Specific Gravity and Absorption of Aggregate by Volumetric Immersion - - PDF document

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Specific Gravity and Absorption of Aggregate by Volumetric Immersion - - PDF document

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9/23/2016 Specific Gravity and Absorption of Aggregate by Volumetric Immersion Method (Phunque Test) ASTM June 2015 Meeting by Bryce Simons, P.E. Eliminating the Guesswork A New Absorption/Specific Gravity Test for Aggregate 1

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Specific Gravity and Absorption of Aggregate by Volumetric Immersion Method (Phunque Test)

ASTM June 2015 Meeting by Bryce Simons, P.E.

Eliminating the Guesswork – A New Absorption/Specific Gravity Test for Aggregate

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Frustrated and Confused

Problems with ASTM C 128/AASHTO T‐84

  • Test is
  • subjective;
  • profoundly influenced by operator;
  • Impossible to repeat the same result;
  • Seriously different between different labs;
  • Unable to predict slumps in concrete;
  • Variability creates construction and payment conflicts with HMA.
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Desired Characteristics

  • Easy to perform;
  • Easy to understand;
  • Easily re‐produced;
  • Operator and laboratory independent

Basic Physics

  • Physically and visually measure total amount of water absorbed into

the sample;

  • Physically and visually measure Volume displacement of dry sample;
  • Physically and visually measure Volume displacement of saturated

sample.

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New Test Requirements

  • Normal absorptions are relatively small, so large amount of aggregate

needs to be tested to allow accurate measurement of total absorbed water;

  • Large waterproof bottom;
  • Narrow, calibrated neck;
  • Ability to add materials quickly without loss.

Finding Equipment

  • Checked existing glassware manufacturers and suppliers without

success;

  • Worked with specialty glass‐blowing company to construct a

container meeting these requirements.

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Develop Procedure

  • How to add material
  • When to take readings
  • How to calculate results
  • How to interpret results

Characteristics Needed

  • Absorption
  • Bulk Dry Specific Gravity
  • Bulk SSD Specific Gravity
  • Apparent Specific Gravity
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Lab Procedure

  • Flask
  • Aggregate
  • Introduction of Water
  • Observations & Measurements
  • Calculations & Corrections

Specialty Flask

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Lab Procedure Documentation

  • Initially, procedure was reviewed and evaluated by:
  • FHWA Research Laboratory in Washington, D.C.;
  • Heidelberg Technology Center in Atlanta, Georgia;
  • Kansas Department of Transportation;
  • New Mexico Department of Transportation (Allowed as alternative test

method for all aggregates tested after July 1, 2006).

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T-84 Absorption Phunque Absorption 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 Materials Bureau (Santa Fe) NMDOT District 6 NMDOT District 2 Billingsley AMEC Turner- Fairbanks Heidelburg Tech Center Kansas DOT

Placitas Fine Aggregate Absorption Comparison

T-84 Absorption Phunque Absorption

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2.480 2.500 2.520 2.540 2.560 2.580 2.600 2.620 2.640 Materials Bureau (Santa Fe) NMDOT District 6 NMDOT District 2 Billingsley AMEC Turner- Fairbanks Heidelburg Tech Center Kansas DOT

Bulk SSD Specific Gravity for Placitas Fine Aggregate

T-84 Bulk SSD Sp Gr Phunque Bulk SSD Sp GR

2.460 2.480 2.500 2.520 2.540 2.560 2.580 2.600 2.620

T-84 Bulk Dry Sp Gr Phunque Bulk Dry Sp GR

Bulk Dry Specific Gravity for Placitas Fine Aggregate

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2.620 2.625 2.630 2.635 2.640 2.645 2.650 2.655

T-84 Apparent Sp Gr Phunque Apparent Sp GR

Apparent Specific Gravity for Placitas Fine Aggregate

The benefit of consistency in Superpave Asphalt Mixes was also considered:

  • Volume determinations
  • QC/QA Pay Factor Calculations
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Specific Gravity & absorption by Volumetric Immersion Method

  • Originally approved by AASHTO as TP‐77 in 2009
  • This method was studied as a part of NCHRP 4‐35 “Testing of Specific Gravity

and Absorption of Aggregates” This study found that:

  • This method applies to coarse aggregate, fine aggregate and

combined aggregate

  • This was the only method suitable for measuring combined

aggregates;

  • It is a relatively simple operation;
  • This method is the most repeatable and reproducible of all

the methods studied;

  • This method is not affected by P200 or particle

shape/angularity;

  • The Initial Reading at 30 seconds is questionable.
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Benefits related to this method

  • Simplicity of test method;
  • Not effected by which technician or laboratory performs the

test;

  • Not affected by fineness or coarseness of gradation;
  • Not affected by particle shape;
  • Can provide actual measurement of blended aggregates

instead of requiring mathematical calculations;

  • Method is sufficiently sensitive to quickly recognize changes

in aggregate or pit characteristics.

Concerns related to use of this method

  • Test vessel made of glass is breakable and somewhat fragile

(This issue has been mitigated by constructing flasks from “Vacuum Grade” heavy duty glass which is very difficult to break);

  • Significant difference between direct result from this method

and the result from T85 or T84;

  • Initial reading at 0.5 minutes (30 seconds) felt to be too late;
  • Existing specifications as well as HMA and PCC mix designs

currently based on results from T85 and T84 would be seriously impacted if these results are directly substituted.

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Evolutionary needs for this test

  • Initial Reading must reflect true beginning water

displacement before any water has been absorbed by any aggregate;

  • Must be able to provide results that can be directly used in

lieu of T84 or T85;

Initial reading

  • Not realistically possible to obtain initial reading more

quickly than 30 seconds;

  • Initial reading at 30 seconds allows air introduced by pouring

dry aggregate sample into flask to escape before it can affect the reading;

  • Water is being absorbed by initial dry particles immediately

upon entering the water bath even though initial reading is not taken until after all particles have been submerged in water and 30 seconds has elapsed since the pouring of aggregate started.

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Adjusted initial reading

  • When actual readings are

plotted on semi‐log graph with volume on the vertical scale and time on the logarithmic horizontal scale, the result is a virtual straight line.

  • Logarithmic regression

analysis provides a correlation coefficient typically significantly better than 0.9 confirming a very strong reliability.

  • To calculate an adjusted

Initial Reading, simply enter the desired Initial Time as the “x” variable and calculate the resulting displacement.

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Calculation of adjusted initial reading

  • From previous slide for Trial #1, the equation for the line is:

y = ‐3.265 * Ln(x) + 4527.7

  • Substitute the desired time at which the Adjusted Initial

Volume is desired (in this case assume it is desired to determine the Initial Reading at 0.01 minutes) y = ‐3.265 * Ln(0.01) + 4527.7 y = ‐3.265 * (‐4.6052) + 4527.7 y = 15.04 + 4527.7 y = 4542.74

  • (Initial Volume read at 30 seconds = 4528.4)

Test results for this example

AASHTO T85 Direct Result Adjusted Result Absorption: 1.52% 1.00% 1.55% Sp Gravity (Dry): 2.588 2.651 2.586 Sp Gravity (SSD): 2.627 2.651 2.627 Apparent Gravity: 2.694 2.695 2.695

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All aggregate sources in new Mexico were tested and summarized in the following table

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Typical aggregate types

  • Gneiss
  • Monzonite
  • Quartzite
  • Rhyolite
  • Shale
  • Igneous
  • Limestone
  • Sandstone
  • Andesite
  • Basalt
  • Caliche
  • Granite
  • Feldspar
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This data was plotted against a 1:1 line and the relationship determined Absorption

T85 vs. Direct Results T85 vs. Adjusted to 0.10 minutes

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Absorption

T85 vs. Adjusted to 0.05 minutes T85 vs. Adjusted to 0.01 minutes

Bulk specific gravity (dry)

T85 vs. Direct Results T85 vs. Adjusted to 0.10 minutes

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Bulk specific gravity (dry)

T85 vs. Adjusted to 0.05 minutes T85 vs. Adjusted to 0.01 minutes

Bulk specific gravity (ssd)

T85 vs. Direct Results T85 vs. Adjusted to 0.10 minutes

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Bulk specific gravity (ssd)

T85 vs. Adjusted to 0.05 minutes T85 vs. Adjusted to 0.01 minutes

Conclusions

  • By using Initial Readings adjusted to 0.01 minutes, the

relationship between T85 and the results using the Adjusted Initial Readings for all properties is approximately equal to

  • r better than for the direct results determined from the

procedure;

  • Results calculated from Initial Readings adjusted to 0.01

minutes can be used directly in existing specifications and in the development of HMA and PCC mix designs.

  • The correlation coefficient for the Absorption is lower

because the inherent subjectivity of the test procedure profoundly effects accuracy, consistency and repeatability of T85.

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Conclusions (Pg 2)

  • Fine aggregates were not included in this evaluation due to

the flawed assumptions and biased effects from this procedure on the resulting properties.

  • Since the basic physics for this test remain the same

regardless of particle size, the conclusions from the evaluation of the coarse aggregate can be applied to fine aggregate and to combined aggregates.

  • TP 77 has been balloted and approved as a full Test: T??.