## 2 Agro-Wastes as Concrete Additives
### Waste from Pineapple  
Pineapple is a typical example of a tropical fruit. The peels of this fruit are mostly utilized for animal feeding and the production of organic compost. However, the crown lacks specific applications and is frequently discarded in landfills as waste material [18]. The primary challenge associated with incorporating pineapple crowns into concrete lies in the extraction process, specifically in effectively removing impurities from the fibers [19]. Therefore, surface treatment of the pineapple crown has been identified as a helpful method in order to eliminate non-cellulosic compounds [20]. Based on the literature, it was found that one of the best treatments for removing hemicelluloses and lignin is the use of NaOH in the compound. Nevertheless, when applying alkaline treatment to the surface of agricultural fibers, environmental concerns cannot be ignored [21]. In addition to these environmental issues, this treatment is very costly. Figure 2 shows SEM images of both treated and natural pineapple crowns. As seen in this figure, alkaline treatment increases surface wrinkling and improves the adhesion between the cement and the fibers. Similar results were obtained when incorporating natural agro-waste like coconut fibers into mortar and concrete [21; 22]. In one study, [PERSON] et al. tested dual-hybrid fibers of jute, sisal, curaau, and ramie, and they emphasized that chemical treatment alters the morphological properties of jute fibers [23]. The researchers concluded that the optimal treatment varies based on the fiber type, noting that alkaline treatment improved the tensile attributes of a significant portion of the fibers, while a combination of alkalization and salinization treatments was more effective for the sisal fiber.  
Lately, [PERSON] et al. tested the addition of 0.5, 1, and 1.5% pineapple fibers into cement and found that inclusion of the pineapple leaf fibers effectively improved the split tensile strength (by a 14.65% increase) and compressive strength (by a 15.61% increase) of concrete [24]. A similar study was conducted using the addition of 0.1, 0.2, and 0.3% pineapple leaf fibers into concrete grade C30 [25]. The results showed that adding 0.3% fibers provided the highest compression (from 33.69 to 44.73 MPa) and tensile (3.69 to 6.55 MPa) strengths and other mechanical properties. Contradictory results were found at the higher levels of added pineapple in the concrete: when 2% fibers were added, significantly lower compressive strength was obtained (from 42 MPa for conventional concrete to 27 MPa for concrete containing 2% fibers) [26]. One of the probable reasons for this is that at higher fiber contents, achieving a uniform distribution and alignment of the pineapple fibers within the concrete matrix becomes challenging [27]. Poor dispersion and alignment can create weak points and voids, leading to a reduction in compressive strength.  
In conclusion, surface treatment enhances the adhesion of fibers to cement, though environmental concerns and high costs accompany this method. Incorporating pineapple leaf fibers into cement shows promising improvements in split tensile strength and compressive strength, but higher levels reduce these strength values.