impact of hydrated cement paste quality and entrained …€¦ · impact of hydrated cement paste...
TRANSCRIPT
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Impact of Hydrated Cement Paste Quality and Entrained Air-Void
System on the Durability of Concrete
Sponsored by Michigan DOT
Larry Sutter, Karl Peterson, Jake Vermillion
University Transportation CenterMaterials in Sustainable Transportation Infrastructure
Michigan Tech, Houghton MI
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Background• Concrete mixtures have undergone numerous changes in
recent years
• As the mixtures have changed, the research linking air-void system parameters to performance has not been updated
• Changes that have occurred (e.g. lower w/cm, use of SCMs, synthetic AEAs) affect not only the quality of the hydrated cement paste but also the characteristics of the entrained air-void system
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Objective• Examine how the durability of concrete is affected
by the quality of the hydrated cement paste and the presence of a properly entrained air-void system
– Focus on the use of SCMs and “synthetic” air entrainers
– Review emerging laboratory test equipment and protocols for application in practice
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Approach• Emerging Methods to Evaluate
– AVA
– Calorimetry
– Cementometer
– Microwave Water Content
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Approach• Emerging Methods to Evaluate
– AVA
– Calorimetry
– Cementometer
– Microwave Water Content
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Approach• Phase II Experiment: Combined Full- and Partial- Factorial
– Cement type: ASTM Type I/II
– Cement factors: 564 lb/yd3, 517 lb/yd3, and 470 lb/yd3
– SCMs: none, Class C fly ash, and Grade 100 ground blast furnace slag
– AEAs: one vinsol resin and one synthetic
– Coarse aggregate: a durable carbonate
– Aggregate gradings: gap gradation and optimized
– Fine aggregate volume altered to adjust yield with changes in w/cm
– w/cm: 0.45, 0.50, and 0.52.
– Two target air contents: 3% and 6%
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Approach• Testing to assess fresh concrete properties
– Slump (ASTM C143)
– Determination of air content using the pressure (ASTM C231), volumetric (ASTM C173) and gravimetric method (ASTM C138)
– Air-void system parameters using the AVA
– Unit weight and yield (ASTM C138)
– Calorimetry to determine heat signatures of concrete
– Maturity (ASTM C1074)
– Water content by microwave method (AASHTO T 318) and Cementometer
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Approach• Testing to assess hardened concrete properties
– Compressive strength (ASTM C39) at 1, 3, 7, and 28 days.
– Determination of air-void system parameters using ASTM C457 calculations – flatbed scanner
– Sorptivity after 56 days (ASTM C1585)
– F-T durability (ASTM C666)
– Limited analysis of thin sections to estimate w/cmcontent of concrete
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Absorptivity plots for mixes with >0.2 mm spacing factor
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Microwave-Oven Drying Method
• AASHTO T 318-02 Standard Method of Test for Water Content of Freshly Mixed Concrete Using Microwave Oven Drying
• Water Content Percentage (WC):
WC = (Wt Fresh – Wt Dry) / Wt Fresh
• Total Water Content (WT):
WT = 27* (WC)*(Unit Wt) / 100
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150
200
250
300
350
400
150 200 250 300 350 400
Targ
et W
ater
Con
tent
(lb/
cy)
Test Result Water Content (lb/cy)
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Aggregate Absorption Correction
• Corrected water content percentage:
( ) ( )ABS ×WT + ABS ×WTWF-WD F FC CWC= 100× -WF-WS UW×V
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150
200
250
300
350
400
150 200 250 300 350 400
Targ
et W
ater
Con
tent
(lb/
cy)
Test Result Water Content (lb/cy)
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150
200
250
300
350
400
150 200 250 300 350 400
Targ
et W
ater
Con
tent
(lb/
cy)
Test Result Content (lb/cy)Average Measured Average Corrected
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Precision Statements
• 1s and d2s limits define the expected variability between individual test results
1s - an indication of the variability of a large group of individual test results obtained under similar conditions
d2s - the difference between two individual test results that would be equaled or exceeded in the long run in only 1 case in 20 in the normal and correct operation of the method
• AASHTO T 318 reports a 1s value of 2.7 lb/cy and a d2s value of 7.6 lb/cy
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Overall Precision
Limits for data grouped by water content
Water Content (lb/cy) 1s Limit d2s Limit197.40 14.22 40.23225.60 12.81 36.23253.80 7.71 21.80282.00 2.49 7.06310.20 7.70 21.79366.60 12.08 34.18
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Overall Precision
1s Limit(lb/cy)
d2s Limit(lb/cy)
Measured Water Content 15.14 42.82Corrected Water Content 12.51 35.37
Limits for entire data set
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Overall Precision
Limits for data grouped by water content
Water Content (lb/cy) 1s Limit d2s Limit197.40 14.22 40.23225.60 12.81 36.23253.80 7.71 21.80282.00 2.49 7.06310.20 7.70 21.79366.60 12.08 34.18
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Overall Precision
1s Limit(lb/cy)
d2s Limit(lb/cy)
Measured Water Content 9.95 28.14Corrected Water Content 8.37 23.66
Limits for limited data set
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Summary
• Although there is reasonable agreement between standard air tests, the AVA tends to underestimate the air content and over estimate the spacing factor
• No mixture failed ASTM C666 with a spacing factor less than 0.20 mm, but many with a greater spacing factor passed
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Summary
• Air-void system parameters (i.e. spacing factor and specific surface) track with air content, but F-T performance often does not
• By AVA, spacing factor and specific surface relate to F-T performance, but the the limit of 0.20 mm does not appear to apply
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Summary
• The microwave water content measurement is best used with an aggregate absorption correction
• The technique seems most accurate in ranges of water content from ~220 -320 lb/cy
• AASHTO published precision is dubious over the range of the test