Capillary absorption

frizzflowerUrban and Civil

Nov 29, 2013 (3 years and 7 months ago)

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Home institution

University of Maribor

Faculty of Civil Engineering

Slovenia

Host institution

Sakarya University

Technical Education Faculty

Turkey

Education and Culture

Lifelong Learning Programme

ERASMUS

Assist.Prof.Dr.

Lucija Hanžič

LECTURE

2

Capillary

absorption

in

concrete

www
.
fg
.
uni
-
mb
.
si/lucija/presentations/
2008
sakarya
-
lecture
2
.
ppt

14


18 April 2008

University of Maribor, Faculty of Civil Engineering

2/
6

Assis.Prof.Dr. Lucija Hanžič

Capillary absorption in concrete

Hydrated

cement

matrix

is

sol
-
gel

where

hydration

products

form

solid

sheets

which

are

separated

by

thin

layers

of

gel

water
.

Gel

water

is

firmly

bonded

and

cannot

be

removed

by

heating

to

100

°
C
.


Microstructure of concrete


Figure 2. Feldman
-
Sereda model of hardened cement paste.

R.F. Feldman, P.J. Sereda, A model for hydrated Portland cement paste as deduced from sorption
-
length change and mechanical properties,
materials and Structures

6 1968) pp.509
-
519.

Figure 1. Microstructure of concrete.

Cement matrix

Coarse aggregate



Hydrated cement



Gel water



Fine aggregate



Pores

Layers

of

sol
-
gel

form

the

three
-
dimensional

structure

which

is

criss
-
crossed

by

interconnected

channels

(pores)

of

various

diameters
.

Due

to

porous

nature

of

concrete

percolation

of

water

and

other

liquids

through

concrete

is

possible
.

Figure 3. Types of pores in materials.

Transport mechanisms of fluids
in porous materials

Difussion

Fick’s law

Suction

Darcy’s law

Capillary absorption

Lucas
-
Washburn equation

University of Maribor, Faculty of Civil Engineering

3/6

Assis.Prof.Dr. Lucija Hanžič

Capillary absorption in concrete


Capillary absorption


Interactions

between

atoms

on

the

solid
-
liquid
-
gass

interface

result

in

surface

tension

(
γ
)
.

(a)

A K
<

> 90°
(b)


< 90°
A K
>
Figure 4. Shape of a droplet on the solid
surface and shape of the meniscus in a
capillary tube when (a) cohesive forces
(K
)
are larger than adhesive forces
(A
) hence
contact angle (
Θ
)

is larger then 90
°

and (b)
when cohesive forces are smaller then
adhesive forces and contact angle is smaller
then 90
°
.

In

the

case

of

narrow

tubes

forces

arising

from

surface

tension

are

of

the

same

magnitude

as

gravitational

forces

acting

on

the

liquid

column
.

Forces

acting

on

the

liquid

column

in

a

capillary

tube
:

Figure
5
.
Forces acting on the liquid column in
a capillary tube.

2
g
π g
g
F m
ρ r s
 
Gravity

force

(
1
)

2
π
k
F o
γ r γ
 
Capillary

force

(
2
)

2
π
p a
l
F r p
l s


Capillary

pressure

force

(
3
)

2
π
a a a
F p A p r
 
Atmospheric

pressure

force

(
4
)

d
8
π
d
v
s
F
η s
t

Viscosity

force

(
5
)

d( )
cos cos
d
k a v g p
mv
F
Θ F F F β F
t
    
(
6
)

Assis.Prof.Dr. Lucija Hanžič

Capillary absorption in concrete

where

γ

is

surface

tension

(N/m),

r

is

capillary

radius

(m),

Θ

is

contact

angle

(
°
),

and

η

is

dynamic

viscosity

of

the

liquid

(Pa

s)
.

where
k

is capillary coeficient

(m s
-
1/2
) defined
as:

By

employing

some

simplifications

and

generalization

derivation

of

Eq
.

(
6
)

yields

Lucas
-
Washburn

equation,

which

describes

liquid

movement

in

porous

material

due

to

capillary

absorption
.

Hight

of

liquid

front

is

determined

as

h k t

(
7
)

cos
2
r
k

 

(
8
)

University of Maribor, Faculty of Civil Engineering

4/6

Figure 6. Graphical presentation of Lucas
-
Washburn equation.


Experiment
setup


Measurements

of

capillary

coefficient

were

carried

out

by

neutron

radiography
.

Several

subsequent

images

were

made

in

time

interval

from

1

to

260

h

and

different

liquids

namely

water,

fuel

oil

and

ethylene

glycol

were

used
.

Figure 7. Experiment setup (a) schematic representation of
specimen wetting, (b) specimens during wetting and (c) specimen
positioned in thermal column of nuclear reactor.

(a)

(b)

(c)

University of Maribor, Faculty of Civil Engineering

5/6

Assis.Prof.Dr. Lucija Hanžič

Capillary absorption in concrete


Results


Lucas
-
Washburn

equation

is

valid

only

in

the

initial

time

interval

after

the

contact

with

the

liquid

has

been

made
.

Duration

of

this

interval

depends

on

the

properties

of

the

porous

material,

properties

of

the

liquid

and

on

temperature

of

the

system
.

Figure 8. Results of capillary absorption analyses obtained by neutron radiography on concrete specimens for different liquid
s (
a) water,
(b) fuel oil and for ethylene glycol at 100
°
C in concrete specimens (c) without additives and (d) with air
-
entraining agent.

(a)

(
b
)

(
d
)

(
c
)

University of Maribor, Faculty of Civil Engineering

6/6

Assis.Prof.Dr. Lucija Hanžič

Capillary absorption in concrete


Further reading


Claisse P.A., Elsayad H.I., Shaaban I.G., 1997. Absorption and sorptivity of cover concrete,
J. Mater.
Civ. Eng.
, Aug., 105
-
110.

Hall, C., 1981. Water movement in porous building materials


IV. The initial surface absorption and the
sorptivity,
Build. Environ.

16 (3), 201
-
207.

Hall C., Hoff W.D., Taylor S.C., Wilson M.A., Beom
-
Gi Yoon, Reinhardt H.
-
W., Sosoro M., Meredith P.,
Donald A.M., 1995. Water anomaly in capillary liquid absorption by cement
-
based materials,
J. Mater.
Sci. Lett.

14, 1178
-
1181.

Hanžič L., Ilić R., 2003. Relationship between liquid sorptivity and capillarity in concrete,
Cem. Concr.
Res.

33 (9), 1385
-
1388.

Hanžič L., Nemec T., Ilić R., 2005. Determination of the capillarity coefficients of distilled water and oil in
concrete by neutron radiography,
Proc. 7th World Conf. on Neutron Radiography, Italian National
Agency for New Technologies, Energy and the Environment
, Rome, pp. 643
-
650.

Martys N.S., Ferraris C.F., 1997. Capillary transport in mortars and concrete,
Cem. Concr. Res.

27 (5),
747
-
760.

Schoelkopf J., Gane P.A.C., Ridgway C.J., Matthews G.P., 2002. Practical observation of deviation from
Lucas
-
Washburn scaling in porous media,
Colloids Surf. A: Physicochem. Eng. Asp.

206, 445
-
454.

Taylor S.C., Hoff W.D., Wilson M.A., Green K.M., 1999. Anomalous water transport properties of
Portland and blended cement
-
based materials,
J. Mater. Sci. Lett.

18, 1925
-
1927.


Vuorinen J., 1985. Depth of water penetration into concrete and coefficient of permeability,
Mag. Concr.
Res.

37 (132), 145
-
153.