The following are the notes from Scott Crist, Product Manager for Cart-Away Concrete Systems as he worked in Nigeria. Mr. Crist and Cart-Away are working with the GEMS2 team to demonstrate modern block mixing technologies to improve the quality of Nigerian block production. This is the third report in Cement Trust on the GEMS2 program – click HERE for additional stories on this effort.
New to Nigeria
It was very hot, very humid, and I was very much in Nigeria. It was my in-person debut in Africa with a consulting/training trip to Abuja and Lagos for Cart-Away and GEMS2. The product that I was training on was the Concrete MD Mixer.
As you may know, the MD comes with the ability to mix concrete with a spiral auger and also mix a block mix using a custom designed paddle auger. Both augers share the same mixing properties in that they each pull material to the outside edges of the hoppers and roll it over to get a very thorough mix. Reversing the rotation sends the materials from the edges to the center of the hopper for discharging. When mixing a block mix, the paddle auger is used because the material is much drier than a concrete mix and the paddles help to blend the material better. We shipped two of the MD’s, with paddle augers, to Nigeria for a program called GEMS2, a development program managed by the World Bank and funded by the UK Department for International Development (DFID). Coffey International Development implements the program and it was they that invited Cart-Away’s participation.
Most buildings in Nigeria are made with block. Actually, just about every building you see is made of block. With their vibrant economy the growth rate is tremendous is building is being done at a furious pace. Which is a very good thing in the construction sector as it expands employment and makes a good environment for entrepreneurs. However, it also makes regulating everything very difficult.
Better block is needed
Concrete block has a standard set by the Standards Organization of Nigeria (SON). The standard regulates the ratio between cement and sharp stone to create a block that’s strong enough to use for building. Where the problems come in is in how the materials are mixed.
In Nigeria there is abundant labor. Block makers make use of this labor force as mixers and loader for their block business. When these laborers mix, they are using very simple instruments: wheelbarrows and shovels. They do all of their mixing on the ground, by hand. These laborers work very hard, there’s no questions about that, but their manner of measuring materials and mixing them leads to varying quantities of materials along with a semi-mixed block mix. This is the challenge the MD was brought in to solve.
Starting in Abuja, with block makers from all over the area surrounding me, I began to teach them how the MD could produce a consistent mix for them every time, over and over, all day long. That, I explained, was key to putting out quality block. Had any of them ever experienced varying quality at their facilities? They all had. I began to show them how the MD could eliminate that.
Consistent recipe required
The first step was to define their recipe of materials. Each one had a common unit to measure material: the wheelbarrow. In Abuja we were making a 9” block and the recipe was four wheelbarrows of sharp sand, one wheelbarrow of soft sand, one 50kg bag of cement. I began by asking one of the workers to please fill a wheel barrow with some sand. He filled it right up to the top; another shovel-full couldn’t have fit on top. I asked the men around me if the wheelbarrow was full. They agreed it was.
I explained that now that we had one unit of measure, we needed to get that put into something we could work with and that would have no variance. I brought out a one gallon paint can. I assigned three men to count and we filled another wheelbarrow until it was as full as the first one had been. Each can full of sand was filled and stuck off so each was the same. In the end we had our figure: 25 cans per wheel barrow.
I then weighed one can of each material. Now I was able to use multiplication to find out how many kg’s of each material they were using for the mix. After that was done I was able to come up with a mix ratio that would use the batching buckets on the MD so that every load would be the same all the time. Everyone followed along with the math and when I pointed out the batch buckets, they caught onto the idea that this was a big step in producing quality blocks.
Once we had the recipe figured out we began to make block mix. I demonstrated the use of the batching buckets and when we put in the soft sand (brown) on top of the sharp sand (almost white) you could really see the mixing action of the paddle auger. In less than 20 seconds the brown sand was completely mixed in. We continued on with the cement and it was mixed in the same short amount of time.
The last thing was to add the water. As with the recipe, I left this up to them. I quickly found out that the amount of water varied widely amongst these producers. I finally decided to defer to the owner of the business where we were set up. His name was Kabir (kuh-BEER) and we added water a little at a time, doing a grab test each time after letting it mix for a few seconds, until he pronounced the mix just right.
A better block!
For these demonstrations we were set up a little ways away from his block molding unit so we had room for all of the people. We transported our mix over to the molder and made some block. I knew the MD performed well, we had tested it plenty, but one can never know how well something will do until you are on site using their materials. Everyone seemed to be milling around the block we had just made. Suddenly, I was pulled through the crowd by one of the block makers and asked to explain the block we had just made.
Take a look at the striking difference in the photo above. The MD block is on the left; very smooth, all the gaps filled in. On the right is a standard one of their blocks using hand mixing on the ground and a varying recipe. Notice all of the gaps between aggregates in the block on the right. The block makers were astonished! I explained to them that with a consistent mix recipe and thorough mixing we could produce blocks like that all day every day.
I continued training that class twice a day for the remainder of the week and at the end each block maker was pleased with the block we made. They also all agreed that block of this quality could fetch a higher price on the market. The next step for them was to do the math and find out how long it would take to pay for one of their own. We did some quick reckoning and found that, depending on how much more they could make per block, and their production rate, pay-off was three months to a year.
The unit remains at Afro Block (Kabir’s business) so he, with the help of the GEMS2 project team, could spread the word to as many block producers as they could that there was a new way to mix block in town. And the results are good for the business owner and great for the people of Nigeria.