When I was younger and fitter I did a slab about the same size, by hand, on my lonesome, in 1 hit without killing myself or screwing up the job.
There's a bit of technique to making things easier:
1. Treat yourself to a decent shovel if you haven't got one
2. Mix on a concrete slab or an 8x4 of ply/osb. Hard work in a barrow
3. Start the mixing as you measure out: 6 shovels of ballast then 1 of cement, then another 6 of ballast on top and another cement so your heap is layered.
4. Slide your shovel along the base at the edge of the heap and then just roll the shovel over, away from the heap. You don't want to waste effort shifting the heap several feet over then back again. That first cut will leave a vertical edge to the heap which will fall down mixing the layers as it goes.
5. Repeat until the whole heap has moved and then do the same in reverse. The heap should be reasonably uniform in colour by now and you can add your water.
6. Flatten the heap and scrape out the middle to form a dam around, water in the middle and work around pulling a bit of naterial into the water. Little and often is the mantra as you don't want the concrete too wet and there comes a point when a little bit more water goes a long way.
7. Pre measure the water though as once you know you need 3 buckets say to this size mix, you can add 2.5 in 1 go.
8. Keep the concrete stiff: it's a wee bit more effort to spread and compact than if you adopt the slop beloved of many builders, but the concrete will be much stronger at the end, it's a whole lot lessmessy to move and you can work across the base to keep a fresh face of concrete where you're working. This way you can take several hours overt the pour without detriment to the concrete. Cover with polythene as soon as you can and water it for a few days after to help the cure.
