## 3.1 Flexural strength of concrete with different fiber types

After organizing, the following three sets of relationship figures (Fig. 3, Fig. 4, and Fig. 5) were obtained to analyze the impact of different types of fibers on the flexural mechanical properties of concrete.

Figure 3 shows the flexural strength of concrete under different conditions of steel fiber dosage. Based on these results, the flexural strength of concrete exhibits a significant strengthening effect under different conditions of steel fiber dosage. With the increase in steel fiber dosage, the rate of increase in the flexural strength of steel fiber concrete exhibits a trend from rapid to slow. Specifically, with a steel fiber dosage of 1.0%, the flexural strength of concrete reached 11.7MPa and 13MPa after 3 and 28 days of curing, respectively, representing enhancement of 134% and 85.7%, respectively, compared to the flexural strength of reference concrete. When the steel fiber dosage is 2.0%, the flexural strengths at 3 days and 28 days increased to 13.9MPa and 15.3MPa, respectively, representing enhancements of 18.8% and 17.69% compared to concrete with 1.0% steel fiber dosage. Furthermore, with consistent steel fiber dosages, concrete cured for 28 days exhibits a flexural strength approximately 2 MPa greater than that of concrete cured for 3 days.

Figure 4 shows the flexural strength of concrete under different glass fiber dosage conditions. Based on these results, the flexural strength of glass fiber concrete tends to increase and decrease as the glass fiber admixture increases. Specifically, when the glass fiber dosage ranges from 0–1.5%, the flexural strength of glass fiber-reinforced concrete gradually increases, with the growth rate remaining essentially constant. After 3 days and 28 days of curing, its flexural strength increased by 60% and 42.9%, respectively, compared to the reference concrete. When the glass fiber dosage varies between 1.5% and 2.0%, the flexural strength of glass fiber-reinforced concrete decreases. The flexural strength of concrete with 2.0% glass fiber dosage after 3 days and 28 days decreases by 6.25% and 7% compared to concrete with 1.5% glass fiber dosage. Thus, when the glass fiber dosage exceeds a certain value, the flexural strength of glass fiber-reinforced concrete continuously weakens.

Figure 5 demonstrates the flexural strength of concrete across varying polypropylene fiber dosages. These results indicate a significant enhancement in concrete's flexural strength with varied polypropylene fiber dosages. The growth rate of the flexural strength in polypropylene fiber reinforced concrete initially increases slowly, then accelerates with higher polypropylene fiber dosages. Specifically, at polypropylene fiber dosages ranging from 0–1.0%, the flexural strength growth rate is relatively slow. After 3 and 28 days of curing, concrete with 1.0% polypropylene fiber dosage exhibited an 18% and 22.9% increase in flexural strength, respectively, compared to plain concrete. At polypropylene fiber dosages between 1.0% and 2.0%, the increase in flexural strength accelerates. After curing for 3 and 28 days, concrete with a 2.0% polypropylene fiber dosage showed a 147.5% and 94.2% increase in flexural strength, respectively, compared to the 1.0% dosage.

## 3.2 Compressive strength of concrete with different fiber types

After organizing, the following three sets of relationship figures (Fig. 6, Fig. 7, and Fig. 8) were obtained to analyze the impact of different types of fibers on the compressive mechanical properties of concrete.

Figure 6 demonstrates the compressive strength of concrete across various steel fiber dosages. These results reveal that with an increase in steel fiber dosage, the compressive strength of steel fiber-reinforced concrete initially rises, then falls. Specifically, for steel fiber dosages from 0–0.5%, compressive strength increases as the dosage rises. However, as dosages rise from 0.5–2.0%, there's a gradual decline in compressive strength. At 3 and 28 days, concrete with 0.5% steel fiber dosage showed a 2.5% and 2.13% increase in compressive strength, respectively, over reference concrete. However, concrete with 1.0%, 1.5%, and 2.0% steel fiber dosages demonstrated a decline in compressive strength compared to reference concrete at both 3 and 28 days. Additionally, steel fibers' impact on concrete's compressive strength is less significant compared to their effect on flexural strength.

Figure 7 demonstrates the compressive strength of concrete across various glass fiber dosages. These findings indicate that the compressive strength of glass fiber-reinforced concrete first increases and then decreases with rising glass fiber dosages. After 3 and 28 days of curing, 1.0% glass fiber-reinforced concrete exhibited increases in compressive strength of 14.1% and 10%, respectively, compared to reference concrete. However, beyond a 1.0% glass fiber dosage, compressive strength gradually declines with further increases. After 3 and 28 days of curing, 2.0% glass fiber-reinforced concrete showed 10.86% and 7.87% increases in compressive strength, respectively, over reference concrete. Thus, a 1.0% glass fiber dosage is identified as the optimal amount for enhancing concrete's compressive strength. Compared to their impact on flexural strength, glass fibers have a more limited effect on concrete's compressive strength.

Figure 8 demonstrates the flexural strength of concrete under various polypropylene fiber dosage conditions. The results indicate that for polypropylene fiber-reinforced concrete, compressive strength initially decreases and subsequently increases as polypropylene fiber dosages rise. Specifically, compressive strength decreases with increasing polypropylene fiber dosages up to 1.0%. After 3 and 28 days, concrete with a 1.0% polypropylene fiber dosage showed a decrease in compressive strength of 10.1% and 7.23%, respectively, compared to reference concrete. As polypropylene fiber dosage increases from 1.0–2.0%, there's a corresponding increase in compressive strength. Concrete with a 2.0% polypropylene fiber dosage exhibited a 20.24% and 18.3% increase in compressive strength after 3 and 28 days, respectively, compared to reference concrete. Polypropylene fibers have a weaker effect on enhancing concrete's compressive strength compared to their impact on flexural strength.

## 3.3 Analysis of the comparative effect of different fiber reinforcement

After summarizing and organizing the above six sets of relationship curves, the maximum increases in the mechanical properties of reference concrete by different types of fibers were determined.

As shown in Fig. 9, there are differences in the maximum enhancement effect of different types of fibers on the flexural strength of concrete and the specific enhancement effect of each type of fiber was shown as follows: From Fig. 3, it can be observed that when the steel fiber dosage reaches 2.0%, the enhancement effect on the concrete's flexural strength is most significant, with the maximum increasing amplification during the 3 days and 28 days curing periods being 178% and 118.6%, respectively. From Fig. 4, it is observed that when the glass fiber dosage reaches 1.5%, the enhancement in flexural strength of concrete is most significant, with the maximum increasing amplification during the 3 days and 28 days curing periods being 60% and 42.86%, respectively. From Fig. 5, it can be observed that when the polypropylene fiber dosage reaches 2.0%, the enhancement in flexural strength of concrete is most significant, with the maximum increasing amplification during the 3 days and 28 days curing periods being 192% and 138.6%, respectively. In summary, the enhancement effect of polypropylene fibers is the most significant, followed by steel fibers, while the effect of glass fibers on improving the flexural strength of concrete is weaker.

As shown in Fig. 10, there are differences in the maximum increase of compressive strength of concrete among different types of fibers. The specific enhancement effects of each type of fiber are as follows: From Fig. 6, it can be observed that when the steel fiber dosage is 0.5%, the enhancement effect on the concrete's compressive strength is most significant, with the maximum increases of 2.5% and 2.13% during the 3-day and 28-day curing periods, respectively. From Fig. 7, it can be observed that when the glass fiber dosage is 1.0%, the enhancement effect on the concrete's compressive strength is most significant, with maximum increases of 14.1% and 10% during the 3-day and 28-day curing periods, respectively. From Fig. 8, it can be observed that when the polypropylene fiber dosage is 2.0%, the enhancement effect on the concrete's compressive strength is most significant, with the maximum increases of 20.25% and 18.3% during the 3-day and 28-day curing periods, respectively. In summary, the enhancement effect of polypropylene fibers is the most significant, followed by glass fibers. In contrast, steel fibers have a relatively weaker effect on improving the compressive strength of concrete, exerting a smaller impact. Compared to the enhancement effect of these three types of fibers on the flexural strength of concrete, their effect on improving the compressive strength of concrete is relatively limited.