dry admix for imprinted concrete
Posted by Jeff on July 19, 2006
Dear Bruce, We are looking to start a small busines supplying the DIY market with products to imprint small pathways themselves without employing large contractors. Can you advise me from your experience what dry admixes we can add to a pigment mix to condition and to reduce efflorescence when applied over the surface of the wet concrete prior to imprinting. Any advice you could give me would be greatly appreciated. Regards, Jeff
Efflorescence is in its matter migration of soluble salts from the inside concrete to the surface. The transportation media in this case is water and salts migrating to the surface because there is higher evaporation rate at the surface. Highest contributor to efflorescence is cement.
In order to fight efflorescence we have to be able to reduce the volume of water migrating to the surface. The most effective way, in my opinion, is to fight it from the inside and actually prevent water migration.
Some admixtures currently available fight efflorescence but all of them (to the best of my knowledge) are liquid.
A powered High Range Water Reducer would help by reducing the water demand and could be used to reduce the cement content but I don’t think any are commercially available.
In short, I don’t know of a powdered efflorescence control product that is available.
Long term effects of HR WR
Posted by Bruce on July 6, 2006
We have recently poured a caisson, and one of the loads was sent back, with a major deviation ($5k CDN)because our slump was 20mm over spec(Spec is 150-180mm). No water was utilized, just chemically enhanced. A tremie was used, the W/C ratio was not affected, the air was in spec. The only problem I see, is that my subcontractor allowed the concrete to be poured while it was being tested. My question is as follows, will the extra slump in an already saturated environment make any difference either short or long term to the quality and longevity of the product?
Since the water/cement ratio was not changed and the final slump was achieved by using a superplasticizer or another water reducing admixture, the compressive strength should not be affected in negative way , neither should any other property of the concrete be significantly altered.
According to ASTM C 143 slump measurement values are rounded to closest ¼” (5mm). Therefore a variation of 20mm (approx ¾ inch) is not a significant change.
The only question is concerning the conditions under which the concrete was placed. If there was no segregation from the higher slump and the distance the concrete was allowed to free fall, the concrete should be structurally sound.
If the conditions are in a saturated environment that will only help the long term strength development.
The only problem I see is that the slump was out of spec, other than that I don’t see anything that should cause a problem.
