This paper mainly investigates the fracture parameters of Basalt Fiber Reinforced Concrete (BFRC) with various fiber lengths and dosages using Double-K fracture model. The model was developed by fracture criterion using ABAQUS Virtual Crack Closure Technique (VCCT), and the results of the model and experiments were compared. The basalt fiber with length of 6 mm and 12 mm was added into concrete in the dosage of 0.0%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% by volume of concrete, respectively. Concrete specimens were cast into three dimensions, i.e., 60 mm × 180 mm × 480 mm, 80 mm × 240 mm × 640 mm, and 100 mm × 300 mm × 800 mm. Then, three-point bending test was conducted on precast-notched beams. The load versus cracking mouth opening displacement (P-CMOD curve) was developed in order to evaluate cracking and breaking load. The initial fracture toughness and unstable fracture toughness were derived from the Double-K fracture model aimed to optimize the fiber length and dosage. The results showed that the initial fracture toughness and unstable fracture toughness increased first and then decreased with the increase in fiber dosage, and basalt fiber with length of 6 mm and dosage of 0.2% performed the best toughening effect on concrete. The comparison results showed that numerical simulation can better simulate the initiation and propagation of BFRC fractures and achieve the dynamic propagation process of fractures.
The concrete panel rock-fill dam is extensively developed due to its low cost, short construction period, and strong adaptability, but concrete panel is vulnerable to cracks, which restricted its application. As a quasibrittle material, concrete has low tensile strength (tensile strength is 1/10 to 1/20 of compressive strength). In the process of casting, the concrete panel is in high risk to yield cracks due to uneven settlement, hydration reaction, and dry shrinkage deformation [
According to previous research, adding fibers, such as steel fiber, carbon fiber, and polypropylene fiber into concrete, can improve the basic mechanical properties, ductility, toughness, crack resistance, and durability of concrete structures [
Carbon fiber has the advantages of high tensile strength, low density, large elastic modulus and strong toughness, so it was believed as a good fiber for improving concrete performance. Tong et al. put forward that proper amount of short-cut carbon fiber can enhance the tensile splitting strength, compressive strength, and flexural strength of concrete [
Polypropylene fiber has been widely used in recent years. Liang et al. found that polypropylene fiber enhanced the bending performance of concrete and greatly improved the initiation toughness [
In recent years, both domestic and foreign scholars have found that basalt fiber can better improve the performance of concrete. Basalt fiber is formed by melting and drawing of basalt ore at high temperature. It has advantages such as high-temperature resistance, chemical resistance, good mechanical properties, and natural compatibility with concrete [
Up to date, most of relevant research programs focused on the basic mechanical properties of BFRC. However, it is rarely employed to analyze fracture performance with Double-K fracture model. In this paper, the BFRC fracture parameters were analyzed by the Double-K fracture model. Double-K fracture model was put forward by Xu and Reinhardt, which described the fracture process of concrete by two stress intensity factors: initiation toughness and unstable fracture toughness. It introduced the unstable fracture toughness parameters and believed that the aggregate and mortar in concrete caused the increase of unstable fracture toughness. And the fracture of concrete could be divided into three stages: crack nonpropagation, crack stable propagation, and crack unstable propagation [
For the constitutive model study of fracture, Bernardi et al. used nonlinear finite element on double-parameter simulation for polypropylene fiber concrete. Their results showed that the simulated results were highly coherent with the experimental results [
As a quasibrittle material, BFRC can be composed of base phase and dispersed phase. Base phase is a mixture of cement, water, fly ash, water-reducing agent, air entraining agent, and basalt fiber, while dispersed phase is the aggregate. The fracture failure of BFRC can be divided into three levels, the first level: the bonding surface of mortar and aggregate is a weak surface, and cracks are generated on the bonding surface of mortar and aggregate firstly; the second level: with the development of cracks between mortar and aggregate binding surfaces, cracks spread into mortar and the interface of sand and hardened cement slurry begins to crack; third level: as cracks between sand and hardened cement slurry develop, hardened cement slurry starts to crack, accompanied by the pulling-out failure of fibers. Xu and Reinhardt put forward the Double-K fracture model to evaluate the fracture properties of concrete more accurately. In Double-K fracture model, the fracture of concrete consists of three processes, namely, the nonpropagation crack, the stable-propagation crack, and the unstable-propagation crack. In order to better describe the fracture process, the initiation toughness (
As a quasibrittle material, the crack propagation starts with linear elastic propagation, where crack has not yet appeared. Next stage is elastoplastic propagation, where the crack is stably propagating until the fracture load. Specimen is damaged in this stage. In P-CMOD curve, the load at turning point from the linear part to the nonlinear part is called the crack initiation load (
The fracture process of BFRC specimen is not all linear due to the bond strength between aggregates and binder and the bridging effect of basalt fiber after matrix cracking. Therefore, the nonlinear characteristic is equivalent to elastic fracture when fracture occurs for calculation of unstable fracture toughness. Hereby, the critical effective crack length can be calculated following equation (
When the load reaches the maximum, the specimen is in unstable state. The corresponding fracture toughness at this moment is the unstable fracture toughness. Based on DL/T 5332-2005 [
In this paper, three-point bending tests were carried out for precast notched BFRC beams with different lengths, admixtures, and specimen sizes. The load versus cracking mouth opening displacement curves (P-CMOD curves) were developed in order to evaluate cracking and fracture load. The initiation toughness and unstable toughness parameters of BFRC were calculated by using the Double-K fracture model. The effects of basalt fiber length and content on fracture properties of BFRC were analyzed as well. Due to the limited test conditions, the entire process of BFRC fracture is difficult to determine. Therefore, VCCT technique was used to simulate the fracture performance of BFRC and analyze the entire process of BFRC fracture.
The properties of used ordinary Portland cement were tested according to GB/T 17671-1999 [
Properties of Portland cement.
Test | Cement type | Strength grade | Rupture strength (MPa) | Compressive strength (MPa) | Setting time (min) | Standard consistency (%) | Soundness (mm) | |||
---|---|---|---|---|---|---|---|---|---|---|
3 d | 28 d | 3 d | 28 d | Initial setting | Final setting | |||||
Result | P.O | 42.5 | 5.20 | 7.8 | 20.1 | 45.2 | 155 | 255 | 28.0 | 1.5 |
Specification | P.O | 42.5 | ≥3.5 | ≥6.5 | ≥17.0 | ≥42.5 | ≥45 | ≤600 | — | ≤5.0 |
II grade fly ash was used in this paper, and its properties are listed in Table
Properties of fly ash.
Test | Fineness (45 |
Water demand ratio (%) | Ignition loss (%) | Moisture content (%) | Stability (mm) |
---|---|---|---|---|---|
Result | 14.7 | 96 | 2.6 | 0.2 | 1.5 |
Specification/II | ≤25 | ≤105 | ≤8 | ≤1.0 | ≤5.0 |
The properties of used water-reducing admixture and air entraining admixture are shown in Tables
Properties of water-reducing admixture.
Test | Dosage (%) | Water educing rate (%) | Air content (%) | Ratio of bleeding rate (%) | Setting time difference (min) | Compressive strength ratio 9%) | |||
---|---|---|---|---|---|---|---|---|---|
Initial setting | Final setting | 3 d | 7 d | 28 d | |||||
Result | 1.0 | 17.0 | 1.3 | 82 | 28 | 32 | 141 | 138 | 129 |
Specification | 0.8∼1.2 | ≥15 | <3.0 | ≤90 | −60∼+90 | −60∼+90 | ≥130 | ≥125 | ≥120 |
Properties of air entraining admixture.
Test | Dosage (%) | Water reducing rate (%) | Air content (%) | Ratio of bleeding rate (%) | 1 h change in air content (mm) | Setting time difference (min) | Compressive strength ratio (%) | |||
---|---|---|---|---|---|---|---|---|---|---|
Initial setting | Final setting | 3 d | 7 d | 28 d | ||||||
Result | 0.04 | 6.0 | 5.2 | 53 | 1.2 | 35 | 26 | 116 | 102 | 96 |
Specification | 0.02∼0.05 | ≥6 | 4.5∼5.5 | ≤70 | −1.5∼+1.5 | −90∼+120 | −90∼+120 | ≥90 | ≥90 | ≥85 |
Coarse aggregate and fine aggregate are natural aggregates (containing artificial crushed pebbles) from the right bank of Yangqu Hydropower Station. Their properties are summarized in Tables
Fine aggregate particle gradation.
Aggregate size (mm) | 4.75 | 2.36 | 1.18 | 0.60 | 0.300 | 0.15 | ≤0.15 |
Accumulated sieve residue (%) | 2.5 | 27.3 | 45.3 | 60.7 | 82.4 | 93.5 | 99.6 |
Coarse aggregate particle gradation.
Aggregate size (mm) | 2.36 | 4.75 | 9.5 | 16 | 19 | 26 | 31.5 | 37.5 |
Accumulated sieve residue (%) | 100 | 98.9 | 82.4 | 54.6 | 50.2 | 33.9 | 11.8 | 0 |
The properties of basalt fibers used in the test are shown in Table
Properties of basalt fibers.
Length (mm) | Diameter ( |
Tensile strength (MPa) | Elasticity (GPa) | Elongation (%) | Density (kg/m3) |
---|---|---|---|---|---|
6/12 | 17.4 | ≥2000 | ≥85 | 2.5 | 2699 |
Basalt fiber of different lengths. (a) 6 mm basalt fibers. (b) 12 mm basalt fibers.
The proportion of BFRC is presented in Table
BFRC proportion (kg).
Fly ash | Cement | Water | Sand | Small stone | Medium stone | AEA | Superplasticizer |
---|---|---|---|---|---|---|---|
57 | 226 | 130 | 688 | 638 | 638 | 1.13 | 2.83 |
In this study, a forced mixer was used to mix BFRC. Coarse aggregate and fine aggregate were mixed for 30 s first. In order to ensure a uniform distribution of the basalt fibers in concrete, a dry fiber mixing method was used to improve the uniformity of fiber distribution based on [
Three different dimensions of specimens used for three-point bending test were 60 mm × 180 mm × 480.6 mm, 80 mm × 240 mm × 640.8 mm, and 100 mm × 300 mm ×801 mm, respectively. Basalt fibers of 6 mm length were added to the mixture in accordance with the dosage of 0%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5%, respectively, the same for the basalt fiber of 12 mm length. The detailed information of specimens is listed in Table
Detailed information of specimens.
Specimen | Dimension (mm) | Span length (mm) | Span-depth ratio | Precast crack length (mm) | Seam height ratio |
---|---|---|---|---|---|
A | 60 × 180 × 480 | 450 | 2.5 | 36 | 0.2 |
B | 80 × 240 × 640 | 600 | 2.5 | 48 | 0.2 |
C | 100 × 300 × 800 | 750 | 2.5 | 60 | 0.2 |
Three-point bending test was carried out at continuous loading rate of 0.4 MPa/min using Kaiwen universal hydraulic machine. A linear variable differential transformer (LVDT) sensor was installed vertically at the bottom of beam two centimeters from the midspan to measure vertical displacement. An extensometer was mounted at precast crack incision to determine CMOD. Resistance strain gauges (model: S2150-150AA, resistance: 149.5 ± 0.2%, sensitivity coefficient: 2.032 ± 0.32%, grid width: 5 mm, grid length: 150 mm) were pasted every 2 cm at the top of the precast crack. The specimen under loading is illustrated in Figure
Three-point bending test. (a) Loading diagram. (b) Under test. Note:
The effects of various basalt fiber dosage on P-CMOD curve were obtained from the tests as shown in Figures
P-CMOD curves for 6 mm and 12 mm basalt fiber with various dosages. (a) Specimen A and fiber length 6 mm. (b) Specimen A and fiber length 12 mm. (c) Specimen B and fiber length 6 mm. (d) Specimen B and fiber length 12 mm. (e) Specimen C and fiber length 6 mm. (f) Specimen C and fiber length 12 mm.
Initiation toughness vs. basalt fiber dosage. (a) The fiber length is 6 mm. (b) The fiber length is 12 mm.
According to the P-CMOD curve analysis, in general, the expansion of concrete cracks can be divided into three stages (stage I, stage II, and stage III). Stage I: at the beginning of load application, the load and displacement were in linear relationship. At this moment, BFRC had not started to crack. In this stage, BFRC elastically expanded. Stage II: with load continuing, the microcracks occurred under steady propagation until the ultimate load was reached. BFRC displayed a nonlinear expansion, with the growth of microcracks. It stepped into matrix fracture Stage III: After ultimate load, unstable fracture took over in crack propagation until the cracks produced over the whole specimen. In this stage, the specimen was completely fractured along with the fibers pulling out. In this test, the fracture process of most tested specimens was exhibited these three stages, while some type A and B specimens only had stage I and stage III. The nonlinear rising stage is not apparent enough. This might be due two reasons: (1) the yield process is relatively short and lose a lot of yield values during force load; (2) the sizes of type A and B specimens are relatively small, and the existed size effect leads to small yield strength for type A and B specimens and the relatively short yield process. In the future tests, displacement loading should be selected to better collect BFRC fracture data and analyze BFRC fracture performance. For a given specimen size, the incorporation of basalt fiber improved the ultimate load and CMOD of concrete because the high tensile strength of basalt fiber inhibited the crack propagation of concrete during pull-out process of fibers.
Using the Double-K fracture model, the BFRC fracture parameters were calculated according to the measured load, displacement, and their corresponding parameters, as shown in Table
BFRC fracture parameters with various basalt fiber content and dosage.
Group | Specimen ID |
|
|
|
|
|
|
|
|
---|---|---|---|---|---|---|---|---|---|
A | A-PC | 5.73 | 18 | 8.1 | 58 | 39.66 | 64 | 0.72 | 1.48 |
A-6-0.1 | 5.97 | 20 | 9.47 | 66 | 37.14 | 61 | 0.75 | 1.64 | |
A-6-0.2 | 9.57 | 42 | 12.35 | 76 | 28.36 | 46 | 1.16 | 1.75 | |
A-6-0.3 | 8.67 | 32 | 11.22 | 72 | 33.72 | 55 | 1.06 | 1.77 | |
A-6-0.4 | 7.47 | 30 | 10.52 | 70 | 30.99 | 53 | 0.92 | 1.63 | |
A-6-0.5 | 7.55 | 30 | 9.58 | 66 | 31.33 | 55 | 0.93 | 1.52 | |
A-PC | 5.73 | 18 | 8.1 | 58 | 39.66 | 64 | 0.72 | 1.48 | |
A12-0.1 | 7.47 | 23 | 9.67 | 68 | 40.42 | 64 | 0.92 | 1.76 | |
A12-0.2 | 10.28 | 34 | 13.22 | 92 | 37.66 | 61 | 1.25 | 2.28 | |
A12-0.3 | 7.98 | 27 | 11.05 | 73 | 36.81 | 59 | 0.98 | 1.85 | |
A12-0.4 | 7.42 | 29 | 10.58 | 72 | 31.84 | 55 | 0.91 | 1.68 | |
A12-0.5 | 6.60 | 31 | 8.48 | 65 | 26.51 | 53 | 0.82 | 1.32 | |
|
|||||||||
B | B-PC | 8.5 | 29 | 11.35 | 57 | 32.06 | 73 | 0.84 | 1.23 |
B-6-0.1 | 13.28 | 42 | 15.20 | 65 | 29.20 | 62 | 1.08 | 1.42 | |
B-6-0.2 | 15.28 | 46 | 17.45 | 68 | 30.68 | 60 | 1.23 | 1.59 | |
B-6-0.3 | 12.53 | 44 | 14.89 | 60 | 26.30 | 54 | 1.03 | 1.29 | |
B-6-0.4 | 10.05 | 31 | 13.37 | 60 | 29.93 | 65 | 0.84 | 1.31 | |
B-6-0.5 | 11.07 | 36 | 12.75 | 63 | 28.38 | 67 | 0.92 | 1.28 | |
B-PC | 8.5 | 29 | 11.35 | 57 | 32.06 | 73 | 0.84 | 1.23 | |
B-12-0.1 | 10.60 | 34 | 13.40 | 72 | 28.78 | 71 | 0.88 | 1.40 | |
B-12-0.2 | 12.60 | 29 | 17.03 | 68 | 40.11 | 73 | 1.03 | 1.78 | |
B-12-0.3 | 11.73 | 36 | 14.62 | 63 | 30.09 | 64 | 0.97 | 1.40 | |
B-12-0.4 | 10.53 | 33 | 13.37 | 63 | 29.47 | 67 | 0.88 | 1.33 | |
B-12-0.5 | 10.07 | 31 | 12.75 | 63 | 29.98 | 70 | 0.84 | 1.32 | |
|
|||||||||
C | C-PC | 13.8 | 31 | 17.48 | 64 | 32.66 | 88 | 0.86 | 1.35 |
C-6-0.1 | 14.65 | 30 | 17.98 | 68 | 35.82 | 95 | 0.91 | 1.47 | |
C-6-0.2 | 19.77 | 46 | 24.62 | 82 | 31.52 | 80 | 1.18 | 1.72 | |
C-6-0.3 | 17.63 | 36 | 19.57 | 75 | 35.93 | 96 | 1.06 | 1.59 | |
C-6-0.4 | 15.18 | 32 | 18.67 | 73 | 34.81 | 95 | 0.94 | 1.52 | |
C-6-0.5 | 15.78 | 39 | 18.42 | 70 | 29.69 | 85 | 0.97 | 1.37 | |
C-PC | 13.8 | 31 | 17.48 | 64 | 32.66 | 88 | 0.86 | 1.35 | |
C-12-0.1 | 14.95 | 34.5 | 19.07 | 79 | 31.79 | 93 | 0.92 | 1.52 | |
C-12-0.2 | 16.68 | 40 | 21.55 | 85 | 30.60 | 88 | 1.02 | 1.63 | |
C-12-0.3 | 17.38 | 41 | 20.17 | 92 | 31.10 | 97 | 1.06 | 1.66 | |
C-12-0.4 | 16.42 | 42 | 19.40 | 81 | 28.67 | 88 | 1.01 | 1.48 | |
C-12-0.5 | 14.08 | 40 | 17.57 | 69 | 25.83 | 79 | 0.88 | 1.25 |
According to Table
BFRC fracture propagation is a complex process. The defects such as microcracks, voids, and weak contact surface between mortar and aggregates exist in BFRC matrix among which most of them are interfacial cracks and very few are mortar cracks. At the beginning of loading, it exhibits the elastic stage because these defects are stable. In the process of increasing the load until it reaches the critical load, these microcracks, voids, and weak surfaces between mortar and aggregate begin to extend or expand, which shows the linear stage for BFRC fracture. The development process of these defects depends on the magnitude of the crack initiation load and initiation toughness. Thus, crack initiation load and initiation toughness play an important role in evaluating crack resistance of concrete materials.
Figure
As the raise of dosage for 12 mm long basalt fiber, initiation toughness increased first and then decreased as well. Compared with the plain concrete, the addition of basalt fiber increased initiation toughness. For different dimensions of specimen, the maximum initiation toughness appeared at different fiber dosage. For instance, the peak values of initiation toughness for A and B specimens are at 0.2% fiber dosage, but it was 0.3% for C specimens. The initiation toughness of A specimens was improved most up to 73.6% among the three dimensions of specimen.
Generally, considering the time of crack development, the optimal dosage of basalt fiber was 0.2%. Regarding the increment of initiation toughness, the BFRC with 6 mm basalt fiber displayed relatively stable increase in initiation toughness. Among the BFRC specimens with 12 mm basalt fiber, only one specimen performed a large raise in initiation toughness probably due to randomness. Overall, the optimal combination of basalt fiber was 6 mm in length and 0.2% in dosage. Basalt fiber could increase the initiation toughness because it had higher strength and ductility than the plain concrete. Basalt fibers scattered and connected with each other in concrete matrix, which could inhibit the development of microcracks, voids, and the weak interface of mortar and aggregate, prolong the linear propagation and increase the initiation toughness. However, it should be noted that if the basalt fibers are distributed inhomogeneously and clustered together, they cannot well restrain the development of microcracks, voids, and weak interface in concrete and even lead to the decline of initiation toughness. This is associated with the voids among the fibers and the very low friction among the fibers.
After linear propagation, BFRC started unstable failure until it reached the ultimate load and failed. Figure
Unstable fracture toughness vs. basalt fiber dosage. (a) The fiber length is 6 mm. (b) The fiber length is 12 mm.
As the load increases, the crack in BFRC ends linear stage and steps into the nonlinear stage. In this stage, the defects such as the microcracks, voids, and weak contact surface between substrate and aggregate continue to develop. Cracks and other defects occurred in the mortar, meanwhile sand and interface of hardened cement slurry were damaged, resulting in crack propagation into the slurry. When the slurry damaged, the specimen failed. The fracture failure limit of BFRC depends upon the unstable load and unstable fracture toughness, which plays an important role in the evaluation of fracture performance.
Based on Figure
According to Figure
BFRC is a quasibrittle material with complex fracture mechanism. The three-point bending fracture test in the laboratory is difficult to keep tracking the fracture behaviors during the loading process beyond the ultimate load. With the development of computer technology, the macromechanical properties can be characterized using mesh division, finite element calculation, and fracture behavior simulation for concrete. It is very helpful to access fracture performance of BFRC under the correct numerical simulation by ABAQUS, a commercial software, which was used for the finite element modeling. Virtual crack closure technique (VCCT) was first proposed by Rybicki and Kanninen when they studied linear crack problems [
VCCT is based on Irwin energy theory, and its core idea is to assume that the energy released from crack propagation equates to the energy for crack closure.
When the crack develops from Figure
Process of crack propagation. (a) Before crack propagation. (b) After crack propagation.
If
Crack propagation diagram.
However, this rule of propagation is only suitable for type I fracture. The equivalent strain energy release rate
BK criterion is the best criterion in this case that critical strain energy release rates on two shear directions are the same. Therefore, BK criterion was adopted in the simulation as shown in the following equation:
The finite element method was used to simulate the experiment in ABAQUS software. Units are mm, N, tonne, MPa, tonne/mm3, and MPa·mm1/2. Hexahedral mesh was selected. The dimension of model and experiment was exactly the same. In order to better simulate the BFRC fracture process, enhanced VCCT was selected because it can simulate the crack initiation, which is more consistent with the real process. The parameters used in this simulation include density, elastic modulus, Poisson’s ratio, crack initiation energy release rate, fracture energy release rate, and damage factor
BFRC model parameters.
Specimen ID | Density | Elastic modulus | Poisson’s ratio | Crack initiation energy release rate | Fracture energy release rate |
|
---|---|---|---|---|---|---|
A-6-0.2 | 2.38 × 10−9 | 3.00 × 104 | 0.190 | 0.034 | 0.054 | 1.75 |
B-6-0.2 | 2.38 × 10−9 | 3.07 × 104 | 0.200 | 0.035 | 0.048 | 1.75 |
C-6-0.2 | 2.38 × 10−9 | 3.15 × 104 | 0.200 | 0.037 | 0.054 | 1.75 |
|
||||||
A-12-0.2 | 2.38 × 10−9 | 3.03 × 104 | 0.193 | 0.040 | 0.072 | 1.75 |
B-12-0.2 | 2.38 × 10−9 | 3.00 × 104 | 0.190 | 0.030 | 0.060 | 1.75 |
C-12-0.2 | 2.38 × 10−9 | 3.14 × 104 | 0.205 | 0..032 | 0.052 | 1.75 |
The mesh division and stress pattern are shown in Figure
It can be seen from Figure
Numerical analysis of mesh division and stress map. (a) Mesh division. (b) Stress pattern.
Comparison of results from numerical simulations and experiments. (a) 6 mm BFRC. (b) 12 mm BFRC.
Based on Figure
In this paper, three-point bending tests were conducted on BFRC with two lengths (6 mm and 12 mm) and five dosages (0.1%, 0.2%, 0.3%, 0.4%, and 0.5%) and plain concrete as well. The optimum dosage of basalt fiber, initiation toughness, and unstable fracture toughness were evaluated. The conclusions are as follows: Basalt fiber can enhance the initiation toughness and unstable fracture toughness of concrete. Moreover, it can be uniformly distributed in the concrete matrix, preventing the development of microcracks, voids, weak interface due to basalt fiber bridging effect and enhancing the crack resistance of concrete. The P-CMOD curves were established by experiments, and the initial crack load was obtained based on the state of crack propagation. The initiation toughness was calculated by initial crack load. Basalt fiber increased initiation toughness. The optimal dosage of basalt fiber was 0.2%, and the toughening effect of 6 mm basalt fiber was better than that of 12 mm basalt fiber. Meanwhile, the slump of BFRC was also good to meet the requirement of engineering construction. Based on P-CMOD curves, when the load reached the maximum, the specimens failure. The buckling load and unstable fracture toughness were determined. Basalt fiber enhanced unstable fracture toughness. The optimal dosage of basalt fiber was 0.2%, while the toughening effect of 12 mm basalt fiber was better compared to 6 mm basalt fiber. The results of three-point bending test for the BFRC were analyzed using VCCT. The overall trend from numerical simulation results and the experiment results showed a high degree in coherence. Numerical simulation can better present the whole process of BFRC fracture. However, the numerical simulation and experimental results have some errors in the critical displacement fitting.
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare that they have no conflicts of interest.
This work was financially supported by the National Natural Science Foundation of China (Grant no. 51969026) and the Natural Science Foundation of Qinghai Province in China (Grant nos. 2017-ZJ-933Q and 2018-ZJ-750).