Which plasticiser?

[malakin]

I am casting 2'6" * 2'6" * 5'0" concrete blocks for use in seawall construction. Small bubbles are seen on the surface of the cast blocks (especially on sloping faces). I am considering the use of plasticiser to improve the quality of the blocks. What type and quantity of plasticiser should I consider? All input very much appreciated.

 

[Ron]

The amount and type of plasticizer will depend upon your mix design, geometry, environmental conditions at placement, etc.

Plasticizer will not likely reduce the "bubbles" you are seeing at the surface. Those are caused by entrapped air and/or solution water channels from bleed water rising to the top during placement.

If you could provide a bit more info on your mix design, perhaps we could help troubleshoot your problem.

 

[RiBeneke]

Bubbles on the formed (as opposed to struck) surfaces of your concrete are formed as Ron says, and you can use some of the following trial and error methods to reduce them :
1) If your formwork is new and smooth, sand it lightly on the inside faces to provide capillary tracks that will help to dissapate the air.
2) If your formwork release agent is too oily, try a different type, perhaps wax or emulsion based.
3) If your vibration intensity is too high it can draw bubbles in, especially near the top, or if it is too low the bubbles will not move. Try adjusting this.
4) There are now special fabric liners available that are placed inside the formwork to dissapate air. They may be worth considering.

 

[Riz]

Its also advantageous to discuss your problem with Sika (

http://www.sika.com

) or vandex. They produce specialist admixtures like Palastiment BV 40 etc.
I used a certain plasticiser (can't remember name) about 10 years back but the trick also is in vibration aspects and on items mentioned by Ron and Ribeneke.

 

[malakin]

Thanks so much for your comments. We are going to carry out some trial and error casts. I will post the outcome. In the meantime my mix design is as follows;

Cement type 1
3000psi strength at 28 days
3/4" nominal aggregates
.55 water cement ratio
500lb/cu yd min cement content
slump 2-4"
chloride less than .3%

per cu yd:
1590 lb aggregate
1660 lb sand
550 lb cement
240 lb water

any further advise is appreciated.

 

[kjde]

Try by reducing sand in total aggregate to 40%. Hence, you may redesign for C.agg - 3/4" = 1950lb and Sand = 1300lb. Normally oversanded mixes entrap more air as well for the same compaction type and shuttering oil.

 

I would like to know the name and cost of the easily available water soluble plasticiser. Is there any plasticiser that can be used in detergent formulations?

Hope to hear from you soon.

My contact id is

mnish11@yahoo.com

Regards
Manish