Pressed bio-crete bricks as a low-carbon locally produced building material. This report by Safuan Azman looks at the workability of biocrete mixes produced in Bongkud, a rural village near Mt. Kinabalu in Sabah, Malaysia. The experiment is funded by Camps International to develop locally appropriate green building materials.
In an earlier article on The Wonders of Biocrete we discussed how building with lime-based materials could be streamlined through the production of pre-cast blocks. A big challenge with lime-based materials is the curing time and we guessed that by using a mechanical brick press we could quickly produce bio-crete blocks that would hold their own shape while they cured.
Using the CETA Ram brick press design widely available on the internet we began our experiment using different locally available natural fibres and varying their proportions together with lime, cement, sand and water. We used cement initially, for reference, and our intention is to learn how to avoid it completely.
by Safuan Azman and Camp Bongkud
Objective of Experiment
Camp Borneo is keen to have their own unique product of construction materials in accordance with their theme and identity of exploring and conserving nature and engaging with communities. Similarly Arkitrek aims to conserve natural resources through design. Popularising bio-crete will allow us to reduce or phase out the energy intensive, environmentally harmful and non-renewable quarrying for cement and mineral aggregates in favour of more responsible alternatives.
What are we looking to find out from this experiment?
• Most suitable ratio of ingredients to produce a bio-crete brick using a brick press.
• Method statement of the overall process: the tools, procedure and the mistakes made.
• How different natural fibres behave in bio-crete.
The types of natural fibre to be tested in this experiment are:
• Coconut coir in big chunks
• Coconut coir in finer fibres
• Rice Husk
• Rice Straw – only available after the harvesting period in April
• Betel Nut – One of the villages proposed the fibre of betel nuts when they saw me working on the coconut coir. We have not tested it yet
To make quantifying easier mix proportions were made up by volume rather than mass. I have decided to adopt the yellow bucket as a unit of measurement.
Method Statement – Experiment 1-3 (see method statement for experiments 4-9 below)
1) Each ingredient was measured with the yellow bucket and was mixed in a wheelbarrow.
2) Coconut coir was soaked in a yellow bucket of water for about 3 hours.
3) Sand, lime and cement were mixed together before the coir was added.
4) Water was added in stages to ensure consistency.
5) When loading the press we pre-pressed by hand to ensure the cement/lime and sand filled the mould evenly to avoid any holes and breakage during compression.
6) We jiggled the press up and down to ensure the brick was fully compressed.
7) The brick produced then was left to harden briefly before being moved onto plywood.
Notes on improving this method
1. Mix using a better surface than a wheelbarrow for a more precise result.
2. Find a better way to transfer the brick straight away from the press for curing so that the next mix can be poured (for continuous production). Perhaps placing a thin plastic sheet on the base plate before loading and pull it out along with the brick once it is pressed.
3. We noticed that when we pressed the mix the lime seemed to come out from the sides of the plate/mould as liquid, which made me think that we used too much water or the mix ratio was otherwise unsuitable.
Test Mix No1
The first experiment saw the brick was too runny/wet and unable to hold its shape, which from my opinion caused by incorrect quantity of water (too much) and sand (too little). During this first try out we have found out that the main problem with the press is the method of moving the wet bricks away to be cured. The best mix may not have enough strength to hold its shape when been lifted up.
Test Mix No2
The second experiment we conducted with the idea to increase the strength by increasing the ratio of sand. We also wanted to learn how a lower water content will affect workability and final strength and also how well the brick retains its’ shape. We reduced the water and increased the lime to ensure better binding strength with the fibre and sand.
The result of the second experiment was much more convincing, the brick has much more strength to hold its shape, but we still think we have to reduce the quantity of water. This time we decided to let the brick dry for 1 hour on the press before we moved it onto plywood. The Brick is still hardening and the next step will be to test its strength.
The second mix we made has a bit of leftover, so the next experiment we will consider reducing a tiny bit of sand or coir.
Test Mix Nos3&4
After the 2nd experiment we have decided to reduce the amount of sand, as to improve its compressibility, and to have less water to see its capability of holding up the shape. This time we used finer coconut coir fibre which been cut to approximately 2inch to see its workability and strength. The finer coir is more compressible and the amount compacted in the wheelbarrow is much more significant.
We improvised the brick press by putting a plastic sheet to the base plate, to help us move the brick right away.
The brick that came out was much sturdier, and the lack of water made it drier and better in holding up the shape. With less sand the brick seemed to be better compressed than before without it’s shape being affected. The finer fibre was pretty impressive as we think it was properly mixed and spread better than the previous one and made the brick easier to compress even though it might have effect on its tensile strength.
The plastic sheet seemed to contain the lime from leaking and it was pretty much collected at the bottom of the brick (where the plastic sheet is).
I made a silly mistake by moving the fresh pressed brick on to uneven plywood which caused the brick to bend a little as it cured.
Test Mix No5
We decided to try maximising the percentage of natural fibre to lime/sand/cement and use less water. We also intended to reduce and then eliminate cement to see how lime behaves on its own. I decided to use small portion of fine sand hoping it can help filling small gap and reduce ‘cave’ all around the brick.
The result was that the brick was too runny and couldn’t hold its shape and we didn’t add enough fibre so that the mould couldn’t be fully filled. Earlier during the mixing, I noticed that bigger chunks of coir prevented the mix from spreading and blended evenly and requiring extra water for workability. During this mix I avoided using the big chunks of coir as shown in the photo below as it will reduce compressibility and won’t blend evenly with others.
Test Mix No6
This time we decided to take longer time (about 30-35mins) to mix the coir and other ingredients thoroughly (figure above). We didn’t use cement because, as from previous experiment with minimal cement, the lime seemed reliable in gluing up the mix. We added more fibre but then we wasted 1 portion when we couldn’t load any more in the mould, hence for the next experiment we were thinking of reducing the ration of fibre or cut them into finer fibre.
The result was pretty impressive. The brick held its shape well, one of the reasons being that we took care to compress the mix by hand during loading (about 15mins). We loaded the press layer by layer and pressed them hard especially at the sides. Lime and sand and water seemed to mix rather perfectly with the coir and the result can be seen in the photo below.
We recommend using finer fibre as it helps make the mix more workable and saves time. It looks good too. With this we have a workable and practical ratio, avoiding cement all together and maximising the use of natural fibre.
Test Mix No7
In this experiment we used rice husk as the natural fibre to investigate its properties compared to coconut coir. I tried the same ratio as the last coconut coir experiment and was dead wrong. The compact rice husks sit together closely leaving a minimum gap for other ingredients to blend in. Unlike coconut coir the 8 portion of rice husk can produce 2 bricks with leftover.
Consequently the lime and sand ratio in this experiment was totally wrong, being too little to hold 8 portions of rice husk. We became aware of the problem during mixing and tried to mitigate by adding 1 portion of cement. This helped a little. We added significantly more water to help the binding but the mix still dried out. During the loading of the press we found it hard to compress the mix and only managed to load about 1.5 portions, wasting the rest of the mix.
Test Mix No8
The objective this time was to get the right amount of mix for one brick. Based on the previous experiment we decided to use 3 portions of the rice husk hoping it would fill the mould perfectly. And it did, after we compacted it carefully and slowly. Every layer was pressed using a piece of wood until a little bit of water came out at at the top and the side. The brick we got was pretty strong, held its shape well and has smooth square edges, except for the top surface where it was a little bit flaky. I think that this happened because we lost some compression due to the last load being too thick. When we closed the lid it just swept away the compressed surface.
Method Statement for Exp 5-8
1. Measure all the ingredients using a marked yellow bucket.
2. Soak the coconut coir in water for 30mins. Remove any big chunks of coir. It is highly recommended to cut the coir into smaller pieces (2”) for better workability and compressibility.
3. Mix dry ingredients (cement/lime/sand) until consistent, removing any big gravel. Mix on a dry, flat and clean surface eg. concrete floor or plywood
4. Mix the coconut coir with dry ingredients thoroughly (we took around half an hour) using either hand or trowel or both. Keep tearing the coir apart to ensure an even mix.
6. Slowly and gradually, add water to the mix until it reaches ‘good consistency’ for pressing. To determine what ‘good consistency’ is we used some of the mix to make a ‘mini ball’ compacted by hand. From this we could judge the bonding strength and whether more water is needed.
7. Slip in a plastic sheet onto the base of the mould beforehand.
8. Carefully load the mix into the mould, layer by layer and pre-compress them by hand or using a piece of wood. Repeat these actions until the mould is full. Remember this step has to be done patiently and carefully so we can ensure that the maximum volume of fibre can be added to the mould.
9. Close the press lid, and press the brick halfway, without opening the lid to ensure it is tightly pressed.
10. Open the lid and press the brick out of the mould at once.
11. Before you move the brick, ensure to have a piece of nice flat plywood next to the press so that the brick can be moved out smoothly.
**For the rice husk, ignore step 2 and 4.