# Effect of Adding Waste Polyethylene and GGBFS on the Engineering Properties of Cement Mortar
## 4 Conclusions  
1. As the added volume of waste PE increased and the replaced volume of GGBFS decreased, the slump and flow declined.
2. The added volume of waste PE increased, and the setting time showed a shortened trend; the replaced volume of GGBFS increased, and the setting time showed a lengthened trend.
3. The compressive, flexural, and tensile strengths of mortar decreased with the increase in the volume of waste PE added. Adding 2% volume of waste PE to the mortar can meet the needs of general engineering use and can achieve the effect of waste recycling. In the later stage of mortar curing, due to the pozzolanic reaction with the addition of GGBFS, with the increase in curing time and the increase in replacement amount, the later-stage strength of mortar increased obviously. When the GGBFS replacement amount was 20%, the strength of the mortar was the best. This amount of replacement increased the overall strength of the specimens.
4. The ultrasonic velocity increased with the curing time. When the addition of waste PE rose from 1% to 4%, the ultrasonic speed decreased by 6.9% to 8.7%. Adding GGBFS can increase the specimen's density in the later stage and then increase the ultrasonic velocity. The ultrasonic speed was the highest at 5172 m/s when using 20% GGBFS instead of cement.  
Figure 12: Weight loss of cement mortars with the addition of different ratios of waste PE and GGBFS replacement.  
5. Adding waste PE to the mortar resulted in the generation of holes in the sample and increased the water absorption ratio. Using GGBFS to replace part of the cement, the produced hydrates could fill the holes of the specimen in the late stage of hydration, making the sample denser and lower in water absorption. When we used 20% GGBFS to replace the cement, the water absorption of the mortar reached its lowest (3.7%).
6. The resistivity decreased as the added volume of waste PE increased. When we gradually increased the replacement of GGBFS, the increase in the mortar resistivity was slow in the early phase, while it increased significantly in the late stage. When the replacement of GGBFS was 20%, we achieved the best result (39 k\(\Omega\cdot\)cm). After 28 days, the results of all proportions of the mortar were higher than 20 k\(\Omega\cdot\)cm, reaching the durability requirement for engineering use.
7. The added volume of waste PE increased, leading to poor resistance to sulfate attack. We used the GGBFS to replace cement, and the hydration of the mortar in the early curing phase was slow and increased the weight loss rate of the sample. The addition of 2% waste PE and the use of 20% GGBFS to replace cement in the range of this study resulted in the sulfate attack resistance of mortar being better.
8. We recommend adding 2% waste PE and replacing the cement with 10% GGBFS, so the cement products have proper engineering application performance. This is expected to simultaneously have the effects of waste recycling, energy savings, and carbon emission reduction.  
Conceptualization, C.-C.H., J.-N.C. and H.-Y.W.; Formal analysis, C.-C.H. and J.-N.C.; Resources, J.-N.C.; Data curation, F.-L.W.; Writing--original draft, C.-C.H. and J.-N.C.; Supervision, H.-Y.W. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The authors declare no conflict of interest.