Construction insights

(Posted by Laurence)

The recent visit of my father-in-law, and his questions about the construction site, made me realise some construction methods that I am already seeing as ‘normal’ might be worthy of comment for the benefit of UK readers, so here is a little insight into some aspects of construction in Uganda.

Excavation

To date, we have exclusively used manual labour for the excavation of foundations; that is, one metre deep trenches in a varying quality of soil.  There are two main reasons for this: job creation, and quality control.  First, our ethos at EMI means that we would rather pay twenty workers for a week, than one digger operator for a day; this isn’t a black-and-white argument, and opinions vary, but that is where I stand for now.  Second, I am wary of using machinery with operators of unknown skill; I have seen before how quickly excavations can go wrong due to an operator’s lack of skill or misunderstanding, resulting in wasted time or extra cost.

There are, however, some situations where machinery is the only option: mass grading for example.  We need to move thousands of cubic metres of soil to create level benches for the two classroom blocks, which means cutting away the hillside in some areas and filling and compacting in others.  To do this by hand, while technically possible, would take far too long and in my opinion would be too mammoth a task to comprehend.  So for mass grading we have hired a contractor who turned up with bulldozers, graders and rollers and reshaped a hillside in a week.

You may be wondering what the cost implications of these choices are, and it depends a lot on the scale of the work of course.  For the foundation excavations we have been doing it works out as comparable or cheaper to use manual labour, even more so if you consider the risk of having machinery on site for longer than planned.

Concrete

Next up, concrete: our method here is not so unusual, but might seem so to the casual observer (we used a similar approach in the Royal Engineers).  All our concrete is prepared on site using a 350 litre mixer in a central location; from there it is carted in wheelbarrows and poured, before being rammed into place and settled using a mechanical poker vibrator (yes, that is a technical term!).

Our biggest single pour so far has been for the chapel floor slab.  The floor will be finished by grinding the exposed concrete, and so we were anxious to avoid cold joints; to that end we cast the slab in two pours, each of 25 cubic metres (see photo above, right).  Once poured, the concrete was floated using a bull float (think of a metal paddle on the end of a long pole), which continued late into the night to achieve the smoothest possible finish.

For the real construction boffins out there, you will be interested to know that we have been doing cubes tests on our concrete (a service provided in Jinja by the Uganda Ministry of Works).

So there you have it.  Comments? Questions? (which I may or may not be able to answer!)

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s