Improved Test Methods for Specific Gravity and Absorption of Coarse and Fine Aggregate (2015) / Chapter Skim
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5 C H A P T E R 3 As shown in Table 2-4, 10 candidate test methods were selected for laboratory evaluation. However, since a production unit of the SG-5 device was not available for evaluation at the time of this study, the list of candidate test methods was revised.
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6Table 3-1. Revised list of test methods selected for laboratory evaluation.
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7 Figure 3-2. Variability of test results determined by three test methods for coarse aggregate.
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8in AASHTO T 85 also are shown in Figure 3-2 for comparison. The AASHTO T 85 precision limits were determined based on aggregates with absorptions of less than 2 percent.
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9 the flask has not been disturbed. There may be two shortcomings for this determination: – Air may be trapped between aggregate particles, resulting in a greater measured volume than the true volume of aggregate and voids.
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10 The results determined by these test methods for fine aggregate were more comparable for the three aggregates with lower water absorption capacities -- Ottawa sand (AASHTO T 84 water absorption = 0.03 percent) , natural sand (AASHTO T 84 water absorption = 0.5 percent)
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11 Table 3-6 summarizes Bartlett's Test for evaluating the variance of test results determined using the five test methods. The variances of the test results were not statistically different.
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12 combined aggregate (i.e., a complete gradation)
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13 Figure 3-6. Comparison of test results for combined aggregates.
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14 4. Modified AASHTO T 84 (Removal of P200)
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15 ANOVA results for coarse and fine aggregate materials are summarized in Tables 3-10 and 3-11, respectively. Detailed ANOVA results are included in Appendix E, which is available on the project web page.
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16 Comparing Test Results for Coarse Aggregate Pairwise comparisons among different levels of material and test method were conducted using Tukey's tests. A summary of Tukey's test results for coarse aggregate materials is presented in Table 3-12.
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Figure 3-7. Comparison of results determined by two test methods for coarse aggregate.
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18 significance level of 0.05, the differences in Gsa of the natural sand measured by the four test methods (Modified T 84, Phunque fine, SSDetect, AASHTO T 84) were not statistically significant.
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19 Table 3-15. Tukey's pairwise comparisons for Gssd of fine aggregate.
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20 Since the Phunque flask consistently produced lower water absorption results for all the fine aggregates, as shown in Figure 3-8(d) , it was suggested that some water penetrates into the surface voids of the aggregate particles within the first 30 seconds of the test before the initial water level reading is taken.
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21 Without P200 Material (A1) Cone #1: Wet Condition (A2)
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22 method. Detailed results of the within- and between-laboratory variance components for each material evaluated in Experiment 2 are presented in Appendix E, which is available on the project web page.
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23 almost all of the comparisons. The comparisons (also confirmed by Bartlett's test)
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24 with absorptions of less than 2 percent) given in the current AASHTO T 85 test method for comparison.
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25 • The AASHTO T 84 method appeared to be the least repeatable and reproducible in the comparisons. • The variability of the Gsb and Gssd test results appeared to have a trend similar to that of the water absorption capacity.
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26 Method Parameter Is Effect of Material Property on W/L Variability Significant? Is Effect of Material Property on B/L Variability Significant?
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27 Table 3-22. Precision information for AASHTO T 84 method for fine aggregate.
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28 • The SSDetect method is probably a better method for testing fine aggregate that contains 10 percent or more of P200 material. Ruggedness and round robin studies for this test method have been completed under another study published in NCAT Report 05-07 (25)
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29 to ASTM D7227) , which would eliminate the cooling period for the sample to return to room temperature.
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30 The third part of Experiment 3 was to investigate the same vacuum method used in the second part, but the testing was conducted on aggregate samples with in-situ moisture instead of oven-dried samples. For each material, four sets of three replicates were tested, based on four combinations of drying and soaking methods.
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31 were evaluated for each test method: oven drying, natural condition, and vacuum drying. The effect of initial drying methods on test results was analyzed in two steps.
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32 Figure 3-18 compares the coarse aggregate test results measured in accordance with AASHTO T 85 using the three initial drying methods. The effects of the initial drying methods were more profound for absorption and Gsa and less significant for Gsb and Gssd.
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35 Figure 3-21. Laboratory testing plan for evaluating soaking methods for AASHTO T 84.
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36 Results Materials P-Value Significant? Grouping Using Tukey Method 15-hr Soak 5-min Vacuum 10-min Vacuum 15-min Vacuum Gsa Ark NS 0.396 No A A A A BF Slag Fine 0.039 Yes A A A B PS Fine 0.033 Yes A A A B RC LMS Fine 0.200 No A A A A TX Sand 0.498 No A A A A Gsb Ark NS 0.269 No A A A A BF Slag Fine 0.745 No A A A A PS Fine 0.002 Yes A A A B RC LMS Fine 0.480 No A A A A TX Sand 0.056 No A A A A Gssd Ark NS 0.361 No A A A A BF Slag Fine 0.792 No A A A A PS Fine 0.001 Yes A A A B RC LMS Fine 0.517 No A A A A TX Sand 0.053 No A A A A Abs Ark NS 0.227 No A A A A BF Slag Fine 0.483 No A A A A PS Fine 0.003 Yes A B B B RC LMS Fine 0.386 No A A A A TX Sand 0.054 No A A A A Note: For each measured property and material, methods that do not share a letter are significantly different.
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39 Figure 3-24. Laboratory testing plan for evaluating soaking methods on in-situ moisture samples for AASHTO T 85 (coarse aggregate)
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40 portland cement concrete, aggregate stockpiles are sprinkled to maintain the moisture content that is often higher than the aggregate absorption capacity, so testing of aggregates in their natural moisture conditions is allowed according to AASHTO T 84 and T 85. However, for production of asphalt concrete, the moisture content of aggregate stockpiles varies, but is often lower than the aggregate absorption capacity, so AASHTO T 84 and T 85 require aggregates be oven-dried before testing.
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Figure 3-27. Effect of soaking methods and use of in-situ moisture samples on AASHTO T 85 test results.
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43 Results Materials ANOVA Grouping Using Tukey's Method* P-Value Significant?
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46 As shown in Table 3-32, the control and 10-minute vacuum methods often had the same letter, which indicated that the difference between these two methods was not significant at the 95 percent confidence interval. Table 3-33 shows the results of Bartlett's and Levene's statistical tests for equal variances.
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47 AASHTO T 85 and 84 methods. Testing the aggregate in the natural moisture condition yielded results closer to those of the oven-dried material, but the differences in the test results were still statistically significant for some materials.
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48 Step 1: Prepare samples for Arkansas Natural Sand and RC Limestone Step 2: Prepare P200 samples from TX Limestone Fine Aggregate Step 3: Prepare samples for testing Step 4: Test samples as follows: • Conduct AASHTO T 84 on the 24 blends (2 materials × 12 blends/material) using three replicates (= 72 tests)
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51 for the other measured results (Gsb, Gssd, and absorption) , the differences were statistically significant between two groups of blends -- with and without adding the clay.
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52 However, since the sand equivalent value of 75 percent was determined based on limited data, it should be verified in the future. Summary Based on the results of the evaluation of the effect of P200 materials with and without clay, the following observations and proposals are offered: • If the P200 material does not contain clays, inclusion of the P200 material in the fine aggregate sample will have a minimal effect on AASHTO T 84 test results.
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