Utilization of Local Ingredients for the Production of High-Early-Strength Engineered Cementitious Composites

*e rapid repair and retrofitting of existing transportation infrastructure requires dimensional stability and ductile repair material that can obtain sufficiently high strength in a few hours to accommodate the large loading and deformation at an early age. Engineering cementitious composites (ECCs) is a class representative of the new generation of high-performance fiber-reinforced cement-based composites (HPFRCC) with medium fiber content. *e unique properties of tremendous ductility and tight multiple crack behavior indicate that ECC can be used as an effective retrofit material. *e wide application of this material in China will require the use of all local ingredients. In this study, based on Chinese domestic ingredients, including matrix materials and all fibers, high-early-strength ECC (HES-ECC) was designed under the guidance of strain-hardening criterion of ECC. *e matrix properties and fiber/matrix interfacial micromechanics properties were obtained from three-point-bending test and singlefiber pullout test. *e mechanical properties of HES-ECC were achieved by direct tensile test. *e experimental results show that HES-ECC was successfully developed by using all Chinese materials. When using the domestic PVA fiber at 2%, the strength requirement can be achieved but only a low ductility. When using the domestic PE fiber at 0.8%, the strength and deformation requirement both can be obtained. *e HES-ECC developed in this study exhibited compressive strength of more than 25MPa within 6 hours, and an ultimate tensile strength of 5-6MPa and tensile strain capacity of 3-4% after 60 days. Moreover, the cost of using domestic fiber can be largely reduced compared with using imported fiber, up to 70%; it is beneficial to the promotion of these high-early-strength ECCs in the Chinese market.


Introduction
With the rapid development of China's economy and the increasing number of transportation infrastructure, the concrete structure for repair and retrofit requires the shortest traffic interruption time.Meanwhile, the demand for highstrength or fast-hardening concrete is also increased.For example, the Road Transport Department often requires repair work to be completed within 6-8 hours in the evening to facilitate the road to be able to reopen in the early morning of the next day [1].In the past three decades, academics and industrial scholars have done a lot of experimental research and successfully developed the repair materials which can attain enough high compressive strength and bending strength at a very early age.ese concrete materials obtain early high strength by using either special fast-setting cement [2][3][4][5][6] or combined use of ordinary cement with accelerating agent [7][8][9], resulting in various strength increasing rates.
Unfortunately, the traditional concrete repairs are often lacking durability.According to conservative estimates, nearly a half of traditional concrete repair is failure [10][11][12].About three-quarters of the failures are attributing to the lack of durability, and one-quarter of failure is due to structural failure.Early damage often occurs in the use of repair location because many of special cementitious materials have an unpredictable performance in different construction conditions.For instance, in many high-early-strength concrete mixtures, the freeze-thaw resistance will be decreased [4].In addition, early cracking, accompanying autogenous shrinkage and rapid hydration caused by heat release under high temperature, will exacerbate the deterioration.
Engineered cementitious composite (ECC, a type of fiber-reinforced cement-based composites (FPFRCC)) is considered to be an ideal repair and retrofit material because it has a very high ductility and a tight crack width.Ductility is increasingly recognized as the most important performance in durability repair.As a repair material, ECC can exhibit excellent deformation compatibility with concrete substrate structure.e high fracture toughness and multiple cracking behaviors can make ECC effectively improve the unstable crack propagation caused by the surrounding concrete or old/new concrete interface.erefore, it reduces the common early damage types in repair structures such as spalling and interlaminar fracture [13][14][15].Unlike conventional fiber-reinforced composites, the crack width of ECC at the strain-hardening stage is an inherent characteristic itself and less than 100 μm.When the crack width is less than 100 μm, the flow rate in cracked concrete is almost 0 [16].
e permeability of water through a crack in ECC will be the lowest [17], so it can prevent the corrosion of steel in reinforced concrete.In preloaded reinforced concrete beams test under dry and wet cycles, Hiraishi et al. [17] found that the corrosion of steel was significantly eliminated while substituting ECC for concrete.Moreover, even if corrosion occurs, the strain-hardening and multiple cracking behavior of ECC will also accommodate the expansion effect caused by corrosion and prevent the occurrence of spalling.
Typical ECC materials consist of cement, quartz sand, fly ash (FA) or silica fume (SF), water, super plasticizer, and chaotic short fibers.Less than or equal to 2% of the volume fraction of fibers is very favorable in terms of mixed construction and economic feasibility of the infrastructure [15,19].For the large-scale application of ECCs, the use of local ingredients has become the first choice from the perspective of economic factors and the sustainability of infrastructure.e feasibility of using ECCs for the local ingredient and imported materials has been developed by a large number of researchers [20][21][22].e use of domestic fiber and local ingredients in ECC has been designed and developed by Zhang and Qian [20], Ma et al. [21], and Pan et al. [22].Zhang and Qian [20] analyzed the feasibility of ECC localization by bending test.Ma et al. [21] successfully developed a strain capacity more than 6% of domestic ECC by optimal design from fly ash and rubber particles.Pan et al. [22] studied the mechanical properties of ECC containing domestic fiber and imported fiber, respectively.
In this study, author focus on high-early-strength ECC (HES-ECC) with all local ingredients, including cement, quartz sand, silica fume, polyvinyl alcohol (PVA), fiber and polyethylene (PE) fiber.In order to get high early strength, the sulfoaluminate cement was used in this investigation.In the ECC design theory, the strain-hardening criterion of the material is determined by the fracture toughness of the matrix, the bridging capacity of fiber, and the size distribution of initial defects.erefore, in order to obtain the domestic HES-ECC, authors measure the micromechanics parameters by single-fiber pullout test and three-point bending test, respectively.Furthermore, the mechanical properties of HES-ECC will also be tested by compression test and direct tensile test, including compressive strength, elastic modulus, ultimate tensile strength, and ultimate tensile strain.

Strain-Hardening Criterion
ECC was developed by Li of the University of Michigan in 1990s, based on the design concept of ISMD (integrated structure and material design), which is a kind of strainhardening behavior characteristics of cement-based composite with a steady crack width of 60 μm, meanwhile, high ductility with strain range from 1% to 4%.ECC effectively linked microcut, mesoscopic material properties, and macromechanical properties.
erefore, the whole design basis of ECC is based on the multiscale link from micro to macro.Li and coworkers [23][24][25] proposed the ECC design theory, which was further improved by Lin et al. [26], Kanda and Li [27], and Yang et al. [28].In this theory, the occurrence of steady-state flat crack propagation must meet two criteria: strength criterion and energy criterion.

Strength Criterion.
In order to make ECC possess the ability of multiple cracking and high ductility, ECC should meet the strength criterion in the design process.e strength criterion stipulates that the first cracking strength σ fc must be less than the bridging stress σ 0 .at is, Based on the strength criterion, the material composition design of ECC can be modulated by adjusting the bridge stress of fiber, fracture toughness, and defect size of the matrix so as to better gain the ability of multiple cracking and high ductility performance.

Energy Criterion.
e steady-state cracking of crack means that the crack width δ ss and the external force σ ss are required to remain stable during the propagation of the crack.It was first proposed by Marshall and Cox [29] in the study of continuous fiber-reinforced ceramic materials.Based on the principle of fracture mechanics, they suggested that the steady-state cracking strength σ ss is calculated by using J-integral.
e general solution of steady-state cracking of crack is shown in (2).Although this equation is designed only based on continuous fiber-reinforced ceramic materials, it is still applicable to other fiber-reinforced materials, including ECC: where σ(δ) is expressed as the relationship between the fiber bridge stress σ and the crack width δ, as shown in Figure 1.J tip represents the crack tip toughness.In case of lower fiber content, J tip is determined by the matrix fracture toughness K m and matrix Young's modulus E m , as shown in the following equation: 2 Advances in Materials Science and Engineering Equation ( 2) represents the energy conservation theorem in the whole steady-state crack propagation process.σ ss δ ss is the external force acting on the crack.e crack tip width changes from 0 to δ ss , where the ber bridging capability has consumed some of the energy, which is the left part of the formula.While the complementary energy is used to cause the matrix to crack at the crack tip, thereby arouse the crack to continue to develop.e ber bridging stress will reach to a peak value σ 0 due to the e ect of ber, matrix, and ber/matrix interface properties so the complementary energy also has a maximum value J b ′ , as shown in Figure 1.In order to ensure that the crack can be steady-state cracking, the maximum complementary energy J b ′ must be greater than or equal to the crack tip toughness J tip , which is the energy criterion: According to formula (4), in order to meet energy criterion, the crack tip toughness J tip is limited by adjusting the mix proportion of the matrix, or the maximum complementary energy J b ′ is enhanced by designing the ber/matrix interface parameters.
Based on the above description, in order to design the ECC materials with strain-hardening and multiple cracking behaviors, (1) and (4) should be satis ed at the same time.In addition, considering the ber in the composites would be fractured, Wu [30] suggested J b ′ /J tip > 3 and σ 0 /σ fc > 1.45 to achieve the saturated strain-hardening capacity of ECC for PVA ber.Meanwhile, for the PE ber, Kanda [31] indicated that the σ 0 /σ fc index observed from crack pattern needs to be modi ed, and it should be greater than 1.2 instead of 1.45.

Materials and Mixture Proportions.
e raw materials used in this study were all produced by local manufacturers.
e sulfoaluminate cement (SAC) [32] and silica fume [33] meet Chinese standards.e chemical compositions of SAC and SF are displayed in Table 1.e particles size of SAC and SF is 60 to 80 μm and 0.15 to 0.20 μm, respectively.SF does not make chemical reaction when water is added, and it, as a high activity supplementary cementitious material, will stimulate the formation of secondary hydration products.
erefore, it will enlarge the hydrated calcium silicate (C-S-H) and contribute to obtain a high compressive strength [32].e aggregates used in this study are silica sand and silica our, which have diameters range of 106 to 212 μm and 25 to 48 μm, respectively.Using such a small aggregate ensures uniform distribution of the bers.Moreover, according to Ranade et al. [34], it also e ectively reduces the fracture toughness of the matrix caused by crack initiation during steady-state at crack propagation and contributes to obtain good ductility of composites.A domestic polyethylene (PE) ber and a domestic PVA ber (BHL, produced by Bao Hua Lin Co. Ltd. in China) were used in this study, both produced in China.As control, the imported PVA ber (REC-15) was also investigated in this paper, produced in Japan.e physical and mechanical properties of all bers are listed in Table 2.
According to the previously mentioned strain-hardening criterion, the strain-hardening and multiple cracking behaviors of ECC are determined by ber, matrix, and ber/matrix interfacial parameters.In this paper, di erent types of bers will be used to research, which would result in di erent ber/matrix interfacial parameters.Four ECC mixtures are listed in Table 3. ECC2, ECC3, and ECC4 have the same mix composition as the control mixture ECC1, but the imported ber (REC-15) is directly replaced by domestic ber.Due to rapid hardening of cement and small diameter of PE ber, a lower PE ber content of 0.5% and 0.8% was selected to facilitate mixing and e cient and uniform ber distribution.e ber content in ECC1 and ECC2 were kept at 2% by mixture volume.
All ECC materials were mixed by using a metal mixer with 10 L capacity.Firstly, all solid materials mixing with low speed for 1 min, so that the mixtures were fully stirred evenly.
en, water and super plasticizer were added, continued to stir at a low speed for 1 min, following at a high speed for another 1 min.When the matrix slurry was homogeneous, the bers were slowly added and sustained stirred at low speed for another 3 min until the bers were dispersed uniformly, without agglomeration, and ECC slurry was in good uidity.e fresh ECC was cast into molds and demolded after 2 hours, then the HES-ECC specimens were cured in a standard curing condition with 95 ± 5% RH and 20 ± 2 °C until testing ages.

Single-Fiber Pullout Test.
To design HES-ECC, it is necessary to experimentally determine the relevant microscopic parameters.Based on the multiscale design of ECC, Advances in Materials Science and Engineering Katz and Li [35] suggested that the microscopic design parameters of ber/matrix interface was measured by single ber pullout test, including chemical bond G d , frictional bond τ 0 and slip-hardening coe cient β.Firstly, a long continuous ber was neatly arranged in the mold.And then pour ECC matrix slurry until it reached the speci ed age.
e dimension of the specimen is approximately 10 × 5 × 1 mm 3 .In order to ensure that the ber can completely draw out from matrix during pullout process, the depth of ber is controlled at 1 mm.e test setup is shown in Figure 2, and the displacement control was used in this test with a rate of 0.4 mm/min.

ree-Point Bending Test.
In order to obtain the crack tip toughness J tip and the matrix fracture toughness K m , this study refers to the three-point bending test in ASTM E399 developed by the American Society for Materials and Testing [36].e solution of the matrix fracture toughness KQ is shown in ( 5) and ( 6). e matrix of ECC is equivalent to   4 Advances in Materials Science and Engineering cement mortar and belongs to a brittle material with linear elasticity.erefore, this method is also suitable for measuring the fracture toughness K m of the ECC matrix.
e test setup and the specimen size are shown in Figure 3.
e dimension of tested specimen is 350 × 76 × 38 mm 3 , and the bottom of the specimen has a notch.e ratio of the notch depth to height is 0.4.e test rate is controlled by displacement with 0.06 mm/min. where ), P Q is the peak load (N), S is the span of support point in the specimen (mm), B is the thickness of the specimen (B B N , mm), W is the width of specimens (mm), a is the notch depth (mm), and f(a/W) is the correction coe cient and the function of (a/W).

Uniaxial Tensile Test.
e uniaxial tensile test is based on the method recommended by the Japan Society of Civil Engineers (JSCE) for testing the properties of berreinforced cement-based composites (HPFRCC) [37].e test setup and dimension of ECC specimen are shown in Figure 4. Two external linear variable displacement transducers (LVDTs), xed on both sides of the specimen, are used to measure the deformation of the specimen during test process.e loading rate of this setup is 0.5 mm/min.e mechanical properties of high-early-strength ECC under compressive and tensile strength are studied in this paper.All specimens will be tested at 6 hours, 24 hours, 7 days, 28 days, and 60 days, respectively.e compressive specimen size is 75 × 75 × 75 mm.Due to the variable of di erent ECC materials, four specimens are prepared for each experiment.

Results and Discussions
4.1.Composites Compressive Strength.Figure 5 shows the results of the compressive test for HES-ECC specimens.Each of the data in Figure 5 is calculated from four compressive specimens.As shown in Figure 5, the compressive strength of the controlled ECC1 specimen was 25.4 MPa at 6 hours.In case of ECC2, ECC3, and ECC4, these values were 23.7, 25.3, and 26.0 MPa, respectively.e compressive strength of all specimens at 6 hours can reach more than 50% that of 28 days.e compressive strength of specimens at 24 hours can gain 70% that of 28 days.
ese results of all compressive strength showed an increasing trend up to 60 days, including all mixtures type.e growth rate at early

Control Composites Tensile Properties. As shown in
Figure 6, all the curves show a signi cantly strain-hardening behavior.As a control mixture, the maximum ultimate tensile strain is more than 3%.e rst cracking strength and ultimate tensile strength of ECC1 increase with the increase of age.It is explained that as the age increases, the unhydrated cement particles in ECC1 continue to hydrate and produce more hydration products, resulting in a denser matrix and a greater matrix fracture toughness K m ; the chemical bond G d and frictional bond τ 0 in the ber/matrix interface were enhanced by increased hydration products, thereby resulting in the increase of the bridging stress σ 0 .
With the increase of age, the tensile strain capacity of ECC1 has a rough decrease trend.For example, the maximum tensile strain of ECC1 is 4.13% at 6 hours, and it is reduced to 3.36% at 60 days.is is because that the increase of matrix fracture toughness K m leads to the strengthening of the crack tip toughness J tip .On the other hand, the complementary energy J b ′ is reduced by the change of ber/matrix interfacial properties, resulting in the decrease of J b ′ /J tip .

Micromechanics-Based Design of Domestic HES-ECC.
e domestic BHL ber has no enough long available length, only REC-15 ber and PE ber can be applied in single-ber pullout test to obtain related micromechanical parameters.6 Advances in Materials Science and Engineering Figure 7 shows the typical pullout load-distance relationship of two di erent bers from the same matrix.e microscopic mechanical parameters in the ber/matrix interface from these gures, including chemical bond G d , frictional strength τ 0 , and slip-hardening coe cient β, both can be calculated.As shown in Figure 7(a), for PVA ber, when ber starts to bear the tensile force, the force value rstly rises to P a during ber/matrix debonding stage, and then suddenly drops to P b , indicating the chemical bond G d in the ber/matrix interface has been destroyed.After, the ber is in a pullout stage under the action of frictional strength τ 0 and strain-hardening capacity, the force value gradually increases to the second peak and drops until the ber is broken.In case of ber without chemical bond, such as PE ber, P a can be approximately equated with P b .When the force value reaches to only one peak P peak (P peak P b ), the buried ber end is justly debonded, and the pullout force value is provided by frictional bond strength τ 0 (in Figure 7(b)).Based on these microscopic parameters, the ber bridging stress-crack opening displacement curve can be calculated by using MATLAB [28] (in Figure 8).e complementary energy J b ′ can also be obtained from this gure.
For the abovementioned related cases, Redon et al. [38] indicate that polymer ber tends to reveal either sliphardening, constant friction, or slip-softening e ect when pulled out from the matrix, de ned as β, which can be a positive value, 0 or a negative value [39].In this study, sliphardening coe cient β was derived from both REC-15 ber and PE ber.
Li et al. [40] have proved that the load carried by the ber was magni ed in both debonding and pullout phases at nonzero inclination angles due to the snubbing e ects between the inclined ber and matrix; the snubbing coe cient f was introduced to describe this behavior.In this investigation, for PVA ber, the snubbing coe cient f was de ned as 0.2 according to Yang et al. [28].e snubbing coe cient f of PE ber is computed from the peak loads of ve specimens with inclined bers.Li et al. [40] indicated that the snubbing e ects can be modeled as ln P peak (ϕ) P peak (0) fϕ, (7) where P peak (ϕ) and P peak (0) are the peak force for a specimen with ber inclination angle of ϕ and 0, respectively.In the case of zero degree, the bers are perpendicular to the crack plane.e left side of (7) was Advances in Materials Science and Engineering plotted in Figure 9 to nd the best-t curve (dashed line) through four di erent ber-inclined angles.To meet the requirement of the model in (7), another best-t curve (solid line) with zero y-intercept is computed.As seen in Figure 9, the considered inclination angle is 0 °, 30 °, 45 °, and 60 °, respectively.e snubbing coe cient f of PE ber in this study is determined as 0.63.
Figure 10 shows the in uence of curing ages on the ber/matrix interface micromechanical parameters in ECC1 with REC-15 ber.e chemical bond G d , frictional strength τ 0 , and slip-hardening coe cient β have a stable growth trend with the increase of age. is is mainly because the nonhydrated cement in ECC continues to hydrate and due to the nucleating e ect of silica fume [41], making the hydration products sustain a stable growth, resulting in the increase of interfacial chemical bond G d ; on the other hand, the interfacial frictional strength τ 0 is enhanced by the denser matrix.Figure 11 shows the in uence of curing age on elastic modulus E m and fracture toughness K m in the matrix.As shown in Figure 11, the elastic modulus E m and the fracture toughness K m increase with the increase of age.It can be explained that the density of the matrix is enhanced by more hydration products, the result of combination of nonhydrated cement with the nucleating e ect of silica fume, resulting in the increase of value.
Figure 12 shows the in uence of curing ages on micromechanical parameters in ECC3 with PE ber.Due to the hydrophobic nature of PE ber, the chemical bond G d can be approximately equal to zero.e frictional strength τ 0 and slip-hardening coe cient β have also a stable increase trend with the increase of age.e larger interfacial frictional bond strength τ 0 is generated by the densely packed ECC matrix.Due to the high strength of PE ber, the continuous increase of the ber bridging capacity is resisted by τ 0 .
Based on the strain-hardening criterion mentioned in Section 2, the strain-hardening performance index (σ 0 /σ fc , J b ′ /J tip ) of ECC with di erent ber is calculated and listed in Table 4.As seen in Table 4, the rst cracking strength σ fc is obtained from direct tensile test for the specimen without ber.e ber bridging stress σ 0 and the maximum complementary energy J b ′ can be measured from the relationship between ber bridging strength and crack-opening displacement curve.e crack tip toughness J tip was calculated by (3) using K m and E m .
As shown in Table 4, it can be seen that both J b ′ /J tip and σ 0 /σ fc are larger than critical values for strain-hardening conditions in case of ECC1 and ECC3 according to Wu [30] and Kanda [31], which ensure that both ECC materials can develop strain-hardening behavior.Nevertheless, the corresponding values of ECC3 are much smaller than that of ECC1 due to small ber volume of 0.5% PE in ECC3 as opposed to 2% PVA in ECC1.Had the mixing issue of domestic PE ber been overcome and more PE bers could be mixed, it is very likely that PE ECC can have a better performance index than PVA ECC.
e above analysis suggests that for the utilization of local ingredients in ECC production, it is feasible to replace imported ber with domestic PE ber to certain extent, even though its strainhardening performance may be lower due to inability to mix 2% PE ber in the cement matrix.

Domestic Composites Tensile Properties.
Figure 13 shows the time-dependent tensile behavior of two domestic bers.As shown in Figure 13, the signi cant strain-hardening behavior occurs in ECC2 and ECC3.Based on the domestic PVA ber, the tensile strain capacity of ECC2 at all ages is less than 2%, indicating the weak micromechanical parameters that occur in the domestic ber/matrix interface.Compared with the imported ber (seen in Figure 6), the tensile properties of ECC2 with domestic ber is lower than ECC1 during all ages.Based on the domestic PE ber, the ultimate tensile strain of ECC3 gradually reduced from 3.9% at 6 hours to 3.1% at 60 days.
e result from ECC3 is consistent with the decrease in the ratio of J b ′ /J tip for ECC3 as discussed before.
It can be seen from Table 4 that the ber bridging stress σ 0 increases with the increase of age.e same growth trend that occurs in the ultimate tensile strength is shown in Figure 14(a).Meanwhile, the maximum tensile strength of all high-early-strength ECC at 28 days is still able to reach more than 4 MPa.In addition, ECC3 based on PE ber materials attains a lower maximum tensile strength due to much smaller ber volume.
Generally, the uniaxial tensile test con rmed that a reasonable tensile ductility can be achieved for ECCs with domestic bers.e experimental data shows that the domestic ECC2 based on BHL ber can obtain a good compressive strength and ultimate tensile strain at the same time, while a relatively lower strain capacity may limit its application.For the ECC containing 0.5% PE ber, it is able to provide a high ductility, but its tensile strength is somewhat sacri ced, with about 4 MPa at 28 days.Based on the PE 8 Advances in Materials Science and Engineering ber, the domestic ECC3 cannot meet the strength requirement of engineering applications due to its low ultimate tensile strength.
erefore, the author attempts to increase the ber volume content and overcome this defect in the next section.

Domestic HES-ECC with Di erent Fiber Content.
As commonly known, increase in ber volume can e ectively enhance the ber bridging ability and therefore the ultimate tensile strength.Nevertheless, it is di cult to mix 1% PE ber into the ECC matrix due to the fast setting time of sulfoaluminate cement (SAC) and smaller ber diameter.
erefore, this study attempts to use a relatively higher ber content (0.8% by volume) to produce the domestic HES-ECC.
e performance indices (σ 0 /σ fc , J b ′ /J tip ) of the strainhardening behavior of HES-ECCs containing PE bers are listed in Tables 5 and 6. e details of derivation of various parameters are the same as before.It can be seen from Tables 5 and 6 that the ber bridging capacity σ 0 and complementary energy J b ′ increase signi cantly when the PE ber content increases from 0.5% to 0.8% by volume, resulting in greatly improved J b ′ /J tip and σ 0 /σ fc .
eoretically, larger strain-hardening indices should lead to a better strainhardening behavior, assuming all bers are randomly distributed.
Figures 13(b), 15, and 16 show the e ect of di erent ber contents on the tensile mechanical properties of ECC3 and ECC4.As shown in Figures 15 and 16(b), the domestic ECC4 exhibits an excellent high ductility.Compared with ECC3, the ultimate tensile strain of ECC4 increases by 18% at 60 days (from 3.2% to 3.8%).Also, the maximum tensile strength of ECC4 reaches to 5.6 MPa at 60 days, an increase of 23% compared with ECC3. Figure 16(a) shows that the maximum tensile strength is enhanced by increasing the ber content from 0.5% to 0.8%, an increase of 167% at 6 hours (from 1.5 MPa to 2.5 MPa).However, the compressive  Compared with ECC3, the rst cracking strength and maximum tensile strength is enhanced by increasing the ber content in ECC4 (seen in Figures 13(b) and 15).Meanwhile, the tensile strain capacity of ECC4 in general is   better when compared with ECC3 (Figure 16(b)), which is consistent with the increase of strain-hardening performance index J b ′ /J tip for ECC4.
Figure 17 shows the in uence of imported ber and domestic ber on tensile properties of ECC1 and ECC4.As shown in Figure 17, the ultimate tensile strength of ECC4 with domestic PE ber at all ages is less than that of controlled ECC1 with imported REC-15 ber, approximately three-quarters of ECC1, due to a relative lower ber content.However, the domestic ECC4 exhibits an excellent tensile    e domestic ber can substitute for the imported ber due to the lower cost.e price of REC-15 ber and PE ber is 225 yuan/kg and 150 yuan/kg in China (in Table 2), respectively.For large-scale applications, for example, the production of 10,000 cubic metre HES-ECCs need the imported REC-15 ber of 260 kg or the domestic PE ber of 104 kg, and then, the cost of imported ber is 58,500 yuan.However, the cost of domestic ber is only 15,600 yuan, about 27% of REC-15 ber.erefore, it is feasible to produce ECC materials with a lower domestic ber, while maintaining high-early-strength and higher material ductility simultaneously.
e average crack width of ECC1, ECC2, ECC3, and ECC4 at 28 days is 61, 58, 55, and 49 μm respectively.e reduction of crack width after load removal can be contributed to more ber bridging capacity from the PE ber/matrix interface.It should be noted that the crack width at the very early age of 24 hours is as low as 50 μm (for ECC4), whereas the tensile strain capacity is as high as 3.2%.is high tensile ductility and very tight crack width at an early age of HES-ECC provide a high resistance to early-age cracking.

Conclusions
is study aims at the production of high-early-strength ECC with excellent mechanical properties using all domestic ingredients, including matrix materials and PE ber.According to the principle of ECC micromechanics and fracture mechanics design, the interfacial micromechanical parameters were analyzed, and the high ductile ECC materials were designed and adjusted by the replacement of ber and the increase of ber content.
e nal recommendation of high-early-strength ECC is ECC4, which contains 0.8% of PE ber by volume, meeting both strainhardening criteria (strength criterion and energy criterion).
e main conclusions were as follows: (1) To realize the localization of high-early-strength ECC, a combination of sulfoaluminate cement, silica fume, and domestic bers is found to be helpful for attaining higher compressive strength and tensile properties at early ages.e compressive strength of more than 25 MPa and tensile strain capacity of 1.8% within 6 hours of all high-early-strength ECCs can be obtained in this study.
(2) Using BHL ber at 2%, it was found that ultimate tensile strength of 5 MPa and compressive strength of 40 MPa at 28 days can be achieved, with a modest tensile strain capacity of about 2%.
(3) It was found that an excellent strain-hardening behavior can be achieved when HES-ECCs use the domestic PE ber with only 0.5% content, but with ultimate tensile strength less than 1.5 MPa within 6 hours.
(4) When 0.8% PE ber was used, domestic HES-ECC (ECC4) can also obtain a good tensile strain capacity of 3% and ultimate tensile strength of 2.5 MPa within 6 hours.Meanwhile, the ultimate tensile strength of more than 5 MPa and ultimate tensile strain of more than 3.5% after 60 days can be easily achieved.e compressive strength for this mixture exceeds 49 MPa at 60 days.
(5) When 2% of imported REC-15 ber was replaced by 0.8% of domestic PE ber, the cost of all materials was signi cantly reduced, approximately up to 70%.Advances in Materials Science and Engineering

Figure 2 :
Figure 2: Single ber pullout test setup: (a) the tested specimens; (b) the dimension of specimens (all dimensions in mm).

Figure 3 :
Figure 3: e setup of three-point bending test: (a) the tested specimens; (b) the dimension of specimens (all dimensions in mm).

Figure 9 :
Figure 9: Deduction of snubbing coe cient f using inclined PE ber pullout specimens.

Figure 14 :
Figure 14: Comparison of tensile properties of HES-ECCs with di erent bers at di erent ages: (a) ultimate tensile strength; (b) ultimate tensile strain.

Figure 16 :
Figure 16: Comparison of tensile properties of PE HES-ECCs at di erent ages: (a) ultimate tensile strength; (b) tensile strain capacity.

Figure 17 :
Figure 17: Comparison of tensile properties of ECC1 and ECC4 at di erent ages: (a) ultimate tensile strength; (b) tensile strain capacity.

Table 1 :
Chemical composition of sulfoaluminate cement and silica fume (by weight percentage).

Table 2 :
Physical and mechanical properties of all bers.

Table 3 :
Mix design of domestic ECCs (weight ratios).

Table 4 :
Strain-hardening performance index of HES-ECCs with di erent ber.