3.2.3. Mechanical Properties

The compressive strength and flexural strength evolution of BSC with different BS contents at three, seven, 14, and 28 days are presented in Figure 11; Figure 12. An increasing substitution of alkali-treated BS content from 1% to 7% decreased the composite compressive and flexural strengths in comparison to the control mortar. The reason for this is that BS addition increased the porosity of matrix, while the strength of porous matrix was consequently weakened. The composite with 1% BS behaved like the control mortar. Only a 10.9% reduction in compressive strength and 7.3% bending strength resulted after 28 days. However, the composite with 7% BS showed a decrease of 66.7% and 50.5% in compression and bending, respectively. The BSC was more resistant to bending than to compression. The difference in strength reduction between the bending and compression was significant with an increase in particle proportion. Ren et al. [41] reported similar results for cement-blended bamboo charcoal with a particle size between 23 and 359 µm, and the mechanical strength decreased after particle addition. All designed specimens met the minimum strength required in Chinese specifications for masonry mortar [42], whereas the compressive strength exceeded 5 MPa. Besides, according to RILEM [43], concrete with a unit weight range of 1600–2000 kg/m<sup>3</sup> and a compressive strength minimum at 15 MPa can be classified as lightweight concrete and can be applied as a load bearing wall. In our case, BSC7 has a compressive strength lower than 15 MPa, which cannot apply to structural components, while both BSC3 and BSC5 are in the light weight concrete class. The density of BSC1 was superior than 2000 kg/m<sup>3</sup> , classified as normal concrete.

**Figure 11.** Compressive strength of alkali-treated BSC.

**Figure 12.** Flexural strength of alkali-treated BSC.

## **4. Conclusions**

This work evaluated the potential of BS as a sustainable substitute for cementitious materials. Bamboo incorporation into mortar as a recycled byproduct of the bamboo industry has not been described previously in the literature. In this work, a new bio-based material that contained recycled BS (BSC) was prepared. The effect of different treatments and particle proportions on the physical, rheological, and mechanical properties of the BSC was evaluated. On the basis of the experimental results, the following conclusions were drawn:


decrease. All BSC composite mortars satisfied the strength requirements for masonry mortar. BSC3 and BSC5 can be classified as load-bearing lightweight concrete.

Compared with traditional building materials, the cementitious composite with BS valorizes local waste, reduces cement consumption, and decreases the carbon emissions. The replacement of recycled BS with cement in the mortar yields a new lightweight and structural material. Further studies should focus on humidity control performance and building comfort regulations of this bio-based composite with recycled bamboo wastes.

**Author Contributions:** Conceptualization, Y.T. and M.L.; methodology, Y.T. and A.-O.S.; validation, Y.T. and A.K.; Investigation, Y.T and A.-O.S.; resources, J.Y.; data curation, A.-O.S.; writing—original draft preparation, Y.T.; writing—review and editing, Y.T., A.-O.S., M.L., A.K., and J.Y. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Natural Science Foundation of Zhejiang Province, grant number LY19E080002.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data is contained within the article.

**Acknowledgments:** The authors wish to thank CY Cergy Paris Université, L2MGC, for their technical support.

**Conflicts of Interest:** The authors declare no conflict of interest.

### **References**

