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Posted: Wed Dec 05, 2007 9:06 am
by Fash
Hi,
Ive just started out in the concrete paving block biz and am manufacturing 90mm paving blocks and need to achieve a 49 N/mm2 or roughly 7200 psi ( compressive strength ) block, im using a standard 1 2 4 mix and the best im able to achieve is 41 N/mm2 after 21-28 days curing. Any thoughts ? Should i change the mix or could it be a problem with my curing?
Regards
Fash
Posted: Wed Dec 05, 2007 3:47 pm
by David Sarti
Give us a clue Fash - where in the world are you and what kit are you trying to use? It may well make a difference as to the amount of help you get.
Posted: Wed Dec 05, 2007 8:19 pm
by seanandruby
Kenya. 
Posted: Wed Dec 05, 2007 9:56 pm
by lutonlagerlout
sounds like one for ted,i am sure he mentioned the aggregate in africa isnt always what it could be
LLL
Posted: Thu Dec 06, 2007 12:21 am
by matt h
seems the mix aint gat what it takes... cant see that its a curing problem... try using a different crete maybe... what about bonding agents?
Posted: Thu Dec 06, 2007 8:14 am
by Ted
Need more info as Mr Sarti says...
Using a water reducer is another way to increase the MPA of concrete.
Posted: Thu Dec 06, 2007 10:53 am
by TheVictorianCobbleCo
If I'm right and 49N/mm2 equates 49 Mpa, then your mix needs to be better than 50kg cement/68kg sand 68kg (9.5 or 13mm)stone, or 50kg cement, 64kg sand and 98kg (19mm) stone. (Ref Cement and Concrete institute) The lower your cement/water ratio, the stronger. Check your slump. adding colour can also affects ultimate strength depending on what amount of water it absorbs(Ref BayerD5090). 49Mpa is huge overkill as commercial applications are in the region of just better than 40. PPC will not give graphs as many factors influence - curing temp, quality of sand and stone, and so on and so on. So check CCI and PPC websites and Bayer. They can all help. Good Luck