A Week in Review: Week 7, Early Testing Results and Carbon Cost
(Filling shrinkage molds at the Cemex concrete lab in Livermore)
Hello reader(s), this week we:
Explored the complex world of assigning carbon dioxide values to various SCMs (Supplementary Cementitious Materials).
Looked at the preliminary results of the concrete mixes made with the new burnt CSA (Coconut Shell Ash).
Made detailed lab procedures based on literature for acid-treatment and alkaline-treatment of CSA. Will be performed soon once equipment is in order.
Counting Carbon Dioxide of SCMs
A massive part of why we use SCMs, besides improving the properties of the concrete made using them, is to be more environmental. Although most SCMs are waste products and therefore technically don't create any new carbon dioxide emissions, reliance on certain SCMs could prolong the usage of their carbon-intensive origins. For example, if everybody wants to buy fly ash to be environmental, this demand could help coal plants stay in business for longer. As you'll see below, coal-burning releases lots of carbon dioxide, so we don't want to rely on the current SCMs alone.
After a lot (and I mean a lot) of searching around, calculating/converting values and weighing varying data, I've come up with this chart showing the emissions of various SCMs. Of course, like most of my estimates, this is far from perfect and has many compounding factors. Still, you get a general idea of the emissions of OPC (Concrete) and some SCMs. Keep in mind that Fly Ash, Rice Husk Ash and Coconut Shell Ash also generate energy when burnt, which I couldn't factor in here. From this standpoint, it seems that RHA is the better option than CSA due to the lower emissions per metric tonne made, but rice is also one of the least environmental crops to farm, so I'll investigate these outside factors more as well.
Concrete Mixing and Mixed Results
Talking with Eric, the results of the concrete are uncertain. There were two faults in the new batches made with the burnt CSA: rusting (again) and high water demand. The rusting from last year's tests were still seen on the shrinkage molds, despite all the burning to get rid of impurities and oxidize everything that could be oxidized beforehand. Rusting of metal is considered bad because steel supports are common in concrete structures (that lack tensile strength). High water demand is also bad because it usually leads to weaker concrete overall. These phenomena are not common to CSA (at least in literature) so investigations will be carried out to determine chemical composition of the burnt and unburnt materials. Still, we may never know what the material is, if it even is CSA. Good thing my project has other parts to it as well.
(Shrinkage molds with rust marks)
Planning Small-Scale Lab Tests with Acids and Bases
Lastly, I worked with Dr. B to plan out some small-scale concrete cube tests at school. The two main ones are an acid treatment and an alkaline* treatment (geopolymer). The acid seeks to enhance the effectiveness of SCMs as part of concrete, while the geopolymer can theoretically create concrete using only SCM (no cement required). I will be varying acid/base concentrations to see if that affects the compressive strength. Thankfully. Nick has compressive strength testing equipment at Fortera I can use.
*alkaline = basic
Dr. B told me not to write too much, yet here we are.
Thank you so much for reading, and let's hope we meet again next week!
Coconut Fact Number 3: "Natives of the Kiribati islands used woven coconut string to construct robust armour." - https://www.unicomtea.com/20-fun-facts-about-coconuts/
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