Effect of Different Periods of Moist

Curing on Near-Surface Drying and

Ingress of Aggressive Fluids

R. Doug Hooton, and Dr. Birgit Meng

UNIVERSITY OF TORONTO

DEPT. CIVIL ENGINEERING

ACI Nov. 2015

The NMR-Mouse• Using device developed by RWTH, Aachen

University and marketed by Magritek.• Uses a permanent magnet to align protons in the

concrete, therefore the amplitude of the relaxation time signal is proportional to water content (mainly from free water in the pores).

• Measures over an area of 50 x 50 mm with a resolution of 0.10 mm.

• Moisture contents were measured at 0.50 mm depth increments from 0 to 15 mm on 150mm cubes sealed on sides.

Different Types of Hydrogen (Water) in concrete

Reference

The Potential of Nuclear Magnetic Resonance (NMR) to Non-Destructively Characterize Early-Age Concrete by an One-Sided Access (OSA) Technique

By G. Dobmann1, M. Kroening1, N. Surkowa1, L. von Bernus2, B. Wolter11 Fraunhofer-Institut fuerzerstoerungsfreie Pruefverfahren(IZFP),Universitaet Geb. 37, 66123 Saarbruecken, Germany gerd.dobmann@izfp.fraunhofer.de2 QNET - Quality Management GmbH, Altenkesseler Str. 17 B5, 66115 Saarbruecken, Germany T1 proton relaxation times:

Chemically combined water <10-4 s.Gel water (adsorbed) 10-3 sFree water 10-2 s

Concrete PropertiesTypical German Highway Concrete Pavement Mixture• 0.45 w/c • CEM I 42.5, 360kg/m3• 22mm greywacke aggregate• Air-entrained: 5.4% at 10 minutes, 4.7% at 30

minutes• Flow Table: 370 mm• 28 days:

– Cube strength: 43.5 MPa– ASTM C1202: 2430 coulombs– Bulk Resistivity: 9.8 kohm-cm

Three Types of Curing were used150 mm cubes were left their molds for the curing and drying periods to get 1-D profiles.

1. Covered with glass plate for 6 hours, then exposed to air at 50% rh at 23oC.

2. Covered for 20 hours, then immersed in water to Day 4, then exposed to air at 50% rh at 23oC.

3. Covered for 20 hours, then immersed in water to Day11, then exposed to air at 50% rh at 23oC.

Each 1-face drying profile was the average of 2 or 3 profiles at different locations

Top Finished Surface: Drying Profiles after 40 Days drying at 50% rh

0

2

4

6

8

10

12

14

0 5 10 15

Mo

istu

re c

on

ten

t (v

ol.

%)

Depth below Surface (mm)

MC % 6h curing

MC% 4 days curing

MC % 11 days curing

Poorly cured concrete dried out much more (~2.5 % less to 15mm depth)

Covered for 6h

4d and 11d wet cure

Moisture Profiles from Bottom face after 40 days drying (150mm below drying surface)

0

2

4

6

8

10

12

14

0 5 10 15

Mo

istu

re C

on

ten

t (v

ol.

%)

Depth from Bottom (mm)

MC % 6h Wet Cure

MC% 4d Wet Cure

MC % 11d Wet Cure

Not much difference but MC surface dried faster after poor curing

Rate of Drying after 0 days wet curing (covered for 6 hours) then 1 to 41 days dried at 50% rh at 23oC

0

1

2

3

4

5

6

7

8

9

0 5 10 15

Mo

istu

re c

on

ten

t, %

Depth, mm

Cube 1, 6h cure

20h dry

4d dry

6d dry

14d dry

21d dry

27d dry

41d dey

Linear (20h dry)

Linear (4d dry)

Linear (6d dry)

Linear (21d dry)

Linear (27d dry)

Linear (41d dey)

Noise & Surface Effects: Water Saturated for 14 days (2 profiles)

-4,000

-2,000

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

0 5 10 15 20

De

pth

fro

m S

urf

ace

[µ

m]

Water Content [V.-%]

P1

P2

Average P1-P2

Outer 2 mm of finished surface has higher paste content>> higher porosity>> 2x higher moisture content

Moisture content can vary by +/- 1% due to noise & aggregate content

1-face, Rate of Absorption Tests• One profile was

measured for each absorption time in the centre of the exposed cube surface

Rate of Absorption after 0 days wet curing (covered for 6 hours) then 40 days dried at 50% rh, then 4d at 40oC

0

5

10

15

20

25

-1 1 3 5 7 9 11 13 15

Mo

istu

re C

on

ten

t (v

ol.

%)

Depth below Surface (mm)

0min abs 1min abs 4min abs 9min abs 16min abs

25 min abs 36 min abs 1230 min abs 2610 min abs Linear (0min abs)

Poly. (1min abs) Poly. (4min abs) Poly. (9min abs) Poly. (16min abs) Poly. (25 min abs)

Poly. (1230 min abs) Poly. (2610 min abs)

Very fast initial ingress (< 4 minutes) of water to 12 mm depthAnd penetrating >15mm by 9 minutes.

Rate of Absorption after 4 days wet curing then 40 days dried at 50%rh, then 5 days at 40oC

0

2

4

6

8

10

12

14

16

0 2 4 6 8 10 12 14

Mo

istu

re c

on

ten

t (v

ol.

%)

Depth from surface (mm)

0min abs

1min abs

4min abs

9min abs

25 min abs

36 min abs

49 min abs

1140 min abs

Linear (0min abs)

Poly. (1min abs)

Poly. (4min abs)

Poly. (9min abs)

Poly. (9min abs)

Poly. (49 min abs)

Poly. (49 min abs)

Poly. (49 min abs)

Poly. (1140 min abs)

From 1 to 49 minutes absorption, get progressive ingress, but at 19 hours, moisture only increased at depths > 8 mm

Note that there is still moisture after 40 days drying

Rate of Absorption after 11 days wet curing then 40 days dried at 50%rh, then 4 days at 40oC

0

2

4

6

8

10

12

14

16

0 2 4 6 8 10 12 14

Wat

er

Co

nte

nt

(vo

l. %

)

Depth from surface (mm)

0min abs 1min abs 4min abs 9min abs

16min abs 25 min abs Linear (0min abs) Poly. (1min abs)

Poly. (4min abs) Poly. (9min abs) Poly. (16min abs) Poly. (25 min abs)

From 1 to 25 minutes absorption, get progressive ingress from surface

Rate of Absorption after 11 days wet curing then 40 days dried at 50%rh, then 4 days at 40oC

0

2

4

6

8

10

12

14

16

0 2 4 6 8 10 12 14

Wat

er

Co

nte

nt

(vo

l. %

)

Depth from surface (mm)0min abs 1min abs 4min abs9min abs 16min abs 25 min abs1140min abs Linear (0min abs) Poly. (1min abs)Poly. (4min abs) Poly. (9min abs) Poly. (16min abs)Poly. (25 min abs) Poly. (1140min abs)

Later, after 19 hours absorption, water content rises about 2% at depths >8 mm

Rate of Absorption Mass Gain vs SQRT Time (min.) for Different curing

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50 60

Wat

er

Ab

sorp

tio

n (

g)

SQRT Time (min)

6h Wet Cure Mass gain (g)

4d Wet Cure Mass gain (g)

11d Wet Cure Mass gain (g)

Much higher absorption with no curing, but no difference between 4 and 11 days wet curing

Effects of 40oC drying on Cube that was wet cured 14 days

• As follows:

Rate of Absorption up to 36 minutes after 14 days wet curing then 41 days dried at 40oC

0

2

4

6

8

10

12

14

16

18

0 2 4 6 8 10 12 14

Wat

er C

on

ten

t (v

ol.

%)

Depth from top surface (mm)

0min abs 1min abs 4min abs 9min abs 16min abs

25 min abs 36 min abs Linear (0min abs) Poly. (1min abs) Poly. (4min abs)

Poly. (9min abs) Poly. (16min abs) Poly. (25 min abs) Poly. (36 min abs)

Early Progressive Absorption of Water into surface

Rate of Absorption to 18 hours after 14 days wet curing then 41 days dried at 40oC

0

2

4

6

8

10

12

14

16

18

0 2 4 6 8 10 12 14

Wat

er C

on

ten

t (v

ol.

%)

Depth from top surface (mm)

0min abs 1min abs 4min abs 9min abs

16min abs 25 min abs 36 min abs 1080 min abs

Linear (0min abs) Poly. (1min abs) Poly. (4min abs) Poly. (9min abs)

Poly. (16min abs) Poly. (25 min abs) Poly. (36 min abs) Poly. (1080 min abs)

Early Absorption of Water into surface

Early Absorption of Water into surface

18h abs: rise in water content by 4% at depths > 9 mm

Rate of Absorption after 14 days wet curing then dried at 110oC

0

2

4

6

8

10

12

14

16

18

0 2 4 6 8 10 12 14

Wat

er C

on

ten

t (v

ol.

%)

Depth from top surface (mm)0min abs 1min abs 4min abs 9min abs

16min abs 36 min abs 16 h abs 38.5h abs

Linear (0min abs) Poly. (1min abs) Poly. (4min abs) Poly. (9min abs)

Poly. (16min abs) Poly. (36 min abs) Poly. (16 h abs) Poly. (38.5h abs)

Progressive water ingress to 16 minutes then water content building up at depths > 6 mm

Effect of Type of Drying on Water Absorption

Effect of Drying history on 16-minute Absorption (11 days wet curing)

0

2

4

6

8

10

12

14

16

0 2 4 6 8 10 12 14

Mo

istu

re C

on

ten

t (v

ol.

%)

Depth below Surface (mm)16min abs 50%rh 16min abs 110C16 min abs 40C Poly. (16min abs 50%rh)Poly. (16min abs 110C) Poly. (16 min abs 40C)

No effect on outer 7 mm from 50% rh, 40oC or 110oC drying

We know 110oC drying damages concrete but does not appear to affect absorption profile relative to 40oC drying, except for different starting moisture content

Conclusions

1. The NMR-mouse provides moisture profiles down to 15 mm depth in concrete, but there is some noise—likely due to variable coarse aggregate content at any given depth.

2. During absorption tests, surface pores were rapidly saturated, then moisture contents increased at depth.

3. Provision of 4 days wet curing at 20oC had a big impact on slowing drying and reducing absorption of water.

4. Wet curing beyond 4 days had little impact on drying or absorption rates (for the 0.45 w/c CEM I concrete cured at 20oC).

Further Research

1. Research on the near-surface impacts of shorter wet curing periods and alternative curing procedures is needed.

2. Research on the impacts of blended cements on curing requirements is also needed.

3. Would be interesting to use the NMR to look at rate of water removal profiles using solvent exchange drying.

Other interesting things in Germany2 m (6.5 ft) diameter pavement cores