Hi Y'all

I'm breaking up my concrete drive prior to installing about 5" of compacted
type 1 aggregate and 1" of compacted gravel.

A couple of questions; Does concrete get harder as it gets older? Some
parts of the drive were laid (I imagine) in the mid 50's when the house was
built, some bits have been added since in the 80's. The older concrete is a
bloody site harder to break up.

Does it get stronger with age or did they just use stronger mixes then?

I'm getting most of it shifted in big sections, leaving behind lots of small
rubble up to about 2" size. Can I just level & compact this and save a lot
of work & a little type 1??

Dave

david lang Wrote:
Hi Y'all

I'm breaking up my concrete drive prior to installing about 5" of
compacted
type 1 aggregate and 1" of compacted gravel.

A couple of questions; Does concrete get harder as it gets older?
Some
parts of the drive were laid (I imagine) in the mid 50's when the house
was
built, some bits have been added since in the 80's. The older concrete
is a
bloody site harder to break up.

Does it get stronger with age or did they just use stronger mixes
then?

I'm getting most of it shifted in big sections, leaving behind lots of
small
rubble up to about 2" size. Can I just level & compact this and save a
lot
of work & a little type 1??

Dave

Conrete mixes can vary greatly depending on proportions used, hand
mixed or machine, or readymix etc etc. Once its full cured thats it.
When you have to break up some concrete you never know how "easy" its
going to be until you start, some you win some you lose.

You can leave behind all the small stuff, its perfectly OK as fill. You
can in fact buy crushed concrete as a fill material.


--
Nick H

Ian Stirling said the following on 26/11/2005 21:46:
david lang wrote:

Hi Y'all

I'm breaking up my concrete drive prior to installing about 5" of compacted
type 1 aggregate and 1" of compacted gravel.

A couple of questions; Does concrete get harder as it gets older? Some
parts of the drive were laid (I imagine) in the mid 50's when the house was
built, some bits have been added since in the 80's. The older concrete is a
bloody site harder to break up.


A bit.
However.
You're talking weeks (IIRC) before it reaches 90% strength, and a year or
so before it's at 99%.
Identical concrete laid in the 50s and 80s will not be measurably different.
But, mixing, quality control, aggregate, and even luck can all play a huge
part in it.

I'm hoping someone can post a "definitive" answer to this but AIUI as a
rule-of-thumb modern concrete mixes gain strength like this:

24 hours - you can "walk" on it.
48 hours - you can "work" on it.
7 days - you can drive over it.
28 days - it is nominally as strong as it will ever be; however,
concrete will continue to gain strength indefinitely.

As the above poster has noted, the difference in strength (hardness)
between the older and newer stuff is much more likely to be down to the
original mix than age per se.

Nick H wrote:

Conrete mixes can vary greatly depending on proportions used, hand
mixed or machine, or readymix etc etc. Once its full cured thats it.

Interesting. You learn a lot about how to lay concrete by breaking up the
old stuff. It's a patchwork of different bits laid at different times
(which is why I'm breaking it up).

The hardest stuff to break up is the oldest, but thats because its a sandy
colour and softer - the breaker point just goes through it without causing a
crack. I assume a weaker mix?

The harder stuff breaks easier because it cracks. One area has 6" of solid
concrete with no hardcore or sub base beneath it, that breaks really easily.
Another was laid on really large hardcore - whole & half brick sizes - that
also breaks easily.

Toughest stuff is that properly laid on smaller compacted hardcore, really
tough.

Just goes to show that if you do it right it really is stronger.

When you have to break up some concrete you never know how "easy" its
going to be until you start, some you win some you lose.

It's been a good learning curve!

You can leave behind all the small stuff, its perfectly OK as fill.
You can in fact buy crushed concrete as a fill material.

Good, just off to hire a wacker plant to compact it in.

Thanks

Dave

david lang Wrote:
Nick H wrote:


Good, just off to hire a wacker plant to compact it in.

Thanks

Dave

Dave, I hope thats just a typo error and your not actually going to
ask
for a "wacker PLANT" instead of a wacker PLATE, its just that someone
might take the pee.

Nick


--
Nick H

Nick H wrote:

Dave, I hope thats just a typo error and your not actually going to
ask
for a "wacker PLANT" instead of a wacker PLATE, its just that someone
might take the pee.

We have some very exotic plants down here in Kent. The wacker plant is a
distant relative of the Triffid and compacts hardcore very well once planted
& watered in, provided it's not is a shady location.

:-)

Dave

david lang Wrote:
Nick H wrote:

Dave, I hope thats just a typo error and your not actually going to
ask
for a "wacker PLANT" instead of a wacker PLATE, its just that someone
might take the pee.

We have some very exotic plants down here in Kent. The wacker plant is
a
distant relative of the Triffid and compacts hardcore very well once
planted
& watered in, provided it's not is a shady location.

:-)

Dave

Now I understand.


--
Nick H