Strength Properties of High-Performance Concrete with Green Banana (Musa acuminata, AAA Group) Peel Ash as Partial Cement Replacement

The Concrete Conundrum: A Sticky Problem with a Green Solution

Imagine the world of construction as a giant, bustling kitchen where everyone is trying to bake the perfect, strongest cake. For decades, the main ingredient in this recipe has been cement. It's the glue that holds our cities together, turning sand and rocks into skyscrapers, bridges, and roads. But here's the catch: making cement is like running a giant, carbon-belching furnace. It's responsible for a huge chunk of the world's pollution, and it's getting harder to ignore the environmental cost of our concrete jungles.

Enter the concept of "High-Performance Concrete" (HPC). Think of this not as regular concrete, but as the super-charged, athlete version of the material. It's designed to be incredibly strong, durable, and resistant to the elements, perfect for the heavy-duty structures of the future. To make it this tough, engineers usually mix in special "mineral admixtures"—secret ingredients like fly ash or silica fume that fill in the tiny gaps and make the concrete denser. But what if we could find a secret ingredient that isn't just good for the planet, but is also a waste product we're already throwing away? That's the question this study asks: Can we turn a common kitchen trash item into a superhero ingredient for our strongest buildings?

Turning Trash into Treasure: The Banana Peel Experiment

In this study, a team of researchers from Kampala International University decided to test a very specific, local waste product: the peels of green bananas. In places like Uganda, these bananas (locally known as Matooke) are a staple food, but the peels often end up as garbage, rotting and releasing gases. The researchers wondered: if we burn these peels and turn them into a fine, gray powder (ash), could that powder replace some of the cement in high-performance concrete?

To find out, they treated the banana peels like a science experiment in a kitchen. They collected the green peels, dried them, and burned them at a very hot, controlled temperature of 800°C. This turned the peels into a fine ash, which they then ground up and sifted to make sure it was as smooth as flour. They analyzed this "Green Banana Peel Ash" (GBPA) to see what it was made of. They found it was rich in silica and alumina, the same chemicals found in other famous concrete additives, suggesting it had "pozzolanic" powers. In plain English, this means the ash can react with the water and cement to form a super-strong glue over time.

The Recipe and the Race

The team set up a race to see how much of this banana ash they could swap into their concrete recipe without ruining the cake. They made five different batches of High-Performance Concrete:

1. The Control: 100% cement, 0% banana ash.
2. The 5% Mix: 5% of the cement replaced by banana ash.
3. The 10% Mix: 10% replaced.
4. The 15% Mix: 15% replaced.
5. The 20% Mix: 20% replaced.

They kept everything else exactly the same—the amount of water, sand, and rocks—so they could be sure that any changes in strength were due to the banana ash. They poured these mixes into molds and waited, testing them at 7 days, 14 days, and finally at 28 days, which is the standard time to see how strong concrete has become.

The Results: The Sweet Spot is Small

The results were a bit like a rollercoaster ride. When they tested the 5% banana ash mix, the outcome was promising but nuanced. While the mix showed a slight increase in strength at 28 days, reaching 69.08 MPa compared to the control mix's 67.06 MPa, the researchers noted that this performance was "comparable" to the control rather than a massive leap. In fact, the study highlighted that the 5% mix actually had lower strength at the early stages (7 days) compared to the control, only catching up and slightly surpassing it later as the pozzolanic reaction took time to develop. Ultimately, the 5% mix demonstrated "satisfactory" mechanical properties, proving it could match the strength of pure cement without a significant drop-off.

However, the story changed when they added more banana ash. As soon as they bumped the replacement up to 10%, the strength started to drop, landing at 60.167 MPa. By the time they hit 15%, the strength plummeted to 39.55 MPa, and at 20%, it was down to 33.314 MPa. It seems that while a little bit of banana ash is a viable ingredient, too much of it weakens the structure, likely because it doesn't bind the rocks together as well as cement does.

The same trend happened with splitting tensile strength (how well the concrete resists being pulled apart). The 5% mix performed well, reaching 5.22 MPa, which was comparable to the control mix's 5.01 MPa, while the 20% mix struggled at just 2.20 MPa.

Durability: Keeping the Water Out

Concrete isn't just about being strong; it's about not letting water sneak in, which can cause rust and cracks over time. The team tested how much water the concrete soaked up. The 5% banana mix was excellent at keeping water out, absorbing only 1.07% of its weight in water, which was comparable to the control mix's 1.1%. But as they added more banana ash, the concrete became more porous, like a sponge. The 20% mix soaked up 1.47% of its weight in water, meaning it was much more vulnerable to damage from moisture.

The Verdict

So, what's the takeaway? The study suggests that Green Banana Peel Ash is a promising, eco-friendly ingredient for High-Performance Concrete, but only if you use it sparingly. Replacing just 5% of the cement with this ash seems to be the "sweet spot." It makes the concrete perform just as well as regular concrete in the long run, maintaining satisfactory strength and keeping water out effectively, all while turning a pile of kitchen trash into a building material.

However, the researchers are careful to say that going beyond 5% is a bad idea for these specific mixes; the strength and durability drop off sharply. They conclude that while this is a great step toward sustainable construction, we need to be precise. It's not a magic bullet that can replace all the cement, but it is a powerful tool for making our concrete greener and stronger, provided we don't overdo it. The paper suggests that with the right amount, we can build a better future without throwing away our bananas.