SPECIAL CONCRETE

A Presentation on Special Concrete

Presented By

        Guruprasath.U,

Rajagopal Polytechnic college

                                                                                          

                      SPECIAL CONCRETE

Self compacting concrete:           

  

DEFINITION:

     Special concrete is a highly flow able concrete that spreads in to the forms without the needs of mechanical vibration.

     It is a non  segregating concrete spreads in to the forms by its own weight.

    The main importance of SCC is that it meets all the expected performance criteria without compensating the strength and durability requirements of concrete

HISTORICAL BACKGROUND:

Research was  started in late 1980’s at the University of Tokyo, Japan to develop SCC.

 By the early 1990’s SCC was developed by Japan that does not require vibration to achieve full compaction.

By the year 2000 SCC has become popular is Japan for prefabricated structures and RMC.

ADVANTAGES OF SC:

 1.Faster construction

 2.Reduction in site manpower

 3.Better surface finish

 4.Easier placing

 5.Improved durability

 6.Greater freedom in design

 7.Thinner concrete sections

MATERIALS FOR SPECIAL CONCRETE:

1. CEMENT

     Ordinary Portland cement, 43 or 53 grade can be used.

2. AGGREGATE

    

  Course Aggregate

    # Maximum size is limited to 20mm.

    #For structures with congested reinforcement 10 to 12mm is desirable.

   Fine Aggregate

    #Can be natural of manufactured.

    #The grading must be uniform throughout.

3. MIXING WATER

     Water quality must be established on the same guide lines as that for using reinforced concrete or prestressed concrete.

4. CHEMICAL ADMIXTURES

     Super Plasticizers are an essential component of SC to provide necessary workability.

5. MINERAL ADMIXTURES

     # Fly Ash

     # GGBS

     # Silica fume

     # Stone powder

     # Fibers

REQUIREMENT OF SPECIAL CONCRETE

    On designing a concrete mix it should be focused to has the following characteristics to be classified it as a self compacting.

Filling ability - Ability to flow under  its own  a

                          weight

Passing ability - Ability to flow through heavily   

                            congested reinforcement under  

                             its own weight

Segregation resistance - Ability to retain 

                                   Homogeneity without 

                                   Segregation.

MIX DESIGN

   AIR CONTENT

      #Generally assumed to be 2%

      # In critical conditions higher percentage is preferable.

  

    COURSE AGGREGATE VOLUME

      # Should be between 50% to 60%  

      #Rounded aggregates can be used at higher percentages than the crushed aggregates

     SAND CONTENT

       #Varies between 40% to 50% depending on paste properties.

       #Paste composition is designed based on the  water to powder ratio for zero flow condition with chosen materials.

     OPTIMUM WATER POWDER RATIO AND SUPER Plasticizer DOSAGE

       #Determined using flow cone test and V-Funnel tests on mortar.

      #These tests performed keeping the sand content as constant and varying water powder ratio and dosages of super plasticizers.

TEST FOR SPECIAL CONCRETE

    SLUMP FLOW TEST

         #To assess the horizontal flow of concrete in the absence of obstructions

         #Gives good assessment of filling ability

         #The test also indicates the resistance to segregation

         #It can be used at site.

      J RING TEST

          #Concrete from the slump cone is passed through the J ring.

          #Flow diameter is measured in two perpendicular directions and average dia is calculated.

          #Similarly average height variation is measured.

           #A height difference of 0 to 10mm is acceptable.

     V-FUNNEL TEST

          #Concrete is filled in V shaped funnel placed on firm ground.

          #Time of emptying is noted.

          #This time should be 8 to 12 seconds

     L-BOX TEST

          #Fill the vertical section of the apparatus with concrete.

          #Leave it standing for 1minutes.

          #Lift the sliding gate and allow the concrete to flow out in horizontal section.

          #Record the time taken for the concrete to reach 200 & 400mm marks.

       U-BOX TEST

           #Fill the one compartment of the apparatus with concrete.

           #Leave it standing for 1 minutes.

           #Lift the sliding gate and allow the concrete to flow to other compartment.

           #Once the concrete has come to rest, measure the height of concrete in the second compartment in two places. Calculate the mean.

      FILL BOX TEST

           #Fill the apparatus by pouring 1.5 to 12 litres concrete taken in a scoop into filling pipe at every 5 seconds until the concrete as just covered the first top obstacle and leave it standing for 1 minutes.

          #After the concrete has rest measure the height at side at two different places.

          #Average filling height is calculated then.

CONCLUSION

           With the mindset of current generation people like us to have anything instantly just like a coffee Self Compacting Concrete is a boon than a gift.