Improved Test Methods for Specific Gravity and Absorption of Coarse and Fine Aggregate (2015)

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53 Ruggedness Study Plan The objective of this ruggedness study was to evaluate the sensitivity of the proposed test methods to the changes in lev- els of operating and environmental factors. The results of rug- gedness testing were used to eliminate or reduce the sources of variation, which would ensure better precision of test results and establish appropriate ranges of operating parameters for standardizing the test methods. This ruggedness study was conducted in accordance with ASTM C1067: Standard Practice for Conducting a Rugged- ness or Screening Program for Test Methods for Construction Materials. The experimental plan involved determination of seven sources of variation, each with potential to influence test results. Each variable factor was assigned high and low values, which represented the tolerance extremes of the variable fac- tor allowed in the test procedure. The experimental plan used in this study was based on the seven-factor Plackett-Burman design presented in ASTM C1067. Depending on the significance of the interaction between variable factors, the ruggedness experiment can be conducted as a full factorial or fractional factorial. Since the test param- eters in the specific gravity measurement were not consid- ered highly interactive, a fractional factorial experiment was considered adequate. Following the ASTM C1067 procedure for a design of fractional factorial, eight determinations (test conditions) were considered sufficient for obtaining valid and objective conclusions with a seven-factor experiment. The development of a ruggedness study as presented in ASTM C1067 included the following steps: • Identifying seven variable factors for each test method; • Determining high and low levels for each factor; • Setting up 8 combinations of 14 factor levels (7 factors × 2 levels) with 2 replicates for each combination; • Identifying at least three laboratories to participate in the study; and • Determining three to five materials that cover the range of materials properties to which the test method is applicable. Following the above steps, plans for ruggedness testing of revised AASHTO T 85 and T 84 were arranged. Details of each plan are presented in the following sections. Variable Factors and Their Levels Considered for Ruggedness Study Variable factors selected for ruggedness testing were based on their probable importance to the final test results. The fac- tors that were most likely to have the greatest effect on the variability of each proposed test method were included in the ruggedness study. The low and high levels of each variable fac- tor were determined based on the allowable tolerance of the factor specified in the test methods. The allowable tolerance of each factor accounted for probable or reasonable variability that was anticipated in practice. Based on the revised AASHTO T 85 and T 84 procedures, different drying and soaking methods may be used for aggre- gate with absorption < or ≥ 2 percent. Thus, seven variable factors were identified for testing aggregate materials with absorption < and ≥ 2 percent. Tables 4-1 and 4-2 provide seven variable factors and their minimum and maximum levels that were anticipated to have the most influence on results of AASHTO T 85 for coarse aggregate materials with absorption < and ≥ 2 percent, respec- tively. Tables 4-3 and 4-4 provide seven variable factors and their minimum and maximum levels that were anticipated to have the most influence on results of AASHTO T 84 for fine aggregate materials with absorption < and ≥ 2 percent, respectively. The levels included quantitative values, such as soak time, or non-quantitative properties, such as drying the aggregate sample using a dry or damp towel. If testing with the selected levels of a variable factor yielded a significant variation in the C H A P T E R 4 Ruggedness Study

54 ID Variable AASHTO T 85 Requirement Comments Low Value High Value A Section 7.2 – Aggregate size Test materials retained on the No. 4 sieve Some aggregates contain significant amount of material finer than No. 4 +#8 +#4 B Section 8.1 – Moisture condition Dry the sample to a constant mass Can the sample be tested without initial oven drying? Oven dried natural condition C Section 8.1 – Cooling time Cool in air for 1 to 3 hrs until comfortable to handle (~50°C) Can the sample be soaked immediately without cooling? 0 3 hrs (~50°C) D Section 8.1 – Soak time Vacuum-soak for 10 ± 1 min. Does this range need to be tighter? 9 min. 11 min. E Section 8.1 – Vacuum pressure 3.7 ± 0.3 kPa (27.5 ± 2.5 mm Hg) Does this range need to be tighter? 3.3 - 3.6kPa 3.8 - 4.1kPa F Section 8.4 – Water temperature 23 ± 1.7°C 23 ± 2°C (ASTM) Does the AASHTO range need to be tighter? 21 - 22°C 24 - 25°C G Section 8.5 – Cooling time Cool in air for 1 to 3 hrs until comfortable to handle (~50°C) Can the sample be weighed immediately without cooling? 0 3 hrs (~50°C) Table 4-1. Seven factors for ruggedness testing of AASHTO T 85 for coarse aggregate with absorption less than 2 percent. ID Variable AASHTO T 85 Requirement Comments Low Value High Value A Section 7.2 – Aggregate size Test materials retained on the No. 4 sieve Some aggregates contain significant amount of material finer than No. 4 +#8 +#4 B Section 8.1 – Moisture condition Dry the sample to a constant mass Can the sample be tested without initial oven drying? oven dried natural condition C Section 8.1 – Cooling time Cool in air for 1 to 3 hrs until comfortable to handle (~50°C) Can the sample be soaked immediately without cooling? 0 3 hrs (~50°C) D Section 8.1 – Soak time Immerse in water for 15 to 19 hrs (24 ± 4 hrs for ASTM) Does this range need to be tighter? 15 hrs 20 hrs E Section 8.3 – Drying sample Dry the sample in a large absorbent cloth to SSD Might need to specify if it is a dry or damp cloth dry cloth damp cloth F Section 8.4 – Water temperature 23 ± 1.7°C 23 ± 2°C (ASTM) Does the AASHTO range need to be tighter? 21 - 22°C 24 - 25°C G Section 8.5 – Cooling time Cool in air for 1 to 3 hrs until comfortable to handle (~50°C) Can the sample be weighed immediately without cooling? 0 3 hrs (~50°C) Table 4-2. Seven factors for ruggedness testing of AASHTO T 85 for coarse aggregate with absorption greater than 2 percent. ID Variable AASHTO T 84 Requirement Comments Low Value High Value A Section 7.1 – Aggregate size Removal of P200 if required Does the P200 content affect test results? 0% as is B Section 7.1 – Aggregate size Remove material passing the No. 200 sieve Should P200 be removed using dry sieving or washing? dry sieving washing C Section 7.1.1 – Moisture condition Dry the sample to a constant mass Can the sample be tested without initial oven drying? oven dried natural condition D Section 7.1.1 – Soak time Vacuum-soak for 10 ± 1 min. Does this range need to be tighter? 9 min. 11 min. E Section 7.2.1 – Cone test Apply 25 blows at once or distribute 25 blows in 10, 10, 3, and 2 drops after filling the cone Do the original and provisional cone tests affect results? 25 blows at once 25 blows in four sets F Section 8.2 – Agitation Manually or mechanically agitate the sample to eliminate air bubbles Do manual and mechanical methods (AASHTO T 209) yield statistically different results? manual mech agitation G Section 8.3 – Cooling time Cool in air for 1 ± 0.5 hrs until comfortable to handle (~50°C) Can the sample be weighed immediately without cooling? 0 1.5 hrs (~50°C) Table 4-3. Seven factors for ruggedness testing of AASHTO T 84 for fine aggregate with absorption less than 2 percent.

55 test results, the difference between the minimum and maxi- mum levels of the factor would be reduced. Experimental Design for Ruggedness Testing For ruggedness testing, test data were collected for specific combinations of the variable factors and their levels. Each combination resulted from simultaneous changes in the vari- able factors. Table 4-5 provides the Plackett-Burman design for seven factors and their two levels, which has been found most effective for a seven-factor fractional factorial design as presented in ASTM C1067. The seven factors were assigned letter designations, A to G, and the two levels of each factor were designated with upper and lower cases. Each variable factor changed between two levels to evaluate the effect of the change in factor levels on the test results. Based on the Plackett-Burman design illustrated in Table 4-5, experimental plans for ruggedness testing of AASHTO T 85 and AASHTO T 84 (Tables 4-6 through 4-9) were developed using the seven factors and their levels pro- vided in Tables 4-1 through 4-4, respectively. Two replicates were tested for each of the eight combinations, resulting in a total of 16 determinants for each material. Materials for Ruggedness Testing Table 4-10 shows the materials proposed for use in the test- ing plans shown in Tables 4-6 through 4-9. Considering two materials for each combination of test method and absorp- tion level, a total of 128 tests (8 combinations × 2 replicates × 4 test method/absorption levels × 2 materials) were con- ducted in each laboratory. Participating Laboratories for Ruggedness Testing As suggested in ASTM C1067, three laboratories partici- pated in the ruggedness study. The laboratories were NCAT, the AASHTO Advanced Pavement Research Laboratory (AAPRL), and the National Institute for Science and Technology (NIST). The test samples were prepared in the Proficiency Sample Pro- gram (PSP) facility of the AASHTO Materials Reference Labo- ratory (AMRL) to ensure that the samples were consistent and ID Variable AASHTO T 84 Requirement Comments Low Value High Value A Section 7.1 – Aggregate size Removal of P200 if required Does the P200 content affect test results? 0% as is B Section 7.1 – Aggregate size Remove material passing the No. 200 sieve Should P200 be removed using dry sieving or washing? dry sieving washing C Section 7.1.1 – Soak type Immerse or add at least 6% moisture to the sample Do these methods yield significantly different results? 6% moisture immerse D Section 7.1.1 – Soak time Immerse in water for 15 to 19 hrs (24 ± 4 hrs for ASTM) Does this range need to be tighter? 15 hrs 20 hrs E Section 7.2.1 – Cone test Apply 25 blows at once or distribute 25 blows in 10, 10, 3, and 2 drops after filling the cone Do the original and provisional cone tests affect results? 25 blows at once 25 blows in four sets F Section 8.2 – Agitation Manually or mechanically agitate the sample to eliminate air bubbles Do manual and mechanical methods (AASHTO T 209) yield statistically different results? manual mech agitation G Section 8.3 – Cooling time Cool in air for 1 ± 0.5 hrs until comfortable to handle (~50°C) Can the sample be weighed immediately without cooling? 0 1.5 hrs (~50°C) Table 4-4. Seven factors for ruggedness testing of AASHTO T 84 for fine aggregate with absorption greater than 2 percent. Factors Combination Number 1 2 3 4 5 6 7 8 A a a a a A A A A B b b B B b B B B C C c C c C C C c D D D d d d D D D E e E e E E E E e F F f f F F F f F G G g g G g G G g Table 4-5. Ruggedness experimental plan for seven factors and two levels.

56 No. Factor Determinations (Test Combinations) 1 2 3 4 5 6 7 8 A Section 7.2 – Aggregate size +#8 +#8 +#8 +#8 +#4 +#4 +#4 +#4 B Section 8.1 – Moisture condition oven dried oven dried natural natural oven dried oven dried natural natural C Section 8.1 – Cooling time 3 hrs 0 3 hrs 0 3 hrs 0 3 hrs 0 D Section 8.1 – Soak time 11 min. 11 min. 9 min. 9 min. 9 min. 9 min. 11 min. 11 min. E Section 8.1 – Vacuum pressure 3.3 -3.6kPa 3.8 -4.1kPa 3.3 -3.6kPa 3.8 -4.1kPa 3.8 -4.1kPa 3.3 -3.6kPa 3.8 -4.1kPa 3.3 -3.6kPa F Section 8.4 – Water temperature 24 - 25°C 21 - 22°C 21 - 22°C 24 - 25°C 24 - 25°C 21 - 22°C 21 - 22°C 24 - 25°C G Section 8.5 – Cooling time 3 hrs 0 0 3 hrs 0 3 hrs 3 hrs 0 Table 4-6. Experimental design for ruggedness testing of AASHTO T 85 for coarse aggregate with absorption less than 2 percent. No. Factor Determinations (Test Combinations) 1 2 3 4 5 6 7 8 A Section 7.2 – Aggregate size +#8 +#8 +#8 +#8 +#4 +#4 +#4 +#4 B Section 8.1 – Moisture condition oven dried oven dried natural natural oven dried oven dried natural natural C Section 8.1 – Cooling time 3 hrs 0 3 hrs 0 3 hrs 0 3 hrs 0 D Section 8.1 – Soak time 20 hrs 20 hrs 15 hrs 15 hrs 15 hrs 15 hrs 20 hrs 20 hrs E Section 8.3 – Drying sample dry cloth damp cloth dry cloth damp cloth damp cloth dry cloth damp cloth dry cloth F Section 8.4 – Water temperature 24 - 25°C 21 - 22°C 21 - 22°C 24 - 25°C 24 - 25°C 21 - 22°C 21 - 22°C 24 - 25°C G Section 8.5 – Cooling time 3 hrs 0 0 3 hrs 0 3 hrs 3 hrs 0 Table 4-7. Experimental design for ruggedness testing of AASHTO T 85 for coarse aggregate with absorption greater than 2 percent. No. Factor Determinations (Test Combinations) 1 2 3 4 5 6 7 8 A Section 7.1 – Aggregate size 0% 0% 0% 0% P200 as is P200 as is P200 as is P200 as is B Section 7.1 – Aggregate size dry sieve dry sieve wash wash dry sieve dry sieve wash wash C Section 7.1.1 – Moisture condition natural oven dried natural oven dried natural oven dried natural oven dried D Section 7.1.1 – Soak time 11 min. 11 min. 9 min. 9 min. 9 min. 9 min. 11 min. 11 min. E Section 7.2.1 – Cone test 25 blows at once 25 blows in 4 sets 25 blows at once 25 blows in 4 sets 25 blows in 4 sets 25 blows at once 25 blows in 4 sets 25 blows at once F Section 8.2 – Agitation mech agitation manual manual mech agitation mech agitation manual manual mech agitation G Section 8.3 – Cooling time 1.5 hrs 0 0 1.5 hrs 0 1.5 hrs 1.5 hrs 0 Table 4-8. Experimental design for ruggedness testing of AASHTO T 84 for fine aggregate with absorption less than 2 percent. No. Factor Determinations (Test Combinations) 1 2 3 4 5 6 7 8 A Section 7.1 – Aggregate size 0% 0% 0% 0% P200 as is P200 as is P200 as is P200 as is B Section 7.1 – Aggregate size dry sieve dry sieve wash wash dry sieve dry sieve wash wash C Section 7.1.1 – Soak type immerse 6% moisture immerse 6% moisture immerse 6% moisture immerse 6% moisture D Section 7.1.1 – Soak time 20 hrs 20 hrs 15 hrs 15 hrs 15 hrs 15 hrs 20 hrs 20 hrs E Section 7.2.1 – Cone test 25 blows at once 25 blows in 4 sets 25 blows at once 25 blows in 4 sets 25 blows in 4 sets 25 blows at once 25 blows in 4 sets 25 blows at once F Section 8.2 – Agitation mech agitation manual manual mech agitation mech agitation manual manual mech agitation G Section 8.3 – Cooling time 1.5 hrs 0 0 1.5 hrs 0 1.5 hrs 1.5 hrs 0 Table 4-9. Experimental design for ruggedness testing of AASHTO T 84 for fine aggregate with absorption greater than 2 percent.

57 homogeneous. After the samples had been prepared, sample numbers were randomized utilizing the same procedure used for proficiency samples before they were sent to the testing laboratories. A total of 384 tests (128 tests/laboratory × 3 labo- ratories) were conducted in the three laboratories. Analysis Method Test results were analyzed according to ASTM C1067 standard practice. ASTM C1067 contains details about cal- culations necessary for determining the significance of the variable factors for each test method. The analysis involved the determination of the error variance corresponding to each of the seven factors. The variation in the response vari- able (specific gravities and absorption) resulted from the low levels and high levels of the seven variable factors and was evaluated using an F-test. To perform an F-test, an F-statistic, which is the ratio of the error variance in test result from one factor to the error variance in test results from all the factors, was calculated using Equation 4-1: FA A Total (4.1)= σ σ where: FA = F-statistic for the effect of Factor A sA = error variance in the test property due to experi- mental Factor A sTotal = pooled error variance in the test property due to all main factors (A to G) For a given variable factor (A to G), the calculated F-statistic was compared to a critical F-value. If the calculated F-statistic was greater than the critical F-value, the main factor was considered to have a significant effect on the measured test property with the main factor being varied between its low and high values. ASTM C1067 recommends the effect of changing a factor between low and high levels to be consid- ered significant at a probability of 5 percent. The critical value determined from the F-distribution table for this level of sig- nificance was 5.59. Therefore, the effect of changing a factor between low and high levels was considered significant if the F-statistic of that factor was greater than or equal to 5.59. Results and Analysis As discussed in the ruggedness study plan, four coarse aggre- gates and four fine aggregates were tested. Detailed testing data are included in Appendix I, which is available on the project web page. A summary of the analysis is provided in this section. Ruggedness Study for Revised AASHTO T 85 The ruggedness study for the revised AASHTO T 85 procedure was conducted in the three laboratories (NCAT, AAPRL, and NIST) using four aggregates (granite, gravel, limestone, and blast furnace slag) that covered a wide range of water absorption. The granite material had the lowest water absorption of 0.5 percent, and the slag aggregate had the highest water absorption of 2.7 percent. A test param- eter was found significant in a lab when its F-statistic was greater than Fcritical (5.59). Tables 4-11, 4-12, 4-13, and 4-14 show F-statistics for Gsb, Gssd, Gsa, and water absorption, respectively, of the four coarse aggregates tested by the three laboratories. In Tables 4-11 through 4-14, NS means “Not Significant,” and the shaded cells show the F-values exceed- ing the critical F-value of 5.59. Tables 4-15 and 4-16 combine the analysis results shown in Tables 4-11 through 4-14. They show the percentage of times each ruggedness factor was found to be significant in Tables 4-11 through 4-14. ASTM C1067 did not provide a quantitative method for selecting significant test param- eters that need to be changed based on the statistical analysis shown in Tables 4-11 through 4-14. Thus, in this analysis, a test parameter or ruggedness factor was considered signifi- cant if it was found to be statistically significant in at least two tests (or at least 33 percent of the tests). Based on the analysis results shown in Tables 4-15 and 4-16, the following observations were made regarding AASHTO T 85: • Coarse aggregate samples retained on the 4.75-mm (No. 4) sieve or the 2.36-mm (No. 8) sieve prepared according to Absorption Coarse Aggregate (AASHTO T 85) Fine Aggregate (AASHTO T 84) Low (< 2%) 1. Granite (abs = 0.5%), Vulcan Materials, Richmond, VA 2. Gravel (abs = 1.4%), Aggregate Industry Rockville, MD (for experiment in Table 4.6) 1. Granite (abs = 0.4%), Vulcan Materials, Richmond, VA 2. Limestone (abs = 1.4%), Aggregate Industry, Rockville, MD (for experiment in Table 4.8) High (> 2%) 3. Limestone (abs = 2.3%), Vulcan Materials, Tuscumbia, AL 4. BF Slag (abs = 2.7%), Alabaster, AL (for experiment in Table 4.7) 3. Limestone (abs = 2.2%), Vulcan Materials, Tuscumbia, AL 4. BF Slag (abs = 2.2%), Alabaster, AL (for experiment in Table 4.9) Table 4-10. Proposed materials for ruggedness testing.

58 Absorption Level Material Lab Avg. Absorption A B C D E F G < 2% Granite AAPRL 0.5% NS NS NS NS NS 8.9 NS NCAT 0.5% NS NS NS NS NS NS NS NIST 0.5% NS NS NS NS NS NS NS Gravel AAPRL 1.4% 6.2 NS NS 9.9 NS 11.0 NS NCAT 1.4% NS NS NS NS NS NS NS NIST 1.4% 13.4 16.3 NS NS NS 19.6 NS 2% AL-LMS AAPRL 2.3% NS NS NS NS NS NS NS NCAT 2.3% NS NS NS NS NS 6.3 NS NIST 2.3% NS NS NS NS 7.6 NS NS AL-Slag AAPRL 2.7% NS NS NS NS 8.8 NS NS NCAT 2.7% NS NS NS NS NS NS NS NIST 2.7% NS NS NS NS NS NS NS Table 4-11. F-statistics for Gsb of coarse aggregates. Absorption Level Material Lab Avg. Absorption A B C D E F G < 2% Granite AAPRL 0.5% NS NS NS NS NS 16.3 NS NCAT 0.5% NS NS NS NS NS NS NS NIST 0.5% NS NS NS NS NS NS NS Gravel AAPRL 1.4% NS NS NS 7.6 NS 6.7 NS NCAT 1.4% NS NS NS NS NS NS NS NIST 1.4% 7.4 NS NS NS NS 9.9 NS 2% AL-LMS AAPRL 2.3% NS 37.7 NS NS NS NS NS NCAT 2.3% NS NS NS NS NS 5.9 NS NIST 2.3% NS NS NS NS NS NS NS AL-Slag AAPRL 2.7% NS NS NS NS NS NS NS NCAT 2.7% NS NS 13.2 NS NS 7.0 NS NIST 2.7% NS NS 9.3 NS NS NS NS Table 4-12. F-statistics for Gssd of coarse aggregates. Absorption Level Material Lab Avg. Absorption A B C D E F G < 2% Granite AAPRL 0.5% 5.9 22.2 NS NS NS 17.6 17.3 NCAT 0.5% NS NS NS NS NS NS NS NIST 0.5% NS 9.4 NS NS NS NS 14.3 Gravel AAPRL 1.4% NS NS NS NS NS NS 6.1 NCAT 1.4% NS 6.1 NS NS NS NS NS NIST 1.4% NS NS NS NS NS NS NS 2% AL-LMS AAPRL 2.3% NS 203.3 NS NS NS 14.1 6.8 NCAT 2.3% NS NS NS NS 8.3 NS NS NIST 2.3% NS 8.2 NS NS NS NS NS AL-Slag AAPRL 2.7% NS NS 6.4 NS NS NS 7.4 NIST 2.7% NS NS 19.1 NS NS 11.6 NS NCAT 2.7% NS 36.7 36.4 NS NS 40.3 NS Table 4-13. F-statistics for Gsa of coarse aggregates. Absorption Level Material Lab Avg. Absorption A B C D E F G < 2% Granite AAPRL 0.5% 7.2 19.4 NS NS NS NS 34.2 NCAT 0.5% NS NS NS NS NS NS 6.3 NIST 0.5% NS 43.8 10.5 NS NS NS 24.6 Gravel AAPRL 1.4% 18.8 NS NS 13.3 NS 23.2 NS NCAT 1.4% NS NS NS NS NS NS NS NIST 1.4% 28.2 67.0 7.0 NS 6.0 47.4 NS 2% AL-LMS AAPRL 2.3% NS 44.1 NS NS NS NS 6.8 NCAT 2.3% NS NS NS NS NS 6.1 NS NIST 2.3% NS 43.9 NS NS 19.2 NS 7.6 AL-Slag AAPRL 2.7% 54.0 NS NS NS 49.0 NS 31.6 NCAT 2.7% NS 132.6 63.0 12.9 NS 121.9 NS NIST 2.7% NS NS 49.0 NS NS 68.3 NS Table 4-14. F-statistics for water absorption of coarse aggregates.

59 Section 7.2 yield statistically different water absorption results for low absorption (< 2 percent) coarse aggregates. • The effect of using a coarse aggregate oven-dried sample or in its in-situ moisture condition in Section 8.1 is signifi- cant on Gsa and water absorption results. • Also in Section 8.1, an oven-dried sample can be submerged in water at room temperature immediately, when it is safe, without waiting for the sample to cool to a temperature (approximately 50°C) that is comfortable to handle. However, doing so significantly affects water absorption results for low absorption aggregate, and Gssd, Gsa, and water absorption results for high absorption aggregates. • In Section 8.1, a low absorption (< 2 percent) coarse aggre- gate sample can be vacuum soaked in water for a period of 9 to 11 minutes at a residual pressure of 3.4 to 4.0 kPa. Also, a high absorption (≥ 2 percent) coarse aggregate sample can be soaked in water for a period of 15 to 19 hours. The low and high levels of the soak times and vacuum pressure were found to be appropriate. • The effect of using a dry cloth versus a wet cloth in Sec- tion 8.2 was found to be significant on the Gsb and absorption results. • The water bath temperature in Section 8.3 is a significant test parameter for determining Gsb, Gssd, and absorption of low absorption coarse aggregates and for determining Gssd, Gsa, and water absorption of high absorption coarse aggregates. • In Section 8.4, the final mass of an oven-dried aggregate sample can be determined immediately after it is removed from the oven when it is safe or after it has been cooled down to a temperature (approximately 50°C) that is com- fortable to handle. However, these methods yield statisti- cally different Gsa and absorption results. Since Gsb and Gssd are used in PCC and AC mix design and production, the test parameters significantly affecting these test properties may need to be tightened. Based on the ruggedness results summarized in Tables 4-15 and 4-16, there are four significant test parameters. Therefore, the following changes are proposed for AASHTO T 85: • In Section 7.2, testing conducted on aggregate samples retained on the 4.75-mm (No. 4) sieve and on the 2.36-mm (No. 8) sieve would yield significantly different testing results. Since the two test samples have different lower lim- its of aggregate size, they may have different surface void structures, affecting their absorption capacity and specific gravities. Thus, testing should be conducted on the same aggregate size (retained on either the 4.75-mm [No. 4] sieve or the 2.36-mm [No. 8] sieve) in the agency’s and contrac- tor’s laboratories. • In Section 8.1, an oven-dried sample should be allowed to cool to a temperature (approximately 50°C) that is com- fortable to handle before being submerged in water at the ID Variable Low Value High Value Gsb Gssd Gsa Abs A Section 7.2 – Aggregate size +#8 +#4 33 17 17 50 B Section 8.1 – Moisture condition oven dried in-situ moisture 17 0 50 50 C Section 8.1 – Cooling time 0 3 hrs 0 0 0 33 D Section 8.1 – Soak time 9 min. 11 min. 17 17 0 17 E Section 8.1 – Vacuum pressure 3.3 - 3.6kPa 3.8 - 4.1kPa 0 0 0 17 F Section 8.4 – Water temperature 21 - 22°C 24 - 25°C 50 50 17 33 G Section 8.5 – Cooling time 0 3 hrs 0 0 50 50 Table 4-15. Percentages of time each ruggedness factor in AASHTO T 85 was found significant when testing low absorption (<2 percent) coarse aggregates (granite and gravel). ID Variable Low Value High Value Gsb Gssd Gsa Abs A Section 7.2 – Aggregate size +#8 +#4 0 0 0 17 B Section 8.1 – Moisture condition oven dried in-situ moisture 0 17 50 50 C Section 8.1 – Cooling time 0 3 hrs 0 33 50 33 D Section 8.1 – Soak time 15 hrs 20 hrs 0 0 0 17 E Section 8.3 – Drying sample dry cloth damp cloth 33 0 17 33 F Section 8.4 – Water temperature 21 - 22°C 24 - 25°C 17 33 50 50 G Section 8.5 – Cooling time 0 3 hrs 0 0 33 50 Table 4-16. Percentages of time each ruggedness factor in AASHTO T 85 was found significant when testing high absorption (>2 percent) coarse aggregates (AL-LMS and AL-slag).

60 room temperature. This is to avoid thermal shock that may cause differential contraction in the hot aggregate particles. This differential contraction may cause cracks to form, changing the void structure, absorption capacity, and spe- cific gravities of the aggregate. • In Section 8.3, using a dry towel or a damp towel to dry the surface of soaked aggregate particles to an SSD con- dition may significantly affect the test results. Depending on the amount of water absorbed in it, the damp towel may absorb water better than a completely dry towel because the skin of a water molecule is polarized, thereby acting like a magnet for other water molecules based on a process known as capillarity. Therefore, the agency’s and contractor’s laboratories should use the same method (either dry towel or damp towel) to dry the surface of soaked aggregate par- ticles to an SSD condition. • In Section 8.3, the water bath temperature was found to be significant because of thermal effects on the aggregate and the density of water. Thus, it is proposed to change the water bath temperature from 23.0 ± 1.7°C (73.4 ± 3°F) to 23.0 ± 1°C (73.4 ± 1.8°F). The tolerance of ± 1°C is proposed because it can be reasonably controlled in a laboratory. Ruggedness Study for Revised AASHTO T 84 The ruggedness study for the revised AASHTO T 84 pro- cedure was also conducted in the NCAT, AAPRL, and NIST laboratories. Four fine aggregates, including one granite (0.4 percent absorption), two limestones (1.4 and 2.2 percent absorption), and one blast furnace slag (2.2 percent absorption), were tested. A test parameter was found to be significant when its F-statistic was greater than Fcritical. Tables 4-17 through 4-20 Absorption Level Material Lab Avg. Absorption A B C D E F G < 2% Granite AAPRL 0.4% 37.0 NS NS 16.4 NS NS NS NCAT 0.4% 52.0 NS NS NS 6.0 NS NS NIST 0.4% 7.6 NS NS NS 5.7 NS NS LS-105 AAPRL 1.4% 52.4 NS NS 28.3 NS NS NS NCAT 1.4% 31.8 NS NS 13.6 NS 7.9 NS NIST 1.4% 111.6 12.1 NS 22.2 6.9 NS 64.2 2% AL-LMS AAPRL 2.2% 80.7 11.8 NS 43.3 NS NS NS NCAT 2.2% 16.4 NS NS 6.5 NS NS NS NIST 2.2% 31.7 10.2 NS 41.9 NS 9.6 1.4 AL-Slag AAPRL 2.2% 309.5 47.4 NS 59.4 NS 10.4 19.0 NCAT 2.2% 71.1 NS NS 23.7 NS NS 7.1 NIST 2.2% 350.7 100.5 NS 91.4 18.2 38.5 237.2 Table 4-17. F-statistics for Gsb of fine aggregates. Absorption Level Material Lab Avg. Absorption A B C D E F G < 2% Granite AAPRL 0.4% 30.2 NS NS 6.8 NS NS NS NCAT 0.4% 54.3 NS NS NS 6.2 NS NS NIST 0.4% NS NS NS NS 6.5 NS NS LS-105 AAPRL 1.4% 26.4 NS NS 18. 6 NS NS NS NCAT 1.4% 30.2 NS NS 12. 4 NS 8.2 6.5 NIST 1.4% 136. 6 8.5 NS 25. 3 6.9 NS 23.3 2% AL-LMS AAPRL 2.2% 59.4 NS NS 20. 4 NS NS NS NCAT 2.2% 7.6 NS NS NS NS NS NS NIST 2.2% 51.5 NS 7.3 30. 3 NS 17. 8 NS AL-Slag AAPRL 2.2% 150. 6 20.4 NS 37. 4 NS 7.6 NS NCAT 2.2% 51.4 NS 6.4 16. 6 NS 11. 5 NS NIST 2.2% 123. 7 61.1 NS 25. 0 11.4 18. 5 69.0 Table 4-18. F-statistics for Gssd of fine aggregates.

61 show F-statistics for Gsb, Gssd, Gsa, and water absorption of the four fine aggregates, respectively. In these tables, NS means “Not Significant,” and the shaded cells show the F-values exceeding the critical F-value of 5.59. The percentage of times each ruggedness factor was found to be significant in Tables 4-15 through 4-18 is summa- rized in Tables 4-19 and 4-20. As discussed previously, a test parameter or ruggedness factor was considered significant in this analysis if it was found to be statistically significant in 33 percent or more of the tests. Based on the analysis results shown in Tables 4-19 and 4-20, the following observations were made regarding AASHTO T 84: • In Section 7.1, testing conducted on fine aggregate samples with and without the P200 yielded statistically different Gsb, Gssd, Gsa, and absorption results. • Also in Section 7.1, the method of separating the P200 from fine aggregates through dry sieving or washing statistically affected the absorption results for low absorption (<2 per- cent) fine aggregates and the Gsb, Gssd, and absorption results for high absorption (>2 percent) fine aggregates. • In Section 7.1.1, testing low absorption (<2 percent) fine aggregate samples in an oven-dried or in-situ moisture condition did not statistically affect the test results. How- ever, for low absorption (<2 percent) fine aggregates, vac- uum soaking test samples in water for 9 or 11 minutes at a residual pressure of 3.4 to 4.0 kPa did yield statistically different Gsb, Gssd, and absorption results. • Also in Section 7.1.1, but for high absorption (≥2 percent) fine aggregates, soaking test samples in water or adding 6 percent moisture yielded statistically different results for Gssd and water absorption. Also, soaking test samples for 15 or 20 hours yielded statistically different Gsb, Gssd, and absorption results. • For the cone test in Section 7.2.1, dropping the tamper 25 times at once or in four sets yielded statistically differ- ent Gsb and Gssd results for low absorption fine aggregates but did not affect the test results for high absorption fine aggregates. • In Section 8.2, eliminating air bubbles using mechanical agitation or manual agitation significantly affected absorp- tion results for low absorption fine aggregates but signifi- cantly affected all the test results (i.e., Gsb, Gssd, Gsa, and absorption) for high absorption fine aggregates. • In Section 8.3, the final mass of an oven-dried aggregate sample can be determined immediately after it is removed from the oven when it is safe or after it has been cooled down to a temperature (approximately 50°C) that is com- fortable to handle. However, these methods yield statisti- cally different Gssd, Gsa, and absorption results for low absorption fine aggregates and Gsb, Gsa, and absorption results for high absorption fine aggregates. Gsb and Gssd are the two most important test results for AASHTO T 84, as they are used in PCC and AC mix design and production. Based on the ruggedness results summa- rized in Tables 4-21 and 4-22, there are several significant test parameters for Gsb and Gssd. Changes to these test param- eters are proposed as follows: • The ruggedness study results showed the significant effect of P200 on AASHTO T 84 test results. The cone and tamp method for determining the SSD condition for fine aggre- gates is based on the observation that the cone of aggregate (~71.6°) is greater than the angle of repose for dry material but less than the angle of repose for aggregate with capil- lary water between particles. However, the angle of repose of fine aggregate is influenced by several material proper- ties, especially the amount and nature (e.g., plasticity) of the P200 fraction. Thus, in Section 7.1, to simplify the test pro- cedure and improve the test variability, the P200 portion should be tested separately. Absorption Level Material Lab Avg. Absorption A B C D E F G < 2% Granite AAPRL 0.4% 17.0 NS NS NS NS NS 26.0 NCAT 0.4% 24.0 NS NS NS NS NS 5.8 NIST 0.4% 10.3 NS NS NS NS NS 19.5 LS-105 AAPRL 1.4% NS NS NS NS NS NS 28.2 NCAT 1.4% 6.1 NS NS NS NS NS 19.8 NIST 1.4% NS NS NS NS NS NS 110.2 2% AL-LMS AAPRL 2.2% 14.1 NS NS NS NS NS 10.0 NCAT 2.2% NS NS NS NS NS NS NS NIST 2.2% 33.4 13.3 NS NS NS 24. 9 NS AL-Slag AAPRL 2.2% NS NS NS NS NS NS 33.3 NCAT 2.2% NS NS 15. 4 NS NS 34. 5 17.7 NIST 2.2% 6.2 NS NS 5.7 NS NS 11.8 Table 4-19. F-statistics for Gsa of fine aggregates.

Absorption Level Material Lab Avg. Absorption A B C D E F G < 2% Granite AAPRL 0.4% 73.8 107.6 NS 184.9 18.7 22.9 231.7 NCAT 0.4% 21.9 NS NS NS NS NS NS NIST 0.4% 12.9 NS NS NS NS NS 9.3 LS-105 AAPRL 1.4% 240.0 NS 15.2 75.7 NS 0.9 120.8 NCAT 1.4% 24.1 NS NS 11.2 NS NS NS NIST 1.4% 55.3 13.0 NS 12.3 NS NS 114.8 2% AL-LMS AAPRL 2.2% 95.0 31.5 11.3 124.9 NS NS 46.3 NCAT 2.2% 51.7 30.2 6.9 10.2 NS NS 5.7 NIST 2.2% 47.1 22.7 NS 52.2 NS NS NS AL-Slag AAPRL 2.2% 846.2 150.6 NS 96.7 NS 13.2 193.9 NCAT 2.2% 98.1 NS NS 34.6 NS NS 26.2 NIST 2.2% 186.3 18.9 NS 63.2 NS 13.6 158.5 Table 4-20. F-statistics for absorption of fine aggregates.

63 • If the P200 portion is tested separately, it can be dry-sieved or washed out of the fine aggregate sample. However, the agency’s and contractor’s laboratories should use the same method for separating the P200 fraction. • The soak time was found to be a significant test parameter. This suggests that aggregate particles, especially absorptive materials, continue to absorb water beyond the time speci- fied. Thus, the soak time should be changed from 10±1 min- utes to 10±0.5 minutes for vacuum soaking. Or, it should be from 15 to 16 hours instead of from 15 to 19 hours for ID Variable Low Value High Value Gsb Gssd Gsa Abs A Section 7.1 – Aggregate size with P200 without P200 100 83 67 100 B Section 7.1 – Aggregate size dry sieve wash 17 17 0 33 C Section 7.1.1 – Moisture condition oven dried in-situ moisture 0 0 0 17 D Section 7.1.1 – Soak time 9 min. 11 min. 67 67 0 67 E Section 7.2.1 – Cone test 25 drops at once 25 drops in 4 sets 50 50 0 17 F Section 8.2 – Agitation mech agitation manual 17 17 0 33 G Section 8.3 – Cooling time 0 1.5 hrs (~50°C) 17 33 100 67 Table 4-21. Percentage of times each ruggedness factor in AASHTO T 84 was found significant when testing low absorption (<2 percent) fine aggregates (granite and LS-105). ID Variable Low Value High Value Gsb Gssd Gsa Abs A Section 7.1 – Aggregate size with P200 without P200 100 100 67 100 B Section 7.1 – Aggregate size dry sieve wash 67 33 17 83 C Section 7.1.1 – Soak type immerse 6% moisture 0 33 17 33 D Section 7.1.1 – Soak time 15 hrs 20 hrs 100 83 17 100 E Section 7.2.1 – Cone test 25 drops at once 25 drops in 4 sets 17 17 0 0 F Section 8.2 – Agitation mech agitation manual 50 67 33 33 G Section 8.3 – Cooling time 0 1.5 hrs (~50°C) 67 17 67 83 Table 4-22. Percentage of times each ruggedness factor in AASHTO T 84 was found significant when testing high absorption (>2 percent) fine aggregates (AL-LMS and AL-slag). hydrostatic soaking. These ranges are recommended because they can be reasonably controlled in the laboratory. • To further improve the test variability, the cone test should be conducted by dropping the tamper 25 times at once so that the material within the cone is compacted with the same amount of compaction effort. Also, to eliminate air bubbles, either mechanical agitation or a manual method should be used consistently. In addition, the final mass of an oven-dried aggregate sample should be determined after it is removed from the oven as soon as it is safe to do so.