point to consider while using mineral admixture in concrete

Points to Consider

  1. Mixing of mineral admixtures with OPC at site should not normally be permitted. However for projects requiring use of blended cement from durability and strength considerations, which is not available from the cement manufacturer blending may be permitted through a specific facility created at site with complete automated process control to achieve the specified design quality or from RMC plants with similar facility.
  2. For concrete made with Portland Pozzolana cement, Portland blast furnace slag cement or mineral admixtures, the setting time and rate of gain of strength are different from those of concrete made with OPC alone. Cognizance of such modified properties shall be taken in deciding deshuttering time, initial time of prestressing, curing period and for early age loading.
  3. Compatibility of chemical admixtures and super plasticizers with Portland Pozzolana cement, Portland blast furnace slag cement and mineral admixtures shall be ensured by trials.
  4. Some other properties of concrete such as modulus of elasticity, tensile strength, creep and shrinkage are not likely to be significantly different. For design purposes, it will be sufficient accurate to take the same values as those for concrete made with OPC.
  5. Rapid chloride ion permeability test as per ASTM C-1202 shall be carried out for severe exposed conditions. The permissible value of chloride ion permeability shall be less than 1500 coulombs at 28 days.
  6. Additional durability tests, such as water permeability test as per DIN:1048 part-5 or initial surface absorption test as per BS:1881 part-5 can also be specified. The permissible values in such tests shall be decided taking into account the severity of the exposure conditions.

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