use of basalt f ibers for concrete structures · pdf filedesign of concrete members reinforced...

of 28

Use of basalt fibers for concrete structures

Cory Higha, Hatem M. Seliemb*, Adel El-Saftyc, Sami H. Rizkallaa

a Department of Civil, Construction and Environmental Engineering, NCSU, Raleigh, NC, USA

b Department of Civil Engineering, Faculty of Engineering, Helwan University, Cairo, Egypt

c School of Engineering, University of North Florida, Jacksonville, FL, USA

Abstract:

This study investigated the use of basalt fiber bars as flexural reinforcement for concrete

members and the use of chopped basalt fibers as an additive to enhance the mechanical

properties of concrete. The material characteristics and development length of two

commercially-available basalt fiber bars were evaluated. Test results indicate that flexural

design of concrete members reinforced with basalt fiber bars should ensure compression failure

and satisfying the serviceability requirements. ACI 440.1R-06 accurately predicts the flexural

capacity of members reinforced with basalt bars, but it significantly underestimates the

deflection at service load level. Use of chopped basalt fibers had little effect on the concrete

compressive strength, however, significantly enhanced its flexural modulus.

Keywords:

Fibers, basalt, fiber-reinforced concrete, bond, flexure, average residual strength,

of 28

1. Introduction

Basalt fibers are produced from basalt rocks, which are melted at 1400 οC. Basalt fibers are

environmentally safe, non-toxic, and possess high stability and insulating characteristics [1].

Basalt Fiber Reinforced Polymer (BFRP) reinforcing bars have been recently introduced as an

alternative to steel reinforcement for concrete structures and as external reinforcement for

retrofitting of concrete structures. Unlike Carbon Fiber Reinforced Polymer (CFRP) and Glass

Fiber Reinforced Polymer (GFRP) materials, basalt fibers have not been widely used. The

limitation of their use may be attributed to the lack of fundamental research and extensive

testing required to establish an appropriate design recommendations and guidelines. Chopped

basalt fibers have been also introduced as an additive to concrete mixes to produce fiber

reinforced concrete (FRC).

The research presented in this paper comprises two main studies. The first study evaluated the

behavior of flexural concrete members reinforced with BFRP bars. The study included

assessments of the mechanical properties and the bond strength of two selected BFRP bars

having two different surface deformations. The first BFRP bars were ribbed and the second

were dented. The second study investigated the use of chopped basalt fibers as an additive to

concrete mix to enhance the mechanical properties of hardened the concrete. Two different

short basalt fiber products were investigated in the second study.

FIRST STUDY: FLEXURAL BEAHAVIOR OF CONCRETE MEMBERS

REINFORCED WITH BFRP BARS

2. Background

Ramakrishnan et. Al. (1998) [1] investigated the use of basalt fiber bars for reinforcing concrete

members. Test results indicated that specimens reinforced with BFRP bars with short bond

of 28

lengths exhibited gradual slip prior to failure. Specimens with long bond lengths exhibited

sudden failures due to rupture of the BFRP bars. Patnaik (2010) [2] studied the flexural strength

of 13 concrete beams reinforced with BFRP bars and compared the measured failure loads to

those predicted by ACI 440.1R-06 guidelines. The study concluded that prediction of moment

capacities by ACI 440.1R-06 agrees well with the measured values. Ovitigala (2013) [3]

investigated the behavior of lightweight and normal weight concrete beams reinforced with

BFRP bars. The study reported that ACI 440.1R-06 [4] predicted 77 to 93 percent of the

measured moment capacities. In addition, the study reported higher deflections for BFRP-

reinforced concrete beams in comparison to steel-reinforced concrete beams with the same

flexural capacity

3. Mechanical Properties of BFRP Bars

A total of ten coupons of each of the ribbed and dented bars were tested in tension according to

ASTM D7205 [5]. The tension coupons had a 305 mm gripping length at each end and a free

length of 610 mm. The gripping length consisted of epoxy-filled steel pipes attached to each end

of the test coupon. The elongation of the tension coupons was measured using a 50 mm

extensometer. The average engineering stress-strain relationships of the ribbed and dented

BFRP bars are shown in Fig. 1. The average measured cross-sectional area of the ribbed and

dented BFRP bars is 109 mm2. The equivalent nominal diameter of both bars is approximately

12 mm. The measured cross-sectional area and equivalent diameter of the bars were

determined by volume water displacement according to ACI 440.3R-04 [6]. It should be noted

that the ribs were excluded from the measured area.

The tension coupons exhibited a linearly elastic stress-strain relationship up to rupture of the

bars. The average measured modulus of elasticity of the ribbed and dented BFRP bars was

approximately 48.3 GPa and 41.4 GPa, respectively, therefore an average value of 45 GPa can

of 28

be used. The average measured ultimate tensile strength for both bars was approximately 1,000

MPa. The average measured rupture strain of the ribbed and dented bars was 2.2% and 2.5%,

respectively.

4. Bond Strength of BFRP Bars

4.1 Test Specimens and Test Setup

Beam-end specimens were used to assess the bond characteristics of the two types of BFRP

bars with different surface deformations (ribbed or dented). A total of eight specimens, four

specimens for each bar type, were tested. The development length according to the equation

provided by ACI 440.1R-06 [4] for GFRP and CFRP bars was 762 mm, which is approximately

equivalent to 65 times the bars diameter. Accordingly, four different bond lengths were selected

for this study, 380 mm, 610 mm, 1015 mm, and 1270 mm, which are equivalent to 32, 51, 85,

and 106 times the bar diameter, respectively.

The concrete beam-end specimens had a total length of 1524 mm to accommodate the longest

bond length. The depth of the specimens was 610 mm to eliminate the influence of the

compressed concrete zone on the bonded length of the bar. A width of 305 mm was used to

provide enough bearing strength. The specimens were cast with the BFRP at the bottom

position and the specimens were rotated prior to testing. Details of specimens are shown in Fig.

2.

All tested bars were 2134 mm long to provide an embedment length of 1524 mm within the

specimen and an overhang length of 610 mm to grip the bar. A PVC pipe was used at the

unloaded end to break the bond and to provide the specified bond length. A 102 mm PVC pipe

was used at the loaded end to avoid possible localized failure of the concrete.

of 28

Two linear potentiometers were attached to the loaded end of the test bar to measure the

elongation of the bar. Similarly, two linear potentiometers were attached to the unloaded end

(free end) of the BFRP bar tested to measure the slip of the bar. Elongation of the test bars was

measured using a 50 mm extensometer located within the free length of the bars. The test setup

is shown in Fig. 3.

4.2 Test Results and Discussion

Test results of the ribbed bars “R” and the dented bars “D” are given in Table 1 including the

observed failure mode, the maximum measured stress in the bar at failure, and the measured

concrete compressive strength at the day of testing. Test results indicate that the ribbed and

dented BFRP bars have similar bond strengths. A bonded length of 380 mm, which is equivalent

to 32 times the bar diameter, was found enough to develop the full strength of the BFRP bars

used in this study.

5. Flexural Behavior of BFRP-Reinforced Members

5.1 Test specimens

Six, one-way slabs reinforced with ribbed BFRP bars only were tested in flexure up to failure.

The specimens were 3658 mm long with a cross-section of 610 mm wide and 152 mm deep.

The BFRP bars were spaced uniformly across the width of the specimens and had a clear

concrete cover of 25 mm. All specimens were tested at concrete age ranging from 58 to 63 days

and the average measured concrete compressive strength was 72.1 MPa at the day of testing.

The balanced reinforcement ratio of the slabs was computed as 0.47 percent.

Two duplicate specimens reinforced with three bars were designed to fail in tension with a

reinforcement ratio of 0.44 percent, which is 0.94 of the balanced ratio. Two duplicate

specimens reinforced with seven bars were designed to fail in compression with a reinforcement

of 28

ratio of 1.04 percent, which is 2.20 of the balanced ratio .The last two duplicate specimens were

reinforced with four bars, resulting in a reinforcement ratio of 0.59 percent, which is 1.26 of the

balanced ratio. The ribbed bars were selected in this study due to their higher modulus of

elasticity compared to the dented bars. The measured average cross-sectional area of the

ribbed bars was 109 mm2.

5.2 Test setup and Instrumentation

The flexural specimens were tested in a four-point bending configuration with a test span of

3353 mm using one hydraulic actuator. The load was applied at two locations spaced 305 mm

apart. The specimens were supported by a pin support at one end and a roller support at the

other end.

Two string potentiometers were used to measure the deflection at mid-span. Five PI-gages

located at the mid-span section were used to measure the strain of concrete. Two PI-gages, 50

mm apart, were placed on the top and two PI-gages on the bottom surfaces of the slabs. The

fifth PI-gage was placed on the side face of the specimens at the depth of the BFRP bars to

measure the concrete strain at the reinforcement level. Fig. 4 shows the test setup and the

instrumentation of typical specimen, BR-1.

5.2.1 Mode of Failure

The under-reinforced specimens (ρf = 0.94 ρfb) failed in in an abrupt manner due to the

complete rupture of all the BFRP bars as shown in Fig. 5(a). The test specimens with a

reinforcement ratio slightly higher than the balanced ratio (ρf = 1.26 ρfb) failed due to crushing of

concrete in the compression zone of the constant moment region as shown in Fig. 5(b). Partial

rupture of the BFRP bars within these two specimens was visibly evident at failure. The over-

reinforced specimens (ρf = 2.20 ρfb) failed in compression due to crushing of concrete on the top

of 28

surface of the specimen in the constant moment region without any evidence of rupture of the

BFRP bars as shown Fig. 5(c).

5.2.2 Load-Deflection Behavior

The load-deflection behavior of the six test slabs is shown in Fig. 6. All specimens behaved

similarly up to first cracking. After cracking, the flexural stiffness was proportional to the BFRP

reinforcement ratio used in each category. The linear behavior of the load-deflection

relationship up to failure is due to the linear elastic nature of the BFRP bars.

The under-reinforced slabs had the least load carrying capacity with an average failure load of

46.3 kN and a corresponding deflection of 178 mm, which is slightly less than the slabs with a

reinforcement ratio slightly higher than the balanced ratio, due to the sudden rupture of the bars.

The slabs with a reinforcement ratio slightly higher than the balanced ratio had an average

failure load of 60.9 kN and corresponding deflection of 201 mm. The over-reinforced slabs failed

at the highest load of an average of 82.6 kN and a corresponding average deflection of 155 mm.

The load-deflection behavior of the test slabs was predicted using the equations proposed by

Bischoff and Gross (2013) with and without consideration of the tension stiffening [7], as well as

the equation recommended by ACI 440.1R-06. The predicted load-deflection behaviors of the

three different approached are compared to the measured behavior in Fig. 7 for the six tested

slabs with different reinforcement ratios. The Comparison clearly indicates that the equation

proposed by Bischoff and Gross (2013) without tension stiffening can accurately predict the

behavior up to failure. The equations recommended by ACI 440.1R-06 and Bischoff and Gross

(2013) with tension stiffening underestimate the deflection after cracking. The behavior of both

approaches highlights that the effect of tension stiffening of concrete is significantly reduced for

flexural members reinforced with BFRP bars due to their low modulus of elasticity.

of 28

5.2.3 Measured Strain

The measured concrete strain at the level of the BFRP bars of the slabs with reinforcement ratio

of 0.94 ρfb and 1.26 ρfb were always higher than the strain of the bars at the same stress level

induced in the bars computed by sectional-analysis of the test slabs, as shown in Fig. 8. This

behavior reflects slippage of the BFRP bars for the slabs with reinforcement ratios equal to 0.94

ρfb and 1.26 ρfb due to the high stress demand of the bars at these low level of reinforcement.

The slip of the BFRP bars was verified by removing of the concrete cover and inspecting the

slabs. The performance of the over-reinforced slabs did not exhibit similar slip behavior. This

behavior highlights the necessity of designing BFRP-reinforced members to fail in compression

and with higher reinforcement ratio in comparison to the typical reinforcement ratios used for

steel.

6. Applicability of ACI 440.1R-06 Guidelines

6.1 Nominal Moment Capacity

Measured flexural capacities were compared to those predicted according to the ACI 440.1R-06

guidelines, as shown in Table 2. The nominal moment capacity was predicted using the

measured concrete compressive strength. Table 2 clearly indicates that ACI 440.1R-06 can

accurately predict the nominal moment capacity of concrete members reinforced with BFRP

bars having different reinforcement ratios.

6.2 Deflection at Service Level

The selected moment level used to compare the deflection at service load (Ms) was estimated

using the following equation:

𝑀𝑠 =∅

𝛼𝐿𝐿𝐿𝐿𝑀𝑛

of 28

where Mn is the measured moment of the slab at failure. αLoad was equal to 1.33 based on a

dead-to-live load ratio of 2:1. According to ACI 440.1R-06, the strength reduction factor “Ф” is

0.65 for ρf ≥ 1.4ρfb and 0.55 for ρf ≤ 1.0ρfb. Therefore, estimated service moment for the three

categories of the test slabs were 0.41Mn, 0.46Mn, and 0.49Mn for reinforcement ratio of 0.94ρfb,

1.26 ρfb, and 2.20ρfb, respectively. The measured mid-span deflection at service load level, Δ,

was compared to that predicted according to ACI 440.1R-06 [4] for all test slabs as given in

Table 3.

Table 3 shows that the ACI 440.1R-06 equation significantly underestimates the deflection at

service load for members reinforced with BFRP reinforcement ratios less than or approximately

equal to the balanced ratio due to slippage of BFRP bars. However, the ACI 440.1R-06

predictions improve as the BFRP reinforcement ratio is increased as the ratio of measured to

predicted deflection reduced from 2.19 to 1.22. This is due to the reduction of stresses in the

BFRP bars and therefore, possible elimination of slippage of the bars. Table 3 also indicates

that the measured deflection-span ratio (L/Δ) at service load level significantly exceeds the

permissible deflection limit under total service load as recommended by ACI 318-11 [8]. This

indicates that the design of flexural members reinforced with BFRP may also be controlled by

serviceability requirements, due to the low modulus of elasticity of the bars.

SECOND STUDY: BASALT FIBER-REINFORCED CONCRETE (BFRC)

7. Background

Ramakrishnan et. Al. (1998) [1] investigated the use of short basalt fibers to enhance the

material properties of concrete. The study concluded that basalt fibers can be easily mixed with

concrete without any balling or segregation. In addition, there was also a noticeable increase in

the post-cracking energy absorption capacity and increase of the impact resistance.

of 28

Ma et al. (2011) [9] conducted an experimental program to investigate the mechanical

properties of concrete with the addition of basalt fibers that were pre-soaked in epoxy. Three

different pre-soaked basalt fiber lengths (10 mm, 20 mm and 30 mm) and three different fiber

dosages (3,000 g/m3, 5,000 g/m3 and 7,000 g/m3) were examined in this study. Test results

showed that as the basalt fiber dosage and fiber length increased the measured slump

decreased. According to this study, the presence of the pre-soaked basalt fibers did not

significantly affect the compressive strength of the concrete, however, use of fibers increased

the concrete flexural modulus. This study concluded that adding 30 mm long basalt fibers to

concrete at a dosage range of 3,000 g/m3 to 5,000 g/m3 resulted in improvement of the

mechanical properties with an acceptable workability.

Borhan (2013) [10] studied the compressive and splitting tensile strengths of BFRC with fiber

volume fractions ranging from 0.1 to 0.5 percent. Test results indicated that increasing the

basalt fiber content increased the splitting tensile strength of the concrete and did not affect the

compressive strength, up to volume fractions of 0.3 percent. Decreased compressive and

splitting tensile strengths were reported for fiber volume content equal to 0.5 percent. This

study also reported a reduction in the concrete slump as the basalt fiber volume content was

increased.

8. Properties of Basalt Fibers

Two different short basalt fiber products were used in this study. The first type consisted of

chopped dry fibers, while the second type was produced by chopping precured fibers as shown

in Fig. 9. The first type of fiber is denoted as “D” for dry and the second type as “P” for precured.

The properties of the two types of fibers are given in Table 4.

of 28

9. Concrete Mixes and Specimens

Two concrete mixes were investigated in this study. Mix “A” was a standard concrete mix with a

target compressive strength at 28 days of 20.7 MPa. Mix “B” had the same target compressive

strength, however contained fly ash and admixtures and therefore, less cement content. Details

of the two mixes are given in Table 5.

For each mix, different contents of basalt fibers were used. The test matrix of the different

batches is given in Table 6. Batches “1A” and “1B” are control batches without any fibers. The

two different types of fiber were used together in different ratios. In order to produce uniform

batches, dry mixing of the constituents was performed prior to adding the water until blending of

the constituents was evident. Afterwards, the water containing all liquid admixtures was

gradually added and the concrete was allowed to mix until a uniform consistency was achieved

in a reasonable time. Workability of all batches for mix “A” was higher than that of mix “B”,

despite the use of admixtures in mix “B”. This could be attributed to the high water/cement ratio

used in mix “A”, which was 0.55 compared to 0.38 used for mix “B”.

Concrete cylinders of 102x204 mm and prisms of 152x152x508 mm were cast from each of the

concrete batches. Neither rodding nor internal vibration was performed during the casting to

avoid the disturbance of the distribution of the basalt fibers. However, the overfilled molds were

vibrated using a vibration table until the concrete was adequately consolidated. The casted

molds remained inside the laboratory at a constant ambient temperature of 22 +/- 2 οC and

relative humidity of 70 +/- 5%. The cylinders and the prisms were de-molded 24 hours after

casting and cured by covering them with continuously wet burlap and plastic sheets to entrain

the moisture until the designated test date.

of 28

10. Test Results and Discussion

10.1 Compressive Strength

The compressive strength of each batch was measured at 3, 7 and 28 days in accordance with

ASTM C39 [11]. Average measured compressive strengths, fc, at different ages for the two

mixes with different fiber content are given in Table 7. The reported strength at ages of 3 and 7

days is an average of three individual tests, while the 28-day reported strength is an average of

six individual tests. The ratios of the measured strength of the different batches to the strength

of the control batches 1A and 1B are also given in Table 7.

The early compressive strength at ages of 3 and 7 days of mixes “A” and “B” as percent of the

28-day strength (fc’) are graphically shown in Fig. 10 and Fig. 11, respectively. The early

strength of mix “A” did not exhibit an increase due to the use of the basalt fibers. However, there

was a trend of increase of the early compressive strength for mix “B” reflected by a ratio up to

65% and 62% for batch “4B” at 3 and 7 days, respectively.

The measured compressive strength for all concrete batches exceeded the target 28-day

compressive strength of 20.7 MPa, with the exception of batch “4A”. Test results indicated that

the concrete compressive strength at 28 days (fc’) of mix “A” was not significantly affected by the

use of the basalt fibers with a maximum increase of 6% for batch “3A”. However, the effect of

the basalt fibers on fc’ was evident for mix “B” in comparison to mix “A”. The 28-day compressive

strength of batch “4B” was increased by 40% in comparison to the control batch “1B”. The

increase of fc’ of mix “B” is also proportional to the high fibers content used of both types of

chopped fibers.

Test results indicate that adding basalt fibers to concrete may slightly increase the 28-day

compressive strength (fc’) of concrete containing fly ash and admixtures with low water-cement

of 28

ratios. In addition, test results suggest that the early strength of concrete containing fly ash and

admixtures may be significantly increased by using basalt fibers.

10.2 Modulus of Rupture

The modulus of rupture at 28 days was measured using a third-point loading test in accordance

with ASTM C78 [12]. Flexural prisms of 152x152x508 mm were tested using a universal testing

machine and an apparatus for third-point loading as shown in Fig. 12.

The average measured modulus of rupture for the two mixes with different fiber content is given

in Table 7. The reported modulus of rupture is an average of three individual tests. It is evident

from test results that using basalt fibers could increase the flexural modulus of the concrete for

both mixes. However, the increase was more pronounced for mix “B” in comparison to mix “A”.

This behavior is in consistent with the increase of the compressive strength; indicating that the

basalt fibers may be effective for concrete mix contains fly ash and admixtures with a low water-

cement ratio.

ACI 318-11 code [8] relates the modulus of rupture (fr) and the compressive strength (fc’) of

normal weight concrete as:

𝑓𝑟 = 0.62 ×�𝑓𝑐′

The measured modulus of rupture was normalized by the square root of the 28-day

compressive strength (fc’) as shown in Fig. 13. The normalized flexural strengths reveal that the

modulus of rupture of concrete containing basalt fiber is higher than that of normal weight

concrete without fibers. The increase in the rupture strength for mix “A” was proportional to the

fiber content and on average was slightly higher than that for mix “B”.

of 28

10.3 Average Residual Strength (ARS)

The toughness (or capability to resist crack opening) of the BFRC was evaluated using the

average residual strength (ARS) test according to ASTM C1399 [13]. ARS provides a measure

of the post-cracking strength of the concrete; as such strength may be affected by the use of

fiber-reinforcement. The test method was developed particularly for FRC with low fiber content

to avoid the instability of tested beams at the onset of cracking, as typically seen during the

withdrawn ASTM C 1018 test method [14].

ARS testing was performed using prisms of 100x100x350 mm, which were cut from the

152x152x508 mm prisms using an abrasive concrete saw approximately 24 hours before

testing. Fig. 14 shows an ARS specimen positioned in the testing apparatus prior to testing.

The average measured ARS for the two mixes with different fiber content is given in Table 7.

The reported values are an average of five individual tests. ARS test values were normalized by

the square root of the 28-day compressive strength (fc’) as shown in Fig. 15. The ARS values of

the tested BFRC specimens appear to be low compared to other studies of FRC using different

type of fibers [15]. Based on these limited tests, the results indicate that the use of basalt fibers

did not enhance the average residual strength of concrete.

11. Summary and Conclusions

The research program presented in this paper comprises two studies. The first study evaluated

the flexural behavior of concrete members reinforced with BFRP bars. As part of the first study,

the mechanical properties and bond strengths of two BFRP bars were investigated. The

applicability of ACI 440.1R-06 design guidelines for predicting the deflection and strength of

BFRP-reinforced concrete members was discussed. The second study investigated the effect of

using two different types of chopped basalt fibers to enhance the characteristics of concrete.

of 28

Based on the test results, the following conclusion can be made:

1. The ribbed and dented BFRP included in this study had an average ultimate tensile strength

of approximately 1,000 MPa with an average modulus of elasticity of 45 GPa. The. The

bond strength of both BFRP bars is essentially the same and the development length is

approximately equivalent to 32 times the bar diameter.

2. Slippage of the BFRP bars could occur for low reinforcement ratio in the range of the

balanced ratio. Slippage of the bars can be avoided by using high reinforcement ratio at

least double the balanced reinforcement ratio. This behavior can be attributed to the high

stress demand on the bars of specimens with low reinforcement ratios. This behavior also

highlights the necessity for designing BFRP-reinforced flexural members to fail in

compression.

3. Design of flexural members reinforced with BFRP bars may be controlled by serviceability

requirements due to the low modulus of elasticity of the bars.

4. ACI 440.1R-06 accurately predicts the nominal moment capacity of flexural members

reinforced with BFRP bars. ACI 440.1R-06 significantly under predicts the deflection at

service load for under-reinforced and balanced reinforcement ratios. However, the ACI

440.1R-06 deflection prediction improves as the BFRP reinforcement ratio is increased.

5. The equation proposed by Bischoff and Gross (2013) without tension stiffening can

accurately predict the deflection of flexural members reinforced with BFRP bars up to failure.

The effect of tension stiffening of the concrete is negligible for flexural members reinforced

with BFRP bars due to their low modulus of elasticity.

6. Using basalt fibers slightly increased the 28-day compressive strength (fc’) of concrete

containing fly ash and admixtures with a low water-cement ratio. In addition, the early

compressive strength of concrete containing fly ash and admixtures may significantly

increase due to the use of basalt fibers.

of 28

7. Use of basalt fibers resulted in an increase of the modulus of rupture of the concrete.

However, the increase in the flexural strength was more pronounced for concrete mix

containing fly ash, admixtures, and with low water-cement ratio.

12. Acknowledgments

The authors would like to acknowledge the Florida Department of Transportation for funding this

project and the National Science Foundation Center of Integration of Composites into

Infrastructure (CICI) at NCSU, Grant No. 2009-1644. Thanks are also due to the staff of the

Constructed Facilities Laboratory of NCSU for their help throughout the experimental program.

13. References

[1] Ramakrishnan, V., Tolmare, Neeraj S., and Brik, Vladimir B. Performance Evaluation of 3-D

Basalt Fiber Reinforced Concrete & Basalt Rod Reinforced Concrete. Final Report for

Highway IDEA Project 45, Transportation Research Board. 1998; 79.

[2] Patnaik, A., Adhikari, S., Bani-Bayat, P., and Robinson, P. Flexural Performance of Concrete

Beams Reinforced with Basalt FRP Bars. 3rd fib. International Congress, Washington D.C.

May 2010: 3821-3833.

[3] Ovitigala, T., Issa, M.A. Flexural Behavior of Concrete Beams Reinforced with Basalt Fiber

Reinforcement Polymer (BFRP) Bars. 11th International Symposium on Fiber Reinforced

Polymer for Reinforced Concrete Structures, Guimarães, Portugal. June 2013: 249-260.

[4] ACI 440.1R-06. Guide for the Design and Construction of Structural Concrete Reinforced

with FRP Bars. ACI Committee 440, American Concrete Institute, Farmington Hills, MI, USA.

2006: 44.

of 28

[5] ASTM D7205/D7205M-06 (Reapproved 2011). Standard Test Method for Tensile Properties

of Fiber Reinforced Polymer Matrix Composite Bars. ASTM International, West

Conshohocken, PA, USA. 2011; 13.

[6] ACI 440.3R-12. Guide Test Methods for Fiber-Reinforced Polymer (FRP) Composite for

Reinforcing or Strengthening Concrete and Masonry Structures. ACI Committee 440,

American Concrete Institute, Farmington Hills, MI, USA. 2012; 40.

[7] Bischoff, Peter H. and Cross, Shwan P. Equivalent Moment of Inertia Based on Integration of

Curvature. ASCE-J of Composites for Constr. 2011; 15(3):263-273.

[8] ACI 318-11. Building Code Requirements for Structural Concrete and Commentary. ACI

Committee 318, American Concrete Institute, Farmington Hills, MI, USA. 2011; 503.

[9] Ma, Jianxun, Xuemei Qiu, Litao Cheng, and Yunlong Wang. 2011. “Experimental Research

on the Fundamental Mechanical Properties of Presoaked Basalt Fiber Concrete.” In

Advances in FRP Composites in Civil Engineering, edited by Lieping Ye, Peng Feng, and

Qingrui Yue, 85–88. Springer Berlin Heidelberg.

http://link.springer.com/chapter/10.1007/978-3-642-17487-2_16.

[10] Borhan, Tumadhir M. 2013. “Thermal and Mechanical Properties of Basalt Fibre Reinforced

Concrete.” Proceedings of World Academy of Science, Engineering and Technology (76):

313.

[11] ASTM C39/C39M-12a. Standard Test Method for Compressive Strength of Cylindrical

Concrete Specimens. ASTM International, West Conshohocken, PA, USA. 2012; 7.

[12] ASTM C78/C78M-10. Standard Test Method for Flexural Strength of Concrete (Using

Simple Beams with Third-Point Loading). ASTM International, West Conshohocken, PA,

USA. 2010; 4.

of 28

[13] ASTM C1399/C1399M-10. Standard Test Method for Obtaining Average Residual-Strength

of Fiber-Reinforced Concrete. ASTM International, West Conshohocken, PA, USA. 2010; 6.

[14] Banthia, N. and Trottier, J.F. Test Methods for Flexural Toughness Characterization of

Fiber-Reinforced Concrete: Some Concerns and a Proposition. ACI Materials J, 1995; 92(2):

48-57.

[15] Jean-Francois Trottier, Michael Mahoney, and Dean Forgeron. Can Synthetic Fibers

Replace Welded-Wire Fabric in Slabs-on-Grade. Concrete International, 2002; 24(11): 59-

68.

of 28

Table 1: Summary of test results of bond strength study

Bonded

Length (mm) Failure Mode

Maximum Stress

(MPa)

Concrete Strength

(MPa)

R-380 Slip/Bar Rupture 1048 53.6

R-610 Bar Rupture 903 48.6

R-1015 Bar Rupture 1000 48.6

R-1270 Bar Rupture 814 NA

D-380 Bar Rupture 910 52.1 D-610 Bar Rupture 807 52.1

D-1215 Bar Rupture 889 51.4

D-1270 Bar Rupture 869 51.4

Table 2: Predictions of nominal moment according to ACI 440.1R-06 (kN-m)

Slab ID Rft. Ratio

(ρf)

Measured ACI 440

Measured/

ACI Mn AVG

UR-1 0.94 ρfb

39.2 38.5 39.0 0.99 UR-2 37.8

BR-1 1.26 ρfb

48.2 49.4 51.4 0.96 BR-2 50.5

OR-1 2.20 ρfb

67.0 66.0 65.9 1.00 OR-2 64.9

Table 3: Predictions of deflection at service load according to ACI 440.1R-06 (kN-m and mm)

Slab

ID

Rft. Ratio

(ρf)

Service Moment Experimental ACI 440

Ms Ms/Mcr Δ ΔAVG L/Δ Δ ΔAVG Ratio

UR-1 0.94 ρfb 16.2 1.30 51 46 73 22 21 2.19

UR-2 15.6 1.25 40 20

BR-1 1.26 ρfb 22.3 1.78 75 72 47 41 44 1.64

BR-2 23.3 1.86 69 47

OR-1 2.20 ρfb 32.6 2.61 67 66 51 55 54 1.22

OR-2 31.6 2.53 65 52

of 28

Table 4: Properties of basalt fibers

Property Dry Fiber Precured Fibers

Density 2.8 gm/cm3 1.9 gm/cm3

Diameter 13-20 μm 2.6 mm

Length 24 mm 40 mm

Elastic modulus 89 Gpa 43 Gpa

Elongation at break 3.15 % 2.20 %

Table 5: Details of mix designs

Material Quantity

Mix Design A Mix Design B

Cement 310 kg/m3 220 kg/m3

Water 170 kg/m3 140 kg/m3

Fine Aggregate 750 kg/m3 700 kg/m3

Coarse Aggregate 990 kg/m3 1015 kg/m3

Fly Ash-Class C NA 145 kg/m3

Adm

ixtu

res

Air-entraining 0.1035 Liters 0.1331 Liters

Water-reducing NA 0.5028 Liters

Accelerating NA 1.2

Mineral NA 84 kg/m3

Table 6: Test matrix of batches

Mix Batch

ID

Fiber Content (g/m3) P:D

Ratio Type “D” Type “P”

A

1A None None NA

2A 1,186 593 1:2

3A 1,779 None 0:3

4A 1,186 1,186 2:2

B

1B None None NA

2B 1,186 593 1:2

3B 1,779 None 0:3

4b 1,186 1,186 2:2

of 28

Table 7: Test results of Basalt FRC

Batch

ID

Compressive Strength (Mpa) Flexural

Modulus (Mpa)

Average Residual

Strength (Mpa) 3 days 7 days 28 days (fc’)

fc Ratio fc Ratio fc’ Ratio fr Ratio

1A 14.6 1.00 17.0 1.00 23.1 1.00 3.4 1.00 NA

2A 14.6 1.00 18.9 1.12 23.4 1.01 3.6 1.06 0.15

3A 15.4 1.05 19.4 1.14 24.4 1.06 4.0 1.16 0.20

4A 10.7 0.73 14.1 0.83 18.4 0.80 3.5 1.02 0.20

1B 11.3 1.00 14.1 1.00 21.2

1.00 3.0 1.00 NA 2B 14.7 1.31 18.3 1.30 25.4 1.20 3.9 1.31 0.25

3B 14.3 1.27 18.1 1.28 24.4 1.15 3.5 1.18 0.15

4B 18.6 1.65 22.8 1.62 29.7 1.40 4.0 1.33 0.15

of 28

Fig. 1: Typical stress-strain relationship of BFRP bars

Fig. 2: Details of beam-end specimens (1 in. = 25.4 mm)

Fig. 3: Schematic of bond strength test setup

Ribbed Bars

Dented Bars

0

200

400

600

800

1000

1200

0 1 2 3

Stre

ss (M

Pa)

Strain (%)

102 mm610 mm

BONDED (LENGTH VARIES)

DEBONDED

PVC BOND BREAKERS381 mm

229 mm

BFRP BARSTEEL GRIP

1524 mm

of 28

Fig. 4: Test setup and instrumentation of specimen BR-1

a) ρf = 0.94 ρfb b) ρf = 1.26 ρfb c) ρf = 2.20 ρfb

Fig. 5: Flexural specimens at the conclusion of the test

Fig. 6: Load-deflection behavior of flexure specimens

0

10

20

30

40

50

60

70

80

90

0 40 80 120 160 200 240

Ap

pli

ed L

oad

(kN

)

M idspan Def lect ion (mm)

OR1

OR2 BR2

BR1

UR1

UR2

of 28

Fig. 7: Prediction of load-deflection behavior of test slabs

Service

0

10

20

30

40

50

60

70

80

90

0 40 80 120 160 200 240

Ap

pli

ed L

oad

(kN

)


S p e c i me n U R 1

S p e c i me n U R 2

B i s c h o f f ( W i t h o u t T e n s i o n S t i f f e n i n g ) A C I 4 4 0 . 1 R - 0 6

Service

0

10

20

30

40

50

60

70

80

90

0 40 80 120 160 200 240

Ap

pli

ed L

oad

(kN

)


S p e c i me n B R 1 S p e c i me n B R 2 B i s c h o f f ( W i t h o u t T e n s i o n S t i f f e n i n g ) A C I 4 4 0 . 1 R - 0 6 B i s c h o f f ( W i t h T e n s i o n S t i f f e n i n g )

Service

0

10

20

30

40

50

60

70

80

90

0 40 80 120 160 200 240

Ap

pli

ed L

oad

(kN

)


S p e c i me n O R 1 S p e c i me n O R 2 B i s c h o f f ( W i t h o u t T e n s i o n S t i f f e n i n g ) A C I 4 4 0 . 1 R - 0 6 B i s c h o f f ( W i t h T e n s i o n S t i f f e n i n g )

of 28

ρf = 0.94 ρfb ρf = 1.26 ρfb ρf = 2.20 ρfb

Fig. 8: Measured and computed strains in the BFRP bars

First type: dry fibers Second type: Precured fibers (matrix)

Fig. 9: Chopped Basalt fibers used for reinforcing concrete (tape measure shows inches)

0

3 0

6 0

9 0

0 . 0 2 . 0 4 . 0 6 . 0

Ap

pli

ed L

oad

(k

N)

S t r a i n ( % )

P r e d ic t e d S p e c i me n U R 1 S p e c i me n U R 2

0

3 0

6 0

9 0

0 . 0 2 . 0 4 . 0 6 . 0

Ap

pli

ed L

oad

(k

N)

S t r a i n ( % )

P r e d ic t e d S p e c i me n B R 1 S p e c i me n B R 2

0

3 0

6 0

9 0

0 . 0 2 . 0 4 . 0 6 . 0

Ap

pli

ed L

oad

(k

N)

S t r a i n ( % )

P r e d ic t e d S p e c i me n O R 1 S p e c i me n O R 2

of 28

Mix “A” Mix “B”

Fig. 10: Compressive strength at 3 days as a percentage of fc’


Fig. 11: Compressive strength at 7 days as a percentage of fc’

67

63 64

61

60 61 62

54

63 63 63

58

50

60

70

80

90

1A (0:0) 2A (1:2) 3A (0:3) 4A (2:2)

Perc

ent o

f fc'

Batch (ratio of fiber type P:D)

54

59 60

64

52

57 57

61

53

58 59

63

50

60

70

80

90

1B (0:0) 2B (1:2) 3B (0:3) 4B (2:2)

Perc

ent o

f fc'


76

83 81

79

71

79 78

73

73

81 79

77

50

60

70

80

90

1A (0:0) 2A (1:2) 3A (0:3) 4A (2:2)

Perc

ent o

f fc'


68

73 76

77

65

71 72

76

67

72 74

77

50

60

70

80

90

1B (0:0) 2B (1:2) 3B (0:3) 4B (2:2)

Perc

ent o

f fc'


of 28

Fig. 12: Flexural test specimen prior to testing


Fig. 13: Normalized flexural strength of BFRC

0.71

0.76

0.84 0.83

0.71

0.72

0.76

0.80

0.71 0.75

0.80 0.81

0.55

0.60

0.65

0.70

0.75

0.80

0.85

1A (0:0) 2A (1:2) 3A (0:3) 4A (2:2)

f r / √f c

'


0.73

0.82

0.73

0.77

0.60

0.70 0.71

0.66 0.65

0.78

0.72 0.73

0.55

0.60

0.65

0.70

0.75

0.80

0.85

1B (0:0) 2B (1:2) 3B (0:3) 4B (2:2)

f r / √f c

'


ACI 318-11 ACI 318-11

of 28

Fig. 14: ARS specimen prior to the initial loading


Fig. 15: Normalized average residual strength of BFRC

0.05 0.06

0.09

0.02 0.03 0.02

0.04 0.04 0.04

0.00

0.05

0.10

0.15

2A (1:2) 3A (0:3) 4A (2:2)

AR

S /

√f c

'


0.12

0.06 0.05

0.01 0.01 0.01

0.05

0.03 0.02

0.00

0.05

0.10

0.15

2B (1:2) 3B (0:3) 4B (2:2)

AR

S /

√f c

'


use of basalt f ibers for concrete structures · pdf filedesign of concrete members reinforced...

Documents