) x 2 inches (thickness)

Minimum paver speed = (60/50) (18 ft./min.) = 21.65 ft./min.

B.    Determine maximum permissible speed of roller

2400 VPM      = 207 ft./min.

10 impacts/ft.

C.    Determine total ft./min. of full width mat that can be compacted with three coverages.

Roller width = 6 feet

Considering a 0.5 ft. drum overhang at each edge of the mat plus a 0.5 ft. overlap between roller passes, three passes per coverage are required.  Nine passes required for three coverages.

Note:  A catch‑up pass is not needed in this case because third pass on third coverage will end at paver end of compacted area.

Completed ft./min. = 207 ft./min.  x 0.80 (efficiency) = 18 ft./min.

                                    9 passes                                 

Paver speed 21.65 ft./min.  Roller capacity is inadequate for the indicated paver speed, and appropriate changes to increase roller capacity will be necessary.

Above example considers a vibratory breakdown roller.  From experience, we know a rubber‑tired intermediate roller is typically needed to achieve interstate density (field voids) requirements.  Same procedure can be used to calculate capacity of rubber roller and compare to paver speed.  The only difference is that roller speed is not based on impacts per foot, but rather effectiveness as determined by nuclear gauge testing.

Uniform operation of paver is a critical factor in obtaining consistent density (field voids) results and smooth pavement.  If paver is operated at erratic or excessive speed in short intervals, satisfactory results are difficult to achieve.  When an excessive number of trucks arrive at paver simultaneously, paver operators are tempted to increase paver speed and quickly unload all waiting trucks, then stop paver, and await their return or next group.  It is better to maintain appropriate paver speed and thereby assist in re-spacing the trucks.  This does not sacrifice production but maintains uniform rate of production which allows roller operator to maintain rolling speed and still keep up with paver.

n Estimate lab density (voids) of plant produced mix

May be slightly higher than job mix lab density depending on aggregate gradation control, aggregate degradation in dryer, and asphalt binder control.

n Check equipment

Determine and record sizes of all rollers to be used for project.  Vibration frequency (discussed earlier), amplitude setting, roller scale weights, tire inflation pressures, tire sizes and contact pressure must be known and documented.  Minimum of 80 psi contact pressure is required.  The specifications require an information plate attached to each roller which shows tire size and ply; and correlation of wheel load and tire pressure with contact pressure.

n Select test site

Wait until approximately 100 tons of mix have been produced so plant has stabilized.  Test area should be about 328 feet long where roller may be tested without being interrupted by ramps, bridges, interchanges, etc.  Mark off section and record stationing.

Establish at least three points where nuclear testing will occur.  Record location of these points.

n Establish preliminary rolling pattern

Remember, the goal is to establish a roller pattern which will consistently obtain required density (field voids).  To meet this requirement, it will be necessary to adjust operating techniques until desired results are obtained.  Variables may include vibration frequency, amplitude, roller speed, contact pressure, number of coverages, and roller operating zone.

Change only one variable at a time.  Always select a combination that will allow rollers to complete at least the same m/min of completed mat as the paver is producing.

All operating techniques are governed by mix behavior during the rolling process.  It will vary from job‑to‑job and from lift‑to‑lift.

n Running test

Using predetermined rolling pattern and placing roller in preselected roller zone, begin compacting mat.  Locate nuclear gauge on mat at established locations and take reading.  Short nuclear counts are normally used initially, so testing does not interfere with rolling.

Continue rolling and checking density (field voids) until effective pattern is established.  Develop density growth curves for each roller pattern used.  Plot density vs. number of passes on graph paper.  Contractor should provide copies of this documentation, including description and location of pattern used, to project inspector. 

After a successful pattern is identified, complete rolling pattern again in another area and take longer nuclear counts to verify results.  Document the successful pattern to be used in field book.

Test strip needs to be established under the same production conditions that will prevail during normal paving operations, such as mix temperature and production rate.

n Cut cores

After mat has cooled or been iced, cut mat cores for acceptance. Eight cores (independent lot) are to be cut in test strip area. The maximum field voids limit is increased by 0.5% for test strips.  This recognizes the potential for inconsistent results when performing a test strip.

n Correlate nuclear readings with core results

Allows for more accurate monitoring of density with nuclear device during production.

n Monitor Use of Selected Pattern

Each day project inspector shall check rolling pattern, including paver speed and roller coverages, and record in field book. 

Resolving Density ‑ Void Conflicts

Project inspector should be aware that laboratory and field voids will be tightly controlled.  This may require more compactive effort and even higher average density for compliance.  Field control will allow no more than 8.5% voids in compacted layer.  Become familiar with other controls by reading Materials I.M. 511 and asking questions of District Materials personnel.

For the case where laboratory voids or field voids are outside designated limits for more than one day, inspector should discuss with District Materials whether to request a test strip.  Test area should be a straight run of about 100 yards.  Contractor will select combination of rollers to be used and preliminary rolling pattern.  Nuclear gauge readings would normally be taken after each pass or series of passes.

Inspector would only observe this process.  Documentation of type and amount of compactive effort shall be recorded.  Inspector will then select and mark out 5 random core sites within test site.  Density cores taken by contractor would be tested and results reported as soon as possible.

Cooperation between project inspector, District Materials, and contractor is essential to reach a timely solution.  If all anticipated results are not met, further experimenting with a different combination of rollers and operation should be performed.  Changes in gradation may be one of the first items looked at by District Materials.  Changes in asphalt binder content would be one of the last items.  Relief from minimum laboratory voids specified may only be approved by the Construction and Materials Bureau.

8.14     TESTING FOR SMOOTHNESS

Appropriate references for acceptable smoothness of HMA surfaces are Specification 2317 and Materials I.M. 341.  See Construction Manual Section 3.60 for additional information.

Use of Straightedge

Pavement smoothness specification does not relieve contractor of responsibility for proper rolling and workmanship.  Each pavement layer is to be inspected visually to ensure that surface is free of roller marks and distortion.  Transverse joints are to be checked with a 10‑foot straightedge.  Surface courses inspected with a straightedge shall meet 1/8 inch tolerance.  For lower courses, 1/4 inch smoothness tolerance may be used.

Corrections for surface irregularities shall be made, if possible, before mixture has cooled to 150 degrees F.  A large percentage of irregularities can be corrected by finish rollers above this temperature.

The inspector should observe surface to ensure that all roller marks or roller wheel depressions are smoothed out during the finish rolling.  The inspector should observe the longitudinal joints carefully to ensure that they have been smoothly rolled as specifications require.  If surface is not being finished as specifications require, inspector shall stop construction until contractor takes corrective action.

8.15     CHECKING TRANSVERSE JOINTS FOR SMOOTHNESS

The specifications require use of a 10‑foot straightedge for checking surface, intermediate, and base course transverse joints for smoothness.  Inspectors shall use straightedge according to the following procedure:

1.   The first check with the straightedge is made before saw cut.  Straightedge is used to determine where full thickness of layer ends and tapered portion begins.  Inspector shall require that saw cut be located in full thickness of layer.  All of the layer extending beyond the saw cut, including tapered portion, is then removed.

While the joint is being constructed and checked, inspector shall require the finishing machine to be stopped approximately 30 to 50 feet from the joint. Construction shall not be permitted to continue until the checking has been completed.  This permits repaving of the joint, with finishing machine, if straightedge should indicate a poor riding surface has been constructed.

2.   The second check with the straightedge is made after paver has constructed the new layer, but before rolling.  Straightedge is used to locate irregularities in newly constructed layer and any irregularities found that must be corrected by hand tools.  When straightedge indicates no high or low spots, compaction should be permitted with initial roller.

3.   The third check with the straightedge is across the joint between cold pavement and hot mixture after compacted with initial roller.  This third check indicates whether the correct amount of material has been placed.  For instance, if freshly rolled layer is too high, it indicates too much material has been placed.  If freshly rolled layer is too low, it indicates not enough hot mixture has been placed.

For that reason, high or low transverse joints are not usually corrected by additional rolling.  Instead, corrections should be made by cutting or filling rolled surface while mixture is still warm and can be manipulated.  If there are unusually high or low areas after rolling, paths must be shoveled through the pavement for paver tracks.  Paver is then backed up to the joint and paving operation is started again.

Above procedure shall be repeated as necessary until straightedge indicates that a good riding joint has been constructed.  If repeated repaving operations cause mixture to cool to the extent that reuse becomes impractical, it should be removed and wasted.

4.   The final procedure for insuring proper construction at transverse joints is checking for true edge alignment.  Edge of the freshly rolled layer should be carefully trimmed by hand tools until it matches the alignment of adjoining cold pavement.