By
Kaushal Kishore
Materials Engineer, Roorkee
Self-compacting concrete (SCC) is a special type of concrete which can be placed and consolidated under it’s own weight without any vibration effort due to it’s excellent deformability, and which at the same time is cohesive enough to be handled without segregation or bleeding.
WORKABILITY:
The workability of self-compacting concrete is measured by the usual slump cone having a base diameter of 200mm, top dia 100mm, and height 300mm. The slump cone is to be placed as usual upon a base plate square in shape is having at least a 700m side. Concentric circles are marked around the center point where cone is to place. A firm circle is drawn at 500mm diameter.
PROCEDURE OF SLUMP FLOW TEST:
About 6 liters of concrete is needed for this test. Place the baseplate on level ground keep the slump cone centrally on the base plate. Fill the cone with scoop. Do not tap. Simply strike of the concrete level with the trowel. Remove the surplus concrete lying on-base plate. Raise the cone vertically and allow the concrete to flow freely at maximum distance. Measure the final diameter of the concrete in two perpendicular directions and calculate the average of the two diameter. This is the slump flow in mm. when the slump cone is lifted T50 slump flow is the taken for the concrete to reach a 500mm mark. Time to be measured by a stop watch. It is suggested the T50 time may be 2 to 5 seconds.
SELF COMPACTING CONCRETE BENEFITS:
1. Improve constructability
2. Labour reduction
3. Bond to reinforcing steel
4. Improved structural integrity
5. Accelerates project schedule
6. Reduces skilled labour
7. Flows into complex form
8. Reduces equipment wear.
9. Minimizes void on highly reinforced areas
10. Produces superive surfaces finish
11. Superior strength and durability
12. Allows for easier pumping procedure
13. Fast placement without vibration or mechanical consolidation
14. Lowering noise levels produced by mechanical vibrators
15. Produces a uniform surface
16. Produces a wider variety of placement techniques
DISADVANTAGES OF SELF COMPACTING CONCRETE:
1. Material selection is more strict
2. Construction cost increase, compared with regular concrete
3. Many trial batches and laboratory texts are requested to use a designed mixture
4. Higher precision is required when meaning and monitoring
MIX DESIGN CONSIDERATION:
While designing a concrete mix of self-compacting concrete, the following points should be taken into consideration
1. The coarse aggregate may be 10, 12.5 or 20mm.
2. Coarse aggregate should be 45% and fine aggregate 55%.
3. Water 180 to 190 Kg/m3. Normally not to exceed 200 Kg/m3.
4. For M-60 and above grade concrete 10 percent of silica fume will be required.
5. No silica fume needed for M-25 to M-50 concrete but 20 to 30 percent good quality flyash will be needed.
6. Superplasticizer, polycarboxylic based 0.5 – 3 percent by weight of total cementious material
7. Viscosity modifying agent, polymer based 0.1 – 0.5 percent by weight of total cementious material.
MIX DESIGN:
A M-40 grade self-compacting pumpable concrete is designed with cement and aggregate given in table 1 and 2. The mix design is given in table 3. The mix design is carried out from reference 1.
Table 1. TEST REPORT OF CEMENT OPC 43-Grade:
| S.No | Test | Test Result | Requirement As per IS:269-2015 |
|---|---|---|---|
| 1. | Fineness (cm 2 /g) | 2910 | 2250 Min |
| 2. | Soundness (mm) | 1.0 | 10 Max |
| 3. | Setting time (minutes) (a) Initial (b) Final |
127 190 |
30 Min 600 Max |
| 4. | Compressive strength (Mpa) (a) 3 days (b) 7 days (c) 28 days |
32.5 |
23 Min |
Table 2. TEST REPORT OF AGGREGATES:-
| I.S. Sieve size | PECENTAGE PASSING BY MASS CRUSHED AGGREGATES | ||
|---|---|---|---|
| Sand | 10mm | 20 mm | |
| 40 mm | X | X | 100 |
| 20 mm | X | 100 | 93 |
| 12.5 mm | X | 100 | X |
| 10 mm | 100 | 97 | 1 |
| 4.75 mm | 90 | 4 | 1 |
| 2.36 mm | 84 | 2 | |
| 1.18 mm | 76 | ||
| 600 micron | 55 | ||
| 300 micron | 28 | ||
| 150 micron | 7 | ||
| Sp gravity | 2.56 | 2.61 | 2.62 |
| Water absorption% | 0.93 | 0.91 | 0.60 |
| Bulk density Kg/lit | 1.75 | 1.56 | 1.59 |
Table 3. M40 grade self-compacting pumpable concrete mix design on the basis of saturated surface dry aggregates.
Water = 190 Kg/m3
Cement, OPC 43 grade = 380 Kg/m3
FlyAsh = 150 Kg/m3
Sand = 856 Kg/m3
10 mm Crushed aggregate = 280 Kg/m3
20 mm Crushed aggregate = 421 Kg/m3
Superplasticizer, Polycarboxylic based = 7.950 Kg/m3
Viscosity Modifying agent, Polymer based = 1.060 Kg/m3
Slump flow after 60 minutes = 600 mm
7 days compressive strength = 35.7 N/mm2
28 days compressive strength = 50.5 N/mm2
Note = Laboratory Strength
REFERENCE:
1. Concrete mix design by Er. Kaushal Kishore civil Engineering Portal.
2. Pumped concrete by Er. Kaushal Kishore google site.
About Er. Kaushal Kishore
Kaushal Kishore is retired from IIT, Roorkee and now a Consulting Materials Engineer. He has written, published and presented over 150 research papers and four books on materials testing, concrete mix design, alternate materials, pollution control, rain water harvesting, non-destructive testing, repair rehabilitation and waterproofing of buildings.
Kaushal Kishore is the recipient of CIDC Vishwakarma Awards-2011 for category Academician/Technologist/Scientist/Innovator. CIDC Best on line publication Award-2013, EETCRS Science & Technology Awards-2013 for Special Achievement Award-Materials Engineering, EETCRS Technology Leadership Awards-2013, EETCRS 2nd Science & Technology Awards-2014 for Special Mention-Excellence in Research and India’s most prestigious National Award in Civil Engineering field namely: INDIAN CONCRETE INSTITUTE – JAYPRAKASH ASSOCIATES, LIFE TIME ACHIEVEMENT AWARD-2011, NAVRATNA AWARD 2017 by builder’s association of INDIA for his academic contribution to the Indian Construction Industry, Award of Incredible Researcher of India 2021
We at engineeringcivil.com are thankful to Sir Kaushal Kishore for sharing his valuable report with us. We hope this would be of immense help to all Civil Engineers.
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