Cover Image

Not for Sale



View/Hide Left Panel
Click for next page ( 165


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 164
164 A Manual for Design of Hot Mix Asphalt with Commentary methods are entered in the worksheet, HMA Tools will use the measured aggregate specific gravity values in estimating the RAP specific gravity values. The estimated water absorption for each RAP stockpile appears in cells C18:F18. RAP Aggregate Specification Properties The specification properties for the RAP aggregates are determined in the same manner as for new aggregates, except that the sand equivalent test, AASHTO T 176, is not performed. The sand equivalent test measures the amount of fine clay particles contained in the aggre- gate. It is an indicator of how well binder will coat the fine aggregate. This test is not needed for RAP material because the RAP aggregate is already coated with binder. Additionally, some of the fine aggregate is lost when the ignition oven or solvent extraction is used to remove the RAP binder. The coarse fraction of the RAP aggregate is tested for fractured faces ("crush count") in accor- dance with ASTM D 5821 and flat and elongated particles in accordance with ASTM D 4791. The fine fraction is tested for angularity in accordance with Method A of AASHTO T 304. Remember that the aggregate consensus properties apply to the blend of all aggregates in the mixture and not the individual stockpiles. Specification properties for the coarse aggregate blend can be computed from stockpile properties based on the proportion of each stockpile used in the HMA. The fine aggregate angularities of the stockpiles can be used to estimate the fine aggregate angularity of the blend. However, because different particle shapes may pack differently when combined, the fine aggregate angularity test, Method A of AASHTO T 304, should be conducted on the final blend of fine aggregates used in the mixture--both from RAP stockpiles and the new fine aggregates used in the mix design. When using HMA Tools to perform a mix design, coarse aggregate specification properties are input in cells C20:F24 of the worksheet "RAP_Aggregates." The data for fractured faces and flat and elongated particles are entered in this range. Up to two user-defined aggregate specification properties can also be entered at the bottom of this cell range. Fine aggregate angularity values for RAP materials are entered in cells C26:F26 of the worksheet "RAP_ Aggregates." As with the coarse aggregate fraction of the RAP, up to two user-defined fine aggregate specification properties can be entered in cells C28:F29. HMA Tools will use values entered in this worksheet to estimate specification properties for the final aggregate blend. These values appear in the worksheet "Trial_Blends" and are also given in the worksheet "Report." RAP Binder Properties When the RAP is limited to a low percentage of the new mixture, 15% or less, it is not necessary to determine the properties of the RAP binder. Small amounts of the aged RAP binder have little effect on the properties of the mixture. When higher percentages of RAP are used, the properties of the RAP binder must be considered through the use of blending charts as described in this section. Some agency specifications adjust the new binder grade to account for the presence of RAP. These adjustments are based on analyses similar to those presented in this section using typical properties of local RAP binders and available new binders. Extraction and Recovery to Determine RAP Binder Properties To determine the RAP binder properties, the binder from the RAP must be extracted by sol- vent extraction, then recovered from the solvent. Historically AASHTO T 164 has been used

OCR for page 164
Reclaimed Asphalt Pavement 165 for solvent extraction and the Abson recovery method, AASHTO T 170, has been used to Table 9-7. recover the binder for testing. There is general consensus among asphalt technologists that this Recommended combination of tests alters the properties of the recovered binder. During the Strategic High- sample size for RAP way Research Program (SHRP), a new method for extracting and recovering binders that does binder extraction not alter the properties of the recovered binder was developed. This method has been stan- and recovery. dardized as AASHTO T 319 and is the extraction and recovery method recommended for RAP RAP Binder Recommended binder analysis. Content, % Sample Size, g 3.0 1833 When using AASHTO T 319 to extract and recover RAP binder for testing, it is extremely 3.2 1719 3.4 1618 important to have the appropriate sample size. At least 50 g of recovered RAP binder are needed 3.6 1528 to perform the testing required to develop a blending chart. AASHTO T 319 becomes inefficient 3.8 1447 if the amount of binder recovered exceeds 60 g. Fortunately, the binder content of the RAP was 4.0 1375 4.2 1310 determined from the stockpile variability analysis, and this binder content can be used to deter- 4.4 1250 mine the size of the sample needed for extraction and recovery. Table 9-7 lists recommended 4.6 1196 RAP sample sizes based on the binder content of RAP. This table is based on a target of 55 g of 4.8 1146 5.0 1100 recovered binder. 5.2 1058 5.4 1019 5.6 982 Recovered RAP Binder Testing 5.8 948 6.0 917 Figure 9-8 is a flowchart of the RAP binder testing required to prepare a blending chart for a specific RAP binder. These are the same tests used for the performance grading of asphalt binders EXTRACT AND RECOVER 50 to 60 g of RAP BINDER AASHTO T319 DETERMINE AS-RECOVERED HIGH CONDITION 35 g OF BINDER IN TEMPERATURE TC ROLLING THIN FILM OVEN TEST AASHTO T315 (RTFOT) AASHTO T240 DETERMINE RTFOT HIGH TEMPERATURE TC AASHTO T315 DETERMINE RTFOT INTERMEDIATE TEMPERATURE TC AASHTO T315 DETERMINE RTFOT LOW TEMPERATURE TC FOR STIFFNESS AASHTO T313 DETERMINE RTFOT LOW TEMPERATURE TC FOR m-VALUE AASHTO T313 Figure 9-8. Flowchart for RAP binder testing.

OCR for page 164
166 A Manual for Design of Hot Mix Asphalt with Commentary Table 9-8. Criteria for determining critical temperatures. Critical Temperature Criteria Sample High Pavement Temperature G*/sin =1.00 kPa As Recovered G*/sin = 2.20 kPa RTFOT Aged Intermediate Pavement Temperature G*sin = 5000 kPa RTFOT Aged Low Pavement Temperature S = 300 MPa RTFOT Aged m = 0.300 RTFOT Aged as discussed in Chapter 3. Laboratories equipped for performance grading of asphalt binders can perform the testing required to characterize RAP binders for blending chart analysis. The RAP binder testing involves determining the critical high, intermediate, and low pave- ment temperatures, TC, for the recovered RAP binder. The critical temperature is the temper- ature where the properties of the RAP binder meet the specification requirements contained in the performance graded binder specification, AASHTO M 320. These requirements are summarized in Table 9-8. For high and low pavement temperature conditions, two criteria must be considered. The critical temperature for the high pavement temperature condition is the lower of the two, while that for the low pavement temperature condition is the higher of the two. This testing, also known as determining the "true" or "continuous" grade of the binder, is performed in the same manner as grading a new binder, except the intermediate and low tem- perature properties are measured on residue from the rolling thin film oven test (RTFOT), AASHTO T 240, instead of residue from the pressure aging vessel (PAV), AASHTO R 28. Research conducted in NCHRP Project 9-12 concluded that the AASHTO M 320 properties of a blend of RAP and new binder could be accurately estimated from the as-recovered and RTFOT aged RAP binder without the need for performing PAV aging of the recovered RAP binder. This finding significantly reduces the testing time and the amount of recovered binder needed for the testing. Using HMA Tools to Grade Asphalt Binders Recovered From RAP The calculations involved in grading binders recovered from RAP materials can be tedious to apply and are not included in this manual. The interested reader can find a detailed procedure for performing these and related calculations in Appendix A of AASHTO M 323. HMA Tools can be used not only as an aid in grading RAP binders, but also in performing all binder grade calculations typically needed when designing HMA mixtures containing RAP. To use HMA Tools to perform grading calculations for binders recovered from RAP, binder test data are entered in the worksheet "RAP_Binders." The final binder grades are given in cells D73, H73, L73, and P73 for each of up to four RAP stockpiles. The continuous grade for high, intermediate, and low temperatures are given immediately below in cells D75:D77, H75:H77, L75:L77 and P75:P77. Because continuous grading information is needed for new binders used in a RAP mix design in order to determine the grade of the blended binder in the HMA mixture, grading data for new binders must also be entered in HMA Tools when RAP designs are being prepared (unless no more than 15% RAP is being used, in which case binder grading information is not required). Binder grading data for new binders used in a mix design are entered in the worksheet "Binders." As with the worksheet "RAP_Binders," HMA Tools performs all needed grading calculations, and the final grading information appears at the bottom of the worksheet.

OCR for page 164
Reclaimed Asphalt Pavement 167 Example Problem 9-4. Critical Temperatures for RAP Binder A sample of RAP binder was extracted, recovered, and tested to provide data for a blending chart analysis. Table 9-9 presents results of tests on the RAP binder as-recovered and after RTFOT conditioning. Determine the critical high, inter- mediate, and low temperatures for the RAP binder. Table 9-9. Test results for extracted RAP binder for example 3. Critical Condition Property Method Temperature Test Result Temperature As- G*/sin AASHTO 88 C 1.57 kPa High Recovered T 315 94 C 0.76 kPa RTFOT G*/sin AASHTO 88 C 4.06 kPa T 315 94 C 2.14 kPa Intermediate RTFOT G*/sin AASHTO 25 C 6,414 kPa T 315 28 C 4,701 kPa -18 C 440 MPa RTFOT S AASHTO -12 C 229 MPa Low T 313 -6 C 120 MPa -18 C 0.220 RTFOT m AASHTO -12 C 0.281 T 313 -6 C 0.336 Solution The binder test data from Table 9-9 are entered in the worksheet "RAP_Binders" in the appropriate cells in columns D and E. The continuous critical high temperature is given as 91.7C in cell E75. The continuous critical intermediate temperature is 27.4C and is given in cell E76. The continuous critical low temperature is -9.8C, and is given in cell E77. The final binder grade for the recovered binder is PG 88-16, given in cell E73. Note that HMA Tools reports the binder grade by including the intermediate temperature grade in parentheses: PG 88-(28)-16. This is done because some agencies have requirements for intermediate temperature grade, and report- ing the grade in this way makes it easy to determine if such requirements are met. Blending Charts For RAP Binders Linear blending charts are used to estimate the properties of blends of new binder and RAP binder. Figure 9-9 is a schematic of a linear blending chart. Separate blending charts for high, inter- mediate, and low temperature properties are used. Equation 9-3 describes the line in Figure 9-9. % RAPB Tc ( Blend ) = Tc ( New ) + (Tc ( RAP ) - TC ( New )) (9-3) 100 where Tc(Blend) = critical temperature for the blend of RAP and new binder Tc(New) = critical temperature for the new binder Tc(RAP) = critical temperature for the RAP binder %RAPB = percentage of total binder content obtained from the RAP, wt %

OCR for page 164
168 A Manual for Design of Hot Mix Asphalt with Commentary 0 -5 Critical Temperature, C -10 Tc(RAP) -15 Tc(New) -20 -25 0 10 20 30 40 50 60 70 80 90 100 % RAP Binder Figure 9-9. Linear blending chart. The blending charts are based on the percentage of the total binder in the mixture that is from the RAP. As discussed earlier, the RAP added to a mixture includes both RAP aggregate and RAP binder. Because computer spreadsheets are now almost universally used to perform the calculations needed to perform HMA mix designs, including the potentially tedious calculations required when the design includes more than 15% RAP, it is not necessary to construct blending charts as part of the mix design process. If a blending chart is needed for an HMA mix design containing RAP, a detailed procedure can be found in AASHTO M 323. There are two different approaches to designing HMA mixtures with RAP so that the result- ing blended binder meets the required grade. The first is to establish the RAP content, and then determine the performance grade of the new binder needed to make sure the blended binder in the final mix is the proper grade. The second approach is to select the new binder grade, and then determine the required RAP content to ensure that the blended binder is the proper grade. A sur- prising twist on this second approach is that the required RAP content can be a maximum or a minimum. A maximum RAP content can occur when a relatively stiff new binder is used, so that addition of too much RAP will make the blended binder too stiff to meet the performance grade requirements at intermediate and/or low temperatures. A minimum RAP content can occur when a relatively soft new binder is used, in which case enough RAP must be added to provide sufficient stiffening to the blended binder so that high-temperature grade requirements are met. In some cases, there may be both minimum and maximum RAP content requirements. HMA Tools provides solutions for both types of RAP content calculation. Once appropriate binder grade information is entered along with the mix composition (aggregate blend data and volumetric data), HMA Tools will calculate the resulting blended binder grade and also estimate the minimum and maximum RAP contents based on binder grade requirements. If RAP from more than one stockpile is used in the mix design, HMA Tools assumes that the relative propor- tions of material in the RAP blend will remain constant as the overall RAP content varies. Two example problems below show how HMA Tools can be used in performing both types of binder grade calculations when designing HMA mixtures containing RAP.

OCR for page 164
Reclaimed Asphalt Pavement 169 Example Problem 9-5. Selection of a New Binder Grade for an HMA Mix Design Containing RAP The RAP binder from Example 4 will be used in an HMA mixture. The RAP will be added to the mixture at 30% of the aggregate blend by weight. The RAP has a binder content of 4.4%, and the HMA mixture has a binder content of 5.2%. Determine the new binder grade that should be used so that the blended binder meets the specification requirements for PG 64-22. Solution Information on the required binder grade is entered in the worksheet "Blended_Binders" in cells C5:C8--performance grade 64-22, high temperature grade 64C, intermediate temperature grade 25C and low temperature grade -22C. The binder content of 5.20% is entered in cell C11, and an absorption value of 0.0 is entered in cell C12. Since only one RAP is being used, 100 is entered in cell C16, and cells C17:C19 are left blank. In cell C22 the RAP binder content of 4.40% is entered, with an absorption value of 0.0 entered in cell D22. Since only one RAP stockpile is being used, cells C23:D25 are left blank. The RAP binder being used is the same as already entered in the worksheet "RAP_Binders," so the grading information (in the form of critical temperatures) appears in cells H30:J30. These values are then copied into cells C30:E30. Again, if more RAP stockpiles were used, additional grading information could be entered in cells C31:E33, but only one RAP is being used in this example so these cells are left blank. The RAP content of 30% by weight of total RAP plus aggregate is entered in cell C70. The required new binder grade of PG 58-28 is reported in the worksheet "Blended_ Binders" in cell C80. Note that the required critical temperatures for the new binder are given in cells C76:C78 as follows: high critical temperature--57.7C, intermediate critical temperature--22.9C, and low critical temperature--15.3C. As in many other locations, HMA Tools reports the required grade by including the intermediate temperature grading of 19C in parentheses, so cell C80 actually reads "58-(19)-28." The worksheet "Blended_Binders" is designed to only provide one binder in this cell, although several others would typically meet the require- ments. The grade reported in cell C80 represents that with the lowest high temper- ature grade and the highest low temperature grade. For instance, in this example a PG 64-28 binder would also meet the grade requirements. When determining whether or not performance grades other than that listed in cell C80 would meet the requirements for an HMA design containing RAP, the engineer or technician must make certain that not only the high and low critical temperature require- ments are met, but also that the intermediate critical temperature requirement (cell C77) is met. In this example, a PG 64-28 binder would have a maximum intermediate critical temperature of 22C and would therefore meet the speci- fied grading requirements. However, a PG 70-28 binder has a maximum interme- diate critical temperature of 25C, which is greater than the calculated maximum intermediate critical temperature of 22.9C and therefore should not be used in this mix design.