Need to accelerate Conc Hardening
Need to accelerate Conc Hardening
(OP)
I need to obtain the full strength of concrete in 14 days rather than 28 days. I believe use of admixture will be cheaper than rapid hardening cement. Please give me your tips






RE: Need to accelerate Conc Hardening
Here is a link for general information
http://www.gogenchem.com/calcium/Ind05.pdf
RE: Need to accelerate Conc Hardening
Good luck.
RE: Need to accelerate Conc Hardening
Another way to get an earlier high strength is to add a 1/2 to 1 bag of cement/cy to the mix design. It is less expensive than high early cement or admixtures. The thing to be careful of is that above 6-1/2 bags of cement/cy shrinkage becomes more of a concern.
During your pouring, take a couple of sets of test cylinders (3 cylinders/set) so you can break them a 3 days, 7 days, and 28 days to verify your final mix design.
RE: Need to accelerate Conc Hardening
Be careful with adding cement to the mix as this will increase your overall shrinkage and water demand, thus increasing your crack potential. This could be detrimental if you are placing slabs or exposed structural components with minimal cover.
I would suggest you check with a reputable ready mix supplier as whymrg suggested. There are admixtures that achieve the same result as using a Type III cement (high early strength). As jheidt2543 stated, most good quality concrete mixes will achieve design strength long before 28 days.
I would suggest a mix with a low water-cement ratio (0.50 or less), and a high-range water reducing admixture to achieve workability. Then wet cure the concrete and watch the temperatures (colder weather will cause slower strength gain).
Good luck.
RE: Need to accelerate Conc Hardening
RE: Need to accelerate Conc Hardening
Zambo
RE: Need to accelerate Conc Hardening
Reference: Materials of Construction, 6th Edition by Lloyd F. Rader, John Wiley & Sons, Inc., 1967:
Page 413:
“The effect of adding SODIUM chloride to concrete cured at temperatures BELOW 32 degrees F is to REDUCE the freezing temperature and to retard the freezing of the concrete, thus permitting its setting and hardening. For curing BELOW 32 degrees F, the addition of UP TO 12 % by weight of mixing water INCREASES the concrete strength, but higher percentages are detrimental to strength. Approximately 1% of salt in the mixing water lowers the freezing point 1 degree F (0.55 degrees C). For curing at NORMAL temperatures, the addition of salt causes a DECREASE in the strength of the concrete. The integral use of CALCIUM chloride causes a more rapid rate of liberation of heat of hydration of the cement, thus promoting early strength development and thereby furnishing materially greater resistance of the concrete to the detrimental effect of low temperatures.” (Emphasizes are mine.)
Page 420:
“T.E. Stanton in a comprehensive series of long-time tests reported a definite increase in compressive strength at 1 year for Portland-cement concrete containing additions of calcium chloride up to 5 % by weight.” (T.E. Stanton: A Study of Calcium Chloride as a Strength Accelerator in Portland Cement Concrete, Proceedings of the Highway Research Board 1950, p. 232)
These statements pertain to the strength characteristics of the concrete and were made without reference to the effects that sodium and calcium chloride may have on the reinforcing steel or other embedded items. However, the addition of .5% to 2% calcium chloride to reinforced concrete that is not exposed to the weather has not been found detrimental. The finishing time of floor slabs is reduced considerably with the addition of calcium chloride and is used more than most engineers realize.
RE: Need to accelerate Conc Hardening
RE: Need to accelerate Conc Hardening
RE: Need to accelerate Conc Hardening
I live in Plainsboro NJ on Maple Ave. Where are you located?
Regards
RE: Need to accelerate Conc Hardening
One other point that is very important is that the cylinder or cube strengths that are cast to "meet" the characteristic strength have no reflection on the real strength in the structure - not only does curing matter, but poor vibration (i.e., compaction) in placement may reduce the structural value by as much as 15%.
RE: Need to accelerate Conc Hardening
I think 14 days is about 70% or so (but check to be sure - I don't have them now), Thus if you want 3500 psi order 3500/.7 = 5000 psi. This eliminates a lot of chemistry (never my best subject)
It has been my experience that concrete will break about 12 to 1500 psi high on the average. I think it is because plants would rather buy a little more cement than have problems with a pour.
If I am trying to do something like this, I always get imput from the quality engineer for the redi-mix supplier
One final note is that Big H has an excellent point that is often forgotten. Cylinders are cured in a warm humid condition which is ideal for strength gain. Curing of the concrete in the field can be radically different (especially this time of year). Willow Island was a tragic example of that.
RE: Need to accelerate Conc Hardening
RE: Need to accelerate Conc Hardening
RE: Need to accelerate Conc Hardening