106.3.2.96 TM-96, Standard Test Method for Chemical Analysis of Concrete Cores by Extraction and Solubility

106.3.2.96.1 Scope

This method evaluates concrete cores by concentrating on three phases (aggregate, paste, and voids) to assist and/or verify the reason(s) for the failure.

106.3.2.96.2 Summary of Method

Aggregate and paste samples are meticulously extracted from the concrete core sample. The aggregate and paste samples are analyzed under a stereoscope for any contamination of paste on the aggregate and aggregate in the paste. The samples are crushed and sieved through a #40 sieve. The minus 40 material is evaluated by instrumental analysis for chemical tracers (indicators) potentially associated with the concrete failure. The remaining portions of the concrete core sample(s) are submerged in distilled water and boiled on a hot plate. A semi-quantitative analysis is performed on the extract for water-soluble elements (tracers) that could be potentially associated with the failure.

106.3.2.96.3 Equipment and Reagents

1. Glass beaker, 2000-ml; Nitric Acid (HNO3), Certified ACS grade
2. Distilled water
3. Mortar and pestle
4. Hammer
5. No. 40 sieve, conforming to ASTM E-11 specification
6. Hook/Straight Fork tip, 5 ½ in. in length
7. Brown waxed paper, for sample collection
8. Graphite crucible, 8-ml capacity
9. Clear plastic (polypropylene) beakers, 400-ml capacity
10. Magnetic stirring bars, length of bars should be ½” less than the inside diameter of the beaker
11. Lithium metaborate (LiBO2), reagent grade, anhydrous
12. Yttrium Stock Solution, 1000 ppm (mg/l)
13. Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES), capable of internal standard correction
14. Filter paper, rapid filtering, #41 or equivalent
15. Filter funnel
16. Semi-quantitative standards, traceable to NIST, 10 ppm
17. Muffle furnace, 1000 C capability
18. Polypropylene digestion vessel with cap, 70-ml capacity
19. Porcelain crucible, 15-ml capacity

106.3.2.96.4 Procedure

Place brown wax paper on floor and set the concrete core sample in the middle of the paper. Strike the sample with a hammer to expose the inside of the core. Examine the sample and choose section(s) to extract aggregate and paste from the concrete core. Sample a minimum of 5 large pieces of aggregate and paste to retain separately for further evaluation. Using a Hook Fork tip tool, chip off excess paste off the extracted aggregate and use a stereoscope to verify aggregate is not contaminated and retain. For extracted paster, use mortar and pestle to gently agitate paste to isolate any aggregate and sand in the paste. View under a stereoscope, remove aggregate and sand from the paste, if present, and retain. Use mortar and pestle to break each individual sample into a fine consistency and sieve through a #40 sieve. Repeat, if necessary, and retain for further testing. Determine the moisture content on the paste and aggregate separately in a 105 C drying oven for 2 hours on a 1 +/- 0.0005-gram sample in a porcelain crucible. Cool, weigh, record, and calculate.

Determine the % Loss on Ignition (LOI) on the moisture free aggregate and paste samples at 950 C in a muffle furnace for 2 hours. Cool, weigh, record, and calculate. Use the % LOI result to calculate corrected weight from 0.25 +/- .0005 grams. As an example, if the % LOI is 35%, take (100% - 35%) = %65%. From there, take 0.25 +/- .0005 grams * 0.65 = 0.1625 grams. This is the corrected weight and is used to fuse with LiBO2. For fusion of aggregate and paste, add ¼ teaspoon of LiBO2 to 2 graphite crucibles and use a test tube with the same inner diameter of the crucible, press down on the LiBO2 to make a bed. Use the % LOI of the aggregate and paste, and determine corrected weight, as described above, to weigh into the bed of LiBO2 in the crucibles. Once weighed up, add another ¼ teaspoon of LiBO2 over the sample in the crucibles. Load crucibles into a 1000C muffle furnace for a minimum of 15 minutes, use tongs to remove crucibles, swirl bead in crucible, and carefully drop fused pellet into a clear plastic beaker containing 200-ml of 1:24 HNO3. Place beaker(s) on a stir plate and stir for at least 10 minutes until dissolved. Filter through a #41 filter paper into a 250-ml volumetric flask. Dilute to volume and analyze on ICP-OES using prescribed test template set up for aggregate analysis. 1-ml of Yttrium can be added initially to the 250-volumetric flask prior to filtration of adjusted accordingly based off elemental analysis and volume.

Take remaining pieces of the concrete core sample, after extraction of aggregate and paste, and place in a 2000-ml beaker. Cover the sample with distilled water, cover with suitable watch glass, and boil on hot plate for at least 30 minutes. Take beaker off hot plate, and cool to room temperature. Pour water extract into at least 3 70-ml polypropylene digestion vessels and cap. Analyze water extract on ICP-OES with blank (1:24 HNO3) and 10 ppm semi-quantitative standards. Dilute, if needed, and print report.

The main analytes to evaluate on aggregates are calcium (CaO), magnesium (MgO), and aluminum (Al2O3). Measure CaO/MgO ratio versus Al2O3 concentration to validate if aggregate is reactive based off MoDOT TM-93 graph.

The paste analysis measures moisture availability and total alkali content, which are variables associated with reactive aggregates. The paste is tested for LOI, CO2, Na2O, and K2O. Total alkali content can be calculated by the following equation:

Na2O + 0.658*K2O

High alkali and moisture contents are indicators of tendencies for reaction to occur.

Chemical analysis by solubility is the last step of the concrete core analysis. This method is done to flush out any chemical tracers (indicators) that assist in pinpointing the cause of pavement distress. A semi-quantitative analysis measures the water extract from the core (entrapped and entrained air) and looks at over 60 analytes. The intensity values are displayed based on the concentration of the analytes present in the water extract.

In addition, chemical analysis of chloride (Cl-), Sulfur (SO3), and Ferric oxide (Fe2O3) should be noted as indicators and can be included in the paste analysis.

The chemical analysis of all three phases can assist in identifying the factors leading to the pavement distress.

106.3.2 Material Inspection Test Methods