Center for By-Products Utilization

FLEXURAL FATIGUE BEHAVIOR OF CONCRETE

CONTAINING VARIOUS SOURCES OF FLY ASH

By Tarun R. Naik, V.M. Malhotra, Shiw S. Singh, and

Bruce W. Ramme

Report No. CBU-1997-25

November 1997

To be submitted for publication in the ACI Materials Journal

Department of Civil Engineering and Mechanics College of Engineering and Applied Science THE UNIVERSITY OF WISCONSIN - MILWAUKEE

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FLEXURAL FATIGUE STRENGTH OF HVFA CONCRETE SYSTEMS

By

Tarun R. Naik, V.M. Malhotra, Shiw S. Singh, and Bruce W. Ramme

ABSTRACT

There is a lack of information on fatigue behavior of fly ash concrete, especially concrete

incorporating large amounts of fly ash. The major focus of this investigation was to

establish fatigue properties of high-volume fly ash concrete systems. In this work, a total

of eight concrete mixtures were proportioned using four sources of fly ash and two Type

I portland cements (low-alkali and high-alkali). The levels of fly ash content (58% of total

cementitious materials) and water to cementitious materials ratio (0.33) were maintained

constant for all test mixtures. Each mixture was tested under both static as well as cyclic

flexural loadings. These loads were applied using third-point loading in accordance with

ASTM C 78. The resulting data were analyzed to establish stress versus number of

cycles to failure curve (S-N curve). Experiments were also carried out to determine the

modified cube compressive strength (ASTM C 116) of each mixture using portions of the

beam, which were previously tested for static flexural strength. Fatigue or endurance

limit was defined as fatigue stress at 2 million of loading cycles. This limit was found to

vary significant from mixture to mixture. The ratio of fatigue limit to static flexural strength

varied in the range of 0.45-0.60. Based on pooled data, a fatigue limit for HVFA concrete

system was found to be 0.51, which is in the range of values observed for non-fly ash

concrete systems.

Keywords: Fly ash; concrete; endurance ratio; fatigue limit; fatigue strength

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INTRODUCTION

Rational design of concrete structures requires an accurate knowledge of concrete

properties under anticipated loading conditions. A large body of information is available

on behavior of concrete under static loading conditions. However, relatively limited

information is available on behavior of concrete subjected to dynamic loadings.

Structures that are subjected to repeated loads are susceptible to failure due to fatigue.

Fatigue is a process of progressive permanent internal changes in the materials that

occur under the actions of cyclic loadings. These changes can cause progressive growth

of cracks present in the concrete system and eventual failure of structures when high

levels of cyclic loads applied for short times or low levels of loads are applied for long

times.

Many concrete structures such as highway pavements, highway bridges, railroad bridges,

airport pavements and bridges, marine structure, etc. are subjected to dynamic loads.

Fatigue strength data of concrete and other materials that are used in these structures

are needed for obtaining their safe, effective, and economical design. A low cycle fatigue

is important for structures subjected to earthquake loads.

Numerous investigations [1-64] have been directed toward evaluation of fatigue behavior

of materials, including concrete. Although fatigue research began almost one hundred

years ago, there is still a lack of understanding concerning the nature of fracture

mechanism in cementitious composite materials due to fatigue. This is partly due to the

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complex nature of structure of such materials and their properties are influenced greatly

by a large number of parameters. Fatigue behavior of concrete is also influenced by

several parameters such as type of loading, range of loading, rest period, material

properties, environmental conditions, etc. Moreover, concrete properties are known to

depend upon the variables such as water-to-cement ratio, cement content, air content,

curing technique, age, admixture content, etc. Consequently, it is quite complex to

develop theoretical models to evaluate fatigue behavior of concrete and to determine

flexural fatigue behavior of fly ash concrete systems.

The specific objectives of this investigation was to present state-of-the-art information on

fatigue behavior of concrete made with and without mineral admixtures and therefore,

this investigation was directed toward determining fatigue behavior of fly ash concrete

systems. Additionally, to establish fatigue behavior of HVFA concrete systems through

laboratory investigation.

BEHAVIOR OF MATERIALS UNDER CYCLIC LOADINGS

The mechanical response of a material is substantially altered by cyclic loadings. In the

case of metals, it depends greatly upon hardness of materials and experimental

conditions. Under cyclic loading conditions, a metal may either harden, soften, remain

stable, or have mix behavior (soften or harden depending upon strain level) [8]. During

constant strain cycling of a material, an increase in stress with time is called strain

hardening and a decrease in stress is called a strain softening. These are related to the

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nature and stability of the dislocation substructure of a given metallic material [8].

In general, the dislocation density is low for soft materials. For such a material, the

increase in density of material resulting from cyclic plastic straining causes strain

hardening. Whereas for a hard metal, the cyclic strain causes a rearrangement of

dislocations. The resulting structure for the metal becomes soft as it offers low resistance

to deformation [8].

A kinematically irreversible microscopic deformation is the precursor to fatigue in both

ductile and brittle solids [1]. It is now well established that the cyclic slip is not only cause

of fatigue damage but it can occur due to microcracking, interfacial sliding or creep, etc.

The irreversible deformation in brittle solids can occur due to various processes. These

include [1]: (1) frictional sliding of the microcracks that are nucleated at grain boundaries,

and along the interfaces between the matrix and the filler, (2) the release of residual

stresses may cause microcracking at the grain boundaries and the interfaces resulting in

plastic deformation strain, etc.

Concrete is a complex hybrid composite material. During cyclic loading fracture to

concrete can occur by fracture of the cement paste, fracture of aggregate, failure of bond

between the cement paste aggregate or any combination of these mechanisms.

Compared to metals, concrete is prone to have a large number of flaws resulting from

hydration, shrinkage and other causes. Mechanism of fatigue in concrete is not well

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established and numerous hypothesis related to crack initiation and propagation have

been proposed by Neal and Kesler [16], Kesler [3], Raithby and Whiffin [25], and several

others [75,76].

Mudock and Kesler [6] proposed that initiation of fatigue failure in concrete is due to

progressive deterioration of the bond between the coarse aggregate and the matrix. This

results in reduction in section of the specimen leading to its failure due to fracture of

matrix. However, most researchers support that during cyclic loading, fatigue of concrete

occurs because of the propagation of the micro cracks and macro cracks present in the

material, especially in the interface region as well as in the matrix. Since the interface

region is the weakest region, there is a very high probability that initiation of fatigue cracks

occurs in this region. However, initiation of fatigue cracks that can occur either in matrix

or at the interfacial region would greatly depend on the size of dominant flaws present in

these regions.

Addition of fiber to concrete restrict crack formation and delays crack growth. Therefore,

unstable cracks produced during loading is transformed into a slow and controlled growth.

Also, crack path length is increased in presence of fibers. The overall tensile rupture

strain of concrete is increased due to the introduction of fiber. This depends greatly upon

the elasto-plastic properties of the fiber and the effectiveness of the bond between the

fibers and the concrete matrix. Due to improved ductibilty of the fiber reinforced concrete,

their dynamic properties including fracture toughness and fatigue life are greatly

improved. To some extent, the presence of fine and coarse aggregates in cement paste

improves its toughness due to increased crack propagation path length.

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PREVIOUS INVESTIGATIONS

A detailed review of fatigue behavior of concrete has been reported to EPRI in a previous

report published by the UWM Center for By-Products Utilization [20]. However, a brief

review is presented here for the sake of completeness of information on the subject.

Fatigue testing of cement-based materials began more than 10 decades ago. Early

studies have been reviewed by a number of investigators including Nordby [16], Murdock

[17], Lloyd et al. [18], Raithby and Whiffin [19], and Naik et al. [20]. Although, the earliest

work on fatigue of mortar specimen in compression was conducted by Considere in 1898,

and concrete specimen by Van Ornum in 1903 as reported by Nordby [16],

comprehensive studies on fatigue behavior of concrete began after 1930.

Several parameters such as stress range, load history, rate of loading, rest periods,

stress gradients, material properties, etc can affect fatigue characteristics of concrete

substantially. More recently, the effects of these parameters on fatigue strength was

extensively reviewed by Naik et al. [20]. However, this paper includes a brief description

of the results reported by previous investigators.

Several studies have shown that the range of stress can influence the fatigue strength of

concrete considerably [21,22,23,24]. A decrease in the stress range seems to increase

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fatigue strength during fatigue testing. Rate of loading is an important variable that

affects fatigue strength of concrete significantly. Several studies [23,25,26,27,28,29,30]

have presented the effect of rate of loading on fatigue behavior of plain concrete. The

frequency of loading in the range of 1-30 CPS does not have an appreciable affect on

concrete fatigue behavior if the maximum stress level remains less than about 75% of the

static strength [23,31]. Applications of stress levels above 75% can cause decrease in

fatigue strength when the frequency of loading is decreased [23,27,29]. This may be

attributed to a significant increase in creep effects, resulting in a reduction in fatigue

strength with decreasing rate of loading.

Under most practical conditions, concrete structures experience cyclic loadings that vary

greatly in magnitude, number, and order [31]. The resulting fatigue damage due to such

loadings is often determined by the Miner hypothesis. This hypothesis assumes that

damage accumulates linearly with the number of cycles applied at a particular load level.

Experimental investigations [22,31] have indicated conservative as well as unsafe

prediction of the Miner hypothesis. Holmen [32] reported that random loadings caused

more cumulative damage compared to the predictions made by the Miner hypothesis.

This occurred primarily due to the loading sequence effect that is ignored in the Miner

hypothesis. As a result, he established a modified version of the Miner hypothesis

involving a loading function to handle variable amplitude loadings. However, some other

investigators found that the Miner hypothesis is appropriate to predict fatigue life of

concrete subjected to variable amplitude loadings [35,36].

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The stress reversal causes reduction in fatigue life of concrete when compared to

concrete loading with stress cycles having positive stress ratio [35,36].

A number of researchers [5,38,14] have shown beneficial effects of previous cyclic

loadings on concrete static strength provided the loadings remain at below endurance

limits. Bennett and Raju [5] found 11% increase in static strength of high strength

concrete specimens which were previously subjected to several million applications of

cyclic loads between 0.5 and 0.7 of the static ultimate strength. Other investigators as

cited by Ramakrishnan et al. [38] indicated increase in the static strength in the range of

5 to 15 percent for specimens loaded below their endurance limits relative to control

specimens. An investigation [14] reported that beams subjected to a similar stress history

endured increased number of load applications when tested later at a higher stress level

compared to control specimens. The above results may be attributed to the release of

residual stresses and strain hardening effects [5].

Rest periods and sustained loading between the repeated load cycles produced a

beneficial effect on the fatigue strength of concrete [22,30,38]. This occurs in absence

of stress reversals and when the sustained stress level is below 75 percent of the static

strength. Hilsdorf and Kesler [22] reported that rest periods of up to 5 minutes increased

the fatigue strength. However, beyond 5 minutes the periods did not exhibit any

appreciable effect.

Ople and Hulsbos [40] investigated the effect of stress gradient on the fatigue strength of

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concrete in compression. In order to simulate the compression zone of a beam, concrete

prisms were eccentrically loaded in the fatigue tests. The results showed increase in the

fatigue strength of eccentric specimens of the order of 15 to 18 percent higher relative to

uniformly stressed specimens for a fatigue life of 40,000 to 1,000,000 cycles. The

authors recommended that the fatigue strength of uniformly stressed specimens be used

as a lower limit of fatigue life of flexural members in compression.

Parameters such as water-to-cementitious materials ratio, curing, cement content, age,

aggregate properties, admixture content, etc. are known to affect fatigue strength of

concrete. The effects of these parameters exhibit the same trend as observed in the

case of static strength. Studies have been carried out to evaluate the effects of age

[23,30,41,42,43], moisture conditions [30,31,42], curing conditions [42,43], air

entrainment [44,45,46], water-to-cement ratio [16,45], type and quality of aggregate, and

concrete strength [30,39,46,47,48], and superplasticizer [51,52] on fatigue strength

behavior of concrete. Previous studies have substantiated that endurance limit is

relatively independent of material properties when expressed as a percentage of static

strength. According to ACI Committee 215 report [24], the fatigue strength for a life of 10

million cycles of load at a 50% probability of failure, is approximately 55% of static

strength, regardless of types of cyclic loading. Test results from some past investigations

showed that endurance limit does not exist for plain concrete [53]. More recently, studies

[38] have proved that endurance limit at 2 million cycles of loading does exist for plain as

well as reinforced concretes. Some studies [24,38] reported a flexural fatigue limit in the

range of 50 - 60 percent of the static strength for loading cycles varying between 106 to

10

107 cycles.

Fatigue behavior of fly ash concretes have been reported by a few researchers [54-57].

Ghosh et al. [54] determined the flexural fatigue strength of plain low cement content

concrete and low cement-fly-ash concrete (lean mixtures). The mixture proportions were

1 cement : 4 sand : 8 coarse aggregate for plain concrete, and 1 cement : 3.5 sand : 3.5

n fly ash : 14 coarse aggregate for lean cement-fly-ash concrete (n is ratio of specific

gravity of fly ash and sand). The flexural stress was applied through third-point loading at

74 CPM using test specimens of 75 x 100 x 500 mm. Test results indicated that at 75%

of the maximum flexural stress level, the number of repetitions to failure was 2,000 and

20,000 cycles for the lean mixtures of cement and cement-fly ash concretes,

respectively.

Tse et al. [56] evaluated compressive fatigue strength of cylindrical concrete specimens

(15() x 300 mm) made with both Class C and Class F fly ashes. The study developed

concrete mixture proportions to have four levels of cement replacements (0, 25, 50, and

75%) by these fly ashes. The cyclic stress range was varied from a minimum level of

about zero to a predetermined maximum stress as a percentage of the compressive

strength (between 55% to 95%) at 4 CPS. The authors reported that concrete with

equivalent or higher compressive and fatigue strength could be obtained with cement

replacement of 25% by weight of low-calcium fly ash or 50% by weight of high-calcium fly

ash.

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Ramakrishnan et al. [57] investigated flexural fatigue strength behavior of high-volume fly

ash concrete systems. Superplasticized concrete mixtures were proportioned to have

zero and 58% cement replacements with a low-calcium fly ash at a water to cementitious

materials ratio of 0.32. From these mixtures, beam specimens of 75 x 100 x 400 mm

were subjected to non-reversed fluctuating flexural loads using a third-point loading

system at a frequency of 20 CPS. A constant lower limit of 10% of the flexural static

strength was used, and the upper limit was varied from about 90% of the static strength

down to the fatigue limit. The fatigue limit values, expressed as proportions of the static

flexural strength, were 0.65 for the non-fly ash concrete and 0.70 for the high-volume

Class F fly ash concrete. However, the values of static flexural strength and fatigue

strength were slightly higher for the reference concrete. They further reported a 15 to

30% increase in the static flexural strength for both the high-volume fly ash concrete and

the non-fly ash concrete specimens which were previously loaded to four million cycles

of fatigue stresses at their respective fatigue limit loads compared to the specimens not

loaded before.

Generally, a plot of the ratio of fatigue stress to static strength (S) versus logarithm of

number of cycles (N), becomes independent of the specimen shape, strength properties,

curing condition age, moisture condition at loading, etc. This curve is adequately

represented by several empirical models [38,39,53,59,60,61]. Aas-Jakobsen [59]

established an empirical relation to express the ratio S as a function of the ratio of

minimum stress to maximum stress (R) and number of load cycles. This model was

found to be adequate to describe fatigue strength of plain normal weight and lightweight

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concretes in both compression [60] and tension [61]. Oh [62] developed a linear relation

between the ratio S and N.

Hsu [53] proposed a more general model to take into accounts of the four parameters

S-N-T-R which includes an additional variable T (time). The product of T and N denotes

duration of loading; and, therefore, the model presents the joint effects of time and

loading rate on fatigue behavior of concrete. The author established empirical models for

both high-cycle and low-cycle fatigue failures.

EXPERIMENTAL PROGRAM

An experimental program was designed to establish fatigue behavior of high-volume fly

ash concrete systems. The work related to material selection and characterization,

mixture proportioning, and specimen preparation was performed at the CANMET, Ottawa,

Canada. The work concerning the fatigue testing was performed at the UWM Center for

By-Products Utilization, University of Wisconsin-Milwaukee.

MATERIALS

Cement

Two different cements designated as S and G were used. Cement S was a low-alkali

(about 0.2% Na2O) ASTM Type I cement, whereas cement G was a high-alkali (about

1.1% Na2O) ASTM Type I cement. The physical and chemical properties of these

cements are presented in Table 1.

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Fly Ash

Four fly ashes obtained from four different sources in the USA were used in this

investigation. Their physical and chemical properties are given in Table 2.

MIXTURE PROPORTIONS

The concrete mixture proportions are summarized in Table 3. The parameters such as

water to cementitious materials ratio, and water, cement, and fly ash contents were

maintained approximately constant for all mixtures. All mixtures were air entrained and

a HRWR was used. Appropriate amounts of air entraining admixtures were added to

entrain air content of 5 ± 0.5%. A napthalene-based HRWR (superplasticizer) was used

to obtain the desired level of slump.

SPECIMEN PREPARATION

Cylindrical specimens (152 x 305 mm) were cast for compressive strength determination.

Prism specimens (75 x l00 x 400 mm) were cast for flexural static and fatigue strength

measurements of concrete. These specimens were cast in two layers using an internal

vibrator. All test specimens were subjected to moist curing in accordance with ASTM C

192. After one year of moist curing at CANMET, all the specimens were shipped to the

UWM Center for By-Products Utilization, University of Wisconsin- Milwaukee, where they

were stored in lime-saturated water until the time of the test.

TESTING OF SPECIMENS

Compressive Strength

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Concrete compressive strength was determined in accordance with ASTM C 39. The

modified cube compressive strengths of concrete mixture using portions of beam

specimens which were previously broken in flexure, were determined in accordance with

the ASTM C 116 at the time of fatigue testing.

Fatigue Strength

Static and fatigue flexural strength of concrete were determined using third-point loading.

In this work, endurance limit was defined as the flexural stress level at which the beam

specimen could withstand two million cycles of nonreversed cyclic loading. The static

flexural strengths of beam specimens (75 x 100 x 400 mm) were determined using a

third-point loading in accordance with ASTM C 78 with a span of 300 mm. Three

specimens were used to determine the average static flexural strength of concrete. All

specimens were tested with respect to their stronger axis.

The upper and lower limits for the cyclic loading were determined from the average static

flexural strength of the mixture. The lower limit was taken as 10% of the static flexural

strength of each mixture. In this investigation, the lower limit was kept constant for all

specimens and upper limit was varied from about 90% of the static flexural strength down

to endurance limit (fatigue limit) of the mixture.

The flexural fatigue test was carried out between the upper and lower limits of the loading

using the third-point loading system. Three specimens were tested for each load

condition. If three specimens failed before two million cycles, the upper limit was reduced

15

by 10% or more depending upon the number of upper load levels needed to establish

endurance limit for a given mixture. Two additional specimens were tested at the load

level at which three beams survived two million cycles. The endurance limit was taken

as an average flexural strength based on the results of the five specimens which survived

two millions cycles of loading. The beams which survived two million loading cycles were

also tested in static loading using the third-point loading.

Since fatigue testing of concrete is very time consuming, it was not possible to test all the

mixtures at a constant age. Each test specimen took up to about 28 hours to test.

Therefore, after completion of testing of one mixture, the next mixture was tested. This

resulted in differences in age among test specimens mixtures tested. However, at about

one year age, at which the fatigue testing was started, the age effect on strength gain was

already negligible. In

order to further eliminate the effect of age to a considerable extent, fatigue strength data

were expressed as a ratio of fatigue flexural strength to static flexural strength for each

mixture.

RESULTS AND DISCUSSION

COMPRESSIVE STRENGTH

The compressive strength at the 28-day age of all concrete mixtures are shown in Table

3. The strength of the mixtures at one year of age was found to be in the range of 30 - 40

MPa, depending upon type of cement and source and type of fly ash used.

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FATIGUE BEHAVIOR

The flexural fatigue strength test data were plotted as a ratio of flexural stress to static

flexural strength (S) versus number of cycles (N) for each mixture. As expected, this type

of plot showed a non-linear trend for all the mixtures (Fig. 1). A plot of S-N curve for each

mixture could be approximated by a linear model when the ratio of flexural fatigue stress

to static flexural strength versus log number of cycles is plotted (Fig. 2). The linear model

was used to represent fatigue for cycles less than 2 million.

The fatigue limit data for each mixture derived from the S-N curves are given in Table 4.

The analysis of test data showed that both static flexural strength and fatigue flexural

strength were heavily dependent upon source of fly ash used. The effect of type of

cement was relatively small compared to fly ashes' effects.

The results revealed that the concrete mixture having the highest flexural strength did not

exhibit the maximum fatigue limit (fatigue stress at two million cycles of loading). This

occurred primarily due to differences in crack propagation patterns during cyclic loadings.

The crack pattern is primarily influenced by size and location of flaws/cracks present in

the test specimens, etc.

A plot of fatigue limit or endurance limit, of test mixture are mixtures (EP9F through

EP16F) are shown in Figure 3. A plot of endurance ratio and fatigue limit of the mixtures

expressed as a proportion of their respective static flexural strengths, is also shown in

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Figure 4.

The results showed that the fatigue limit varied from 2.6 MPa to 3.3 MPa for the mixtures

tested. Whereas, the endurance ratio, defined as the ratio of flexural fatigue limit to static

flexural strength, varied between 0.5-0.6 for the concrete specimens tested. The results

further indicated that endurance ratio when expressed as proportion of static strength,

was relatively unaffected by the type of cement and source and type of fly ash used. This

is in agreement with results reported by a majority of researchers on concrete fatigue [20].

Based on pooled data, the endurance ratio for the test mixtures was found to be

approximately 0.51.

CHANGE IN STATIC FLEXURAL STRENGTH AFTER TWO MILLION CYCLES

In general, the reduction was found to vary between 0% and 32.2% compared to the

reference specimens. all test specimens which had undergone 2 million cycles of fatigue

loading showed reduced static flexure strength compared to the respective reference

specimen not loaded previously (Table 4). This indicates that high-volume fly ash

concrete specimens tested in this work displayed a strain softening behavior, in contrast

to a strain hardening trend reported by some researchers [38,20]. The strain softening

behavior may be a the results of slippage caused between the unreacted fly ash particles

and the paste during the cyclic loading, internal structure of concrete, presence of flaws,

etc. during the cyclic loading used. Probably the increased slippage caused considerable

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cracks which resulted in reduced strength after the fatigue loading.

MODIFIED CUBE COMPRESSIVE STRENGTH

The modified cube compressive strength data were determined in accordance with

ASTM C 116. Average modified cube strengths were 46.3 MPa for EP9F, 45.2 MPa for

EPl0F, 40.5 MPa for EP11F, 43.2 MPa for EP12F, 36.4 MPa for EP13F, 35.6 MPa for

EP14F, 36.1 MPa for EP15F, and 45.3 MPa for EP16F. The corresponding compressive

strength values for these mixtures measured according to ASTM C 39 were at one year

age were 63.1 MPa, 61.2 MPa, 54.7 MPa, 58.7 MPa, 49.2 MPa, 51.4 MPa, 58.2 MPa,

and 57.5 MPa, respectively.

The results revealed some difference between the strength values determined by ASTM

C 39 and ASTM C 116. The major reason for the difference is due to variation in

geometry of test specimens. Other factors such as difference in age and previous strain

history might have slightly affected the compressive strength results. The specimens

used for the modified cube compressive tests might have experienced some previous

strain because they were already obtained from specimens which were subjected static

to flexural strength tests.

CONCLUSIONS

The major conclusions based on experimental data collected in this work are as follows.

(1) Static flexural strength of concrete was significantly influenced by the

source of fly ash used. The effect of cement type had a little influence on

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the flexural fatigue strength of high-volume fly ash concrete systems.

(2) The effect of fly ash source was significant on the flexural fatigue stress of concrete.

(3) The concrete mixture having the highest static flexural strength did not attain the

highest fatigue limit. This revealed that fatigue flexural strength was more sensitive

to internal structure of concrete structure and flaws than of static flexural strength.

(4) As anticipated, the S-N curve exhibited a non linear trend.

(5) The relation between the ratio of flexural fatigue stress to static flexural

strength and logarithmic of number of cycles can be modelled by a linear

model. This is consistent with results obtained from previous investigations,

as the relationship between the strength ratio and number of cycles

becomes relatively independent of age, strength, and material properties to

a marked extent. Based on the pooled data, the value of endurance ratio

was approximately 0.51, in the same range as observed for fly-ash free

concrete.

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Subjected to High Repeated and Sustained Loads," Ph.D. Thesis, University of Illinois at Urbana - Champaign, Illinois. 1971.

24. ACI Committee 215, "Consideration for Design of Concrete Structures Subjected to Fatigue Loading," ACI Manual of Concrete Practice, 1990, Part 1, pp. 215R-1 to 215R-25.

25. Kesler, C.E., "Effect of Speed of Testing on Flexural Fatigue Strength of Plain

Concrete," Highway Research Board, Vol. 32, 1953, pp. 251-258. 26. Assimacopoulos, B.A., Warner, R.F., and Ekberg, C.E., "High Speed Fatigue

Tests on Small Specimens of Plain Concrete, "Journal of Prestressed Concrete Institute, Vol. 4, No. 2, Sept. 1959, pp. 53-70.

27. Sparks, P.R., and Menzies, J.B., "The Effect of the Rate of Loading upon the

Static and Fatigue Strengths of Plain Concrete in Compression," Magazine of Concrete Research, Vol. 75, No. 83, June 1973, pp. 73-80.

28. Galloway, J.W., and Raithby, K.D., "Effects of Rate of Loading on Flexural

Strength and Fatigue Performance of Concrete," Department of the Environment, TRRL Report LR 547, Crowthorne, Transport and Road Research Laboratory,

22

1973. 29. Awad, M.E., and Hilsdorf, H.K., "Strength and Deformation Characteristics of Plain

Concrete Subjected to High Repeated and Sustained Loads," Fatigue of Concrete, ACI Special Publication, SP-41, 1974, pp. 1-13.

30. Raithby, K.D., and Galloway, J.W., "Effects of Moisture Condition, Age, and Rate

of Loading on Fatigue of Plain Concrete," Fatigue of Concrete, ACI Special Publication, SP-41,1974, pp.15-34.

31. RILEM Committee 36-RDL, "Long Term Random Dynamic Loading of Concrete

Structures," Materials and Structures, Research and Testing (RILEM, Paris), Vol. 17, No. 97, Jan. 1984, pp. 1-28.

32. Holmen, J.O., "Fatigue of Concrete by Constant and Variable Amplitude Loading,"

ACI Special Publication, SP-75, S.P. Shah, Ed., Detroit, 1982, pp. 47-69. 33. Siemes, A.J.M., "Miner's Rule with Respect to Plain Concrete Variable Amplitude

Tests," ACI Special Publication, SP-75, S.P. Shah, Ed., Detroit, 1982, pp. 343-372.

34. Sakata, K., Yamura, K.. and Nishibayashi, S., "Study on Fatigue Properties of

Concrete Under Variable Repetitive Compressive Loading," Transactions of the Japan Concrete Institute, Vol. 7, Published by Japan Concrete Institute, Tokyo, 1985, pp. 257-262.

35. Tepfers, R., "Fatigue of Plain Concrete Subjected to Stress Reversals,"

Proceedings of the Abeles Symposium on Fatigue of Concrete Structures, ACI Special Publication, SP-75, S.P. Shah, Ed., Detroit, 1982, pp. 195-215.

36. Zhang, B.S., and Phillips, D.V., "Fatigue Life of Plain Concrete Under Stress

Reversal," Proceedings of the International Conference on Fracture of Concrete and Rock: Recent Developments, University of Wales, College of Cardiff, School of Engineering, S.P. Shah, S.E. Swartz, and B. Barr, Ed., Sept. 20-22, 1989,

pp. 183-192.

37. Cornelissen, H.A.W., and Siemes, A.J.M., "Plain Concrete Under Sustained

Tensile or Tensile and Compressive Fatigue Loadings," Proceedings of the 4th International Conference on Behavior of Offshore Structures, 1985, pp. 487-498.

38. Ramakrishnan, V., and Lokvik, B.J., "Fatigue Strength and Endurance Limit of

23

Plain and Fiber Reinforced Concretes–A Critical Review," Proceedings of the

International Symposium on Fatigue and Fracture in Steel and Concrete Structures, Madras, India, 1991, pp. 381-407.

39. Ramakrishnan, V., Bremmer, T.W., and Malhotra, V.M., "Fatigue Strength and

Endurance Limit of Lightweight Concrete," Presented at the ACI Meeting in Dallas, TX, November 1991.

40. Ople, F. S., and Hulsbos, C.L., "Probable Fatigue Life of Plain Concrete with

Stress Gradient." ACI Journal, Proceedings Vol. 63, No. 1, January 1966, pp. 59-82.

41. Galloway, J.W., Harding, H.M., and Raithby, K.D., "Effects of Age on Flexural

Fatigue and Compressive Strength of Concrete," TRRL Report No. 865, Crowthorne, Transport and Road Research Laboratory, 1979, 20 pages.

42. Galloway, J.W., Harding, H.M., and Raithby, K.D., "Effects of Moisture Changes

on Flexural and Fatigue Strength of Concrete," TRRL Report No. 864, Crowthorne, Transport and Road Research Laboratory, 1979, 30 pages.

43. Raithby, K.D., "Some Flexural Fatigue Properties of Concrete-Effects of Age and

Methods of Curing," First Australian Conference on Engineering Materials, University of New South Wales, 1974, pp. 211-229.

44. Antrim, J.C., and McLaughlin, J.F., "Fatigue Study of Air-Entrained Concrete," ACI

Journal, Proceedings Vol. 55, No. 11, May 1959, pp. 1173- 11 82. 45. Lee, D.Y., Klaiber, F.W., and Coleman, J.W., "Fatigue Behavior of Air-Entrained

Concrete," Engineering Research Institute, Iowa State University, Ames, Iowa Department of Transportation, Final Report, July 1977; also, Transportation Research Record No. 671, 1978. pp. 20-23.

46. Klaiber, F.W., Thomas, T.L., and Lee, D.Y., "Fatigue Behavior of Air-Entrained

Concrete: Phase II," Report, Ames, Iowa, Engineering Research Institute, Iowa State University, Feb. 1979.

47. Gary, W.H., McLaughlin, J.F., and Antrim, J.C., "Fatigue Properties of Lightweight

Aggregate Concrete," ACI Journal, Proceedings Vol. 58, No. 2, Aug. 1961, pp. 149- 161.

48. Bennett, E.W., and Muir, S.E.St.J., "Some Fatigue Tests of High-Strength

24

Concrete in Axial Compression," Magazine of Concrete Research, London, Vol. 19, No. 59, June 1967, pp. 113-117.

49. Sparks, P.R., "The Influence of Rate of Loading and Material Variability on the

Fatigue Characteristics of Concrete," Proceedings of the Abeles Symposium on Fatigue of Concrete Structures, ACI Special Publication SP-75, S.P. Shah, Ed., Detroit, 1982, pp. 331-341.

50. Tepfers, R., and Kutti, T., "Fatigue Strength of Plain, Ordinary, and Lightweight

Concrete," ACI Journal, Proceedings, Vol. 76, No. 5, May 1979, pp. 635-652. 51. Whiting, D., "Evaluation of Super-Water Reducers for Highway Applications,"

Report No. FHWA/RD-80/132, Federal Highway Administration, Washington, D.C., 1981.

52. Lee, D.Y., Yang, J.J.F., and Klaiber, F.W., "Fatigue Behavior of Superplasticized

Concrete," ASTM Cement, Concrete, and Aggregates, CCAGDP, Vol. 7, No. 1, Summer 1985, pp. 1924.

53. Hsu, T.T.C., "Fatigue of Plain Concrete," ACI Journal, Proceeding Vol. 78, No. 4,

July-August 1981, pp. 292-305. 54. Ghosh, R.K., Sethi, K.L., and Arora, V.P., "Laboratory Studies on Lean

Cement-Fly Ash Concrete as Construction Material," IRC Highway Research Board, No. 19, 1982, pp. 13-26.

55. Burcharth, H.F., "Fatigue in Breakwater Concrete Armour Units," Proceedings of

the Nineteenth Coastal Engineering International Conference, Vol. 3, No. 19, pp. 2692-2607.

56. Tse, E.W., Lee, D.Y., and Klaiber, F.W., "Fatigue Behavior of Concrete Containing

Fly Ash," Proceedings of the Second International Conference on the Use of Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, Madrid, Spain, V.M. Malhotra, Ed., Vol. 1, ACI Special Publication, SP-91, 1986, pp. 273-289.

57. Ramakrishnan, V., Malhotra, V.M., and Longley, W.S., "Comparative Evaluation

of Flexural Fatigue Behavior of High Volume Fly Ash and Plain Concrete," Presented at the 70th Annual Meeting of the Transportation Research Board, Washington, D.C., Jan. 1991.

58. Ozaki, S., and Sugata, N., "Fatigue of Concrete Composed of Blast Furnace Slag

or Silica Fume Under Submerged Conditions," Proceedings of the Fourth International Conference, Istanbul, Turkey, May 1992, pp. 1509- 1524.

25

59. Aas-Jakobsen, K., "Fatigue of Concrete Beams and Columns," Bulletin No. 70-1, NTH Institute for Betonkonstruksjoner, Trondheim, Norway, Sept. 1970, 148 pages.

60. Tepfers, R., and Kutti, T., "Fatigue Strength of Plain, Ordinary, and Lightweight

Concrete," ACI Journal, Proceeding Vol. 76, No. 5, May 1979, pp. 635-652. 61. Tepfers, R., "Tensile Fatigue Strength of Plain Concrete," ACI Journal,

Proceeding, Vol. 76, No. 8, August 1979, pp. 919-933.

62. Oh, B.H., "Fatigue Analysis of Plain Concrete in Flexure," Journal of Structural

Engineering, ASCE, Vol. 112, No. 2, Feb. 1986, pp. 273-288. 63. Oh, B.H., "Fatigue-Life Distribution of Concrete for Various Stress Levels," ACI

Materials Journal, Vol. 88, No. 2, March-April 1991, pp. 122-128. 64. Ye, C., "Shrinkage and Fatigue Properties of Concrete Containing High Volumes

of Fly Ash," M.S. Thesis, May 1993. REP-337 SSS/llm

26

Table 1: Physical and Chemical Characteristics of Portland Cements

Property

Cement S

Type 1

(low alkali)

Cement G

Type 1

(high alkali) Physical Properties:

Fineness: Passing 45 μm, %

Blaine, m2/kg

Specific Gravity

Compressive Strength (ASTM C 109)

of 51-mm Mortar Cubes, MPa

3 days

7 days

28 days

93.6

371

3.14

21.2

31.5

45.0

94.9

376

3.14

31.5

34.5

41.9 Chemical Composition (Mass %)

SiO2

Al2O3

Fe2O3

CaO

MgO

Na2O

K2O

TiO2

MnO

P2O5

SO3

LOI

21.16

4.75

3.65

64.99

1.24

0.07

0.18

0.31

0.02

0.10

2.27

1.11

19.20

5.79

2.03

63.48

2.52

0.33

1.16

0.28

0.06

0.10

3.50

2.61 Compound (Bogue) composition:

C3S

C2S

C3A

C4AF

CaCO3 (TGA)

CSH2 (QXRD)

65.37

11.35

6.41

11.11

0.52

4.4

63.65

7.03

11.91

6.18

3.02

4.0

27

Table 2: Physical and Chemical Characteristics of Fly Ashes

Property

Fly Ash Source

Coal Creek (CC)

Belews Creek

(BC) Gorgas (GO)

Navajo (N)

Physical Properties:

Fineness (% -45 μm)

Blaine (m2/kg)

Density (g/cm3)

Pozz. activity with PC:

PC G 7d

28d

PC S 7d

28d

80.2

256

2.50

95.9

101.7

89.0

93.4

72.1

211

2.30

81.1

88.5

83.7

87.6

85.4

289

2.43

88.2

92.3

87.8

93.6

82.7

320

2.39

89.2

95.8

90.4

93.8 Chemical Composition

(%):

SiO2

Al2O3

Fe2O3

CaO

MgO

Na2O

K2O

SO3

Carbon

46.38

15.32

7.38

19.34

5.48

0.83

1.82

1.45

0.04

54.54

31.53

6.28

1.17

0.85

0.22

2.00

0.40

0.95

47.33

25.44

13.82

1.81

1.52

1.18

2.80

0.90

1.38

55.39

18.54

6.38

9.51

2.16

3.08

1.22

0.92

0.31

Mineralogical*

Composition (%):

Glass

Quartz (Qz)

Mullite (Mu)

Ferrite/Spinels (Sp)

Hematite (Hm)

Other

89 (GII)

8

0

3

0

Pc,Mw,Lm

61 (GI)

4

31

2

2

--

68 (GI)

5

21

2

3

--

73 (GII)

15

10

1

1

Lm

28

* GI/GII = aluminaocilicate glass (glass I or glass II); Pc = periclase: Mw = merwinite;

Lm = lime.

29

Table 3: Mixture Proportions and Properties of Freshly-Mixed Concrete for Mix No. 1 (EP1F) through Mix No. 16 (EP16F)

Mix

No.

W/(C+FA)

Water

(kg/m3)

Cement

Type

Cement

(kg/m3)

Fly Ash

Source

Fly

Ash

(kg/m3)

Coarse

Agg.

(kg/m3)

Fine

Agg.

(kg/m3)

AEA*

(mL/m3)

SP**

(L/m3)

Slump

(mm)

Unit

Weight

(Kg/m3)

Entraine

d Air

(%)

28-Day

Strength

Entrained

f'c

(MPa)

9

0.33

119

S

153

CC

212

1205

648

175

1.9

160

2345

5.3

34.5

10

0.33

120

G

153

CC

212

1205

648

75

2.1

140

2345

5.7

39.1

11

0.33

120

S

154

BC

214

1211

651

325

3.2

95

2360

4.8

28.7

12

0.33

120

G

153

BC

213

1203

647

335

4.2

135

2345

5.3

34.6

13

0.33

120

S

153

GO

212

1205

647

290

2.4

120

2360

5.7

33.5

14

0.33

119

G

152

GO

211

1202

645

200

3.7

100

2330

5.8

33.7

15

0.33

119

S

151

N

210

1195

642

280

3.0

100

2320

6.1

30.2

30

16 0.33 119 G 152 N 211 1199 644 210 3.4 125 2330 5.9 38.1

* Air-Entraining Admixture

** Superplasticizer

Table 4: Change in static Flexural strength Test After Fatigue testing for Mixture No. 9 to No. 12 (EP9F to EP12F)

Mix No.

(1)

Specimen No.

(2)

Maximum

Stress in

Fatigue (psi)

(3)

f

f

r

max

(4)

Static Flexure

Stress After

Fatigue (psi)

(5)

Static Flexure

Stress Before

Fatigue (psi)

(6)

Change in

Stress,

Percent

(5) - (6)

EP9F

12

443

0.45

704

977

-27.9

13

499

0.51

746

977

-23.6

14

440

0.45

814

977

-16.7

16

439

0.45

778

977

-20.4

17

447

0.45

867

977

-11.3

EP10F

14

459

0.56

792

827

-4.3

31

16

458

0.55

731

827

-11.6

17

420

0.51

775

827

-6.3

18

419

0.51

652

827

-21.2

EP11F

13

423

0.50

815

844

-3.4

14

440

0.52

647

844

-23.3

15

440

0.52

715

844

-15.3

17

437

0.52

684

844

-19.0

EP12F

13

435

0.51

771

870

-11.4

14

433

0.50

750

870

-13.8

15

431

0.50

781

870

-10.2

16

429

0.50

710

870

-18.4

18

436

0.51

692

870

-20.5

32

Table 4 (cont'd): Change in Static Flexural strength After Fatigue Testing for Mixture No. 13 to No. 16 (EP13F to EP16F)

Mix No.

(1)

Specimen

No.

(2)

Maximum

Stress in

Fatigue (psi)

(3)

f

f

r

max

(4)

Static

Flexure

Stress

After

Fatigue

(psi)

(5)

Static Flexure

Stress Before

Fatigue (psi)

(6)

Change in

Stress,

Percent

(5) - (6)

EP13F

7

369

0.45

672

817

-17.7

8

372

0.46

496

817

-39.3

9

371

0.45

613

817

-25.0

10

373

0.46

554

817

-32.2

EP14F

5

361

0.45

650

801

-18.9

6

356

0.44

688

801

-14.1

7

355

0.44

721

801

-10.0

8

360

0.45

676

801

-15.6

9

357

0.45

703

801

-12.2

EP15F

5

419

0.56

742

754

-1.6

11

420

0.56

722

754

-4.2

13

460

0.61

756

754

0.3

15

454

0.60

653

754

-13.4

17

446

0.59

662

754

-12.2

EP16F

13

460

0.59

694

774

-10.3

14

468

0.60

847

774

9.4

15

461

0.61

773

774

-0.1

16

468

0.60

719

774

-7.1

17

389

0.50

772

774

-0.2

33

f max. = maximum flexural fatigue stress at two million cycles of loading