There is a lot of concrete in Haiti.
Driving down the streets of Port-au-Prince reveals the mounds of crumbling concrete that prove Haitians use concrete for building just about everything.
Unfortunately, the evidence is overwhelming that the concrete in Haiti needs to be improved dramatically. If they don’t fix concrete production and construction practices, this devastation and the massive rubble piles will happen again.
At first blush we could suggest that Haiti needs more ready-mix trucks delivering better quality concrete, like we have in the industrialized countries. However, we read engineering reports that suggest only a couple of Haitian contractors even use the existing ready-mix trucks.
Haitians work with their hands, with simple tools and with large workforces. The question is, how can we help them make better concrete and still let them use their traditional methods of construction?
A Portland, Oregon company formed a team called Project Haiti, to work on this problem. The team reviewed the images of crumbling concrete from the January quake and determined that a simple change in Haitian construction practices would change the outcome dramatically. The goal was to build a mechanical device that would replace a part of the concrete production system. They found that many of the problems would go away if they replaced the shovels on the ground with something better.
The first step was to design a mixing action that replicated the blending process of several shovels working at the same time. They developed a counter-rotating auger in the bottom of a simple metal and rubber trough, which would allow materials to flow in two directions and to fold back and forth.
As the project moved forward, it was determined that the accurate measurement of raw materials was critical to the consistent quality of the concrete. So they designed batch-buckets, fashioned from different wheelbarrow sections, to meter the correct stone and sand ratios into the mixing trough. These batch-buckets don’t remove the Haitian workers shovels; they just give them a level of consistency that helps them produce a better product with every batch.
Building in the correct proportions of sand and stone allowed the team to provide recipes that instruct the workers to put in so many bags of Portland cement with “X” liters of water and a specific number of batch-bucket dumps of sand and stone, to yield a strong concrete mixture. When they follow the recipe they can produce a ½ meter of quality ready-mix that should give them confidence in their concrete again.
The next step was to build in a simple unloading method for the mixer. The carrying-bucket is a commonly used tool in Haitian concrete construction, and the Project Haiti team integrated bucket processes into the mixer discharging step as well.
When the mixture of wet concrete is blended completely in the mixing trough, the finished product is dispensed out into buckets to be carried to the forms. There is a 6” discharge tube attached to the bottom of the mixer that allows the flow of concrete to pour directly into a bucket.
This design fits within the “Bucket-Brigade” style of concrete production that is used by many in developing nations and is very common in Haiti. One of these mechanical units can employ 10-12 workers and be very efficient in building foundations, walls and floors with a quality of concrete that could not be achieved by mixing on the ground.
The Project Haiti team from Cart-Away Concrete Systems is now reaching out to individuals, NGOs, engineers and architects who have worked in Haiti, to solicit input before producing a final product for shipment into the country.
Raising the level of concrete quality and still allowing the Haitian construction workers to use their standard operating methods is a delicate dance, but this mixer just might contribute to the cure for Haiti’s crumbling concrete structures.