LairdBlog: Know Your Construction Material - Concrete! {Liberia Edition}

As we get started on the Outpatient Clinic and Administration building I thought I'd start a new series, Know Your Construction Materials {Liberian Edition}. Nothing is easy here and even the seemingly simple materials, like concrete, require a lot of energy to produce. In Liberia most of that energy is in the form of manual labor and sweat.

A mason plumbing up a column

Concrete has 4 basic ingredients. That is the same anywhere you build. They are:
*Water
*Cement
*Fine Aggregate (sand)
*Coarse Aggregate (rock)

In the US when you want to cast a concrete foundation you call up your local ready mix company and tell them how many cubic yards you want and where to deliver...and you are finished. Here in Liberia we don't have that luxury. Well, that's not entirely true. West Construction started delivering concrete about 6 months ago. For the low price of $200/CY you can get concrete delivered to your job site. Besides the trouble they have had keeping their trucks with the wheels facing the road, Liberian's are generally skeptical of what you will actually get when it all shows up already mixed together.

Waiting in line to deliver the concrete

So where do the materials come from...

The first component is water. Something that seems pretty straight forward, but water can be a problem by itself. Liberia has a government water and sewer utility, but it has a very limited distribution network. Here at ELWA we have to rely on our own network of wells and pumps. They are generally unreliable and this time of year specifically it can be hard to get water of significant volume because it is dry season and the wells are running low/dry. Yesterday we had to send a truck with water drums in the back down the the lowest point on the ELWA campus because the pressure was so low the water wasn't running at all at the hospital site. Concrete mixing was delayed for about 30 minutes while they waited for the drums to fill.

Water is stored in barrels next to the mixer

Next we have cement. In Liberia you typically buy cement from cargo containers that have been set up on the side of the road as cement depots. Usually there is one about every 100 yards along the highway. They sell cement from the Liberian company Cemenco, which is a division of the German company Heidelberg. We found out on the Kitchen/Laundry building that not all cement is created equal. Because the grinding plant in Liberia can't keep up with the demand, they import cement from Turkey and Germany. We found the cement ground in Turkey gave us concrete that was barely half as strong as cement sold in the US. After more testing we found the Liberian ground cement and the bags imported from Germany yielded concrete that was within 10% of what we expected.

Liberian Cemenco Cement

The sand used for cement in Liberia almost exclusively came from the beach until a few months ago. Dump trucks would back down within feet of the ocean and 5-10 men with shovels would throw the sand up into the truck. Significant beach erosion led to the president putting a moratorium on beach sand mining in 2012. Besides the beach erosion, the use of beach sand also compromises any reinforcing steel in concrete due to the salt mixed in with the sand. Sand now comes from a handful of different pit and river dredge locations. None are washed and most are fairly dirty. All the sand used on the kitchen/laundry building had to be hand screened by the contractor's crew using window screen. We have found a source now that is much cleaner and does not require screening.

A sand pile ready for use

The last component is the coarse aggregate. With pit mined aggregate nowhere to be found around Monrovia, all aggregate used in concrete is fractured from larger rocks. While there are two large "rock crusher" machines that I know of, most Liberian's use hand fractured rock. The entire process uses a tremendous amount of "man power". It starts with burning old tires in the rock pits to create enough heat to crack large section of rock from the solid rock. Then large rocks are slowly broken into smaller rocks with progressively smaller hammers, and usually progressively smaller workers. Large men work in the pits and typically women or children work to break the small rocks into the 1/2" sized rock used in concrete. A man, woman or child who works in this profession will typically bring in around $3-$5 per day for their effort.

A young woman breaking rock with a sledgehammer

A boy in the Rock Crusher community crushing rock

Not quite the typical protective footware

So all those materials are gathered and mixed together in a variety of different proportions, depending on how strong you want your concrete to be. CJ Construction uses a 1/4 yard, diesel powered, cement mixer with a pulley and shaft run "automatic" loader. The components are all added to the bin, which is then raised and dumped into the mixer. The load is mixed until it all materials are well blended, then the mixing drum is rotated and cement is dumped into the waiting wheelbarrows. With enough men working at the task, the entire mixing cycle can take less than 5 minutes. Doing that math, that means you can cast somewhere around 3 cubic yards per hour.