effects of various fineness moduli of fine

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Journal of the Chinese Institute of Engineers, Vol. 24, No. 3, pp. 289-300 (2001) 289

EFFECTS OF VARIOUS FINENESS MODULI OF FINE

AGGREGATE ON ENGINEERING PROPERTIES OF

HIGH-PERFORMANCE CONCRETE

Ta-Peng Chang1* Shi-Hong Lin1,2 Huang-Chin Lin1 Ping-Ru Lin31Depar tment of Construct ion Engineering

Nat ional Taiwan University of Science and Technology

Taipei, Taiwan 106, R.O.C.2Department of Civil Engineering

Nanya Col lege of Technology

Chung-Li, Taiwan 320, R.O.C.3Department of Civil Engineering

Tung Nan Institute of Technology

Taipei, Taiwan 222, R.O.C.

Key Words: fineness modulus, fine aggregate, high-performance

concrete.

ABASTRCT

The effects of various fineness moduli (FM) of fine aggregate on

the engineering properties of high-performance concrete (HPC) were

studied. Two kinds of coarse aggregates (stiff and soft) and three kinds

of fine aggregates (FM=3.24, 2.73 and 2.18) were used. The results

indicate that the slump and flowability for all fresh concrete in this

study right after mixing are between 265 and 280 mm, and 670 and 790

mm , respectively. The compressive strengths at the age of 28 days

range from 60.2 to 68.7 MPa (stiff coarse aggregate), and 42.0 to 46.0

MPa (soft coarse aggregate), respectively. The corresponding moduli

of elasticity are in the range between 27.5 and 29.1 GPa (stiff aggre-

gate), and 23.4 and 25.2 GPa (soft aggregate), respectively. Using the

same concrete mixture, the coarsest fine aggregate (FM=3.24) has bet-

ter positive effects on the properties of the fresh and hardened HPC.

*Correspondence addressee

I. INTRODUCTION

At an early stage of development in the 1980s,

the high-performance concrete (HPC) was regarded

as a concrete that had many advantageous engineer-

ing properties such as high strength, high modulus of

elasticity, high workability, low permeability, etc.

(Mehta, 1999). During the progress of HPC

development, various definitions for HPC have been

given (Russels, 1999). Due to its versatile features,

there has not appeared a conclusive definition of HPC

that is unanimously accepted by the worldwide con-

crete society. However, some necessary requirements

of HPC have been regarded as the most essential parts

in the meaning of HPC, such as high workabality, easy

pumpability without segregation, sufficient strength,

proper durability, etc. In addition, through interven-

ing years of research, the basic amounts of some of

the ingredients required by HPC have also become

commonly known. For example, the volumetric


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290 Journal of the Chinese Institute of Engineers, Vol. 24, No. 3 (2001)

proportion of aggregates in HPC is in the range of 60

to 70% of concrete, and the fine aggregate occupies

about 40 to 60% of the volume of the aggregate mix-

ture (Mehta and Aitcin, 1990; Feraris and Lobo, 1998;

Mailer, 1994; Chan et al. 1999). The effects of the

engineering properties of coarse aggregates on theelastic properties of HPC have been commonly re-

ported (Aitcin and Mehta, 1990; Baalbaki et al., 1991;

Zhou et al., 1995). On the other hand, the literature

on the subject of the influence of the characteristics

of fine aggregates on the properties of HPC is limited.

Kronlof (1994) considered the effect of fine

aggregate, which consists of 63.3% by weight of 0.5

- 6.0 mm aggregate particles and 36.7% of 0.0001- 0.

5 mm quartz powders, on the water requirement and

strength evolution of the superplasticized concrete.

The water requirement for constant workability fell

sharply with the increasing amount and fineness ofthe very fine aggregate, and the concrete strength in-

creased with the increase of quartz powders. Ahmed

and El Kourd (1989) reported that water demand in-

creased rapidly with increase of the very fine sand

(VFS), which denoted the sand passing a No. 200 (75

m) sieve. But the compressive strength of concrete

also decreased linearly with the increase of VFS at a

constant slump of 100 mm.

According to ASTM, the fineness moduli for

most concrete range between 2.3 and 3.2. Some of

the finer particles passing through a #50 sieve are

usually needed in order to retain the cohesion and

flowing ability of concrete. However, the finer the

fineness modulus is, the more the cement paste is re-

quired to maintain the workability of fresh concrete

and the lower the flowability of concrete will be

(Mehta and Monteiro, 1993). In general, the coarser

fine aggregate has a smaller surface area and will not

compete with the finer binding constituents of

concrete, such as cement, fly ash and blast furnace

slag, to consume water during the hydration stage.

Meanwhile, it is unanimously understood that fine

aggregate with a higher fineness modulus is benefi-

cial to the workability and strength of HPC. However,

there is still a lack of enough experimental data tospecifically and quantitatively provide sound justifi-

cation on this particular subject. Thinking along this

line, in this study, fine aggregates with three differ-

ent values of fineness moduli (FM=3.24, 2.73, 2.18)

incorporating two kinds of coarse aggregates (hard

and soft) were used to investigate their effects on the

properties of the fresh and hardened HPCs.

II. EXPERIMENTAL PROGRAM

1. Material Properties and Specimen Casting

The constituents of HPC in this study are given

as follows:

(i) Type I Portland cement complying with CNS 61

and ASTM C 150 Specifications with a specific

gravity of 3.15;

(ii) Coarse aggregates from both crushed sandstonedenoted by CA1 and crushed brick denoted by

CA2.;

(iii)Fine aggregates from river siliceous sands with

three different values of fineness moduli denoted

by FA1 (F.M.=3.24), FA2 (F.M.=2.73) and FA3

(F.M.=2.18), respectively;

(iv)Type F fly ash from local fossil fuel power plants

complying with ASTM C 618 specification with

a specific gravity of 2.29;

(v) Ground blast-furnace slag from a local steel mill

complying with ASTM C 989 specification with

a specific gravity of 2.87;(vi)Type G superplasticizer in liquid form from the

local manufacturer with a specific gravity of

1.20.

The mechanical properties for coarse and fine

aggregates are given in Table 1. The compressive

strengths of coarse aggregates in Table 1 were tested

and determined by volume-average compressive

strength (Chang, 1996a). 70 individual particles of

coarse aggregate were used in the test. The results of

sieve analysis for both aggregates are given in Table

2. The mix proportioning of high-performance con-

crete follows the concepts of the so-called Least-

void method (Chang, 1996b). A water/binder ratio

(W/B) of 0.31 and a water/cement ratio (W/C) of

0.454 were used. The percentage of replacement of

cement with blast furnace slag in the binder is 5%,

and that of fine aggregate with the fly ash in the ag-

gregate packing is 13%. Final mix proportions of

HPC are summarized in Table 3. There are six sets

of concrete mix proportions, S-series (S1, S2 and S3)

using crushed sandstone and SB-series (SB1, SB2 and

SB3) using crushed brick. Due to the high percent-

age of absorption (about 9.0%), the pieces of crushed

brick were saturated in water for about an hour, andthen sifted out of the water until they were in the satu-

rated-surface dry condition (SSD) right before they

were used in the concrete specimen casting. Although

the percentage of absorption of the crushed sandstone

was low of about 1.3%, these crushed pieces of sand-

stone were also kept in an SSD condition by water

soaking and then sifting. The main purpose of keep-

ing these coarse aggregates in an SSD condition in

casting the concrete specimen is to avoid any addi-

tional absorption of either water or superplasticizer

in the cement paste by coarse aggregates during the

fresh concrete stage. All concrete specimens werecast in the 100 mm by 200 mm steel module. 24


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T.P. Chang et al.: Effects of Various Fineness Moduli of Fine Aggregate on Engineering Properties 291

hours after the concrete casting, the steel module was

disassembled and the concrete specimens were stored

in lime water until about one day before the testing.

The wet specimen was then left in the atmosphere for

air drying for about 24 hours before the relevanttesting was performed.

2. Testing Program

The properties of concrete investigated in this

study included slump, slump flow (flowability), unit

weight, compressive strength, splitting tensilestrength, static modulus of elasticity and Poissons

Table 1 Mechanical properties of coarse and fine aggregates

Coarse aggregate Fine aggregate (river sand)

Designation Designation

Item CA1 CA2 FA1 FA2 FA3

(Sandstone) (Brick)

Dmax(mm) 9.52 9.52 4.75 4.75 4.75

Specific gravity (SSD) 2.64 2.07 2.65 2.64 2.59

Absorption (%) 1.3 9.0 1.85 1.90 2.10

Unit weight (kg/m3) 1522 1229 1761 1741 1601

Passing #50 sieve (%) 0.0 0.0 8.6 17.8 30.0

Fineness modulus (FM) 6.32 6.32 3.24 2.73 2.18

Compressive strength (MPa) 93.55* 42.37*

Modulus of elasticity (GPa) 51.04# 21.80$

Notes: *volume-average compressive strength (Chang, 1996a).#100200 mm cylindrical drilled rock specimen.$

5050100 mm prim specimen.

Table 3 Concrete mix proportions

CA1 Crushed sandstone (kg/m3) CA2 Crushed brick (kg/m3)

Component S1 S2 S3 SB1 SB2 SB3

(+FA1) (+FA2) (+FA3) (+FA1) (+FA2) (+FA3)

Coarse aggregate 751 751 751 589 589 589

Fine aggregate 980 976 958 980 976 958Fly ash 146 146 146 146 146 146

Slag 19 19 19 19 19 19

Cement 353 353 353 353 353 353

Water 139.9 138.6 134.7 139.9 138.6 134.7

Superplasticizer 20.7 22.0 25.9 20.7 22.0 25.9

Table 2 Sieve analysis of aggregates

Fine aggregate

Sieve # FA1 FA2 FA3

Sieve # Retaining % Retaining % Retaining % Retaining %

1-1/2" #4

1" #8 11.6 8.9 4.0

3/4" #16 36.5 22.2 12.1

1/2" 4.0 #30 27.8 25.6 22.2

3/8" 33.7 #50 15.7 25.5 31.7

#4 56.8 #100 5.9 11.8 19.4

#8 5.5 Pan 2.7 6.0 10.6

F.M. 6.32 F.M. 3.24 2.73 2.18

Coarse aggregate


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ratio, and dynamic modulus of elasticity and Poissons

ratio tested by the Resonant Frequency Tester. The

slump and slump flow (flowability) of the fresh

concrete right after concrete mixing was measured.

Afterwards they were monitored at intervals of 30

minutes for two hours. Unit weight and compressivestrength of the hardened concrete specimens were

measured at the ages of 7, 28, 56 and 120 days. The

static and dynamic moduli of elasticity and Poissons

ratios were measured at the age of 56 days. The

ASTM C 469 standard compressive test and ASTM

C 496 splitting tensile test were used. The static chord

modulus of elasticity directly measured from the com-

pressive stress-strain curve of concrete specimens

according to the ASTM C469 standard test method

was used.

III. THEORETICAL CONSIDERATION

1. Unit Weight and Packing Structure of Aggre-

gates

High-performance concrete (HPC) is a mixture

of aggregates, cement, mineral admixture, chemical

admixture and water. The unit weight of fresh HPC

can be regarded as composed of two parts: the solid

par t of aggregates and the o ther f lu id par t ,

cementitious paste. The specific gravities for both

normal coarse and fine aggregates range between

about 2.5 and 2.7, which are higher than those for the

cementitious paste ranging from about 1.9 to 2.1 in

this study. Therefore, the more aggregates used in a

unit volume of concrete, the heavier the unit weight

of concrete will be. In order to reach this goal, a

maximum packing density of the granular aggregate

is required. The porosity of a granular mixture with

such densest packing density allows the use of the

least possible amount of cementitious paste in the

HPC. Various theoretical models have been proposed

to predict the packing density of a granular mix, such

as Linear Density Packing Model (Stovall et al.,

1986), Solid Suspension Model (de Larrard et al.,

1994), etc. (Johansen et al., 1991). A detailed de-scription and discussion of these rather complicated

models is surely beyond the scope of this paper.

However, these theoretical models clearly indicate

that the density and porosity of the aggregate mix-

ture solely depend on its characteristics of mixture,

such as the maximum aggregate size (MAZ), the size

gradation and shape of aggregates. A well-graded

aggregate mixture with a coarser MAZ usually has a

higher density. In practical application, the fineness

modulus (FM) of aggregate, which is computed by

adding the cumulative percentage of aggregate re-

tained on each sieve in a set of ten standard sievesand dividing by 100, is commonly used to reflect this

characteristic. The value of FM is a very importantindex to calculate the amount of coarse aggregate in

a unit volume of concrete by the well-known ACI 211.

1 Standard Practice for Selecting Proportions for

Normal, Heavy Weight and Mass Concrete. As shown

in Fig. 1, by the ACI 211.1 Standard, the amount of

fine aggregate in a unit volume of concrete is in-

creased by increasing the FM values and decreasing

the MAZ values. Thus the density of a fine aggre-

gate mixture will be increased by the increase of its

FM values, which has been confirmed by the experi-

mental results in this study as is shown in the later

discussion.

2. Influence of Coarse Aggregate on the Modulus

of Elasticity of Concrete

By considering concrete as a two-phase compos-

ite material composed of the coarse aggregate and the

mortar, various analytical models have been proposed

to predict the theoretical values of the modulus of

elasticity of concrete, e.g., the Voigt Model, Reuss

Model, Counto Model, Hashin Model, etc. (Mindess

and Young, 1981). By assuming the mortar as the

matrix and the coarse aggregate as the inclusion in a

composite material, an analytical equation, based onmicromechanics, to predict the modulus of elasticity

of concrete has been published as follows (Yang, et

al., 1995):

C = {C 1

+f[ (1f)(C C*) Sf(C C

*)

+C] 1(C C

*)C

1}

1(1)

where C , C andC*

are the tensors of material elas-

tic constants for the concrete, matrix and coarse

aggregate, respectively; S is the Eshelby tensor;fis

the volumetric fraction of coarse aggregate. Basedon Eq. (1), a computer program using FORTRAN

Fig. 1 FM of fine aggregate verse volume of coarse aggregate

based on ACI 211.1


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language was written for calculating the global modu-

lus of elasticity of a composite material at various

conditions. Thus the relation among the volumetric

fraction f, the ratios of Ec/Emand Ea/Em, where Ec,

EmandEaare the moduli of elasticity for the concrete,

mortar and coarse aggregate, respectively, can be

shown in Fig. 2. From Fig. 2, it is obvious that the

more stiff coarse aggregate used in the concrete, the

higher the modulus of elasticity of concrete will be.

This analytical result will be verified experimentally

later in this study.

IV. RESULTS AND DISCUSSION

Average values of test results are presented in

Table 4. The effects of various fineness moduli of

fine aggregate on the engineering properties of HPC

are addressed as follows:

1. Flowing Properties, Fresh Stage

Although a very low value of water/binder ratio

(W/B) of 0.31 was used, an HPC with a high

flowability and workability could still be reached

using the proper amount of mineral admixture andsuperplasticizer. The experimental data on slump and

flowability for all six sets of concrete mixtures indi-

cate a satisfactory flowing consistency and high-

workability of fresh concrete as shown in Table 4,

Figs. 3 and 4. Their slumps and values of flowability

range from 265 to 280 mm, and from 670 to 790 mm,

respectively, right after the concrete was well mixed.

Even after 2 hours, these two values still range from

235 to 260 mm, and from 570 to 610 mm. It is noted

that, for the HPC with crushed sandstone (S-series),

the highest values of slump appear at 30 minutes

after the concrete mixing. These beneficial effectson the workability could be attributed to the slag s

ability to retain the free water, during the early ce-

ment and water mixing stage, without participating

in the early hydration process of the cement paste.

However, this situation was not observed for HPC

with crushed brick (SB-series) due to its higher ab-

sorption capacity (9%). By using crushed brick pieces

as the coarse aggregates, the fresh SB-series HPC with

the finer fine aggregate (FM=2.18) reveals a biggerslump loss of 45 mm in two hours than that of 25

mm, using the larger fine aggregate (FM=3.24).

However, for the S-series HPC with crushed sand-

stone as coarse aggregates, the slump loss within the

same time period is only 10 mm, using either coarser

or finer fine aggregate. A similar trend is also

detected in the flowability of fresh HPC but with rela-

tively less influence as shown in Table 4 and Fig. 4.

There was no segregation nor bleeding found through-

out the slump test. In order to obtain a comparable

slump and flowability, both S-series and SB-series

HPCs with finer fine aggregates (FM=2.18) and thehigher percentage of finer particles passing through

Fig. 2 Influence of Ea and f on the modulus of elasticity of con-

crete Ec

Fig. 3 Variation of slumps for fresh concrete at different times

Fig. 4 Variation of flowability for fresh concrete at different time

intervals


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a #50 sieve require more dosage of superplasticizer

as shown in Table 4 and Fig. 5. The figure shows

that the percentages of superplasticizer are 4%, 4.25%

and 5% for coarse sand (S1), medium sand (S2) and

fine sand (S3), respectively. The finer the fine ag-

gregate is, the more superplasticizer in HPC is re-

quired to maintain its high workability. The require-

ment for a higher dosage of superplasticizer for HPCwith finer fine aggregate could be also attributed to

the higher percentages of fine aggregate that passes

through the #50 sieve, which are 8.6% (S1), 17.8%

(S2) and 30% (S3), respectively. SB-series test re-

sults show similar numbers.

2. Unit Weights

Figure 6 shows the relationship between the unitweights of hardened HPC and ages. Unit weights

Table 4 Average values of test results

Item Age S1 S2 S3 SB1 SB2 SB3

Slump 0 min. 270 270 265 275 280 280

(mm) 30 min. 275 270 270 270 270 275

60 min. 270 270 265 260 270 27090 min. 265 260 260 250 260 260

120 min. 260 260 255 250 245 235

Flowability (mm) 0 min. 740 730 670 730 790 750

30 min. 700 700 650 700 750 710

60 min. 680 670 620 670 715 650

90 min. 650 630 590 650 660 615

120 min. 610 600 570 610 600 590

Unit weights 7 days 2410 2397 2367 2242 2219 2182

(kg/m3) 28 days 2421 2408 2372 2255 2239 2197

56 days 2424 2404 2375 2257 2240 2198

120 days 2427 2405 2377 2267 2252 2203

Compressive 7 days 50.0 48.0 44.0 36.3 34.3 27.0

strength 28 days 68.7 66.6 60.2 46.0 44.8 42.0

(MPa) 56 days 77.0 76.6 68.0 52.0 51.7 45.4

120 days 82.3 81.6 71.3 58.1 57.8 49.7

fsp (MPa) 28 day 3.51 3.46 2.73 3.01 2.55 2.53

Ed(GPa) 56 days 43.0 41.6 42.5 30.6 29.7 27.6

vd 56 days 0.33 0.33 0.30 0.29 0.30 0.30

Ed (GPa) 120 days 45.7 42.9 42.5 32.9 32.1 28.9

vd 120 days 0.30 0.31 0.31 0.30 0.29 0.28

Es(GPa) 56 days 29.1 28.6 27.5 25.2 24.4 23.4

vs 56 days 0.20 0.24 0.18 0.19 0.25 0.21

Es(GPa) (Eq. (2)) 56 days 45.03 44.36 41.04 33.25 32.78 29.86

Cement efficiency 7 days 0.141 0.135 0.125 0.103 0.097 0.077

(MPa/kg) 28 days 0.194 0.189 0.171 0.130 0.127 0.119

56 days 0.218 0.217 0.192 0.147 0.146 0.129

120 days 0.233 0.232 0.202 0.165 0.164 0.141

Binder efficiency 7 days 0.098 0.092 0.085 0.070 0.067 0.052

(MPa/kg) 28 days 0.132 0.132 0.117 0.089 0.086 0.081

56 days 0.149 0.148 0.131 0.100 0.100 0.087

120 days 0.159 0.158 0.137 0.112 0.112 0.096

Notes:fsp=splitting tensile strength; Ed=dynamic modulus of elasticity; vd=dynamic Poissons ratio; Es=static

modulus of elasticity; vs=static Poissons ratio.


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increase with the increase of concrete ages from 7 to

120 days. The unit weights at 28-day for S-series

HPC are in the range between 2372 and 2421 kg/m3,

which is close to that of normal strength concrete,

2400 kg/m3. For the SB-series HPC, due to the lighter

specific gravity of 2.06 for its soft coarse aggregate,

lighter unit weights in the range from 2182 to 2267

kg/m3 are shown. The theoretical explanation forthe unit weight of aggregate mixture as stated previ-

ously in this study and Fig. 1 have indicated that

a fine aggregate mixture with a larger MAZ will

have a denser packing density. This is confirmed

by the increase of unit weight of fine aggregate

mixture from 1601 to 1761 kg/m3for three different

FM values as shown in Table 1. Fig. 6 also shows

that the HPC using coarser fine aggregate will

have higher unit weights because of the denser pack-

ing existing in the aggregate packing that is made

of the coarser fine aggregate. This result matches

previously published data (Domone and Soutsos,1994).

Fig. 5 Ratios of superplasticizer to binder and particle passing a

#50 sieve

Fig. 6 Unit weights at various curing ages

Fig. 7 Typical uniaxial compressive stress-strain curves for S-se-

ries HPC

Fig. 8 Typical uniaxial compressive stress-strain curves for SB-

series HPC

3. Compressive Strengths

Typical stress-strain curves of the uniaxial

compressive tests for both S-series and SB-series are

shown in Figs. 7 and 8. Both Fig. 7 and Fig. 8 show

that the strains at maximum loads for both HPCs arein the range between 0.0028 and 0.0034. The 28-day

compressive strengths of concrete in the S-series and

SB-series HPCs range from 60.2 to 68.7 MPa and 42

to 46.0 MPa, respectively, as shown in Table 4 and

Fig. 9. Table 4 shows that both concrete mixtures S1

and SB1, which incorporate the coarsest fine

aggregates, have the highest compressive strengths.

The difference between the highest and the lowest

compressive strengths in each individual mixture se-

ries is about 10%. Since the higher compressive

strength of coarse aggregate of 71.86 MPa used in

the S-series specimen, which is about 69.6% higherthan that of 42.37 MPa in the SB-series specimen,


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the increase of corresponding concrete strengths is

substantially raised by between 41.2 and 49.8 % for

the concrete ages of 28, 56 and 102 days, respectively.

The significant influence of the engineering proper-

ties of coarse aggregates on the compressive strength

of HPC is appreciated. The ratios of the 7-day com-

pressive strength to the 28-day range from 0.72 to

0.73 for S-series HPC, and 0.64 to 0.79 for SB-series

as shown in Table 4 and Fig. 9. Both ranges areslightly higher than the common value of about 0.67

for normal concrete (Mehta and Monteiro, 1993).

W i t h t h e a d d i t i o n o f m i n e r a l a d m i x t u r e ,

superplasticizer and the low water/cement ratio, HPC

tends to obtain higher early strength. Except for the

compressive strength at 7 days, Fig. 10 shows that

the ratios between compressive strengths of S-series

and SB-series HPCs at ages of 28, 56 and 120 days

are in the range of 1.4 and 1.5 for concrete with these

three kinds of fine aggregates. It indicates that the

variation of FM values of fine aggregate has less ef-

fect than the variations of strength of coarse aggre-gate on the strength gain of HPCs. As expected, the

compressive strength of HPC seems also increased

with the increase of the unit weight as shown in Fig.

11.

4. Splitting Tensile Strengths

Figure 12 shows the splitting tensile strengths

and the their strength ratios to the corresponding com-

pressive s trengths for the two series of HPC

specimens. In the S-series, the splitting tensile

strengths for HPCs with FA1, FA2 and FA3 fine ag-gregates are 3.51, 3.46 and 2.73 MPa, respectively,

which indicates that an HPC incorporating coarser

fine aggregates has a better chance of obtaining a

higher splitting tensile strength. It is interesting to

note that the ratios of the splitting tensile to the

corresponding compressive strength for these three

types of HPC are the same, 0.05. Therefore, the val-

ues of fineness moduli of fine aggregates affect the

compressive strengths as well as the splitting tensile

strengths of HPC in a similar manner. There is no

additional gain in the splitting tensile strengths due

to the variation of fineness modulus in the HPCs.When the strength of mortar is higher than that of

Fig. 9 Compressive strengths at various curing ages

Fig. 10 Ratio between strengths at different ages

Fig. 11 Compressive strengths at various unit weights of HPC

Fig. 12 Splitting tensile strength and strength ratios


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coarse aggregate in HPC, this kind of effect is stillsimilar as shown in Fig. 12 for the SB-series HPCs

where the strength ratios are in the slightly higher

range between 0.06 and 0.07 due to the low compres-

sive strengths. Therefore the variations of the fine-

ness moduli of fine aggregate and the strengths of

coarse aggregate have insignificant effects on the ra-

tios of splitting tensile strength to compressive

strength in HPC. It is also noted that these strength

ratios are much lower that those between 0.08 and

0.14 for most normal strength concrete (Metha and

Monteiro, 1993). For this reason, concerning HPC,

one needs to realize that the ratio of increase of split-ting tensile strengths with the lapse of age is not in a

linear proportion with that of the compressive

strengths.

5. Modulus of Elasticity and Poissons Ratio

The static moduli of elasticity of S-series and

SB-series HPCs range from 27.5 to29.1 GPa, and

23.4 to 25.2 GPa, respectively as shown in Table 4

and Fig. 13. Obviously, the higher strength of coarse

aggregate and the coarser fine aggregate in HPC as

well as the higher compressive strength result in

higher values of the modulus of elasticity. Fornormal strength concrete, in general, the modulus of

elasticity of concrete, Ec, is proportional to the

compressive strength c , and the density of the con-

crete as indicated in ACI code (ACI 318-95) by the

following equation:

Ec = 431.5(fc)

0.5 10

6GPa (2)

where and c are expressed in kg/m3 and MPa,

respectively. This equation predicts rather high

values for modulus of elasticity as shown in Table 4.

Therefore, it seems not applicable to the HPCs in ourcurrent study. Since the average specific gravity of

aggregate mixture is about 2.7, compared with that

of about 2.17 for hardened cement paste using a W/C

value of 0.454, a concrete with the larger unit weight

must contain a higher volumetric proportion of ag-

gregate in the concrete. This implies that, for the spe-

cific size gradation of coarse aggregates (Dmax=13

mm) used in this study, the coarse aggregate mixture

incorporating the coarser fine aggregates (FM=3.24)

has a denser packing structure. From Table 4, it is

noted that both the S-series and SB-series HPCs with

the coarser fine aggregate (FM=3.24) have the larger

unit weight of concrete in the individual group. As a

result, the increase of the unit density of aggregate

packing in concrete will increase the strengths as well

as the modulus of elasticity for HPC. But it seems

not to affect the Poissons ratio as shown in Table 4.

The measured dynamic moduli of elasticity, Ed, for

S-series and SB-series HPCs at the age of 56 daysrange from 41.6 to 43.0 GPa, and 27.6 to 30.6 GPa,

respectively. In comparison with the static modulus

of elasticity, the dynamic values are about 50% higher

for S-series HPC and 30% higher for SB-series HPC

in the current study. It is interesting to note that, in

general, the dynamic modulus of elasticity is usually

20 to 30 percent higher than the static modulus of

elasticity for high- and medium-strength concretes

(Metha and Monteiro, 1993). The dynamic modulus

of elasticity is measured by resonant vibration on the

end surface of a concrete specimen by a pick-up de-

vice while a driving exciter is placed against the other

end surface to exert vibration through a Resonant

Frequency Tester. The exciter is driven by a vari-

able frequency oscillator with a range of 100 to 10000

Hz. The wave propagating speed as well as the fun-

damental resonant frequency of a concrete specimen

may be strongly increased by the increase of the

modulus of elasticity of the medium along the straight

line between the driving point on one end surface and

the pick-up point on the other end surface. Whether,

incidentally, a pile of stiffer coarse aggregate is

aligned along the wave propagating line or some other

cause exists such that rather higher values of dynamic

modulus of elasticity for the S-series HPC occurredin this study might require further through study. The

increase ofEdfrom the age of 56 days to 120 days is

less than 10% for both HPCs. Substituting the val-

ues off=0.285, Ea=51.04 GPa for S-series specimen,

Ea=21.8 GPa for SB-series specimen and Em=22.91

GPa into Eq. (1) gives the values of Ec=28.50

( S - s e r i e s ) a n d Ec= 2 2 . 5 9 G P a ( S B - s e r i e s ) ,

respectively. The analytical result matches the ex-

perimental data for S-series specimens in Table 4

quite well. For the SB-series specimens, there exists

an average discrepancy of about 7%, which may still

be reasonable from the practical point of view.Both ACI code (ACI 363R-92) and European

Fig. 13 Static and dynamic moduli of elasticity at different ages


10/12


code (CEB-90) provide an empirical equation relat-

ing the modulus of elasticity to the compressive

strength of concrete shown as follows:

Ec = 3.32 fc + 6.9GPa(21MPafc 83MPa)(ACI363)

(3)

Ec = 10(fc + 8)1/3GPa(CEB 90) (4)

Both the values of dynamic and static moduli of

elasticity of HPC together with the values predictedby Eqs. (2) and (3) are shown in Fig. 14. The values

predicted by these two empirical equations seem to

be fit well with those dynamic moduli of elasticity.

Fig. 15 shows the values of static and dynamic

Poissons ratios for both S-series and SB-series HPCs.

The static and dynamic Poissons ratios for both HPCs

are in the range between 0.18 and 0.25, and 0.28 and

0.33, respectively. These values are higher than the

static Poissons ratios ranging between 0.15 and 0.2

for normal-strength concrete, but close to the values

ranging between 0.2 and 0.28 for high-strength con-

crete (Metha and Monteiro, 1993). The variation of

fineness modulus of fine aggregate seems to havelittle effect on the Poissons ratio of HPCs.

6. Efficiency Indices of Cement and Binder

The efficiency index of cement and binder in

units of MPa/kg is defined as the ratio of the 28-day

compressive strength of HPC to the amount of ce-

ment and binder used in the units of kg per cubic meter

of HPC. These indices are used to indicate the effec-

tiveness of the cement or binder used in concrete pro-

portioning to develop its compressive strength. The

higher the efficiency index of cement is, the smallerthe amount of cement is needed to reach the required

concrete strength. For traditional normal-strength

concrete, the efficiency of cement is as low as 0.069

MPa/kg at the age of 28 days (Metha and Monteiro,

1993).. In this study, the efficiency indices of ce-

ment for S-series and SB-series HPCs at age 28 days

range from 0.171 (S3) to 0.194 (S1) MPa/kg, and

0.119 (SB3) to 0.130 (SB1) MPa/kg, respectively, as

shown in Table 4 and Fig. 16. Therefore, both the

strength of coarse aggregate and the coarser fine ag-

gregate result in a higher efficiency index for cement.

A similar trend can be seen for the efficiency indexof binder in either S-series or SB-series HPC as shown

in Table 4.

V. CONCLUSIONS

Based on the experimental data and discussion

presented in this study, the following conclusions can

be drawn:

1. By using finer fine aggregates, the HPC with

crushed porous brick pieces has a larger slump loss

of fresh concrete in two hours than that usingcoarser fine aggregate. For concrete with dense

Fig. 14 Estimated and experimental static and dynamic moduli of

elasticity

Fig. 15 Static and dynamic Poissons ratios for HPCs

Fig. 16 Efficiency indices of cement and binder at various ages


11/12


crushed sandstone, the slump loss is the same re-

gardless of the different fineness moduli of fine ag-

gregates in HPC. The effects of different fineness

moduli of fine aggregates on the loss of flowing

properties of HPC seem to be insignificant com-

pared with the increase of the density of the coarse

aggregate.

2. There is no additional gain in the splitting tensile

strength in HPC using coarser fine aggregate in con-

trast to compressive strengths where the coarser the

fine aggregate is, the higher the compressive

strength in HPC will be.

3. To achieve similar workability in fresh concrete,

HPC using smaller fineness modulus of fine aggre-

gates requires a bigger amount of superplasticizer

in the concrete mixing.

4. For the specific size gradation and maximum ag-

gregate size of coarse aggregates used in this study,the aggregate mixture incorporating the coarser fine

aggregates results in a denser packing structure. In

turn, the HPCs with a denser aggregate packing

have a 10% higher strength and modulus of

elasticity. Fine aggregate with fineness moduli in

the range of 2.18 and 3.24 seems to not substan-

tially affect the compressive strengths and moduli

of elasticity of HPC.

5. With the same fineness modulus and size grada-

tion of fine aggregate, stronger coarse aggregates

substantially increase the compressive strength and

modulus of elasticity of HPC, but have little effect

on the Poissons ratios.

6. Both the higher strength of coarse aggregate and

coarser fine aggregate in HPC result in higher ef-

ficiency index of the cement.

ACKNOWLEDGMENT

The authors are grateful to the National Sci-

ence Council of Taiwan, R.O.C., for sponsoring the

research project under the contract number NSC85-

2211-E-011-010 to the National Taiwan University

of Science and Technology.

NOMENCLATURE

CA1 Coarse aggregate (crushed sandstone)

CA2 Coarse aggregate (crushed brick)C Tensor of material elastic constants for the con-

crete

C Tensor of material elastic constants for the ma-

trixC*

Tensor of material elastic constants for the

coarse aggregate

Ea Modulus of elasticity for coarse aggregate

Ec Modulus of elasticity for concreteEm Modulus of elasticity for mortar

f Volumetric fraction

FA1 Fine aggregate FM=3.24



FM Fineness modulus of aggregate

HPC High performance concrete

MAZ Maximum aggregate size

S1 CA1 mix with FA1

S2 CA1 mix with FA2

S3 CA1 mix with FA3

SB1 CA2 mix with FA1



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Manuscript Received: Apr. 24, 1999

Revision Received: Aug. 03, 2000

and Accepted: Sep. 21, 2000

1 1,2 1 3

1 2

3

FM=3.24 2.73 2.18

265 280mm670 790mm28 60.2

68.7MPa 42.0 46.0MPa

27.5 29.1GPa 23.4 25.2GPa

(FM=

3.24)

effects of various fineness moduli of fine

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