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104 A P P E N D I X C AASHTO Style Standards
105 Standard Method of Test for Determining the Expansion and Collapse of Foamed Binder by Using the Laser Distance Measurement Device AASHTO Designation: T xx-xx 1. SCOPE 1.1. This test method describes the procedure for determining the expansion and collapse of foamed binder produced by a laboratory foaming unit or sampled at a hot-mix plant using a laser distance measurement device. 1.2. While working with or handling foamed binder, lab personnel may be exposed to extreme heat and pressure, hazardous materials, and dangerous equipment operations. This standard does not address procedures and practices needed to ensure a safe and hazard-free working environment in the laboratory or at a hot-mix plant. Hence, it is the responsibility of the user of this standard to ensure safety. 1.3. SI UnitsâThe values stated in SI units are to be regarded as the standard. 2. REFERENCED DOCUMENTS xx 3. SIGNIFICANCE 3.1. The test standard is used to measure the change in height and corresponding volume of the foamed binder in real time. The laser-based sensor is comprised of an emitter and detector to measure the distance from the sensor to a reflecting surface based on the phase-shift principle. The laser sensor measures the height of the surface by reflecting light of different wavelengths over a very small circular spot of about 1 mm in diameter. The laser sensor collects data at a frequency of 1 Hz. 3.2. The test standard is used to determine the expansion and collapse characteristics of asphalt binders. The results obtained by following these procedures can be used to: Determ⢠⢠ine the maximum expansion ratio, ERmax, at different conditions (i.e., temperature, water content, binder type, foaming unit, and/or pressure); Characterize the decaying rate of the foam at different conditions (i.e., temperature, water content, binder type, foaming unit, and/or pressure);
106 Use ⢠⢠the data obtained from this test for a foam decaying model to determine asphalt foam characteristics as a function of time; and Investigate the influence of binder type, water content, foaming unit, temperature, and pressure on foam expansion and decay properties. 4. APPARATUS 4.1. Laboratory foaming unit that produces a specified amount of foamed binder or sampling port in a hot-mix plant that can be controlled to dispense a specified amount of foamed binder. 4.2. Laser distance meter (LDM) device that uses phase-shift principle to measure distances with a resolution of 0.1 mm or better, repeatability of ±0.3 mm or better, and a data collection rate of 1 data point per second or better. The device must also acquire the time at which the measurement was made with a resolution of 100 milliseconds or better. 4.3. Tripod or other suitable means to mount the laser distance meter. 4.4. Clean cylindrical metal cans for each measurement (1-gallon or 5-gallon capacity). 4.5. Personal protective equipment and other safety gear as needed. 4.6. Computer to collect data acquired by the laser distance meter. 5. PROCEDURE 5.1. Calibrate the laboratory foaming unit according to the manufacturerâs recommendations. 5.2. Calibrate the height of the binder in the metal can with respect to the weight of the binder in the can. Although the metal may be cylindrical, the bottom of the can may be grooved in order to strengthen it. For small amounts of binder dispensed during foaming, the groove can accommodate a significant mass fraction of the binder (Figure 1). In order to avoid errors in volumetric measurement it is important to calibrate the weight of binder to the height of binder in the can. For this calibration, mount the LDM device on a tripod at a suitable location (Figure 2). The tripod and the LDM should be stable and not susceptible to vibrations. Weigh the empty metal can and place it under the LDM. Point the LDM to the bottom of the empty can. The laser should point at a flat portion of the can, preferably in the center. The distance to the bottom of the can should be recorded and the exact location of the can should be marked. Pour enough hot binder in the can so that a smooth and flat binder surface is created. Measure the mass of the binder dispensed in the previous step and measure the distance from the LDM to the surface of the binder. Subtract the last two measurements to obtain the height of the binder in the can. Repeat the procedure at least twice after adding more binder to the can and weighing it each time. The weight versus height of binder will be used for future calculations.
107 Figure 1. Illustration of the bottom of a 1-gallon can. Figure 2. Illustration of the LDM pointing into an empty can for calibration. 5.3. Prepare the LDM to make measurements for the foamed binder. Mount the LDM on the tripod at a suitable location that is not susceptible to movement or vibration. Weigh the empty metal can and place it under the LDM. Point the laser from the LDM to the bottom of an empty can. The laser should point as close to the center of the can as possible. Start data acquisition to get at least 5 points that correspond to the distance between the LDM and the bottom of the can 5.4. Dispense the specified amount of foamed binder into the metal can. Depending on the foaming equipment (or location in case of a field test), it may or may not be possible to dispense the foamed binder while the LDM is pointing into the can. In situations where the can must be moved away from the LDM to collect the foamed binder sample, ensure that the location of the can is marked and that the can is placed under the LDM as soon as possible after collecting the sample. Also, in this case the time at which the sample was dispensed must be recorded using the LDM. 5.5. Record the distance between the top of the foamed binder and the LDM at regular intervals (i.e., every 1 second). Record the data for at least 90 seconds or until the change in the height of the binder sample is less than 0.1 mm, whichever comes later. Note that if the measurements are conducted at room temperature, the binder sample may cool before all the bubbles can escape. In this case, the binder may not collapse completely. 5.6. Weigh the can to obtain the actual mass of the foamed binder dispensed. Use the measured weight of the binder sample dispensed to verify the calibration of the foaming unit and to obtain the minimum height of the unfoamed binder using the binder weight-height calibration from before, hfinal.
108 6. CALCULATION OF RESULTS 6.1. Obtain the distance between the top of the foamed binder and the LDM as a function of time from the computer and report it to the nearest 0.1 mm. Convert the distance measured by the LDM to height of the foamed binder at any time t, ht, by subtracting it from the distance measured to the bottom of the container. 6.2. Determine the final height of the foamed binder, hfinal, from the weight-to-height relationship established in the calibration. 6.3. Calculate the expansion ratio of the binder at any time t, ER(t) final final as . For the maximum expansion ratio, the maximum height of the foamed binder measured from the marking left behind by the collapsing foam on the inside of the can is used. Note that the start time is the time when the binder sample was dispensed to the metal can. 6.4. Plot the expansion ratio versus time. The data from the LDM can be smoothened using Equation 1: Where: ER(t), the expansion ratio of the foamed binder at any time t. a, b, and c, fitting coefficients. ERmax, the maximum expansion ratio of the foamed binder. 6.5. Determine the foamability index referred as the area underneath the ER curve by Equation 2: 6.6. Use the ER data after 10 seconds of foaming to determine the rate of collapse of the semi-stable foamed binder, k-value. The rate of collapse of the semi-stable foam is determined as the parameter k obtained by fitting the ER versus time to an exponential curve expressed as Equation 3: Where: h, fitting coefficient. k, the rate of collapse of the semi-stable foamed binder. 7. REPORT 7.1. The report shall include the following: 7.1.1. Make and model of the laboratory foaming unit or plant foamer. 7.1.2. Source and grade of the binder. 7.1.3. Foaming water content in percent of dry mass of binder. (3) ER (2) ERFI (1) ER ERmax
109 7.1.4. Type and dosage of foaming additive (if used). 7.1.5. Maximum expansion ratio of the foamed binder, ERmax. 7.1.6. Foamability index of the foamed binder, FI. 7.1.7. The rate of collapse of the semi-stable foamed binder, k-value.
110 Standard Method of Test for Determining the Size Distribution and Surface Area of Binder Foam Bubbles During the Foaming Process AASHTO Designation: T xx-xx 1. SCOPE 1.1. This test method describes the procedure for evaluating the evolution of the size and amount of binder foam bubbles over time during the foaming process using a digital camera. 1.2. While working with or handling foamed binder, lab personnel may be exposed to extreme heat and pressure, hazardous materials, and dangerous equipment operations. This standard does not address procedures and practices needed to ensure a safe and hazard-free working environment in the laboratory or at a hot-mix plant. Hence, it is the responsibility of the user of this standard to ensure safety. 1.3. SI UnitsâThe values stated in SI units are to be regarded as the standard. 2. REFERENCED DOCUMENTS xx 3. SIGNIFICANCE 3.1. The test standard is used to capture the image of the surface binder foam bubbles during the foaming process using a digital camera. The digital camera collects images at a frequency of 1 Hz. The results obtained by following these procedures can be used to: 3.1.1. Determine the size distribution of binder foam bubbles at different conditions (i.e., temperature, water content, binder type, foaming unit, and/or pressure); 3.1.2. Calculate the surface area of binder foam bubbles at different conditions (i.e., temperature, water content, binder type, foaming unit, and/or pressure); and 3.1.3. Investigate the influence of binder type, water content, foaming unit, temperature, and pressure on characteristics of binder foam bubbles during the foaming process. 4. APPARATUS 4.1. Laboratory foaming unit that produces a specified amount of foamed binder or sampling port in a hot-mix plant that can be controlled to dispense a specified amount of foamed binder. 4.2. Digital camera with at least 12-megapixel resolution and continuous timed shutter release able to capture images every 1 second from the start of the foaming process (or the sample being placed under the tripod).
111 4.3. Tripod or other suitable means to mount the digital camera. 4.4. Clean cylindrical metal cans for each measurement (1-gallon or 5-gallon capacity). 4.5. Personal protective equipment and other safety gear as needed. 4.6. Computer to collect data acquired by the laser distance meter. 5. PROCEDURE 5.1. Calibrate the laboratory foaming unit according to the manufacturerâs recommendations. 5.2. Set up a tripod on a leveled surface and use bubble levels to ensure the center post is vertical and perpendicular to the ground. Mount the digital camera on the tripod as shown in Figure 1. Figure 1. Camera setup for digital image capture of foamed binder sample. 5.3. Place an empty metal can below the tripod. Adjust the location to ensure that the camera can capture the inside of the 5-gallon bucket and that the laser is pointed into the bucket and is free of obstructions. After the adjustment, use a marker to identify the position of the metal can and the tripod. 5.4. Connect the digital camera with the computer. Turn on the digital camera and run appropriate software on the computer to remotely control the digital camera. 5.5. After filling the metal can to between â and ½ of its height with the foamed binder, stop the laboratory foaming unit or turn off the sampling valve connected to the plant foamer unit. Move the metal can containing the foamed binder sample to the location under the tripod marked in Step 5.3. 5.6. Stop the digital camera when no significant changes in the foaming height can be observed. Save all digital images.
112 6. CALCULATION OF RESULTS 6.1. Download the set of images captured during the foaming experiment from the camera to a computer. 6.2. Select an original image (as shown in Figure 2) acquired at a specific desired time and label it using the a) binder source, b) binder grade, c) foaming water content, and d) time the image was acquired counting from the discharge of the foamed asphalt binder into the test container. Figure 2. Original image of binder foam bubbles. 6.3. Adjust the contrast of the original image using Adaptive Histogram Equalization in Matlab® with the following code. The adjusted image is shown in Figure 3. img = imread; pic = rgb2gray(img); fin = adapthisteq(pic); imshow(fin) imsave Figure 3. Adjusted image of binder foam bubbles. 6.4. Select the inner part of the image to avoid the reflection of the foamed binder on the surface of the metal can. Set the scale of the image using as reference the rim of the can holding the foamed binder sample (e.g., 6.5 inches for a typical 1-gallon can as show in Figure 4). Figure 4. Scale calibration for a 1-gallon can.
113 6.5. Segment the image by drawing four lines through its center. The lines extend from side to side of the container separated by a 45-degree angle from each other as illustrated in Figure 5 (i.e., lines in the N/S, W/E, NW/SE, and SW/NE directions). Figure 5. Image segmentation. 6.6. Print the image and manually detect and draw circles around all foamed bubbles that intersect the lines sketched in Step 6.5. 6.7. Count and measure the diameter (in mm) of the bubbles identified in Step 6.6 using a ruler. Record the measured diameter of each bubble and then use the scale established in Step 6.4 to adjust the measurements (i.e., adjusted diameter in Table 1). Table 1. Bubble count and size data. 6.8. Generate a bubble size distribution histogram using JMP® or other similar software (Figure 6), and fit a curve to the histogram using a gamma function (Figure 7). Figure 6. Bubble size distribution histogram.
114 Figure 7. Fitted gamma function to the bubble size distribution histogram. 6.9. Report the gamma function curves at the selected time intervals to illustrate the change in bubble size distribution with time (as shown in Figure 8). Figure 8. Gamma function curves at selected times. 6.10. Calculate the volume of the foamed and unfoamed binder using min Equation 1 and Equation 2, respectively. The terms used in the two equations are defined in Figure 9. 6.11. (1) (2) Figure 9. Schematic of binder sample after foaming. The difference in volume between the foamed binder at time t and the unfoamed binder is the expanded volume created by foaming bubbles. Therefore, the volume of all foaming bubbles at time t can be calculated using Equation 3.
115 (3) 6.12. Knowing the total number of surface binder foam bubbles, ns min (t), and the diameter of each surface binder foam bubble, Ds-i(t), where i is from 1 to ns(t), the surface binder foam bubbles at time t can be expressed using Equation 4. (4) 6.13. Assuming all surface binder foam bubbles are sphere shaped, calculate the volume of all surface binder foam bubbles at time t using Equation 5. (5) 6.14. Assuming all binder foam bubbles in the foamed binder volume have the same diameter distribution as the surface ones, estimate the total number of binder foam bubbles at time t per Equation 6. (6) 6.15. Determine the total surface area SA SA of all binder foam bubbles at time t and the surface area of the unfoamed binder using Equation 7 and Equation 8, respectively. (7) (8) 6.16. Calculate the surface area index (SAI) SAI SA SA at time t as the ratio of SAt(t) over SA0 as expressed in Equation 9. (9) 7. REPORT 7.1. The report shall include the following: 7.1.1. Make and model of the laboratory foaming unit or plant foamer. 7.1.2. Source and grade of the binder. 7.1.3. Foaming water content in percent of dry mass of binder. 7.1.4. Type and dosage of foaming additive (if used). 7.1.5. Gamma function for size distribution of binder foam bubbles at certain times. 7.1.6. Surface area index of all binder foam bubbles, SAI. min
116 Standard Method of Test for Evaluating the Workability of Foamed Warm Mix Asphalt by a Laboratory Foaming Unit Using a Superpave Gyratory Compactor AASHTO Designation: T xx-xx 1. SCOPE 1.1. This test method describes the procedure for evaluating workability of foamed warm mix asphalt (WMA) by a laboratory foaming unit using a Superpave gyratory compactor (SGC). 1.2. While working with or handling foamed binder, lab personnel may be exposed to extreme heat and pressure, hazardous materials, and dangerous equipment operations. This standard does not address procedures and practices needed to ensure a safe and hazard-free working environment in the laboratory or at a hot-mix plant. Hence, it is the responsibility of the user of this standard to ensure safety. 1.3. SI UnitsâThe values stated in SI units are to be regarded as the standard. 2. REFERENCED DOCUMENTS AASHTO T 312, Preparing and Determining Density of Hot Mix Asphalt (HMA) Specimens by Means of the Superpave Gyratory Compactor 3. SIGNIFICANCE 3.1. The test standard is used to evaluate the workability of foamed asphalt mixture produced by a laboratory foaming unit using an SGC. The standard is essential for determining the optimum foaming water content that is able to produce foamed asphalt mixture with the best workability in the laboratory. 4. APPARATUS 4.1. Laboratory foaming unit that produces a specified amount of foamed binder or sampling port in a hot-mix plant that can be controlled to dispense a specified amount of foamed binder. 4.2. Portable asphalt mixer to mix foamed asphalt with aggregates. 4.3. Draft dry oven to short-term age foamed asphalt loose mix prior to compaction. 4.4. SGC to compact foamed asphalt loose mix with capacity of recording shear stress during compaction.
117 5. PROCEDURE 5.1. Prepare the aggregate batch following the mix design gradation, and place the aggregate batch in a shallow rectangular metal pan in the oven at 275°F (135°C) and leave overnight. Place the mixing bucket and other mixing tools in the oven at least 1 hour prior to foaming. 5.2. Calibrate the laboratory foaming unit according to the manufacturerâs recommendations. 5.3. Pour the preheated aggregate batch in the bucket mixer and make a crater in the middle of the aggregate material. Dispense the specific amount of foamed binder into the bucket mixer. 5.4. Start the bucket mixer and place the metal paddle in the support. To help achieve complete aggregate coating, while the bucket mixer is turning, push the arm down and to the side of the bucket; a flat spatula can also be introduced into the bucket to scrape the material from the sides and the bottom. 5.5. When all aggregates appear to be completely coated, empty the foamed asphalt loose mix into a shallow rectangular metal pan, uniformly spread the loose mixture, and place inside the oven. Change the temperature of the oven to 240°F (116°C). Keep the loose mix in the oven for 2 hours. 5.6. Place the SGC molds and other compaction tools in the oven one hour prior to compacting. Stir the foamed asphalt loose mix and then start preparing the loose mix in individual specimen size batches (4,700 g per batch) 30 minutes prior to compacting. Return the loose mix to the oven immediately after batching to guarantee compaction temperature. 5.7. Obtain an individual specimen size batch and a preheated compaction mold from the oven. Place a piece of paper at the bottom of the compaction mold. Pour the individual specimen batch in the compaction mold and manually level the loose mix. Place another piece of paper on top of the loose mix. Slide the compaction mold into the SGC and start the compactor. 5.8. During compaction, height of the loose mix in the SGC mold and the shear stress are continually monitored for each gyration. Compaction will cease after 300 gyrations. 5.9. After compaction, remove the mold containing the compacted specimen from the compactor and slowly extrude the specimen from the mold. Remove the pieces of paper from the top and bottom of the specimen and allow the specimen to cool undisturbed. 5.10. Place the mold and base plate back in the oven to reach compaction temperature for the next specimen. Repeat the compaction procedure for each specimen. 6. CALCULATION OF RESULTS 6.1. Obtain the shear stress data from the SGC. Figure 1 presents a typical plot of the shear stress versus number of SGC gyrations during compaction. As illustrated, the shear stress plot can be divided into three main phases: ⢠First Phase â The slope of the shear stress curve is steep, the loose mix particles are being reoriented due to compaction, and there is a significant increase in internal friction within the mix due to the stone-on-stone contact.
118 ⢠⢠Second Phase â The shear stress starts to level off. The density of the specimen is expected to be near or at target value. Third Phase â The shear stress starts to decrease significantly from a maximum stress level. The reduction in shear stress is attributed to the degradation of the aggregate and pore pressure. Figure 1. Typical shear stress compaction curve. 6.2. Evaluate the workability of foamed asphalt mixture using the maximum shear stress. Asphalt mixtures with more compaction in the first few cycles are expected to have higher shear stress afterwards due to the increased internal friction within the mix. Additionally, mixtures with better workability are expected to have a lower level of shear stress. 7. REPORT 7.1. The report shall include the following: 7.1.1. Make and model of the laboratory foaming unit or plant foamer. 7.1.2. Source and grade of the binder. 7.1.3. Mix design information. 7.1.4. Foaming water content in percent of dry mass of binder. 7.1.5. Type and dosage of foaming additive (if used). 7.1.6. Maximum shear stress obtained during compaction, Ïmax. 7.1.7. Number of SGC gyration where the maximum shear stress is obtained.
119 Standard Method of Test for Evaluating the Coatability of Foamed Warm Mix Asphalt by a Laboratory Foaming Unit Using a Superpave Gyratory Compactor AASHTO Designation: T xx-xx 1. SCOPE 1.1. This test method describes the procedure for evaluating the coatability of foamed warm mix asphalt (WMA) by a laboratory foaming unit based on the aggregate absorption method. 1.2. While working with or handling foamed binder, lab personnel may be exposed to extreme heat and pressure, hazardous materials, and dangerous equipment operations. This standard does not address procedures and practices needed to ensure a safe and hazard-free working environment in the laboratory or at a hot-mix plant. Hence, it is the responsibility of the user of this standard to ensure safety. 1.3. SI UnitsâThe values stated in SI units are to be regarded as the standard. 2. REFERENCED DOCUMENTS AASHTO T 255, Total Evaporable Moisture Content of Aggregate by Drying 3. SIGNIFICANCE 3.1. The test standard is used to evaluate the coatability of foamed asphalt mixture produced by a laboratory foaming unit based on the aggregate absorption method. The standard is essential for determining the optimum foaming water content that is able to produce foamed asphalt mixture with the best coatability in the laboratory. 4. APPARATUS 4.1. Laboratory foaming unit that produces a specified amount of foamed binder or sampling port in a hot-mix plant that can be controlled to dispense a specified amount of foamed binder. 4.2. Portable asphalt mixer to mix foamed asphalt with aggregates. 4.3. Draft dry oven to short-term age foamed asphalt loose mix prior to compaction.
120 4.4. Water container to soak foamed asphalt loose mix. 4.5. Terry cloth to achieve saturated surface dry (SSD) condition for the aggregate and the foamed asphalt loose mix. 5. PROCEDURE 5.1. Prepare approximately 4,000 g coarse aggregate batch (retained on the 3/8-inch sieve) following the percentages specified in the mix design. Wash and dry them to constant weight per AASHTO T 255. 5.2. Separate the coarse aggregate batch into two samples and record the dry weights of each sample as Wagg OD-1 and Wagg OD-2. Place the first coarse aggregate sample in a metal pan in the oven at 275°F (135°C) and leave overnight. Store the second coarse aggregate sample at room temperature. 5.3. Calculate the amount of binder for the first coarse aggregate sample, based on the total binder content specified in the mix design and the surface area distribution of the combined aggregates. The amount of binder is calculated per Equation 1. (1) Where: Wb-coarse, amount of binder for the first coarse aggregates sample. Wagg OD-1, oven-dry weight of the first coarse aggregates sample. Pb, total binder content of the combined aggregates. SAcoarse, surface area of the coarse aggregate fraction retained on the 3/8-inch sieve. SST, total surface area of the combined aggregates. Ps-coarse, percentage of coarse aggregates retained on 3/8-inch sieve by weight of the combined aggregates. 5.4. Place the mixing bucket and other mixing tools in the oven at least 1 hour prior to foaming. Calibrate the laboratory foaming unit according to the manufacturerâs recommendations. 5.5. Pour the first coarse aggregate batch in the bucket mixer and dispense the calculated amount of foamed binder into the bucket mixer. 5.6. Start the bucket mixer and place the metal paddle in the support. To help achieve complete aggregate coating, while the bucket mixer is turning, push the arm down and to the side of the bucket; a flat spatula can also be introduced into the bucket to scrape the material from the sides and the bottom. Stop the mixer after 60 s. 5.7. Empty the foamed asphalt loose mix into a pan and place inside the oven. Change the temperature of the oven to 240°F (116°C). Keep the loose mix in the oven for 2 hours. 5.8. Take the pan with loose mix out of the oven and let it cool to room temperature in front of a fan. Separate the loose mix sample into two smaller samples of about 1000 g each and record the dry weight of each group as Wloose OD-1 and Wloose OD-2. coarse agg OD SAcoarse coarseSST
121 5.9. Submerge the second coarse aggregate sample and two loose mix samples in a water container at ambient temperature for 60 minutes. 5.10. Damp-dry the coarse aggregate sample and two loose mix samples with a terry cloth to achieve the SSD condition and record the SSD weights as Wagg SSD-2, Wloose SSD-1, and Wloose SSD-2, respectively. 6. CALCULATION OF RESULTS 6.1. Calculate the water absorption of the foamed asphalt loose mix samples per Equations 2â4. (2) (3) (4) 6.2. Determine the mixture coatability index as the relative difference in water absorption between the aggregate sample and the foamed asphalt loose mix sample per Equation 5. (5) 6.3. Foamed asphalt mixtures with higher coatability index values are expected to have a better coatability. 7. REPORT 7.1. The report shall include the following: 7.1.1. Make and model of the laboratory foaming unit or plant foamer. 7.1.2. Source and grade of the binder. 7.1.3. Mix design information. 7.1.4. Foaming water content in percent of dry mass of binder. 7.1.5. Type and dosage of foaming additive (if used). 7.1.6. Coatability index, CI.
