Evaluation of the modified slab test for resistance of concrete to internal frost damage. Nordtest project 1485-00

Dirch Bager

Stefan Jacobsen

Heikki Kukko

Gísli Gudmundsson

Evaluation of the Modified Slab Test

for Resistance of Concrete to Internal

Frost Damage

NORDTEST Project No. 1485-00

SP

Swedish National Testing and Research Institute

Building Technology

Evaluation of the Modified Slab Test for Resistance of

Concrete to Internal Frost Damage

- Nordtest project No. 1485-00

Abstract

This report presents the results from the precision evaluation of the modified slab test for

resistance of concrete to internal frost damage. Two round Robin tests, one at the Nordic

level and another at the RILEM level, were carried out in the project. Three

non-destructive detecting techniques, Ultrasonic Pulse Transmission Time (UPTT), Dilation

(length change) and Fundamental Frequency (FF), were evaluated through the round

Robin tests. A destructive method (flexural strength test) was employed to examine the

deterioration of concrete in mechanical properties due to internal frost damage. The

results show that all the three techniques can be employed in the slab test for detecting

internal damage of concrete subjected to frost attack. The dilation method reveals a better

repeatability, but has a reproducibility similar to the UPTT technique. The temperature

effect on test precision seems not significant. Therefore, the same frost test procedure as

described in the Swedish standard SS 72 13 44 can be used in the modified slab test. Due

to a very small number of laboratories participated in the FF test the precision estimate

for this technique involves a large uncertainty. Since the FF test reveals promising

sensitivity to detecting internal damage, further collaboration study is needed for

evaluating the precision of this technique.

Key words: concrete, freezing-and-thawing, internal damage, test methods.

SP Sveriges Provnings- och

Forskningsinstitut

SP Rapport 2000:34

ISBN 91-7848-835-4

ISSN 0284-5172

Borås 2000

SP Swedish National Testing and

Research Institute

SP Report 2000:34

Postal address:

Box 857, SE-501 15 BORÅS

Sweden

Telephone +46 33 16 50 00

Telex 36252 Testing S

Telefax +46 33 13 55 02

Contents

Page

Abstract ii

Preface iv

1 Introduction

1

2

Techniques for Detecting Internal Damage

3

2.1 Dilation

measurement

3

2.2 UPTT

measurement

3

2.3 FF

measurement

5

2.4 Destructive

test

7

3 Nordtest

RRT

8

3.1

Standard test programme

8

3.2

Extra test programme

9

3.3

Manufacture and distribution of specimens

9

3.4 Test

results

10

4 RILEM

RRT

18

4.1 Test

programme

18

4.2

Distribution of specimens

18

4.3 Test

results

18

5 Discussions

25

5.1

Effect of the 24 hours storage at 20 °C

25

5.2

Relations between internal damage and measured values

25

5.3

Precision of the dilation and UPTT techniques

25

5.4

A special discussion of the FF test

27

6 Concluding

Remarks

30

7 References

31

Appendix 1 - Distribution of specimens for the Nordtest RRT

32

Appendix 2 - Raw data from the Nordtest RRT

33

Preface

In order to continuously improve our knowledge and understanding of frost attack to

concrete, and to evaluate the repeatability and reproducibility of the modified Slab Test, the

Nordetest granted this project. Five institutions in the Nordic countries, that is, CBL in

Denmark, IBRI in Iceland, NBRI in Norway, SP in Sweden and VTT in Finland participated

the project. The project includes two parts: 1) evaluation of the modified slab test through

round Robin tests and 2) evaluation of models of frost damage through cooperative studies.

Two round Robin tests, one at the Nordic level and another at the RILEM level, were carried

out in the project. The above five institutions participated the round Robin tests at both levels,

while HUT in Finland, ItalCem in Italy and NorCem in Norway participated in the test at the

RILEM level. This is the final report for Part 1 - evaluation of the modified slab test. The

results from Part 2 will be reported elsewhere.

Tang Luping

1 Introduction

In the previous two Nordtest projects, the incorporations of the ultrasonic measurement and

the dilation measurement in the Slab Test have been developed and evaluated /1, 2/. The

results from these projects show that the Slab Test with modifications can also be used for

testing internal frost damage (cracking) in concrete. Owing to a small number of laboratories

participated in the previous studies and the lack of unified test procedures, deviations in the

test results were inevitably large, especially for the dilation measurement. Nevertheless, from

those previous projects, a draft version of the modified Slab Test was proposed. In order to

continuously improve our knowledge and understanding and to evaluate the repeatability and

reproducibility of the modified Slab Test, the Nordtest granted this project. The main purpose

of the project is, through round-robin tests and individual laboratory experiments, to evaluate

the precision of the modified Slab Test and to improve the knowledge and understanding of

frost damages in concrete. In this report the results from the precision analysis is presented.

The models for frost damage will be presented in another report authored by Bager et al /3/.

Two round-Robin tests (RRT) have been conducted. The first one was in the Spring 2000

through a Nordtest project. Five Nordic laboratories (CBL, IBRI, NBRI, SP and VTT)

participated in this Nordtest RRT. Four types of concrete were tested in the Nordtest RRT.

The second one was in the Summer 2000 through the cooperative action of RILEM TC-IDC.

Eight laboratories (CBL, HUT, IBRI, ItalCem, NBRI, NorCem, SP and VTT) participated in

this RIELM RRT. Three types of concrete manufactured in Essen, Germany, were tested in

the RILEM RRT. Due to the equipment problem (out of order) IBRI could not produce any

data, while due to the delivery delay of ultrasonic equipment NorCem could not supply the

initial data of UPTT, resulting in a discard of its UPTT data.

Three detecting techniques, Ultrasonic Pulse Transmission Time (UPTT), Dilation,

Fundamental Frequency (FF) were employed in the RRTs, as listed in Table 1.1.

Table 1.1. Techniques used in the RRTs for detecting internal damage of concrete

UPTT

Dilation

FF

Laboratory Nordtest

RILEM Nordtest RILEM Nordtest

RILEM

CBL X

X

X

X

HUT

X X

IBRI X

X

ItalCem

X

X

NBRI X

X

X

X

NorCem

X

SP X

X

X

X

X*

X

VTT X

X

X

X

X*

X

Number of laboratory

5

5

5

7

3

The frost test was basically in accordance with the Swedish standard SS 72 13 44, but a 24

hours storage at 20 °C after specified freezing-and-thawing cycles was included to study the

temperature influences on the measurements, which was thought as one of the reasons to the

large deviations in the test results, especially for the dilation test.

It should be noted that the FF testing is a new approach for the slab specimen and previously

unused in the previous Nordtest projects and most European facilities, even though the similar

method has been specified in ASTM C 215 /4/, where the relative dynamic modulus (RDM),

which is proportional to the squared ratio of the measured frequency to the initial frequency,

is defined to evaluate the deterioration of concrete.

Since the dimensions must be consistent in order to compare different detecting techniques,

the priority was, in this study, given to the consistency in dimensions in the precision

evaluation. Thus the following equations were used for presenting the test results:

UPTT

0 0 UPTT

t

t

t

i

−

=

ξ

(1.1)

where

t is the transmission time in

µs, and subscript i denotes the number of

thawing cycles and subscript 0 represents the initial value measured before the

freezing-and-thawing test start.

FF

0 0 0 0 FF

f

f

f

f

f

f

i

−

=

−

i

−

=

ξ

(1.2)

where

f is the fundamental frequency in kHz.

Dilation

100

150

100

0 0 0 0 L

×

+

−

=

×

−

=

l

l

l

L

L

L

_{i i}

ξ

[%]

(1.3)

where L is the specimen length in mm, l is the reading from the micrometer in mm, and the

factor 100 is in order to make the value of ξ

L

comparable with ξ

UPTT

and ξ

FF

.

The precision analysis was carried out in accordance with the international standard ISO

5725-2 /5/. The 1% significance level of Mandel’s k-statistic and h-statistic was employed as

outlier criteria. Due to the limited number of laboratory, only the outliers at the first running

of calculation were rejected. According to ISO 5725-1 /6/, the repeatability conditions should

be those under which independent test results are obtained with the same method on identical

test items in the same laboratory by the same operator using the same equipment within short

interval of time, and the reproducibility conditions should be those under which independent

test results are obtained with the same method on identical test items in different laboratories

with different operators using different equipment. For concrete specimens, however, it is

difficult to manufacture “identical items”. Thus the variation in specimens is included in the

precision results. In addition, due to a long term of the frost test, the operator in each

laboratory may not always the same. Therefore, the variation in operators may also be

included in the precision results.

2

Techniques for Detecting Internal Damage

2.1 Dilation

measurement

A “three points” expansometer was employed for measuring the length of a specimen. An

example of expansometer is shown in Fig. 2.1. The expansometer was calibrated with a 150

mm long reference steel block before the test.

Fig. 2.1. Specimen on the three-points expansometer.

2.2 UPTT

measurement

The UPTT (Ultrasonic Pulse Transmission Time) was measured using 50-60 KHz conic

transducers. The measurement arrangement is shown in Fig. 2.2.

Rubber cloth Transducers

Specimen

Fig. 2.2. Illustration for the UPTT measurement (a side view).

Marked points

Steel frame

Micrometer gauge

Flat studs

Test surface

50

Specimen

Rubber sheet

Alignment mark

Nib with R > 4 mm

2.3 FF

measurement

Different modes used in the FF (Fundamental Frequency) measurement are illustrated in Figs.

2.3 and 2.5. In the RILEM RRT, the transverse mode (by tapping at the centre) was used at

VTT, while the longitudinal mode was used at SP and ItalCem. SP also tested both the

longitudinal mode and the transverse mode (by tapping at the edge) and got a good linear

relationship between them, as shown in Fig. 2.6.

Fig. 2.3. Longitudinal mode (a side view).

Fig. 2.4. Transverse mode by tapping at the centre (upper – a bird view, lower – a side view).

Rubber cloth

Accelerometer

Specimen

Tapping

Rubber pad

Accelerometer

Specimen Tapping

Rubber cloth

Accelerometer

Specimen

Tapping

Rubber pad

Accelerometer

Specimen Tapping

Accelerometer

Specimen Tapping

Rubber cloth

Accelerometer

Specimen

Tapping

Rubber pad

Rubber cloth

Accelerometer

Specimen

Tapping

Rubber pad

Accelerometer

Specimen

Tapping

Rubber cloth

Accelerometer

Specimen

Tapping

Rubber pad

Accelerometer

Specimen

Tapping

Accelerometer

Specimen

Tapping

Rubber cloth

Accelerometer

Specimen

Tapping

Rubber pad

Rubber cloth

Accelerometer

Specimen

Tapping

Rubber pad

Fig. 2.5. Transverse mode by tapping at the edge (upper – a bird view, lower – a side view).

Fig. 2.6. Relationship between transverse and longitudinal modes.

0

5

10

15

20

0

2

4

6

8

10

FF (Transverse mode), kH z

FF

(

L

on

gi

tu

d

ina

l m

o

de

),

k

H

z

Series 1.1

Series 1.2

Series 1.3

Mix I-W

Mix I-S

Mix II-B

Mix III

R egres s ion

2.4 Destructive

test

Destructive test is employed to check the actual deterioration of concrete after the action of

freezing-and-thawing cycles. From the previous study /1/ it was found that the compressive

strength test is not very sensitive to the internal damage. It should, therefore, be better to test

flexural strength instead. The test can be carried out on a compression machine in such a way

as shown in Fig. 2.7. The change in flexural strength R is expressed as

0 0 0 0 R

R

R

R

R

R

R

_i

−

_i

=

−

−

=

ξ

(1.4)

Fig. 2.7. Illustration of bending test for flexural strength.

Specimen

120 mm

Test surface

Rubber cloth

Specimen

120 mm

Test surface

Rubber cloth

3 Nordtest

RRT

3.1

Standard test programme

The standard test programme was, or should be, carried out at all the participating

laboratories. Four qualities of Swedish concrete including three w/c (0.32, 0.50 and 0.70)

were tested in the Nordtest RRT. The Mixture proportions and physical properties of concrete

are given in Table 3.1. These qualities are similar to those used in the previous Nordtest

projects /1, 2/. The measurements (see Table 1.1) were made before preconditioning

(wetting), before frost start, before and after a 24 hrs storage at 20 °C after 2, 6, 12, 18, 24, 37

and 50 freezing-and-thawing cycles. For series I-S, I-W and II-A, the freezing-and-thawing

cycles were prolonged up to 91 at some laboratories.

Table 3.1. Mixture proportions and physical properties of concrete used in the

Nordtest RRT.

Test series

Mix I-S

Mix I-W

Mix II-A

Mix II-B

Mix III

Freezing medium

3%NaCl

Water*

3% NaCl

Water*

Water*

Cement type

Swedish SRPC (corresp. to CEM I 42.5R)

Cement content, kg/m

3

500 375 375 285

Water-cement

ratio 0.32 0.50 0.50 0.70

Aggregate, 0∼8 mm,

kg/m

3

839 910 910 1041

Aggregate, 8∼16 mm,

kg/m

3

946 840 840 818

Water reducer: Type

Dose, wt% of cement

Medcrete

0.012

None None None

AEA: Type

Dose, wt% of cement

None Cementa

L16

0.007

None None

Air content, vol%

1.5

3.7

0.8

0.9

Slump, mm

125

85

95

80

Strength** at 28 d, MPa

86.7 ± 2.3

50.5 ± 0.0

55.6 ± 3.3

36.5 ± 0.6

* demineralised ; ** according to Swedish standard SS 13 72 10.

3.2

Extra test programme

The extra test programme was carried out at some of the participating laboratories. The

programme is listed in Table 3.2. The results of flexural strength will be presented in this

report, while other results from the extra tests will be presented elsewhere /3/.

Table 3.2. Extra test programme.

Code Test

Mixtures/Series

Laboratory

A

Continuous dilation measurement

Mix I-S, I-W, II-B, III SP, VTT

B

Moisture distribution

Mix I-S, I-W

CBL, IBRI, SP

B1

Using Aalborg (Denmark) tap water

as freezing medium

Mix I-W, II-B

CBL, SP

B2

Using Borås (Sweden) tap water as

freezing medium

Mix I-W, II-B

CBL, SP

C

Sealed during the 24 hrs storage at 20

°C

Mix I-S, I-W

SP

D

Sealed during freezing, immersion in

water during thawing

Mix I-S, I-W, III

CBL, NBRI

D’

Water binding effect

Paste samples

CBL

E

Water uptake at 20 °C

Mix I-W, II-B, III

SP

F

Flexural strength or others

Mix I-S, I-W, II-B, III SP, CBL

For flexural strength test, one specimen was taken out of the freezer after specified

freezing-and-thawing cycles and stored at 20 °C with the test surface water covered. At the end of frost

test, all the specimens from the relevant series of the standard test programme were used for

testing the final flexural strength, while the specimens from the extra test program E were

used for testing the initial flexural strength. The specimens were stored at 20 °C and 65%RH

with the test surface dry for about two weeks before being bent on a compression machine.

3.3

Manufacture and distribution of specimens

All the concrete specimens were produced at SP in Sweden. Each concrete was mixed in one

batch by using a 250 l paddle mixer. The concrete cubes of size 150 mm were cast in steel

moulds and numbered in order of casting. The moulds with the fresh concrete were covered

with thick plastic films to prevent evaporation from the concrete surface. One day after

casting the cubes were demoulded, grouped (see Appendix 1) and cured in the ways

according to SS 72 13 44. At the age of 21 days, two slab specimens of size 150×150×50 mm

were sawn from each of the concrete cubes as listed in Appendix 1. The sawing direction is

illustrated in Fig. 3.1. Directly after sawing, the specimens were washed with water and the

excess water on the surfaces of the specimen was wiped off with a moist sponge. The

specimens were then returned to the climate chamber overnight. On the next day the

specimens were in groups sealed in plastic bags and were assorted for four laboratories

according to Appendix 1. The assorted specimens were then packaged and transported to

different laboratories.

Test surface

50 ± 2 mm

50 ± 2 mm

Casting direction

Fig. 3.1. Illustration for sawing of slab specimens from a concrete cube.

3.4 Test

results

The raw data reported from the participating laboratories are listed in Appendix 2, and the

results of flexural strength are presented in Table 3.3. The results of precision analysis as well

as changes in FF and flexural strength are summarised in Tables 3.4 and 3.5, and illustrated in

Figs. 3.2 and 3.3, where m denotes the general mean of relevant parameters, s

r

and s

R

denote

the standard deviation of repeatability and reproducibility, respectively. Some of the plots of

m at different freezing-and-thawing cycles are shown in Figs. 3.4 to 3.6.

Table 3.3. Results of flexural strength from the Nordtest RRT measured at SP, MPa.

Series Cycle

0 2 6 12 18 24 37

50

91

I-S

8.05 ± 0.57*

6.43 ± 1.09

I-W

8.05 ± 0.57*

8.02 8.38 8.19 7.27 7.41

8.04 ± 1.44

II-B

8.36 ± 0.27

8.17 7.29

6.73

5.57 ± 0.99

III

7.12 ± 0.70

6.85 6.36 4.46 3.48 3.09 1.91 2.31 ± 0.32

Table 3.4. Summary of the precision analysis results from the Nordtest RRT

(according to the data measured before the 24 hrs storage at 20 °C).

* FF measured at VTT only.

(f

0

-f

i

)/f

0

Series

Level j m

s

r

s

R

m

s

r

s

R

m*

Mix I-salt

Wetting 0.003 0.008 0.008 -0.004 0.005 0.005

Cycle 0 0.000 0.000 Cycle 2 -0.008 0.011 0.014 -0.012 0.015 0.021 Cycle 6 -0.006 0.017 0.017 -0.003 0.018 0.019 0.001 Cycle 12 -0.005 0.013 0.019 0.000 0.011 0.011 -0.003 Cycle 18 -0.014 0.012 0.013 0.004 0.009 0.012 -0.001 Cycle 24 -0.008 0.021 0.021 0.006 0.011 0.012 -0.003 Cycle 37 -0.022 0.013 0.013 0.014 0.009 0.019 -0.002 Cycle 50 -0.028 0.011 0.013 0.014 0.014 0.029 -0.006 Cycle 65 -0.034 0.015 0.015 0.015 0.016 0.016 -0.007 Cycle 78 -0.031 0.005 0.010 0.014 0.017 0.021 -0.004 Cycle 91 -0.025 0.017 0.017 0.027 0.018 0.018 -0.001

Mix I-water

Wetting -0.009 0.014 0.016 -0.001 0.008 0.011

Cycle 0 0.000 0.000 Cycle 2 -0.006 0.012 0.020 -0.006 0.010 0.016 Cycle 6 -0.005 0.021 0.021 -0.004 0.008 0.014 0.001 Cycle 12 -0.015 0.018 0.020 -0.002 0.008 0.012 -0.002 Cycle 18 -0.019 0.022 0.023 0.002 0.011 0.015 -0.004 Cycle 24 -0.025 0.028 0.028 0.005 0.010 0.015 -0.002 Cycle 37 -0.026 0.020 0.021 0.008 0.014 0.019 -0.002 Cycle 50 -0.034 0.018 0.023 0.009 0.013 0.022 -0.003 Cycle 65 -0.029 0.025 0.025 0.002 0.007 0.013 -0.005 Cycle 78 -0.035 0.016 0.020 0.004 0.009 0.016 -0.006 Cycle 91 -0.027 0.034 0.034 0.004 0.010 0.012 -0.013

Mix II-A

Wetting -0.003 0.013 0.017 -0.006 0.004 0.006

Cycle 0 0.000 0.000 Cycle 2 0.006 0.005 0.006 -0.006 0.008 0.014 Cycle 6 -0.005 0.007 0.012 -0.011 0.013 0.014 -0.003 Cycle 12 -0.017 0.010 0.012 -0.012 0.017 0.022 -0.005 Cycle 18 -0.009 0.009 0.019 -0.010 0.028 0.030 -0.010 Cycle 24 -0.018 0.009 0.009 -0.011 0.029 0.029 -0.010 Cycle 37 -0.027 0.007 0.017 -0.008 0.019 0.027 -0.011 Cycle 50 -0.035 0.015 0.017 -0.008 0.028 0.033 -0.014 Cycle 65 -0.044 0.009 0.013 -0.005 0.011 0.017 -0.020 Cycle 78 -0.038 0.011 0.011 -0.011 0.008 0.008 -0.018 Cycle 91 -0.049 0.014 0.014 -0.003 0.019 0.019 -0.023

Mix II-B

Wetting -0.002 0.019 0.019 -0.006 0.008 0.008

Cycle 0 0.000 0.000 Cycle 2 -0.001 0.010 0.012 -0.006 0.009 0.012 Cycle 6 -0.002 0.011 0.015 -0.005 0.011 0.013 0.009 Cycle 12 -0.013 0.017 0.018 -0.003 0.017 0.019 0.054 Cycle 18 -0.015 0.023 0.026 0.007 0.015 0.021 0.156 Cycle 24 -0.005 0.027 0.034 0.026 0.018 0.028 0.250 Cycle 37 0.018 0.032 0.051 0.072 0.035 0.056 0.343 Cycle 50 0.091 0.053 0.082 0.123 0.047 0.067 0.459

Mix III

Wetting 0.005 0.011 0.012 -0.004 0.006 0.013

Cycle 0 0.000 0.000 Cycle 2 -0.002 0.007 0.007 0.000 0.005 0.006 0.008 Cycle 6 0.005 0.024 0.034 0.004 0.005 0.007 0.077 Cycle 12 0.087 0.046 0.061 0.054 0.019 0.031 0.316 Cycle 18 0.205 0.033 0.036 0.158 0.039 0.066 0.462 Cycle 24 0.315 0.087 0.162 0.263 0.045 0.089 0.573 Cycle 37 0.682 0.210 0.329 0.423 0.072 0.143 0.630 Cycle 50 0.922 0.190 0.340 0.566 0.114 0.230 0.715

Before storage

(t

i

-t

0

)/t

0

100x(L

i

-L

0

)/L

0

Table 3.5. Summary of the precision analysis results from the Nordtest RRT

(according to the data measured after the 24 hrs storage at 20 °C).

* FF (transverse mode) measured at VTT.

** FF (transverse mode) and flexural strength measured at SP.

(R

0

-R

i

)/R

0

Series

Level j m

s

r

s

R

m

s

r

s

R

m*

m**

m**

Mix I-S

-3 0.003 0.008 0.008 -0.004 0.005 0.005 0 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 2 0.001 0.011 0.013 0.005 0.016 0.018 6 0.002 0.008 0.010 0.008 0.015 0.015 0.000 12 -0.006 0.015 0.016 0.007 0.012 0.012 0.000 18 -0.014 0.011 0.011 0.009 0.009 0.013 -0.001 24 -0.002 0.016 0.023 0.014 0.010 0.020 -0.002 37 -0.018 0.013 0.013 0.014 0.009 0.010 -0.004 50 -0.023 0.013 0.018 0.022 0.016 0.025 -0.002 0.033 65 -0.025 0.018 0.027 0.024 0.012 0.015 -0.004 0.030 78 -0.031 0.009 0.012 0.021 0.017 0.017 -0.007 0.029 91 -0.031 0.012 0.012 0.026 0.014 0.016 -0.006 0.027 0.201

Mix I-W

-3 -0.009 0.014 0.016 -0.001 0.008 0.011 0 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 2 0.000 0.014 0.021 0.002 0.008 0.011 0.005 6 -0.002 0.020 0.025 0.002 0.009 0.012 -0.002 -0.016 0.004 12 -0.007 0.010 0.016 0.001 0.011 0.013 -0.007 0.012 -0.041 18 -0.011 0.021 0.026 0.003 0.011 0.013 -0.004 0.018 -0.017 24 -0.007 0.016 0.020 0.008 0.010 0.017 -0.006 -0.015 0.097 37 -0.011 0.012 0.021 0.008 0.009 0.009 -0.010 0.016 0.080 50 -0.014 0.020 0.027 0.006 0.010 0.016 -0.019 0.018 65 -0.011 0.020 0.031 -0.014 0.010 0.029 -0.011 0.010 78 -0.024 0.014 0.020 0.007 0.013 0.020 -0.013 0.008 91 -0.030 0.022 0.022 0.014 0.009 0.020 -0.021 0.007 0.001

Mix II-A

-3 -0.003 0.013 0.017 -0.006 0.004 0.006 0 0.000 0.000 0.000 0.000 0.000 0.000 2 -0.001 0.006 0.006 -0.005 0.008 0.009 6 -0.005 0.007 0.010 0.000 0.010 0.010 0.001 12 -0.009 0.010 0.011 -0.011 0.024 0.025 -0.002 18 -0.016 0.008 0.008 -0.006 0.025 0.028 -0.004 24 -0.014 0.011 0.011 -0.007 0.029 0.031 -0.005 37 -0.021 0.012 0.016 -0.010 0.031 0.031 -0.008 50 -0.027 0.013 0.015 -0.008 0.028 0.033 -0.014 65 -0.033 0.017 0.017 0.003 0.004 0.005 -0.013 78 -0.027 0.014 0.025 -0.001 0.009 0.009 -0.012 91 -0.049 0.027 0.027 0.000 0.008 0.009 -0.018

Mix II-B

-3 -0.002 0.019 0.019 -0.006 0.008 0.008 0 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 2 0.002 0.015 0.022 -0.003 0.011 0.015 6 -0.003 0.015 0.015 0.002 0.010 0.010 0.013 12 -0.010 0.015 0.015 0.006 0.012 0.012 0.039 0.009 0.023 18 -0.013 0.016 0.022 0.012 0.015 0.020 0.111 24 -0.005 0.025 0.033 0.031 0.018 0.030 0.180 0.010 0.129 37 0.020 0.033 0.045 0.073 0.033 0.054 0.275 0.033 0.195 50 0.056 0.053 0.070 0.088 0.038 0.038 0.406 0.122 0.334

Mix III

-3 0.005 0.011 0.012 -0.004 0.006 0.013 0 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 2 -0.012 0.007 0.014 0.001 0.005 0.005 0.005 -0.012 0.038 6 0.001 0.021 0.032 0.007 0.007 0.008 0.053 0.007 0.107 12 0.060 0.030 0.047 0.060 0.018 0.029 0.224 0.053 0.374 18 0.166 0.040 0.046 0.155 0.032 0.061 0.353 0.114 0.511 24 0.282 0.075 0.081 0.266 0.045 0.087 0.469 0.208 0.566 37 0.501 0.145 0.201 0.420 0.074 0.146 0.580 0.455 0.732 50 0.670 0.204 0.234 0.550 0.090 0.238 0.668 0.716 0.676

After storage

(t

i

-t

0

)/t

0

100x(L

i

-L

0

)/L

0

(f

0

-f

i

)/f

0

Fig. 3.2. Standard deviation of repeatability (upper) and reproducibility (lower)

from the Nordtest RRT, measured before the 24 hrs storage at 20 °C.

before 24 h storage at 20 °C

0

0.1

0.2

0.3

0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Ge ne ra l m e a n m

S

td

d

e

v

o

f

re

p

e

a

ta

b

ilit

y

s

r

UP TT

Dilation

before 24 h storage at 20 °C

0

0.1

0.2

0.3

0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Ge ne ra l m e a n m

S

td

d

e

v

o

f r

e

p

ro

d

u

c

ib

ilit

y

s

R

UP TT

Dilation

Fig. 3.3. Standard deviation of repeatability (upper) and reproducibility (lower)

from the Nordtest RRT, measured after the 24 hrs storage at 20 °C.

after 24 h storage at 20 °C

0

0.1

0.2

0.3

0.4

-0.2

0

0.2

0.4

0.6

0.8

Ge ne ra l m e a n m

S

td de

v

of

r

e

pe

a

ta

b

il

it

y

s

r

UP TT

Dilation

after 24 h storage at 20 °C

0

0.1

0.2

0.3

0.4

-0.2

0

0.2

0.4

0.6

0.8

Ge ne ra l m e a n m

S

td

d

e

v

of

r

e

pr

oduc

ib

il

it

y

s

R

UP TT

Dilation

Fig. 3.4. Plot of general mean m to freezing-and-thawing cycles from the

Nordtest RRT for concrete with w/c 0.32 (measured before the 24 hrs

storage except for SP’s strength and FF data).

Concre te M ix I-S , w /c 0.32, non-AEA

Fre e z ing m e dium : 3% Na Cl

-0.1

0

0.1

0.2

0.3

0.4

0.5

0

20

40

60

80

100

Fre e z ing-a nd-tha w ing cycle s

G

e

n

e

ra

l m

ean

S trength

UP TT

Dilation

FF,V TT

FF, S P

Concre te M ix I-W , w /c 0.32, non-AEA

Fre e z ing m e dium : de m ine ra lise d w a te r

-0.1

0

0.1

0.2

0.3

0.4

0.5

0

20

40

60

80

100

Fre e z ing-a nd-tha w ing cycle s

G

e

n

e

ra

l m

ean

S rength

UP TT

Dilation

FF,V TT

FF,S P

Fig. 3.5. Plot of general mean m to freezing-and-thawing cycles from the

Nordtest RRT for concrete with w/c 0.5 (measured before the 24 hrs

storage except for SP’s strength and FF data).

Concre te M ix II-B, w /c 0.5, non-AEA

Fre e z ing m e dium : de m ine ra lise d w a te r

-0.1

0

0.1

0.2

0.3

0.4

0.5

0

10

20

30

40

50

60

Fre e z ing-a nd-tha w ing cycle s

G

e

n

e

ra

l m

ean

S trength

UP TT

Dilation

FF,V TT

FF,S P

Concre te M ix II-A, w /c 0.5, AEA

Fre e z ing m e dium : 3% Na Cl

-0.1

0

0.1

0.2

0.3

0.4

0.5

0

20

40

60

80

100

Fre e z ing-a nd-tha w ing cycle s

G

e

n

e

ra

l m

ean

_{UP TT}

Dilation

FF,V TT

Fig. 3.6. Plot of general mean m to freezing-and-thawing cycles from the

Nordtest RRT for concrete with w/c 0.7 (measured before the 24 hrs

storage except for SP’s strength and FF data).

Concre te M ix III, w /c 0.7, non-AEA

Fre e z ing m e dium : de m ine ra lise d w a te r

0

0.2

0.4

0.6

0.8

1

0

10

20

30

40

50

60

Fre e z ing-a nd-tha w ing cycle s

G

e

n

e

ra

l m

ean

S trength

UP TT

Dilation

FF,V TT

FF,S P

4 RILEM

RRT

4.1 Test

programme

Three qualities of German concrete (Series 1.1, 1.2 and 1.3, see Table 4.1) were tested. The

concrete cubes of 150 mm were manufactured at the University of Essen in Germany and

later (after 10 days age) transported to SP for sawing for and distribution of specimens. The

measurements (see Table 1.1) were made before preconditioning (wetting), before frost start,

before and after a 24 hrs storage at 20 °C after 6, 12, 18, 24, 37 and 50 freezing-and-thawing

cycles. At some laboratories (SP and NorCem), flexural strength was tested after ending the

frost test. The initial flexural strength was tested at SP based on one extra specimen of each

series.

Table 4.1. Concrete qualities used in the RILEM RRT.

Test series

Series 1.1

Series 1.2

Series 1.3

Cement type

German OPC (corrsp. to CEM I)

Water-cement ratio

0.40

0.50

0.60

Freezing medium

_{Demineralised water}

4.2

Distribution of specimens

After reception the package with the concrete cubes was stored at room temperature and kept

unopened until an age of 21 days. At that age, two slab specimens of size 150×150×50 mm

were sawn from each of the concrete cubes in the same way as described in Section 3.2. The

specimens were grouped for 8 laboratories by considering their casting order as shown in

Table 4.2. Afterwards they were in groups sealed in plastic bags and packaged. The packages

with the grouped specimens were randomly labelled with the laboratory’s address and later

transported to the respective laboratories.

Table 4.2. Groups of specimens for the RILEM RRT.

Group 1 2 3 4 5 6 7 8

Casting

No.

1a,

5a,

9a,

13a

1b,

5b,

9b,

13b

2a,

6a,

10a,

14a

2b,

6b,

10b,

14b

3a,

7a,

11a,

15a

3b,

7b,

11b,

15b

4a,

8a,

12a,

16a

4b,

8b,

12b,

16b

4.3 Test

results

The raw data reported from the participating laboratories are listed in Appendix 3 and the

results of flexural strength are presented in Table 4.3. The results of precision analysis are

summarised in Tables 4.4 and 4.5, and illustrated in Figs. 4.1 and 4.2, where m denotes the

general mean of relevant parameters, s

r

and s

R

denote the standard deviation of repeatability

and reproducibility, respectively. The plots of m at different freezing-and-thawing cycles are

shown in Figs. 4.3 to 4.5.

Table 4.3. Results of flexural strength from the RILEM RRT, MPa.

Series

R

0SP*

R

50SP

R

50NorCem

(R

0SP

- R

50SP

)/ R

0SP

1.1 7.81

7.88 ± 0.51

7.59 ± 0.75

-0.01

1.2 7.89

3.90 ± 0.56

2.62 ± 0.39

0.506

1.3 6.33

3.08 ± 0.69

1.41 ± 0.16

0.509

* from 1 specimen, others from 4 specimen (with

± value as a standard deviation).

Table 4.4. Summary of the precision analysis results from the RILEM RRT

(according to the data measured before the 24 hrs storage at 20 °C).

* Involving a large uncertainty due to a very small number (2) of participating laboratories.

Series

Level j m

s

r

s

R

m

s

r

s

R

m

s

r

s

R

Series 1.1

Wetting -0.005 0.008 0.008 -0.005 _{0.008 0.009} -0.001 0.007 0.007 Cycle 0 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Cycle 6 -0.005 0.007 0.011 0.005 _{0.007 0.009} 0.004 0.002 0.004 Cycle 12 -0.008 0.012 0.014 0.011 _{0.018 0.020} 0.002 0.003 0.003 Cycle 18 -0.016 0.011 0.016 0.003 _{0.009 0.010} 0.002 0.001 0.003 Cycle 24 -0.010 0.015 0.018 0.008 _{0.015 0.016} 0.004 0.002 0.003 Cycle 37 -0.011 0.014 0.017 0.014 _{0.019 0.019} 0.006 0.003 0.004 Cycle 50 -0.008 0.028 0.035 0.034 _{0.031 0.031} 0.007 0.003 0.009

Series 1.2

Wetting -0.007 0.016 0.016 -0.002 _{0.006 0.007} -0.004 0.006 0.006 Cycle 0 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Cycle 6 0.000 0.010 0.016 0.002 _{0.009 0.012} 0.012 0.005 0.007 Cycle 12 -0.010 0.012 0.014 0.003 _{0.011 0.012} 0.014 0.004 0.004 Cycle 18 -0.007 0.015 0.015 0.024 _{0.022 0.026} 0.032 0.019 0.019 Cycle 24 0.012 0.022 0.026 0.032 _{0.020 0.027} 0.057 0.021 0.026 Cycle 37 0.110 0.038 0.051 0.117 _{0.024 0.053} 0.159 0.047 0.071 Cycle 50 0.180 0.039 0.048 0.197 _{0.046 0.075} 0.205 0.091 0.091

Series 1.3

Wetting -0.004 0.007 0.014 -0.004 _{0.005 0.005} -0.008 0.004 0.004 Cycle 0 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Cycle 6 -0.004 0.010 0.015 0.005 _{0.019 0.022} 0.015 0.007 0.007 Cycle 12 0.008 0.023 0.023 0.014 _{0.033 0.033} 0.075 0.051 0.061 Cycle 18 0.096 0.073 0.073 0.064 _{0.049 0.057} 0.196 0.117 0.117 Cycle 24 0.159 0.089 0.089 0.144 _{0.057 0.066} 0.213 0.104 0.118 Cycle 37 0.248 0.081 0.081 0.227 _{0.062 0.080} 0.281 0.087 0.154 Cycle 50 0.310 0.107 0.107 0.296 _{0.072 0.098} 0.302 0.078 0.129

Before storage

(t

i

-t

0

)/t

0

100x(L

i

-L

0

)/L

0

(f

0

-f

i

)/f

0

*

Table 4.5. Summary of the precision analysis results from the RILEM RRT

(according to the data measured after the 24 hrs storage at 20 °C).

* Involving a large uncertainty due to a very small number (3) of participating laboratories.

Series

Level j m

s

r

s

R

m

s

r

s

R

m

s

r

s

R

Series 1.1

Wetting -0.005 0.008 0.008 -0.001 _{0.012 0.014} 0.000 0.006 0.006 Cycle 0 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Cycle 6 0.005 0.012 0.014 0.008 _{0.006 0.007} 0.008 0.002 0.006 Cycle 12 -0.003 0.011 0.012 0.011 _{0.018 0.018} 0.009 0.003 0.007 Cycle 18 -0.003 0.017 0.018 0.008 _{0.007 0.007} 0.006 0.002 0.003 Cycle 24 -0.007 0.015 0.019 0.016 _{0.025 0.025} 0.008 0.004 0.007 Cycle 37 -0.002 0.013 0.013 0.019 _{0.024 0.026} 0.006 0.003 0.004 Cycle 50 -0.003 0.015 0.016 0.039 _{0.024 0.026} 0.006 0.002 0.007

Series 1.2

Wetting -0.010 0.014 0.014 -0.002 _{0.006 0.007} -0.004 0.006 0.006 Cycle 0 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Cycle 6 -0.005 0.010 0.016 0.010 _{0.012 0.014} 0.010 0.005 0.006 Cycle 12 -0.007 0.008 0.011 0.016 _{0.022 0.023} 0.014 0.006 0.006 Cycle 18 -0.008 0.018 0.018 0.027 _{0.026 0.027} 0.023 0.006 0.011 Cycle 24 0.016 0.014 0.025 0.044 _{0.027 0.034} 0.032 0.019 0.029 Cycle 37 0.083 0.038 0.043 0.123 _{0.046 0.063} 0.110 0.032 0.051 Cycle 50 0.152 0.035 0.039 0.195 _{0.045 0.073} 0.155 0.035 0.042

Series 1.3

Wetting -0.004 0.007 0.014 -0.001 _{0.008 0.010} -0.010 0.004 0.005 Cycle 0 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 Cycle 6 -0.010 0.011 0.013 0.006 _{0.023 0.025} 0.011 0.006 0.006 Cycle 12 0.004 0.029 0.029 0.030 _{0.040 0.041} 0.048 0.032 0.036 Cycle 18 0.080 0.057 0.057 0.080 _{0.052 0.052} 0.126 0.075 0.083 Cycle 24 0.139 0.081 0.081 0.148 _{0.060 0.063} 0.164 0.110 0.110 Cycle 37 0.223 0.087 0.087 0.229 _{0.065 0.075} 0.243 0.109 0.126 Cycle 50 0.285 0.099 0.099 0.299 _{0.078 0.105} 0.264 0.068 0.118

After storage

(t

i

-t

0

)/t

0

100x(L

i

-L

0

)/L

0

(f

0

-f

i

)/f

0

*

Fig. 4.1. Standard deviation of repeatability (upper) and reproducibility (lower)

from the RILEM RRT, measured before the 24 hrs storage at 20 °C.

before 24 h storage at 20 °C

0

0.05

0.1

0.15

0.2

-0.1

0

0.1

0.2

0.3

0.4

Ge ne ra l m e a n m

S

ta

d

d

e

v

o

f r

e

p

e

a

ta

b

ilit

y

s

r

UP TT

Dilation

FF

before 24 h storage at 20 °C

0

0.05

0.1

0.15

0.2

-0.1

0

0.1

0.2

0.3

0.4

Ge ne ra l m e a n m

S

td de

v

of

r

e

pr

oduc

ib

ilit

y

s

R

UP TT

Dilation

FF

Fig. 4.2. Standard deviation of repeatability (upper) and reproducibility (lower)

from the RILEM RRT, measured after the 24 hrs storage at 20 °C.

after 24 h storage at 20 °C

0

0.05

0.1

0.15

0.2

-0.1

0

0.1

0.2

0.3

0.4

Ge ne ra l m e a n m

S

ta

d

d

e

v

o

f r

e

p

e

a

ta

b

ilit

y

s

r

UP TT

Dilation

FF

after 24 h storage at 20 °C

0

0.05

0.1

0.15

0.2

-0.1

0

0.1

0.2

0.3

0.4

Ge ne ra l m e a n m

S

td de

v

of

r

e

pr

oduc

ib

ilit

y

s

R

UP TT

Dilation

FF

Fig. 4.3. Plot of general mean m to freezing-and-thawing cycles from the

RILEM RRT for concrete with w/c 0.4 (measured before the 24 hrs

storage).

Fig. 4.4. Plot of general mean m to freezing-and-thawing cycles from the

RILEM RRT for concrete with w/c 0.5 (measured before the 24 hrs

storage).

Concre te M ix 1.1, w /c 0.4, non-AEA

Fre e z ing m e dium : de m ine ra lise d w a te r

-0.1

0

0.1

0.2

0.3

0.4

0.5

0

10

20

30

40

50

60

Fre e z ing-a nd-tha w ing cycle s

G

e

n

e

ra

l m

ean

_{UP TT}

Dilation

FF

Concre te M ix 1.2, w /c 0.5, non-AEA

Fre e z ing m e dium : de m ine ra lise d w a te r

-0.1

0

0.1

0.2

0.3

0.4

0.5

0

10

20

30

40

50

60

Fre e z ing-a nd-tha w ing cycle s

G

e

n

e

ra

l m

ean

_{UP TT}

Dilation

FF

Fig. 4.5. Plot of general mean m to freezing-and-thawing cycles from the

RILEM RRT for concrete with w/c 0.6 (measured before the 24 hrs

storage).

Concre te M ix 1.3, w /c 0.6, non-AEA

Fre e z ing m e dium : de m ine ra lise d w a te r

-0.1

0

0.1

0.2

0.3

0.4

0.5

0

10

20

30

40

50

60

Fre e z ing-a nd-tha w ing cycle s

G

e

n

e

ra

l m

ean

_{UP TT}

Dilation

FF

5 Discussions

5.1

Effect of the 24 hours storage at 20 °C

The initial consideration of this 24 hours storage at 20 °C was to eliminate the influence of

temperature on the measurements, especially on the length measurement that is generally

thought to be very sensitive to temperature. The test results from two RRTs show, however,

that the temperature effect on test precision seems not significant, as shown in Fig 5.1. The

reasons could be that temperature may influence the absolute but not the relative values of

measurements and 2) temperature effect is covered by the uncertainties involved in the

measurement techniques. Nevertheless, according to the findings from this study, it is not

necessary to have the 24 hours storage at 20 °C in the practical test procedure. Thus the same

frost test procedure as described in SS 72 13 44 can be employed in the modified slab test.

5.2

Relations between internal damage and measured values

According to the results of flexural strength test as shown in Tables 3.3 and 4.3, the concretes

of Mixes II-B and III for the Nordtest RRT and Mixes 1.2 and 1.3 for the RILEM RRT were

significantly damaged due to the frost attack. All the techniques used in this project have

indeed detected the damages, as shown in Figs. 3.5, 3.6, 4.4 and 4.5. Since SP tested the

flexural strength on the identical specimens used for different non-destructive measurements,

it is possible to find the relations between internal damage and measured values from

non-destructive methods. Figure 5.2 shows such relationships. It can be seen that the changes in

UPTT, dilation or FF are linearly related to the square of changes in flexural strength.

5.3

Precision of the dilation and UPTT techniques

Since the precision estimate for the FF technique involves a large uncertainty due to a very

small number of laboratories, the precision data for this technique are not included in this

comparison. A special discussion of the FF test will be given in section 5.4.

As discussed above, the 24 hours storage at 20 °C in the practical test procedure could be

skipped. Thus in this section only those data measured before the storage will be used for

determination of the precision of different techniques. By applying linear regression to the

data shown in Tables 3.4 and 4.4 one can obtain expressions of repeatability and

reproducibility for different methods, as expressed in the following equation.

b

a

s

=

ξ

+

(5.1)

The regression constants a and b together with the correlation coefficient r are listed in Table

5.1. It can be seen from the table that, the dilation method reveals a better repeatability, but its

reproducibility seems similar to the UPTT technique.

Fig. 5.1. Comparison between the results measured before and after the 24 hrs

storage at 20 °C.

U P TT 0 0.1 0.2 0.3 0.4 0.5 -0.2 0 0.2 0.4 0.6 0.8 1 Ge ne ra l m e a n m S td de v of r e pe a ta b ilit y s r B efore s torage A fter s torage U P TT 0 0.1 0.2 0.3 0.4 0.5 -0.2 0 0.2 0.4 0.6 0.8 1 Ge ne ra l m e a n m S td de v of r e pr o duc ib ilit y s R B efore s torage A fter s torage D ilation 0 0.1 0.2 0.3 0.4 0.5 -0.2 0 0.2 0.4 0.6 0.8 1 Ge ne ra l m e a n m S td d e v o f r e p eat ab il it y s r B efore s torage A fter s torage D ilation 0 0.1 0.2 0.3 0.4 0.5 -0.2 0 0.2 0.4 0.6 0.8 1 Ge ne ra l m e a n m S td d e v of r e pr odu c ibil it y s R B efore s torage A fter s torage FF 0 0.1 0.2 0.3 0.4 0.5 -0.2 0 0.2 0.4 0.6 0.8 1 Ge ne ra l m e a n m S td de v of r e pe a ta b il it y s r B efore s torage A fter s torage FF 0 0.1 0.2 0.3 0.4 0.5 -0.2 0 0.2 0.4 0.6 0.8 1 Ge ne ra l m e a n m S td de v of r e pr oduc ibil it y s R B efore s torage A fter s torage

Fig. 5.2. Relationships between changes in flexural strength and other measured

parameters (based on the data measured after the 24 hrs storage at 20 °C).

Table 5.1. Regression constants a and b, and correlation coefficient r.

Repeatability

s

r

Reproducibility

s

R

Data source

Technique

_{a b r a b r}

Nordtest

RRT

UPTT

0.215 0.019 0.955 0.374 0.024 0.971

Dilation 0.163 0.013 0.933 0.341 0.016 0.973

RILEM

RRT

UPTT

0.285 0.016 0.912 0.282 0.020 0.927

Dilation 0.206 0.014 0.895 0.301 0.016 0.958

5.4

A special discussion of the FF test

It can be seen from Figs. 3.5, 3.6, 4.4 and 4.5 that the FF test detected a remarkable change at

earlier stages (less freezing-and-thawing cycles) than the other two techniques. It implies that

this technique is more sensitive to detecting internal damage. This is in agreement with the

findings reported by Jacobsen /7/. In addition, the technique itself is very reliable and has

been used in North America for many years. Therefore, the FF technique is a promising

method for detecting internal frost damage on slab specimens. However, the spread in the FF

measurement from this study appears relatively large, as shown in Figs. 4.1 and 4.2. A small

number of laboratories including inexperience in some laboratories might be a reason, but it

cannot explain the internal spread in an experienced laboratory as shown in Fig. 5.3.

UP TT: y = 1.1115x - 0.0301

R

2

= 0.9061

Dilation: y = 0.8957x - 0.0009

R

2

= 0.9156

FF: y = 1.0176x - 0.0124

R

2

= 0.815

-0.2

0

0.2

0.4

0.6

0.8

-0.2

0

0.2

0.4

0.6

0.8

(1 - R

i

/R

0

)

2

C

h

a

nge

s

i

n

U

P

TT,

D

il

a

ti

on a

nd FF

Nordtes t UP TT

Nordtes t Dilation

Nordtes t FF, S P

RILE M UP TT

RILE M Dilation

RILE M FF

Regres s ion UP TT

Regres s ion Dilation

Fig. 5.3. Internal spread in the FF test measured in an experienced laboratory.

It should be kept in mind that the frost test is carried out on 4 different specimens from each

test series. The imhomogeneity of concrete material will certainly contribute to the

within-laboratory spread. As mentioned in Introduction, the repeatability in this study was not

obtained strictly under the repeatability conditions but included the variation of test items.

The FF test has a better sensitivity, implying that the technique can more easily detect the

imhomogeneity of material. Thus the within-laboratory spread under such conditions could

not be expected to be smaller than the other two techniques.

As well known, the preconditioning and freezing-and-thawing environments play important

role in the frost test. Besides ordinary reproducibility conditions (different laboratories,

different equipment and different operators), different frost test environments may add a

significant portion of the between-laboratory spread. An example is given in Fig. 5.4. It can

be seen that the measured values from VTT for those test series are always higher than those

from SP, no matter which techniques were used. This may imply that the frost environments

at VTT for those test series were more severe than those at SP. Thus it is not strange that the

FF data in Figs. 3.5 and 3.6 from these two laboratories differ considerably. The difference in

frost environments will certainly influence the mechanical properties of concrete. It was a pity

that only SP in this study measured the flexural strength on the specimens at different stages

of the frost test. A large scale of investigation is needed to find more reliable comparison

between destructive and non-destructive tests.

FF Measurement from V TT

0

0.05

0.1

0.15

0.2

0

0.1

0.2

0.3

0.4

M e a n

S

ta

nda

rd

de

v

ia

ti

o

n

S eries 1.1

S eries 1.2

S eries 1.3

Fig. 5.4. Comparison between the results from two laboratories (measured

after the 24 hrs storage).

Concre te M ix II-B, w /c 0.5, non-AEA

Fre e z ing m e dium : de m ine ra lise d w a te r

0

0.2

0.4

0.6

0

10

20

30

40

50

60

Fre e z ing-a nd-tha w ing cycle s

La

bor

a

tor

y

m

e

a

n

UP TT, V TT

UP TT, S P

Dilation, V TT

Dilation, S P

FF,V TT

FF,S P

Concre te M ix III, w /c 0.7, non-AEA

Fre e z ing m e dium : de m ine ra lise d w a te r

0

0.2

0.4

0.6

0.8

1

0

10

20

30

40

50

60

Fre e z ing-a nd-tha w ing cycle s

La

bor

a

tor

y

m

e

a

n

UP TT, V TT

UP TT, S P

Dilation, V TT

Dilation, S P

FF,V TT

FF,S P

6 Concluding

Remarks

From the results of two round Robin test it can be seen that

• All the three techniques (UPTT, Dilation and FF) can be employed in the slab test for

detecting internal damage of concrete subjected to frost attack.

• The temperature effect on test precision seems not significant. Therefore, the 24 hours

storage at 20 °C could be skipped to simplify the test procedure. Thus the same frost

test procedure as described in the Swedish standard SS 72 13 44 can be used in the

modified slab test.

• The dilation method reveals a better repeatability, but has a reproducibility similar to

the UPTT technique.

• The FF technique shows a promising sensitivity to detecting internal damage, but

further collaboration study is needed for evaluating the precision of this technique.

• It has been found from this study that changes in UPTT, dilation or FF are linearly

related to the square of changes in flexural strength. A large scale of investigation is

needed to find more reliable comparison between destructive and non-destructive

tests.

7 References

/1/

Tang, L., Bager, D., Jacobsen, S. and Kukko, H., “Evaluation of the Ultrasonic Method

for Detecting Freeze/thaw Cracking in Concrete - NORDTEST Project No. 1321-97”,

SP Report 1997:37, SP Swedish National Testing and Research Institute, Borås,

Sweden, 1997.

/2/

Jacobsen, S., Bager, D., Kukko, H., Tang, L. and Nordström, K., “Measurement of

Internal Cracking as Dilation in the SS 13 72 44 Frost Test - NORDTEST Project No.

1389-98”, NBI Project Report 250-1999, Norwegian Building Research Institute (NBI),

Oslo, Norway, 1999.

/3/

Bager, D., et al, to be published 2001.

/4/

ASTM C 215-91, “Standard Test Method for Fundamental Transverse, Longitudinal,

and Torsional Frequencies of Concrete Specimens”, American Society for Testing and

Materials, West Conshohocken, PA., USA, 1991.

/5/

ISO 5725-2:1994, “Accuracy (trueness and precision) of measurement methods and

results - Part 2: Basic method for the determination of repeatability and reproducibility

for a standard measurement method”, International Standard Organisation, Genève,

Switzerland, 1994.

/6/

ISO 5725-1:1994, “Accuracy (trueness and precision) of measurement methods and

results - Part 1: General principle and definitions”, International Standard Organisation,

Genève, Switzerland, 1994.

/7/

Jacobsen, S., “Scaling and cracking in unsealed freeze/thaw testing of Portland cement

and silica fume concretes”, Doctoral thesis, NTH 1995:101, Div. of Structural

Appendix 1 - Distribution of specimens for the Nordtest RRT

Mix I-S Mix I-W Mix II-A Mix II-B Mix III

Cube No. Slab 1 Slab 2 Cube No. Slab 1 Slab 2 Cube No. Slab 1 Slab 2 Cube No. Slab 1 Slab 2 Cube No. Slab 1 Slab 2 1 Comp. Strength 29 SP SP_C 1 Comp. Strength 1 Comp. Strength 1 Comp. Strength

2 SP SP_C 30 NBI SP_B1 2 SP VTT 2 SP SP_B2 2 SP SP_B2

3 NBI IBRI 31 CBL CBL_C 3 NBI IBRI 3 NBI SP_B1 3 NBI SP_B1

4 CBL VTT 32 VTT SP_B2 4 CBL SP 4 CBL CBL_B2 4 CBL CBL_B2

5 SP_E SP_E 33 IBRI CBL_B2 5 VTT NBI 5 VTT CBL_B1 5 VTT CBL_B1

6 SP SP_C 34 SP_B1 CBL_B1 6 IBRI CBL 6 IBRI SP_E 6 IBRI SP_F

7 NBI IBRI 35 SP SP_C 7 Comp. Strength 7 SP SP_B2 7 SP SP_B2

8 CBL VTT 36 NBI SP_A 8 VTT_A VTT_A 8 NBI SP_B1 8 NBI SP_B1

9 SP_A SP_F 37 CBL CBL_C 9 SP VTT 9 CBL CBL_B2 9 CBL CBL_B2

10 SP SP_C 38 VTT SP_B2 10 NBI IBRI 10 VTT CBL_B1 10 VTT CBL_B1 11 NBI IBRI 39 IBRI CBL_B2 11 CBL SP 11 IBRI SP_E 11 IBRI SP_F

12 CBL VTT 40 SP SP_C 12 VTT NBI 12 SP SP_B2 12 SP SP_B2

13 SP SP_C 41 SP_B1 CBL_B1 13 IBRI CBL 13 NBI SP_B1 13 NBI SP_B1 14 NBI IBRI 42 NBI SP_B2 14 Comp. Strength 14 VTT_A VTT_A 14 VTT_A VTT_A 15 CBL VTT 43 CBL CBL_C 15 SP_E SP_E 15 Comp. Strength 15 Comp. Strength

16 CBL_D NBI_D 44 VTT SP_F 16 CBL CBL_B2 16 CBL CBL_B2

17 CBL_D NBI_D 45 IBRI CBL_B2 17 VTT CBL_B1 17 VTT CBL_B1

18 CBL_D NBI_D 46 SP_B1 CBL_B1 18 IBRI SP_F 18 IBRI SP_E

19 CBL_D NBI_D 47 SP SP_C 19 SP SP_B2 19 SP SP_B2

20 CBL_B CBL_B 48 NBI SP_B2 20 NBI SP_B1 20 NBI SP_B1

21 CBL_B CBL_B 49 CBL CBL_C 21 CBL CBL_B2 21 CBL CBL_B2

22 CBL_B CBL_B 50 VTT CBL_B1 22 VTT CBL_B1 22 VTT CBL_B1

23 CBL_B CBL_B 51 IBRI CBL_B2 23 IBRI SP_F 23 IBRI SP_E

24 CBL_B CBL_B 52 CBL_D NBI_D 24 SP_F SP_F 24 SP_F SP_F

25 SP_B SP_B 53 CBL_D NBI_D 25 IBRI_B IBRI_B 25 IBRI_B IBRI_B 26 SP_B SP_B 54 CBL_D NBI_D 26 IBRI_B IBRI_B 26 IBRI_B IBRI_B 27 SP_B SP_B 55 CBL_D NBI_D 27 IBRI_B IBRI_B 27 IBRI_B IBRI_B 28 Comp. Strength 56 CBL_B CBL_B 28 IBRI_B IBRI_B 28 IBRI_B IBRI_B

57 CBL_B CBL_B 29 IBRI_B IBRI_B 29 IBRI_B IBRI_B

58 CBL_B CBL_B 30 Comp. Strength 30 Comp. Strength

59 CBL_B CBL_B 31 SP_E SP_E 60 CBL_B CBL_B 61 Comp. Strength 62 SP_F SP_F 63 SP_F CBL_F 64 SP_F CBL_F 65 SP_F CBL_F 66 SP_F CBL_F

Appendix 2 - Raw data from the Nordtest RRT

100x(L

i

-L

0

)/L

0

Mix I-S, before the 24 hrs' storage at 20 °C

Code

Pre-wetting

Cycle

0

2

6

12

18

24

37

50

65

78

91

-0.006 0 0.01 0.031 0.017 0.027 0.03 0.031 0.034

Lab 1

-0.001 0 0.009 0.007 0.009 0.009 0.016 0.096 0.053 -0.047 0 -0.027 -0.027 -0.053 0.001 0.008 0.047 0 -0.017 0 0.03 0.01 0.029 0.006 0.018 0.016 0.02 0.001 0 -0.02 -0.02 -0.007 -0.001 -0.005 0.006 -0.011 -0.009 -0.013

Lab 2

-0.009 0 -0.025 -0.019 0.004 -0.011 -0.01 0.03 0.036 0.022 -0.009 0 0 -0.041 -0.021 0.002 -0.009 0.013 0.014 -0.055 -0.098 0.019 -0.013 0 0 0 0 0.007 0.013 0.04 0.047

Lab 3

0 0 0.007 0 0.007 0.02 0.013 0.04 0.04 0 0 -0.007 0 0 0.02 0.007 0.033 0.033 -0.007 0 -0.007 0 0 0.007 0.007 0.033 0.033 -0.007 0 -0.007 0 0.013 0 0.007 0.007 0.013 0.013 0.026 0.033

Lab 4

0 0 -0.007 -0.013 -0.013 -0.007 -0.007 0 0.007 0.013 0.02 0.013 -0.007 0 -0.007 -0.013 -0.007 0 0 0 0.007 0.007 0.013 0.027 -0.007 0 -0.007 -0.013 -0.007 0 0 0.013 0.033 0.046 0.06 0.053 0 -0.012 0.05 0.025 0.021 0.023 0.01 -0.021 0.006 -0.001 0.001

Lab 5

0 -0.052 -0.017 -0.014 -0.009 -0.011 -0.014 -0.029 0.008 0.006 0.013 0 -0.043 -0.007 -0.007 -0.01 -0.014 -0.007 -0.03 -0.003 0.012 0.045 0 -0.013 -0.009 0.005 0.005 0.008 0.005 -0.014 0.028 0.025 0.028

100x(L

i

-L

0

)/L

0

Mix I-S, after the 24 hrs' storage at 20 °C

Code

Pre-wetting

Cycle

0

2

6

12

18

24

37

50

65

78

91

-0.006 0 0.035 0.037 0.035 0.022 0.042 0.031 0.031

Lab 1

-0.001 0 0.033 0.017 0.013 0.013 0.032 0.031 0.058 -0.047 0 0.028 -0.002 -0.011 0.003 0.054 -0.016 -0.004 -0.017 0 0.002 0.027 0.01 0.012 0.016 0.009 0.016 0.001 0 0 -0.002 -0.009 0.001 0.001 0.009 -0.005 -0.007

Lab 2

-0.009 0 -0.002 -0.004 0.002 -0.005 0.001 0.002 0 0.034 0 0 0.002 0.007 0.016 0.013 0.025 0.02 0.02 0.025 -0.013 0 0 0.007 0.007 0.027 0.033 0.027 0.047

Lab 3

0 0 0.007 0.013 0.013 0.033 0.033 0.027 0.06 0 0 0 0 0.013 0.027 0.027 0.02 0.047 -0.007 0 0 0.007 0.007 0.013 0.02 0.013 0.066 -0.007 0 0.007 0.033 0.013 0.007 0.007 0.007 0.02 0.026 0.026 0.033

Lab 4

0 0 0 0 -0.013 -0.007 0 0 0.013 0.027 0.007 0.013 -0.007 0 -0.007 0 0.007 0 -0.007 0.007 0.007 0.02 0.02 0.033 -0.007 0 0 0 0.013 0 0.007 0.02 0.033 0.053 0.046 0.053 0 0.032 0.03 0.01 0.02 -0.007 0.027 0.024 0.009 0.009 0.005

Lab 5

0 -0.033 -0.016 -0.005 -0.006 -0.008 0.005 -0.007 0.018 0.011 0.016 0 -0.025 -0.011 0.003 -0.003 -0.007 0.003 -0.005 0.009 0.019 0.024 0 0.011 0.003 0.008 0.011 0.007 0.02 0.003 0.026 0.036 0.03