3.1.2. Morphological Properties

The morphological changes to the bamboo particles from the different treatments are presented in Figure 5. Compared with (hot) aqueous treated particles (Figure 5b,c), cell walls of the untreated particles were wrapped in wax, pectin, and impurities (Figure 5a).

Figure 5b shows that cold water removed the impurities, where the particle surface was neater and smoother compared with the untreated particles. Cellulosic defibrillation is shown in Figure 5c,d, where rougher and larger surfaces are visible. Alkali treatment was more violent and intensive than hot water. The surface area increased and the network porosity decreased because of the disruption in hydrogen bonding in the network structure by alkali attack, so the surface roughness increased [34]. This effect may improve the particle compatibility with cement by creating a more effective bonding area. Some authors reported that alkali treatment could break the microfibril bundles and produce individual fibers, so that the mechanical interaction between the particles and the matrix can be improved [35,36].

**Figure 5.** SEM analysis of BS (**a**) without treatment, (**b**) with aqueous treatment, (**c**) with hot aqueous treatment, (**d**) 10% concentration alkali treatment.

### 3.1.3. Setting Time and Workability

Plant particle addition delays the setting and inhibits strength development due to the presence of hemicellulose and lignin [37]. The initial and final setting times of cement paste with 3% BS by mass with different treatments were measured to meet construction material requirements. Table 4 shows the initial and final setting time of BSC paste using different treatments BS. Meanwhile, the final setting of aqueous-treated BSC paste occurred more than 2 h after the control. Owing to the removal of lignin, which is soluble in water, the

final setting time of hot aqueous-treated was 40 min faster than the aqueous-treated. The setting was accelerated by approximately 1 h for the alkali-treated particle compared with the control paste due to the dissolution of hemicellulose in alkaline solution. These results confirmed that adding vegetable particles may inhibit the cement hydration and delay the setting time. Cold and hot water treatment can remove some extractives. However, plant particles require a more violent alkaline extraction to remove hemicellulose.


**Table 4.** Evolution of setting time with different treatments.

\* Value compared with control cement paste.

Even though the same amount of pre-wetting water was used in each treatment, slump was measured at 41 mm, 40.7 mm, 34.5 mm, and 9.8 mm for the control mortar, cold aqueous, hot aqueous, and alkali-treated BSC3, respectively. Hot aqueous and alkalitreated BSC3 showed a weak slump. A possible explanation for these results is cellulosic defibrillation, whereas the expanded rougher fiber surface probably absorbed more water. The same results have been reported previously in [35]. The water absorption was more significant for the sodium-hydroxide treatment because of the removal of the lignin layer, which is an impermeable layer of vegetable fiber.

### 3.1.4. Physical and Mechanical Properties

Despite the various treatments, no significant difference resulted for the density and porosity, which were ~1994 <sup>±</sup> 10 kg/m<sup>3</sup> and 16.4 <sup>±</sup> 0.04%, respectively. The same results were reported in [38] that only 0.7% difference was found between mortar incorporated alkali-treated and non-treated jute fiber.

The experimental results for the mechanical behavior are shown in Figure 6; Figure 7. Figure 6 shows that the compressive strength of BSC3 was lower than that of the control mortar. The compressive performance between the cold and hot water treatments were close, with only a 3% difference observed. The alkali-treated BSC3 exhibited a higher compressive strength of 16.1% and 13.9% than the cold and hot aqueous treatments, respectively. The alkali-treated BSC3 strength was 73% of the control mortar strength.

**Figure 6.** Compressive strength of BSC3 with different treatments.

**Figure 7.** Flexural strength of BSC3 with different treatments.

The flexural strength *f<sup>b</sup>* was obtained from:

$$f\_b = \frac{3F \times l}{2b \times h^2} \tag{5}$$

where *F* is the applied load and *l*, *b*, and *h* are the specimen length, width, and height, respectively.

Data from the three-point bending tests indicate that the flexural strength of the cement matrix was attenuated because of the addition of BS (Figure 7). The degraded mechanical behavior of the BSC is related to the lower modulus of the bamboo particles compared with the cement. No significant difference in bending performance resulted between the three treatments using the ANOVA analysis. The alkali-treated BSC3 had an 8.2% and 7.6% higher flexural strength than the cold and hot aqueous treatments, respectively. The flexural strength of the alkali-treated BSC3 decreased by 37% compared with the control mortar.

Both the compressive and flexural strength value of alkali-treated BSC were higher than for the two other treatments, which confirmed the efficiency of alkali treatment. Besides, a more obvious advantage of alkali-treated BSC can be noticed on compressive behavior. It can be explained that after alkaline attack, the particles bundle into microfibrils (Figure 5d), which simplified their dispersion in the matrix, making the composite more homogenous.

### *3.2. Effect of BS Content on Composite*

Results in Section 3.1 show that the BSC with alkaline treatment had a quicker setting and better mechanical behavior than the other treatments, which indicates that a better compatibility exists between BS and the cementitious matrix. Hence, alkaline treatment was chosen in the following studies to evaluate the effect of particle proportion on the physical and mechanical properties.
