Human powered cement mixers are a step in the right direction for better quality concrete production in poor nations. We join with Cemex, CHF, ADIG and Multiquip-Cipsa in exploring ways to change the way that cement is mixed in Haiti.
The following promotional video was produced to illustrate the difference in speed between ground mixing with shovels and peddle mixing in a small concrete mixer. These mixers are being promoted as a way to improve the quality of the work of Haitian masons.
What we should also gain from this exercise (pun intended) is that measured batching and mechanical blending are two important parts of the quality control process for concrete. Maintaining accurate recipes of cement, water, sand and gravel will allow for a more sustainable construction process for Haiti.
It is interesting to watch the race between the common practice of ground mixing and this peddle-powered unit, but please pay attention to a few issues as you view the video…
- Watch the shovels and see if there are any opportunities to waste some of the mixture or to get different levels of consistency in the mixing area on the ground. The female announcer discovered that the shovel team had some water-loss as it was absorbed into the ground. It is hard to keep to a recipe when the ground is taking an unknown quantity of the water from the mixture.
- Also consider how many of these little batches (3-4 cubic feet) would be required to replace the 540-million cubic feet (20-million cubic yards) of concrete estimated for the rebuilding effort. It will take enormous cement mixing capacity on all levels to reach the volume of concrete necessary to rebuild this country, or a great deal of peddling from these little units.
- Watch how “soupy” the mix is as it flows into the wheelbarrow from the mixer. Too much water allows the stones to settle while moving the wheelbarrow to the forms. This material separation is what causes pockets of weakness in a concrete pour, resulting in failures. Both styles of mixing create a very soupy mix. They use more water to make it easier to move the materials, both on the ground and in the drum.
- Finally, pay attention to the energy that the bicycle rider has expended to produce only about 3 cubic feet of concrete. Using hundreds of these little mixers will certainly make a dent, but will also build some very strong leg muscles… So I guess a side benefit might be to field a competitive Haitian Olympic bicycle team!
NOTE: you will need to click-through to YouTube to watch the video…
We would suggest that mixing concrete in significant quantity requires enormous torque and capacity. A meter of concrete weights as much as a full-size American sedan, so blending will require more power than what a bicycle rider can be expected to produce. Every mechanical mixer in use will be helpful, but many projects will need greater volumes than what would be reasonable with a bicycle mixer.