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

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2The first task of this study was to (1) conduct a literature review of new and revised test methods for measuring the specific gravity and absorption of coarse and fine aggregates and (2) to consult with the NCHRP technical panel to select candidate test methods for further evaluation in this study. The results of this task are summarized in this chapter. Specific Gravity and Water Absorption of Aggregate Volumetric properties are important for mix design/ proportioning and production of PCC and HMA. However, since mass measurements are usually much easier, they are typically taken during testing and converted to volumes by using specific gravities. According to ASTM C125: Standard Terminology Relating to Concrete and Concrete Aggregates, spe- cific gravity is defined in Equation 2.1 as the ratio of mass of a volume of material to the mass of an equal volume of distilled water at a stated temperature. G M V M V M V s W W W (2.1)= = γ where: Gs = specific gravity M = mass of material V = volume of material Mw = mass of water Vw = volume of water = V gw = unit weight of water = 1 g/cm3 In Equation 2.1, the mass is simply taken in air, and the vol- ume is measured using the water or gas displacement method. Since coarse and fine aggregate particles generally have internal and surface porosity as well as rough surfaces, measurements of a particle’s volume must take into account the volume of permeable pores. As a result, depending on the mass and vol- ume measurements used for the calculation in Equation 2.1, the following three specific gravity values are defined for coarse and fine aggregates (1, 2). G M V sa s s w (2.2)= γ G M V V sb s s pp w (2.3)( )= + γ G M M V V ssd s wpp s pp w (2.4)( )= + + γ where: Gsa = apparent specific gravity Gsb = bulk specific gravity Gssd = bulk specific gravity (saturated-surface-dry basis) Ms = mass of dry solids Mwpp = mass of water filled in permeable pores Vs = volume of solids Vpp = volume of permeable pores gw = unit weight of water The mass and volume measurements also are used to determine the water absorption capacity of aggregate. ASTM C125 defines water absorption as the increase in the mass of aggregate due to the water filled in the permeable pores of the aggregate particles that may be dried out in an oven at a temperature between 100° and 110°C. The water absorption capacity is expressed as a percentage of the mass of oven- dried solids, as shown in Equation 2.5. Absorption M M wpp s 100 (2.5)= × where: Absorption = water absorption capacity of aggregate, percent C H A P T E R 2 Selection of Test Methods for Evaluation

3 Application of Aggregate Specific Gravity and Water Absorption The specific gravity and absorption capacity of coarse and fine aggregates are measured for use in mix design/ proportioning and quality assurance (QA) of PCC and HMA. The ability to quickly measure these properties of aggregate materials with a high degree of accuracy and repeatability is essential to specifying agencies and contractors. For PCC, the bulk specific gravity of aggregate is used in calculating the percentage of voids and the solid volume of aggregates in computation of yield. Using an inaccurate spe- cific gravity value may cause an error in the calculated yield or volume of concrete. In addition, since concrete is often sold by volume, this error means that either the purchaser is receiving less concrete than ordered or the producer is supplying more concrete than is being purchased (3). The absorption capac- ity of an aggregate is used for adjusting the batching water quantities and achieving the target water-cement ratio or water-cementitious material ratio. The absorption capacity can also be used as an indicator for the aggregate’s resistance to freezing and thawing. Accurate determination of absorp- tion is important to ensure the workability and durability of PCC (4, 5). The bulk specific gravity of aggregate (Equation 2.3) is critical information for mix design and QA of HMA (6). It is used in calculating the voids in mineral aggregate (VMA) and effective binder content (Pbe), which are then used to calcu- late the voids filled with asphalt (VFA) and dust proportion (DP). In HMA mix designs, VMA, VFA, and DP are used as specification criteria to help ensure that the mixture has volu- metric properties needed to provide desired performance. An error in the aggregate specific gravity, therefore, can cause an error in the mix design volumetric calculations, which can lead to several asphalt pavement performance problems such as raveling, bleeding, and cracking. In addition, since some agencies require the determination of VMA as part of accep- tance testing, there is a potential risk of accepting poor mix or rejecting good quality mix due to errors in determining the bulk specific gravity. For HMA evaluation, the absorption capacity of aggregate can be used as an indicator of asphalt absorption (7). In addition, some deleterious particles are lighter than the higher quality aggregates. Therefore, tracking specific gravity over time can sometimes indicate a change of material or possible contamination (8). Test Methods for Determining Specific Gravity and Water Absorption Current standard test methods for determining the specific gravity and water absorption of coarse and fine aggregates are AASHTO T 85 (or ASTM C127) and AASHTO T 84 (or ASTM C128), respectively. In addition, there also are several modified and new test methods, and they range from simple modifications to how the saturated, surface-dry (SSD) state is determined in the standard test methods to new test methods with more complex and costly equipment. Comparisons of these test methods are provided in Tables 2-1 through 2-3. These test methods were compared in terms of precision, ruggedness of equipment, ease of use, soaking and testing time, equipment cost, and potential problems or problem- atic materials. Detailed information about these test methods is included in Appendix C, which is available on the project web page. Selection of Test Methods for Evaluation in This Study After reviewing the findings of the literature review in Task 1, the NCHRP technical panel conducted a ballot. The results of the ballot are presented in Table 2-4. The panel selected 10 test methods that received at least seven “yes” votes for further evaluation in this study. ID Test Method Vendor Precision Ruggedness of Equipment Ease of Use Time Eqmt. Cost Potential Problems / Problematic Matl. Soak Test 1 AASHTO T 85 and ASTM C127 Various Standard Very good Manual 15 hrs 30 min $100 ~ $600 High absorption aggregates 2 AggPlus System using CoreLok Device InstroTek Mixed results Good Manual None 30 min $7,840 High absorption aggregates 3 Rapid AASHTO T 85 with CoreLok InstroTek Unknown Good Manual None 30 min $6,860 High absorption aggregates 4 SG-5 Specific Gravity and Absorption System Gilson Unknown Good Fully automated None 20 min $4,500 Unknown 5 Volumetric Immersion using Phunque Flasks Humboldt Unknown Good Manual None 25 hrs $500 High absorption aggregates Table 2-1. Comparison of test methods for determining specific gravity and absorption of coarse aggregate.

4ID Test Method Vendor Precision Ruggedness of Equipment Ease of Use Time Eqmt. Cost Potential Problems / Problematic Matl. Soak Test 1 AggPlus System using CoreLok Device InstroTek Unknown Good Manual None 30 min $7,840 High P200, high absorption aggregates 2 SG-5 Specific Gravity and Absorption System Gilson Unknown Good Fully automated None 20 min $4,500 Unknown 3 Volumetric Immersion using Phunque Flasks Humboldt Unknown Good Manual None 25 hrs $1,000 Unknown Table 2-3. Comparison of test methods for determining specific gravity and absorption of combined aggregate. ID Test Method Select for Evaluation? Test Selected for Evaluation Yes No % Yes I. Test Methods for Determining Specific Gravity and Absorption of Coarse Aggregate 1 AASHTO T 85 and ASTM C127 7 2 78 2 AggPlus System using CoreLok Device 2 7 22 3 Rapid AASHTO T 85 with the CoreLok 7 2 78 4 SG-5 Specific Gravity and Absorption System 7 2 78 5 Volumetric Immersion using Phunque Flasks 5 4 56 II. Test Methods for Determining Specific Gravity and Absorption of Fine Aggregate 1 AASHTO T 84 and ASTM C128 7 2 78 2 Modifications to Determination of SSD Condition in AASHTO T 84/ASTM C128 2 7 22 3 Modification to Materials Tested in AASHTO T 84/ASTM C128 8 1 87 4 SSDrier Device 4 5 44 5 SSDetect System 9 0 100 6 AggPlus System using CoreLok Device 2 7 22 7 SG-5 Specific Gravity and Absorption System 7 2 78 8 Volumetric Immersion using Phunque Flasks 8 1 89 III. Test Methods for Determining Specific Gravity and Absorption of Combined Aggregate 1 AggPlus System using CoreLok Device 3 6 37 2 SG-5 Specific Gravity and Absorption System 7 2 78 3 Volumetric Immersion using Phunque Flasks 7 2 78 Table 2-4. Results of Task 1 ballot (courtesy of NCHRP). ID Test Method Vendor Precision Ruggedness of Equipment Ease of Use Time Eqmt. Cost Potential Problems / Problematic Matl. Soak Test 1 AASHTO T 84 and ASTM C128 Various Standard Very good Manual 15 hrs 30 min $100 ~ $300 Angular, high P200, high absorption aggregates 2 Modifications to Determination of SSD Condition in AASHTO T 84 / ASTM C128 Various Worse Good Manual 15 hrs 30 min Unknown Highly subjective 3 Modification to Materials Tested in AASHTO T 84/ ASTM C128 Various Better Very good Manual 15 hrs 30 min $100 ~ $300 Angular and high absorption aggregates 4 SSDrier Device Gilson Worse Good Partially automated 15 hrs 1 day $4,500 Problems associated with the device 5 SSDetect System Thermo Fisher Better Good Automated None 2 hrs $7,056 None 6 AggPlus System using CoreLok Device InstroTek Mixed results Good Manual None 30 min $7,840 High P200, high absorption aggregates 7 SG-5 Specific Gravity and Absorption System Gilson Unknown Good Fully automated None 20 min $4,500 Unknown 8 Volumetric Immersion using Phunque Flasks Humboldt Unknown Good Manual None 25 hrs $500 High dust, high absorption aggregates Table 2-2. Comparison of test methods for determining specific gravity and absorption of fine aggregate.