A Concrete Pour

A concrete pour is quite an event on an All Hands and Hearts site. I’ve done a couple in Mexico and a few here in Nepal too. They are more of a choreographed ballet than the usual work. They need lots of people doing different things and working reasonably quickly and effectively and not getting in the way of anyone else.

First we need the concrete. So we get the number of bags of the right kind of cement that we guess are going to be right for the volume of concrete we need. We need an infinite number of buckets plus an additional five! We need piles of sand and the right type of gravel. We need a ready source of water. We need the mixer (with enough fuel) and additive if required. We need wheelbarrows to move the concrete around. We need shovels and masala trays (these are circular trays that the concrete gets put onto for then tipping into the right place). We need the pencil vibrator which is a tube that goes into the concrete and vibrates it to ensure it settles all the way to the bottom and to ensure the air bubbles come to the surface (holey concrete is not a good idea!). We need reciprocating saws (without the saw blades) which we also use as vibrators to run along the wooden formwork to help with settling the concrete and removing air bubbles.

There may be slight differences on different programmes and for different pours (footings vs foundation tie beams vs PCC layers vs columns etc). But here’s a description of a fairly typical situation.

• The cement team open the bag of cement and split the contents evenly into two buckets (maybe about 5cm from the top of the bucket). These two buckets are put on the table next to the mixer.
• The sand team fill the right number of buckets (depending on the particular concrete mix, say 2 buckets of cement to 3 buckets of sand to 6 buckets of gravel) with sand to the same level as the cement (5cm from the top) and put these buckets on the mixing table.
• The gravel team fill the right number of buckets to the right level and put these on the mixing table.
• Someone on the mixing team checks that each bucket is filled to the right level and adjusts if required (they have a bucket of sand and a bucket of gravel they can use to top up or absorb any excess) and checks that the right number of buckets of all the stuff goes in the mix (we don’t want the gravel team getting overexcited and providing 7 buckets when we only need 6!).
• There is someone on the mixing team standing on the table who lifts each bucket and passes it to the two people who throw the contents into the mixer. One of them then throws the empty bucket to someone who then passes them back to the relevant team who can start refilling ready for the next batch.
• Someone on the mixing team adds the additive (if required) and keeps track of the number of batches we’ve done.
• Someone on the mixing team adds the right amount of water to get the mix to the right consistency and runs the mixer for the right length of time to get it appropriately mixed.
• Once the mix is ready the concrete is poured into the waiting wheelbarrows (maybe 5 wheelbarrows per mix).
• The wheelbarrow wranglers take the wheelbarrow to the right place.
• Someone on the passing team then shovels the concrete into the masala trays which are passed into the trench to the people who then put it into the right bit of formwork.
• The levelling team then ensure the concrete is vibrated and levelled and smoothed out, etc.
• With each batch a small bit of concrete is put into a metal cube mould (about 20cm on each side) with the batch number. These are then sent off later for structural testing. There may also be a slump test where the concrete is poured into an upside cone mould, the cone is removed to see how much the concrete slumps which gives an indication of the viscosity of the concrete to make sure it is ok. I don’t know much about these parts of the process, other than they happen.

The work is a bit stop-start for each team. As soon as me and my teammate are given empty buckets we shovel gravel into them and then carry the buckets to the table. We then wait around till the mix is ready to be made and I get ready to catch the empty buckets from the mixing team and pass them to the right teams, I then get back to helping my teammate refill the buckets with more gravel. While we’re standing around waiting, others are beavering away on their part of the process. Their breaks come at different parts of the process.

Someone pays enough attention to make sure we don’t make any more concrete than we need. We don’t really get a break once we go, because we have to use the concrete as soon as it is ready. But depending on the scale of the pour it may be all done in an hour or two or may take half the day.

In any case it is a beautiful choreography of productivity and teamwork. And good fun, despite the noise and the dust!