The Cemforce Slab

The Cemforce slab is made up of the same sandwich material used for the panels, but with some steel reinforcement cast in the bottom half of the mould, to increase the bending strength of the slab. Wicus, one of the owners of Cemforce, carried out a pretty impressive test on the slab, which is only 65mm thick, by supporting the slab on two supports and slowly adding bags of cement across the middle. With 900kg of cement on the slab, it only deflected by 5mm!

In rural areas, when a toilet pit fills up, they are rarely emptied, since this requires a tanker to come and suck the c##p up, which costs money. Instead people tend to dig a new pit and install a whole new toilet. Cemforce had designed a cool little buggy thing which is bolted together around the edge of the slab. The frame and the slab is then lifted up using a big lever, and wheels are fitted onto little brackets at the corner of the buggy. It can then be wheeled over the new pit and lowered into position, and the buggy frame removed. This way people don’t have to buy a new toilet every time the pit fills up… (as long as they can call up cemforce to get hold of one of those buggies)

Look Away Perfectionists...Testing the Panels

So now that I'd made a load of Textile Concrete test panels, I had to find a way of working out which ones were stronger (or more specifically, stiffer) than the rest. If I was at uni, I'd be able to take then down to the lab and use the machines to test them using lots of nice shiny equipment and computers and stuff.

But I'm not. I'm in Jozini... so I had to build a little testing rig using bits and pieces I could get from the hardware shop in town, and eventually, I managed to build... Gareth's test rig!!!

Using this rig I could apply an even load across the centre of the panel, by adding measured amounts of water to the bucket. I added 500ml (0.5kg) of water at a time and using the ruler measured how far the panel bent in the middle (or deflected to use the proper term). From this I could work out which panels were stiffer than others, and find the best combination of cement:sand:water:additive and the best curing times. Hurrah :-)

Testing the Slab

Today I uncovered both of my dome shaped slabs. Slab#1 (which i made too thin) broke as me and Siyabonga were trying to lift it off the ground :-(
But.. Slab#2 survived!! :-)
So we tested it, first with just my weight, which was ok!:-) Then with 3 people. It managed to hold for about 2 seconds...and then broke into bits!:-(

I reckon it broke partly because we didn't have enough big stones in the concrete mix (so its easy for cracks to propogate).