Self-compacting concrete (SCC) is considered as a concrete which can be placed and compacted under its own-weight with no vibration .

It is not affected by the skills of workers, the shape and amount of reinforcing bars or the arrangement of a structure.

Due to its high-fluidity and resistance to segregation it can be pumped longer distances .It consists of the same components as conventionally vibrated concrete, which are cement, aggregates, and water, with the addition of chemical and mineral admixtures in different proportions .

Usually, the chemical admixtures used are super plasticizers and viscosity-modifying agents.

SCC is especially useful in confined zones where vibrating compaction is difficult

Development of SCCIn 1986, concrete capable of compaction by its own weight with no need of vibration was proposed (Concept given by Professor Hajime Okamura).In 1988, first successful prototype of self compacting concrete was developed in the University of Tokyo by Prof. K. Ozawa.SCC, that can be compacted in every corner of form work by its own weight, gained market thereafter*Three essential features envisaged during design

Achieving self compactabilityIncreased w/c ratio increases deformability but increases segregation tooReducing coarse aggregate reduces friction and collision, supplying intense energy for flowIncrease in deformability with constant viscosity became possible by superplasticizer

Key Characteristics of SCCFilling ability:-Ability of scc to flow into all spaces within the formwork under its own weight. Passing ability:-Ability of scc to flow through tight openings under its own weight.Resistance to segregation:- Maintaining homogeneity throughout mixing & during transportation & casting.

EXPERIMENTAL PROGRAM Materials:-Locally available materials were used for preparing the concrete mixes. (a) Cement: OPC 43 grade having soundness 0.6 mm, initial setting time 52 mins & final setting time 430 mins.(b) Fine aggregate :Natural river sand having sp.gr.2.64,fineness modulus 2.7 & water absorption1%(c) Coarse aggregate : Maximum size of aggregate is limited to 20mm. 10-12mm is desirable for structures having congested reinforcement. (f) Water: Potable tap water having pH of 7.3(e)Fly Ash: Some quantity may be added to improve the quality and durability of SCC.(d) GGBS: Some quantity may be added to improve rheological properties.(g) Chemical admixture: Super plasticizer & Viscosity Modifying Agents are used. An experimental program was developed to study the effect of size of aggregates on the strength of self compacting concrete made with two filler materials viz. Fly-ash and GGBS.

Generally air content may be assumed to be 2%.Coarse aggregate content in concrete is fixed at 50% of the solid volume.Fine aggregate is fixed at 40% of the mortar volumeW-p ratio by volume is assumed between 0.9 to 1Superplasticizer dosage and the final water-powder ratio are determined so as to ensure self compactabilityProcedure:-The following sequence is followedDetermine the desired air content.Determine the coarse aggregate volume.Determine the fine aggregate content.Finally the concrete properties are assessed by standard test.

The most basic test for self-compact ability is U-flow testLaboriousFigures: U-test apparatus(Source: H. Okamura & M. Ouchy/ J. Adv. Conc. Tech. 1(1), 5-15, 2003)

This test gives good assessment of filling ability of concrete. The higher the flow value, the greater its ability to fill formwork under its own weight. Fill the cone with the scoop. Raise the cone vertically and allow the concrete to flow out freely .Time taken for the concrete to reach the 500mm circle was recorded (This is the T50 time).Measure the final diameter of the concrete in two perpendicular directions. Calculate the average of the two measured diameters. (This is the slump flow in mm).6 ltrs

This test gives filling ability of the concrete.The apparatus consists of a V-shaped box is made with a narrow opening at the bottom (a gate is fixed ) & a bucket of 12 liters capacity.

The total time taken by the SCC discharge was in the range of 6- 12 sec in the experimentAbout 12 liters of concrete was filled into V-funnel without any compaction and concrete was leveled with a trowel After 5 second trap door was opened and concrete was allowed to flow under gravity. The time taken was recorded for the complete discharge using a stop watch..12 ltrs

This test is a measure of the passing ability as well as filling ability of concrete.The apparatus consists of a rectangular section box in the shape of 'L' with a vertical and horizontal section separated by a movable gate.The computed ratio of h2/hl for the SCC mix was between 0.8-0.9.The computed ratio of H2/H1 for the SCC mix was between 0.8-0.9.Figure:-L-Box Test14 liters of concrete neededWhen the concrete stops flowing , height H1 and H2 are measured.The time taken by the concrete to reach these points were recorded .The horizontal section was marked with 200 mm and 400mm markings from gate.

METHOD(TEST)UNITTYPICAL RANGE OF VALUESMINIMUMMAXIMUMSlump Flow (T50 cm)Seconds25Slump Flow by Slump Cone mm650800V- Funnel at t = 5seconds612L BoxH2/H10.80.9U - Box( H1-H2 ) mm030

SCC is considered as the most revolutionary development in concrete construction for several decades(Source: EFNARC guidelines)

Uses of SCC*SCC has been successfully utilized in almost all sectors that utilized conventional concrete: like dam, bridge, tunnel, culverts, walls, ordinary and high rise buildings*Proved highly beneficial for precast concrete industry*As of 2006, SCC makes up about 5% of the Japanese concrete market and around 15% of the Danish and Swedish markets.Osaka Gas Terminal: the Worlds Largest PC LNG Storage TanksRemains the largestsingle application ofSCC (500 000 m3)Opened in April 1998.

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