Construction Review in Nairobi

Some habits are hard to change and for me that includes stopping to stare at each building under construction or being repaired.  Nairobi is currently going through an "economic boom" in their construction industry and as I walk to the SIM office each day I've been noticing the progress of this 6-storey residential apartment building.

At first I wasn't sure if the scaffolding was safe.  It's definitely not what I'm used to seeing in Canada so last week I decided to stop and see if I could talk to "someone in charge".  I didn't expect to have an impromptu tour of the construction site (especially since I was wearing my sandals and didn't have a hard hat) but no one seemed to mind.  They were very happy to show me around.

My new friends (Broadrick and Shadrach from MOD Builders) gave me the tour.

The building has the following:
Parking Level 2 (slab on grade)
Parking Level 1
Ground Floor
1st Floor (in Canada we'd call this the 2nd Floor)
2nd Floor
3rd Floor
4th Floor
5th Floor
Penthouse

Similarities of construction of this building compared to Canada include:
a) the construction sign indicating the parties involved

b) the basement foundation walls, the P1 and ground floor slabs are cast in place concrete
c) the interior walls are concrete/stone blocks which varied in size from 6"x4" up to 9"x6"
d) Portland cement (10kg bags marked maximum 32.5MPa) is used for beams, columns and floors.  Broadrick and Shadrach stated that they are using "Class 25" concrete for the slabs and columns (which means 25MPa).  However the bags of Portland cement that I saw on site were labelled 32.5MPa.  So I'm not sure.  Either way the 32.5MPa bags of cement should meet the stated Class 25 requirement if mixed properly.
e) they stated that during the concrete pour cubes are cast and then tested in the laboratory prior to removing the formwork

Differences include:
a) formwork was only to be removed 14 to 21 days after the concrete was poured.  (In Canada it's  common for the concrete to reach 75-80% of the specified strength by 7 days).



b) Kenya uses the European system for reinforcing steel designation.  In Canada we have 10M, 15M, 20M, 25M bars etc., and I knew that in the US they have #3, #4, #5, #6 bars etc., but I didn't realize in Europe (and here in Kenya) they use designations like Y8, Y10, Y12, Y14, Y16, Y20, Y25, Y32.  Y16 is used in the beams and Y25 in the columns. The reinforcing steel is not epoxy coated.
 
c) they were using wood posts nailed together as the scaffolding, with "stoppers" to secure the scaffolding back to the building (see yellow arrow)  

d) at the upper floors (1st Floor to the roof slab) the Contractor stated hollow concrete blocks were being used to supplement the cast in place concrete. Instead of hollow-core precast slabs (like we might see in Canada) they used "hollow port" concrete blocks which are 12"x8".

The blocks are positioned so that the slab is 12" thick.  From what I understand the Y10 rebar and wire mesh is installed on top of the blocks, and then a 2" layer of concrete is added on top.  Using the "hollow port" concrete blocks reduces the load of the slabs and allows for larger spans. For example, if a room is 10'x10' then the interior 6'x6' part of the slab would consist of the "hollow port" concrete blocks.

  

e) PPR piping is being used for interior hot and cold water risers. PVC piping is being used for the electrical and waste drainage piping.  I knew about PVC, but PPR was something new.  Check out these websites linked here and here for more on PPR.

That's all for now... stay tuned for my next post on "Building a Prefab House in South Sudan".