Cement & Concrete Composites 12 (1990) 271-277

Durability of Concrete Incorporating High-Volume of Low-Calcium (ASTM Class F) Fly Ash V. M. Malhotra

Concrete Technology Section, Canada Centre for Mineral and Energy Technology (CANMET), 405 Rochester Street, Ottawa, Ontario K1A 0G1

(Received 29 November 1989; accepted 4 July 1990)

Abstract

Research on structural concrete incorporating high volumes of low-calcium (ASTM Class F) fly ash has been in progress at CANMET since 1985. In this type of concrete, the cement content is kept at about 150 kg/m 3. The water-to-cementitious materials ratio is of the order of 0"30, and fly ash varies from 54 to 58% of the total cementitious material. A large dosage of a superplasticizer is used to achieve high workability.

This paper presents data on the durability of this new type of concrete. The durability aspects con- sidered are: freezing and thawing cycling; resistance to chloride ion permeability; and the expansion of concrete specimens when highly reactive aggregates are used in the concrete.

The investigations performed at CANMET indicate that concrete incorporating high volumes of low-calcium fly ash has excellent durability with regard to frost action, has very low permeability to chloride ions and shows no adverse expansion when highly reactive aggregates are incorporated into the concrete.

Keywords: Concrete durability, fly ash, cement replacement, alkali-aggregate reaction, chloride ion permeability, concretes, water-cement ratio, freeze-thaw durability, superplasticizers, flexural strength, dynamic modulus, expansion, strength of materials.

INTRODUCTION

In recent years, CANMET has been involved increasingly in research and development associated with the use of supplementary cementing materials in Portland cement concrete and mine-

© 1991 The Government of Canada 271

backfill applications. Special emphasis has been given to the utilization of low-calcium fly ash from Nova Scotia. One of the results of this research has been the development of high-volume fly ash concrete which has excellent mechanical pro- perties and long-term durability. 1,2,3,4 This type of concrete incorporates high volumes of fly ash, has low cement content and the water-to-cementitious materials ratio is about 0"30. Workability is achieved by using superplasticizers in rather large dosages.

This paper presents data on the performance of high-volume fly ash concrete when subjected to repeated freezing and thawing cycling, and the results of permeability testing using a rapid chloride permeability test. Results are also presented on the expansion of concrete test prisms made with a very reactive limestone aggregate.

RESISTANCE OF HIGH-VOLUME FLY ASH CONCRETE TO REPEATED CYCLES OF FREEZING AND THAWING

The durability of high-volume fly ash concrete prisms exposed to repeated cycles of freezing and thawing was determined using Procedure A of ASTM standard C 666. At present, this is the most commonly used test method in North America. Briefly, the method consists of alter- nately lowering the temperature of specimens from 4.4°C to minus 17.8°C and raising it from minus 17.8°C to 4.4°C in 3 h 51 min, resulting in about six cycles in a 24 h period. The durability of concrete is determined from the changes in measurements of weight, length, resonant fre- quency and pulse velocity of test prisms before and after the cycling, and by calculating the dur-

272 V. M. Malhotra

ability factors. Following the freezing and thawing cycling, the reference and test prisms are broken in flexure.

The physical properties and chemical analyses of the cement and the two fly ashes used in this investigation are shown in Table 1, and the mixture proportions and properties of fresh and hardened concrete are given in Table 2.

The freezing and thawing tests were done on both fly ash concretes following varying periods of initial moist-curing. The strength and freezing and thawing data are shown in Tables 3 and 4. The air-void parameters of the hardened concrete are given in Table 5. The test prisms from mixture

C4 of the fly ash S concrete were subjected to freezing and thawing after 14 days of initial moist- curing. They showed no significant distress in freezing and thawing cycling, and indicated a durability factor of 99 after 300 cycles. The prisms did, however, exhibit some surface scaling.

The test prisms from mixture B8 of fly ash L concrete were subjected to freezing and thawing cycling following initial moist curing periods of 14, 21 and 28 days. All three sets of prisms performed satisfactorily in the freezing and thaw- ing cycling, with durability factors of about 99 after 300 cycles. Again, some surface scaling was observed on the test prisms.

T a b l e 1. Physical properties and chemical analyses of cement and fly ashes

Portland cemenP Fly ash L ~ Fly ash S h (ASTM Type I)

Physical tests Fineness -- passing 75 #m %

-- passing 45/zm % 92.8 - - Blaine, mZ/kg

Setting time, min - - Initial 130 - - Final

Autoclave expansion % 0.16

Compressive strength of 5 l-ram Cubes, MPa: 3-day 25-1

7-day 31.5 28-day 39.3

82'7 80'6 289 326

Chemical analysis Insoluble residue 0.20 Silicon dioxide (SiO 2) 21'24 47.1 55"6 Alu minium oxide (AI_~ O~ ) 4.09 23"0 23' 1 Ferric oxide (Fe203) 2.81 20.4 3.48 Calcium oxide (CaO), total 62.21 1.21 12.3 Calcium oxide (CaO), free 0.59 -- -- Magnesium oxide (MgO) 3.75 1-17 1.21 Sulphur trioxide (SO3) 3.03 0.67 0.30 Sodium oxide (Na20) -- 0-54 1'67 Potassium oxide (K20) -- 3" 16 0'50 Loss on ignition 1.64 2'88 0.29

Bogue potential compounds" C3 S 51"63 C2S 22"03 C.~A 6"09 C4AF 8"54

Pozzolanic activity with Portland cement Water requirement, % Activity index at 28 days, % Accelerated activity index at 7 days, %

Pozzolanic activity index with lime at 7 days, MPa

92 92 98"2 94"6 90'1 85"5

6'8 6"3

"Manufacturers' data. hCANMET data.

Durability of concrete incorporating low-calcium fly ash

Table 2. Properties of fresh and hardened concrete ~

273

Mixture ser ies Properties of fresh concrete Properties of hardened concrete

Temp. Slump Unit weight Air content Compressive strength Flexural strength Splitting tensile (~C) (ram) (kg/m 3) (%) ofl5Ox3OOmm of 76×lO2×406-mm strengthofl50×3OOmm

cylinders at prisms at 14 days cylinders at 28 days 28 days (MPa) (MPa)

B8 (fly ash L) 25 175 2 365 5.6 39.7 4.1 - - C4 (fly ash S) 24 190 2 365 4.4 41.2 4.6 3.5

aTypical mixture proportions: Cement = 155 kg/m 3, fly ash = 215 kg/m 3, water = 115 kg/m 3, coarse aggregate = 1265 kg/m 3, fine aggregate = 615 kg/m 3, superplasticizer = sulfonated naphthalene formaldehyde product, air entraining admixture = synthetic resin type.

Table 3. Flexural strength of reference prisms and test prisms subjected to repeated cycles of freezing and thawing

Mixture W no. C+F

Flexural strength of 77 x 102 × 406 mm prisms (MPa)

Reference prisms, moist-cured

At the beginning At the end of testing of testing

Initial Strength moist-curing (MPa)

Test prisms

At the end of testing

Residual flexural strength (%)

B8 0"31 14-d 4.1 5"8 5"5 94.8 B8 0.31 21-d 5'0 5'7 5"0 87"7 B8 0.31 28-d 5'1 5'7 4.7 82.5 C4 0.31 14-d 4.6 5'7 5"0 87.7

Table 4. Summary of test results onconcre te prisms after 300 cycles of freezing and thawing

Mixture W Air Initial no. C + F content moist-

76 × 102 x 390 mm test prisms

(%) curing Weight Length Pulse, velocity Resonant period (kg) (mm) (m/s) frequency (Hz)

Wo W~¢~ Change Lo L.u~) Change V o Vs¢x) Change No Nu~a Change (%) (%) (%) (%)

Relative Durability dynamic factor modulus

of elasticity

c%)

B8 0-31 3'5 14-d 7"282 7.193 B8 0"31 3-5 21-d 7'316 7-193 B8 0'31 3'5 28-d 7-375 7'097 C4 0"31 4-0 14-d 7"370 7-173

-1.22 361"08 361-15 +0"019 4782 4872 +1'88 5420 5430 +0-18 100 -1-68 361"47 361'51 +0"011 4788 4695 -1.94 5370 5460 +1"68 100 -3 '77 361"05 361"22 +0-047 4947 4735 -4"29 5540 5510 -0-54 99 -2"67 361'63 361'72 +0'025 4701 4800 +2.11 5390 5350 -0 '74 99

100 100 99 99

Table 5. Ai r void parameters of hardened concrete

Mixture Air content of no. fresh concrete

I%) Voids in hardened concrete

I%)

Air- void of hardened concrete

Voids Specific Spacing per surface factor mm (mm: /mmO (ram)

B8 5"6 3"5 0"22 25"2 0"203 (fly ash L)

C4 4.4 4.0 0"36 36.1 0.141 (fly ash S)

274 V. M. Malhotra

PERMEABILITY OF HIGH-VOLUME FLY ASH CONCRETE

Research at C A N M E T has indicated that high- volume fly ash concrete has very low permeabil i ty and a very dense microstructure. The A A S H T O T 2 7 7 - 8 3 1 test method, entitled 'Rapid Deter- mination of the Chloride Permeabili ty of Con- crete', was adopted as one of the techniques to measure permeability. Briefly, the test method consists of monitoring the amount of electrical current passed through a 102 mm diameter by 51 mm thick concre te specimen when a potential difference of 60 Vdc is maintained across the specimen for a per iod of 6 h. Chloride ions are forced to migrate out of a NaCI solution subjected to a negative charge through the concrete into a sodium hydroxide solution maintained at a positive potential.

The condit ioning of the concre te disc speci- mens for the test p rocedure consists of 1 h of air drying, 3 h of vacuum (pressure < 1 mmHg), 1 h

of additional vacuum with specimens under de- aerated water, fol lowed by 18 h of soaking in water. The total charge passed, in coulombs, is used as an indicator of the resistance of the con- crete to the passage of chloride ions.

Fly ashes f rom five Canadian sources were incorpora ted in five concre te mixtures and two batches were made for each type of fly ash. The water- to-cement i t ious materials ratio was kept constant at 0.30. T he fly ash/(fly a s h + cement) ratio was 0-58.

The chemical analyses and physical propert ies of the fly ashes and Portland cement used are given in Table 6. T he mixture proport ions, the proper t ies of fresh and hardened concrete, and the values of electrical charge passed in cou lombs are given in Table 7.

The test results indicated that, regardless of the fly ash used, the permeabil i ty of concrete at 91 days as measured by the charge in coulombs ranged f rom 197 to 973. These values are very low indeed, and are comparab le with or superior

Table 6. Physical properties and chemical analyses of cement and fly ashes

Portland cement Fly ash Fly ash Fly ash Fly ash Fly ash ASTM Type I D t: S L W

Physical tests Fineness

-- passing 45 pm, % 92-8 80.0 66.8 80"6 82.7 54"0 -- Blaine, m2/kg 417 198 215 326 289 240

Autoclave expansion, % 0.16 . . . . .

Specific gravity 3" l 5 2.96 1.90 2.05 2-53 2" 11

Compressive strength of 5 l-ram cubes, MPa

3-day 24.7 . . . . . 7-day 3 0 - 5 . . . . .

28-day 38.7 . . . . . Coal type" -- B SB SB B SB

Chemical analysis SiO~ 21'5 38.2 55.7 55"6 47.1 61" l AI20 ~ 4-00 12'8 20'4 23'1 23"0 21"4 Fe20~ 2'56 39"7 4'61 3"48 20"4 2-99 CaO 62.7 4.49 10.7 12.3 1.21 11.0 MgO 3"70 0.43 1.53 1'21 1.17 1.76 Na20 0"48 0.14 4.65 1-67 0-54 0.30 K20 0'67 1'54 1"00 0-50 3' 16 0.72 TiO~ 0'21 0.59 0.43 0"64 0.85 0.65 P205 0.07 1.54 0.41 0.13 0" 16 0.10 MnO -- 0'20 0'50 0.56 0-85 0"69 BaO -- 0.04 0.75 0.47 0.16 0.33

- - - - 0.78 - - SrO 0"06 -- SO~ 3"09 1'34 0'38 0'30 0"07 0' 16 LOI h 1"42 0'88 0"44 0-29 -- 0"70

°B -- bituminous; SB -- sub-bituminous. 1'For the cement, loss at 1050°C. For the fly ashes, loss between 105 and 750°C.

Durability of concrete incorporating low-calcium fly ash

Table 7. H igh-vo lume fly ash concre te : a res is tance to ch lor ide ion p e n e t r a t i o n

275

Mixture Fly ash Compressive strength no. Properties of fresh concrete at various ages (MPa) Charge (coulombs)

Temp. Slump Unit weight Air content 7-day 28-day 91-day 365-day 7-day 28-day 91-day (°C) (mm) (kg/m 3) (%)

M C 1 6 D 21 190 2 340 6"6 15"9 26 '9 35"5 42"7 6 930 1 549 690 M C 1 7 D 20 100 2 350 7"0 - - 24"5 - - - - 9 130 1 596 737

M C 1 9 F 22 200 2 2 9 5 5"0 17"8 28-2 35"9 39"1 8 989 2 130 - - M C 2 0 F 21 200 2 300 5"0 - - 28"1 - - - - 6 252 1 092 - -

M C 2 1 S 21 175 2 295 6 '4 23"1 40 '7 48"5 54"1 3 389 599 221 M C 2 2 S 22 140 2 325 5'3 - - 42"0 - - - - 3 161 627 197

M C 2 3 L 21 100 2 345 5"7 - - 28"9 - - - - 4 545 994 391 M C 2 4 L 22 140 2 375 5"0 19"0 31"2 43 '8 52 '2 5 446 1 049 354

M C 2 5 W 22 200 2 315 4 '9 15"6 27"2 32"9 36"6 7 821 935 539 M C 2 6 W 22 200 2 260 6"3 - - 20"0 - - - - 9 969 3 230 973

aMixture p r o p o r t i o n s were kept cons tan t for all the mix tures and were:

Water C e m e n t con t en t = 15 5 kg/m3; C e m e n t + fly ash

F ly ash 0-30; 0"58

C e m e n t + fly ash

C e m e n t type = A S T M Type I. C.A. = 19 m m l imestone; fine aggregate = na tura l sand; A .E .A. = synthet ic resin type; Superp las t ic izer = sul fonated n a p h t h a l e n e f o r m a l d e h y d e produc t .

to the values reported for silica fume concrete made with about 400 kg/m 3 of cement and in- corporating 8 to 10% silica fume.: It is generally agreed that for very low permeability concrete, the values of charge in coulombs passed through the concrete test specimen should not exceed 1000, and should preferably be less than 600. Thus, it was concluded that high-volume fly ash concrete test specimens, when tested in accord- ance with AASHTO T277-831, had a high resist- ance to the passage of chloride ions.

ROLE OF HIGH-VOLUME FLY ASH CONCRETE IN CONTROLLING ALKALI-AGGREGATE REACTION

Research at CANMET 5 and other published data 6 indicate that alkali-silica reactions in con- crete can be controlled using fly ash as a partial replacement for cement. Furthermore, the per- centage of cement replacement by fly ash should preferably be between 30 and 40%. As mentioned earlier, in high-volume fly ash concrete the percentage of fly ash is about 60% by weight of cement and large dosages of superplasticizers are used. It was, therefore, considered prudent to perform investigations to ensure that the con- tribution of alkalis, both from the fly ash and the superplasticizers, will not adversely affect the

ability of high-volume fly ash concrete to control the above reaction when reactive aggregates are used.

In order to determine the changes in length of test prisms of high-volume fly ash concrete in- corporating a very reactive aggregate, four con- crete mixtures were made; two of these were made without fly ash and two incorporated high- volumes of low calcium fly ash designated as fly ash 'L'. The Portland cement used was ASTM Type I with alkali content expressed as Na20 equivalent of 1"13. In two of the mixtures, with and without fly ash, additional alkalis were added to bring the alkali level of the system to 5 kg/m 3. The mixture proportions are given in Table 8. The coarse aggregate was 19 mm crushed limestone known locally as the 'Pratt aggregate'. This lime- stone contains a highly reactive silica phase. The fine aggregate was natural sand. The properties of the fresh and hardened concrete are given in Table 9.

The test prisms, 75 × 75 × 304 mm in size, were cast and subjected to the following four test regimes to determine the expansion due to the alkali-silica reaction.

Test regime 1: Continuous curing of the prisms in a moist-curing room main- tained at 23 _+ 1-7°C.

276

Table 8. Mixture proportions

V. M. Malhotra

Mixture W F no. ( '+F C+F

Alkali content (kg/m ~)

Cement Additional Total Water

Quantities (kg/m 3)

Cement Fly ash Coarse Fine Super- Air entraining aggregate aggregate plasticizer admixture

(mllm 3)

1 0"32 -- 4'124 -- 4"124 115 2 0'32 - - 4"124 0'876 5-00 115 3 0"31 0"58 1"75 -- 1"75 114 4 0'31 0"58 1'75 3'25 5'00 114

365 -- 1291 627 9"3 365 -- 1291 627 9'3 155 212 1 264 616 6"2 155 212 1264 616 6"2

m

1921

Table 9. Properties of fresh and hardened concrete

Mixture W F no. C+F C+F

Temp. (°c)

Properties of fresh concrete

Slump Unit weight Air entrained (mm) (kg/m 3) (%)

Compressive strength, of 150 x 300 mm cylinders (MPa)

28-day

1 0.32 -- 22 105 2 420 2 0.32 -- 23 100 2410 3 0.31 0"58 23 145 2 380 4 0.31 0'58 24 170 2340

2'0 47'8 2'2 46"3 1"5 36"4 6"2 33"2

Table 10. Expansion of concrete at different storage conditions

Storage Mix no.

7days 14 days

% Expansion at different ages

28days 56days 84days 112days

1 Moist 1 Control 0.009 0.003 room 2 Control temp. 23°C + alkali 0.008 0.004

3 Fly ash Nil Nil 4 Fly ash

+ alkali - - 0.015

3 Water 1 Control 0.005 0'008 temp. 38°C 2 Control

+ alkali 0"005 0.002 3 Fly ash Nil Nil 4 Fly ash

+ alkali -- 0'007

4 5%NaC1 1 Control 0"003 0.001 temp. 38°C 2 Control

+ alkali 0"001 0 3 Fly ash Nil Nil 4 Fly ash

+ alkali 0 0.003

7 5%NaCl 1 Control 0 0"018 temp. 80°C 2 Control

+ alkali 0.036 0-052 3 Fly ash Nil Nil 4 Fly ash

+ alkali 0 0

0"001 0"004 0"008 0"005

0"003 0"009 0"009 0'011 Nil Nil Nil Nil

0.012 0-016 0"014 0"021

0-003 0"028 0"056 0-063

0"003 0"034 0"059 0"072 Nil Nil Nil Nil

0"002 0'011 0"013 0"019

0"001 0"014 0"032 (I.044

0 0"024 0'052 0'078 Nil Nil Nil Nil

0"004 0"006 0'01 0'012

0"062 0-064 0.083 0"086

0'065 0'093 0'102 0-108 Nil Nil Nil Nil

- 0'003 0'017 0-019 0"03

Test regime 2: Continuous curing of the prisms in water, both maintained at 38°C after an initial 24 h moist- curing.

Test regime 3: Continuous curing of the prisms in 5% NaCI solution maintained at 38°C after an initial moist- curing of 24 h.

Durability of concrete incorporating low-calcium fly ash 277

Test regime 4: Continuous curing of the prisms in 5% NaCI solution maintained at 80°C after an initial moist- curing of 24 h.

The expansion test results after 112 days are given in Table 10, and the tests are still being con- tinued.

The test results indicate that, regardless of the test procedure used, the test prisms cast from the high-volume fly ash concrete, with or without added alkali, did not show any expansion in spite of the reactive, coarse aggregate used in the con- crete mixtures. Notwithstanding the limited nature of the test data, the effectiveness of the high- volume fly ash concrete in controlling the alkali-silica reaction is confirmed.

CONCLUDING REMARKS

Investigations performed at CANMET, and briefly reported in this paper, show that air- entrained high-volume fly ash concrete has excel- lent durability characteristics as regards freezing and thawing cycling. The concrete offers con- siderable resistance to the passage of chloride ions and considerably reduces the expansion due to alkali-silica reaction. In addition to the low heat of hydration and low cement content which makes

it suitable for mass concrete structures, high- volume fly ash concrete has considerable poten- tial for application in concrete construction.

REFERENCES

1. Malhotra, V. M., Superplasticized Fly Ash Concrete for Structural Applications. ACI Concrete International, 3 (12) (December 1986) 28-31.

2. Sivasundaram, V., Carette, G. G. & Malhotra, V. M., Pro- perties of concrete incorporating low quantity of cement and high volumes of calcium fly ash. Mineral Sciences Laboratories Division Report MSI 88-4 (OP dd), CANMET, January 1988.

3. Giaccio, G. M. & Malhotra, V. M., Mechanical properties and freezing and thawing resistance of high-volume fly ash concrete made with ASTM Type I and III cements. ASTM Concrete Cement and Aggregates, 10 (2) (1988) 88-95.

4. Langley, W. S., Carette, G. G. & Malhotra, V. M., Early- age strength properties and freezing and thawing resis- tance of high-volume fly ash concrete. MSL Division Report 87-113 (OP&J), 1987.

5. Soles, J. A., Malhotra, V. M. & Suderman, R. W., The role of supplementary cementing materials in reducing the effects of alkali-aggregate reactivity: CANMET Investiga- tions; In Proceedings of the 7th International Conference on Concrete Alkali-Aggregate Reactions, 1985, ed. P. E. Gratten-Bellew, pp. 79-84.

6. Alasali, M. M., Alkali-aggregate reaction in concrete: investigations of concrete expansion from alkali con- tributed by pozzolans or slag; Mineral Sciences Labora- tories Division Report MSL 88-65 (OP&J), CANMET, May 1988.