CMT

• Portland cement


  Used for general construction purposes where special properties are not required. Normally used for reinforced concrete buildings, bridges, pavements, and where soil conditions are normal. Also used for most concrete masonry units and for all uses where the concrete is not subject to special sulfate hazard or where the heat generated by the hydration of cement is not objectionable. Has great resistance to cracking and shrinkage but has less resistance to chemical attacks.
• Portland Cement


  A grinding mixture of limestone and clay, named after the inventor Joseph Aspdin who took out the patent in 1824 on a hydraulic cement and found it resembled that of the stone quarried on the Isle of Portland in Dorset England.
• Hydration of cement


  The chemical reaction that takes place between cement and water. This reaction is exothermic in nature, due to which considerable amount of heat is released during hydration of cement. This is called as 'heat of hydration'. The hydration of cement is not a sudden process. This reaction is faster in early period and continues indefinitely at a decreasing rate.
• Types of cement


  • Type 1—Normal Portland cement
  • Type 2—Used for structures in water or soil containing moderate amounts of sulfate, or when heat buildup is a concern
  • Type 3—High-early strength. Used when high strengths are desired at very early periods
  • Type 4—Low-heat Portland cement. Used where the amount and rate of heat generation must be kept to a minimum
  • Type 5—Sulfate-resistant Portland cement. Used where the water or soil is high in alkali
• Sulfate attack of concrete is a complex process, which includes physical salt attack due to salt crystallization and chemical sulfate attack by sulfates from soil, groundwater, or seawater. Sulfate attack can lead to expansion, cracking, strength loss, and disintegration of the concrete
• Types of cements and their uses

  • Ordinary Portland Cement (OPC)
  • Portland Pozzolana Cement (PPC)
  • Rapid Hardening Cement
  • Quick setting cement
  • Low Heat Cement
  • Sulfates Resisting Cement
  • Blast Furnace Slag Cement
  • High Alumina Cement
  • White Cement
  • Colored cement
  • Air Entraining Cement
  • Expansive Cement
  • Hydrographic cement
• Properties of cement


  • Chemical composition
  • Fineness
  • Temperature for testing
  • Consistency of standard cement paste
  • Soundness
  • Setting time
  • Compressive strength
  • Tensile strength
• Chemical composition


  Loss on ignition, Insoluble residue, Lime and alumina
• Fineness


  Finer cements react quicker with water and develop early strength, though the ultimate strength is not affected. However, finer cements increase the shrinkage and cracking of concrete.
• Temperature for testing


  The following physical tests should be carried out, as far as possible, between the temperature range of 25ºC to 29ºC. ASTM C 1064-86 set a maximum limit between 27 °C and 35°C
• Consistency of standard cement paste

  The standard consistency of a cement paste is defined as that consistency which will permit the Vicat plunger to penetrate to a point 5 to 7mm from the bottom of the Vicat mold.
• Soundness


  It is essential that cement concrete does not undergo large changes in volume after setting. This change in volume is known as Unsoundness and may cause cracks, distortion and disintegration of concrete.
• Setting time


  To enable the concrete to be laid in position properly the initial setting of cement should not start too quickly. Once the concrete has been laid it should harden rapidly so that the stage in the process of hardening after which any cracks that may appear do not reunite. Final setting is that when it has attained sufficient strength and hardness.
• Compressive strength


  The compressive strength of cement is judged by finding the compressive strength of cement and sand mortar. For this purpose one part by weight of cement is mixed dry with three parts by weight of IS sand.
• Tensile strength


  After 3 days not less than 20 kg/sq cm, After 7 days not less than 25 kg/sq cm.
• ASTM C10 - Maximum Allowed Loss on Ignition Value is 12%
• Indian Standard - Maximum Percentage of Weight Retained in 90 microns sieve
• Soundness test of cement

  Le Chatelier Apparatus, Soundness Value Shall not be Greater than 10
• Tensile test of cement

  After 3 days not less than 20 kg/sq cm, After 7 days not less than 25 kg/sq cm.