## 2 Agro-Wastes as Concrete Additives
### Waste from Sugarcane  
Sugarcane is a chief source of sugar and alcohol [28], with Brazil being a major producer. During the COVID-19 pandemic, alcohol consumption was increased and in consequence the environmental worries surrounding sugarcane waste increased [29; 30]. However, sugarcane is used for animal feeding and it has low added value, so it is not a very interesting subject for researchers. Nevertheless, some researchers have studied burning the sugarcane bagasse and using its ash as a additive material for cement [31]. Using agro-waste ash as a supplementary material for cement in construction is the most studied subject among the research in this field (Figure 3). Some findings disclosed that the temperature of burning bagasse influences the quality of the ash and subsequently  
Figure 2: Pineapple fiber images under SEM: (**a**) without treatment; (**b**) treated using NaOH [20]. the mortar and concrete [32]. This finding is consistent with the prior literature, which indicates that burning conditions are a key parameter when utilizing ash as a cement supplementary [33]. In a comprehensive review, [PERSON] et al. surveyed the result of sugarcane bagasse ash as an additive in cement-based composites and asserted that the high amount of amorphous silica in the ash compound renders it a valuable pozzolanic material (a substance that, when combined with lime in the presence of water, forms cementitious compounds and enhances the strength and durability of concrete) and useful as a supplementary material for cement, leading to the diminishing of environmental concerns through reducing CO\({}_{2}\) emissions [34]. Also, they found that the use of sugarcane ash incurs lower costs (8.65%) when employed in cement. One positive aspect of utilizing agro-waste ash in cement, often overlooked in discussions by other researchers, is the fact that using ash reduces the amount of water needed (from 0.9% for conventional concrete to 0.5% for concrete containing 15% ash) for the same workability because of the glassy surface texture of the ash. [PERSON] et al. concluded that the strength properties of the suggested concrete increased with an optimal ratio (5-15%) of the ash. A comparable approach for this is presented in Figure 4. It was found that the addition of 20% sugarcane bagasse ash into concrete could highly increase its resistance to different acidic environments; however, its compressive strength decreased for the other ratios (5, 10, and 15%) [35]. This could be ascribed to the presence of silica in the ultra-fine particles of the ash, which reduces the porosity of the concrete matrix [36]. Similarly, [PERSON] and [PERSON] conducted comprehensive experimental tests by adding 3% and 6% nano-silica as well as 10-30% (with a span of 5%) sugarcane ash into cement. They discovered that the compound could withstand chloride environmental conditions for up to 90 days [37]. In a very recent study, [PERSON] et al. emphasized that adding 3% sugarcane bagasse ash improved the compressive strength by 18% and 10% after 28 and 90 days of curing, respectively [38]. The enhancement in strength achieved through the addition of sugarcane bagasse ash can be attributed to the amorphous nature of sugarcane  
Figure 3: Network map of keywords that have been used in published papers about additives used in concrete and cement, obtained from Web of Science. bagasse ash particles. These particles react with calcium hydroxide over time, leading to the formation of an increased amount of calcium silicate hydrate gel. The authors examined two additional ash samples (from cotton and rice) and observed similar results. The results showed a high accelerated corrosion process with respect to normal conditions. In addition, improvements in both the bulk resistivity and charge transfer resistance of the concrete were achieved through utilization of these nano-ash samples.