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AAEC (Civil/Environmental) (OP)
28 Sep 10 23:03
Does the concrete expand when sulfuric acid come in contact with the concrete? I have this secondary containment concrete trench with an acid proof lining. The lining was compromised over the years and now the sulfuric acid had worked its way to the bottom portion of the concrete trench wall on both sides. I can actually easily scour the said area with a hammer claw since it is very soft and damp. We will take a sample in the soft area and test for PH level.  Expect the sample to be way below 7.

Any help will be appreciated.    
Helpful Member!  JedClampett (Structural)
28 Sep 10 23:30
I'm sure there is some expansion from the attack on the cement matrix. But what's the difference?  The sulfuric acid has damaged the concrete.  Take out the bad concrete, repair and recoat it.
Helpful Member!  bimr (Civil/Environmental)
28 Sep 10 23:38
Concrete is susceptible to acid attack because of its alkaline nature. The alkaline components of the cement paste (calcium hydroxide) break down with acid exposure.

 H2SO4 + Ca(OH)2 -> CaSO4 + 2 H2O
 
Sulphuric acid is very damaging as it combines an acid attack and a sulfate attack.

The reaction between sulfuric acid and the calcium compound in concrete will form calcium salts, which are soluble in water. These water soluble salts leach away, causing a loss of volume and cohesion of the cement paste  
Helpful Member!  Ron (Structural)
29 Sep 10 5:50
The concrete will not expand under sulfuric acid attack or exposure.  It will disintegrate until the reaction is consumed, which could affect just the surface or could go through the concrete section depending on the amount and concentration of the acid.

The reaction that bimr noted is the typically the first and most significant, though sulfuric acid also reacts with the alumina compounds and others.
Helpful Member!  SlideRuleEra (Structural)
29 Sep 10 15:24
For the repairs, suggested above, consider using Type V cement in the concrete. It has high inherent sulfate resistance, but is sometimes difficult to obtain. There are other ways to improve sulfate resistance if Type V cement is not available, see:
http://www.cement.org/tech/cct_cement_specifying.asp

However, NONE of these products are a substitute for a proper "acid proof" lining, just another step that may be taken.  What you describe is classic deterioration that happens in water treatment areas of industrial plants.

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

AAEC (Civil/Environmental) (OP)
29 Sep 10 17:02
Thank you all for your answers. I have provided a sketch and photos of the trench to see if you can be able to help me answer why the trench wall is moving upward. I am not sure if the acid attack on the lower walls are causing all these concrete cracks or is it the soil around the trench although the soil looks good to me. Notice the discolaration on the bottom of the trench walls. This is where the soft spot as indicated in my sketch.
AAEC (Civil/Environmental) (OP)
29 Sep 10 17:14
Opps-disregard the photos.

The type of concrete we will use is from Sauereisen-Epoxy Novolak Polymer Concrete No. 265. This supposed to resist a wide range of solvents, oils, acids and acid salts (except hydrofluoric) over a pH range of 0.0 t 14.0. Maximum service temperature of 180 def F and low porosity.
rconner (Civil/Environmental)
29 Sep 10 17:24
I believe hydrated calcium sulphate is in effect "gypsum" (of maybe similar soft consistency as you are describing gouging with a claw hammer?)  While I don't know about swelling of corroded concrete per se, if there is any steel mesh or other reinforcement in the concrete I have heard that will indeed swell if corroded (per some authorities I've heard maybe up to 3-8 times its original steel volume).  [While I guess "acid proof" are efective marketing words, from an Engineering standpoint (and particularly for concrete coatings) that may be a pretty tall order for any material!]     

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