Asphalt Plant Level 1 Module 7 -AC Content by Ignition Plant 1/09-Mod_7-Asph_Plant… · The mesh...

Module 7 - AC Content by Ignition

Release 10 4/19/2016

Asphalt Plant Level 1

7-1

This module covers the Asphalt Content by the Ignition Oven Method, FM 5-563. This test method is used to determine the asphalt content of the mix.

The asphalt content will provide the basis for the acceptance of the mixture and composes 25% of the pay for the mix for dense graded mixtures and 40% of the pay for the mix for open graded friction course mixtures (FC-5). This method replaces the time consuming solvent extraction method that was used in the past. The ignition oven has proven to be a very effective quality control tool.


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November 1, 2001 Revised: January 26, 2015

Florida Method of Test for

QUANTITATIVE DETERMINATION OF ASPHALT CONTENT FROM ASPHALT PAVING MIXTURES BY THE IGNITION

METHODDesignation: FM 5-563

1. SCOPE

This method covers the quantitative determination of asphalt content in asphaltconcrete pavement mixtures and pavement samples by removal of the asphalt through ignition in a furnace at 538°C (1000°F). Aggregate remaining from this method may be used for sieve analysis using FM 1-T 030.

The values stated in metric (SI) units are to be regarded as standard. Values given in parenthesis are for information and reference purposes only.

This standard does not purport to address all of the safety or environmental problems associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health and environmental practices and determine the applicability of regulatory limitations prior to use.

2. APPLICABLE DOCUMENTS

2.1 AASHTO Standards:

M 231Standard Specification for Weighing Devices Used in the Testing of Materials

T 308Standard Method of Test for Determining the Asphalt Binder Content of Hot Mix Asphalt (HMA) by the Ignition Method

2.2 Florida Test Methods:

FM 1-T 030 Mechanical Analysis of Extracted Aggregate

FM 1-T 168 Sampling Bituminous Paving Materials

2.3 Furnace Manufacturer’s User’s Manual

3. SUMMARY OF METHOD

3.1 The asphalt content of a paving mixture is determined by burning off theasphalt by ignition at 538°C (1000°F). The asphalt content is calculated from the initial weight of the sample, the final weight of the remaining

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aggregate, a temperature compensation factor for the measurement system, and a calibration factor for the mix. The asphalt content is expressed as both a weight loss in grams, and as a weight percentage of the initial sample weight.

3.2 This test procedure contains provisions for the user to establish a mix calibration factor to account for the aggregate weight loss due to ignition for the particular mixture.

4. APPARATUS

4.1 Ignition Furnace - A forced-air furnace capable of maintaining atemperature setting of up to 650°C (1200°F). The furnace is to include an internally mounted balance or load cell, accurate to 0.1 g, which is thermally isolated from the furnace chamber. This balance shall be capable of weighing samples of at least 2500 g in addition to the weight of the sample baskets. An automated system shall also be included for data collection and processing. The system shall provide a printout of the initial specimen weight, specimen weight loss, temperature compensation factor, mix calibration factor, calibrated asphalt content (%), test duration time, and furnace set-point temperature. An exhaust with filter, afterburner, or some combination that reduces the furnace emissions to an acceptable level shall be incorporated into the furnace. The furnace shall also include an audible alarm and indicator light to signal the end of the test. The test is deemed complete when the measured weight loss does not exceed 0.01% of the total sample weight for three consecutive minutes. The furnace door must lock automatically when the test is initialized and remain locked until completion of the test.

NOTE 1: See precautions in Section 5.

4.2 Baskets - A minimum of two tempered stainless-steel baskets, of perforated sheet or mesh. The mesh or perforations should be small enough to minimize the loss of sample during burn off. The baskets shall nest together and provide shielding on the corners to minimize loss of aggregate. The nested baskets shall sit in a catch pan approximately 25 mm (1 in.) deep. The bottom basket shall sit higher than 40 mm (1.6 in.) above the catch pan. The overall dimensions of the nested baskets in the catch pan shall be such that the assembly can be easily placed onto the balance tray inside the furnace without scraping the chamber sides. The pan shall incorporate a system (handle or tongs) to lift the basket assembly for placement into and removal from the furnace. This system shall minimize the exposure of the operator to the high temperature in the furnace.

4.3 Balance - A balance, with a capability of 8 kg or greater, accurate to 0.1 g.

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It shall conform to the requirements of AASHTO M231, Class G2.

4.4 Oven - An oven capable of maintaining a temperature of 149°C ± 5°C(300°F ± 9°F).

4.5 Safety Equipment - Safety face shield, high temperature gloves, and a long sleeve jacket. A heat resistant surface capable of withstanding temperatures up to 650°C (1200°F) and a protective cage to surround and isolate the sample baskets shall also be provided.

4.6 Miscellaneous Equipment - A pan with internal dimensions larger than the outside dimensions of the baskets, catch pan for transferring samples after ignition, wire and soft bristle brushes, spatulas, and bowls may be needed.

5. PRECAUTIONS5.1 The oven must be placed in a well-ventilated area and properly vented to

the outside (see manufacturer’s recommendations).

5.2 Prior to initiating the test, verify that the ignition oven door has been properly closed. This ensures that the door lock will engage when the test is started.

6. SAMPLING

6.1 The test samples shall be obtained in accordance with FM 1-T 168.

6.2 Preparation of test specimens:

6.2.1 If the mixture is not sufficiently soft to separate with a spatula or trowel, place it in a large, flat pan and heat to a temperature not to exceed 149°C (300°F) until it can be handled or mixed.

6.2.2 The size of the test samples shall be governed by the nominal maximum aggregate size of the mixture, and shall be as shown in Table 1.

NOTE 2: When the sample size exceeds the capacity of the equipment used, the sample may be divided into suitable increments. The specimens may then be tested, and the results mathematically combined for calculation of the asphalt content (weighted average).

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TABLE 1

Mixture Type Minimum Sample Size (grams) ATPB (No. 57 stone) 3000 SP-19.0 ABC-3 S-IIATPB (No. 67 stone)

2000

SP-12.5 FC-12.5 (FC-6) SP-9.5 FC-9.5 FC-5 S-I

1500

FC-2 and FC-3 S-IIISP-4.75FC-4.75TYPE III

1200

TYPE II ABC-1 and ABC-2 SAHM

1000

7. MIXTURE CALIBRATION

7.1 This test method may be affected by the type of aggregate used in themixture. Accordingly, to optimize accuracy, an asphalt binder calibration factor must be established for each mix.

7.2 Two calibration specimens conforming to the size requirements of Section 6.2.2 shall be prepared at the design asphalt content. A “butter mix” shall also be prepared in each mixing bowl at the designasphalt content, mixed and discarded prior to mixing any of the calibration specimens to ensure an accurate asphalt content.

NOTE 3: The freshly mixed specimens may be placed directly in the sample baskets. If allowed to cool, the samples must be pre-heated in an 149°C (300°F) oven until workable. Do not preheat the sample baskets.

7.3 Weigh and record the weight of the sample baskets and catch pan (with guards in place).

7.4 Place the bottom sample basket in the catch pan. Evenly distribute approximately one half of the calibration specimen in the lower basket, keeping the material approximately 25 mm (1 in) away from the edges of

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the basket.

7.5 Place the upper sample basket on the bottom basket assembly. Evenly distribute the remaining specimen in the top basket as in Section 7.4.

NOTE 4: If the basket assembly contains more than two baskets, divide the sample into equal proportions and distribute them equally in each one of the sample baskets.

7.6 Weigh the sample and the sample basket assembly. Subtract from this weight the weight measured in Section 7.5 and record. This is the initial weight, WI, of the sample specimen.

7.7 Preheat the ignition furnace to 538°C (1000°F).

7.8 Enter a calibration factor of 0.00 in the ignition furnace.

7.9 Input the initial weight, W1 of the sample specimen, rounded to the nearest gram, into the ignition furnace controller. Verify that the correct weight has been entered.

7.10 Using protective equipment, open the chamber door and place the sample basket assembly in the furnace. Ensure that the basket assembly is not touching the furnace sides. Close the chamber door and initiate the test by pressing the start/stop button.

7.11 Allow the test to continue until the stable light and audible stable alarm indicate that the test is complete. Press the start/stop button. Print out the test results.

7.12 Using protective equipment, open the chamber door, remove the sample baskets, place on an insulated heat resistant surface and cover the basket assembly with the protective cage. Allow to cool to room temperature (approximately 30 minutes), and then determine the final weight, WF, of the sample specimen, as in Section 7.6, before discarding or performing a gradation analysis, if required.

7.13 Once the testing of a calibration specimen has been completed, the actual percent weight loss attributed to the aggregate in the mix shall be determined as follows:

WL = ACActual - ACMeasured

where: WL = aggregate weight loss of the calibration sample, percent by weight of the total mix;

ACActual = percent asphalt in the mix, by weight of the total mix, before ignition (design asphalt content as

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per Section 7.2). ACMeasured = percent asphalt in the mix, by weight of the total

mix, after ignition as given in the furnace printout.

7.14 The asphalt binder calibration factor is calculated as follows:

[ ]2

21 LL WWACCF

+=

where: CF[AC] = asphalt binder calibration factor, percent by total weight of mix;

WL1 = aggregate weight loss of the first calibration sample, percent by weight of the total mix;

WL2 = aggregate weight loss of the second calibration sample, percent by weight of the total mix.

7.15 The ignition test significantly affects the gradation of some types of aggregate. Consequently, if the value of the asphalt binder calibration factor, CF[AC], exceeds 0.50%, aggregate correction factors for the percent passing the #8 [2.36 mm] and #200 [75 µm] sieves shall be determined according to the correction factor procedure in AASHTO T 308, or other method approved by the Engineer. Aggregate correction factors for other sieve sizes may be required by the Contract Documents.

8. TESTING PROCEDURE

8.1 Preheat the ignition furnace to 538°C (1000°F).

8.2 Enter a correction factor of 0.00 in the ignition furnace.

8.3 Weigh and record the weight of the sample baskets and catch pan (with guards in place).

8.4 Prepare the sample as described in Section 6. Place the bottom sample basket in the catch pan. Evenly spread approximately one half of the test specimen in the lower basket, keeping the material approximately 25 mm (1 in) away from the edges of the basket.

8.5 Place the upper sample basket on the bottom basket assembly. Evenly distribute the remaining specimen in the top basket as in Section 8.4.

8.6 Weigh the sample and the sample basket assembly. Subtract from this weight the weight measured in Section 8.3 and record. This is initial weight, WI, of the sample specimen.

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8.7 Input the initial weight, WI, of the sample specimen, rounded to the nearest gram, into the ignition furnace controller. Verify that the correct weight has been entered.

8.8 Using protective equipment, open the chamber door and place the sample basket assembly in the furnace. Ensure that the basket assembly is not touching the furnace sides or back of the furnace. Close the chamber door and initiate the test by pressing the start/stop button.

8.9 Allow the test to continue until the stable light and audible stable alarm indicates the test is complete. Press the start/stop button. This will initiate the printout of the test results and stop the test.

8.10 Using protective equipment, open the chamber door, remove the sample baskets, and place on an insulated heat resistant surface. Cover the basket assembly with the protective cage, and allow to cool to room temperature (approximately 30 minutes). The final weight WF, of the sample specimen may then be determined, as in Section 8.6.

8.11 If required or necessary, perform a gradation analysis on the residual aggregate as indicted in Section 10.

NOTE 5: If the basket assembly contains more than two baskets, divide the sample into equal proportions and distribute them equally in each one of the sample baskets.

9. CALCULATIONS

9.1 The calibrated asphalt content shall be computed as follows:

ACCalibrated = ACMeasured + CF[AC]

where: ACCalibrated = calibrated asphalt content, percent by weight of the total mix;

ACMeasured = measured asphalt content as obtained from the furnace printout, percent by weight of the total mix;

CF[AC] = asphalt binder calibration factor of the specific mix being tested as determined in accordance with Section 7, percent by weight of the total mix.

9.2 If the furnace printout is not available due to an equipment issue, and if approved by the Engineer, the measured AC content may be calculated manually as follows:

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100W

WWACI

FIMeasured ×

−=

where: WI = initial weight of the sample; WF = final weight of the sample.

9.2 If necessary, the calibrated percent passing the #8 [2.36 mm] sieve shall be computed as follows:

P-8Calibrated = P-8Measured + CF[P-8]

where: P-8Calibrated = calibrated percent passing the #8 [2.36 mm]sieve, percent by total weight of the aggregate;

P-8Measured = measured percent passing the #8 [2.36 mm]sieve by ignition method, percent by total weight of the aggregate;

CF[P-8] = aggregate correction factor for the #8 [2.36 mm] sieve for the specific mix being tested asdetermined in accordance with Section 7,percent by total weight of the aggregate.

The calibrated percent passing for other sieve sizes is determined in the same manner as described above for the #8 [2.36 mm] sieve.

10. GRADATION

10.1 After allowing the sample to cool to room temperature, empty the contentsof the baskets into a flat pan. Use a small wire sieve brush, and/or a bristle brush to ensure that any residual fines are removed from the baskets.

10.2 Perform a gradation analysis according to FM 1-T 030.

11. REPORTING

11.1 Report the calibrated asphalt content, mix calibration factor, temperaturecompensation factor, total percent loss, sample weight, and test temperature. Attach the original printed ticket to the report.

NOTE 6: The thermal paper used for some of these machines may darken beyond legibility when exposed to heat or after handling and aging. It is recommended that a copy be made of the ticket to prevent the loss of this information.

12. PRECISION AND BIAS

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12.1 Precision (plant produced mix)

The following precision statements were determined in a round-robin study and were based on nine plant produced surface mixtures containing a wide variety of aggregate types. There were four replicates per mix type with twelve laboratories participating.

Standard Deviation (1S) % Asphalt Content

Acceptable Range of Two Test Results (D2S) % Asphalt Content

Single-Operator Precision

0.114 0.32

Multi-Laboratory Precision

0.156 0.44

12.2 Precision (laboratory fabricated samples)

The following precision statements were determined in a round-robin study and were based on six laboratory fabricated surface mixtures containing six aggregate types. There were three replicates per mix type with twelve laboratories participating. The results from one laboratory were deleted as outlying observations.

Standard Deviation (1S) % Asphalt Content

Acceptable Range of Two Test Results (D2S) % Asphalt Content

Single-Operator Precision

0.047 0.13

Multi-Laboratory Precision

0.141 0.35

12.3 Bias

The bias of this test method has not been determined.

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There are several manufacturers of this equipment. The general design concept uses a high temperature oven with a built in scale that measures the sample weight as the asphalt binder is burned off the aggregate. When the sample weight stops decreasing, the asphalt has been burned off.


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Shown here are some of the specifications on the oven.


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Shown here is additional information on the wire mesh baskets used to contain the sample while in the oven.


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Photo of assembled basket. A minimum of two mesh baskets is required.


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Additional equipment needed for the test.


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Its very important to observe and follow all safety precautions when working around this device. In addition, always assume the baskets are hot and handle carefully.

Safety:Face shieldHigh temperature glovesLong sleeve jacket


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There are a variety of different types of heat shields to be placed over the baskets once they are removed from the oven. Regardless of the type, they need to be used and in place.Safety:

Heat resistant surfaceProtective cage


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Oven is hot.Do not open during testing. Do not disengage safety features. Use all safety items.


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These ovens operate at very high temperatures (1,000ºF) and must be properly vented. Follow all local code requirements when installing these devices.

Safety:Good ventilationProperly vented to outside


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These doors have an indicator to ensure the door is locked during a test.

Safety:

Make sure the door is completely closed.


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There is a standard procedure to calibrate these ovens with all the mix design used on FDOT projects. A calibration factor is developed for each mix design and is shown on the mix design sheet. It starts with hand batching a mix design with a known asphalt content and comparing it to the results from the oven. The steps are summarized in the slide. Two identical mix batches are made up for the calibration procedure.


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The photos show the steps. A “buttered” bowl (top left) is a bowl that has a thin film of asphalt mix left on it. This is commonly used in the mix design procedure and here as well. The trick is to leave the same amount in the bowl. If a clean bowl was used for calibration, it is impossible to get all the asphalt out of the bowl and it will affect the calibration. Top right shows the mix design aggregate being added to the bowl followed by the correct binder content (lower left). The final step shown here is mixing thoroughly (bottom right).


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Here is an example. Two batches were created and tested in the oven. The results are averaged and subtracted form the known asphalt content resulting in calibration factor. This positive calibration factor indicates that not all the asphalt cement was removed from the sample.


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Here is another example. Two batches were created and tested in the oven. The results are averaged and subtracted form the known asphalt content resulting in a calibration factor. This negative calibration factor indicates that all the asphalt cement and some of the aggregate was lost from the sample. It is common for softer aggregates to breakdown slightly and have some of the very fine material leave the oven through the exhaust system.


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Some aggregates (mainly soft limestones) will break down under excess heat. The limit for determining the calibration factor by this test method is 0.5%. If it exceeds this amount, the solvent extraction procedure must be used. Very few mixes used in Florida require the use of this alternative procedure.


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Shown here is the procedure to develop an aggregate correction factor. This is not normally used.


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In looking at the slide, the majority of the mixes used in Florida will fall under a sample size of 1,500 grams. Only the SP-19 mm mix would require a larger sample of 2,000 grams, but it is not used much anymore.


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Once the calibration procedure is complete, normal testing can begin. As shown earlier, the sample of mix will be obtained in accordance with FM 1-T 168.

Obtain by FM 1-T 168. If necessary, warm sample in large, flat pan until it can be broken apart. Temp not to exceed 300 + 9oF


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Weigh the entire basket assembly including catch pan and guards.

Place bottom basket in catch pan. Weigh and record weight of the baskets and

catch pan with the guards in place.


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Add the mix to the baskets with roughly equal amounts in each basket. Keep the mix approximately 1 inch away from the edges. Spread the mix into an even layer. Be careful of buildup on the spatula. Scrape the build up into the baskets as you go.

Note: Some baskets only have two levels, not three.


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Once all the baskets are charged, reassemble and weigh. Subtract the weight of the assembly to get the mix weight.


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The oven should be preheated well before the time to load the sample. Enter 0.00 for the calibration factor and enter the actual mix weight.

Preheat oven to 538°C (1,000°F).Enter:Calibration factor of 0.00.Actual weight of mix (nearest gram).


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Although not shown in this picture, it is recommended to wear long sleeves to protect the skin against the heat of the oven.

With safety equipment on:Open door.Place sample basket assembly in furnace.Basket should not be touching the sides of the oven. Close door.Start test.


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The test will continue until the weight loss stabilizes. The alarm will sound. Print out the results and attach it to the gradation data sheet.

Allow test to continue until alarm sounds or indicator shows test is finished. Press start/stop button to get printout of results.


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Carefully remove the basket, set it on a heat resistant plate, andcover with the protective cage. Allow a minimum of 30 minutes to cool beforeprocessing. Weigh the basket assembly.

With safety equipment on:Open door.Remove the sample baskets.Place the basket assembly on a heat resistant counter.Cover the basket assembly with a protective cage.Allow to cool to room temperature. Wait a minimum of 30 minutes.Determine the weight left in baskets, WF.


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The calibrated asphalt content will be the measured AC content from the printout plus the correction factor.


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The example shown here adds a negative correction factor to the measured asphalt content yielding a final AC content of 5.40 %.


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Shown here are the acceptable ranges between two test results for a plant produced mix. Values are given for single operator and multi-lab.


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Shown here are the acceptable ranges between two test results for lab created samples. These values are slightly tighter than those for the plant produced samples. Values are given for single operator and multi-lab.


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The difference between the two tests (single operator) shown on the slide is 0.14%. If the mix was plant produced, the results would be acceptable (less than or equal to 0.32%). If the mix was lab created, the results would not be ok (not less than or equal to 0.13%).


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In this example, we show two different labs. Use the multi-lab precision. For plant produced mix, the difference allowed is 0.44%. For lab produced mix the difference allowed is 0.35%. In both causes, the actual (0.14%) is well within the allowable tolerances.


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Again, the job is not complete until the paperwork is done. This is the information that is needed.


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Once the final weight is obtained, the material left in the baskets will be cleaned out carefully and a gradation analysis will be performed. This is discussed in the next module.


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Shown here are some potential problems that may arise; generally attributed to the aggregate and its condition.

Moisture trapped in an aggregate subject to extreme heat turns to steam. The aggregate could fracture and may even cause the basket assembly to move in the oven.


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Asphalt Plant Level 1 Module 7 -AC Content by Ignition Plant 1/09-Mod_7-Asph_Plant… · The mesh...

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Transcript of Asphalt Plant Level 1 Module 7 -AC Content by Ignition Plant 1/09-Mod_7-Asph_Plant… · The mesh...