Concrete Mix for Headworks at WWTP 1

[jjezmarlo3]

This is for all of you WWTP designers out there. What mix design have you been using for Headworks structures, or other structures with relatively high exposure to sulfates? We have generally been using the same mix design we use for all watertight structures (f'c = 4,500 psi, w/c = 0.42, Type II cement, 6% air) as recommended by ACI350-06 Table 4.3.1 for 'moderate' sulfate exposure, and then recommending the Headworks be lined with a protective coating. But I'm wondering if it might be beneficial to jump to the 'severe' sulfate design mix for the headworks (f'c = 5,000 psi, w/c = 0.40, Type V cement, 6% air) instead. My only concern here is that for some of the small municipalities, Type V cement might be hard to come across. Any thoughts?

 

[dik]

Not sure of your application (WWTP?), but we have high sulphate soils and usually use w:c <= 0.4 and regular type 10 cement (here, GUb) with 25% flyash... low slump and strength noted is good. 5% to 7% air for exterior exposure for freeze-thaw...

Lean towards fly-ash with type 10 because of chloride issues. Type 50 (here HS) is contraindicated for chloride resistance.

Dik

 

[JedClampett]

We've not had problems with sulfate attack, at least on the inside of our headworks. We use a .4 w/c concrete with type II cement and fly ash content of 15 to 18% (amount of fly ash usually at the disgression of the batch plant). We're in Phoenix and we routinely don't add air entrainment.
I'd be much more worried about hydrogen sulfide attack on the inside head space of the channels. And there's no concrete mix known that's going to be resistant to that. You're either going to need to put a liner on the concrete (T-Lok) or coat with a hydrogen sulfide resistant coating like Plasite or Sauereisen.

 

[WWTEng]

WWTP=waste water treatment plant. In my limited experience, sulfate attack hasn't been an issue. Actually I haven't seen anyone use epoxied or galvanized rebar on environmental projects.