and Moisture Change

frizzflowerUrban and Civil

Nov 29, 2013 (3 years and 6 months ago)

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Faculty of Engineering

Division of Built Environment

Laboratory of Engineering

for Maintenance System



Hokkaido University

Clarification of Frost Damage
Mechanism Based on Meso scale
Deformation and Temperature
and Moisture Change


EVDON LUZANO SICAT, M1

LOGO

Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change

Laboratory of Engineering for
Maintenance System

Contents

RESEARCH OUTLINE

B

EXPERIMENTAL OUTLINE

C

BACKGROUND:

FORST DAMAGE MECHANISM

A

LOGO

Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change

Laboratory of Engineering for
Maintenance System

Background

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.


LOGO

Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change

Laboratory of Engineering for
Maintenance System

Background

Frost Damage Mechanism

Concrete Condition: Unsaturated


The pore structure is filled by small amount of water.


Once temperature drops to 0
º
C


Thermal contraction
occurs.


From 0
º
C to minimum temperature


Water in larger
pores freezes.









From freezing temperature to thawing


ice melts and
water flows to pore spaces.





ice

water


LOGO

Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change

Laboratory of Engineering for
Maintenance System

Background

Frost Damage Mechanism


Concrete Condition: Saturation Process

-
Possible only if water is available outside during thawing at
temperature above 0
º
C.

-
When freezing for temperature below 0
º
C


water freezes and
volume expands (can create tension to concrete).

-
At temperature below
-
10
º
C to minimum temperature


ice
contracts in larger pores.

-








-
From minimum temperature to
-
5
º
C during thawing


ice expands
more than surrounding concrete.




Contracted Ice


water


Increment pore space


LOGO

Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change

Laboratory of Engineering for
Maintenance System

Background

Frost Damage Mechanism

Concrete Condition: Saturated Condition

-
In this condition, the pore structure is totally filled by water.

-
As temperature continues to drop, the expansion of water creates
a very high positive hydraulic pressure.

-
For lowest temperature


water in smaller pores also freezes.



Ice



Larger cracks

Smaller pores

begin to freeze

LOGO

Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change

Laboratory of Engineering for
Maintenance System

Research Outline


Objective:


To clarify the effect of temperature history and
moisture conditions on concrete that are under the
effect freezing and thawing actions.



Previous Model Consideration (Oiwa
-
san’s Model):


Strains caused by temperature difference and ice
formation.








Where:
ε
T

is linear expansion strain,

α

is linear
expansion coefficient;10 [/

]Ⱐ
T
d

is temperature
difference,
ε
i

is expansion strain caused by ice formation,
α
i

is freezing expansion coefficient; 6250 [
μ
],
Ψ
i


is ice
content.



d
T
T




i
i
i





LOGO

Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change

Laboratory of Engineering for
Maintenance System

Research Outline

Some considerations:


Residual strain was not taken into account
during freezing and thawing cycles.



Specimens are analytical model, for its
viability: results must have a comparison
with experimental data.



Super cooling and expansion of water when
freezing are not considered.


LOGO

Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change

Laboratory of Engineering for
Maintenance System

Research Outline

Model Proposal (Arai
-
san’s Paper):



The total strain
ε

for the transformation model of
mortar due to frost damage is assumed to be
composed of three strains which are presented as
follows:









ε
i
: Expansion strain when freezing


ε
s
: Shrinkage strain when freezing


ε
t
: Temperature strain


t
s
i







LOGO

Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change

Laboratory of Engineering for
Maintenance System

Research Outline


The model of expansion strain when freezing
ε
i

is a function of ice
content ratio
Ψ
i
. When moisture content ratio is small, the
expansion is not caused.


Then, the following expressions are assumed.





α
i
: Constant of proportion that changes by rigidity of mortar


Ψ
ic
: Ice content ratio when transformation began to depend on ice
content ratio



The shrinkage when freezing is thought to be shrinkage by the
movement of the unfrozen water. It is expressed as follows by
assumption that the transformation depends on the unfrozen rate.







α
s
: Constant of proportion that shows unfrozen rate contributes to
shrinkage. It changes by the rigidity of mortar.)


ψ
: moisture content ratio



The temperature strain is expressed as follows by linear
coefficient of expansion αt.





Δ
T
:

Temperature difference



ic
i
i
i




-




i
s
s




-


T
t
t





LOGO

Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change

Laboratory of Engineering for
Maintenance System

Experimental Plans

Purpose of the Experiment:



To obtain the following coefficients experimentally;
thermal expansion , freezing expansion , and
shrinkage contraction and then apply them in the
proposed frost damage mechanism model.







-

Freezing strain







-

Shrinkage strain







-

Thermal Strain



ic
i
i
i




-




i
s
s




-


T
t
t





t

i

s

LOGO

Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change

Laboratory of Engineering for
Maintenance System

Experimental Plans


Specimens to be Used


Mortar will be use as test specimen in this experimental
program.


A. Materials Characteristics:



Cement


Ordinary Portland cement (Density: 3.14 g/cm3)






Fine Aggregate
(from Mukawa) (Size: 1.2mm and Density:


2.67 g/cm3)






Air
-
Entraining Agent


None (To Promote Frost Damage)

Water cement ratio

(%)

Water


kg/m
3


Cement


kg/m
3


Fine Aggregate


kg/m
3


50

244.6

489.2

1467.6

Table
-
1 Mix Proportions (Mortar)

LOGO

Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change

Laboratory of Engineering for
Maintenance System

Experimental Plans



Preparation of Specimens



Casting and mold
-

40 x 40 x 160 mm form



Curing Period


60 days (Moist Condition
-

23ºC)



Specimen dimension
-

40 x 40 x 2 mm










Table
-
2 (Specimen set and Moisture Conditions)


5 Specimens/Set

Moisture Condition

Purpose

A

Absolutely Dry

Thermal Expansion

B

(Nearly or Fully) Saturated

Freezing Expansion

C

20
-

50% Saturated

Shrinkage Contraction

D

80

90% Saturated

Comparison to Model’s Output

LOGO

Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change

Laboratory of Engineering for
Maintenance System

Experimental Plans


To attain different kind of moisture conditions on
specimens, they will be subjected in different desiccators
with different kind of salt solution.



Table
-
3

Salts solutions



Desiccators

Salts

(Potassium Nitrate) KNO
3

(Potassium Chloride) KCl

Chloride) NaCl

Graph from
AGM Container Controls, Inc. (AGM)

LOGO

Clarification of Frost Damage Mechanism based on Mesoscale Deformation and Temperature and Moisture Change

Laboratory of Engineering for
Maintenance System

Experimental Plans


Experimental Set
-
up

Specimens

Data

logger

PC

Environmental

Chamber

Temperature

sensor

Specimen

support

Temperature History Cycle for Set A, B, and C Specimens

Temperature History Cycle for Set D Specimens

Temperature increment: 0.5ºC/minute


O
L
L



)
(
0
T
T
L
L
O




Coefficients , , and can be approximated

by formula of coefficient of linear expansion.

t

i

s

Faculty of Engineering

Division of Built Environment

Laboratory of Engineering

for Maintenance System



Hokkaido University

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