EFFECTS ON CONCRETE SUBJECTED TO SULFURIC ACID
INTRODUCTION:
A claimed use of DRYCRETE Moisture Stop is as a protective barrier in Portland cement concrete wastewater structures.
Previous sulfate expansion testing has shown promising results.
A more aggressive, quick indication was desired to gauge the effectiveness of DRYCRETE Moisture Stop against attack from sulfur-based corrosives.
Figure 1: Sulfuric Acid Attack Cycle On Concrete (from Girardi)
EXPERIMENT:
Four concrete specimens, approximately 1 year of age, and approximately measuring 3” x 3” x 4” were obtained. These specimens had previously been exposed to flexural strength testing and had 4 to 6 fractured faces. The fractured faces and assumed accompanying micro-cracking were chosen to allow easier access for the corrosive solution. Beginning masses of each sample were determined.
Two of the samples were treated with DRYCRETE Moisture Stop and two were not. The samples were allowed to sit for 24 hours before testing. All four were submerged in a 3 molar concentration of sulfuric acid ( H2SO4 ) for 26 hours.
Samples were removed, rinsed with tap water, dried by hotplate, and masses determined.
Figure 3: Five (5) minutes into testing
RESULTS:
Within five minutes of introducing the samples into the sulfuric acid, differences were observed between the control and experimental groups:
Notice the activity of the control (untreated) vs the relative inactivity of the treated sample as evidenced by bubbles.
Samples were removed at 26 hours, dried, and mass loss determined:
PHENOLPHTHALEIN (pH) TESTING RESULTS:
Samples were broken open and subjected to a spray phenolphthalein (Rainbow Indicator by German Instruments.)
Specimen 1 & 2 are from the untreated cores and specimen 3 & 4 are from the treated cores.
Figure 5: pH Indicated By Phenolphthalein On Split Samples
Figure 6: Closeup Of Sample 3 Showing pH Gradient
CONCLUSIONS:
The samples treated with DRYCRETE Moisture Stop showed approximately 63% less mass loss than the control samples.
The pH gradient of the interior of the samples demonstrates that DRYCRETE Moisture Stop treated samples are retarding the ingress of acid and/or not allowing the acid to react with the interior of the concrete.
Note: The tests were conducted by the reputed moisture testing company Flood Testing Laboratories, Inc. in Chicago, Il. All tests were performed on site, under normal exterior atmospheric conditions during a period of heavy precipitation with record rainfall recorded during the month of June 2011.