Tuesday, April 3, 2018

SEGREGATION AND BLEEDING


SEGREGATION
Definition
      Separation of constituent materials in concrete.

Types of Segregation
      Separation of coarse aggregate from concrete mixture
      Separation of cement paste from concrete during its plastic stage
      Separation of water from the cement mix (Bleeding)

Primary cause of Segregation
      Difference in specific gravity of constituent
      Constituent of Concrete = coarse aggregate + fine aggregate + cement + water
      Specific gravity of cement = 3.1 to 3.6
      Specific gravity of aggregate = 2.6 to 2.7
      Specific gravity of water = 1
      Lighter particle moves upward and heavier particle tends to move downward and hence segregation occurs.

Other causes
      Dropping concrete from more than 1 metre
      Vibrating for long time
      Poorly proportioned mix

Minimizing Segregation
      By proportioning the mix
      By peculiar handling, placing, transporting, compacting and finishing
      Use air entraining agent, admixture and pozzolanic materials in the mix

BLEEDING
Definition
·        Generally, occurs in wet mix of concrete
·        form of segregation
·        Water present in concrete is pushed upwards due to settlement of cement and aggregate
·        Specific gravity of water is low so it tends to move upward

Cause of Bleeding  
·        High water cement ratio
·        Not well compacted or excess compaction

Control of Bleeding         
·        Air entraining admixture
·        Control water-cement ratio i.e. add minimum water

Note:
ü Bleeding is not harmful if the rate of evaporation is equal to the rate of bleeding
ü Normal bleeding is quite good and it enhances the workability of concrete




No comments:

Post a Comment

MOST RECENT

BITUMEN, ASPHALT, COAL TAR, CUTBACK BITUMEN

Ever wondered what is Bitumen? What is Asphalt? What is difference between these two? What is MC 30 Bitumen? What is cutback bitumen? We wil...