Low water / cement ratio durability issues

[maddog67]

Have been trying to comply with a concrete specification for an XD3 exposure class . BS 8500-1 Table A4 dictates that for an intended working life of 50 years with 40mm+ reinforcement cover a C45/55 is required with a minimum CEM content of 380 and maximum w/c ratio of 0.35 . Having difficulty achieving such a low w/c ratio while maintaining workability of the concrete . I note that in a subsection it states " in some parts of the UK it is not possible to produce a practical concrete with a maximum water cement ratio of 0.35 . " . Can anyone elaborate on this clause , i.e is it climate related ?

 

[dik]

I'm a bit out of my league, and you may want to talk to a concrete/cement tekkie. I've used mixes to about 0.38 w/c and it may be a feature of the fineness of the cement product or local aggregates or maybe something else. I often use 0.4 w/c. The lower the w/c the more difficult it is to use, generally. Can the w/c requirement be mitigated? Is it possible to increase the concrete cover or percent steel and up the w/c to 0.4 or maybe a little lower. Can use use an admixture that will achieve the same permeability?

Dik

 

[dik]

Was this resolved? and how?

Dik

 

[TomDOT]

Are you using sufficient superplasticizer?

http://www.fhwa.dot.gov/infrastructure/materialsgrp/suprplz.htm