introduCtion The following summary of the experience of the Bureau of Reclamation provides the most authoritative guidelines available on sulfate attack on concrete: Concrete Pipe • Reducing the C3A content of the concrete is the most direct way to increase resistance of concrete to sulfate attack. • Steam curing increases the resistance of concrete to sulfate attack. • Assuming equal C3A content in the cement, higher cement content increases sulfate resistance of the concrete. For example, a 7 bag, 658 pounds, mix provides from 5 to 10 times the resistance of a 5 1/2 bag, 517 pounds, mix. • Use of calcium chloride as an admixture reduces sulfate resistance. • Concrete pipe has been designed using Type V cement, plus approved pozzolans, for exposure of up to 240,000 parts per million of sulfate. • Resistance to sulfate attack decreases as absorption increases, regardless of cement type. Exposure Conditions • Sulfates in the soil must be water soluble. • Concentration effects, such as those that develop at an evaporative surface, produce the most severe exposure for any given sulfate content of the water. • Unbalanced hydraulic pressures provide the most severe exposure. ConCrete pipe stormwater treatment teChnologies Requirements for Concrete Subjected to Sulfate Attack6 Class of Exposure S-1 S-2 S-3 Relative Degree of Sulfate Attack Very Severe Severe Moderate Percent Water-Soluble Sulfate (as SO4) in Soil Samples Over 2.00 0.20 to 2.00 0.10 to 0.20 PPM Sulfate (as SO4) in Water Samples Over 10,000 1,500 to 10,000 150 to 1,500 Minimum Specified 56-day Compressive Strength 35 32 30 Maximum Water to Cementing Ratio box seCtions 0.40 0.45 0.50 Generally speaking, the natural resistance of the standard Lafarge concrete mix to sulfate is high. However, should sulfate attack be a cause for concern (i.e. SO4 > 15,000 ppm), your local Lafarge representative should be contacted for assistance. manhole and CatCh basin material 6 Design and Control of Concrete Mixtures, 7th Edition, Cement Association of Canada, 2002, page 28. LAFARGE PIPE eMANUAL PAGE 51