The production and use of durable materials in construction are considered as one of the most challenging things for the professional engineers. Therefore, this research was conducted to investigate the mechanical properties and the durability by using of different percentages of steel fiber with high-strength flowable mortar (HSFM) and also the use of the hybridization of steel fibers, palm fibers, and synthetic fiber (Barchip). Different experimental tests (compressive strength, splitting tensile strength, flexural strength, and static modulus of elasticity among others) were determined after 90 days of normal water curing and 180 days of seawater exposure. The results indicate that hybrid fibers of 1.5% steel fibers + 0.25% palm fibers + 0.25% Barchip fibers provide significant improvement in the different mechanical properties of HSFM. Besides, the hybridization of fibers was found to be effective in the terms of durability (exposure to seawater). Therefore, the minimum reduction in static modulus of elasticity, compressive, splitting and flexural strength was obtained for the HSFM mixes of hybrid fibers using steel fibers with palm fibers and also for the use of steel, palm, and Barchip fibers.
High-strength concrete or mortar subjected to axial compression is known to be a brittle material with almost no strain-softening behavior. Adding fibers to plain matrix has little or no effect on its precracking behavior but does substantially enhance its postcracking response, which leads to a greatly improved toughness and impact behavior [
Shah and Naaman [
Sustersic et al. [
Therefore, the objective of this paper is to determine the basic characteristics of high-strength flowable mortar (HSFM) reinforced by steel fibers as well as the hybridization of three different type of fibers namely, steel fibers, palm fibers, and synthetic fibers (Barchip fibers) in terms of compressive strength, splitting tensile strength, flexural strength, modulus of elasticity, ultrasonic pulse velocity test, absorption and voids ratio. Consequently, these mechanical properties of the specimens of HSFM have been tested after exposure to seawater to study the durability of HSFM reinforced by fibers.
The cement used in concrete mixtures was ordinary Portland cement type I from Tasek Corporation Berhad. Silica fume was obtained from Scancem Materials Sdn. Bhd. and was used as a partial replacement for cement. The chemical compositions of ordinary Portland cement and silica fume are given in Table
Chemical composition of ordinary portland cement and silica fume.
Constituent | Ordinary portland cement | Silica fume |
---|---|---|
Percentage by weight | Percentage by weight | |
Lime (CaO) | 64.64 | 1.0% (max) |
Silica (SiO2) | 21.28 | 90% (max) |
Alumina (Al2O3) | 5.60 | 1.2% (max) |
Iron oxide( Fe2O3) | 3.36 | 2.0% (max) |
Magnesia (MgO) | 2.06 | 0.6% (max) |
Sulphur trioxide (SO3) | 2.14 | 0.5% (max) |
N2O | 0.05 | 0.8% (max) |
Loss of ignition | 0.64 | 6% (max) |
Lime saturation factor | 0.92 | — |
C3S | 52.82 | — |
C2S | 21.45 | — |
C3A | 9.16 | — |
C4AF | 10.2 | — |
The superplasticizer (SP) is Conplast SP1000 obtained from Fosroc Sdn. Bhd. and was used to establish the desired workability of mixes. The fine aggregate was natural sand, with fineness modulus of 2.86 and maximum size of less than 5 mm. The palm fiber was supplied by Fiber-X (M) Sdn. Bhd, and their characteristics are shown in Table
Physical properties of palm fiber.
Fiber Properties | Quantity |
---|---|
Average fiber length (mm) | 30 |
Average fiber width, micron | 21.13 |
Tensile strength (MPa) | 21.2 |
Elongation at break (%) | 0.04 |
Specific gravity | 1.24 |
Water absorption (%), 24/48 hrs | 0.6 |
Physical properties of synthetic fiber (Barchip).
Fiber properties | Quantity |
---|---|
Average fiber length (mm) | 30 |
Average fiber width (mm) | 0.52 |
Tensile strength (MPa) | 550 |
Young’s modulus (GPa) | 8.2 |
Specific gravity | 0.92 |
Melting point (°C) | 150–165 |
Physical properties of steel fiber.
Fiber Properties | Quantity |
---|---|
Average fiber length, (mm) | 30 |
Average fiber diameter, (mm) | 0.56 |
Aspect ratio (L/d) | 54 |
Tensile strength (MPa) | >1100 |
Ultimate elongation (%) | <2 |
Specific gravity | 7.85 |
The mixes proportions of the different mortar mixes are given in Table
Mortar mixes proportions.
Index | Cement | Silica fume | Water | SP | Sand | W+S P/B | Steel fibre | Palm fibre | Synthetic fibre | Flow |
---|---|---|---|---|---|---|---|---|---|---|
(Kg/m3) | (Kg/m3) | (Kg/m3) | (%) | (Kg/m3) | (%) | (%) | (Barchip) | (mm) | ||
M0 | 550 | 55 | 260 | 1.8 | 1410 | 0.43 | 0 | — | — | 160 |
M1 | 550 | 55 | 260 | 1.8 | 1410 | 0.43 | 0.25 | — | — | 155 |
M2 | 550 | 55 | 260 | 1.8 | 1410 | 0.43 | 0.50 | — | — | 145 |
M3 | 550 | 55 | 260 | 1.8 | 1410 | 0.43 | 0.75 | — | — | 145 |
M4 | 550 | 55 | 260 | 2.0 | 1410 | 0.43 | 1.00 | — | — | 155 |
M5 | 550 | 55 | 260 | 2.0 | 1410 | 0.43 | 1.25 | — | — | 150 |
M6 | 550 | 55 | 260 | 2.0 | 1410 | 0.43 | 1.50 | — | — | 150 |
M7 | 550 | 55 | 260 | 2.2 | 1410 | 0.43 | 1.75 | — | — | 145 |
M8 | 550 | 55 | 260 | 2.2 | 1410 | 0.43 | 2.00 | — | — | 140 |
M9 | 550 | 55 | 260 | 2.2 | 1410 | 0.43 | 1.75 | 0.25 | — | 140 |
M10 | 550 | 55 | 260 | 2.2 | 1410 | 0.43 | 1.50 | 0.50 | — | 145 |
M11 | 550 | 55 | 260 | 2.2 | 1410 | 0.43 | 1.25 | 0.75 | — | 145 |
M12 | 550 | 55 | 260 | 2.2 | 1410 | 0.43 | 1.0 | 1.0 | — | 150 |
M13 | 550 | 55 | 260 | 2.2 | 1410 | 0.43 | 1.0 | 0. 5 | 0. 5 | 145 |
M14 | 550 | 55 | 260 | 2.2 | 1410 | 0.43 | 1.25 | 0.5 | 0.25 | 145 |
M15 | 550 | 55 | 260 | 2.2 | 1410 | 0.43 | 1.25 | 0.25 | 0.5 | 145 |
M16 | 550 | 55 | 260 | 2.2 | 1410 | 0.43 | 1.5 | 0.25 | 0.25 | 140 |
Each test result is represented by three cube samples 50 mm and tested to determine the compressive strength at 90 days of normal water curing and further 90 days and 180 days of seawater exposure. The flow test for the mixes was performed according to ASTM C230 [
The results of flow of the mortar mixes are shown in Table
The effect of the inclusion of palm and Barchip fibers (M13–M16) on the flowability of mortar was found to be better than that of steel fibers. Therefore, the inclusion of palm and Barchip fibers provides better flowing or working capacity than that of the mixes with only steel fiber [
The results of the compressive strength of HSFM mixes show that the incorporation of steel fibers increases the compressive strength due to the improvement in the mechanical bond strength between the steel fibers and mortar where the fibers contribute to delay of microcrack formation and arrest their propagation afterwards up to a certain extent of fiber volume fraction [
The splitting tensile strength results of the HSFM mixes show that there is a significant increase in splitting tensile strength by the inclusion of fibers. The results of steel fiber-mortar mixes show that as the splitting tensile strength of flowable mortar increases as the steel fibers inclusions increase. Therefore, the effect of using 2% of steel fiber on the splitting tensile strength is the most significant. The increases in splitting tensile strength by using this percentage of steel fiber (M8) were found to be as much as 38% higher than that of the control mortar mix (M0) in the latter ages [
The flexural strength results of HSFM mortar mixes show that the increase of the flexural strength is compatible with the increase of steel fiber volume fractions. The increase of the flexural strength of the mix containing 1.75% volumetric fraction of steel fiber (M7) is about 102% higher than the control mix (M0), and this is possibly due to the better compaction and homogeneity of fiber distribution in HSFM [
However, the results of hybrids fibers indicate that the increases in flexural strength are much effective. It can be noticed that the increase in flexural strength by hybrid fibers containing 1.5% steel fiber + 0.5% palm fiber was found to be about 107% higher than that of the control mortar. Consequently, the flexural strengths of hybrid fibers HSFM by using steel fibers, palm fibers, and Barchip fibers showed that the highest increase in flexural strength is 116%, which was derived from the mix containing hybrid fibers of 1.5% steel fibers + 0.25% palm fibers + 0.25% Barchip fibers. This effective increase in flexural strength maybe resulted from better compaction and homogeneity of fibers distribution in mortar mixes and the ability of different types of fibers to restrain and bridge the cracks [
The moduli of elasticity results showed that there is a significant improvement in static modulus of elasticity for HSFM mixes by the inclusion of the steel fibers. The comparison between (M0) and (M8) shows that the use of 2.0% steel fibers leads to an increase in static modulus of elasticity. The static modulus of elasticity increased by about 28% with the inclusion of steel fibers. This could be due to the fact that steel fibers have high stiffness resulting in a higher modulus of elasticity for HSM [
The ultrasonic test results for all HSFM are given in Table
Ultrasonic, absorption, and voids for HSFM.
Mix type | SF (%) | PF (%) | BF (%) | Ultrasonic (m/s) 90 days | Absorption (%) 90 days | Voids (%) 90 days |
---|---|---|---|---|---|---|
M0 | — | — | — | 3770 | 10.62 | 20.3 |
M1 | 0.25 | — | — | 3860 | 10.54 | 19.86 |
M2 | 0.50 | — | — | 3920 | 10.14 | 19.56 |
M3 | 0.75 | — | — | 4030 | 9.93 | 19.17 |
M4 | 1.0 | — | — | 4070 | 9.81 | 19.10 |
M5 | 1.25 | — | — | 4280 | 9.56 | 18.98 |
M6 | 1.50 | — | — | 4190 | 9.32 | 18.53 |
M7 | 1.75 | — | — | 4130 | 9.21 | 18.38 |
M8 | 2.0 | — | — | 4110 | 9.1 | 16.78 |
M9 | 1.75 | 0.25 | — | 4140 | 9.18 | 17.73 |
M10 | 1.50 | 0.50 | — | 4100 | 9.22 | 18.14 |
M11 | 1.25 | 0.75 | — | 4080 | 9.45 | 18.74 |
M12 | 1.0 | 1.0 | — | 4060 | 9.6 | 18.92 |
M13 | 1.0 | 0.50 | 0.50 | 4020 | 9.54 | 18.81 |
M14 | 1.25 | 0.50 | 0.25 | 4080 | 9.36 | 18.37 |
M15 | 1.25 | 0.25 | 0.50 | 4100 | 9.28 | 18.22 |
M16 | 1.50 | 0.25 | 0.25 | 4160 | 9.14 | 17.32 |
Relation between volume fraction of steel fiber and ultrasonic pulse velocity for HSFM at 90 days.
The results for all hybrid fibers also show that the ultrasonic results increases with the fibers inclusions. The highest value of hybrid fibers for HSFM was 4160 m/s, which was obtained in mortar mix (M16) using 1.50% steel fiber + 0.25% palm fiber + 0.25% Barchip fiber. In general, for the all hybrid fibers (HSFM reinforced with steel fibers + palm fibers and also HSFM reinforced with steel fibers + palm fibers + Barchip fibers), the ultrasonic pulse velocity is also related to compressive strength as illustrated in Figure
Relationship between compressive strength and ultrasonic pulse velocity for HSFM reinforced by hybrid fibres.
The results of the absorption and voids ratio of HSFM mixes are shown in Table
Relationship between volume fraction of steel fibre and percentage of absorption for HSFM.
Absorption reduction percentage of HSFM by using hybrid fibres [steel fibres (SF) + palm fibres (PF)].
Absorption reduction percentage of HSFM by using hybrid fibres [steel fibres (SF) + palm fibres (PF) + Barchip fibres (BF)].
The results of the HSFM mixes exposed to seawater are represented from Tables
Compressive strength of HSFM exposed to seawater.
Mix type | SF (%) | PF (%) | BF (%) | Compressive strength (MPa) 90-day normal water curing | Compressive strength (MPa)180 days (90-day normal water curing + |
Compressive strength (MPa) 270 days (90-day normal water curing + |
---|---|---|---|---|---|---|
M0 | — | — | — | 59.6 | 58.1 | 53.3 |
M1 | 0.25 | — | — | 66.5 | 64.3 | 61.2 |
M2 | 0.50 | — | — | 68.1 | 64.7 | 62.4 |
M3 | 0.75 | — | — | 69.1 | 65.1 | 63.2 |
M4 | 1.0 | — | — | 70.4 | 66.1 | 64.3 |
M5 | 1.25 | — | — | 71.8 | 66.0 | 64.6 |
M6 | 1.50 | — | — | 68.4 | 64.5 | 62.1 |
M7 | 1.75 | — | — | 66.1 | 63.6 | 61.1 |
M8 | 2.0 | — | — | 61.4 | 58.6 | 56.7 |
M9 | 1.75 | 0.25 | — | 65.6 | 62.9 | 60.1 |
M10 | 1.50 | 0.50 | — | 67.7 | 65.5 | 63.0 |
M11 | 1.25 | 0.75 | — | 61.1 | 59.5 | 57.3 |
M12 | 1.0 | 1.0 | — | 60.9 | 58.7 | 57.2 |
M13 | 1.0 | 0.50 | 0.50 | 59.8 | 58.2 | 56.7 |
M14 | 1.25 | 0.50 | 0.25 | 61.9 | 60.4 | 58.8 |
M15 | 1.25 | 0.25 | 0.50 | 63.8 | 61.7 | 60.7 |
M16 | 1.50 | 0.25 | 0.25 | 68.2 | 65.9 | 64.0 |
Splitting tensile strength of HSFM exposed to seawater.
Mix type | SF (%) | PF (%) | BF (%) | Splitting tensile strength (MPa) 90 days | Splitting tensile strength (MPa)180 days (90-day normal water curing + 90-day seawater curing) | Splitting tensile strength (MPa) 270 days (90-day normal water curing + 180-day seawater curing) |
---|---|---|---|---|---|---|
M0 | — | — | — | 2.34 | 2.28 | 2.22 |
M1 | 0.25 | — | — | 2.46 | 2.41 | 2.36 |
M2 | 0.50 | — | — | 2.68 | 2.62 | 2.58 |
M3 | 0.75 | — | — | 2.78 | 2.72 | 2.68 |
M4 | 1.0 | — | — | 2.90 | 2.86 | 2.81 |
M5 | 1.25 | — | — | 2.96 | 2.88 | 2.85 |
M6 | 1.50 | — | — | 3.0 | 2.91 | 2.87 |
M7 | 1.75 | — | — | 3.12 | 3.04 | 2.97 |
M8 | 2.0 | — | — | 3.21 | 3.11 | 3.02 |
M9 | 1.75 | 0.25 | — | 3.33 | 3.26 | 3.16 |
M10 | 1.50 | 0.50 | — | 3.41 | 3.37 | 3.27 |
M11 | 1.25 | 0.75 | — | 2.79 | 2.75 | 2.70 |
M12 | 1.0 | 1.0 | — | 2.65 | 2.62 | 2.59 |
M13 | 1.0 | 0.50 | 0.50 | 2.87 | 2.81 | 2.80 |
M14 | 1.25 | 0.50 | 0.25 | 2.93 | 2.86 | 2.84 |
M15 | 1.25 | 0.25 | 0.50 | 3.08 | 2.98 | 2.97 |
M16 | 1.50 | 0.25 | 0.25 | 3.74 | 3.66 | 3.59 |
Flexural strength of high-strength flowable mortar exposed to seawater.
Mix type | SF (%) | PF (%) | BF (%) | Flexural strength (MPa) 90-day normal water curing | Flexural strength (MPa) 180 days (90-day normal water curing + 90-day seawater curing) | Flexural strength (MPa) 270 days (90-day normal water curing + 180-day seawater curing) |
---|---|---|---|---|---|---|
M0 | — | — | — | 9.12 | 8.96 | 8.50 |
M1 | 0.25 | — | — | 9.88 | 9.64 | 9.22 |
M2 | 0.50 | — | — | 11.24 | 11.02 | 10.50 |
M3 | 0.75 | — | — | 12.68 | 12.32 | 11.92 |
M4 | 1.0 | — | — | 14.43 | 13.95 | 13.60 |
M5 | 1.25 | — | — | 14.85 | 14.28 | 13.90 |
M6 | 1.50 | — | — | 15.33 | 14.72 | 14.25 |
M7 | 1.75 | — | — | 18.42 | 17.72 | 17.11 |
M8 | 2.0 | — | — | 17.36 | 16.56 | 16.0 |
M9 | 1.75 | 0.25 | — | 17.64 | 17.10 | 16.51 |
M10 | 1.50 | 0.50 | — | 19.22 | 18.70 | 18.15 |
M11 | 1.25 | 0.75 | — | 14.95 | 14.58 | 14.16 |
M12 | 1.0 | 1.0 | — | 13.26 | 12.85 | 12.65 |
M13 | 1.0 | 0.50 | 0.50 | 14.15 | 13.90 | 13.52 |
M14 | 1.25 | 0.50 | 0.25 | 15.11 | 14.70 | 14.30 |
M15 | 1.25 | 0.25 | 0.50 | 15.24 | 14.81 | 14.50 |
M16 | 1.50 | 0.25 | 0.25 | 19.67 | 19.15 | 18.50 |
Static modulus of elasticity (
Mix type | SF (%) | PF (%) | BF (%) | Static modulus of elasticity, |
Static modulus of elasticity, |
Static modulus of elasticity, |
---|---|---|---|---|---|---|
M0 | — | — | — | 36.3 | 35.8 | 34.1 |
M1 | 0.25 | — | — | 36.8 | 35.9 | 34.6 |
M2 | 0.50 | — | — | 38.1 | 36.9 | 35.9 |
M3 | 0.75 | — | — | 38.9 | 37.7 | 36.9 |
M4 | 1.0 | — | — | 40.1 | 39.0 | 37.9 |
M5 | 1.25 | — | — | 41.1 | 39.9 | 38.7 |
M6 | 1.50 | — | — | 43.7 | 42.1 | 41.0 |
M7 | 1.75 | — | — | 45.2 | 44.0 | 42.3 |
M8 | 2.0 | — | — | 46.3 | 44.7 | 42.9 |
M9 | 1.75 | 0.25 | — | 48.3 | 46.8 | 45.3 |
M10 | 1.50 | 0.50 | — | 45.8 | 44.9 | 43.2 |
M11 | 1.25 | 0.75 | — | 43.0 | 42.0 | 41.0 |
M12 | 1.0 | 1.0 | — | 42.2 | 41.3 | 40.5 |
M13 | 1.0 | 0.50 | 0.50 | 41.5 | 40.4 | 39.9 |
M14 | 1.25 | 0.50 | 0.25 | 48.4 | 47.2 | 46.2 |
M15 | 1.25 | 0.25 | 0.50 | 49.7 | 48.6 | 47.6 |
M16 | 1.50 | 0.25 | 0.25 | 51.7 | 50.6 | 49.1 |
Compressive strength reduction percentage of HSFM after exposure to seawater.
The results of the splitting tensile strength of mortar mixes showed that the effect of seawater on the splitting tensile strength was marginal. However, it can be seen from Figure
Splitting tensile strength reduction percentage of HSFM after exposure to seawater.
In addition, the results of the flexural strength of mortar indicated that the reduction of about 4.5–8% was obtained for the flexural strength of HSFM exposed to seawater. The flexural strength reduction of the mixes is shown in Figure
Flexural strength reduction percentage of HSFM after exposure to seawater.
The results of static modulus of elasticity show that there is a reduction between 4–7% in elastic modulus of elasticity of mortar after 180 days of exposure to seawater as shown in Figure
Static modulus of elasticity reduction percentage of HSFM after exposure to seawater.
The study of high-strength flowable mortar (HSFM) reinforced by various fibers was carried out to understand the different mechanical properties and the durability of HSFM exposed to seawater. The major findings of this study are the compressive strength results for HSFM show that the use of the steel fibers increases the compressive strength. The highest increase (about 21%) was obtained for the HSFM mixes with 1.25% of steel fiber. The compressive strength results of HSFM reinforced by hybrid fibers of 1.5% steel fibers + 0.25% palm fibers + 0.25% Barchip fibers provide a significant increase in the compressive strength of cement mortar; the flexural strength of HSFM mixes containing steel fibers increased with the increasing volume fraction. The highest values for these properties were obtained when 1.75% of steel fiber was included in the mix. Whereas, the flexural strength of HSFM of hybrid fibers (1.5% steel fiber + 0.25% palm fiber + 0.25% Barchip fibers) boasts the highest flexural strength compared to other HSFM mixes; the hybridization of 1.5% steel fibers with the 0.5% of palm fibers for the HSFM increases the splitting tensile strength by about 38%. Whereas the hybrid fibers of 1.5% steel fibers + 0.25% palm fibers + 0.25% Barchip fibers increases the splitting tensile strength by about 60%; hybridization was also found to be effective in enhancing the modulus of elasticity of HSFM. Combining the volume fractions of 1.75% steel fiber and 0.25% palm fibers or 1.5% steel fibers, 0.25% palm fibers and 0.25% Barchip fibers increases the static modulus of elasticity by about 33% and 42%, respectively; the results indicated that the steel fibers improved the results of the velocity of the ultrasonic test. The ultrasonic velocity increased from 3770 m/s to 4190 m/s from the inclusion of 2% vol. of steel fibers in HSFM mixes. The highest value of the ultrasonic pulse velocity test (4280 m/s) was obtained when 1.25% vol. of steel fibers was used; the inclusion of 2% of steel fibers in HSFM reduced the absorption and voids ratio from 10.62% and 20.3% to 9.1% and 16.72%, respectively. Besides the reduction of absorption and voids ratio, it was also observed that the Barchip fibers have better ability to improve these properties than palm fibers in all hybrid HSFM mixes tested; in terms of durability, after seawater exposure, the minimum reduction in compressive strength was obtained for the HSFM mixes of hybrid fibers in the cases of using steel fibers with palm fibers and also for the use of steel, palm, and Barchip fibers; the reduction in splitting tensile strength and flexural strength for HSFM was between 2–6%, and the maximum reduction was obtained in case of using 2% steel fibers in the mortar mixes. Besides, the reduction in static modulus of elasticity for HSFM was between 3–8% in the modulus of elasticity of mortar after 180 days of exposure to seawater. The minimum reduction of static modulus of elasticity was also obtained for the HSFM mixes of hybrid fibers of steel, palm, and Barchip fibers.
The paper has not been previously published, is not currently submitted for review in any other journal, and will not be submitted elsewhere before any decision is made by the authors of this journal.
The work described in this paper was a part of Ph.D. research program of the first author which is supported by a research grant and USM fellowship from the Universiti Sains Malaysia.