Experimental Investigation on Rock Filled Self-Compacting Concrete

MATERIALS USED

1. `Fine Aggregate = M-sand

2. Coarse Aggregate

   • 12.5mm gravel

   • 5cm rock gravel

3. Cement

   OPC grade-53

4. Superplasticizers

GLENIUM C-303

MEDHODS

1. Rock Gravel

   Process of RFC involves two major steps:

   [i].Filling in-situ formwork with large-scale rocks (grain size >30 cm).
   [ii].Pouring fresh SCC into pre-packed rock skeleton to fill the voids between rocks.

   Manufactured sand (M-Sand) is a substitute of river sand for concrete construction.Manufactured sand is produced

   from hard granite stone by crushing. The crushed sand is of cubical shape with grounded edges, washed and graded to as a construction material. The size of manufactured sand (M- Sand) is less than 4.75mm. Manufactured sand is an alternative for river sand. Due to fast growing construction industry, the demand for sand has increased tremendously, causing deficiency of suitable river sand in most part of the world. Due to the depletion of good quality river sand for the use of construction, the use of manufactured sand has been increased. Another reason for use of M-Sand is its availability and transportation cost.

   In the case of SCC, rounded aggregates would provide a better flowability and less blocking potential for a given water-to-powder ratio, compared to angular and semi-rounded aggregates. Moreover, the presence of flaky and elongated particles may give rise to blocking problems in confined areas, and also increase the minimum yield stress.The maximum aggregate size varying from 10 to 20mm.Incorporation of aggregate shape in the mixture design would enable the selection of appropriate paste content required to overcome these difficulties. It is possible that the highly flowable nature of SCC could allow a higher proportion of flaky aggregates compared to normal concrete. However, this aspect needs to be checked.

2. Superplasticizers,

It also known as high range water reducers(HRWR), are chemical admixtures used where well-dispersed particle suspension is required. It is a essential component of SCC. GLENIUM C-303 is used because it is essential component of SCC to provide workability.

Ordinary Portland water normally of pH 7 is used for mixing & curing the concrete specimen.

Fig 1Glenium C-303

EXPERIMENTAL PROCEDURE

The cement, sand and coarse aggregates were weighted according to the mix proportion of 1:1.8:1.7. In order to study the effect on fresh concrete properties in SCC the rock gravel is added in concrete at bed level. To this dry mix the required quantity of water was added and thoroughly mixed. To this the super plasticizers was added at the rate of 1.5lit/m3 of cementitious material and mixed immediately. The entire mix was thoroughly mixed once again. At this stage, almost the concrete was in a flowable state.

Now, the flow characteristic experiments for self- compacting concrete like slump flow test, V-funnel test,

L-box test, & U box test were conducted. In terms of slump flow, all SCC exhibited satisfactory slump flows in range of 550-800mm, which is an indication of a good deformability.

After conducting the flow characteristic experiments the concrete mix was poured in the moulds required for the strength assessment. After pouring

the concrete in the moulds, no compaction was given either through vibrated or through hand compaction.

Even the concrete did not require any finishing operation. After 24 hours of casting, the specimens were demoulded & were transferred to the curing tank. Wherein they were allowed to cure for 28 days.

For compressive assessment, cubes of size 150mm x 150mm x 150mm were prepared. For tensile strength assessment, cylinders of diameter 150mm & length 300mm were prepared. Indirect tension test ,was carried on these cylindrical specimens. After 28 days of curing the specimens were tested for their respectively strengths. The test results were studied and the optimum SCC were found.

Same procedure of mixing is repeated for the adding of rock gravel in bed level to optimum SCC mix. The 5cm rock gravel was settled down in moulds at bed level. The entire mix was thoroughly mixed & poured into the moulds without any compaction. After 28 days curing, the specimens were tested for their respectively strength and the optimum value of SCC has been found.

Self-compacting concrete is a high performance concrete that can be compacted into every corner of a formwork, purely by means of its own weight and without the need for vibrating compaction .This concrete is defined as follows at the three stages of concrete: Fresh: self-compactable; Early age: avoidance of initial defects; After hardening: protection against external factors.

The addition of super plasticizers in the truck during transit is a fairly new development within the industry. Admixtures added in transit through automated slump management systems, allows concrete producers to maintain slump until discharge without reducing concrete quality. I Summarized here that the addition of super plasticizers in SCC and improves the mechanical properties mainly the tensile and compressive strength of self compacting concrete (SCC).

1. Fresh Properties Of Scc

   The main properties of SCC in plastic state are :

   1. Filling ability (Slump-flow, V-funnel).

   2. Passing ability ( J-ring, L-box )

   3. High resistance to segregation ( V-funnel at T5 minutes )

1. Filling Ability of Self Compacting Concrete

   It is the ability of SCC to flow into all spaces within the formwork under its own weight. Tests, such as slump flow, V-funnel etc, are used to determine the filling ability of fresh concrete.

2. Passing Ability of Self Compacting Concrete

   It is the ability of SCC to flow through tight openings, such as spaces between steel reinforcing bars, under its own

   weight. Passing ability can be determined by using U-box, L- box, Fill-box, and J-ring test methods.

3. Segregation Resistance

The self compacting concrete must meet the filling ability and passing ability with uniform composition throughout the process of transport and placing.

FRESH CONCRETE PROPERTIES

1. Flowability Tests:

   1. Slump flow test (1) and T 50cm test (2)

      1. Introduction

         The slump flow is used to assess the horizontal free flow of SCC in the absence of obstructions. It was first developed in Japan (1) for use in assessment of underwater concrete. The test method is based on the test method for determining the slump. The diameter of the concrete circle is a measure for the filling ability of the concrete.

      2. Assessment of test

   This is a simple, rapid test procedure, though two people are needed if the T50 time is to be measured. It can be used on site, though the size of the base plate is somewhat unwieldy and level ground is essential. It is the most commonly used test, and gives a good assessment of filling ability. It gives no indication of the ability of the concrete to pass between reinforcement without blocking, but may give some indication of resistance to segregation. It can be argued that the completely free flow, unrestrained by any boundaries, is not representative of what happens in practice in concrete construction, but the test can be profitably be used to assess the consistency of supply of ready-mixed concrete to a site from load to load.

2. J Ring test

   1. Introduction:

      The principle of the JRing test may be Japanese, but no references are known. The JRing test itself has been developed at the University of Paisley. The test is used to determine the passing ability of the concrete. The equipment consists of a rectangular section (30mm x 25mm) open steel ring, drilled vertically with holes to accept threaded sections of reinforcement bar. These sections of bar can be of different diameters and spaced at different intervals: in accordance with normal reinforcement considerations, 3x the maximum aggregate size might be appropriate. The diameter of the ring of vertical bars is 300mm, and the height 100 mm.

   2. Assessment of test

      These combinations of tests are considered to have great potential, though there is no general view on exactly how results should be interpreted. There are a number of options for instance it may be instructive to compare the slump-flow/JRing spread with the unrestricted slump-flow.

3. V funnel test and V funnel test at T 5minutes

   1. Introduction

      The test was developed in Japan and used by Ozawa et al. The equipment consists of a V-shaped funnel, shown in Fig.D.4.1. An alternative type of V- funnel, the O funnel, with a circular section is also used in Japan.The described V-funnel test is used to determine the filling ability (flowability) of the concrete

      with a maximum aggregate size of 20mm. The funnel is filled with about 12 litre of concrete and the time taken for it to flow through the apparatus measured.After this the funnel can be refilled concrete and left for 5 minutes to settle. If the concrete shows segregation then the flow time will increase significantly.

   2. Assessment of test

Though the test is designed to measure flowability, the result is affected by concrete properties other than flow. The inverted cone shape will cause any liability of the concrete to block to be reflected in the result if, for example there is too much coarse aggregate. High flow time can also be associated with low deformability due to a high paste viscosity, and with high inter-particle friction.

While the apparatus is simple, the effect of the angle of the funnel and the wall effect on the flow of concrete is not clear.

TABLE 1 Flowability Test Results

MIX DESIGN

The mix design of self-compacting concrete is a trial and error method. Many references available for mix proportioning of SCC. Here we use mix proportioning based on previous investigation strength data using Japanese method and also based on EFNARC-2002 guidelines. In the Japanese method coarse and fine aggregate contents are initially fixed so that self compactability is achieved by adjusting the water/powder ratio and super plasticizer dosage. Strength requirements are assessed from field trails of SCC at a later stage. In our investigation we incorporate the procedures of EFNARC-2002 guidelines. These guidelines gives the range for coarse aggregate and fine aggregate content and based on the limit the approximate mix design for M40 grade of concrete is obtained.

1. Mix Design Ratio

   Ratio Of Mix Design is 1: 1.8: 1.7

   TABLE 2 Scc Mix ratio

   Cement (kg\m3)	459
   Fine aggregate (kg\m3)	823
   Coarse aggregate (kg\m3 )	810
   Water (kg\m3)	146
   Fibers (kg\m3)	0.0
   Super plasticizer (ml)	45.9

HARDENED CONCRETE TEST

1. Compressive Strength Test

   Compressive strength test results are primarily used to determine that the concrete mixture as delivered meets the requirements of the specified strength, in the job specification. Strength test results from cast cylinders may be used for quality control, acceptance of concrete, or for estimating the concrete strength in a structure for the purpose of scheduling construction operations such as form removal or for evaluating the adequacy of curing and protection afforded to the structure. Cylinders tested for acceptance and quality control are made and cured in accordance with procedures described for standard-cured specimens in ASTM C 31 Standard Practice for Making and Curing Concrete Test Specimens in the Field. For estimating the in-place concrete strength, ASTM C 31 provides procedures for field-cured specimens. Cylindrical specimens are tested in accordance with ASTM C 39.

   TABLE 3 Compressiom test results

   Specimen	7 days (N/mm2)	28 days (N/mm2)
   M40 mix Without rock filled	27.8		41
   M40 mix With rock filled 4cm	28.3	41. 9
   M40 mix With rock filled 5cm	28.5	42. 5
   M40 mix With rock filled 6cm	29.3	43. 2

   Fig 2 Bar chart showing compression test results

2. Split Tensile Strength Test

   This test method is used for the determination of splitting tensile strength of cylindrical concrete specimen. Splitting tensile strength is helpful for the following purposes;

   Splitting tensile strength is generally greater than the direct tensile strength and lower than the flexural strength (modulus of rupture).

   Splitting tensile strength is used in the design of structural light weight concrete members to evaluate the shear resistance provided by concrete and to determine the development length of the reinforcement.

   T=2P/(ld)

   This test method consists of applying a diametrical force along the length of a cylindrical concrete at a rate that is within a prescribed range until failure. This loading induces tensile stresses on the plane containing the applied load and

   relatively high compressive stresses in the area immediately around the applied load. Although we are applying a compressive load but due to Poissons effect, tension is produced and the specimen fails in tension. The maximum load sustained by the specimen is divided by appropriate geometrical factors to obtain the splitting tensile strength. Same procedure of mixing is repeated for the adding of rock gravel in bed level to optimum SCC mix. The 5cm rock gravel was settled down in moulds at bed level.

   TABLE 4 Split tensile test results

   Specimen	28 days (N/mm2)
   M40 mix (Without Rock fill)	3.56
   M40 mix (Rock filled 4cm)	3.90
   M40 mix (Rock filled 5cm)	4.25
   M40 mix (Rock filled 6.5cm)	4.95

   Fig 3 Bar chart showing split tensile test results

CONCLUSIONS