*3.4. Compressive Strength*

As shown in Table 7 and Figure 5, at the age of 28 days, when the W/B ratio is 0.4, the content of GGBFS is 20%, the content of waste PE is 0%~4%, and the compressive strength is 54.1~48.9 MPa; when the W/B ratio is increased to 0.5, the compressive strength is 48.5~44.9 MPa (reduced by 8.2~10.4%); when the W/B ratio is increased from 0.5 to 0.6, the compressive strength is 37.2~34.7 MPa; the compressive strength is reduced by 11.9~16.6% when the W/B ratio is increased from 0.4 to 0.5 and reduced by 30.1~31.2% when the W/B ratio is increased from 0.5 to 0.6, indicating that the compressive strength is decreased with increasing W/B.

**Table 7.** Compressive strength of cement mortar with different W/B ratios and waste PE (unit: MPa).


**Figure 5.** Compressive strength of cement mortar with different W/B ratios and waste PE.

When the W/B ratio is 0.5 and the content of slag is 20% at the age of 3 days, the strength of the control group is 24.7 MPa, and the compressive strength is 23.0~20.3 MPa (reduced by 6.9~17.8%) for a waste PE content of 1~4%. At the age of 28 days, the strength of the control group is 48.5 MPa and the compressive strength is 47.8~44.9 MPa (reduced by 1.4~7.5%) for a waste PE content of 1~4%. At the age of 91 days, the strength of the control group is 59.1 MPa and the compressive strength is 57.4~53.8 MPa (reduced by 2.0~9.1%) for a waste PE content of 1~4%, meaning that the compressive strength is decreased as the waste PE fiber material content is increased. As the waste PE is fibrous, the balling phenomenon is likely to occur in the specimen when the specimen is compacted. As this leads to the formation of fiber agglomerates inside the specimen, the pores inside the specimen are enlarged, and the waste PE is relatively soft, which cannot provide effective compressive strength for the specimen. When the content increases, the compressive strength decreases.

When the W/B ratio is 0.5 and the substitution amount of GGBFS is 20%, at the age of 28 days, the strength is reduced by 1.4~3.5% for a waste PE content of 1~2%, and the strength is reduced by 5.4~7.3% for a waste PE content of 3~4%. At the age of 56 days, when the waste PE content is 1~2% and 3~4%, the compressive strength is reduced by 1.9~4.5% and 6.5~7.9%, respectively. When the waste PE content is 1~2% and the strength reduction is controlled within 5%, the waste can be effectively eliminated, and the economy of the waste is enhanced, with a reduction in waste generation and a reduction in environmental pollution.

The compressive strength of the PE fiber material added at 2% showed a decreasing trend at 28 days of age with W/B ratios of 0.4, 0.5, and 0.6 compared to the control specimen without PE fiber material. The ratios were 0.94, 0.96, and 0.94, respectively. The decrease in compressive strength of the PE material added at 2% could be controlled within 5%. However, at 56 days of age, the compressive strength development in the three different W/B series exceeded the compressive strength of the control specimens at 28 days of age. Therefore, although the hardening properties of the compressive strength tended to decrease with the addition of 2% PE material, the compressive strength at late ages was 58.1, 50.0, and 42.6 MPa with W/B ratios of 0.4, 0.5, and 0.6, respectively, by adding GGBFS, and all of them exceeded the compressive strength of the control specimens. In addition, with the addition of PE fiber material to 4% of the specimen, the compressive strength at 56 days of age was also the same. The test results showed that by adding PE material to eliminate the waste, the compressive strength could be no lower than the test value of the control specimen without PE material by adding GGBFS to extend the concrete curing age.

## *3.5. Flexural Strength*

As shown in Figure 6, at the age of 28 days, for a GGBFS content of 20%, W/B ratios of 0.4, 0.5, and 0.6, and a waste PE content of 0~4%, the flexural strengths are 20.2~17.4 MPa, 18.1~15.5 MPa, and 12.3~9.9 MPa, respectively, meaning that the flexural strength is decreased with increasing W/B ratio.

At the age of 3 days, when the W/B ratio is 0.5 and the GGBFS content is 20%, the flexural strength is 7.7~5.3 MPa, indicating that the flexural strength decreases as the content increases (6.5~29.8%). At the age of 28 days, the flexural strength of the mortar without waste PE is 18.1 MPa, and as the waste PE content is increased to 4%, the flexural strength is 15.5 MPa (reduced by 14.1%). At the age of 91 days, the flexural strength of the mortar without waste PE is 26.3 MPa; the flexural strength of the mortar with 4% waste PE is 24.3 MPa, and when the waste PE content is increased from 1% to 4%, the flexural strength is reduced by 3.1~7.6%, indicating that the flexural strength is decreased with increasing waste PE content. At the age of 56 days, when the amount of substituted GGBFS is 20% and the waste PE content is 1~2%, the strength is 2.2~5.2%, but the strength is reduced by 9.5~10.3% when the waste PE content is 3~4%. At the age of 91 days, the strength is reduced by 3~5.3% for a waste PE content of 1~2%, and the strength is reduced by 6.5~7.6% for a waste PE content of 3~4%. This indicates that the strength reduction can be controlled to within 6% when the waste PE content is lower than 2%. This value is the closest to that of the control group; hence, the waste can be effectively eliminated to reduce environmental pollution.

**Figure 6.** Flexural strength of cement mortar with different W/B ratios and waste PE.
