Hi, this is Wayne again with a topic “Primitive Technology: Geopolymer Cement (Ash and Clay)”.
At the brick making hut Making fire by friction, Wood is burnt for ash (, also drying bricks, ) The wood ash To the brick hut. The ash is sifted to get most of the charcoal out. Water is mixed with the ash to form a paste. The ash is formed into pellets or clinkers to be fired. One pellet is set aside to air dry. Only The rest of the pellets are calcined in the forge One by one, the pellets are burnt with wood in the forge. The pellets must glow red hot for them to be properly calcined To form the cement.
The pellets are mixed with water again and formed into shape. This is a cube of calcined ash. Only no aggregate added Old, broken bricks/pottery made previously will be crushed to form aggregate. The brick is crushed to a fine aggregate 1:1 ash to fired clay 1:2 ash to fired clay 1:3 ash to fired clay. I tried 1:4, but it wouldn’t hold together. So I just made a big block about 1:2 ratio ash to fired clay.
Uncalcined pellet has a dull surface: Calcined block has a glossy surface A week of curing the samples are put in water to for a dissolving resistance test Time lapsing about 30 minutes. Watch the uncalcined pellet (, far right ), The uncalcined ash pellet dissolved.. All samples that used calcined ash survived The lesson here is that only ash that gets very hot is suitable for cement, A tame lizard, Making a grate for a furnace Making ash for the next batch. The ash is sifted of charcoal water added to form paste. A single cylindrical clinker is formed, that is less than 1/2. The width of the grate Ash clinker on grate, Adding clay to hold up grate in furnace Grate into position in furnace Clinker in furnace on grate.
This time the firing will work by natural draft (, no blower ) to save labor and simplify the process. Raising the height of the furnace for better natural draft Sealing joints with mud. The furnace is stacked with wood.
The fire is lit from the top ( less smoke. This way, ) wood is periodically added, so it’s nearly full Burning. Wood on a grate is more efficient and hotter than a fire on the ground.
After an hour, the clinker is well and truly calcined Calcined clinker. Half the clinker is taken and crushed Using sand instead of fired clay for this one as an experiment: 1:3 ash to sand Ash sand, sample 1:3 ash to fired clay, Same material but different shapes 2 days later. A water test is done After 24 hours. All samples have survived.
The sand. Sample works like the others, but is more easily scratched being slightly weaker. The next experiment will only use the ash left over from the previous firing, as it is ( no more calcining ). In theory, the ash from wood burnt on the grate should have gotten so hot. It needs no further heat treatment. A 1:3 ratio ash to fired clay is tried, It’s not sticking.
So more ash is needed.. The ash is less dense than the clinker. So more needs to be added. This is more like 1:1 ratio now, 6 hours later, the sample is water tested. Astoundingly after setting for only 6 hours, the sample survived 24 hours in water.. We now have a simple method for producing a fast setting, geopolymer cement., More experiments need to be done to scale up the process and see what structures can be made.
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