Faculty of Engineering. Division of Built ... Laboratory of Engineering for.
Maintenance System ... Thermal expansion of ice is higher than mortar (or
concrete). 3.
Hokkaido University
EVDON LUZANO SICAT, M2
Faculty of Engineering Division of Built Environment Laboratory of Engineering for Maintenance System
Clarification of Frost Damage Mechanism Based on Mesoscale Deformation and Temperature and Moisture Change
Contents
A
B
C
LOGO
Overview of the Study
Experimental Methods and Results
Initial Findings
Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change
Laboratory of Engineering for Maintenance System
Overview
LOGO
Freeze-thaw Deterioration Concrete, like other highly divided porous media, has the ability to absorb and retain moisture. This characteristic has an important consequence since unprotected concrete structures in contact with water are usually susceptible to frost damage.
Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change
Laboratory of Engineering for Maintenance System
Overview
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Research Objective: To clarify the effect of temperature history and moisture conditions on concrete that are under the effect of freezing and thawing actions by developing a material model in mesoscale.
Important Facts in FTC (Freezing Thawing Cycle) 1. Volume of water expands by 9% when converted to ice 2. Thermal expansion of ice is higher than mortar (or concrete) 3. The freezing point of water in pores gets lower as their size gets smaller
Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change
Laboratory of Engineering for Maintenance System
Pore Structure
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Three Kinds of Pores in Concrete
Gel Pores
Consists of a system of very fine pores within the dense packing of cement hydration products. The radii of these pores are very small. Water present in this class of pores seldom freezes under usual freezing conditions of concrete use. (pore size 0.0005 – 0.01 μm)
Capillary Pores
These pores are the remnant of the original water filled spaces of fresh concrete mix. These pores are larger than the gel pores. The smaller the capillary size the lower the freezing temperature. (pore size 0.02 – 10 μm)
Structural and Material Performance Evaluation of Frost Damaged RC Members
Entrainedair
The sizes of these air bubbles are very much larger than the other two classes of pores. Normally the capillary pores are separated from the air bubbles by layers of cement hydration products with associated gel pores. (recommended at 50 μm)
Laboratory of Engineering for Maintenance System
Pore Structure
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Freezing Temperature vs. Pore Radius
Structural and Material Performance Evaluation of Frost Damaged RC Members
Laboratory of Engineering for Maintenance System
Experimental Methods
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Casting and Molding 40 x 40 x 160mm
Cutting of Specimens 40 x 40 x 2mm
100 % Saturated 20% - 50% Saturated
Oven drying for 24 Hours to Determine Dried Weight
FTC
Dried Specimen (RH 0%)
SEALED
Water Curing for 2 Months
80% - 90% Saturated
Attaching of Strain Gauges Water Curing Until Mass is Constant
Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change
Laboratory of Engineering for Maintenance System
Experimental Methods
Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change
LOGO
Laboratory of Engineering for Maintenance System
Experimental Methods
LOGO
Experimental Set-up Specimens
PC
Temperature History (5/20 cycles) 10 °C 0.25°C/min -28 °C
Data logger
Environmental Chamber
2.5 h
2.53 h
2.5 h
2.53 h
Specimen support Temperature sensor Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change
Laboratory of Engineering for Maintenance System
Experimental Methods
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Moisture Conditions Moisture Condition
Relative Humidity
Absolutely Dry
Moisture Content (g/cc) -
0%
Specimens per Condition 3 sets
100% Saturated (Set A)
0.228
100%
3 sets
92% Saturated
0.208
99%
3 sets
68.4% Saturated
0.152
80%
3 sets
100% Saturated (Set B)
0.289
100%
2 sets
85% Saturated
0.206
89%
2 sets
Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change
-6 to 0 0 to max (9.4) max steady temp 10000 12000
Time (minutes) FTC Strain Diagram less Thermal Strain - 93% Saturated Mortar Strain (µ)
500 400 300 200
Temperature 93% Average Saturated Mortar Strains less Thermal Strains
100 0 -100 0
2000
4000
6000
8000
10000
12000
Time (minutes) Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change
Laboratory of Engineering for Maintenance System
Experimental Results
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100% Saturated Mortar Set B - Strain 500 400 300 200 100 0 -100
Temperature
-200
100% Saturated Mortar Set B
-300 -400 0
500
1000
1500
2000
2500
3000
3500
Time (minutes) 1000
100% Saturated Set B Mortar Less Thermal Strains - Strain (μ)
800 600 400 200 0
Temperature
-200
100% Saturated Mortar Set B
-400 0
500
1000
1500
2000
2500
3000
3500
Time (minutes) Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change
Laboratory of Engineering for Maintenance System
Experimental Results
LOGO
89% Saturated Mortar - Strain (μ)
400
300 200 100
0 -100
Temperature
-200
89% Saturated Mortar
-300 -400 0
500
1000
1500
2000
2500
3000
3500
Time (minutes) 89% Saturated Mortar less Thermal Strains - Strain
500 400 300 200 100 0 -100
Temperature
-200
89% Saturated Mortar
-300 -400 0
500
1000
1500
2000
2500
3000
3500
Time (minutes) Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change
Laboratory of Engineering for Maintenance System
Experimental Results
LOGO
68.4% Saturated Mortar Strains - Strain (µ) 50
ice
-50 -150 -250
water
Temperature (˚C)
-350
Strain
-450 0
500
1000
1500
2000
2500
3000
3500
Time (minute)
68.4% Saturated Mortar Less Thermal Strains - Strain (µ) 100
50
0
-50
Temperature (˚C) Strain
-100 0
500
1000
1500
2000
2500
3000
3500
Time (minute)
Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change
Laboratory of Engineering for Maintenance System
Findings
LOGO
It is evident that the degree of saturation dictates the behavior of concrete mortar under FTC cycles. The level and variation in deformation of mortar specimens depends on the amount of moisture. The deformation of mortar specimens caused by the effect of moisture can be observed after the thermal expansion of mortar is removed. The expansion or tensile strain was not caused during the freezing process for test specimens having saturation condition of 92% and below. Though the expansion was not evident during the freezing process for test specimens having saturation condition of 92% and below, a residual strain resulted at the end of the FTC. However if the thermal expansion/contraction strain of mortar is removed, the behavior of moisture causes a slight expansion strain at the freezing temperature, this is due to the expansion of water as it forms to ice. The level of the resulting residual strain is dependent on the amount of moisture present on the specimens. The higher the moisture content the higher is the resulting expansion and residual strain. For test specimens having full saturation, higher expansions were observed during the freezing process. As the number of cycles increased so is the amount of expansion at every FTC even though moisture was not supplied. Supercooling was marked for all test specimens with moisture content, the level of supercooling and behavior of mortar after the supercooling is dependent on the amount of moisture present in the specimens. For mortar specimens with 100% saturation, after the supercooling moisture behavior continued to exhibit positive pressure while specimens having 92% saturation and below shrinkage was observed after the supercooling. The dry mortar specimens show a constant behavior during the entire FTC process. This constant behavior is the product of the absence of moisture in the test specimens.
The results presented prove that the presence of moisture in concrete specimens or structures can alter its structural integrity once subjected in a FTC even for low moisture content specimens. Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change
Laboratory of Engineering for Maintenance System
Hokkaido University
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Faculty of Engineering Division of Built Environment Laboratory of Engineering for Maintenance System
