nist self-desiccation seminar june 20, 2005 l-o nilsson a macro-model for self-desiccation in hpc a...

NIST self-desiccation seminar June 20, 2005 L-O Nilsson

A MACRO-MODEL FOR SELF-DESICCATION IN HPC

A MACRO-MODEL FOR SELF-DESICCATION IN HIGH PERFORMANCE

CONCRETE

Lars-Olof Nilsson

Div. of Building MaterialsLund Institute of

TechnologyLund University

Kristina Mjörnell

Dept. of Building PhysicsSwedish National Testing and Research Institute,

Borås



Outline

1. Introduction2. The model for self-desiccation3. Physical binding of water4. Chemical binding of water5. Internal curing6. Predictions with the model 7. Conclusion



HPC in Sweden

1. A few important marine concrete structures where a service-life of some 100 years is required in harsh marine environments (a SRPC/silica fume HPC)

2. 1000’s of concrete floor slabs where a moisture sensitive flooring is to be used (OPC HPC; w/C 0.40: Main reason for using HPC is the controlled and rapid drying by self-desiccation.



Drying of HPC

NB HPB

HPCNC



Dominating mix parameters for self-desiccation

SRPC

OPC

70

75

80

85

90

95

100

0.2 0.3 0.4 0.5 0.6

w/C

RH

(%

), 2

8 da

ys

Self-desiccation 28 days,

Norling-Mjörnell (1997)

cement typeand w/c

Really true?



Self-desiccation in the sorption isotherm

RH [%]0 100

W [kg/m3]

W0

Wn

We

RHself

RH [%]0 100

W [kg/m3]

W0

Wn

We

RHself

wwwwRH

wRH

ne

eself

0

)(



The model for self-desiccation

))(),(()),(),(()( ttTttTwRHtRH Ceself

)()(),()( 0 twttTwwtw ne where



Physical binding of water

0

300

0 20 40 60 80 100

RH [%]

We/C

w/C 0.3

w/C 0.8

0

700

0 20 40 60 80 100

RH [%]

We

w/C 0.3

w/C 0.8

0

0.2

0.4

0.6

0.8

1

0 20 40 60 80 100

RH [%]

Scap

w/C 0.3

w/C 0.8

we/C we Scap

Alkalieffect



Desorption isotherms for HPCf(w/B, Si)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 20 40 60 80 100

RH [%]

We/

C

4005 V

3005 V

2505 V

w /B=0.25, 0.30 & 0.40; 5% Si

data from Helsing-Atlassi

0

0.05

0.1

0.15

0.2

0.25

0.3

0 20 40 60 80 100

RH [%]

We/

C

2510 V

2505 V

2500 V

w /B=0.25; 0, 5 & 10% Si

data from Helsing-Atlassi





the desorption isotherm at different ages



Desorption isotherms for HPCat early ages (room temperature)

0

0.1

0.2

0.3

0.4

0 20 40 60 80 100

RH (%)

We

/C

0.1 0.4 0.70.1-0.2 0.2-0.3 0.3-0.40.4-0.5 0.5-0.6 0.6-0.70.7-0.8

w/C=0.40

Data from Norling Mjörnell (1997)

0

0.1

0.2

0.3

0.4

0 20 40 60 80 100

RH (%)

We

/C

0.1 0.3 0.50.1-0.2 0.2-0.3 0.3-0.40.4-0.5

w/C=0.25

Data from Norling M jörnell (1997)





)()(),()( 0 twttTwwtw ne where

= chemical binding of water at different T & RH(t)



Chemical binding of water

S0.34C0.25w SCn

ref

CTCw

C

t

t

t

t

)()(/



0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 0.2 0.4 0.6 0.8 1

Degree of cement reaction,

w

/C

w/C = 0.70.4

0.25

Chemical binding of waterlack of space

a

C

CCCw

max,

max,/

w/c

c



Chemical binding of watermoisture effects

G 1510 20 40 60 80 100

RH [%]

W /cn

0.16

0.14

0.12

0.10

0.08

0.06

0.04

0.02

0

Parrott et al /1986/

1

Powers /1947/

Norling/1994/

carbonation?

RHwn/C(RH, t1)



75 % RH

85 % RH

95 % RH

sealed

water

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

1 10 100 1000 10000 100000

Time (h)

Wn

/C

curing:

TGA-studies on reactivity at shortage of water

Norling-Mjörnell (1997)

SRPC, w/C=0.3, 5% Si-fume




G 1510 20 40 60 80 100

RH [%]

W /cn

0.16

0.14

0.12

0.10

0.08

0.06

0.04

0.02

0


1

Powers /1947/

Norling/1994/

OPCMjörnell (1997)

RHwn/C(RH, t1)




G 1510 20 40 60 80 100

RH [%]

W /cn

0.16

0.14

0.12

0.10

0.08

0.06

0.04

0.02

0


1

Powers /1947/

Norling/1994/

OPCSi-fume Mjörnell (1997)

RHwn(RH, t1)




G 1510 20 40 60 80 100

RH [%]

W /cn

0.16

0.14

0.12

0.10

0.08

0.06

0.04

0.02

0


1

Powers /1947/

Norling/1994/

RHwn(RH, t1)

f()

alkali effect?




0

0.2

0.4

0.6

0.8

1

50 60 70 80 90 100

RH [%]

w/C=0.4 SRPC

0.7

0.1

, w

4

0, 19.0/

CwgC

Cwge

w kCw

kC

w

c

,w

cf. Snyder & Bentz(2004)



Chemical binding of watertemperature effects

273

11

TT

Trefe

3

10

30

Tref



Predictions with the model- cement hydration

w/C 0.4 OPC

100%

95%

85%

75%

59%

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 14 28 42 56 70Time (days)

c

c

w/c 0.4 OPC



Predictions with the model- self-desiccation, room temperature

OPC w/C=0.4

SRPC w/C=0.4

SRPC w/C=0.25

70

75

80

85

90

95

100

0 100 200 300 400

Time (days)

RH (%)



Predictions with the model- cement hydration, curing effects

water cured

seal cured

seal cured at 5°C

0

0.2

0.4

0.6

0.8

1

0.01 0.1 1 10 100 1000

Time (days)

C

c

SRPC with w/c 0.4



Predictions with the model- self-desiccation, low temperature

20°C

5°C

80%

82%

84%

86%

88%

90%

92%

94%

96%

98%

100%

0 200 400 600 800

Time (days)

RH

But later findings indicate quite another low-temperature curing effect! cf. Persson (2005)

SRPC with w/c 0.4



Conclusions

•The model for self-desiccation seems very promising and potentially useful for many applications of HPC

•The model is especially designed for concrete floor slabs, where self-desiccation is beneficial.

•Could very well be applied to concrete structures of HPC were the main concern of self-desiccation is shrinkage and early age cracking, and including internal curing.

•The model can easily be integrated into a model that includes moisture transport (has been done!)

•The most uncertain part of the model is the moisture effect on rate of reaction, where more research is needed, especially at very early ages.

•The effect of early curing at low temperature may require special attention!

nist self-desiccation seminar june 20, 2005 l-o nilsson a macro-model for self-desiccation in hpc a...

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