PERMEABILITY OF CONCRETE - cpaa.asn.au · Permeability of Concrete Page 2 Absorption: A process whereby concrete takes in a fluid to fill spaces within the material. Diffusion: A

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PERMEABILITYOF CONCRETE

Daksh Baweja

November 1993

Concrete Pipe Associationof Australasia

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2.19 CONCRETE PIPE ASSOCIATION OF AUSTRAtASl'A . .

Ae.N, CC7 067 656 ;;;~ICj ...

Cement and Concrete Association of Australia Seminar on Waterproofing Concrete

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PERMEABILITY OF CONCRETE

Daksh Baweja BE(Hons), M.Eng.Sc., SMIE(Aust), CP.Eng

Civil Engineer Concrete Technology Group

CSIRO Division of Building, Construction and Engineering PO Box 310

NORTH RYDE NSW 2113

Tel: (02) 934 3444 "'b: (02) 934 3555

November 9, 1993

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'Permeability of Concrete Page 1

1. INTRODUCTION

Long term durability of concrete structures may be directly related to the permeability of the concrete. The engineer aims to restrict the flow of aggressive substances in concrete thereby mitigating potential problems. Permeability of concrete is imporumt in terms of:-

o Restricting the flow of liquids. ions and gasses, and

o Its impact on corrosion of embedded reinforcement which can occur in normally reinforced and prestressed concrete structural elements.

Roper 1 notes the following factors to be important with respect to reducing permeability:·

o Materials selected for use and their interactions,

o Concrete water:cement ratio.

o Cement content,

o Type and gradings of aggregates,

o Control of the construction procedure (handling, placing, compaction and curing).

o Crack widths, and

o Avoidance of structural defects.

He further highlights the following areas that main! y contribute to the permeability of concrete:-

0 Voids in the cement paste,

0 Aggregate pores.

0 Bleed channels.

0 Air voids.

0 Discontinuities. and

0 Cracks.

2. DEFINITIONS

The following are definitions of permeability and porosity as reported by the Concrete Society2.

". Penneability: A flow property which characterises the ease with which a fluid will

pass through a material under the action of a pressure differential.

Porosity: A volume property representing the content of pores which are not necessarily inter-connected and therefore may not allow the passage of fluid

Their report states that permeability is often used to describe other transport mechanisms such as absorption and diffusion. Importantly. they make the distinction between permeability and diffusion. Definitions for adsorption, absorption and diffusion are provided below.

Adsorption: A process in which molecules adhere to the surface of a material.

CSIRO Division of Building. Construction and Engineering· North Ryde

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Permeability of Concrete Page 2

Absorption: A process whereby concrete takes in a fluid to fill spaces within the material.

Diffusion: A process by which a liquid, gas or ion can pass through concrete under the action of a concentration gradient. This is defined for a particular material by a 'diffusion coefficient' or 'diffusivity' value.

3. PERMEABDUTYRELATEDPERFORMANCEOFCONCRETE

Permeability related tests generally measure the penetration of deleterious substances into concrete. Permeability related performance measurements can also provide some indirect information as to the likely performance of concrete in terms of embedded steel corrosion after depassivation of steel has taken place and in the absence of cracking. A major review of permeability test methods was recently published by the Concrete Society2. They classified permeability tests into those that could be conducted in situ or those that were conducted in the laboratory on samples removed from site. They identified three processes by which liquids, ions or gases could penetrate into concrete, viz:·

I. Absorption and capillary effects,

2. Pressure differential permeability, and

3. Ionic and gas diffusion.

In Table I, a summary of in situ tests referenced by the Concrete Society working party are presented. Information is given on test types, specific examples oftests, descriptions of measurements taken and measurement writs of data acquired. Information is also presented on the durability parameters which were thought to be relevant to the particular test method. An assessment was made as to the relevant transport mechanism involved with each test.

CSIRO Division of Building, Construction and Engineering· North Ryde

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Table I - Summary of In Situ Test Methods Referenced in the Concrete Society Technical Report No. 3 I (After Ref. 2)

Test Type Exampksof Measuran<m Dcsaipti ... Asscsso:I Durabilil.y M<osIlnmcot Utits Tr~ CurrcolT .... Par_ Med>aaisms

.Iovolvcd

Jmtial sun"", BS 1881 PartS Rate ofwato- absorptim m Durability of rebar mLJmlls Waler absaptim

Absorpti ... Test

(ISAT)

thcswface Frost resistance

Weathering

FiggTrst FiggMdhod Prqlcrties of swface skin ()[" Possible Sees for an arbitrary Watrr .absc.ptioo

Modified FiSS con:1" ooocrde permeability airprCSSlU"C «water Gas diffus:i. CD

Mdhods ass=,,,,,, vol\UDC maoRe

Pressure Applied Maltg<may& W3I.apeoetratim at a Penneability Volume of waler Waurpenncability

Suna", Adams Test particular hoad Oowingioto Permeability Slioart Test coocrctc at a

"articular hoad

CarbcuatiCIJ. Pomt at "'rich the pH of Cm-osim of steel mm1(tim.p·S Gas diffusicn Dcoth CQlQ'etc is bdween 8 and 10

Icnic Diffusim ASfMC120l- Charge. passed over a six Chlc:ride Coulcmbs over a six Ienic diffusioo 91 bourncriod permeability hour test period

Drill Hole Prc:ssure & flow rate ofwater Air permeability Pressure & Oarw rate Gas diffusim Permeability or air injcailrl or withdrawn

Water permeability War.erpenneability from a sealed drill hole in

""""". Leak Testing of

Complete

Suu=

The report further points out a range of laboratory tests which can be used on specimens acquired from site. The tests are categorised in the from of transport mechanism involved which are:-

• Absorption of water

• Permeation of liquids or gasses resulting from pressure gradients, or

• Diffusion of gases water vapour or ions due to a concentration gradient.

A summary of the test methods reported for use in the laboratory are presented in Table 2. Table 1 would also be useable Wlder laboratory situations.

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CSIRO Division of Building, Construction and Engineering - North Ryde

Tests shown in

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Penneability of Concrete Page 4

Test T)pc

w"or Absorpticu

Pressure Induoed Liquid Row

Presrure IoducedGas Row Gas Diffusioo

Water Vapour Diff'usim

Icnie Diffusioo

Table 2 - Surrunary of Laboratory Test Methods Referenced in the Concrete Society Technical Report No. 31(After Ref. 2)

Sp«ificT ... TcstDcscriptim A=-I MeasurmIull Thits

Da.iJs Darability -Shall"", Dry a specimco to a CCDStant Wata abstxptico Measure specimen weight immcn:i.m weight and immerse in water increase as a % of dry

woioht Capill2ry rise Same as shallow immasim Water absorptim Measure increase in the (&.ptivity) PCI'osity mass of sample following

mallow imm~cn

M""""=mt FleM' rate ciliquid. measured Penneability Liquid flow rate

by flow UDdor an applied bead COITOOOO of steel (H2O aod Cl)

Measurcmc:nt Apply prcssurised water CIl W_ Measure the depth of bv ~cndtaticn CCIlaete swface for a SJ;1veo time p""",,",ility penctratioo

As for liquid except with the use COlTosim of steel of a cbO$l!:ll gas (oxyg..,)

Applying dissimili!r gasses to two Gas diffusicn Measure COlCCDtraticn of qrpo.smg surfaces of a CXIlcm.c ~:7ofstccl sd«ted diffused gas soec::imcn throuoh .,ecimeo Speci:mCD. placed in a chambCf" Water vapour Weight of~ vapour CXIltaining water vapour at koO\W. diffusim allows detenninatioo: of vapour pressure. After COITosioo of steel wala vapour diffu.sJoo. oquilibrium, desiccaot applied 00

eoposinR surface Sample analysis T akinS scd.ioo.s of CCIlact.c at looie diffusioo CClJocntratim (% by mass

differeat depths and analysing for Conosioo of steel ofsampl'l chloride

Ccncmtratloo. Placing speci.mm in aU having looie ditfusiw RoguJarlyanalysing differencc t:q)osurc to two dissimilar liquids, CCC'osioo of steel solutiw opposed to the ooe

ooe being of inta-est. of :interest fa the COlecntratim oftbc soluticn of interest

T~M M..:haoisms Invo1.vtd

wator abSlXpticn

wator absorptiCll

w"" (liquid) pcnneability

Wa10r (liquid) p=eability Gas difl'usim

Gas diffusim

Water vapour diffusim

lcaic diffusicn

Icnie diffusioo

In addition to the test methods outlined in Tables 1 and 2, the report also notes the following test methods which could be used to assess the penneability of concrete:-

• Radiation attenuation

• Concrete resistivity

• High pressure tests

• Transient pressure pulse and pressure decay tests, and

• Osmotic pressure tests.

Feldman3 has conducted an extensive review ofpenneability assessment methods. He suggested that oxygen and chloride diffusion were most apt for perfomoance assessment with respect to corrosion of steel. In addition to those mentioned by Feldman, a further commonly used penneability assessment technique relating to corrosion of steel is carbonation depth measurement.

3.1. DETAll..S FOR SELECTED TEST METHODS

3.2. Water Absorption

Commonly used tests for water absotption are shallow immersion and capillary rise measurements. These are thought to reflect the passage of water through concrete in the absence of a pressure differential. A significant amown of research has been conducted on sotptivity of concrete by the CSlR04 The influences of concrete grade and curing on water penetration are highlighted. Values of 4 hour penetration have estimated in the range of 10 to 20 nun for t~ical concretes. A review of tests for water penetrability have also been presented by Papworth and Green . Readers are referred to literature sources for further infonnation2,6

CSlRO Division of Building, Construction and Engineering - North Ryde

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CONCRETE PIPE ASSOCIATION OF AUSTR A.C.N. 0670676<6 ALASJA

'Permeability of Concrete - Page 5

3.3. Chloride Penetration

3.3.1. Chloride Ion Concentration

Reinforced concrete structures are often subject to chloride exposure from marine environments. Utis is particularly so in Australia where 95% of the population is concentrated in major coastal capital cities. A significant amount of the country's heavy engineering infrastructure assets are also located in coastal regions. Chloride ions disrupt the normal passivity of steel imparted by alkaline concrete. Once passivity has been lost, corrosion of steel commences. Corrosion of reinforcement leads to an increased volume of corrosion products relative to the original steel. Utis can ultimately result in cracking and spalling of concrete.

Chloride ion penetration occurs when concrete members are exposed to sea-water or other chloride bearing liquids (as is the case for much of Australia's infrastructure). Work suggests that chloride ions can be further bound by the use of blended cement systems in concrete. Rose 7 reports that blast furnace slag cement concretes show lower permeability to chloride ion ingress than other binder types.

The measurement of chloride ion concentrations in concrete is subject to some conjecture. Dhir and coworkers8 reported on the determination of total and soluble chlorides in concrete. They noted that the proportion of acid-soluble chlorides measured is dependent upon the strength and contact time of the acid and that different methods of acid extraction would result in different values of chloride ion concentration. Using water extraction procedures, the authors found that chloride ion concentrations were independent of methods used provided that the extraction time was greater than 24 hours. No equilibrium relationship was found between water-soluble chloride ion concentration and bound chloride ion concentration .

It is generally thought that critical levels of chloride are required in concrete to cause steel depassivation. Schiessl and Raupach9 suggest two possible definitions for critical levels of chloride in concrete, which are:-

I. The chloride content at the steel surface which causes depassivation of reinforcement, and

2. The chloride ion concentration at the steel surface which leads to a deterioration or damage of the concrete structure.

The authors found in studies of chloride ion concentration influences on corrosion that both factors were dependent upon many parameters including binder type, water:binder ratio, temperature and relative hwnidity. As a result, they found values of critical chloride ion concentrations for reinforcement corrosion to vary greatly. In reports of work by TrittbartlO, it was also concluded that there was no one critical level of chloride but that this value differed for different concretes.

3.3.2. Chloride Diffusion Rates

In many cases, Fick's second law of diffusion ilrused to model chloride ingress into concrete. Berke and Hicks II note that chloride ion ingress into concrete can be modelled as follows.

C = co( 1-er1 2. ~(;'ff . t) ]) ............................................................................... (1)

where C: Co: x: I:

Deff.

Chloride ion concentration at depth x, Surface chloride ion concentration, Depth from the surface, Time of measurement, and Effective diffusion coefficient.

The term eifrefers to the standard error function. Those authors presented data on chloride diffusion for a series of concretes. Relationships were found between concrete reo :.' vity and the effective diffusion coefficient as follows.


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Penneabilityof Concrete Page 6

D'ff = 54. 6 x 10-' (Resistivity f lO' ...••.. ,",.,""', ............................................... , ........... (2)

3.3.3. Rapid Estimation of Chloride Ion Permeability

Assessments of chloride ion diffusion are regularly made in accordance with ASTM C 1202, the Standard Test Method for Electrical Indication of Concrete's Ability to Resist Chloride Ions 12. In this test, a potential difference of 60±l V is applied across an approximate 100 mm diameter by 50 mm thick disk which is placed between a sodium hydroxide solution and a sodium chloride solution, Values of chloride penneability are expressed in tenns of charge passed (coulombs) over a six hour period.

Much work has been conducted on concrete performance based on this test procedurel3 ,14 and its predecessor specification put out by the American Association of State Highway and Transport Officials (AASFITO), Indications are that concretes incorporating mineral additives show better perfonnance when compared to OPC concretes based on results from this test procedure. Some workers believe that the ASTM procedure for rapid determination of chloride permeability measures only total charge and not chloride diffusivityl5, Berke and Hicksll found that concrete resistivity was inversely proportional to the AASFITO rapid chloride ion permeability of the set of concretes investigated .

3.4. Carbonation

Carbonation, or reduced alkalinity, describes the influence of carbon dioxide, usually from the atmosphere, on reinforced concrete. The ingress of carbon dioxide into reinforced concrete structural elements can have a detrimental effect on the steel because the alkalinity of the concrete is reduced, Reactions between C02 and calcium hydroxide in the concrete typically reduce the pH characteristics from 12,6 to values below 8.3, A comprehensive recent review of the carbonation phenomena has been made by Richardson I 6 He considers many factors relating carbonation to durability, some of which include:-

• Concrete age;

• Aggregate characteristics;

• Use of blended cements;

• Mix design factors;

• Exposure conditions;

• Construction factors;

• Cracks;

• Curing;

• Density, and;

• Member geometry,

Many workers have carried out studies into the carbonation characteristics of various concretes. Here in Australia, Ho and Lewis 17 have conducted much work into the area of carbonation of concrete and its prediction. They noted that curing was very irtlportant with regard to carbonation of concrete, They further indicated that resistance to carbonation was increased by increasing strength. Bakkerl8 suggests that important parameters for the assessment of carbonation of concrete are:-

• The cement composition, • The amount of cement within a concrete mix, • The composition of the concrete, • Compaction, • Curing, and • The environment within which the concrete is to perform.

There is much debate regarding the use of accelerated carbonation tests to predict the long-term carbonation characteristics of concrete l9 . Such studies caution against simple extrapolation of accelerated carbonation results for long-term performance predictions. Typically under field situations, carbonation and chloride exposure are likely to occur simultaneously in service. Baweja, Roper and Cook20 found that the water:cement ratio of concrete was usually a good predictor of carbonation characteristics in the field.


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Studies by Roper and Baweja21 on interactions between carbonation and chlorides showed that these effects occurring together lead to much more rapid corrosion than if the two phenomena occurred individually. The presence of high chloride concentrations in the concrete was found to retard carbonation activity in this study. Such phenomena were observed on studies carried out on two wharf structures by Roper, Heiman and Baweja22.

3.S. Concrete Resistivity

Resistivity of concretes is commonly monitored using the Wenner Bridge four-electrode method, a testing method for concrete structures on site. It was adapted from methods originally developed for the determination of soil resistivity23,24,25 The resistivity of the concrete is determined by passing a current through the outer two electrodes and measuring the potential difference between the inner two electrodes. The resistivity determined in this way is calculated as described below.

p= 271ll(~)............................................... .......................................... ..H.... .. (6)

where, p: Resistivity of the concrete, V: Potential difference between inner resistivity electrodes, and J: Current flowing between 0= resistivity electrodes.

1: r..as bee"! roporuO thai: ancr<re resisti'lIY is scruiri\"e to moisrure = ofrhe coocr<re. embedded remforcement, temper.lIUTe and bar diameter. .\foisrure and reinforcement locatioo appear to be more influential than temperarure and bar diameter. Low resistivity concrere surface layers will also significantly influence measured concrere resistivity. Browne26 suggests that values in excess of 20,000 ohm em could be indicative of passive reinforcement corrosion states within concrete, particularly where high chloride levels are present. It has also been suggested that a measured resultant resistivity value below 5000 ohm em coupled with a copper-copper sulphate half cell potential measurement more negative than -350 m V could point to a strong possibility of corrosion activity24

4. TYPICAL VALUES FOR TEST RESULTS

Typical values reported by the Concrete Society2 of permeability and related properties are presented in Table 3. The report notes that the values shown are typical test values and should not be used for specification purposes.

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Table 3 - Typical Values of Concrete Permeability and Related Properties2

Test Method Units Concrete PermeabilityJAbsoIptionJDiffusion

Low Average High

Liquid permeability m2 <10-19 10-19 to 10-17 >10-17

Gas Permeability m2 <7xlO-18 7xlO-18 to 7x10-16 >7xlO-16

Coefficient of permeability to water mi. <10-12 10-12 to 10-10 >10-10

ISAT 10 min mlIm2J. <0.25 0.25 to 0.50 >0.50

ISAT 10 min mlIm2J. <0.17 0.17 to 0.35 >0.35

ISAT 10 min mlIm2Js <0.10 0.10 to 0.20 >0.20

ISAT 10 min mlIm2J. <0.07 0.07 to 0.15 >0.15

Figg water absoIption - 50 mm (Dry concrete) s >200 100 to 200 <100

Modified Figg air permeability (Ove Arup) -55 S >300 100 to 300 <100 to -50 kPa

Water absorption 30 mins 5 <3 3 to 4 >4

4 hour sorptivity mm <10 101020 >20

DIN 1048 depth of penetration (4 days) mm <30 30 to 60 >60

Oxygen Diffusion coefficient (28 days) m2Js <5xlO-8 5x10-8 to 5xlO-7 >5x10-7

Apparent chloride diffusion coefficient m21s <lxHrl2 Ix 10-12 to 5xlO-12 >5xI0-12

5. CONCLUSIONS

An attempt has been made to briefly review concepts behind permeability and the measurement of permeability of concrete. hnportant differences between the terms permeability, porosity, absorption and diffusion have been highlighted. Permeability test methods have been classified into those relating to:-

• Absorption and capillary rise,

• Pressure differential, and

• Ionic and gas diffusion having a concentration gradient.

Factors important in minimising corrosion of steel have been discussed. These are also important for the production of good, dense concrete. Good, dense concrete production is a prerequisite for achieving low concrete permeability .

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DEFERENCES

Roper, H., "Design of Impermeable Concrete", Concrete Institute of Australia Seminar on Waterproofing Concrete, 1992 .

Concrete Society, "Permeability Testing of Site Concrete: A Review of Methods and Experience", Report ofa Concrete Society Working Party, Technical Report No. 31, ISBN 0 946691 21.5, August, 1988, Published by the Concrete Society, Devon House, 12-15 Dartmouth Street, London SWIH9BL.

Feldman, R.F., "Pore Structure, Permeability and Diffusivity as Related to Durability", Eighth International Conference on the Chemistry of Cement, Rio de Janeiro, Brazil, September 22-27, 1986, P 1-21.


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REFERENCES CONTINUED

4 Ho, D.W.S. and Lewis, R.K., "The Specification of Concrete for Reinforcement Protection -Perfonnance Criteria and Compliance by Strength", Cement and Concrete Research, Vol. 18, No.4, 1988, pp 584-594.

5 Papworth, F. and Green, W., "Concrete Penetrability", In Taywood Engineering Life Cycle Manual, 2nd Edition, Taywood Engineering, Australia, 1988

6 Whiting, D. and Cady, P.D., "Condition Evaluation of Concrete Bridges Relative to Reinforcement Corrosion - Volume 7: Method for Field Measurement of Concrete Permeability", Strategic Highway Research Program, SHRP-SIFR-92-109, Washington USA, 1992.

7 Rose, J., "The Effect of Cementitious Blast Furnace Slag on Chloride Permeability of Concrete", ACI, SPI02-7, F.w. Gibson Editor, 1987, pp 107-126.

8 Dhir, R.K., Jones, M.R. and Ahmed, H.E.H, "Detennination of Total and Soluble Chlorides in Concrete", Cement and Concrete Research, Vol. 20, No.4, 1990, pp 579-590.

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Schiessl, I.P. and Raupach, I.M., "Influence of Concrete Composition an~ Microclimate on the Critical Chloride Content of Concrete", Third International Symposium on Corrosion of Reinforcement in Concrete Construction, Society of the Chemical Industry, UK, May, 1990, pp 49-58.

Tritthart, J., "Pore Solution Composition and Other Factors Influencing the Corrosion Risk of Reinforcement in Concrete", Third International Symposium on Corrosion of Reinforcement in Concrete Construction, Society of the Chemical Industry, UK, May, 1990, pp 96-106.

Berke, N.S. and Hicks, M.e., "Estimating the Life Cycle of Reinforced Concrete Bridge Decks and Marine Piles Using Laboratory Diffusion and Corrosion Data", Corrosion Fonus and Control for Infrastructure, ASTM STP 1137, V. Chaker Editor, American Society for Testing and Materials, Phiiadelphia, 1992, pp 207-231.

American Society for Testing and Materials, "Standard Test Method for Electrical Indication of Concrete's Ability to Resist Chloride Ions", ASTM C1202-91, 1991.

Whiting, D., "Permeability of Selected Concretes", ACI Special Publication on Permeability of Concrete, SP 108, Detroit Michigan, 1988, pp 195-222.

Plante, P. and Beaudoin, A., "Rapid CIiloride Ion Permeability Test: Data on Concretes Incorporating Supplementary Cementing Materials", Third International Conference on Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, CANMET/ACI SP 114-30, Trondheim, Norway, 1989, pp 625-644.

Luping, T. and Nilsson, L.O., "Rapid Detennination of the Chloride Diffusivity in Concrete by Applying an Electrical Field", ACI Materials Joumal, Vol. 89, No. I, January-February, 1992, pp 49-53.

Richardson, M.G., "Carbonation of Reinforced Concrete: Its Causes and Management", Citis Ltd., ISBN 0-948564-03-2, 1988.

Ho, D.w.S. and Lewis, R.K., "The Compliance of Concretes With the Durability Requirements of AS 3600", Concrete for the 90's, CIA and CSIRO Division of Building, Construction and Engineering, Leura, Australia, September, 1990.


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REFERENCES CONTINUED

18 Bakker, R.F.M., In "Corrosion of Steel in Concrete", Report of the RILEM Teclmical Committee, 60-CSC, P. Schiessl Editor, 1989, Chapter 3, "Initiation Period", pp 22-55.

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De Ceukelaire, L. and Van Nieuwenberg, D., "Accelerated Carbonation ofa Blast Furnace Cement Concrete", Cement and Concrete Research, Vol. 23, No.2, 1993, pp 442-452.

Baweja, D., Roper, H. and Cook, OJ., "Carbonation Characteristics of In Situ Portland Cement and Fly Ash Concretes in Australia, England and the United States", Fourth International Conference on Durability of Building Materials and Components, Singapore, November, 1987 .

Roper, H. and Baweja, D., "Carbonation-Chloride Interactions and Their Influence on Corrosion Rates of Steel in Concrete", Second International Conference on Durability of Concrete, CANMET/ACI, SP 124, Montreal, Canada, August, 1991.

Roper, H., Heiman, J.L. and Baweja, D., "Site and Laboratory Evaluation of Repairs to Marine Concrete Structures and Maintenance Methodologies - Two Case Studies", Second International Conference on Performance of Concrete in a Marine Environment, CANMET/ACI, SP 109, St Andrews By-The-Sea, Canada, 1988.

Uhlig, H.H. and Revie, R.W., "Corrosion and Corrosion Control - An Introduction to Corrosion Science and Engineering", John Wiley and Sons, Wiley Interscience Publication, Third Edition, pp 424-425.

Heiman, J.L., "The Durability of Cast In Situ Reinforced Concrete", Technical Record No. 511, National Building Technology Centre, CSIRO Division of Building, Construction and Engineering, June, 1986.

American Society for Testing and Materials, "Standard Test Method for Field Measurement of Soil Resistivity Using the Wenner Four-Electrode Method", G 57-78, 1984.

Browne, R.D., "The Mechanisms of Corrosion of Steel in Concrete in Relation to Design, Inspection and Repair of Offshore and Coastal Structures", ACI Special Publication SP-65, St Andrews by-theSea, New Brunswick, Canada, April, 1980 .


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PERMEABILITY OF CONCRETE - cpaa.asn.au · Permeability of Concrete Page 2 Absorption: A process whereby concrete takes in a fluid to fill spaces within the material. Diffusion: A