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Publication Number: FHWA-HRT-13-085
Date: October 2013

 

Accelerated Determination of ASR Susceptibility During Concrete Prism Testing Through Nonlinear Resonance Acoustic Spectroscopy

CHAPTER 3. Sample Preparation

Mix Designs

For this study, the researchers chose aggregate sources that would provide a range of alkali reactivity for assessment using the NIRAS technique. The aggregate sources were selected after discussion with the teams at Clemson University and University of Texas at Austin, as well as with input from members of Federal Highway Administration’s Technical Working Group on ASR. Some of the same aggregate sources were examined by while maintaining a range of alkali reactivity.

The reactivity of the aggregates, shown in their “as received” condition in figure 8, figure 9, figure 10 through figure 13, was initially assessed by AMBT. Each of the aggregates was crushed, when necessary, to fit the grading requirements prescribed in ASTM C1260. The dimensions of mortar bars created were 1 by 1 by 11.25 inch(es) (25 by 25 by 285 mm). For each mix design, three samples were created. The samples were cured at about 100-percent relative humidity and 73.4 °F (23 °C) for 24 hours. After demolding, the samples were cured for an additional 24 hours while immersed in tap water at 176 °F (80 °C). The initial length measurements were performed after this curing period. ASR was then induced in the mortar bars by immersing them in a 1N sodium hydroxide (NaOH) solution at 176 °F (80 °C). The samples were removed from the NaOH solution at regular intervals for expansion measurements as prescribed by ASTM C1260.

Table 1 presents the average expansion of the three samples at 14 days. Again, these results were used as an initial means for assessing the reactivity of the individual aggregates used in the concrete prisms. According to ASTM C1260, expansion at the end of the test that is less than 0.10 percent indicates innocuous behavior, expansion greater than 0.20 percent indicates potentially deleterious expansion, and expansion between 0.10 and 0.20 percent may be innocuous or deleterious in field behavior.

In this research, all specimens for evaluation by NIRAS and CPT were cast according to the ASTM C1293 standard. The mix design matrix, described in table 2, was developed to examine a range of ASR behavior, including the combination of two non-reactive aggregates (Mix 1), and the use of aggregates termed here as “moderately to highly reactive” (HR) and “potentially (or may be) reactive” (MR) aggregates, each in combination with the same non-reactive aggregate (NR). (The nonreactive aggregate used in all the mix designs is a limestone from Adairsville, GA.) Considering the ASTM C1260 results, along with historical aggregate standard test results and field performance history of these aggregates, each of the aggregates was preliminarily classified as NR, MR, or HR. Table 2 gives these classifications, along with other details about the concrete prism mixtures, including the sample naming scheme.

In addition, an ASTM C150 Type I cement with alkali equivalent of 0.88 percent, meeting the ASTM C1293 requirements, was used in the casting of CPT samples; the alkali content of the concrete was “boosted” to 1.25 percent by mass cementitious materials, in accordance with the standard.

Table 3 summarizes the physical and chemical properties of this cement.

This image shows the “as received” Las Placitas gravel aggregate used in mix designs. The “as received” aggregates were assessed and crushed if necessary to fit ASTM C1260 grading requirements before being used to create concrete prism samples under the ASTM C1293 testing procedure.
Figure 8. Photo. Las Placitas gravel aggregate as received

The image shows the “as received” Spratt limestone aggregate used in mix designs. The “as received” aggregates were assessed and crushed if necessary to fit ASTM C1260 grading requirements before being used to create concrete prism samples under the ASTM C1293 testing procedure.
Figure 9. Photo. Spratt limestone aggregate as received

The image shows the “as received” Adairsville limestone (coarse) aggregate used in mix designs. The “as received” aggregates were assessed and crushed if necessary to fit ASTM C1260 grading requirements before being used to create concrete prism samples under the ASTM C1293 testing procedure.
Figure 10. Photo. Adairsville limestone (coarse) aggregate as received

The image shows the “as received” Adairsville limestone (fine) aggregate used in mix designs. The “as received” aggregates were assessed and crushed if necessary to fit ASTM C1260 grading requirements before being used to create concrete prism samples under the ASTM C1293 testing procedure.
Figure 11. Photo. Adairsville limestone (fine) aggregate as received

The image shows the “as received” Alabama sand aggregate used in mix designs. The “as received” aggregates were assessed and crushed if necessary to fit ASTM C1260 grading requirements before being used to create concrete prism samples under the ASTM C1293 testing procedure.
Figure 12. Photo. Alabama sand aggregate as received

The image shows the “as received” Illinois gravel aggregate used in mix designs. The “as received” aggregates were assessed and crushed if necessary to fit ASTM C1260 grading requirements before being used to create concrete prism samples under the ASTM C1293 testing procedure.
Figure 13. Photo. Illinois gravel aggregate as received

Table 1. ASTM C1260 results for the aggregates examined


Aggregate Source

14-day AMBT Expansion (percent)

AMBT Classification

Limestone, GA

0.0787

Innocuous

Las Placitas, NM gravel

0.8533

Potentially deleterious

Spratt limestone, Canada (crushed)

0.2661

Potentially deleterious

Alabama sand, AL

0.1555

Innocuous or potentially deleterious

Central Illinois sand, IL

0.2088

Potentially deleterious

Table 2. Mix design matrix for NIRAS and ASTM C1293 concrete prisms


Mix ID

Coarse Aggregate

Fine Aggregate

Supplementary Cementing Materials

Mix 1 NR/NR

Limestone, GA

Limestone, GA

Mix 2 HR/NR

Las Placitas, NM gravel

Limestone, GA

Mix 3 NR/HR

Limestone, GA

Las Placitas, NM gravel (crushed)

Mix 4 HR/NR

Spratt limestone, Canada

Limestone, GA

Mix 5 NR/HR

Limestone, GA

Spratt limestone, Canada (crushed)

Mix 6 NR/MR

Limestone, GA

Alabama sand, AL

Mix 7 NR/MR

Limestone, GA

Central Illinois Sand, IL

Mix 8 HR/NR—25% FA

Spratt limestone, Canada

Limestone, GA

25% Class F FA

Mix 9 NR/HR—25% FA

Limestone, GA

Spratt limestone, Canada(crushed)

25% Class F FA

Mix 10 NR/HR—25% FA

Las Placitas, NM gravel

Limestone, GA

25% Class F FA

NR = nonreactive
MR = potentially or “may be” reactive
HR = moderately to highly reactive
FA = fly ash
— = no supplementary cementing materials

Table 3. Chemical analysis data for Type I cement


Chemical Requirements
ASTM C114

Test Result,
(percent by mass)

Specification Limits
Type 1
ASTM C150
(percentage by mass)

Silicon Dioxide (SiO2)

19.11

Aluminum Oxide (Al2O3)

4.99

Ferric Oxide (Fe2O3)

3.55

Calcium Oxide (CaO)

60.66

Magnesium Oxide (MgO)

3.24

Sulfur Trioxide (SO3)

3.96

3.0 maximum

Ignition Loss

2.71

3.0 maximum

Insoluble Residue

0.24

0.75 maximum

Carbon Dioxide—CO2 Percentage

1.71

Limestone Percentage

4.1

5 maximum

CaCO3 Percentage in Limestone

94.5

70 minimum

Tricalcium Silicate (C3S)

42.9

Tricalcium Aluminate (C3A)

7.0

< 8

C3S + 4.75C3A

76

100 maximum

Equivalent Alkalis (Na2O+.658K2O) 

0.88

Chloride (Cl)

0.01

— No specification

Concrete Prism Samples

All CPT samples were prepared using the ASTM C1293 testing procedure. Each sample, with a water-to-cement ratio of 0.45, is 3 inches long with a 3-inch square cross section (76 by 76  by 285 mm). The gradation for coarse aggregate was as specified in ASTM C1293. For fine aggregates, the gradation was adjusted through sieving or crushing to achieve a fineness modulus of 2.71. This was done to minimize any variability in NIRAS and expansion measurements that may have arisen owing to differences in fine aggregate gradation. For each mix design, eight specimens were cast, six with studs for expansion measurements and two without studs for petrographic examination. The samples were initially cured for 24 hours in a moist environment for 23.5 ±0.5 hours. After demolding, the initial lengths of three samples were recorded. Subsequently, those samples, along with one sample for petrography, were transferred to a container that is kept at 100.4 °F (38 °C) in an environmental chamber. The container also allows the elevation of the specimens above water, providing high relative humidity, which is necessary for inducing ASR. The remaining specimens were kept for reference at room temperature; when examined, these samples of the same composition as mixes 1 through 10 (table 2) but stored at ambient conditions are hereafter referred to as “reference” samples.

 

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