Cracking to Alkali-Silica Reaction - University of Toronto T-Space · 2020. 4. 7. · fiom damage...

Cracking due to Alkali-Silica Reaction and

its Effect on Durability Properties of Coocrete

Nelson K. C. Or

A thesis submitted in conformity with the requirements for the degree of Master of Applied Science Graduate Department of Civil Engineering

University of Toronto

0 Copyright by Nelson K. C. Or (1999)

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Around the world, many structures built during the last few decades have suffered

fiom damage due to alkali-silica reaction (ASR). Some of these structures were

considered structurally inadequate and have been replaced or repaired. Most of the others

are stmcturally safe but the concrete might have failed as a protective barrier to the

reinforcement. ASR causes microcracks in concrete which may lead to inserviceability of

structures by providing easy access for other deterioration processes to take place.

This thesis work investigates the effect of ASR-induced microcracks on the

durability of concrete. Specifically, mass transfer properties and fieeze-thaw resistance of

damaged, non-air-entrained concrete were assessed.

Due to the hydrophilic natural of the alkali-silica gel, it was found that the role it

plays in concrete durability is significant. Microcracks caused by ASR increased the rate

of diffusion of chloride and gas pemeability through concrete. However, it reduced water

permeability. The gel exists in the pores and microcracks may mitigate the detrimental

effect of cracks on mass transfer. Nevertheless, the net effect is unfavourable to the

durability of concrete. The expansion due to ASR had an adverse effect on the fieeze-

thaw resistance of concrete. The relative dynamic modulus of sarnples with expansion

levels of 0.092%, 0.122% and 0.205% dropped below 60% in less than 50 cycles. Other

sarnples with lower level of expansion lasted about 150 cycles before 60% of relative

dynamic modulus was reached.

Crac king due to Alkali-S iiica Reaction and its EfEect on Dwability Properties of Concrete

Further research using sarnples with higher expansion in mass transfer tests and

air-entrained concrete in fieeze-thaw test is recommended by the author.

Cracking due to Alkali-Silica Reaction and its Effect on Durability Properties of Concrete

Acknowled~ments I I I

The author would like to express his gratitude to the thesis supervisors, Prof. N.

Hearn and Prof. M. D. A. Thomas for their support, inspiration and excellent guidance.

The author also would like to acknowledge Ursula Nytko for the charitable help and

advise offered throughout this research.

The author is grateful for the assistance fiom Peter Seibert in sample preparations.

Special thanks to Kelvin Leong for the generous help in ordering and setting up the

permeability cells.

The author also appreciates the help provided by Terrence Holder, Katherine

Hong, Kyle Stanish, Melissa Titherington, Hassan Zibara and Italia Ponce. The rest of the

Concrete Materials Group had created such an enjoyable environment for research. The

author is very proud of being a member of the Concrete Materials Group.


Table of Contents IV

2.1 ALKALI-AGGREGATE REACTIONS ................................................................................ 6 2.1 . 1 Alkali-Silica Reaction .................................... ,..,.. ................................................ 7

2.2 FREEZING AND THAWING IN CONCRETE ................................................................ 1 1 ........................................................... 2.3 MASS TRANSFER MECHANISMS IN CONCRETE 13

2.3.1 Perrneation ....................................................................................................... 1 5 2.3.1. I Water Permeability ...................................................................................... 16 2.3.1.2 Gus Permeability ......................................................................................... 16

2.3.2 Diffusion ............................................................................................................ 1 7 2.3.3 Migration ............................................................................................................ 18 2.3.4 Rapid Chloride Penetrability Test ...................................................................... 19

2.4 EFFECT OF MICROCRACKS ON WSS TRANSFER ........................................................ 20 .................................................. 2.4.1 Hypothesis of Gel Obstruction in Microcracks 24


Table of Contents V

4 RESULTS AND DISCUSSIONS........~~ . . . . . . . . . .mm~~.m~m~..mmm.m..m..m.. . .m.m.mmmm 46 4.1 SAMPLE EXPANSION .................................................................................................. 47

........................................................................................ 4.2 RAPID FREEZE-THAW TEST 49 4.3 WATER PERMEABILITY TEST ..................................................................................... 53 4.4 GAS PERMEABILITY TEST .......................................................................................... 57 4.5 COMPARISON OF WATER AND GAS PERMEABILITY RESULTS ..................................... 60 4.6 RAPID CHLORIDE PENETRATION TEST ....................................................................... 64 4.7 CHLORIDE MIGRATION TEST ..................................................................................... 67 4.8 CHLORIDE BULK DIFFUSION TEST ............................................................................. 72 4.9 SUMMARY OF MASS TRANSFER RESULTS .................................................................. 75

5 CONCLUSIONS AND ~COMMENDATIONS ................................................. 80

APPEND~X D TABULATED SUMMARY OF RCPT RESULTS

Cracking due to Alkali-Silica Reaction and its Effect on Durability Properties o f Concrete

List of Tables VI

.............................................................................. Table 3.1 . 1. Concrete mix proportions 28 Table 3.1.2. Summary of testing program ......................................................................... 30 Table 4.5.1 : Results of penneability conversion O lab-cast samples ................................. 61 Table 4.5.2. Results of pemeability conversion . MT0 sarnples ..................................... 61 Table A . 1 : Summary of prism expansion measurement ................................................ A2 Table B . 1 : Raw data and tabulated calculations of dynamic modulus - 7 17/8611 ........... B2 Table B.2. Raw data and tabulated calculations of dynamic modulus . 7 1 7/86/2 ........... 8 3 Table 8.3. Raw data and tabulated calculations of dynamic modulus O 730/86/1 ........... B4 Table B.4. Raw data and tabulated calculations of dynamic modulus . 730/86/2 ........... B5 Table B.5. Raw data and tabulated calculations of dynamic modulus = 730/86/4 ........... B6 Table 8.6. Raw data and tabulated calculations of dynamic modulus œ 73018615 ........... B6 Table B.7. Raw data and tabulated calculations of dynamic modulus = 733/8614 ........... B7 Table B.8. Raw data and tabulated calculations of dynamic modulus = 73318615 ........... B7 Table B.9. Raw data and tabulated calculations of dynarnic modulus œ 733/8617 ........... B8 Table B . 10: Raw data and tabulated calculations of dynamic modulus O 733/8618 ......... B9 Table B . 1 1 : Raw data and tabulated calculations of dynamic modulus O 752/86/7 ....... BI0 Table B.12. Raw data and tabulated calculations of dynamic modulus O 752/8618 ....... BI0 Table B.13. Raw data and tabulated calculations of dynarnic modulus . 753/8617 ....... BI 1 Table B . 14: Raw data and tabulated calculations of dynarnic modulus O 753/86/8 ....... BI1 Table G . 1 : S m a r y of calculations of durability factor ................................................. G3

Cracking due to Alkali-Silica Risaction and its Effect on Durability Properties of Concrete

List of Figures VI1

Figure 2.1 . 1. The microstructure of the aggregate-paste interface influences by the ............................................................................................. course of ASR 10

....................................................... Figure 2.4.1 : Development of cracking due to AAR 2 1 .................................................... Figure 3.1 . 1. Details of preparation for prism sarnples 31

Figure 3.5.1 : Sketch of water permeability ce11 ................................................................ 35 Figure 3.6.2. Sketch of gas pemeability ce11 ................................................................... 37

.............................................................. Figure 3.8.1 : Chloride migration test apparatus 4 0 Figure 3.8.2: Glass Luggin capillary and reference electrode used to accunitely

set voltage drop across the samples ........................................................... 40 Figure 4.1.1 : Graph of expansion vs age of concrete samples ......................................... 48 Figw 4.2.1 : Graph of relative dynamic modulus vs . nurnber of fieeze-thaw cycles ...... 51 Figure 4.2.2: Graph of relative ultrasonic pulse velocity vs . No . of fieeze-thaw cycles .. 52

......................... Figure 4.2.3 : Graph of relative mass vs . number of Freeze-thaw cycles 52 Figure 4.2.4. Graph of durability factor vs . expansion level ............................................ 53 Figure 4.3.1 : Graph of pemeability coefficient vs . expansion level for

......................................................................................... lab-cast samples 5 5 Figure 4.3.2: Graph of penneability coefficient vs . expansion level for MT0 samples . 56 Figure 4.3.3. Combined results of water pemeability test ............................................... 56 Figure 4.4.1. Graph of specific penneability vs . expansion level for lab-cast samples ... 59

...... Figure 4.4.2. Graph of specific pemeability vs . expansion level for MT0 samples 59 .................................................. Figure 4.4.3. Combined results of gas permeability test 60

Figure 4.5.1 : Cornparison of intrinsic pemeability and gas permeability O lab-cast sarnples ........................................................................................ 62

Figure 4.5.2: Cornparison of intrinsic pemeability and gas pemeability . MT0 samples ........................................................................................... 62

Figure 4.6.1 : Graph of RCPT results vs . expansion level for lab-cast samples .............. 66 Figure 4.6.2. Graph of RCPT results vs . expansion level for MT0 samples ................. 66 Figure 4.7.1. Graph of chloride passed vs . elapsed time - SPRT/OS and SPRT/09 ......... 69

................................................. Figure 4.7.2. Surnmary of test results . lab-cast sample 6 9 .................................................... Figure 4.7.3 : Sumrnary o f test results O MT0 samples 7 1

Figure 4.7.4. Graph of breakthrough t h e vs . expansion level ..................................... ... 71

Cracking due to AUcali-Silica Reaction and its Effect on Durability Properties of Concrete

List of Fimires Vlll

.................................... Figure 4.7.5. Trend of breakthrough tirne vs . expansion level 7 2 Figure 4.8.1 : Chloride profile of samples 733/86/11 and 755/86/1 ............................... 74 Figure 4.8.2. Sumrnary of bulk diffusion test results ....................................................... 75 Figure 4.9.1 : Summary of transport coefficients . MT0 specimens ..................... ... ... 76 Figure 4.9.2. S u m a s , of transport coefficients O lab-cast specimens ........................... 76 Figure A . 1 : Graph of expansion vs . age of concrete samples ......................................... A2 Figure C.1. Water oudlow vs . elapsed time . SPRTl03 ................................................. Cl

.................................................. Figure C.2. Water outfiow vs . elapsed time . SPRTl04 Cl Figure C.3 : Water outflow vs . elapsed time . SPRT/OS ................................................. C2 Figure C.4. Water outflow vs . elapsed time O SPRTl06 .................................................. C2 Figure CS: Water outfiow vs . elapsed time . SPRTl07 .................................................. C3 Figure C.6. Water outflow vs . elapsed time . SPRTI08 .................................................. C3 Figure C.7. Water outfiow vs . elapsed time = SPRT/09 ................................................ C4 Figure C.8. Water outfiow vs . elapsed time = SPRTII O ................................................. C4 Figure C.9. Water outflow vs . elapsed time O SPRTII 1 .................................................. C5 Figure C.10. Water outflow vs . elapsed time . SPRTll2 ................................................ C5 Figure C . 1 1 : Water outflow vs . elapsed time . 72018611 .............................................. C6 Figure C . 12: Water outflow vs . elapsed time . 72018612 ................................................ C6 Figure C . 1 3: Water outflow vs . elapsed time . 73318611 ................................................ C7 Figure C . 14: Water outflow vs . elapsed time . 733/86/2 ................................................ C7 Figure (2.1 5: Water outflow vs . elapsed time . 733/86110 .............................................. C8 Figure C . 16: Water outflow vs . elapsed time . 733/86/11 .................................... . . . . C8 Figure C.17. Water outflow vs . elapsed time . 753/8611 ................................................ C9 Figure C.18. Water outflow vs . elapsed tirne . 75318612 ................................................ C9 Figure C . 19: Water outflow vs . elapsed time = 753/86/10 ............................................ Cl0 Figure C.20. Water outflow vs . elapsed time . 753/86/11 .................................... ... . Cl0 Figure C.2 1 : Mrater outflow vs . elapsed time . 755186/1 ............................................ Cl1 Figure C.22. Water outflow vs . elapsed time a 75518612 ............................................. Cl1 Figure C.23 : Water outflow vs . elapsed tirne = 75 Y8617 .............................................. Cl2

O .............................................. Figure C.24. Water outflow vs . elapsed t h e 75518618 Cl2 Figure C.25 : Water outfiow vs . elapsed t h e . 755/86110 .................................... ... . Cl3 Figure C.26. Water outfiow vs . elapsed tirne . 75 5/86/11 .................................... ... . Cl3


List of Figures IX

. Figure D 1 : Summary of RCPT results O lab-cast samples .............................................. D2 Figure D.2. Summary of RCPT results O MT0 samples ................................................. D3 Figure E . 1 : Summary of migration test results . lab-cast sarnples ................................... E2 Figure E.2. Sumrnary of migration test results O MT0 sarnples ....................................... E3 Figure E.3. Individual migration test results O SPRTIO2 .................................................. E4 Figure E.4. Individual migration test results O SPRT/04 .................................................. E5 Figure ES: individual migration test results O SPRTIOS .................................................. E6 Figure E.6. Individual migration test results O SPRT/O6 .................................................. E7 Figure E.7. Individual migration test results O SPRTl07 .................................................. E8 Figure E.8. Individual migration test results O SPRTIO8 .................................................. E9 Figure E.9. individual migration test results O SPRTl09 ................................................ El0 Figure E . 1 0: Individual migration test results O SPRT/l O ................................... ...... . El1 Figure E . 1 1 : Individual migration test results O SPRTII 1 .............................................. El2 Figure E . 1 2: Individual migration test results O SPRTII 2 .............................................. El3 Figure E . 1 3 : Individual migration test resuits O 72018611 ............................................... El4 Figure E . 14: Individual migration test resdts O 720186/2 ............................................... El5 Figure E . 1 5: Individual migration test results œ 733186/1 ............................................... 1 6 Figure E . 16: Individual migration test results O 73318612 ............................................... El7 Figure E . 17: Individual migration test resuits O 733186110 ............................................. El 8 Figure E . 18: Individual migration test results O 733/86/11 ............................................ 9 Figure E.19. Individual migration test resuits O 75318611 ............................................... E20 Figure E.20. Individual migration test resdts . 753/86/2 ............................................... E21 Figure E.2 1 : Individual migration test resuits . 753/86110 ............................................. E22 Figure E.22. Individual migration test results O 753/86111 ............................................. E23 Figure E.23. Individual migration test results O 75518611 ............................................... E24 Figure E.24. Individual migration test results O 75518612 ............................................... E25 Figure E.25. Individual migration test results O 75518617 ............................................... E26 Figure E.26. Individual migration test results O 755/8618 ............................................... E27 Figure E.27. Individual migration test results O 755186110 ............................................. E28 Figure E.28. Individual migration test results O 755/86/11 ............................................. E29 Figure F . 1 : Chloride profile O 72018611 ............................................................................ F2 Figure F.2. Chloride profile O 72018612 .......................................................................... F3

Cracking due to Alkali-Silica Reaction and its Effect on Dwability Properdes of Concrete

List of Figures X

Figure F.3 : Chloride profile . 73318611 ........................................................................... F4 Figure F.4. Chloride profile . 733/86/2 .......................................................................... F5 Figure F.5. Chloride profile . 733186/11 .......................................................................... F6 Figure F.6. Chloride profile . 733/86/10 .......................................................................... F7 Figure F.7. Chlonde profile O 75318611 ............................................................................ F8 Figure F.8. Chloride profile O 75318612 ........................................................................ F9 Figure F.9. Chloride profile . 753/86/10 ........................................................................ FI0 Figure F . 10: Chloride profile O 75318611 1 ...................................................................... FI1

. Figure F 1 1 : Chloride profile O 755/86/1 ..................................................................... F12

. Figure F 12: Chloride profile O 755/8612 ........................................................................ F13 Figure F . 13: Chloride profile . 75518617 .................................................................... F14

. Figure F 14: Chloride profile . 75518618 ....................................................................... FI 5

. ...................................................................... Figure F 15: Chloride profile . 755186110 F16 Figure F . 16: Chloride profile O 75518611 1 .................................................................... F17

Cracking due to Alkali-Silica Reaction and its Effêct on Durability Properties of Concrete

Nomenclature X 1

N O M E N C L A T U R E

= penetrated area (m2) 2 2 = 0.00245 ( L ~ T I ~ ? ) for a prism (s /in )

= concentration of diffising substance (mo1/m3)

= background chloride concentration (% mass)

= corrected chloride concentration (% mass)

= chloride concentration at the surface (mol/m3)

= chloride concentration at time t and depth x (rnol/m3)

= diffision coefficient (m2/s)

= sample diameter of sample (mm)

= durability factor

= pressure head (m)

= potential drop across the sample (V)

= dynamic modulus of elasticity (MPa)

= error function

= Faraday's nurnber = 96487 (Clequiv)

= acceleration due to gravity (mls2)

= mass flux in x direction per unit area (mol/m2s)

= coefficient of permeability ( d s )

= intrinsic permeability (m2)

= coefficient of gas permeability (m2)

= thickness of penetrated section (m)

= specified number of cycles at which the exposure is to be tenninated

= number of cycles at which P reaches the specified minimum value for discontinuing the test

= porosity of concrete

= pressure at which gas outflow is measured (Nlrn2)

= relative dynamic modulus at N cycles (%)

= pressure at entry of gas (N/m2)

= pressure at exit of gas @I/m2)

= flow rate (m3/s)


Nomenclature XII

= charge passed adjusted for standard size sample (C)

= measwd charge passed (C)

= density of water (kg/&)

= universal gas constant = 8.3 14 x 1 o - ~ WmoiK = coefficient of correlation

= time

= test temperature (K)

= velocity of electrolyte (rnls)

= increment of distance in x direction (m)

= ion valence (equiv/mol)

= viscosity (Ns/rn2)

= density (kg/m3)

= applied axial stress (MPa)

= ultimate stress (MPa)

Cracking due to Alkali-Silica Reaction and its Efféct on Durability Roperties of Concrete

Introduction 2

Concrete is a cornmonly used building material due to its excellent compressive

strength. However, it is very weak and unreliable in resisting tension. For this reason,

concrete has been used in conjunction with steel in structures. Apart from structural

purposes, steel is embedded in concrete because it is wlnerable to corrosion. Therefore,

concrete also serves as a protective banier to the steel in reinforced concrete structures.

Concrete is generally accepted by the public as a durable building material. Its

main constituents are cernent, aggregates and water. in order to make concrete

economical, as well as to reduce drying shrinkage, more aggregates are being added to

reduce the amount of cernent required to obtain the volume. Aggregates obtained fiom

different geological sites are composed of different mineralogical compounds. Some of

these compounds are reactive with the alkalis in cement and may cause adverse effects on

the intended durability behaviour of the concrete. One of the most commonly seen and

detrimental reactions of this type is the alkali-silica reaction (ASR). It was once

considered "concrete cancer" in the past as there was no cure of this reaction. The

reaction causes volurnetric expansion of concrete which may lead to inse~ceability of

structures and provide easy access for other deterioration processes to take place.

ASR can be eliminated by using low ailcali cement or non-reactive aggregates in

concrete. However it would not be econornically feasible to use aggregates fiom certain

non-reactive sources only. More problems arise realizing that many existing structures

were constructed with reactive aggregates and have undergone significant expansion.

Cracking due to Aikali-Silica Reaction and its Effect on Durability Properties of Concrete

Introduction 3

Expansion due to ASR can lower the strength and stifiess of concrete. In

reinforced concrete structures, damage found are usually not severe enough to pose

structural concems. Nevertheless, the damage can shorten the service life of a structure

and unexpected major repair is required to reinstate its intended service behaviour.

Figures I . 1 and 1.2 illustrate a bridge parapet damaged by ASR. While the structural

integrity of this structure may be adequate for the service, the durability can be impaired.

The structure is exposed to hi& concentrations of chloride fiom road de-icing salt as

vehicles pass by and splash contaminated water ont0 the surface. Moreover, it is also

subjected to wetting and Ming as well as fieezing and thawing cycles. Such a harsh

environrnent is favourable to the ingress of harmfùl agents through the concrete cover.

The cracks that exist in the concrete mass rnay intensiQ the problem. In this exarnple, the

concrete rnay not have failed as a structural component. However, it may not be

satisfactory as a protective bamer.

The objective of this thesis is to investigate the effects of ASR-induced

microcracks on the durability of concrete. Specifically, mass transfer properties and

fieeze-thaw resistance of non-air-entrained, ASR-damaged concrete have been assessed.

Cracking due to AlkalCSilica Reaction and its EfFect on Durability Properties of Concrete

Literature Review 6

2.1 Alkali-Aggregate Reactions

Alkali-aggregate reactions involve chernical interactions between the alkali

hydroxides in the pore solutions of the cement paste in concrete and the reactive

components in certain types of aggregates. The reactions take place in c w d concrete to

fom an alkali-silica gel or carbonate reaction products. In the presence of moisture, the

hydrophilic gel fonned will expand and place the surrounding cernent matrix in tension.

As a result, cracking and, in severe cases, differential movements in structures are

manifested. Furthemore, the cracks generated by the reactions "provide access to the

interior of the concrete and allow other deletenous mechanisms to operate" (Swamy,

1992).

Three types of Alkali-aggregate reactions have k e n identified (Swamy, 1992).

(a) Alkali-carbonate reaction (ACR) occurs between the alkalis in pore solutions

and certain types of argillaceous dolomitic limestones. Dark carbonate

reaction products fonn around the margin of the limestone aggregate particles

which cause expansion and extensive cracking of the concrete.

(b) Mi-silicate/silica reaction (ASSR) appears to occur in alkali-rich

environments with the presence of certain types of quartz-bearing aggregates.

The silicate mineral constituents in the aggregates appear to absorb water and

expand, causing disruption of the concrete.

Cracking due to Alkaii-Silica Reaction and its Efféct on Durability Properties of Concrete

Literature Review 7

(c) Alkaii-silica reaction (ASR) involves chernical interactions of the alkaline

pore solution in concrete with various foms of poorly crystalline reactive

silica contained in certain types of aggregates. It also causes expansion and

cracking in concrete but differs fiom ACR and ASSR by forming an alkali-

silica gel as a reaction product. Upon absorption of water, the gel expands and

cracks the swounding concrete fabric.

The third type of the reaction is more cornmonly observed and is the main theme

of this thesis. For this reason, it is described in more depth below.

2.1.1 Alkali-Silica Reactioa

Alkali-silica reaction is a series of deleterious chemicai reactions between the

reactive silica constituents of the aggregate and the alkalis in the smunding cernent

paste. In fact, it is the hydroxyl anions (OH7 associated with the alkali cations (Na* and

K') that initiate the attack on the siliceous minerais. The alkali-silica reaction product

foms subsequent to this attack. The microstructure of the aggregate-paste interface is

illustrated in Figure 2.1. The final reaction product is a hydrophilic gel. Ideally, the

reaction progresses as shown in the following equation was suggested by West (1996).

Yet unfominately, due to the widely variable and indefinite chemicai composition

of the alkali-silica gel, there is no exact chernistry identified for the formation of the gel.

The reaction can be visualized as a two-step process. The first step involves the formation


Literature Review 8

of the gel reaction product between the reactive silica and the alkalis in concrete. The

actual damage to concrete, however, is caused by the second step. in this step, the gel

reaction product absorbs water and swells. It is observed that this gel has a large affinity

for water imbibition. As it absorbs moisture, it increases in volume and tensile stresses

are generated within the concrete. It has been found experimentally by Diamond (1986)

that the gel can expand up to 80% and extend a swelling pressure in excess of I 1 MPa to

its surrounding. These pressures are intense enough to cause intemal rupture of the

microstructure of the concrete fabnc which weakens the strength and stifiess of the

concrete. In a macroscopic view, volumetric expansion of the concrete is the result. This

usually causes cracking, spalling and misalignment leading to possible inserviceability of

the structure. It also makes the afFected concrete more wlnerable to other detrimental

processes. "The effects of ASR can be very profound and severely detrimental to concrete

structures, affect ing strength, sti fbess, serviceability, safety, and stability" (Swamy,

1 992).

In order to sustain destructive ASR, the following factors are required:

(1) reactive silica in the aggregate

(2) alkali hydroxides in the pore solution

(3) sufficient moisture

The rate of ASR cm be suppressed if any of the principle factors can be

eliminated. Reactive silica and alkalis are the reactants required to sustain the production

of the alkali-silica gel. Without the input reactants, the output product shply cannot be

fonned. Water is what causes the alkali-silica gel to expand when imbibed by the gel.


Literature Review 9

Studies (Diamond, 198 1) have s h o w that the expansion due to ASR ceases when the

humidity of the intemal pores drops below a threshold limit of 80%. In new

constructions, low alkaii cernent, non-reactive aggregates and supplementary cementing

materials can be used to eliminate the risk of ASR. However the removai of silica and

alkalis in existing structures is obviously not feasible. If the intemal humidity of the

concrete can be reduced below the threshold limit, the expansion due to ASR ceases. This

can be achieved by using drainage in combination with suitable sealants in some concrete

structures. Such an approach may not be practical in some water-retaining structures such

as hydraulic dams. Like many other chernical reactions, the rate of ASR is temperature

dependent. At lower temperature levels the reaction rate tends to slow down.

Nevertheless, it is expensive or perhaps impossible to keep the intemal temperature of

concrete structures low in warm or hot climate. The alkalinity of the pore solution can be

reduced by injecting carbon dioxide (CO2). By lowering the pH of the pore solution, the

rate of ASR is slowed down due to the lowered alkalinity. Despite the positive effects of

carbon dioxide on ASR, its introduction can lead to a break down of the passive layer on

embedded steel reinforcement, thereby leading to corrosion.

It has been shown recently that lithium compounds are effective in mitigating the

expansion due to ASR (Blackwell et al, 1997). The compounds tested include lithium

fluonde (LiF), lithium carbonate (LilC03) and lithium hydroxide (LiOH). However,

insufficient quantities of lithium salts added to concrete containing reactive aggregates

will result in higher degree of expansion. Given s a c i e n t amount of lithium salts, the

reaction is altered and the final product is a lithium-bearing silicate. This lithium-bearing


Literature Review 1 O

gel is nonexpansive and therefore the detrimental effects are eliminated. The amount of

lithium required to eliminate the expansion due to ASR varies with alkali content and

type of reactive aggregates contained in the concrete.

THE ALKALI-SILICA REACTION IN CONCRETE

Figure 2.1.1: The microstructure of the aggregate-paste interface influences by the course of the alkali-silica reaciion. (Swamy, 1992)


Literature Review 11

2.2 Freezing and Thawing in Concrete

Freeze-thaw damage is a physical attack of the concrete due to the expansion of

the freezing of water. The chernical composition of concrete therefore has little, if any,

effect on the freeze-thaw resistance except at early ages when concrete is first exposed to

fieezing. An adequate strength is required for concrete to survive the fiost attack at early

age even when other protective measures have been taken. The susceptibility of concrete

to fieeze-thaw cycles is sensitive to the physical characteristics of the concrete.

Hardened concrete exposed to altemating fieezing and thawing temperatures cm

undergo severe deterioration. If the concrete is satmted and the temperature drops below

the fkezing point, water contained in the pore solution will fieeze and expand. In

saturated and non-air-entrained concrete, there is no room to accommodate the fieezing

water and thus hydraulic pressure builds up. As a result, the cernent paste matrix

surrounding the fiozen pore is put in tension and expansion takes place. This process is

repeated after thawing, re-saturation and re-fieezing. The cyclic fieezing and thawing has

an accumulative effect on building up the tension. If the tension becomes higher than the

tensile strength of the concrete, cracking results. The tensile force generated by the

expansion can cause intemal disintegration and surface scaling in concrete. Freeze-thaw

darnage can occur in concrete or in aggregates. This physical process could also be

initiated by the presence of frost-susceptible aggregates. To prevent fieeze-thaw damage,

an adequate entrained air-void system can be introduced in concrete. This is achieved by

mixing hydrophobie air-entraining agents with fiesh concrete to form tiny air bubbles in

the concrete matrix. These air bubbles provide suflicient room for fkezing water to

Cracking due to Alkali-Silica Reaction and its Efféct on Durability Properties of Concrete


migrate into, hence prevents hydraulic pressure fiom accurnulating. When the concrete

thaws, the hydrophobie air bubbles repels water back into the pores; the empty bubbles

are therefore ready for the next cycle of fieezing.

In concrete, the inter-co~ectivity of the capillary and gel pores is one of the most

important properties that affect the fieeze-thaw resistance. Better comectivity between

pores ensures the ease of rnuisportation of fieezing water to adjacent pores to release the

pressure and protect the concrete. However, better connectivity of pores implies more

permeable concrete which in turn reduces the durability of concrete because there is less

resistance to the ingress of harmful agents. In frost susceptible aggregates, small pores

and water-saturated pores are present. The deficiency in the escape of fieezing water to

the adjacent pores is once again the cause of the damage.

In ASR-damaged concrete, microcracks filled with silica gel are spread

throughout the microstmcture of the concrete. Due to the hydrophilic nature of the gel, a

respectively large amount of water (compared to the amount of water presence in pore

solution) tends to reside in and amund the vicinity of the gel. This could have an adverse

effect on fieeze-thaw resistance of the concrete. Under fieezing, a respectively much

larger amount of expanding water is now competing to migrate into the nearby air

bubbles to relieve the pressure build-up. Nevertheless, the volume of the air bubbles does

not supply enough room for the larger amount of water to move into. Moreover, fieezlng

water accumulates in the cracks cm widen the cracks M e r as it expands. This can

cause dismption and disintegration of the concrete. In such a case, air entrainment might


not provide sufficient fiost protection for the af5ected concrete and the service life of the

concrete could be drastically shortened.

Thomas (1997) had fond no significant difference in the resistance to fieezing

and thawing in concrete infected by AAR, as assessed by changes in pulse velocity.

However, the cracks were observed to widen for the specimens that had expanded

0.104% during the test.

Triiganlh and Lagerblad (1996) had performed fieeze-thaw test on air-entrained

concrete damaged by ASR. The results indicate that the level of water saturation is higher

in ASR-affiected concrete than in uncracked concrete (ie. it is easier for ASR-damaged

concrete to reach the critical degree of water saturation). Consequently, the fieeze-thaw

resistance of the infected concrete was significantly reduced compared to its uncracked

counterparts.

Bolton and Wang (1992) had found that the rate of fieeze-thaw damage in

concrete with higher level of expansion was greater than the ones with lower expansion.

Both research papers indicate that the cracks caused by AAR or ASR expanded M e r

due to the effect of cyclic fieezing and thawing.

2.3 Mass Transfer Mechanisms in Concrete

Many concrete structures have failed to meet their expected service lives. The

unexpected poor performance is attributed by the harsh environment in which the

concrete is exposed to or by intemal activities which may occur within the concrete itself.

Extemal causes are due to weathering (eg. min, wind, tidal erosion), abrasion (eg. heavy



M c on pavement) and extreme temperatures (eg. fkezing and thawing). An exarnple of

intemal causes is AAR. in addition, combinations of extemal and intemal activities are

more ofien found in the field. Such activities include sulfate attack, carbonation and

chloride contamination which lead to corrosion of reinforcement. In any case, the

deterioration of concrete is seldom the result of a single isolated cause. In most of the

incidents, the darnage is initiated by the transport of hamiful species fiom an extemal

source to the interior of the concrete; which in tum triggers the deterioration processes to

take place.

Concrete is used as a structural material; at the same time, it acts as a bmier to

harmfùl organic and inorganic liquids to protect the reinforcement and the concrete itself

fiom being darnaged prematurely. In a concrete structure, the durability is solely

detennined by the vulnerability of the concrete components (Neville, 1995). The

vulnerability of concrete to harmfbl agents is largely dependent on its ability to resist the

ingress of hamifil species (eg. water, Cl', SQ), which in tum is controlled by its pore

structure. The mass transfer properties of concrete are in a complex relationship with the

water-cernent ratio (which determines the porosity), degree of hydration, moisture

content, an the size, distribution and inter-connectivity of the pores (Hearn, 1994). The

pores in a concrete matnx consist of gel pores and capillary pores. Gel pores are relatively

small and contribute little to mass transport processes. Capillary pores are much larger in

cornparison and are responsible in providing passageways to the ingress of harmfui

substances into the concrete. The inter-connectivity of the pores magnifies the effect of

mass traasportability.

Cracking due to Aikali-Silica Reaction and its Effcet on ~urability Properties of ~oncrete


The mass transport properties are influenced mainly by the water-cernent ratio

since it defines the initial porosity and limits the arnount of cernent that is available for

hydration. The higher the water-cernent ratio, the greater the mass transportability that is

achieved. Smaller pores have higher resistance to mass transfer through the pore system.

An even distribution of pores is attained in a homogeneous mix. When pores are evenly

distributed through the cernent paste, the pore structure is more likely to be

discontinuous. The continuity of pores is reduced as the hydration of cementitious

matenal progresses. An inter-connected pore system provides flow channels for fluids. In

contrast, as concrete matures and more hydration products are formed, the flow channels

are effectively blocked. Additionally, transportability is al20 influenced by the cernent

grain size (Neville, 1995). Coarse cernent forms a high porosity paste and hence high

mass transfer is expected. This is due to the small available surface are* per unit mass of

cernent, for the reactions to occur. The opposite is tnie for fine-grained cernent.

Other potential passages may be developed in the form of microcracks. These fine

cracks can be developed in the mortar and at the paste-aggregate interface as a result of a

combination of shrinkage, loading and other chernical reactions (e.g. sulfate attack and

AAR)*

2.3.1 Permeation

Permeation is defined as the flow of fluids (liquids or gases) through the pore

structure of a medium, driven by a pressure head. The flow may be laminar or turbulent

depending on the pore structure and the viscosity of the fluid.



2.3.1.1 Water Permeability

Water is the most important fluid among liquids penetrating through concrete. It is

most commonly found in the field. It can cany harmW agents into structures when

penetrating through the concrete causing shortened serviceability (e.g. road de-icing salt

cmied by melted snow on a bridge deck). Water permeability is measured by the rate of

ingress of water under hydraulic pressure. High water-penneable concrete tends to more

prone to intemal chemical and physical damages such as corrosion of steel reinforcement

and scaling and cracking due to fieeze-thaw cycles. The permeability of water into

concrete under Iarninar flow is expressed by the coefficient of water permeability, K in

mk, and is govemed by Darcy's Law (Kropp et al, 1995), which may be written as:

where K = coefficient of permeability (rn/s) Q = flow rate (m3/s) L = thickness of penetrated section (m) A = penetrated area (m2) Ah = pressure head (m)

2.3.1.2 Gas Pemeability

Unlike water, gas is compressible, therefore the compressibility as well as the

viscosity must be taken into account in gas permeability. For laminar flow of gas through

concrete, the coefficient of gas permeability is denved fiom the following equation

(Kropp et al, 1995).

- -

Cracking due to Alkali-Silica ~eactionand its Effect on Durability Roperties of Concrete


where Kg It Q L A P Pl p2

= coefficient of gas penneability (m2) = viscosity of gas (Ns/m2) = gas fiow rate (m3/s) = thickness of penetrated section (m) = penetrated area (m2) = pressure at which gas outflow is rneasured (Nlm2) = pressure at entry of gas m/m2) = pressure at exit of gas (N/m2)

2 3 Diffusion

Diffision is defined as the mass transfer by random movement of fiee molecules

or ions in the pore solution driven by a concentration gradient. The net transfer of

substance is fiom regions of high concentration to low concentration. The ability of

concrete to the transfer for a given substance is characterized by the difision coefficient,

D in m2/s. The determination of D is govemed by Fick's laws of diffision. For steady-

state difision, Fick's first law states that the rate (flux) of transfer of mass is proportional

to the concentration gradient.

where J = mass flux in x direction per unit area (moI/m2s) D = diffusion coefficient (m2/s) c = concentration of diffusing substance (moI/m3) x = increment of distance in x direction (m)

For transient diffision processes, Fick's second law of diffision describes the

change in concentration per unit volume with t h e as follows:



When the boundary condition, c = c, for x = O, t > O and the initial condition c = O

for x > O, t = O are specified, a solution to Equation 2.3.1 (Kropp et al, 1995) is given by:

where c, = chloride concentration at time t and depth x (mol/m3) CS = chloride concentration at the surface (mol/m3) .Y = depth fiom surface (mm) D = diffusion coefficient (m2/s) t = time erf = error function

The error function cm be easily programmed and calculated with the help of a

math package or a spreadsheet. If an array of data of c vs. x at time t is known, then D can

be detemined fiom Equution 2.3.5 with the help of a cornputer.

233 Migration

Migration is the transfer of ions in electrolyte due to a driving force provided by a

electrical potential gradient. Positively charged ions are attracted to the cathode and the

negative ions are attracted to the anode. The migration of ions can generate a

concentration gradient in a homogeneous solution and may provoke ionic diffision in the

direction of the concentration gradient. The mass transfer in electrolyte is govemed by the

Nernst-Plank equation (Kropp et al, 1995). Which in essence States that the movement of

charged species in an electrolyte is the sum of the diffusion, migration and convection.

Cracking due to Alkali-Silica Reaction and its EtTect on Durabiiity Propenies of Concrete


where D = diffusion coefficient (m2/s) J = steady state flux (mol/m2s) R = universal gas constant = 8.3 14 x IO--' k.i/molK T = test temperature (K) z = ion valence (equiv/mol) F = Faraday's number = 96487 (C/equiv) AV = potential &op across the sample (V) x = distance (m) Ve = velocity of electrolyte (rn/s) c = bulk concentration (mol/m3)

Assurning steady-state flow of ions and ignoring the diffision component

(assuming it is comparatively small), there exist a solution to Equation 2.3.6. Which may

be written in the following form and thus used to determine the diffision coefficient from

electrical migration tests (McGrath, 1996).

JRTL D=- zFA Vc

2.3.4 Rapid Chloride Penetrability Test (RCPT, ASTM C1202)

The RCPT is a widely used test to determine concrete quality to resist chloride

penetration. The most significant advantage of this test is that it is simple to carry out and

can yield results in a very short time (total test time is 6 hours). The result is an indirect

indication of the resistance of concrete to the penetration of chloride ions. The actual

measurement is the total charge passed through the sample in a given tirne. The

movement of the charged species is dnven by a 60 V potential for 6 hours. The high

voltage used creates a shortcoming for this test method. The total charge passed is



affected by the conductivity of the concrete. Which is govemed by the degree of

saturation of the pores and the composition of the pore solution (Pm, 1997). The total

charge passed is not necessary a true indication of the resistance to chloride penetration.

2.4 Effect of Microcracks on Mass Transfer

The existence of microcracks can have a profound impact on mass transfer.

Microcracks can be rnicroscopic in width, but that alone may not increase the mass

transportability of concrete significantly. However, if the microcracks are inter-comected

they can be expected to have a significant impact on the rate of mass transfer and play a

major role in providing access passages into the concrete matrix. Figure 2.41 (Thomas,

1997) illustrates the development of cracking due to AAR with different degrees of

expansion. In Case (a), when the concrete is undarnaged, the mass transfer properties are

controlled rnainly by the pore size, distribution and inter-connectivity. At the early stage

of damage due to AAR, cracks begin to develop around the pores as show in Figure

2.4.1fi). Due to the lack of connectivity between the cracks, there would not be any

significant contribution to mass transfer. However, cracking in the microstructure would

resdt in reduced stiflhess and strength of the concrete (Thomas, 1997). At high levels of

expansion, extensive microcracks are formed as shown in Figure 2.4.l(c), and inter-

connectivity between cracks is established. Consequently, flow channels are created for

mass transfer to take place with little effort.

The effect of load-induced microcracks on mass transfer had been investigated by

a number of researchers (Samaha and Hover, 1992; Lok, 1997). In general, it was found

Cracking due to AMi-Silica Reaction and its Effect on Durability Properties of Concrete

Literaîure Review 2 1

that over a threshold limit, microcracks have some positive effects on water and gas

permeability, RCPT and chlonde migration.

Samaha and Hover (1992) rnechanically induced microcracks into concrete

samples and then tested them in RCPT, water absorption and hollow cylinder test (which

measures the ease of water movement through concrete by the combined effect of

absorption, vapour transmission and wicking). In summary, the researchers concluded

that "the severity of mortar cracking appeared to determine the extend of the concrete's

resistance to water flow and m a s transport" (Samaha and Hover, 1992). A higher water

absorption rate was detected as the extemal loading increased (ie. increased extent of

microcracking, thus total porosity).

(a) Undamaged Low iransportability

(b) Low expansion Low transportability

(c) High expansion H igh transportability

Figure 2.4.1: Development of cracking due to AAR (Thomas, 199 7)

Cracking due to Alkali-Silica Reaction and its Effect on Durability Froperties o f Concrete

Literahue Review 22

Lok (1997) had developed a test method to measure gas permeability while

increasing the uniaxial load on mortar cylinders simultaneously. It was discovered that

load-induced microcracks will not increase gas permeability until inter-connectivity

between cracks is established. The threshold at which inter-connectivity is assumed (by

sudden increase in gas permeability) was when an axial stress applied to the specimen is

greater than approximately 0.83 times that of the ultimate stress (ie. when a, > 0.83 a,~,).

Above this threshold stress, gas permeability increases with the increase in axial load and

the associated increase in microcracking.

Limited research had been done on the effect of microcracks due to AAR on the

durability of concrete. In perfonning laboratory tests on samples removed fiom AAR-

damaged structures, Raphaël et al (1 989) observed that AAR did not cause any significant

increase in water permeability and mechanical properties of concrete unless the

deterioration is well advanced. Thomas (1997) had found similar results in permeability

and stated that it is not affected adversely when the expansion is below 0.10%. However,

mechanical response can be affected even at low levels of expansion.

Concrete cores with different levels of expansion fiom existing structures were

tested by Raphaël et al (1989). In particular, water pemeability, microstructure and

mechanical strengths were studied. Despite the evidence of localized AAR, the concrete

samples were generally in good condition. It was concluded that increased water

permeability and reduction in strength do not necessarily accompany increased expansion

due to AAR unless the damage is extensive.

Cracking due to Alkali-Silica Redon and its Effect on Durability Properties of Concrete


Thomas (1997) reported results fiom tests on AAR-infected samples with

different degrees of damage. Specifically, these samples were tested in compression and

evaluated by RCPT, gas permeability and cyclic fieeze-thaw test. The extent of the

damage was assigned to 3 categories (as shown in Figure 2.4.1):

(a) undarnaged

(b) low expansion (0.04% to 0.06%)

(c) high expansion (> 0.1 0%)

For sarnples which fa11 into Cutegory (a), mechanical and durability properties

were not afTected by AAR because there is no damage. At low levels of expansion (b),

due to the lack of inter-connectivity between cracks, mass transfer is not influenced; yet

stifhess and strength are reduced due to the increase in total porosity caused by the

cracks. Finally, specimens with expansion above 0.10% (c), both mechanical and

transport properties are afTected adversely due to the inter-connectivity of crack and

pores,

Hamada et al (1989) studied the durability of AAR-damaged concrete under

marine environrnents. Three series of samples containing reinforced concrete beams,

prestressed concrete beams and theù control cylinders have been exposed at ports at 3

different locations for 10 years. M e r the exposure period, samples at one port were found

damaged only by chloride attack; sarnples fiom another port were suffered from AAR as

well as chloride attack; at the last port, laumontite related reaction and chloride attack

were found to be the contribuhg factor to the damage of the samples. The strength and

stiffhess of the AAR-damaged samples were very low compared to other samples. Yet the



ultimate load carrying capacity of the beams were not afTected significantly. Chloride

contents in the AAR-darnaged specimens were much higher, and consequently heavier

corrosion, than those damaged only by chloride attack. Finally, only the concrete

damaged by AAR was found susceptible to sulfate attack in marine environrnents.

2.4.1 Hypothesis of Gel Obstruction in Microcracks

Unlike microcracks caused by loading, microcracks generated by ASR result fiom

the production of an alkali-silica gel. It is expected that the cracks are filled or partially

filled with the gel in ASR-damaged concrete. As suggested by some researchers (Hobbs,

1988; Swamy, 1992), the gel is usually very viscous and in the microcracks of afTected

concrete, the gel can be considered non-flowable. The expansive gel puts the surrounding

cernent paste matrix in tension. As a reaction force, the cernent matrix confines and

compresses the gel inside the pores. Even with the presence of microcracks, there is

aiways some confinement to the gel. Simply stated, the pores and the microcracks inside

the infected concrete are filled with gel under a pressure slightly less than that of the

tensile strength of the concrete. If the pressure becomes higher than the tensile strength of

the concrete, it will rupture and more microcracks are formed. Once cracks are fomied,

there is now more space for the gel to expand into and the pressure is relieved. If the

environment favours and there are enough reactants to fhrther sustain ASR, more gel will

be produced and the pressure is built up again. This process repeats until the condition is

unfavourable to ASR or the expansion of the gel. The blockage of the pores and

microcracks could partially immobilize the traasport abilities of the concrete.

Cracking due to AU&-~ilica R e d o n and its Effect on hvability Roperties of Concrete


Katayarna and Bragg (1 996) carried out petrographic analysis on concrete samples

removed fiom 50 to 70 year-old structures. The samples are damaged severely by alkali-

silica reaction combined with fieeze/thaw attack. In the deteriorated concrete specimens,

some C-S-H gels in the cernent paste were found to be replaced by ASR gels in a fom of

large veins. Abundant amount of gel was also identified in the following areas:

(1) large cracks in the cernent paste

(2) cracks of the reacted aggregates

(3) air voids in the cement paste

(4) reaction zones at the paste-aggregate interface

ASR gel has the ability to migrate and react chemically with the C-S-H gel in

vimüilly everywhere within the concrete m a s . Despite microcracks induced by ASR, the

net effect of crack widening and gel filling could reduce the intensity of the detrimental

effects on concrete durability. Due to the hydrophilic nature of the gel in microcracks, its

presence may mitigate the mass transportability of concrete.


3.1 Concrete Specimens

Two types of concrete samples, concrete cylinders and pnsms, were used for

testing. The cylinders were cast in-house at the University of Toronto and were 100 mm

in diameter and 200 mm in height. The concrete pnsms, having dimensions of 75 mm x

75 mm in cross-section and 400 mm in length, were generally 1 1 years old and were

supplied by the Ministry of Transportation of Ontario (MTO). The samples tested

contained a variety of aggregates ranging fiom non-reactive Nelson aggregate to reactive

aggregates such as Sudbury, Spratt and Pittsburgh, the latter being alkali-carbonate

reactive. Most samples tested were chosen to have similar water-cernent ratio (wk),

ranging fiorn 0.40 to 0.44, for comparative reason. A few samples having w/c fiom 0.50

to 0.54 were also used.

Eighteen concrete cylinders (SPRT/Ol to SPRTI18) and 3 concrete prisms

(SPRTPI TO SPRTlP3) with stainless steel inserts for length rneasurements were cast

fiom a 50 L batch of concrete having rnix proportions as shown in Tuble 3.1.1. The

samples were de-moulded at 24 hours of age. With the initial gage length recorded prior

to casting, the prisms were used to monitor the expansion due to alkali-silica reaction. To

accelerate the rate of ASR to achieve significant expansion for testing during the course

of the experiment, the samples were stored at 100% relative hurnidity (rh) and 38 O C

initially. As the experiment progressed and the rate of expansion began to cease, the

samples were stored at 60 OC and in 1 mol.& NaOH solution to boost the rate of


Exrierimental P r o m 28

expansion. At 6 different levels of expansion due to ASR (0.023% to 0.304%), a total of

12 cylinders were removed from storage and a senes of tests were conducted. Two

sarnples were used at each level of expansion to perfonn the following tests: Rapid

Chloide Penetration Test (RCPT), Water Permeability, Gas Permeability and Chloride

Migration.

Alkali OPC, 0.81% alkali content) Spratt Aggregate - 20 mm - 10 mm Sand (non-reactive) Water NaOH Na20, (by mass of cernent) w/c

Component Cernent (St Lawrence Tl0 High

Table 3.1. /: Concrete mrjc proporrions

Arnount [kp/rn3] 420

At each level of expansion selected for testing, the cylinders (2 cylinders each

time) were removed from the storage container and approximately 15 mm of the top and

bottom faces of the cylinders were cut and discarded to eliminate any end effects. The

rernaining sarnples were cut into three samples of 50 mm thick per cylinder and labelled

SPRT/##T, SPRT/##M and SPRT/##B which denoted the top, middle and bottom portion

of the cylinder, respectively. The top slice of the cylinder was used for RCPT, the middle

section was used in testing of water and gas penneability and the bottom part was tested

for chloride migration.


Fourteen prisms, with expansion from 0.041% to 0.592% and w/c ratio fiom 0.40

to 0.53, were tested for rapid fieeze-thaw resistance. Twenty-five other pnsms, with

expansion fiom 0.040% to 0.205% and w/c ratio fiom 0.40 to 0.54, were used in testing

of RCPT, water permeability, gas penneability, chioride migration and chlotide bulk

diffision. Al1 the prisms had k e n stored in different environments and had reached

terminal level of expansion. Storage conditions in which the prisms were cured can be

found in Table 3.1.2. A swnmary of the testing program is also tabulated in the table.

With the exception of prisms tested for fkeze-thaw resistance, one end of each

M T 0 prism was cut and discarded and a sarnple of 50 mm thick was cut and prepared for

chloride bulk diffision test (Section 3.9). A layer of impervious epoxy resin mortar was

then cast around the perimeter of the remaining portion of the prism using steel or

alurninum cylindrical mold having inside diameter of 125 mm with the prism located at

the centre. Afier curing of 24 hom, each prism was cut into 3 samples with thickness of

50 mm for other tests. Figure 3.1.1 illustrates the details of the sarnple preparation.

3.2 Expansion Measurement

The expansion level of the lab-cast samples were monitored on the prisms

(SPRT/Pl to SPRTP3) by comparative measurements. This test was conducted

according to ASTM C1293. The length of the prisms was measured and compared to an

invar bar having a known reference length. It was assumed that the expansion that

occurred in the cylinders was equai to that measured on the prisms as they were cast fiom

the same mix batch and were exposed to the same conditions. Initially, the measwments


Table 3.1.2: Sunimary of Tesring Program

were taken every 4 weeks. Later during the test, the measurement interval was adjusted

accordingly to suit the rate of expansion. Prior to the comparative measurements, al1 the

samples (prisms as well as cylinders) were removed fiom the oven and allowed to cool to

room temperature for 24 hours. This step was canied out to eliminate any unwanted

effects of thermal expansion.

One end of the prism was cut and discarded to remove the metal stud and to avoid end effects. A 50 mm slice was then cut and used in bulk diffusion test.

Concirie prism

A layer of impervious epoxy resin mortar was cast around the perimeter of the remaining portion of the prism.

Three 50 mm-thick slices were then cut fiom the resulting sample.

Figure 3. I . 1 : Details of preparaîion for prhm samples


3.3 Sample Vacuum Saturation

in a number of tests, the samples were satwated with water by vacuum saturation

prior to testing. The procedures are described briefly in this section. Two plastic

desiccators in which one contained the samples to be saturated and the other contained

tap water were connected to a vacuum pump. The air in the desiccaton, hence in the

samples and water, was evacuated for at least 4 hours. The vacuum in the desiccator

which contained the de-aired water was released, One end of a vacuum hose was then

connected to the valve of the desiccator which contained the samples and the other end

was submerged into the de-aired water. The valve was opened and the de-aired water was

forced into the sample desiccator by atmospheric pressure until al1 the sarnples were

submerged under the de-aired water. M e r that, the sample desiccator was again

connected to the vacuum pump for air evacuation for 1 to 2 hours. Afterwards, the valve

was opened to allow air into the desiccator for about 18 * 1 hours. During this time period, de-aired water was forced into the vacuumed pores of the concrete sarnples by

atmospheric pressure.

3.4 Ftapid Freae-Tbaw Test

Fourteen MT0 prisms (non-air-entrained) with various levels of expansion were

chosen for the testing of fieeze-thaw resistance. This test was based on Procedure A of

ASTM C666. The dimensions of the samples were carefully measwd and recorded.

Given the storage condition of 100% rh for 1 1 years (i.e. in a fog room), the sarnples were

assumed Mly saturated with water prior to the first cycle of fieezing. They were placed

into special stainiess steel containers and submerged in water with the water level

Cracking due to Alkali-Silica Reaction and its Effect on Duability Properties of Concrete

approximately 2 mm above the top of the pnsms. The containers were then placed into a

freeze-thaw charnber capable of generating 5 to 6 freeze-thaw cycles per day. The

temperature in the chamber was altemated fiom approximately -1 8 "C to +5 O C for each

cycle. At the beginning of the test, measurements were taken at every 5 cycles. At the

later stage of the test, measurements were performed at approximately 10-cycle intervals

due to the unexpected durability of the samples. The fieeze-thaw charnber was switched

off at the end of the thawing cycle (i.e. +5 O C ) for measurements. The samples were

removed fiom the containers and any spailed debris was rinsed off. The natural fiequency

of longitudinal vibration, the time required for ultrasonic pulse to travel through the

prisms and the mass were measured and recorded. These properties were also measwd

before the start of this test. ASTM C2lS was followed closely for the measurement of

natural longitudinal fiequency and for the calculation of dynamic modulus of elasticity.

The ultrasonic pulse velocities through the concrete were also calculated. The relative

dynamic modulus of elasticity, ultrasonic pulse velocity and mass were plotted versus

number of fieeze-thaw cycles. The durability factor for each tested sample was then

caiculated according to Section 9 of ASTM C666 and plotted versus expansion level.

3.5 Water Permeability Test

Twelve cylinders and 16 MT0 pnsms were tested for water permeability. The

dimensions of the sarnples were measured and recorded. The samples were then fully

saturated in water prior to testing, as described in Section 3.3. The room-temperature

vulcanized (RTV) rubber rings used in the permeability ce11 were also vacuum saturated

with water before use. For the testing of cylinder sarnples, the inside R W rubber ring

Cracking due to Alkali-Silica Reaction and its Eff'ct on Durability Properties of Concrete

having inside diameter of 100 mm was used whereas an RTV rubber ring having inside

diameter of 125 mm was used for prism samples coated with epoxy resin mortar. A

diagrammatic ovewiew of the test equipment set-up can be found in Figure 3.5.1. The

saturated RTV rubber rings were first seated in place in the cell. The test sarnple was

removed fiom the desiccator and the surface was dried with paper towers. It was then

inserted into the ce11 with the top facing upward (Le. infîow side). AAer that the ce11 was

covered with the top cover plate. The top cover plate was secured in place by fastening a

threaded stud with a half metre long lever. The RTV rubber rings were in tum squeezed

by this force to seal the ce11 fiom leakage as well as to provide the necessary confining

pressure (provided by high Poisson's ratio of the rubber) so that water would not by-pass

the sarnple by leaking through the sample-rubber ring interface. Then, the trapped air

inside the test ce11 and the tubing was removed by vacuum. The vacuum pump was

comected to the system for at les t 15 minutes to ensure complete evacuation of the air.

After this step, the vacuumed space inside the test ce11 and tubing were filled with de-

aired water previously prepared and stored in a steel cylinder under pressure. The pressure

was provided by a pressurized tank of nitrogen gas. Nitrogen gas was used here for

convenience and to provide the àriving pressure only. Other types of gas can also be used

because there is no interaction between the gas and the sample. Once the system was

filled with water, the outfiow was routed to a calibrated glass capillary tube having inside

diameter of 1 mm. The system was then allowed to reach steady flow. This usually took

10 to 30 minutes. M e r the system was in steady flow, the initial water level in the

capillary tube, water temperature and the t h e were recorded. The same data were

recorded 2 to 4 times d u ~ g the course of the test which usually lasted 1 to 2 days. The

Cracking due to Alkali-Silica Reaction and its Effect on DurabiIity Properties of Concrete

outflow water volume was plotted versus time and the rnean slope was calculated and

taken as the flow rate through the sarnple. The permeability coefficient, K in mis, was

then calculated using Equation 2.3.2. The pemieability coefficient was plotted against

expansion level. The test procedures were repeated for al1 the samples tested in this

section.

" Pi-cssiii*izcd - De-airecl w a t e r

P ~ C S S I I I Y inflow watci.

C'el1 w a l l

O u t side RTY ri.ihbci. ring

Inside RTI' iaiibber ring

Botlorn covei. p l a t e

I \Vat er ou t f l o w to capillaru tube

Figure 3.5.1: Sketch of water permeability ce11

Cracking due to Alkali-Silica Reaction and its Effect on hirability Properties of Concrete

3.6 Gas Permeabiüty Test

The same pieces of samples used in water permeability test were re-used in the

test. To prepare the samples for this test, the samples were placed in a 50 OC vacuum oven

with silica gel until the change of weight of the sarnples is less than approximately 0.1%

per day. On average, 6 to 10 weeks were required for the samples to reach the

aforementioned degree of dryness for this test. A test ce11 similar to the one used in water

permeability test with different measuring attachments was used in this test. A sketch of

the gas pemeability test ce11 is shown in Figure 3.6.1. The dry RTV rubber rings, the test

sample and the top cover plate of the test ce11 were put in place in the sarne manner as

mentioned in the water pemeability test. Instead of a threaded stud, the gas penneability

ce11 was secured by a hydraulic jack to provide the extra sealing pressure required. A

much larger force was required to "seal" the sample for the testing of gas pemeability.

AAet the test ce11 was prepared, nitrogen gas under a pressure of about 346 kPa

(converted form actual measurement of 50 psi) was applied to the inflow side of the

sample. The outflow of gas was measured using a bubble flow meter with a volume of

100 mL. A bubble of soapy water was intmduced into the tube. The time required for the

bubble to travel fiom the zero mark to the 100 mL mark was recorded. The test was

repeated 4 times per sample for al1 the samples in this test. The recorded data fiom the

first time of each sample was discarded as it generally took longer for 100 rnL of Nt gas

to pass through the sample due to the time delay for the system to reach equilibriurn. The

remaining data was averaged and used in the calculation of coefficient of gas

pemeability, Kg in m2 using Equation 2.3.2. Finally, the calculated results were plotted

against the expansion levels.


C ' d l wal1

Ou tsicle RTY 1.u t ~ b e

Iiisicie RT\' riibbci .

c;iic; ollt flow t o glass t i i b c

- -

Figure 3.6.2: Sketch of gus permeabili~ cell

3.7 Rapid Chloride Peaetration Test

This test closely resembled the test method described in ASTM C1202. Samples

fiom al1 of the cylinders and MT0 prisms (except for the prisms tested destructively in

fieeze-thaw resistance) were used in RCPT. The dimensions of al1 the samples were

measured and recorded pnor the test. To prepare for the test, the 50 mm-thick disc

samples cut from cylinders were allowed to surface-dry in air to ensure proper bonding of

the grey epoxy. Afier the sudace of the samples were dry to touch, the top and bottom

faces were covered by masking tape to prevent any blockage of the test surfaces

accidentally. Aftenvards, a thin layer of grey epoxy (about 2 to 3 mm) was applied to the

Cracking due to Aikali-Silica Reaction and its E f f a on Durability Properties of Concrete

curved surface of each cylinder sample. The epoxy was allowed to harden partially for

about 1 hour to facilitate the removal of the masking tape. With the tape removed, the

epoxy was allowed an additional 5 to 6 hours in air to complete the hardening process. An

impervious layer of epoxy resin mortar was already cast around the perimeter of the prism

samples and therefore grey epoxy was not needed for these samples. m e r the epoxy was

fully hardened, the samples were vacuum sahinited with water using the technique

described in Section 3.3. For each sample (maximum of 4 for each run), the top face was

inserted into the recess of the anode cell. The gap between the ce11 and the concrete

sarnple was sealed with silicone caulking. The bottom of the sample was inserted into the

recess of the cathode ce11 and the gap sealed with caulking. The assembled cells were then

placed aside and the caulking was allowed to set for about 30 minutes. AAer the caulking

was set, the anode ce11 was filled with 3.0% by mass of sodium chloride solution and the

cathode ce11 was filled with 0.3 N sodium hydroxide solution. The completed cells were

then checked carefully for leakage before k ing c o ~ e c t e d to the RCPT device. The

anode ce11 was connected to the negative terminal of the device while the cathode ce11

was connected to the positive terminal for each sample tested. Once the connections were

checked, the test was started by applying a potential difference of 60 V DC across of the

specimens for 6 hours. At every 30 minutes, the cumulative charge passed (in coulombs)

through each specimen was recorded automatically by the RCPT machine. During the

duration of the 6-hour test period, the temperature in each test ce11 was monitored

regularly in order to avoid boiling of the solution and damage to the cell. If the

temperature of the solution inside any ce11 exceed 85 O C , the applied voltage for that

particular specimen would be switched off to terminate testing of the correspondhg

Cracking due to Alkali-Silica Reaction and its Effect on ûurability Properties of Concrete

specimen. None of the samples tested in this section exhibited over-heating problem and

a 6-hoü; test period was completed for each sample. The final results were adjusted for

sarnple size variation and plotted against expansion level.

A set of 4 slightly modified RCPT cells were prepared for testing of the prism

samples. These cells were modified by enlarging the messes to accept 125 mm diameter

samples instead of 100 mm standard size samples. With the exception of not using grey

epoxy in these samples, al1 other testing procedws were unchanged.

3.8 Chloride Migration Test

Samples from 12 cylinders and 16 MT0 prisms were tested using this method.

The labçast samples were coated with a 10 mm thick annulus of epoxy resin mortar

around the circumference. The M T 0 samples were previously cast with the same epoxy.

Prior to testing, the samples were vacuum saturated as described in Section 3.3. The

chloride migration test apparatus illustrated in Figure 3.8.1 was developed at the

University of Toronto (McGrath, 1996). The test cells were washed and rinsed thoroughly

with distilled water, with particular attention paid to the anode chamber since the test

results are highly sensitive to chloride contamination. The samples were also washed

thoroughly in distilled water and initial mess and dimensions were measured. The

samples and the cells were then assembled as show in Figure 3.8.1. The cathode

chamber was filled with approximately 1.5 L of electrolyte which contains 0.5 mol/L

NaCl and 0.3 moVL NaOH; the anode chamber was filled with a carefiilly measured

volume (required for the analysis) of electrolyte containhg 0.3 m o n NaOH. The


Exwrimental Proesam 40

completed cells were then connected in parallel to a common power supply at the desired

voltage. The voltage output of the power supply was set 2.3 V in excess of the desired

driving potential to compensate for the potential &op across the electrodes as suggested

by McGrath (1996). Some samples were tested at 12 V when the test was first conducted.

It was discovered later that the samples had a fairly high resistance to chlonde ion

migration. The test voltage was therefore increased to 20 V for the second group of

samples to reduce the test duration.

A number of sarnple solutions were collected fkom the anode chamber of each test

ce11 during the test. A calibrated automatic pipettor was used to collect 10 mL aliquots.

The potential difference across the 2 R resistor and the date and time of the coilection

were recorded. The samples were stored in 20 mL plastic vials for later analysis. Each

time when a 10 mL sample was removed fiom the anode chamber, 10 rnL of 0.3 moln

NaOH was replaced to keep the electrolyte volume constant. More fiequent sampling was

done at the beginning of the test to estirnate chloride breakthrough time more accurately.

Chloride breakthrough was determined by titration of 1 mL of collected sarnple. If the

concentration of the sample was above 25 ppm of chloride, breakthrough was assurned.

AAer chloride breakthrough, samples were collected less fiequently to minimized

disturbance to steady state flux. When a concentration of 2500 ppm was reached, the test

was terminated to prevent corrosion of the stainless steel mesh. The potential difference

across the specimen was measured by a double junction AdAgCl electrode placed inside

a Luggin capillary tube, see Figure 3.8.2. The tip of the Luggin capillary tube was placed

as close to the specimen surfàce as possible (2 to 3 mm) for accuracy.

Cracking due to Alcali-Silica Reaction and its Effect on Durability Properties of Concrete

3 16 Stainless steel wire mesh electrode 7

End

Cast rubber gasket Concrete Anode chamber gasket sample (0.3 moüL NaOH)

Cathode chamber (0.5 moVL NaCl and (0.1 0.3 moVL NaOH)

Figure 3.8.1 : Chloride migrotion test apparatus

AgiAgCl reference electrode

Filled with cathodic or anodic electrolyte

Glass Luggin capillary tube

Figure 3.8.2: Glas Luggin capillary and reference electrode used to accurate& set voltage &op across the samples

plate

Cracking due to Alkali-Silica Reaction and its Effect on Durability Roperties of Concrete

At the end of the test, the collected samples fiom each specimen were analyzed by

potentiometnc titration of chloride with silver nitrate using a Metrohm DMS 760

automatic titrator. The chlonde concentration was measured by the tiûator by

automatically dispensing a titrant with 0.01 molL AgNOl into the solution to be

analyzed. The entire 10 mL of the low chloride concentration samples collected before

and shortly after breakthrough was used in the titration process. The sample was poured

into a 100 mL beaker and the remaining solution in the vial was rinse several times with

distilled water to transfer al1 the sample into the beaker. A drop of methyl orange

indicator was added to the sample solution. Then concentrated nitric acid was arlded

drop-wise until the colour was changed from a yellow-orange colour to pink (i.e. fiom

basic to acidic). The beaker was then filled up to approximately 60 mL with distilled

water and the solution was exarnined on the titration device. The chloride concentration

measured was then recorded for M e r analysis. Concentrated samples collected near and

at the end of the test were titrated using only 1 mi, of sample representative to reduce the

arnount of titrant used and time required. The 1 rnL sample was measured and transferred

by a calibrated automatic pipettor, having an accuracy of 1 PL, to a 100 mL beaker. The

above description was followed for the remaining steps.

The chloride mass passed through the concrete specimen at different times were

calculated and plotted versus tirne. Chionde breakthrough time and diffusion coefficient

were determined using Equation 4.7.1 and 4.7.2. The graph of diffusion coefficient

versus expansion level was also plotted.

Cracking due to Mi-S i l i ca Reaction and its Effect on Durability Properties of Concrete

3.9 Cbloride Bulk Diffusion Test

Sarnples fiom 16 M T 0 pnsms were tested for bulk diffusion. The 50 mm thick

samples cut fkom the prisms were cover by masking tape at one end of the cross-section.

The exposed surfaces were coated with a layer of 2 to 3 mm thick of grey epoxy. The

masking tape was removed and the epoxy was allowed to harden. AAer the epoxy was

hardened, the samples were vacuum saturated as described in Section 3.3. A solution bath

of 5 moln NaCl was prepared in a large container. The samples were then removed From

the desiccator and the surface was dried with paper towels. Afterwards, the samples were

immersed in the NaCl solution and the container was covered and sealed with duct tape to

avoid evaporation. The container was stored at room temperature for a period of 40 days

to allow chlonde to difise into the concrete samples through the uncovered surface.

Afier the 40-day diffision period, the samples were fiozen at -1 8 O C to stop the

movement of ions in the pore solution of the concrete. While the sample was still fiozen,

it was ground and the dust was collected and stored in 20 rnL vials in 16 layers with each

layer advanced 1 mm in depth. The plastic vials containhg the dust samples with the cap

open were then place in a 105 OC oven to evaporate the moisture for 24 hours.

Ten layers of the sample dust, at depths of 2 to 6 mm and every other layer from 8

to 16 mm inclusive, were chosen and used to estimate the chloride concentration profile.

The analysis of the dried concrete dust is based on ASTM Cl14 and Cl218 and involved

the following procedures: weighing, digestion, filtration and titration.


The dust collected fiom each l

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