Homebrew

[david s]

Yes, so how about you making some tests with your brick dust too, to see how they compare. For mortars I always dry and sieve my graded sand, before mixing, removing any grains larger than 2mm which usually contributes 6.5% (measured) of the graded sand volume.

There is a test potters use for clay body workability and that is to roll out a coil about as thick as your finger then wrap it around your finger. If it breaks the body is not considered workable enough. i mix 1:1 grog or fine sand with a commercial clay (which already has some grog in it), to seal around my kiln door. At 1:1 it does not pass the finger workability test, but works well as it's sacrificial. Try this test with your brick dust.

Mortar mix tests 11.4.’25

Materials: graded sand GS, ,
hydrated lime HL
ordinary Portland cement OPC
0.3-0.6mm grog G
bricklayers clay BC

All materials measured by volume then mixed with water



Mix 1 3:1:1:0.5 GS, HL, OPC, BC (plus 3 finger sized samples)

Mix 2 3:1:1:0.5 GS, HL, G, BC (plus 3 finger sized samples)

Mix 3 3:1 GS, HL

Mix 4 3:1 G, HL

Mix 5 1:1 HL, BC (1 finger sample)

Mix 6 4:2;1 GS, HL, G (1 finger sample)

Results to come

[MikeD55]

David

Just curious why samples 1 and 2 are 3 finger sized samples. Mix 3 is interesting as I used it last year on an arch I built for fun. It takes forever to set up and thus allowed us to take it down.

Mike

[david s]

David

Just curious why samples 1 and 2 are 3 finger sized samples. Mix 3 is interesting as I used it last year on an arch I built for fun. It takes forever to set up and thus allowed us to take it down.

Mike

My idea was to use the larger sized samples to break, to test their comparative strength and maybe fire the finger sized samples to 500C to see what happens to the one with OPC compared to the one with grog.
Maybe this could show a weakness in Mix 1 with the OPC being killed by temperature and also maybe show some strength enhancement from some interaction with the grog and lime.

[MikeD55]

Interesting. This is great stuff. Excited to hear the results

[david s]

Sorry for the delay in reply. Because the industry standard for concrete is 28 days of curing instead of just giving it a week, I gave it two weeks of damp curing, wrapping all samples up in plastic.
On de-moulding the samples Mix 2 cracked which gives an indication of its relative strength. All sample were approximately 12-15mm thick, the finger samples 12mm. On braking the samples by hand, I was unable to break Mix1, but all other samples broke with what I'd consider the strength of a piece of chalk. I was not expecting such a marked disparity of strength and surprised by the strength of Mix 1 and the weakness of the others. I have a method of testing the relative strength of the finger samples which I'll do next week and report back. It is posssible that the strength of the lime as a cementious ingredient is more dependant on time for its carbonation process. I'm unsure about this, does anyone else have some knowledge about this and can provide an opinion or information?

[MikeD55]

Interesting

[MikeD55]

So David what’s your opinion on all this?

[david s]

After 8 days of air drying (22 days since casting the samples) I broke, by hand again, Samples 2,3,4and 6 Sample 1 was still not able to be broken by hand.
All the other samples exhibited similar strength, easily broken, but a little stronger than the 14 days test.

I am setting up the flexural strength tests today for the finger samples of mixes 1-6, although mix 6 was so unworkable, it broke after I rolled it out and set it aside to cure.
These tests might reveal something, fingers crossed (pardon the pun).

[david s]

Here are the results. The pics show my testing method using water for the load, metric 1 kg = 1 litre, a calibrate jug, containers hung at the load point with 45 mm from load to stress point for all samples.
Obviously there is some inconsistency in sample thickness which were also 12-15 mm thick. I used a piece of chalk shaved down to 13mm as a comparison.

Flexural Strength Tests

Chalk sample 1.7 Kg
Mix 1 sample at max test weight of 2.4 Kg It would not break
Mix 2 sample 0.71 Kg
Mix 5 sample 0.56 Kg
Mix 6 sample 0.48 Kg

I did not make finger samples for Mixes 3 and 4

Because the Homebrew Mix 1 sample didn't break I did it by hand and was only just able to snap it.
It was very strong. I have 2 left so it may be interesting to see what happens to samples 1 and 2 when taken to 500C and comparing their relative strengths.

Make of these results what you will.