Valorization of Wastepaper Ash and Waste Ceramic Powder as Supplementary Cementitious Materials in Cement Mortar Production

Imagine the construction world as a giant, hungry monster that eats up massive amounts of cement to build our houses and roads. This monster is also a bit of a troublemaker, belching out huge clouds of carbon dioxide that warm up our planet. Meanwhile, we have a pile of "trash" sitting around: old office papers and broken ceramic tiles. Usually, these end up in landfills or get burned, which is bad news for the air and soil.

This study asks a simple, curious question: What if we could feed that trash to the cement monster instead of making new cement?

The researchers took two specific types of waste—wastepaper ash (WPA) (the ash left after burning paper) and waste ceramic powder (WCP) (crushed-up tiles)—and mixed them together in a 2:1 ratio. They then tried swapping out different amounts of the cement in mortar (the glue that holds bricks together) with this "trash mix," which they called WPACP. They tested 0%, 5%, 10%, 15%, and 20% replacements.

The "Goldilocks" Zone: Finding the Perfect Mix

Think of the mortar mix like a cake batter. If you add too much flour, it's dry and crumbly. If you add too little, it's a soggy mess. The researchers found that this WPACP "trash mix" had a very specific sweet spot.

• The Workability Dip: As soon as they started adding the trash mix, the mortar got "thirstier." It needed more water to stay smooth and spreadable. The more trash they added, the harder it was to work with. By the time they hit 20%, the mortar was getting stiff and sluggish.
• The Strength Surge: Here is where it gets exciting. When they replaced 15% of the cement with the WPACP mix, the mortar didn't just hold up; it got stronger.
  • At 28 days of curing (letting it harden), the 15% mix was 25.3% stronger in compression than the regular cement mix.
  • At 56 days, it was still 16.1% stronger.
  • However, if they went too far and used 20%, the strength started to drop back down. The paper explicitly rules out the idea that "more trash is always better." The 20% mix actually performed worse than the control, proving there is a limit to how much waste you can swap in before the structure weakens.

The Invisible Shield: Durability and Density

Why did the 15% mix win? Imagine the mortar as a sponge. A regular sponge has big holes where water can sneak in and cause damage. The WPACP particles are super tiny and angular. When added at the 15% level, they act like a microscopic puzzle, filling in all the tiny gaps and holes between the bigger sand grains.

• The "Filler" Effect: This created a much denser, tighter structure. The 15% mix had the lowest water absorption and the lowest porosity (fewer holes).
• The Sonic Test: They used sound waves (Ultrasonic Pulse Velocity) to check the inside of the mortar. Sound travels faster through dense, solid things and slower through spongy, hole-filled things. The 15% mix let sound travel faster, confirming it was packed tight. By 56 days, this mix was classified as "Good" quality, beating the regular cement.
• The Sulfate Shield: They even dunked the samples in a salty sulfate solution (like harsh seawater) to see if they would crumble. The 15% mix lost the least amount of strength, proving it was the best at resisting chemical attacks.

The Microscopic Detective Work

To be absolutely sure what was happening inside, the researchers used high-tech "microscopes" that look at heat and light:

1. Thermal Analysis (TGA/DTA): They heated the samples up to 900°C to see what evaporated. They found that the 15% mix had the least amount of weight loss. This means it had the most stable structure and the least amount of "free" water or weak spots. It also showed that the waste ash and powder were reacting with the cement to create extra "glue" (C-S-H gel) and eat up the weaker parts (calcium hydroxide).
2. Infrared Spectroscopy (FT-IR): This is like taking a fingerprint of the chemicals. The scans showed that the 15% mix had a much stronger signal for the "super glue" (C-S-H gel) and a weaker signal for the weaker parts (calcium hydroxide). This confirmed that the waste materials were actively helping to build a stronger matrix, not just sitting there as filler.

The Verdict

The paper concludes that you can't just dump unlimited waste into cement. 20% is too much, and 0% is missing out on the benefits. But 15%? That's the magic number.

By swapping 15% of the cement with a 2:1 mix of wastepaper ash and waste ceramic powder, you get a mortar that is:

• Stronger (up to 25.3% more compressive strength at 28 days).
• Denser (less water absorption and porosity).
• More durable (better resistance to sulfate attacks).
• Greener (less cement needed, less waste in landfills).

The study suggests this is a viable, real-world option for making construction materials that are tougher on the environment and tougher on the job site. However, the authors note that while the lab results are promising, future research is still needed to optimize this for large-scale use. They haven't declared it a solved problem for the whole world yet, but they've definitely found a very strong recipe for the future.