merbas: I am looking for informatin that can be used by field technicians to control the addition of water to a redimix truck to improve the workability of the concrete, especially in hot weather in Houston. At what point does the concrete begin to lose strength? Assume a 2500 psi mix.
Not sure about practices in the US but here in the UK adding water on site is seriously frowned upon. Accurate measurement of the volume of water added is not readily achievable. The added water obviously affects the water/cement ratio and therefore the design strength of the mix. Added to this are further problems with bleeding and plastic settlement on curing. If you have problems with heat then consider a) Batching the concrete with chilled or iced water b) Keep aggregate bins shaded c) Inject liquid nitrogen coolant at the batching plant d) Use super plasticisers or retarders. Beware when using option (d) as the mix will stay fluid longer than your average mix but will tend to set in a flash in the mixer if you're not careful.<br>
Best Regards<br>
Ginger
I am completely agree with ginger.Adding water before placing concrete is too dangerous, because of change W/C ratio and long term strenght of concrete. Pratically prefer the casting concrete at night in summertimes.
Adding water in the field is to be avoided. A better alternative is to add a water reducer or the like to increase workability. It is no trouble for a driver to have a water reducing and an air entraining agent in the cab of the truck.<br>
<br>
The rule of thumb when I worked at the D.O.T. was that increasing the slump by 1" by adding water would cause a decrease in 28-day strength of about 10%. Of course, this was a very rough and very empirical rule...
1). In addition to Ginger I could suggest the usage of mineral admixture like fly ash or blended cement. Been combined with plasticizer, superplasticizer or retarder, it will provide strong retarding effect and will prevent slump loss. <br>
2). Adding a portion (up to 1/2 dosage) of plasticizer or superplasticizer in construction site might help to improve the workability without strength loss. <br>
3). Combination of 1) and 2) is very effective.
