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PHILLIPS MINING, GEOTECHNICAL & GROUTING, INC. <br />may be produced during setting. Internal build-up of heat within the mass, due to the <br />cement hydration process may result in thermal cracking that would significantly impair <br />the integrity of the structure. The use of a low heat cement in the concrete will help <br />eliminate this possibility. <br />The water that is being retained by the plug is acidic, with a pH that may be as low as 3. <br />The cement and the aggregate comprising the concrete must be resistant to attack and <br />dedradation by water of this acidity. <br />Shrinkage of the concrete will not be a problem if the concrete mix is designed properly. <br />The use of superplasticizers enables the water/cement ratio of the basic mix to be kept to a <br />minimum, thereby ensuring that very little water is lost during the curing stage. This will <br />prevent excessive shrinkage. <br />The required concrete properties are given below. <br />• Minimum unconfined compressive strength at 28 days; 3500 psi. <br />• A low heat, acid-resistant cement, such as Fosroc Terracem or equivalent. <br />• A low water:cement ratio. <br />• Water; drinking quality. <br />• Coarse aggregate; s inch maximum, siliceous. <br />• Sand; siliceous. <br />• Capable of being pumped. <br />• Slump inside the forms; 9 to 10 inches. <br />• Resistant to degradation by acids with a pH of 3. <br />• The temperature of the concrete at placement must not exceed 70° F. <br />Page 7 <br />