Effect of water to binder ratio and sand to binder ratio on shrinkage and mechanical properties of High-strength Engineered Cementitious Composite

Construction and Building Materials 226 (2019) 899–909

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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

Effect of water to binder ratio and sand to binder ratio on shrinkage and mechanical properties of High-strength Engineered Cementitious Composite Binbin Ye a, Yaoting Zhang a, Jianguo Han b,⇑, Peng Pan b a b

School of Civil Engineering & Mechanics, Huazhong University of Science and Technology, Wuhan 430074, China Department of Civil Engineering, Tsinghua University, Beijing 100084, China

h i g h l i g h t s  Total shrinkage of HSECC decreases along with the increase of W/B and S/B.  Magnitude of autogenous shrinkage approaches that of drying shrinkage along with the increase of S/B.  Summit of tensile strength and compressive strength appeared with the increase of S/B.  Ductility of HSECC is injured with the increase of S/B, especially when S/B greater than 0.6.  Decreased mortar workability and fiber distribution quality injures HSECC strength and ductility.

a r t i c l e

i n f o

Article history: Received 2 June 2019 Received in revised form 12 July 2019 Accepted 26 July 2019

Keywords: HSECC Water-to-binder ratio Sand-to-binder ratio Shrinkage Strength

a b s t r a c t High-strength Engineered Cementitious Composite (HSECC) usually features with low water-to-binder ratio (W/B) and low sand-to-binder ratio (S/B), for obtaining expected workability, mechanical property and multi-crack behavior. However, the low W/B and low S/B of HSECC can cause high shrinkage, which will jeopardize its volume stability and durability. In this paper, the influence of W/B and S/B on HSECC volume stability including chemical shrinkage, autogenous shrinkage and drying shrinkage, mechanical properties including compressive strength, tensile strength, tensile strain and tensile strain energy were investigated. Experiment results showed that in the W/B range of 0.13–0.24, S/B range of 0.3–0.9, the magnitude of chemical shrinkage overwhelms autogenous shrinkage and drying shrinkage; meanwhile, along with the increase of W/B and S/B, the total shrinkage is lowed and the magnitude of autogenous shrinkage tends to be comparable with drying shrinkage. In the W/B range of 0.13–0.24, along with the increase of S/B from 0.3 up to 0.8, the compressive strength and tensile strength was enhanced, however, the ductility of HSECC was lowed especially when S/B was greater than 0.6; when S/B was enhanced to 0.9, all the mechanical properties and ductility was severely injured. So, the optimum S/B of HSECC should be decided by systematically considering its influence on volume stability, mechanical strength and ductility. Ó 2019 Published by Elsevier Ltd.

1. Introduction Generally speaking, the fracture behavior of cementitious materials can be classified into three categories, as shown in Fig. 1, (1) Normal concrete, which usually manifests quasi-brittle failure behavior; (2) Strain-softening fiber reinforced concrete (FRC), which usually manifests gradual failure behavior, benefiting from the bridging effect of light dosaged fiber; (3) Strain-hardening ⇑ Corresponding author. E-mail address: [email protected] (J. Han). https://doi.org/10.1016/j.conbuildmat.2019.07.303 0950-0618/Ó 2019 Published by Elsevier Ltd.

FRC, which usually manifests stain-hardening behavior and distinguishing matrix crack strength and composite failure strength [1]. Meanwhile, Strain-hardening FRC can be further classified into Steel fiber FRC [2], Normal strength ECC (NSECC) [2] and HSECC [3], by selecting proper type of fiber and regulating the mix proportion of Strain-hardening FRC. Both NSECC and HSECC are made with high fiber dosage (volume percentage usually not less than 2%) to obtain the expected strain-hardening property and the multi-crack behavior, by facilitating the fiber bridging ability and the fiber-matrix pull out energy. Based on their high ductility and multi-crack behavior,

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Fig. 1. Properties of cementitious materials under tension.

NSECC and HSECC has been used in the plastic hinge area in structure, such as beam-column joint and shear wall base; meanwhile, NSECC and HSECC has also been used as protection layer of reinforce concrete to promote structure durability, by facilitating its multi-crack behavior and micro-crack self-healing ability [1]. Tension strain of NSECC and HSECC is usually in the range of 0.03–0.08 and the multi-crack width is usually less than 200 lm [3–11] Compared with NSECC, HSECC features with higher composite failure strength (over 7.5 MPa) and comparable tensile ductility. To obtain the expected workability, fiber distribution homogeneity, tensile strength, strain-hardening and multi-crack behavior, HSECC has been made with low W/B (less than 0.20) and low S/B (less than 0.45) as shown in Table 1. As can be seen from Table 1 that HSECC developed in published paper is of W/B varied from 0.13 to 0.20, S/B varied from 0.083 to 0.42, and fiber dosage varied from 2.0% to 2.2%. The low W/B (less than 0.20) of HSECC can cause severe autogenous shrinkage due to the hydration of binder with unsaturated capillary pore; the low S/B can hinder the restraining effect of aggregate on shrinkage and increase the paste volume percentage which severs as the origin of shrinkage. Under internal or external restriction, the shrinkage can result in crack of HSECC specimen. Although HSECC can partially relief shrinkage stress by forming multi-crack, however, to guarantee the mechanical property, anti-penetration ability, ductility and serviceability of HSECC structure, the volume stability of HSECC still merits further research [11–17].

In Japan JSCE standard, it is recommend that some measurements should be adopt for optimizing the volume stability of ECC [13]. Ahmaran showed that autogenous shrinkage and drying shrinkage of NSECC can be reduced by 67% and 37% respectively, by partially replacing sand by saturated lightweight aggregate, however, the tensile and flexural strength of NSECC is injured [14]. Yu showed that the combination of calcium sulfoaluminate cement and shrinkage reducing admixture can lower NSECC drying shrinkage up to 30%. Using zeolite as internal curing particle, Zheng showed that drying shrinkage of NSECC can be lowered to about 25% of the control specimen, the tensile strength can be enhanced by 14% and the multi-crack width can be decreased by 50% [17]. Up to now, research about the volume stability of HSECC is limited. For optimizing the volume stability, mechanical properties and ductility of HSECC, the origin of shrinkage and the effect of aggregate volume percentage on shrinkage, mechanical properties and ductility should be clarified. In present paper, HSECC made with UHMWPE fiber, varied W/B (0.13–0.24) and S/B (0.3–0.9) were investigated, to explore the influence of these factors on HSECC chemical shrinkage, autogenous shrinkage, drying shrinkage, compressive strength, tensile strength, tensile strain and tensile strain energy. 2. Experiment 2.1. Material and mix proportion Materials adopted for preparing HSECC include cementitious materials (binder), aggregate, UHMWPE fiber, Polycarboxylate Superplasticizer and water. Type I Portland cement, slag, silica fume and cenosphere were used as binder, their chemical composition is given in Table 2. Silica sand was used as aggregate. Particle size distributions of cement, slag and silica sand measured by Laser Particle Size Analyzer are give in Fig. 2. Particle size of silica fume and cenosphere cannot be accurately determined by laser particle size analysis method, thus, the particle size of these material is observed by SEM. Properties of UHMWPE fiber is given in Table 3. Morphology of binder, silica sand and UHMWPE fiber observed by SEM is shown in Fig. 3. Mix proportion of HSECC designed in this paper is given in Table 4, in which the range of W/B is 0.17–0.24, and the range of S/B is 0.3–0.9. HSECC with W/B = 0.13 and S/B = 0.3 is also designed for the purpose of comparison. The volume dosage of UHMWPE fiber is set as 2%. 2.2. Specimen preparation and mixing regime Fresh HSECC was prepared by a planetary mixer, with rotating speed of 285 rpm and rotating torque of 18.43 Nm. The preparation of fresh HSECC includes two stages, first, adding silica sand, binder, water and superplasticizer to mixer to get fluid mortar; second, adding UHMWPE fiber to mixer gradually to get HSECC paste. After the preparation of HSECC paste, the paste was casted into mold and given proper vibration to guarantee the casting quality. After casting, HSECC specimen was covered by plastic membrane and cured under room temperature for 24 h. After demolding, the HSECC specimen was cured in calcium hydroxide saturated water of 20 °C until testing.

Table 1 Matrix and fiber properties of HSECC in published paper. Organization

Nagoya University 2008 [4] University of Michigan 2013 [5] Dresden University of Technology 2017 [6] Tongji University 2018 [7] Hong Kong University of Science and Technology 2018 [8] Southeast University 2019 [9] Chongqing University 2019 [10]

Matrix properties

Fiber properties and dosage

W/B

S/B

Fiber type

L/mm

D/lm

Strength/GPa

E/GPa

Dosage/Vol%

0.18 0.15 0.18 0.13 0.15 0.15 0.20

0.1 0.42 0.083 0.29 0.3 0.36 0.3

UHMWPE UHMWPE HDPE UHMWPE UHMWPE UHMWPE UHMWPE

6 12.7 6 18 12 12 18

12 28 20 20 24 24 26

2.7 3.0 2.5 3.0 3.0 2.9 3.0

– 100 80 100 120 116 –

2.0 2.0 2.0 2.0 2.2 2.0 2.0

Notes: W/B—Water to binder ratio, S/B—Sand to binder ratio, L—length of fiber, D—Diameter of fiber, E—Elastic modulus of fiber, UHMWPE—Ultra-high molecular weight polyethylene, HDPE—High density polyethylene.

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B. Ye et al. / Construction and Building Materials 226 (2019) 899–909 Table 2 Chemical composition of cementitious materials (% by Weight). Name

CaO

SiO2

Al2O3

Fe2O3

SO3

MgO

K2O

Ti2O

Na2O

L.O.I.

Cement Silica fume Cenosphere Slag

66.11 0.48 7.55 39.49

19.25 93.39 58.15 32.66

3.79 0.58 16.57 14.65

3.21 0.10 7.65 1.19

1.75 0.29 0.20 2.47

1.56 0.39 0.88 7.13

0.58 1.36 1.86 0.49

0.29 0.00 0.88 0.79

0.19 0.19 0.88 0.49

2.76 3.02 1.87 1.02

Relative density of HSECC specimen was measured using 100 mm cubic sample, according to ASTM C127 standard [19].

2.3.3. Tensile performance test HSECC specimen of size 200 mm*100 mm*20 mm was used for tensile performance test. As illustrated in Fig. 8, the HSECC sample was clamped between two hydraulic grip, with 4 MPa clamping stress. Two extensometers were installed at both sides of the sample, with the measuring distance of 50 mm. Tensile test of HSECC sample was performed at constant displacement speed of 0.5 mm/min. The typical stress strain curve obtained from tensile test of HSECC sample is illustrated in Fig. 9. The stress strain curve shows the strain hardening behavior of HSECC and the zigzag fluctuation of stress during tensile process. Meanwhile, from this curve, the matrix crack stress, matrix crack strain, composite failure strength, composite failure strain can be identified. Tensile strain energy corresponding to composite failure stress was calculated by integrating the stress strain curve up to the composite failure strain, as the Gt area shown in Fig. 9 [7].

3. Results and analysis Fig. 2. Particle size distribution of cement, slag and silica sand.

3.1. Effect of W/B and S/B on chemical shrinkage and autogenous shrinkage 2.3. Testing methods 2.3.1. Shrinkage test According to the shrinkage mechanism, shrinkage of cementitious materials can be classified into chemical shrinkage, autogenous shrinkage and drying shrinkage. chemical shrinkage and autogenous shrinkage usually happens under sealed condition. The separation point of chemical shrinkage and autogenous shrinkage locates at the initial set point [18]. The aforementioned three types of shrinkage are illustrated in Fig. 4. The chemical shrinkage and autogenous shrinkage of HSECC was measured by laser displacement sensor under sealed condition, as illustrated in Fig. 5. After the preparation of HSECC paste, the paste was filled into a cone shape container, a smooth epoxy plate was placed into the paste surface and the surface of the paste was covered by a plastic film, a circle aperture was cut in the plastic film to expose the epoxy plate to laser beam. Meanwhile, the temperature of HSECC paste was also measured by thermo-sensor. The HSECC cone sample was 125 mm in diameter and 125 mm in height, the epoxy plate was a 5 mm cube, the sample for temperature test was 20 mm in diameter and 100 mm in height. The measurement of the shrinkage and temperature of HSECC paste was began right after the sample installation, about 30 min after adding water to binder. The initial set point was defined by the measured temperature curve, which locates at the beginning point of the acceleration period, as illustrated in Fig. 6. The chemical shrinkage and autogenous shrinkage under sealed condition was measured for 42 h. Drying shrinkage test of HSECC was performed on 40 mm*40 mm*160 mm prism sample. The HSECC specimen was demolded 24 h after casting and transferred to environment room of T = 20 °C and RH = 60%. After 16 h humidity equilibrium time, the sample was installed into the testing apparatus as shown in Fig. 7, the initial reading of the dial gauge was recorded at 42 h after adding water to binder for the preparation of HSECC specimen. The value of the dial gauge was recorded every day for 28 days. Drying shrinkage was calculated based on sample size and dial gauge readings. 2.3.2. Compressive strength and relative density measurement Compressive strength of HSECC specimen was tested using 40 mm cubic sample, with loading speed of 2.4 kN/s.

The combined chemical shrinkage and autogenous shrinkage of HSECC with different W/B and S/B is show in Fig. 10. As can be seen that the combined chemical shrinkage and autogenous shrinkage decrease along with the increase of W/B and S/B. According to the initial set time decided by the measured temperature curve, as given in Fig. 6, chemical shrinkage and autogenous shrinkage can be separated from Fig. 10, and the magnitude of each type of the shrinkage is shown in Fig. 11. As can be seen that along with the increase of W/B and S/B, the chemical shrinkage and autogenous shrinkage is decreased accordingly. The chemical shrinkage comes from the volume difference of hydrated cement and consumed water with the volume of hydration products [20–22]; the autogenous shrinkage comes from chemical shrinkage and the volume shrinkage due to capillary tension resulted from the unsaturation of capillary pore. The decrease of W/B can enhance cement volume percentage in per unit volume of HSECC and aggravate the unsaturation status of the capillary pore, thus the decrease of W/B will enhance chemical shrinkage and autogenous shrinkage [23–25]. The enhancement of S/B can decrease cement paste percentage in per unit volume of HSECC, which serves as the origin of chemical shrinkage and autogenous shrinkage, so, the enhancement of S/B can decrease the magnitude of chemical shrinkage and autogenous shrinkage. Autogenous shrinkage of NSECC is usually less than 1000 le [14]. As can be seen from Fig. 11b that the autogenous shrinkage of HSECC with S/B equals to 0.3 is greater than that of NSECC, however, with the increase of S/B, the autogenous shrinkage of HSECC can be reduced to comparable value or even less than that of NSECC.

Table 3 Properties of UHMWPE fiber. Density /g/cm3

L/mm

D/lm

Aspect ratio

Strength/GPa

E/GPa

Elongation/%

Melting point/oC

0.97

12

25

480

3.0

100

2.2

150

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(a) Cement

(b) Slag

(c) Silica fume

(d) Cenophere

(e) Silica sand

(f) UHMWPE fiber

Fig. 3. Morphology of binder, aggregate and fiber.

Table 4 Mix proportion of HSECC (Mass ratio). No.

Cement

SF

Slag

Cenosphere

Sand

Water

S/B

W/B

WRA

MSF/mm

Fiber/Vol%

H-1 H-2 H-3 H-4 H-5 H-6 H-7 H-8 H-9 H-10 H-11 H-12 H-13

0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65

0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1

0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1

0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15

0.3 0.6 0.8 0.9 0.3 0.6 0.8 0.9 0.3 0.6 0.8 0.9 0.3

0.17 0.17 0.17 0.17 0.20 0.20 0.20 0.20 0.24 0.24 0.24 0.24 0.13

0.3 0.6 0.8 0.9 0.3 0.6 0.8 0.9 0.3 0.6 0.8 0.9 0.3

0.17 0.17 0.17 0.17 0.20 0.20 0.20 0.20 0.24 0.24 0.24 0.24 0.13

0.017 0.028 0.044 0.049 0.010 0.018 0.025 0.032 0.008 0.011 0.016 0.019 0.025

205 185 150 120 227 205 185 155 247 220 195 185 195

2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0

SF: Silica fume; MSF: Mortar slump flow before the adding of fiber.

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W/B and S/B, the magnitude of chemical shrinkage overwhelms that of the other two kinds of shrinkage; the magnitude of autogenous shrinkage is dominant over or comparative with that of drying shrinkage along with the increase of S/B.

3.3. Effect of W/B and S/B on strength

Fig. 4. Shrinkage classification.

3.2. Effect of W/B and S/B on drying shrinkage Drying shrinkage of HSECC with different W/B and S/B is given in Fig. 12. As can be seen that drying shrinkage decreases with the decrease of W/B and the increase of S/B. During the drying process, water loss from HSECC sample causes drying shrinkage, the decrease of W/B can lower the content of capillary pore and hinders connectivity of capillary pore; meanwhile, the decrease of W/B can narrow the size distribution of capillary pore and increase water loss barrier (according to the Kelvin equation). So, the decrease of W/B can lower the tendency of drying shrinkage. The increase of S/B can lower volume percentage of cement paste and facilitate the skeleton effect of aggregate, thus decrease the magnitude of drying shrinkage. It can be seen from Fig. 12 that drying shrinkage of HSECC at 28 days is less than 1000 le, and the reported drying shrinkage of NSECC at 28 days is in the range of 1200 le and 1800 le [15,16]. So, the drying shrinkage of HSECC is usually less than that of NSECC. Fig. 13 shows the total shrinkage of HSECC, including chemical shrinkage, autogenous shrinkage and drying shrinkage. As can be seen that the total shrinkage decreases along with the increase of

Tensile stress strain curve of HSECC with different W/B and S/B is given in Fig. 14. For each type of HSECC, two stress strain curve is given for demonstrating its repeatability. As can be seen from Fig. 14 that under each specific S/B, tensile strength (including matrix crack strength and composite failure strength) is lowered along with the increase of W/B. Meanwhile, along with the increase of S/B, the average composite failure stain is lowered when S/B is greater than 0.6. Representative sample (H-3 and H-13) of the HSECC specimen prepared in this paper after tensile test are shown in Figs. 15 and 16 respectively, in which the fiber morphology on fracture surface and multi-crack on specimen surface are revealed, to demonstrating the fiber pull-out failure behavior and the multi-crack failure pattern of HSECC specimen. From Fig. 14, the tensile strength of HSECC is determined and given in Figs. 17 and 18. It can be seen from Figs. 17 and 18 that along with the decrease of W/B, the tensile strength of HSECC is increased accordingly. Along with the increase of S/B, the tensile strength first increase to a summit and then decreased, and the summit locates at S/B = 0.80. Zhang also revealed that continuously increasing S/B over 0.8 will decrease NSECC strength [16]. Compressive strength of HSECC is given in Fig. 19, as can be seen that the influence of W/B and S/B on compressive strength is of the same trend as that on tensile strength. Along with the decrease of W/B, the tensile strength and compressive strength are enhance, this can be attributed to the narrowing effect of decreasing W/B on capillary pore content, size distribution and connectivity of HSECC. Along with the increase of S/B, the appearance of tensile strength and compressive strength summit at S/B = 0.8, could be attributed to the following reason: (1) Along with the increase of S/B (from 0.3 to 0.8), there is less cement paste in unit volume of HSECC, resulted in less shrinkage and internal crack, which is beneficial to strength. Chen also found that increasing S/B up to 0.8 was beneficial to tensile strength of HSECC [8]. (2) Along with the increase of S/B, the mutual interlock and friction of sand particles will lower the workability of mortar; and this negative effect can only be partially compensated by increasing WRA dosage, over dosage of WRA would result in

Fig. 5. Chemical and autogenous shrinkage test.

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Fig. 6. Determination of initial set time on measured temperature curve. Fig. 9. Illustration of the stress strain curve of HSECC.

paste volume percentage will decrease the fiber distribution homogeneity and affect HSECC preparation quality. In Fig. 20, it can be seen that along with the increase of S/B, the relative density of HSECC revealed a summit at S/B = 0.8 also. Meanwhile, in Fig. 20 the number in brackets shows the porosity of the HSECC sample, which is calculated based on the mix proportion of HSECC, material specific density and measured relative density; it can be seen that all the HSECC with S/B = 0.9 has high porosity and this abnormally high porosity is resulted from poor mortar workability and fiber distribution quality. So, the injured strength of HSECC at S/B = 0.9 was caused by the abnormal porosity resulted from poor mortar workability and fiber distribution quality, especially the later factor. 3.4. Effect of W/B and S/B on ductility Fig. 7. Drying shrinkage test.

segregation and bleeding of mortar. The lowered workability could introduce more defect to mortar during preparation stage (3) The increase of S/B will decrease the volume percentage of cement paste in per unit of HSECC; the lowered workability and cement

Composite failure strain of HSECC characterizes its ductility. The influence of W/B and S/B on composite failure strain is given in Fig. 21. As can be seen that under each specific S/B, the influence of W/B (from 0.13 to 0.24) on the ductility of HSECC is not significant. However, the ductility of HSECC is significantly lowered with the increase of S/B, especially when S/B is greater than 0.6. The ten-

(a) Direct tension test diagram of HSECC Fig. 8. Tensile performance test of HSECC.

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(a) S/B=0.30

(b) S/B=0.60

(c) S/B=0.80

(d) S/B=0.90

Fig. 10. Combined chemical shrinkage and autogenous shrinkage of HSECC.

(a) Chemical shrinkage

(b) Autogenous shrinkage

Fig.11. Separated chemical shrinkage and autogenous shrinkage.

sile strain ability of HSECC depends on fiber failure mode and fiber distribution quality, the former is determined by fiber tensile strength and fiber-matrix bonding quality, the latter is determined by mortar workability, mixing quality and available fiber distribu-

tion space. The UHMWPE fiber used in this paper is of high tensile strength, resulting in pull-out failure mode as shown in Fig. 15, which is beneficial to tensile strain. Along with the increase of S/ B, the mortar workability and cement paste volume percentage

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(a) S/B=0.30

(b) S/B=0.60

(c) S/B=0.80

(d) S/B=0.90 Fig. 12. Drying shrinkage of HSECC.

tensile strain energy is significantly lowered when S/B is greater than 0.8.

4. Conclusion

Fig. 13. Total shrinkage of HSECC.

in per unit of HSECC is lowered, resulted in the damaged fiber distribution quality and the injured HSECC ductility. The influence of W/B and S/B on tensile strain energy (the Gt area in Fig. 9) of HSECC is given in Fig. 22. The combined effects of tensile strength and tensile ductility showed that tensile strain energy decreases along with the increase of W/B; meanwhile, the

(1) The total shrinkage of HSECC, including chemical shrinkage, autogenous shrinkage and drying shrinkage, decreases along with the increase of W/B and S/B. (2) The magnitude of chemical shrinkage overwhelms autogenous shrinkage and drying shrinkage; along with the increase of S/B, the magnitude of autogenous shrinkage is dominant over or comparative with that of drying shrinkage. (3) In the S/B range of 0.3–0.8, at each specific S/B value, along with the decrease of W/B, the tensile strength (including matrix crack strength and composite failure strength) and compressive strength is enhanced. However, at S/B = 0.9, the tensile strength, compressive strength and relative density of HSECC is injured, due to the high porosity resulted from poor mortar workability and fiber distribution quality. (4) The ductility of HSECC is significantly influenced by S/B compared with that of W/B, especially when S/B is greater than 0.6, over which the ductility of HSECC is substantially injured.

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(a) S/B=0.30

(b) S/B=0.60

(c) S/B=0.80

(d) S/B=0.90 Fig.14. Tensile stress strain curves of HSECC.

( a) H-3 (W/B=0.17,S/B=0.8)

(b) H-13 (W/B=0.13,S/B=0.3)

Fig.15. Fracture surface HSECC.

(a) H-3 (W/B=0.17, S/B=0.8)

( b) H-13 (W/B=0.13,S/B=0.3)

Fig.16. Multi-crack pattern of HSECC.

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Fig. 20. Relative density of HSECC. Fig.17. Matrix crack strength of HSECC.

Fig. 21. Effect of W/B and S/B on HSECC ductility. Fig.18. Composite failure strength of HSECC.

Fig. 19. Compressive strength of HSECC.

Fig. 22. Effect of W/B and S/B on tensile strain energy.

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