Magazine of Concrete Research Volume 43 Issue 157 1991 [Doi 10.1680%2Fmacr.1991.43.157.233] Bamforth, P. B. -- The Water Permeability of Concrete and Its Relationship With Strength

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Magazine o Concrete Research,

1991, 43, No. 157, Dec., 233-241

The water permeability of concrete and its

relationship with strength

P

B.

Bamforth, BSC, PhD,

MICE

T A Y W O O D

N G I N E E R I N G L T D

As par t

o

a much broader programme to evaluate the

performance

o

concretes fo r use

in

reinforced and pre-

stressed containments for liquid gases, seventeen con-

crete mix es, anging in strength fr om

16

to

1

Njmm’,

were subjected

to

screening tests bymeasurement of the

water perm eability oefficient. Specimens were tored in

sealed conditionsat 20°C and tests were also carried out

to determine the compressivend tensile splitting

strengths. The relationships between perm eability and

strength are discussed, as w ell as the influence of con-

creting materials, mix proportions and curing.

Introduction

There are two essential requirements for the pre-

vention of leakage from a concrete containment struc-

ture: low permeability concrete, and the avoidance of

construction defects. This Paper is concerned primar-

ily with the inherent permeability of the concrete, but

the selection process forcandidate mixes included

consideration of construction aspects such as place-

ability and minimizing the risk of cracking. The tests

reported here comprised part of a much larger pro-

gramme to identify concretes which would be suitable

for use in reinforced and pre-stressed concrete tanks

for hestorageof liquefied naturalgas at

a

tem-

perature of 165°C. Measurements of the water per-

meability coefficient, the compressive strength and he

tensile splitting strength at 20” were used to screen

seventeen candidate mixes. As part of this screening

process the compressive strength and tensile splitting

strength tests were also carried out both at cryogenic

temperature

(

165°C) and after hermal cycling. The

results of these low-temperature tests are reported in

detail elsewhere.’ This Paper is concerned only with

properties measured at 20°C.

Selection

of

concrete mix parameters

Concretes for studyn the screening test programme

were selected not solely on the basis of proven or

expected gooderformance at cryogenic tem-

peratures. Other propertieswhich have been shown to

influence constructionandsubsequentperformance

undernormalenvironmentalconditions were also

considered.

Strength grade

It has been demonstrated that concretes with low

waterlcement atios (w/c) are less ikely to be dis-

rupted by ice formation during cooldown.’ Also, low

w/c concretes have been shown to exhibit low per-

meability, particularly at values of w/c below about

0.4.3Six mixes, designated Sl-S6, were designed to

encompassa wide rangeofw/c atios,and hence

strength grades (see Table l . These include typical

structural concretes with values of w/c in the range

0.4-0.55, as well as mixes with very high (0.84) and

very low (0.32) w/c ratios. The latter was achieved

by the use of a superplasticizer to reduce the water

demand.

Air entrainment

The use of air entraining agents (AEA) is common

in concretes which are to be exposed to freeze-thaw

conditions. AEAs have also been shown to provide

resistance to degradation under conditions ofxtreme

thermal cycling to cryogenic

temperature^.^

Three

dosage levels of a proprietary AEA were used: X+,

standard and x 2, for mixes designated AE1 to AE3,

respectively.

Aggregate type

During cooling to very

low

temperatures, disruption

233



Bamforth

Table l . Concrete mix proportions for the 17 candidate m ixes

Mix

no

S1

S2

S3

S4

S5

S6

AEI

AE2

AE3

AI

A2

A3

A4

C l

c 2

c 3

c 4

*PFA

t G G B S

35

10

50

50

85

85

35

35

35

35

35

35

35

35

35

35

35

Nominal

or

kg/m’

trength

PFA’

PC:

grade

GGBS*:

kg/m3

355

215

420

370

455

475

~

~

405

440

500

365

400

410

480

280

3007

30

2557

I O

1

so

55

I20*

Crushed Dolerite

fiLytag, sintered PFA, 12mm

20 mm

aggregate:

kg/mi

760

795

770

770

800

805

770

790

755

820:

8451

~

730

730

760

765

10 mm

aggregate:

kg/m’

300

315

305

305

355

355

305

310

300

375:

3851

6955

6955

290

290

300

295

may occur, not only due to the formation of ice but

also due to thedifferential thermal contraction of the

aggregate and cement paste. Studies of strength loss

resulting from exposure o elevated temperatures have

identified that the extent towhich damage occurs is a

function of the difference in the modulusof elasticity

and the thermal xpansion coefficient of the aggregate

and cement paste.5n general, aggregates have a uch

lower thermalxpansion coefficient thanement

paste, and a much higher modulus of elasticity.

Three ggregateshave been tested: agravel,

crushed dolerite and a lightweight aggregate (sintered

PFA); these provide a range ofalues of both modulus

and thermal expansion coefficient.6The two crushed

dolerite mixes have been designated AI and A2 and

the two ightweightmixes A3and A4. The gravel

mixes are S1 and AE2, described above.

Cement type

The use

of

pulverized fuel ash (PFA) and ground

granulatedblastfurnace lag GGBS) is becoming

increasingly common in large civil engineering struc-

t u r e ~ . ~n addition to providing economiesn materials

costs,

a

number of construction benefits havealso

been reported, including

( a ) improved placing characteristics, i.e. better flow,

h)

delayed setting ime, minimizing the occurrence of

improved pumpability, easier compaction’

cold joints in large pours7

234

Sand:

kg/m’

740

815

685

750

620

625

670

600

530

655

560

560

505

700

605

735

580

Water:

185

180

I80

165

165

I

55

185

170

160

200

185

220

205

185

185

180

I75

AEA

or

SP

~

SPI

SP

SPI

AEA

1

AEA

2 AEA

~

I

AEA

AEA

AEA

1

AEA

I

AEA

Air

content:

Yo

.o

1.3

I

.2

1.5

0.9

0.9

1.7

3.5

1.2

0.5

2.4

6.0

9.4

0.9

.o

0.9

4.8

Slump:

mm

60

60

75

90

I00

90

70

70

85

80

75

75

85

85

85

95

85

wlc

0.5 1

0.85

0.43

0.45

0.36

0.32

0.46

0.39

0.32

0.55

0.46

0.54

0.43

0.46

0.37

0.49

0.41

( c )

reduced rate of heat evolution during hydration,

reducing the temperature ise and hence the risk

of

thermal cracking at early age’

It has also been reported that concretes containing

either PFA or GGBS have a potential for lower per-

meability than equivalentgrades of OPC concrete

under conditions of continued moistcuring.’

Mixes containing either PFAor GGBS partially to

replace OPC have herefore been investigated. The

two PFA mixes have been designated C1 and C2, the

two GGBS mixes, C3 and C4.

Concrete mix details

Based on the above criteria, a total of 17

no.

con-

crete mixeswere selected. Twocontrol mixeswere

designed to achieve a grade 35N concrete, using OPC

and gravel aggregate, one containing a standard dose

of air-entraining agent. Details f the 17 no. mixes are

given in Table

1

Manufacture

of

test specimens

Each mix comprised 14 no. 100mm ubesor

strengthmeasurement and 2

no.

cylindrical speci-

mens, l00mm in diameter and 50mm thick, for the

measurement of water permeability. Batching, mixing

andcasting of the specimenswere carried out

in

generalccordance with BS 1881. However, the

method of curing was modified, with specimens being

Mugazine of Concrete Research,

1991, 43 No. 157



Water permeabili ty

of

concrete

sealed in heavy-duty plastic bags mmediately after

beingstrippedfrom heirmouldsatanageof 24

hours, and stored atOoC until testing. This methodof

‘sealed’ curing simulates he in situ moisture condition

in which the only water available for curing is that

which is introduced a t the mixing stage, this being the

condition that exists in the bulk of a thick structural

member.

Measurement of compressive and tensile splitting

strength

Two cubeswere tested in compression for each mix

at an age of 28 days. As far as possible, cubes were

tested according to BS 188 although changes to the

standard testing procedure were required to enable

direct comparisonwith ow-temperaturespecimens

which were placed n special stainless steel rigs prior to

testing, as shown in Fig. 1

Tensile strengths were measured by splitting 2 no.

concrete cubes. Restraining rigswere used, asalso

shown in Fig. 1. The test differed from a conventional

splitting test in that the spacers at the top and bottom

of the cube, through which theine loads were applied,

were stainless steel rods. At ambient temperaturesoft’

timber spacers are normally used, hence the load is

spread over a small area. Thereas concern, however,

that a soft spacer would change its properties at low

d

V

.

’

pring washers

Restraining rig with

---

est specimen

(100 mm cub e)

pacer block

--- Insulated box

oading machine

platens

I

Y

Fig.

I .

Testing arrangement fo r the measurement o

compressive and tensile splitting strengths

Magazine

of

Concrete Research,

1991, 43, No

57

temperaturesand hat this would invalidate com-

parisonsbetween tensile splittingstrengthover he

range of test temperatures. Stainless steel rods were

therefore chosen, as their hardness andtiffness would

be similar at ambient and cryogenic temperature. It

was recognized, however, that this may influence the

absolute values ofensile splitting strength. The ensile

strength was calculated using the equation

2P

. L =

na2

wheref; is the tensile stress (N/mm’), P is the maxi-

mum load applied (N), and

a

is the side of cube (mm).

Measurement

of

water permeability

The water permeability of concreteiscs at ambient

temperature, was determined at an ageof 28 days

using the rig shown in Fig. 2.’’ The l00mm dia. test

specimens were prepared by placing them in tapered

cylindrical brass moulds,

1

10mm maximum diameter,

and filling the 5 mm annular space with epoxy esin to

form a tapered resin sleeve. After the resin had cured

for 24 hours, the specimens were removed from the

mouldsand placed in thepermeability test rig. A

rubber ‘0’-ringwas used to form a watertight seal. A

water pressure equivalent to lOOm head was applied

over the bottom surface of the specimen.

When full penetration of water was observed on the

top surface, a reading was taken to calculate the rate

of flow through the specimen. This was achieved by

connecting a 4mm diameter glass tube to the top of

the rig and measuring the movement of the meniscus

over a period of

I O

minutes. A second reading was

taken 24 hours after the application of pressure. For

high-permeability concretes the measurement period

was l minute. For the very low permeability concrete

complete penetration was not always achieved within

24 hours, and in such cases the specimens were main-

tained under pressure for a period of 7 days. If com-

plete penetration had still not occurred the specimens

were then removed from their rigs and split to expose

the penetration front. A permeability coefficient was

then calculated from the average penetration depth.

The equations used to calculate the coefficient of per-

meability” were as follows

By $ow:

Q x

K d

=

h

By penetration:

d 2V

2ht

, =

__

where

K

is the coefficient of permeability (m/s),

Q

is

the volume flow rate m3/s), A is the cross-sectional

area (m’), x is the specimen thickness in the direction

of flow (m),

h

is the head of water (m),

d

is the depth

235



Bamforth

t

Fig.

2.

Test cell for the measurement o the water permeability coejicient.

of penetration (m), V is the volume of voids filled

by water in thepenetrated one, determined by

measuring weight gain), and

t

is the time to penetrate

to depth d s ) .

Test results and discussion

Individual values of compressive cube strength, ten-

sile splittingstrength and coefficient of water per-

meability, obtained 24 hours after the startof the test

Tensile strength:

of compressive strength

Compressive strength: Nimm

Fig. 3 . The relationship between compressive strength and

tensile splitting strength

236

(or by observation of penetration depth at a later ge

if complete penetrationwas not achieved), are given in

Table

2.

Compressive and tensile strength

Averagevalues are summarized in Table 3. The

relationship between tensile and compressive strength

is shown in Fig. 3. The results indicate that the tensile

strength is generally 3-5% of the compressive cube

strength. When testing in accordance with BS 1881,

the tensile strength would normally be expected to be

5-7% of the cube strength.12 It isbelieved that the

lower ratio is due to the application of load via the

rigid stainless steel rods which will have concentrated

the stress and reduced the load required to cause a

splitting failure.

Water permeabili ty

The average results are ummarized

in

Table 3

together with strength ata.

In

general the per-

meability coefficients fell within the range 1.5 x lo-''-

1.5 x

lo- ' '

m/s, these values being a t the high end of

the range of values normally expected for structural

concrete. Notable exceptions to this were mixes S2,

S5

S6, A3 and A4. Mix S2 was a low-grade high wlc

ratio mixwith a significantly higherpermeability

coefficient. Mixes S5 and S6 were high-grade low wlc

ratio concretes with significantly lower permeability

coefficients. Mixes A3 and A4 were lightweight con-

cretes with strengths in the range40-50 MPa, exhibit-

ing very low permeabilities. The reasons for this are

Mugazine

of

Concrere

Reseurch

1991.

43,

No. 157



Water permeabi l i tyof concrete

Table

2 .

Individual results from strength and water permeability tests

Mix

SI

S2

S3

S4

S5

S6

AE

1

A E 2

A E 3

A I

A 2

A 3

A 4

c 1

c 2

c 3

c 4

Strength

Compressive:

N/mm2

52.0

51.0

16.5

16.5

59.5

63.0

57.2

63.9

97.0

97.0

102.0

98.5

46.5

43.6

54.0

46.0

41.5

48.0

4 8 3

48.5

55.7

56.2

46.5

51.3

41.8

40.0

42.9

42.6

53.0

57.0

35.8

33.9

36.3

37.8

Tensile splitting:

N/mmz

1.48

1 1 1

1

os

1.08

2.93

1.91

2.78

2.62

3.98

2.70

3.94

3.82

2.13

1.39

1.91

1.72

1.91

1.91

2.42

2.1 1

2.10

2.78

2.3 1

2.16

2.13

2.07

1.85

1.39

.59

1.91

l

70

1.30

1.17

1 1 1

T

Rise in 4 mm

dia. pipe: mm

83

66

I50

135

8

11

30

8

~

18

19

23

35

20

17

75

106

40

42

__

24

24

28

17

60

145

60

75

Flow

measurements

not immediately obvious but it

s

believed that the low

permeability was the result of a combinationf factors

including

( a )

the high cement content and low free w/c ratio

required to achieve concrete of structural quality

with lightweight aggregate

( b )

absorption of mix water into the aggregate caus-

ing a further reduction in w/c ratio

( c )

internal curing provided by water absorbed into

the ggregate particles, resulting in agreater

degree of hydration, and hence a less permeable

cement paste phase

( d ) a possible reaction between the sintered PFA

aggregate and the cement, resulting in chemical

bonding between the aggregate and cement paste,

and a consequent reductionf potential leak paths

at aggregate-cement paste boundaries

( e )

the spherical shape and low modulus of elasticity

of theaggregate minimizing theoccurrenceof

microcracking.

Magazine of Concrete Research, 1991, 43, No.

157

Time:

S

600

600

60

90

600

600

600

600

7 days

7 days

7 days

7

days

600

600

600

600

900

600

600

600

600

600

8 days, 5 h

8 days, 5 h

7 days

90 days

600

600

600

600

600

600

600

600

Flow rate at 24 h:

10-'Om'/s

17.38

13.82

314.10

188.50

1.68

2.53

6.28

1.68

3.77

3.98

4.82

7.34

2.78

3 3 6

15.71

22.23

8.37

8.80

5.03

5.03

5.87

3 3 6

1237

30.37

12.57

15.71

T

Permeability

coefficient: lo- ' ' m/s

11.06

8.80

180.73

108.62

1.01

1.61

3.54

1.03

0.048

0.040

0.027

0.02 1

2.31

2.53

3.07

4.67

1 .54

2.27

10.00

14.17

5.33

5.60

0.048

0.034

0.0

10

0.014

3.08

3.20

3.73

2.23

8.00

20. I O

8.00

10.00

The relative contribution of each of the above factors

has not been established, this being outside the scope

of the study. However, this is clearly an area where

further research would be beneficial.

Permeability versus

W I

ratio

It has been identified in previous research that the

w/c ratio has a significant influence on pe rm ea bi li t~ .~

The reduction n water permeability with reducing w/c

ratio was reported as long ago as 1926 by G1an~ille .l~

These data, with results from seven other sources

showing similar trends, have been reviewedy

Lawrence,14 and are presented in Reference

11.

Therelationship between permeability coefficient

and w/c is plotted in Fig. 4. For the dense aggregate

concretes which arenon-air-entrainedandcontain

OPC, a single relationship clearly exists. The effect

of

air ntrainment an lso be seen. While the air-

entrained concretes were, in all cases, less permeable

than the control mixes with no air entrainment, it is

237



Bamforth

Table

3 .

Average values of compressive strength, tensile

splitting strength and water permeability

Mix

Permeability

ensile

ompressive

strength: N/mm2

coefficient: lo-’’m/strength: N/mm2

S1

S2

S3

S4

S5

S6

AEI

AE2

AE3

A1

A2

A3

A4

51.5

16.5

61.3

60.6

97.0

100.3

45.1

50.0

44.8

48.5

56-0

48.9

40.9

1.30

1.06

2.42

2.70

3.34

3.88

1.76

1.82

1.91

2.27

2.44

2.24

2.10

9.87

140.1

1.28

1.91

0.044

0.024

2.41

3.79

1.87

11.90

5.46

0.040

0.012

clear that the reduction was due not to the air itself,

but primarily due to he reduced w/c ratioachieved in

the air-entrained mixes at a constant level of work-

ability. The results indicate that at a given w/c ratio,

air entrainmentmay cause an increase in permeability.

Similar findings have been reported by Murata,Is the

effect of air entrainment being to increase the water

permeability in concretes with w/c ratios ess than 0.6.

1

10

j 4

0.2

0 4

0.6 0.8

Waterkernem ratlo

Fig.

4 .

The relationship between the water cement ratio and

the coeficient of water permeability; open symbols

represent air-entrained concrete, and the shaded area shows

the range of results reviewed by LawwnceI4

238

At higher w/c ratios Murata found that air entrain-

ment reduced permeability. The use of both PFA and

GGBS also resulted in a small increase in permeability

at a given w/c ratio.

The lightweight concretes deviated significantly

from thegeneral relationship, having much lower per-

meability coefficients than could be attributed simply

to the w/c ratio. Possible reasons for this have been

discussed above.

The rangeof results reviewed by Lawrence is shown

in Fig. 4. While the data from different sources

resulted in different relationships between w/cand

permeability, the trend in behaviour was consistent.

TheAuthor’s results represent anupperbound on

permeability coefficient, the majority of published

data yielding much low permeability values at a

specific value of w/c ratio.

Permeability versus strength

In practice concretes are specified by strength. The

relationship between water permeability and com-

pressive strength is illustrated in Fig. 5. Again a

relationship clezrly exists, with the permeability

reducing logarithmically as the strength increases.

Increasing he air content (while adjusting he mix

proportions to maintain strength) tends to result in

reduced permeability. Theuse

of

PFA andGGBS had

no significant influence on permeability at

28

days

when designed to achieve equal strength with OPC

concrete.

Again, the most significant deviation from the

general relationship occurred with lightweight mixes

A 3 and A4, which achieved considerably lower per-

meability in relation to their strength.

10

I 1 I

40

80

120

Compressive strength:

Nlrnrn’

Fig.

S

The relationship between compressive strength and

the coefirient o water permeab ility; open symbols

represent air-entrained concrete, and the straight line shows

the best j i t fo rcontrol mixes Sl-S6

Magazine of Concrete Research, 1991,

43,

No. 157



Water permeabili ty

of

concrete

The relationship between permeability and tensile

splitting strength is illustrated in Fig. 6 . Once again

there is a log-linear relationship,withpermeability

reducing as the splitting strengthncreases. This is not

surprising in view of the proportionality between ten-

sile and compressive strength.

There is currently much debate about factors nflu-

encing durability, and in particular about the way in

which durability can be specified in codes of practice.

If it can be assumed that the water permeability of

concrete is a good indicator of durability, then the

results obtained, taken n isolation, would suggest that

specification by strengthgrade is an ppropriate

means of specifying for durability.

Comparison

with published results

Theelationshipetweenaterermeability

andstrength is supported by the results ofother

researchers who have imited the degree of curing.or

example, as part of a comprehensive examination of

thefactors affecting water permeability, GlanvilleI3

carried out a few tests on concretes which were air-

cured. As part f another programme, the Author has

measured strength and permeability on cores cut from

larger blocks16 which had been exposed at

24

hours to

ambient conditions, but protected from rainfall and

direct sunlight. The cores were tested at an age of 28

days, and results were obtained for a range of con-

cretes including mixes containing PFA,

GGBS

and

A 3

W\

l

f

I

4 \;S

1 0 . 1 ~

0 1

2

3 4

Tensile splittmg strength:

N/mrn'

Fig. 6 . The relationship between tensile splitting strength

and the coeficient of water permeability; the straight line

shows the best

i t

fo r control mixes

SI-S6

Magazine of Concrete Research, 1991, 43

No. 157

microsilica. Thomas

et a l l 7

and Dhir

et

al.'' have also

investigated the effect

of

curing o n permeability and

strengthand included pecimensexposedafter 24

hours. Kasai et

al.19

easured the influence of curing

on air permeability. In Fig. 7 thepermeabilityhas

been presented as the ntrinsic permeability in units of

m2 to enable the dataof Kasai to be included. Values

of water permeability coefficient have been calculated

from measured values of air permeability using the

conversion described in Reference 10. While there is

some scatter of the results shown in Fig. 7, it will be

seen that the roposed relationship broadly represents

all the data.

EfSect

of

curing

While it was beyond hescope of theAuthor's

programme o investigate the effect

of

curing, an

analysis has been carried out based

on

the identified

published results. In Fig. 8, results from References

13,

16, 17

and 19 are presented for concretes ubjected

to extended periodsof curing. Two points are immedi-

ately obvious.

a)

The relationship between compressive strength

and water permeability derived for sealed cured

concrete approximates o an upper bound, and

broadly applies to thoseconcretes whichwere

water-cured for one day or less.

b)

For concretes whichere water-curedor

periodsongerhanoneday the relationship

between compressivetrength ndwater per-

meability changes, with the ate of change in per-

meabilitywith respect totrengthecoming

greater

as

the curing period increase^.^^^^^^^ , ^

The results of Dhir et

al.

are presented in a similar

manner in Fig. 9. While the magnitude of the change

B

E 10-1

10-'8' I

l

0

10 2 30

40

50

Compressive strength: N/mm2

Fig.

7 .

The relationship betw een compressive strength and

intrinsic permeability for concretes subject

to

one-day water

curing or less; the straight line represents the best j t or

sealed cured mixes

S I 3 6

(Fig.

5):

G l a n~i l l e . ' ~

Bamforth et al., 0 Kasai t Thomas et al.,

+

Dhir et al.''

239



B a m f o r t h

10-15~

Compressive strength: N/mm z

Fig. 8. The relationship between compressive strength and

intrinsic permeability for concretes water cured fo r up to

28

days; the straight line

is

the bes t j i t for sealed cured mixes

S1-S6 (Fig . 5 ) and the curves are suggested relationships:

W

G l ~ n v i l l e ‘ ~ f o r

8

days’ water curing; a 0 0 Thomas et

al.‘7 for

28,

7 and 3 day s’ curing, respectively; 0 and 0

Kasai et d l 6 or 7 and 3 days’ curing, respectively; A

Bamforth et

al.”

f o r 3 day s’ curing

in the strength-permeabilityelationship resulting

from prolonged curing is much less than suggested by

the results of Gl an ~i ll e, ’~amforth et a1. I6 Thomas

et

al.”

and Kasai

et

al. ” a similar trend is indicated. A s

suggested by Dhir

et

a1.,I8 he difference in absolute

values is most likely to be attributable to the different

test methods employed, and it is beyond the scope of

this Paper to investigate such factors in detail. Never-

theless, the various sourcesall support the hypotheses

of ahangingelationship between compressive

strength and permeability as the period of curing is

increased.

To the author’s knowledge theeasonor the

change in the strength-permeability relationship has

not been investigated experimentally, but it s believed

that the different curves reflect different changes in

pore structure. Strengths generally determined by the

total porosity, while permeability is also related to the

pore continuity. The relatively small change in per-

meability with respect to strength when the period of

water curing is less than one day, is believed to reflect

a change in total porosity, but little change in pore

continuity. With longer periods

of

curing the conti-

nuity of the pore system is believed to become increas-

240

0

curing

water

water

water

l l

1

20

40

60 80

Compressive strength: N/mm2

Fig. 9. The relationship between compressive strength and

intrinsic permeability”

ingly broken, having a greater effect on permeability

than strength.

Hence, a series of strength-permeability relation-

ships exist for concretes which have been cured for

different periods. The implications of this are that the

permeability of concrete cannot be derived from a

measurement of strength, unless the curinghistory has

been very well-defined. For example, concrete with a

compressive strength of40 MPa may have a coefficient

of water permeability as low as 1Op2’rn2 (l op ” m/s) if

water-cured for 28 days, increasing by three orders of

magnitude, to about

10-

7 m2 (10-

’

m/s)

if

the curing

period is reduced

to

one day oress. The use of in situ

strength measurement alone is unlikely, therefore, to

provide a sufficiently accurate method forassessing in

situ permeability and the inferred durability of the

concrete.

Conclusions

A series of tests has been carried out tomeasure the

coefficient of water permeability for sealed cured con-

cretes with values of compressive strength in the range

of 16-100N/mm2. The results have been compared

with published data and the following conclusions

have been drawn.

For concretes which have been water-cured for one

day or less there is a semi-logarithmic relationship

Magazine of Concrete Research, 1991, 43, NO. 57



between water permeability and compressive (or ten-

sile strength). With the exceptionf lightweight aggre-

gate, the mix constituents did not have a significant

influence on the permeability-strength relationship.

For a given strength, substantially lower values of

water permeability can be achieved using lightweight

concrete. This is believed to be due to the combined

effects

of

the initially lower w/c ratio, being further

reduced by the aggregate absorption, improved

aggregate-cement paste bond, and a lower level of

microcracking due to the shape and stiffness of the

lightweight aggregate particles.

Comparing the Author’sesults with publisheddata

indicates that as the periodf water curing s increased

the rate ofchangeofpermeabilitywith respect to

strength also increases.

These findings suggest that the coefficient of water

permeability, and hence hedurability of concrete,

cannot be inferred from a measurement of strength

without a detailed knowledge of the curing history.

The use of in situ strength measurement is unlikely,

therefore, toprovidea reliable meansforderiving

durability without an ndependent recording of the

period of water curing.

Acknowledgements

The Author wishes to thank the Directors of Tay-

wood Engineering Ltd for permission to publish this

Paper. The financial support from theCommission of

theEuropeanCommunityand heDepartment of

Energy is also gratefully acknowledged. The work

formed part of an external PhD thesis undertaken in

association withAston University, and hanksare

also extended to Dr Roger Kettle for his sustained

support and guidance.

References

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Magazine of Concrete Research, 1991, 43, No. 157

24

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Documents

Magazine of Concrete Research Volume 43 Issue 157 1991 [Doi 10.1680%2Fmacr.1991.43.157.233] Bamforth, P. B. -- The Water Permeability of Concrete and Its Relationship With Strength