Rods for rebar ?

[premmington]

I am just about replace a man hole cover in one of our lawns - broken frame and concete cracked at all four corners.

I bought another cover/frame today - will get all broken concrete out tomorrow - clean brickwork up and set new frame - put some wooden shuttering around it.

Then in the week I will weld up some 8 or 10mm rebar - flat bar/round scrap (anything I got lying about) into rectangles to drop into the form when I pour the concrete next weekend. In the vain hope it holds the corners together.

Need so little concrete - I gonna buy some 40nm in premixed bags from Wickes and mix it in a wheelbarrow.

 

[Dcal]

Re-bar or smooth round bar or even thread bar will be better then flat bar.
Concrete is great in compression but useless in tension.
Steel is great in tension and ok in compression but 8 or 10mm bar can only do so much but sounds fine for your job.

What dimensions are you stuck with?
It's good to have maximum of 40 or 50mm cover between the steel reinforcement and the face of the concrete.
Too much cover and the concrete can crack, too little and the rebar can corroded and blow the face of the concrete.

Make up (weld up) the reinforcent cage and leave enough room for the concrete to get around the bars. The bigger the max stone size (20mm is standard) the larger the spacing required.

If the volume of concrete required is small and you can get it locally, consider using a micro concrete. It's easy to use and will come in bags and you just add water.
Another excellent way to make micro concrete is to add 6mm chippings to GP Grout
Add about 10kg of chippings per bag of grout.
A 20kg bag will make about 12 litres of grout (or micro concrete) with the chippings you will get about 16 litres.
Use a paddle mixer to mix it up, a slow speed drill with a stirrer will suffice and do not exceed the recommended amount of water.
Once it's placed, smooth it off and cover the exposed concrete with plastic.

The number one reason for concrete failing is too much water being added during mixing.
The grout and micro concrete have additives that reduce the amount required.
If you are mixing the concrete yourself, don't add any more water than you really need.

A paddle mixer is great for mixing small quantities of ordinary concrete.

 

[Agroshield]

Then in the week I will weld up some 8 or 10mm rebar - flat bar/round scrap (anything I got lying about) into rectangles...

You may already be doing this, but making L-shapes and welding at the lap would be better than four straight pieces welded at the corners.

In a big slab, you would put 'cracker bars' at 45 degrees to a sharp corner. With a thin manhole surround, that's not practical, but a nice corner radius on the bar passing the corner will help (rather than a 90 degree welded corner).

Don't watch the video here, just look at the opening screenshot still to see the idea:

Listen to the advice above - too much water is the enemy of good concrete.

 

[premmington]

Would guess the manhole cover and frame is cira 1963 when house was built.

So makes is: 63 years old - it done it's shift.

Dry summers - lawn mowers hitting it - cas it too high. Gonna top dress reseed lawn around - so it is flat to lawn.

If It lasts another 60years - I will be pushing up daisies and I won't care....