After two weeks of brick pressing – we are done.
We pressed a total of five thousand, six hundred, and ninety one open source CEB bricks. We are using The Liberator – the open source, high performance (6 brick per minute), manually-loaded and controlled CEB press.
Here are some conclusions on production rates, machine performance and durability, and future evolution of the CEB/LifeTrac project. These conclusions provide useful baselines and points of departure for future developments. These are valuable lessons learned from field performance in a scenario where we – machine developers and users – are the evaluators. This is not a simulated scenario, but a scenario in which we are producing building material for a part of our facility – a digital fabrication workshop facility for the production of the CEB machines themselves.
Process Ergonomics Overview and Discussion: We spent about 2 full days digging all the soil with the LifeTrac tooth bar bucket – about 16 tons of soil. We then rototilled the rough chunks to <1/2″ size. then shoveled into buckets, loaded the soil into the hopper, ran the machine, and stacked bricks. With 5 people, we had a dedicated person loading the hopper, one person on the machine controls, one person rototilling with a small walk-behind rototiller full time, and the rest of the people (2+) shoveling the soil into buckets. If there were more than 5 people, two rototillers would be useful. With a 3 person scenario, one person loaded, operated the machine, and stacked bricks. The other two tilled, filled buckets, and carried buckets to the hopper loading area. The 3 person team made about 500 bricks per day, and the 5 person team made about 1000 bricks per day. In practice, a typical 3 person work crew would take about 10 days of hard, physical labor to produce bricks for a 1000 square foot structure.This, in our evaluation, does not meet the criteria of a technique which optimizes quality of life, as in the requirement for all Global Village Construction Set technologies. 10 days of such labor cost about $5000 at $20 per hour. It is less expensive to make further improvements in the machine that eliminate the huge human labor requirements – simply by adding a larger hopper that may be loaded with a tractor front end loader.Personally speaking, 200 bricks per person per day sounds pathetic – it means 1 brick per minute using a 3 person team. This is 1/3 a brick per person per minute – not the 3 bricks per minute that I thought a two person team can do. The point is that there is a poor match between available machine performance (6 bricks per minute) and available human power (3 person typical team). There are not many situations where an 18 person team could be gathered to make full use of the machine.In conclusion, ergonomic optimization requires a large hopper and loading via front end loader. The realm of applicability of a manually-loaded machine may be only for small projects – not the building of entire villages. This is not to say that the latter cannot be done – but that with a little bit of improvement, the CEB machine can be competitive with ‘mainstream’ construction.
Process Ergonomics Optimization: For about $500 more in off-shelf components, automatic control can be added to the machine. For about another $100-500, a large hopper can be constructed on top of the machine, or the machine itself can be redesigned to accomodate a larger hopper that may be loaded with a front-end loader. This is a sound investment – under $1k – for labor savings that will pay for themselves in one day of brick production. A 3 person team can produce 500 bricks per day with manual loading. With a front-end loader, a 3 person team can produce 3000 bricks per day – and this will be our next point of development. We already have the loader as part of the LifeTrac infrastructure, so no additional project cost arise from this point. In practice, this would mean that we spend not 14 days of pressing, but 2 days of pressing – for all the bricks for the current workshop addition. The latter will provide a great deal of satisfaction to the workers, while the former is grueling labor.
Ergonomics of Brick Pressing: The ergonomic baseline for the CEB press is that one person can produce 200 bricks per day, in a sustained (multiday) production scenario. This is because one able-bodied person can shovel, fill, and carry only about 100 five gallon buckets of soil per day – where each bucket makes about 2 bricks. We are assuming a short walking distance – about 20 feet – from place of soil digging to machine hopper. We conclude that such a rate of manual machine loading is not well-suited for structures on the order of 1000 or more square feet. With a 3 person team – a typical construction scenario – it would take at least 10 days of hard labor to press all the bricks for a structure of about 1000 square feet.
Realm of Applications: Thus, a large team of people – 8 or so – making a small structure, such as a 20 foot diameter shelter, which requires 2500 bricks – is feasible in a 2 – day period, or a ‘weekend warrior’ scenario. The point is, only small structures, or availability of large work crews – make the present, manually-loaded implementation of The Liberator useful. As useful as it may be, this is in no way optimal.
Soil Conditions: It turns out that achieving excellent soil conditions is not easy. The ground cannot be too wet or too dry. Surface soil becomes too dry, and deeper soil becomes too wet – even with our prepared pile of soil. This was exacerbated by the cold weather. The problem is that the CEB machine eats soil at such a rate that one uncovers wet soil beneath the surface layers so quickly that it does not get a chance to dry. Wet soil is difficult to break up with a tiller.
Soil Conditioning Suggestions: First, it’s better to work in warm weather, where the soil can dry better. It is also useful to pre-dig soil, and pile it up in small, wide piles, perhaps rows 4 feet high by 10 feet wide. This takes a sizeable soil preparation area. An earth preparation area of at least 50×50 feet is desirable, and to get the right moisture, perhaps 100×100 feet is optimal.
Machine Performance: Overall, the machine performed better than expected – 6 brick per minute capacity or higher, while we were designing for 3-5 bricks per minute. We don’t really know the maximum pressing rate, as we never used full tractor throttle nor did we ever have a sufficient supply of free-flowing soil, nor did we have enough workers to feed the machine fast enough. We are quite certain that we can reach 6 bricks per minute, but I suspect that we can get up to 8 bricks per minute if we had the soil and manpower. This figure may be as high as 10 bricks per minute if we add automatic control.
Structural Integrity of Machine: No signs of structural failure were observed in the 5000 brick pressing regimen. We were concerned whether the simple, bolt-together frame design would hold up, given that eight, 1/2″ bolts are used to hold the 20 tons of pressing force. Outside of the threads flattening, no visible damage was observed on the bolts or on the integrity of the structure.
Abrasion Liner: At the same time, the machine showed a large number of problems, such that almost no day went by without problemsolving. All issues were solved readily, given that the machine features design for disassembly. The most difficult issue was the Nylon 6/6 abrasion resistant liner, which lines the inside of the compression chamber and the surface of the hopper table. This liner had to be secured firmly to the structure, especially so that no earth would go under the liner. We did this by using small metal screws, with holes drilled into the structure.
The liner inside the chamber ripped on a couple of occasions, but this was due to operator error. We simply took the liner out and continued. The hopper table liner ripped when soil got under it, the liner bulged up, and the hopper eventually ripped it. Likewise, we simply took the liner out and continued pressing.
Abrasion Liner Suggestions: We are considering eliminating the abrasion liner all together. It turns out that the metal plate is not more expensive than the nylon, which is $10/sq foot for 1/8″ liner. It is actually easier to replace the metal than the nylon – and a large amount of labor needed to attach the liner properly is avoided. This is definitely one of the major points to resolve – either an easy way to attach the liner, or eliminating it all together. We saw insignificant metal-on-metal abrasion damage after about 2000 bricks being pressed without the liner. It may indeed turn out, after further testing, that the liner is not necessary.
Hopper Tracking: The hopper needs to move back and forth in a straight line, above the compression chamber. Because of the way in which the hopper cylinder is attached, the hopper would move up and down slighly, jamming the machine. We installed a track that prevented this up-down motion.
Hopper Performance: The hopper suffered from a lot of bridging – soil would not go down. Only with loose soil would the soil load the compression chamber by itself. In general, we would load the bucket and then poke the soil with a stick so it would fall down into the compression chamber. We need to redesign the hopper aperture and angles so that bridging is minimized.
Hopper Screen: 1″ screen is used on other machines to prevent large soil chunks or rocks from entering the compression chamber. The advantage is the production of higher quality bricks – as large particles make the bricks weaker by adding larger fault lines. The disadvantage is that if a screen is used, one may not be able to press bricks at all in poor soil conditions – such as soil that is too wet or too chunky. Under emergency or special conditions, it is useful to produce any brick that one can – as was useful in our case. A lot of the time, the soil was too wet and clumpy, and some clay would squeeze out the sides of the compression chamber. This does not mean that the bricks were useless – only less perfect. Moreover, not all bricks need to be structural. Some bricks can be used for structural support, others can be used as filler or insulating material. I suspect that in general, a screen is not desirable on the hopper itself.
Soil Combine: We are considering a combination tiller/loader for LifeTrac that would till and dig the soil in one step – such that under certain conditions, pre-digging of soil can be eliminated. We have not evaluated the feasibility of this in detail, but it may be a route to cutting the soil preparation time in half, by eliminating the pre-digging requirement.
Result Summary: Performance results are encouraging. While we pressed 400 bricks per day on average – the full production capacity of The Liberator is between 3000 to 4800 bricks per day. To achieve this production rate, we will install a large hopper, and load it with a front-end loader. We will also add automatic controls to the machine. The cost predictions are only $1000 in additional materials, making this a highly desirable improvement. This proposition pays for itself in 1 day of brick production at $10/hour labor rates. Moreover, to optimize the soil preparation procedure, we are considering a soil combine.
Your Comments and Suggestions: All these results are up for discussion and review by YOU. Please comment if you have any useful insights, questions, or suggestions.