From Idea to More Ideas: A Summary of the Project Before Senior Project

Key Words:

CSA- Coconut Shell Ash

SCM- Supplementary Cementitious Material

ASTM- ASTM International, formerly "American Society for Testing and Materials"

SEM- Scanning Electron Microscope

The Long Story:

In 11th grade, I wanted to try using agricultural SCMs* (Supplementary Cementitious Materials) to partially replace cement in concrete (since cement production creates massive carbon emissions inherent in the chemical reactions), and after searching online for days, the only agricultural SCM I found available in larger quantities was Coconut Shell Ash (CSA).

Then, I cold-called/emailed various professors/companies seeing if they could help me create concrete mixes. The reason external help was necessary was that the concrete industry uses very specific ASTM standards with special equipment (some of which can be seen below) that can be expensive/difficult to procure. Miraculously, when I visited Cemex's San Jose office out of desperation, I got in contact with my current advisor, Nick (now at Fortera), who set me up with Eric to make concrete samples at 15, 25 and 35% replacement of cement (by weight) in the concrete, along with normal concrete ingredients like small, medium and large aggregates being added in. The compressive strength f the concrete cylinders created was tested with hydraulic press at 7, 14, 28, and 56 days after making the concrete. Concrete usually gains strength over time, gaining strength up to months after mixing.

*Note: SCMs work (usually) by containing Silica (SiO2) and/or Alumina (Al2O3) and participating in pozzolanic reactions, which are complex reactions that pretty much work to create a strong "CSH" chemical network that adds strength to the concrete.

Summary of Key Findings/Results:

1. As seen below, oxidation was caused on the steel shrinkage test molds, with oxidation increasing with CSA concentration.

   1. This is very rare for SCMs, and is also very bad because concrete is often used with steel reinforcement (to add tensile strength), and corrosion of steel can degrade/weaken the steel. Cemex told me that any material that oxidizes steel won't do well in the industry

   2. Potential Solution(s): Using a powerful magnet to extract iron chunks (seen in Scanning Electron Microscope images) and using a chemical wash to purify the ash.
      

2. As seen in the graph below, compared to the similar Rice Husk Ash concrete (graph from literature in Figure 5), the Coconut Shell Ash concrete I made (data in Figure 4) had significantly lower strength, especially as replacement percentage increased.

a. Through "back-scatter" chemical analysis of the CSA at Fortera, we saw that a large portion of the CSA was actually carbon (with plants like coconut being largely carbon-based), and since carbon does not really contribute to the concrete strength, as we added more, strength decreased.

b. Solution: Using controlled burning in an oven (at 600-900 C) to burn off some of the carbon, leaving a higher proportion of silica and alumina and calcium (which contribute to strength).

The key (and problem) is balancing burning time, as burning for too long of course will emit more carbon and use more energy, both un-environmental things to do.

(Back-Scatter chemical composition data of raw CSA)