24 hour strength improvement
Posted by stephen on October 12, 2006
I have reading about the new polycarboxylate water reducers. I am making a concrete product that has to be polished within 24 hours. Normal water reducers create too many problems with finishability for my application but I understand that the EOPO water reducers can improve surface finishing.
I’m looking for improved 24 strength witout loss of workability. I have heard that additions of Calcium Nitrite along with the water reducer will significantly increase strength.
Which product would you reccomend for my application.
thanks
Stephan,
Water reducers either increase the workability of the concrete or allow you to reduce the amount of water needed to be added to concrete to achieve workability.
Accelerating admixtures are chemical accelerators which when added to concrete increase the rate of hydration of the cement, making the concrete set faster and give high early strength.
Calcium Nitrate is a type of an accelerating admixture, so it would help you to achieve high early strengths.
Water reducers allow you to reduce the amount of mixing water. This marginally increases the early age strength (within 24 hours) but significantly increases later age strengths. Whereas accelerators only help to increase the early age strength and do not increase the later age strengths.
In your case, I would suggest you to do the following. Try making small concrete samples by adding only an accelerator at a medium and highest allowable dosage as recommended by the supplier and see the finish of the concrete after 24 hours. If you feel the concrete is still too weak to be finished at 24 hours then in the next concrete sample add a water reducer to reduce the mixing water. Keep the accelerator at the same dosage. This should allow you faster set times.
Make sure the water reducer is not based on lignosulphonates, as lignosulphonates delay the set time of concrete. Polycarboxylates (PC’s) are the most powerful water reducers, but there are several versions of PC’s available. Ask the admixture supplier for a PC which enables high water reduction and faster set time.
