CONCRETE PIPE Sulfates Sodium, magnesium and calcium sulfates in soil, groundwater, or effluent can be highly aggressive to portland cement concrete by combining chemically with certain constituents of the concrete, principally hydrates of C3A, to form calcium sulfoaluminate. This reaction is accompanied by expansion and eventual disruption of the concrete. The situation is typical of those conditions where sulfate concentration has taken place because of an exposed evaporative surface. Experience with this phenomenon in the United States has primarily occurred in the alkali soils of the west and southwest and has been almost exclusively limited to cast-in-place, exposed concrete structures. The Bureau of Reclamation has wide experience in concrete construction in these areas and has developed the general criteria shown in the table below for evaluating and dealing with this problem. These criteria apply to a wide range of exposure conditions for cast-in-place concrete where concentration effects are anticipated. Application of these criteria to buried concrete pipe is extremely conservative. They should not be applied unless evaluation of installation conditions indicates high concentration effects are likely to develop. Relative Degree of Sulfate Attack Negligible Positive Severe Very Severe Percent Water-Soluble Sulfate (as SO4) in Soil Samples 0.00 to 0.10 0.10 to 0.20 0.20 to 2.00 PPM Sulfate (as SO4) in Water Samples 0 to 150 150 to 1,500 1,500 to 10,000 10,000 or more N/A Use Type II cement Use Type V cement, or approved Portland-pozzolan cement providing comparable sulfate resistance when used in concrete. Use Type V cement, plus approved pozzolan which has been determined by tests to improve sulfate resistance when used in concrete with Type V cement. Recommended Action 2.00 or more PAGE 50 LAFARGE PIPE eMANUAL