self compacting concrete

INTRODUCTIONBy the early 1990's, Japan has developed and used SCC.

Self compacted concrete is highly engineered concrete with much higher fluidity without segregation and is capable of filling every corner of formwork under its self weight .

Thus SCC eliminates the vibration for the compaction of concrete without affecting its engineering properties.

 As of the year 2000, SCC used for prefabricated products (precast members) and ready mixed concrete (cast-in-situ) in JAPAN, USA and later on INDIA etc. 

DEVELOPMENT OF SCC In 1983, the problem of the durability of the concrete structures was a major topic of interest in Japan.

The creation of durable concrete structures requires adequate compaction by skilled workers.

Solution for the achievement of durable concrete structures independent of the quality construction work is the use of SCC.

The necessity of this type of concrete was proposed by Okamura in 1986.

Studies to develop SCC have been carried out by Ozawa and Melawi at the university of Tokyo.

Present-day SCC can be classified as an advanced construction material.

FATHER OF SCC TECHNOLOGYProf.Dr.Hajime Okamura

Developed Self compacting concrete in 1986 in JAPAN.

Currently President of Kochi University of Technology .

CANMET/ACI AWARD for Outstanding contributions in the development of SELF COMPACTABLE HIGH PERFORMANCE CONCRETE (1995) .

OKAMURA solved the issue of degrading quality of concrete construction due to lack of compaction by the employment of SCC which is independent of the quality of construction work.

CONSTITUENTS OF SCC With regard to its composition, SCC consists of

the same components as conventionally vibrated concrete, which are Cement Aggregates Water Chemical Admixtures i.e. Super plasticizers

and Viscosity Modifying Agents Mineral Admixtures i.e., Fly ash, Silica Fume,

GGBFS etc.

TYPICAL MIX PROPORTION VALUES

Constituent Typical range by volume(liter/m3)

Powder 160-240

Water 150-210

Coarse aggregate 270-360

water to powder ratio 0.80-1.10

Fine aggregate 48-55% of total aggregate weight

PROPERTIES OF SCC

IN FRESH STATE, SCC HAVE FOLLOWING PROPERTIES-

Filling ability (excellent deformability) - flows easily at suitable speed into formwork

Passing ability (ability to pass reinforcement without blocking) -passes through reinforcements without blocking

High resistance to segregation- the distribution of aggregate particles remains homogeneous in both vertical and horizontal directions

Static segregation due to gravity, vertical directionDynamic segregation due to flow, horizontal direction

COMPARISON BETWEEN CONVENTIONAL CONCRETE AND SCC

Self Compacting Concrete (Admixture: Superplasticizer)

Air WPowder

S G

Air W C S G

Conventional Concrete

Mechanism for achieving Self Compact ability (Okamura &

Ozawa)Reduction of water to binder

ratio

Limitation of coarse

aggregate content & maximum

size

Addition of mineral admixture

Usage of Super

plasticizer & VMA

High segregation resistance of

mortar & concrete

High Deformability of

mortar & concrete

Self compactibility

MEASUREMENT OF SCC FLOW PROPERTIES

IN FRESH STATE

Slump Flow & T50 test: Slump flow test is used to find the filling ability

of the SCC.

The SCC sample is poured in to the slump cone then the slump flow diameter is measured.

The flow time is measured & that is know as T50 slump time.

The higher the slump flow value, the greater its ability to fill formwork under its own weight.

APPARATUS

Test Procedure:

ACCEPTABILITY OF SLUMP FLOW:

L-BOX TEST The L-Box test is used to find the passing ability of SCC.

The SCC sample is poured in to the L-Box apparatus, now the plate is removed to allow flow.

The L-box ratio is calculated as H2/ H1. According to EFNARC , when the ratio of h2 to h1 is larger than 0.8, self compacting concrete has good passing ability.

APPARATUS

Test Procedure

V-FUNNEL TEST AND V-FUNNEL TEST AT T5MINUTES:

The V-Funnel test is used to find the Segregation Resistance of SCC.

The SCC sample is poured in to the V-Funnel apparatus, now its allowed to flow by its weight.

The emptying time of V-Funnel is noted.

This test measured the ease of flow of the concrete, shorter flow times indicate greater flow ability. After 5 minutes of setting, segregation of concrete will show a less continuous flow with an increase in flow time.

TEST APPARATUS

TEST PROCEDURE

TESTS ON HARDENED CONCRETE

Compressive Strength Test

Split Tensile Strength Test

Split cylinder test

Standard Beam test

Flexural Strength Test

Preparation of SCC specimens: All the materials are placed in the mixer & mixed well

The sample is taken out and poured in to the moulds.

The moulds are socked in water & allowed for curing .

ACCEPTANCE CRITERIA FOR SCC IN FREE STATE

Test Results on Fresh Concrete and Acceptance Criteria for SCC

S. No

Method UnitWater/Cement Ratio EFNARC[3]

SpecificationRemarks

0.23 0.24 0.25 0.26 0.27

1Slump Flow Test

mm 655 660 665 680 700

SF1: 550-650

SF2: 660-750

SF3: 760-850

SF2

2 T500 sec 3.94 3.88 3.82 3.32 2.50

VS1: T500 ≤ 2

VS2: T500 > 2

VS2

3V-

Funnelsec 8.50 8.35 8.10 7.95 6.89 VF1: ≤ 8

VF2: 9-25VF2

4 T5min sec 11.89 10.92 10.66 10.23 9.95

5 L-Box h2/h1 0.950 0.959 0.969 0.9750.98

0

PA1: > 0.8 (2 rebars)

PA2: > 0.8 (3

rebars)

PA2

6 U-Box mm 9 7 6 5 4 0-30 [23] OK

Test Results on Hardened Concrete

Concrete Mix

Compressive Strength(N/mm2)

Split tensile Strength

(N/mm2)

Flexural Strength(N/mm2)

7days 28days 7days 28days 7days 28daysM1 (W/

C=0.23)61.64 82.22 3.72 4.09 5.92 6.76

M2 (W/

C=0.24)59.73 82.07 3.63 4.08 5.84 6.52

M3 (W/

C=0.25)53.11 81.62 3.43 4.05 5.72 6.20

M4 (W/

C=0.26)52.53 81.29 3.40 3.99 5.46 5.86

M5 (W/

C=0.27)52.48 80.53 3.37 3.89 5.18 5.69

ACCEPTANCE CRITERIA FOR SCC IN HARDENED STATE

DISCUSSION ON TEST RESULTS

Based on the above experimental results, the observations are as follows:

Slump flow increases with the increase of water/cement ratio.

T500 time, V-funnel time, T5 time and U-box values are decreases with the increase of w/c ratio.

L-box value increases with the w/c ratio and Compressive strength, tensile strength and flexural strengths are decreasing as the w/c ratio increases.

Marginal increase in the compressive strength at 28 days of concrete as the w/c ratio decreases.

Compressive strength and split tensile strength decreases at higher rate for 7 days strength when compared to 28 days strength, whereas it is also observed that flexural strength value decreases at higher rate for 28 days strength when compared to 7 days strength.

ADVANTAGES OF SCC

Elimination of problems associated with vibration. Faster construction Improves working conditions and productivity in

construction industry. Greater freedom in design. Less noise from vibrators and reduced danger from

hand-arm vibration syndrome (HAVS). Ease of placement results in cost savings through

reduced equipment and labour requirement. Improves the quality, durability, and reliability of

concrete structures due to better compaction and homogeneity of concrete.

Reduced wear and tear on forms from vibration.

Reduced permeability.

DISADVANTAGES OF SCC

More precise measurement and monitoring of the constituent materials.

Requires more trial batches at laboratory as well as at ready-mixed concrete plants. Costlier than conventional concrete based on concrete material cost (exception to placement cost). Lack of globally accepted test standards and mix designs More stringent requirements on the selection of materials .

SCC has high potential for greater acceptance and wider applications in highway bridge construction in the all over world. An NCHRP Research Project has been initiated to develop design and construction specifications to supplement the AASHTO LRFD Bridge Design and Construction Specifications.

Based on above results and discussions the following conclusions are drawn-

Self Compacting Concrete (SCC) technology can save time, cost, enhance quality, durability and Moreover it is a green concept.Since the concrete is capable of self-consolidating and reaching the difficult areas in moulds, manual variables in terms of placing and compacting concrete is nil. This factor ultimately yields defect less, better-quality concrete structures.Cast-in-place concrete construction in tight space and congested reinforcement, such as, drilled shafts, columns and earth retaining systems, can be accelerated by using SCC.

CONCLUSION

REFERENCES1. Brain Paulson. EFNARC, Secretary General, ‘Specifications and

Guidelines for Self-Compacting Concrete”, February 2002.

2. Nan Su, K.C. Hsu, H.W. Chai. A Simple mix design method for self-compacting concrete, cement and concrete Research 2001.

3. 3.Okamura.H.‘Self-Compacting High Performance Concrete’, Concrete International, Vol. 19, No.7, pp. 50-54, July 1997

4. 4. M.S. Shetty. “Concrete technology (theory and practice), S. Chand & Company LTD. 2002

5. IS 456-2000 Code of practice for plain and reinforced concrete (3rd revision)

6. 16. IS 516-1959 Method of test for strength of concrete

7. SK Singh “Self Compacting Concrete - A Paradigm Shift”, Journal of New Building Materials & Construction World, Vol. 15, No. 3, pp 164-180,September , 2009.