Toughness of steel fiber reinforced silica fume concrete under compression.
Ramadoss, P. ; Prabakaran, V. ; Nagamani, K. 等
Introduction
Steel fiber reinforced concrete (SFRC) has gained acceptance for a
variety of applications, namely industrial floors, bridge decks,
pavements, hydraulic and marine structures, precast elements, nuclear
vessels, repair and rehabilitation works, blast resistance structures
[1, 2, 3]. Balaguru and Shah [1] and ACI Committee 544-1989 [3] have
reported that the addition of steel fibers into concrete improves all
engineering properties of concrete such as tensile strength, compressive
strength, impact strength, ductility and toughness. The improved
toughness in compression imparted by fibers is useful in preventing
sudden and explosive failure under static loading and in absorption of
energy under dynamic loading [3].
High-performance concrete (HPC) is achieved by using
super-plasticizer to reduce water-binder ratio and by using
supplementary cementing materials such as silica fume, which usually
combines high-strength with high durability [1]. Addition of fibers has
shown to improve ductility of normal and HSC/ HPC, particularly concrete
containing silica fume [4].
The demand for HSC/ HPC has been growing at an ever-increasing rate
over the past years, which lead to the design of smaller sections.
Reduction in mass is also important for the economical design of
earthquake resistant structures [10, 11]. ACI Committee 363-1992 [11]
reported that as the concrete strength increases for HSC, the post peak
portion of the stress-strain diagram almost vanishes or descents
steeply. The application of high-strength or high-performance concrete
in practice is severely limited by its more brittle behavior. However,
the brittleness of HSC/ HPC can be eliminated by the addition of
discrete fibers of small diameter in the concrete matrix [5, 6]. To
incorporate such improvement in structural design, it is necessary to
establish the complete stress-strain response of the resulting fiber
reinforced concrete. While the compressive strength is used for the
assessment of the structural components, the stress-strain curve is
needed to evaluate the toughness of the material.
Nataraja et al. [14] have generated the complete stress-strain
curve experimentally and proposed an analytical expression similar to
Ezeldin and Balaguru [15]), for SFRC using crimped fibers for
compressive strength ranging from 30 to 50 MPa. Equations were proposed
to quantify the effects of fibers on compressive strength, strain at
peak stress and toughness of concrete in terms of fiber reinforcing
index (RI). Mansur et al. [16] proposed an analytical model to generate
the complete stress-strain curve of high-strength fiber concrete with
strength ranges from 70 to 120 MPa derived from cylinders and
horizontally cast prisms. In their study, the toughness index is
determined as the ratio of the area under stress-strain curve up to a
strain of 3[[epsilon].sub.o] to the area up to a strain of
[[epsilon].sub.o]. Ramadoss and Nagamani [17] have generated the
complete stress-strain curve experimentally for high performance fiber
reinforced concrete in compression.
In the present study, an experimental work has been carried out to
study the complete stress-strain response and toughness of steel fiber
reinforced silica fume concrete (SFRSFC) with compressive strength
ranging from 52 to 75 MPa. Crimped fibers having an aspect ratio of 80,
with four fiber volume fractions of 0%, 0.5%, 1.0% and 1.5% (0, 39, 78
and 117.5 kg/[m.sup.3]) were used in this investigation. The variation
in concrete strength was achieved by varying the w/cm ratio with 10%
silica fume replacement. The influence of fiber content in terms of
fiber reinforcing index (RI) on compressive strength and toughness of
HSFRC, were investigated. Based on the test data, complete stress-strain
([sigma]-[epsilon]) curves have been drawn and toughness ratios
evaluated for steel fiber reinforced silica fume concrete.
Experimental Programme
Materials, Mixture Proportioning, and Preparation of Specimens
Ordinary Portland cement--53 grade, having 28-day compressive
strength = 54.5 MPa and fineness by Blaine's fineness by specific
surface = 245 [m.sup.2]/ kg, conforming to IS: 12269-1987 and silica
fume having fineness by specific surface area = 23000 [m.sup.2]/kg,
specific gravity = 2.25 were used. The chemical analysis of silica fume
(Grade 920-D) is: silicon dioxide = 88.7%, LOI at 975[degrees]C = 1.8%
and carbon = 1.8%, are conforming to ASTM C1240-1999, AASHTO M307--1990
and Canadian Standard Association 1986.
Fine aggregate of locally available river sand passing through 4.75
mm IS sieve, conforming to grading zone-II of IS: 383-1970 was used.
Sand has fineness modulus of 2.65, a specific gravity of 2.63 and water
absorption of 0.98 % @ 24 hrs. Coarse aggregate of crushed granite
stones with maximum size of 12.5 mm, conforming to IS: 383-1978 was
used. The characteristics of coarse aggregate are: Specific gravity =
2.70, Fineness modulus = 6.0, Dry rodded unit weight = 1600 kg/[m.sup.3]
and Water absorption = 0.65 % @ 24 hrs.
Superplasticizer of sulphonated naphthalene formaldehyde (SNF)
condensate as HRWR admixture conforming to ASTM Type F (ASTM C494) and
IS: 9103-1999, which has a specific gravity of 1.20, was used.
Crimped steel fiber conforming to ASTM A820-2001 has been used in
this investigation. Properties of crimped fibers (undulated) are: length
= 36 mm, diameter = 0.45 mm, aspect ratio = 80, ultimate tensile
strength, [f.sub.u] = 910 MPa and elastic modulus, Esteel = 2.1 x
[10.sup.5] MPa.
Mixtures were proportioned using guidelines and specifications
given in ACI 211.4R-1993 [7], and recommended guidelines of ACI
544--1995 [8]. Mixture proportions used in this test programme are
summarized in Table 1. This aspect of work has been carried out
elsewhere [13]. For each water--cementitious materials ratio (w/cm), one
plain concrete (silica fume concrete) mix, and three fibrous concrete
mixes having fiber volume fractions ([V.sub.f]) of 0.5, 1.0 and 1.5
percent by volume of concrete (39, 78 and 117.5 kg/[m.sup.3]) were
prepared. Superplasticizer with dosage range of 1.75 to 2.5% by weight
of cementitious materials (Cm = OPC + SF) has been used to maintain the
adequate workability of silica fume concrete and fiber reinforced
concrete mixes. Slump value obtained was 75 [+ or -] 25 mm for silica
fume concrete and Vebe value of 12 [+ or -] 3 sec. for fibrous concrete
mixes.
Eight series of fiber reinforced silica fume concrete mixes were
used in this investigation. Concrete was mixed using a tilting type
mixer and specimens were cast using steel moulds, and compacted by using
table vibrator. For each mix at least three 150 mm diameter cylinders
were prepared. Specimens were demoulded 24 hours after casting, and
water cured at 27 [+ or -] 2[degrees] C until the age of testing at 28
days. For maintaining uniform curing all the specimens were cured in the
same curing tank.
In mix designation FC1 * to FC4 *, silica fume replacement is 10
percent by weight of cementitious materials, after hyphen denotes fiber
volume fraction in percent.
Water present in Super plasticizer is excluded in calculating the
water to cementitious materials ratio (w/cm).
[V.sub.f] (%) denotes Steel fiber volume fraction in percent in
total volume of concrete.
Compressive strength test
Compressive strength tests were performed according to ASTM C
39-1992 [12] standards using 150 mm diameter cylinders loaded
uniaxially. Before testing, the cylinders were capped with a hard
plaster on the cast faces to ensure parallel loading faces of the test
specimens and constant height for all the cylinders. A compressometer
equipped with dial gauges available in the laboratory was used to record
the deformation of the cylinder. Efforts were made to take as many
readings as possible, to get considerable length of post-peak portion of
the stress-strain curve. In the descending portion readings were taken
at random intervals. Stresses and corresponding strains were evaluated
and average values are reported with the compressive strength ranges
from 52 to 75 MPa, as given in Table 4.
Results and Discussion
The shape of the stress-strain curve in uniaxial compression is
strongly affected by the testing conditions and concrete
characteristics. To minimize the testing condition effects, careful
attention was exercised to avoid variations in the testing setup and
specimen's instrumentation. Ultrasonic pulse velocity measurements
show the SFRC mixes having uniform mixing; compaction and fiber
distribution (Table 2). The stress-strain relationship of concrete
essentially consists of two distinct branches--an ascending branch up to
the peak stress followed by a descending branch until the concrete
crushes.
Compressive Strength ([f.sub.0])
Concrete strength was achieved in the range of 55-75 MPa, by
varying the water-cementitious materials ratio (w/cm) and fiber volume
fraction ([V.sub.f]) with 10% silica fume replacement, is presented in
Table 2. Figure 1 shows the effect of fiber reinforcing index (RI) on
compressive strength at 10% silica fume replacement. The peak
compressive strength [f.sub.o] or [f.sup.'.sub.cf] and the
corresponding strain [[epsilon].sub.0] depend on the response of the
specimen at ultimate load. At this stage, cracks will form in the
specimen due to lateral expansion of the concrete. Fibers aligned normal
to the loading direction will therefore, be intercepted by these cracks
and offer some resistance to their growth. The effect of fibers on the
compressive strength of concrete may be evaluated from the stress-strain
curves for fiber reinforced concretes. It may be seen from Table 2 that
the inclusion of fibers in silica fume concrete (plain concrete) results
in moderate increase in compressive strength.
[FIGURE 1 OMITTED]
A least square regression analysis was performed using the
experimental results to establish a possible relationship between the
peak compressive stress and the fiber-reinforcing index. The proposed
expression for the steel fiber reinforced silica fume concrete for
compressive strength ranging from 52 to 70 MPa is given as:
Compressive strength ([f.sub.o] or [f.sup.'.sub.cf])
[f.sup.'.sub.cf] = [f.sup.'.sub.c] + 1.397 (RI) (R= 0.95)
(1)
where [f.sup.,.sub.c] and [f.sup.,.sub.cf] are the compressive
strength of silica fume concrete (HPC) and SFRSFC, respectively in MPa.
RI = fiber reinforcing index.
The percentage variation in absolute value has been obtained as
3.35.
Stress-Strain Curves
The stress-strain response of silica fume and SFRC with compressive
strength ranging from 52 to 70 MPa has been investigated. Typical
stress-strain ([sigma]-[epsilon]) curve for silica fume concrete and
steel fiber reinforced concrete is shown in Fig. 2. Figures 3, 4 and 5
show the stress-strain ([sigma]-[epsilon]) curves for fiber reinforced
silica fume concrete in compression with different fiber volume
fractions ([V.sub.f]). It clearly shows (Figs. 3, 4, and 5) that the
post-peak segment of the [sigma]-[epsilon] curve is affected by the
addition of steel fibers. From the stress-strain curves generated in
this study, it can be observed that an increase in concrete strength
increases the extent of curved portion in ascending branch and renders
the drop in the descending part more steeper for non-fibrous concrete
and gradually flatter for SFRC. An increasing in the slope of the
descending part of the stress-strain curve is also observed by
increasing the fiber volume fraction. The gradual change in shape with
an increase in strength have, however, been reported on by many
investigators in the past. Previous researchers noticed that crimped and
hook end fibers are effective in improving the mechanical properties,
and energy absorption at post peak load capacity and ductility.
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
[FIGURE 4 OMITTED]
[FIGURE 5 OMITTED]
Modulus of Elasticity ([E.sub.c])
Modulus of elasticity (secant modulus) was defined according to ACI
Building code (ACI 318-1995) as the slope of the line drawn from a
stress of zero to a compressive stress of 0.45 [f.sup.,.sub.c].
The static modulus of elasticity evaluated from the stress-strain
curves are in the range of 29.68 x [10.sup.3] Mpa--41.06 x [10.sup.3]
MPa (Table 2). Results of modulus of elasticity obtained for various
concrete mixes show that modulus of elasticity increases with increase
in fiber volume fraction or fiber reinforcing index.
Based on the experimental results, using least square regression
analysis, the expression obtained for the elastic modulus ([E.sub.c]) as
a function of compressive stress is given as:
[E.sub.c] = 1515 [f.sub.o.sup.0.75] (R = 0.99) (2)
where secant modulus, [E.sub.c] and compressive strength, [f.sub.o]
are all expressed in megapascals.
The equation (2) gives the lower bound values for the steel fiber
reinforced concretes to that of ACI 318-1995, ACI 363-1992 and IS:
456-2000 recommended equations. On comparing the CEB-FIP model code
(1990) and BS code (BS: 8110) formulae for modulus of elasticity, the
proposed formula for modulus of elasticity gives the upper bound values.
Compressive Toughness
Toughness is a measure of the capability of the material to absorb
energy during deformation when subjected to compressive load, estimated
using the area under stress-strain curve. The energy absorption per unit
volume under compression is expressed mathematically as, Toughness =
[[integral].sup.[epsilon]] [sigma]. d[epsilon]
The convenient way to quantify ductility is to use toughness ratio,
TR (Fig. 6).
TR = Area (OABC)/ [f.sup.'.sub.cf] x 0.015 (3)
where Area(OABC) = area of OABC in stress-strain diagram (Fig. 6)
and [f.sup.,.sub.cf] = peak compressive strength of concrete.
Fanella and Naaman [5], Hsu and Hsu [4] have defined the toughness
index of FRC as the ratio of the toughness of FRC matrix to that of
unreinforced control matrix. Ezheldin and Balaguru [15] have proposed a
rigid plastic approach to define the toughness ratio. In the results
presented in this paper, the toughness is measured as the total area
under stress-strain curve up to a strain of 0.015 mm/mm, which is five
times the ultimate concrete strain of 0.003mm/mm as adopted in the ACI
building code 318-95 [18]. Fanella and Naaman [5], and Ezheldin and
Balaguru [15] have also used an ultimate strain of 0.015 for computing
the toughness as it is sufficient to represent the trend of post peak
behavior of SFRC. This toughness is compared to the toughness of a rigid
plastic material in the form of toughness ratio (TR) as indicated in
Fig. 4. It is observed in the present investigation that the area under
stress-strain curve increases with the increase in fiber content, and
fiber type and geometry (crimped steel fiber) compared with other fibers
used by previous researchers. To combine the effect of both fiber volume
fraction and their aspect ratio, the fiber reinforcing index, (RI =
[w.sub.f] * (l/d)) can be used as the fiber reinforcing parameter for a
given type of fiber. Weight fraction ([w.sub.f]) is approximately equal
to 3.27 times the volume fraction of fibers. The increase in fiber
reinforcing index, RI would yield a large area under the stress-strain
curve making a flatter descending part and a higher toughness ratio as
shown in Fig.2. Table 2 presents the experimental values of toughness
ratios for various SFRSFC. Nataraja et al. [14] have obtained maximum
toughness ratio of 0.77 for SFRC with w/c = 0.38 and RI = 2.67, which is
comparable with the experimentally calculated maximum value of 0.685 for
SFRC with w/cm = 0.25 and RI= 3.88.
[FIGURE 6 OMITTED]
A least square regression analysis was performed using the
experimental results to establish a possible relationship between the
toughness ratio of the concrete based on the stress-strain behavior and
fiber-reinforcing index as shown in Fig. 7. Results of this equation are
presented in Table 3 and the predicted values match with the values
computed from the experimental results. The proposed equations (linear
and nonlinear models) from the complete stress-strain behavior of the
steel fiber reinforced silica fume concrete for the compressive strength
ranges from 52 to 70 MPa are given as:
Toughness ratio of concrete ([TR.sub.f])
[TR.sub.f] = [TR.sub.c]+ 0.142 (RI) (R = 0.78) (4)
[TR.sub.f] = [TR.sub.c] + 0.03241 (RI) - 0.0548 [(RI).sup.2] (R =
0.98) (5)
where [TR.sub.c] and [TR.sub.f] are the toughness ratio of HPC and
SFRSFC, respectively.
The percentage variation in absolute value has been obtained as
2.56. The above equations can be used for reinforcing index (RI) up to
3.9 for the crimped steel fibers. The experimentally determined peak
stress-RI and toughness ratio-RI relationships are given in Figures 8
and 9 for SFRSFC with w/cm ratio = 0.40. It is observed from Figures 8
and 9 that toughness ratio as a function of RI increases as peak stress
increases.
[FIGURE 7 OMITTED]
[FIGURE 8 OMITTED]
[FIGURE 9 OMITTED]
Conclusions
Based on the experimental study, following conclusions can be drawn
from the compression response of steel fiber reinforced silica fume
concrete.
(1) Addition of crimped steel fibers to silica fume concrete (HPC)
chances the basic characteristics of its stress-strain response. The
slope of the descending branch increases with increasing the fiber
reinforcing index (RI).
(2) Compressive toughness and ductility are increased considerably
for steel fiber reinforced silica fume concrete. The increase in
toughness is directly proportional to the reinforcing index.
(3) A moderate increase in compressive strength, strain at peak
stress is also observed, which is proportional to the reinforcing index.
The expression proposed is valid for steel fiber reinforcing index
ranging from 0 to 3.9.
(4) The toughness ratio predicted based on the empirical equation
arrived based on the stress-strain curves, matches with values
calculated from the experimental results. The proposed expression is
giving good correlation with the experimental values.
Acknowledgement
The authors would like to thank the Structural Engineering Division
of Anna University, India for extending the facilities for the above
research work.
Notations
HPC = high-performance concrete
SFRSFC = steel fiber reinforced silica fume concrete
[f.sup.'.sub.cf] or [f.sub.o] = cylinder compressive strength
of SFRSFC, MPa
[f.sup.'.sub.c] = compressive strength of silica fume concrete
(HPC), MPa
[TR.sub.f] = toughness ratio of SFRSFC
[TR.sub.c] = toughness ratio of HPC
[V.sub.f] = volume fraction of fiber, percent
[w.sub.f] = weight fraction of fiber
l/d = aspect ratio of fiber
RI= fiber reinforcing index.
References
[1] Balaguru, N., and Shah, S.P. (1992), "Fiber reinforced
concrete composites", McGraw Hill International edition, New York.
[2] ACI Committee 544 (2006), "State-of-the-art report on
fiber reinforced concrete", ACI 544.1R-82, American Concrete
Institute, Detroit.
[3] ACI Committee 544 (1989), "Design considerations for steel
fiber reinforced concrete", ACI 544.4R-89, American Concrete
Institute, Detroit.
[4] Hsu, L.S., and Hsu, C.T.T. (1994), "Stress-strain behavior
of steel fiber reinforced high-strength concrete under
compression", ACI Structural Journal, 91(4), pp. 448-457.
[5] Fanella, D.A. and Naaman, A.E. (1985), "Stress-strain
properties of fiber reinforced mortar in compression",. ACI
Journal, 82(4), pp. 475-583.
[6] Ezeldin, A.S., and Balaguru, P.N. (1989), "Bond behavior
of Normal and high strength fiber reinforced concrete", ACI
Materials Journal, 86(5), pp. 515-523.
[7] ACI Committee 211 (1999), "Guide for selecting proportions
for High strength concrete with Portland cement and Fly ash", ACI
211.4R-93, ACI Manual of concrete practice.
[8] ACI Committee 544 (2006), "Guide for specifying, mixing,
placing and finishing steel fiber reinforced concrete", ACI
544.3R-93, American Concrete Institute, Detroit.
[9] ACI Committee 544 (2006), "Measurement of properties of
fiber reinforced concrete", ACI 544.2R-89, American Concrete
Institute, Detroit.
[10] Chin, M.S., Mansur, M.A., and Wee, Y.H. (1999), "Effects
of shape, size and casting direction of Specimens on Stress-strain
curves of high strength concrete", ACI Materials Journal, 94(3),
pp. 209-219.
[11] ACI Committee 363 (1992), "state-of-the-art report on
high strength concrete", ACI 363-1992, American Concrete Institute,
Detroit.
[12] ASTM C39--1992, "Standard test method for compressive
strength of fiber reinforced concrete", Annual book of ASTM
standards. American Society for Testing and Materials.
[13] Ramadoss, P., and Nagamani, K. (2008), "A new strength
model for high-performance fiber reinforced concrete", Computers
and Concrete--an International Journal, 5(1), pp. 21-36.
[14] Nataraja, M.C., Dhang, N., and Gupta, A.P. (1999),
"Stress-strain curve for steel fiber reinforced concrete in
compression", Cement and Concrete Composites, 21(5/6), pp. 383-390.
[15] Ezeldin, A.S., and Balaguru, P.N. (1992), "Normal and
high strength fiber reinforced concrete under compression", ASCE,
Journal of Mate. in Civil Eng., 4(4), pp. 415-429.
[16] Mansur, M.A.., Chin, M.S., and Wee, Y.H. (1999). Stress-strain
relationship of high strength fiber concrete in compression. ASCE
Journal of Mate. in Civil. Eng, 13(1), pp. 21-29.
[17] Ramadoss, P., and Nagamani, K. (2008), "Stress-strain
curves for high-performance fiber reinforced concrete under
compression", Journal of Civil Engineering Research and Practice,
5(1), pp. 1-14.
[18] ACI Building code 318 (1995), "Building code requirements
for structural concrete", ACI 318-1995, American Concrete
Institute, Detroit.
P. Ramadoss (1), *, V. Prabakaran (2) and K. Nagamani (3)
(1,2) Department of Civil Engineering, Pondicherry Engineering
College, Pondicherry-605014, India.
(3) Department of Civil Engineering, Anna University, Chennai-600
025, India.
* Corresponding author: Email: dosspr@gmail.com
Table 1: Mix proportions for SFRSFC (data for 1 [m.sup.3]).
Mix W/Cm C, kg FA, kg CA, kg SF, kg W, kg
Designation
FC1 * - 0 0.4 394.2 691 1088 43.8 175
FC1 * - 0.5 0.4 394.2 687 1079 43.8 175
FC1 * - 1 0.4 394.2 682 1071 43.8 175
FC1 * - 1.5 0.4 394.2 678 1062 43.8 175
FC2 * - 0 0.35 437.4 664 1088 48.6 170
FC2 * - 0.5 0.35 437.4 660 1079 48.6 170
FC2 * - 1 0.35 437.4 655 1071 48.6 170
FC2 * - 1.5 0.35 437.4 651 1062 48.6 170
FC3 * - 0 0.3 495 624 1088 55 165
RC3 * - 0.5 0.3 495 620 1079 55 165
FC3 * - 1 0.3 495 615 1071 55 165
FC3 * - 1.5 0.3 495 611 1062 55 165
FC4 * - 0 0.25 576 562 1088 64 160
FC4 * - 0.5 0.25 576 558 1079 64 160
FC4 * - 1 0.25 576 553 1071 64 160
FC4 * - 1.5 0.25 576 549 1062 64 160
Mix Steel SP, kg
Designation fiber,
[V.sub.f]
(%)
FC1 * - 0 0 7.66
FC1 * - 0.5 0.5 7.66
FC1 * - 1 1.0 7.66
FC1 * - 1.5 1.5 7.66
FC2 * - 0 0 9.72
FC2 * - 0.5 0.5 9.72
FC2 * - 1 1.0 9.72
FC2 * - 1.5 1.5 9.72
FC3 * - 0 0 13.75
RC3 * - 0.5 0.5 13.75
FC3 * - 1 1.0 13.75
FC3 * - 1.5 1.5 13.75
FC4 * - 0 0 17.60
FC4 * - 0.5 0.5 17.60
FC4 * - 1 1.0 17.60
FC4 * - 1.5 1.5 17.60
Table 2: Experimental results for steel fiber reinforced concrete
and SF concrete.
Mix RI UPV [f.sup.'.sub.cf] [[member of].sub.o]
Designation (m/sec) (MPa) (mm/mm)
FC1 * -0 0 4398 52.56 0.00260
FC1 * -0.5 1.29 4377 54.77 0.00305
FC1 * -1 2.58 4367 56.01 0.00320
FC1 * -1.5 3.88 4524 57.40 0.00330
FC2 * -0 0 4318 55.85 0.00305
FC2 * -0.5 1.29 4382 59.65 0.00325
FC2 * -1 2.58 4435 61.05 0.00338
FC2 * -1.5 3.88 4559 61.44 0.00345
FC3 * -0 0 4516 63.86 0.00335
FC3 * -0.5 1.29 4603 67.12 0.00335
FC3 * -1 2.58 4667 68.91 0.00365
FC3 * -1.5 3.88 4790 69.67 0.00370
FC4 * -0 0 4615 74.87 0.00360
FC4 * -0.5 1.29 4716 77.42 0.00376
FC4 * -1 2.58 4889 79.96 0.00388
FC4 * -1.5 3.88 5004 80.41 0.00395
Mix [E.sub.c] TR
Designation (GPa)
FC1 * -0 29.68 0.2038
FC1 * -0.5 30.14 0.6155
FC1 * -1 30.92 0.6507
FC1 * -1.5 31.78 0.6715
FC2 * -0 30.87 0.2161
FC2 * -0.5 32.32 0.6061
FC2 * -1 33.26 0.6343
FC2 * -1.5 33.97 0.6647
FC3 * -0 34.14 0.2252
FC3 * -0.5 35.96 0.6340
FC3 * -1 36.52 0.6592
FC3 * -1.5 36.98 0.6851
FC4 * -0 37.65 0.2454
FC4 * -0.5 39.47 0.6313
FC4 * -1 40.52 0.6469
FC4 * -1.5 41.06 0.6789
UPV = Ultrasonic pulse velocity (m/sec.)
[f.sup.'.sub.cf] = 150 x 300 mm cylinder compressive strength of
SFRSFC (MPa)
[E.sub.c] = secant modulus (GPa), [[member of].sub.o] = strain at
peak stress and TR = toughness ratio.
Fiber reinforcing index (RI) = [w.sub.f] * (l/d) and average density
of SFRSFC = 2415 kg/[m.sup.3]
Weight fraction ([w.sub.f]) = (density of fiber/density of fibrous
concrete) * [V.sub.f]
Aspect ratio (l/d) = length of fiber/diameter of fiber.
Table 3: Calculating results for fiber reinforced concrete and
SF concrete.
Mix RI Calculated values
Designation [f'.sub.cf] % error [E.sub.c] % error
(MPa) (GPa)
FC1 * -0 0 52.56 0.00 30.293 -2.065
FC1 * -0.5 1.29 54.36 -0.75 31.115 -3.235
FC1 * -1 2.58 56.16 0.27 31.571 -2.105
FC1 * -1.5 3.88 57.98 0.98 32.078 -0.938
FC2 * -0 0 55.85 0.00 31.512 -2.080
FC2 * -0.5 1.29 57.65 -3.35 32.890 -1.764
FC2 * -1 2.58 59.45 -2.62 33.390 -0.391
FC2 * -1.5 3.88 61.27 -0.28 33.528 1.301
FC3 * -0 0 63.86 0.00 34.381 -0.706
FC3 * -0.5 1.29 65.66 -2.18 35.512 1.246
FC3 * -1 2.58 67.46 -2.10 36.124 1.084
FC3 * -1.5 3.88 69.28 -0.56 36.383 1.614
FC4 * -0 0 74.87 0.00 38.126 -1.264
FC4 * -0.5 1.29 76.67 -0.97 38.965 1.279
FC4 * -1 2.58 78.47 -1.86 39.791 1.799
FC4 * -1.5 3.88 80.29 -0.15 39.936 2.737
Calculated Values
Mix TR % error
Designation
FC1 * -0 0.204 0.00
FC1 * -0.5 0.622 -0.982
FC1 * -1 0.648 0.397
FC1 * -1.5 0.675 -0.518
FC2 * -0 0.216 0.00
FC2 * -0.5 0.622 -2.555
FC2 * -1 0.648 -2.178
FC2 * -1.5 0.675 -1.537
FC3 * -0 0.225 0.00
FC3 * -0.5 0.622 1.957
FC3 * -1 0.648 1.676
FC3 * -1.5 0.675 1.488
FC4 * -0 0.245 0.00
FC4 * -0.5 0.622 1.546
FC4 * -1 0.648 -0.187
FC4 * -1.5 0.675 0.589