Self Compacting Concrete

INDEX CHAPTER 1 INTRODUCTION--------------------------------------------------------1.1

Background of self compacting concrete(SCC)----------------------------

1.2

Need for this research----------------------------------------------------------

1.3

Scope & objectives-------------------------------------------------------------

CHAPTER 2 LITERATURE REVIEW----------------------------------------------2.1

Development of SCC---------------------------------------------------------

2.2 Specifications-----------------------------------------------------------------2.2.1 Workability-------------------------------------------------------------------2.2.2 Durability---------------------------------------------------------------------2.2.3 Mechanical characteristics-------------------------------------------------2.3 Properties of hardened concrete ------------------------------------------2.3.1 Compressive, tensile & bond strength-----------------------------------2.3.2 Modulus of elasticity-------------------------------------------------------2.3.3 Shrinkage & creep----------------------------------------------------------2.3.4 freeze/thaw resistance------------------------------------------------------2.3.5 Water permeability---------------------------------------------------------2.3.6 Rapid chloride permeability-----------------------------------------------2.4 Test methods on SCC------------------------------------------------------2.4.1 Slump flow test & T50cm concrete--------------------------------------2.4.2 V funnel test & V funnel test at T5 mins--------------------------------2.4.3 L-box test--------------------------------------------------------------------2.4.4 U-box test-------------------------------------------------------------------2.4.5 Fill box test------------------------------------------------------------------

CHAPTER 3 MIX DESIGN OF SCC-------------------------------------------------3.1

General requirements in the mix design

-------------------------------

3.2

Mixing procedure------------------------------------------------------------

CHAPTER 4 TRANSPORTATION, CATING ON SITE & FORM SYSTEM 4.1

Transportation-----------------------------------------------------------------

4.2 casting on site----------------------------------------------------------------4.2.1 Planning----------------------------------------------------------------------4.2.2 Filling of formwork---------------------------------------------------------4.2.3 Finishing of formwork-----------------------------------------------------4.2.4 Curing------------------------------------------------------------------------4.3

Form system------------------------------------------------------------------

CHAPTER 5 ECONOMICS OF SCC -----------------------------------------------5.1

Advantages of SCC----------------------------------------------------------

5.2

SCC v/s NCC-----------------------------------------------------------------

CHAPTER 6 CASE STUDY------------------------------------------------------------CHAPTER 7 CONCLUSIONS---------------------------------------------------------BIBLIOGRAPHY--------------------------------------------------------

CHAPTER 1 INTRODUCTION 1.1

BACKGROUND OF SELF COMPACTING CONCRETE Self compacting concrete (SCC) represents one of the most significant

advances in concrete technology for decades. Inadequate homogeneity of the cast concrete due to poor compaction or segregation may drastically lower the performance of mature concrete in-situ. SCC has been developed to ensure adequate compaction and facilitate placement of concrete in structures with congested reinforcement and in restricted areas. SCC was developed first in Japan in the late 1980s to be mainly used for highly congested reinforced structures in seismic regions (Bouzoubaa and Lachemi, 2001). As the durability of concrete structures became an important issue in Japan, an adequate compaction by skilled labors was required to obtain durable concrete structures. This Requirement led to the development of SCC and its development was first reported in 1989 (Okamura and Ouchi, 1999). SCC can be described as a high performance material which flows under its own weight without requiring vibrators to achieve consolidation by complete filling of formworks even when access is hindered by narrow gaps between reinforcement bars. SCC can also be used in situations where it is difficult or impossible to use mechanical compaction for fresh concrete, such as underwater concreting, cast in-situ, pile foundations, machine bases and columns or walls with congested reinforcement. The high flow ability of SCC

makes it possible to fill the formwork without vibration. Since its inception, it has been widely used in large construction in Japan (Okamura and Ouchi, 2003). Recently, this concrete has gained wide use in many countries for different applications and structural configurations (Bouzoubaa and Lachemi, 2001). The method for achieving self-compactability involves not only high deformability of paste or mortar, but also resistance to segregation between coarse aggregate and mortar. Homogeneity of SCC is its ability to remain unsegregated during transport and placing. High flow ability and high segregation resistance of SCC are obtained by: 1. A larger quantity of fine particles, i.e., a limited coarse aggregate content. 2. A low water/powder ratio, (powder is defined as cement plus the filler such as fly ash, Silica fumes etc.) And 3. The use of super plasticizer Because of the addition of a high quantity of fine particles, the internal material Structure of SCC shows some resemblance with high performance concrete having self compactibility in fresh stage, no initial defects in early stage and protection against external factors after hardening. Due to the Lower content of coarse aggregate, however, there is some concern that: (1) SCC may have a lower modulus of elasticity, which may affect deformation characteristics of prestressed concrete members and (2) Creep & shrinkage will be higher, affecting prestress loss and long-term deflection.

Self compacting concrete can be produced using standard cements and additives. It consists mainly of cement, coarse and fine aggregates, and filler, such as fly ash, water, super plasticizer and stabilizer. The composition of SCC is similar to that of normal concrete but to attain self Flow ability, admixtures such as fly ash, glass filler, limestone powder, silica fume, Superpozzoluna, etc; with some super plasticizer is mixed. Fineness and spherical particle shape improves the workability of SCC. Three basic characteristics that are required to obtain SCC are: high deformability, restrained flow ability and a high resistance to segregation. High deformability is related to the capacity of the concrete to deform and spread freely in order to fill all the space in the formwork. It is usually a function of the form, size, and quantity of the aggregates, and the friction between the solid particles, which can be reduced by adding a high range water-reducing admixture (HRWR) to the mixture. Restrained flow ability represents how easily the concrete can flow around obstacles, such as reinforcement, and is related to the member geometry and the shape of the formwork. Segregation is usually related to the cohesiveness of the fresh concrete, which can be enhanced by adding a viscosity-modifying admixture (VMA) along with a HRWR, by reducing the free-water content, by increasing the volume of paste, or by some combination of these Constituents. Two general types of SCC can be obtained: (1)One with a small reduction in the coarse aggregates, containing a VMA, and (2) One with a significant reduction in the coarse aggregates without any VMA.

To produce SCC, the major work involves designing an appropriate mix Proportion and evaluating the properties of the concrete thus obtained. In practice, SCC in its fresh state shows high fluidity, self-compacting ability and segregation resistance, all of which contribute to reducing the risk of honey combing of concrete. With these good properties, the SCC produced can greatly improve the reliability & durability of the reinforced concrete structures. In addition, SCC shows good performance in compression and can fulfill other construction needs because its production has taken into consideration the requirements in the structural design.

1.2 NEED FOR THIS RESEARCH Despite its advantages as described in previous section, SCC has not gained much local acceptance though it has been promoted in the Middle East for the last five years. Awareness of SCC has spread across the world, prompted by concerns with poor consolidation and durability in case of conventionally vibrated Normal concrete. The reluctance in utilizing the advantages of SCC are, 1. Lack of research or published data pertaining to locally produced SCC, 2. The potential problems for the production of SCC, if any, with local marginal aggregates and the harsh environmental conditions prevailing in the region. Therefore, there is a need to conduct studies on SCC.

1.3 SCOPE AND OBJECTIVES The scope of this work was limited to the development of a suitable mix design to satisfy the requirements of SCC in the plastic stage using local aggregates and then to determine the strength and durability of such concrete exposed to thermal and moisture cycles. The general objective of this study was to conduct an exploratory work towards the development of a suitable SCC mix design and to evaluate the performance of the selected SCC mix under thermal and moisture variations. The specific objectives were as follows: 1. To design a suitable SCC mix utilizing local aggregates, and 2. To assess the strength development and durability of SCC exposed to thermal and moisture variations.

CHAPTER 2 LITERATURE REVIEW 2.1 DEVELOPMENT OF SELF COMPACTING CONCRETE The idea of a concrete mixture that can be consolidated into every corner of a formwork, purely by means of its own weight and without the need for vibration, was first considered in 1983 in Japan, when concrete durability, constructability & productivity became a major topic of interest in the country. During this period, there was a shortage of number of skilled workers in Japan which directly affected the quality of the concrete. In order to achieve acceptable concrete structures, proper consolidation is required to completely fill and equally distribute the mixture with minimum segregation. One solution to obtain acceptable concrete structures, independently of the quality of construction work, is the employment of SCC. The use of SCC can reduce labor requirements and noise pollution by eliminating the need of either internal or external vibration. Okamura proposed the use of SCC in 1986. Studies to develop SCC, including a fundamental study on the workability of concrete, were carried out by Ozawa and Maekawa at the University of Tokyo, and by 1988 the first practical prototypes of SCC were produced. By the early 1990’s Japan started to develop and use SCC and, as of 2000, the volume of SCC used for prefabricated products and ready-mixed concrete in Japan was over 520,000 yard3 (i.e. 400,000 m3).

SCC has been used successfully in a number of bridges, walls and tunnel linings in Europe. During the last three years, interest in SCC has grown in the United States, particularly within the precast concrete industry. SCC has been used in several commercial. Numerous research studies have been conducted recently with the objective of developing raw material requirements, mixture proportions, material requirements and characteristics, and test methods necessary to produce and test SCC. The latest studies related to SCC focused on improved reliability and Prediction of properties, production of a dense and uniform surface texture, improved durability and both high and early strength permitting faster construction and increased productivity. 2.2 Specifications 2.2.1 Workability A good SCC shall normally reach a slump flow value exceeding 60cm without segregation. • If required SCC shall remain flow able & self compacting for at least 90 minutes. • If required SCC shall be pumpable for at least 90 minutes & through pipes with a length of at least 100m. 2.2.2 Durability • Should have freeze/thaw resistance • No increased risk of thermal cracks compared with traditional vibrated concrete.

• Target values & acceptable ranges for the slump flow have to be design when the mix design is decided. The evidence in hand & data from other sources suggested that the durability performance of SCC is likely to be equal or better than that of traditional vibrated concrete. 2.2.3 Mechanical Characteristics • Characteristics compressive strength at 28 days shall be 25-60 MPa. • Early age compressive strength shall be 5-20MPa at 12-15 hours. (equivalent age at 20°C) • Normal” creep & shrinkage.

2.3 PROPERTIES OF HARDENED SCC 2.3.1 Compressive, Tensile, and Bond Strength SCC with a compressive strength around 60 MPa can easily be achieved. The strength could be further improved by using fly ash as filler. The characteristic compressive and tensile strengths have been reported to be Around 60 MPa & 5 MPa, respectively & 28-days compressive strength values ranging from 31 to 52 MPa. Compressive strength was in the range of 28 and 47 MPa & a compressive strength of up to 80 MPa with a low permeability, good freeze-thaw resistance, and low drying shrinkage. SCC mixes with a high volume of cement – limestone filler paste can develop higher or lower 28-day compressive strength, compared to those of vibrated

concrete with the same water/cementitious material ratio and cement content, but without filler. It appears that the strength characteristics of the SCC are related to the fineness and grading of the limestone filler used. SCC with water/cementitious material ratios ranging from 0.35 to 0.45, a mass proportion of fine and coarse aggregates of 50:50 with cement replacement of 40%, 50% & 60% by Class F fly ash and cementitious materials content of 400 kg/m3 being kept constant, obtained good results for compressive strength ranging from 26 to 48 MPa. The bond behavior of SCC was found to be better than that of normally vibrated concrete. The higher bond strength was attributed to the superior interlocking of aggregates due to the uniform distribution of aggregates over the full cross section and higher volume of cement-binder matrix. 2.3.2 Modulus of Elasticity Modulus of elasticity of SCC & that of a normally vibrated concrete, produced from the same raw materials, have been found to be almost identical. Although there is a higher paste matrix share in SCC, the elasticity remains unchanged due to the denser packing of the particles. The modulus of elasticity of concrete increases with an increase in the quantity of aggregate of high rigidity whereas it decreases with increasing cement paste content & porosity. A relatively small modulus of elasticity can be expected, because of the high content of ultra fines and additives as dominating factors and, accordingly, minor occurrence of coarse and stiff aggregates at SCC.

The modulus of elasticity of SCC can be up to 20% lower compared with normal vibrated concrete having same compressive 34 strength and made of same aggregates reported an average modulus of elasticity of SCC to be 16% lower than that of normal vibrated conventional concrete for an identical compressive strength. Results available indicate that the relationships between the static modulus of elasticity (E) and compressive strength were similar for SCC and normally vibrated concrete. Average 28-days modulus of elasticity of SCC has been reported to be 30 GPa corresponding to average 28-days cube strength of 55.41 MPa. 2.3.3 Shrinkage & Creep Shrinkage and creep of the SCC mixtures have not been found to be greater than those of traditional vibrated concrete. 0.03% for mixes with cement tested at 14 days, 0.03% to 0.04% for mixes with slag cement tested at 28 days, and 0.04 to 0.045% for mixes with calcined shale cement tested at 28 days. Shrinkage and creep of SCC coincided well with the corresponding Properties of normal concrete when the strength was held constant. The shrinkage and creep rates of SCC have been found to be approximately 30% higher at an identical compressive strength; this is because of the high amount of paste. Since SCC is rich in powder content and poor in the coarse aggregate fraction, addition of fiber will be effective in counteracting drying shrinkage.

2.3.4 Freeze/thaw resistance This property was assessed by loss of ultrasonic pulse velocity(UPV) after daily cycles of 18 hours at -30°C & 6 hours at room temperature . No significant loss of UPV has been observed after 150 cycles for the SCC or higher strength concrete. The lower strength SCC ix has performed less well than the reference in this freeze/thaw regime. (Note: None of the concrete was air entrained.) 2.3.5 Water Permeability SCC with high strength and low permeability can easily be produced. The permeability of SCC significantly lower as compared to that of normally vibrated concretes of the same strength grade have reported a water permeability value of 5 mm for SCC against 10 mm for normal vibrated concrete. The water permeability test, which is most commonly used to evaluate the permeability of concrete. This test is useful in evaluating the relative Performance of concrete made with varying mix proportions & incorporating admixtures.. Permeability tests, particularly those involving water penetration & chloride permeability, are increasingly used to test concrete to evaluate its conformance with these specifications, particularly for concrete exposed to aggressive conditions. 2.3.6 Rapid chloride permeability

Rapid chloride permeability of concrete is determined using a standard test method for electrical indication of concrete’s ability to resist chloride ion penetration. The rapid chloride permeability test evaluates the performance of various cementitious materials based on the accelerated diffusion of chloride ions under the application of an external electric field. For SCC against 1970 coulombs for normal vibrated concrete, obtained through the rapid chloride permeability test. 2.4 Test methods on SCC It is important to appreciate that the test method for SCC has yet been standardized, & the test described are not yet perfect or definitive. The method presented here are descriptions rather than fully detailed procedures. They are mainly methods which have been devised specifically for SCC. Existing rheological test procedure have not considered here, though the relationship between the results of these tests & the rheological characteristics of the concrete is likely to figure highly in future work, including standardization work. In considering these tests there are number of points which should be taken into account: • There is no clear relation between test results & performance on site. • There is little precise data, therefore no clear guidance on compliance limits. A concrete mix can only be classified as SCC if the requirements for all the following three workability properties are fulfilled. 1. Filling ability, 2. Passing ability, &

3. Segregation resistance. Filling ability: 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. Passing ability: 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. Segregation resistance: The SCC must meet the filling ability and passing ability with uniform composition throughout the process of transport and placing. The test methods to determine the workability properties of SCC are described as follows: 2.4.1 Slump flow test and T50cm test: Introduction: The slump flow test is used assess the horizontal free flow of in the absence of obstructions. It was first developed in Japan for use in assessment of underwater concrete. The test method is based on the test method for determining the slump .T diameter of the concrete circle is a measure for the filling ability of the concrete. 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 booking, but may give some indication of resistance to segregation.

It can

be argued that the completely free flow, unrestrained by any foundries, is not representative of what happens in concrete construction, but the test can be profitably be used to assess the consistency of supply of supply of readymixed concrete to a site from load to load. Equipment: The apparatus is show in figure; • Mould in the shape of a truncated cone with the internal dimensions 200 mm diameter at the base, 100mm diameter at the top and a height of 300 mm. • Base plate of a stiff none absorbing material, at least 700mm square, marked with a circle marking the central location for the slump cone, and a further concentric circle of 500mm diameter • Trowel • Scoop • Ruler • Stopwatch(optional)

Accessories for

Flow cone

Flow table

Slump test

Fig. 2.4.2 Slump flow test and T50cm test

Procedure: About 6 liter of concrete is needed to perform the test, sampled normally. Moisten the base plate and inside of slump cone, place base plate on level stable ground and the slump cone centrally on the base plate and hold down firmly. Fill the cone with the scoop. Do not tamp, simply strike off the concrete level with the top of the cone with the trowel. Remove any surplus concrete from around the base of the cone. Raise the cone vertically and allow the concrete to flow out freely. Simultaneously, start the stopwatch and record the time taken for the concrete to reach the 00mm spread circle (This is the T50 time).floatable test, might be appropriate. The T50 time is secondary indication of flow. A lower time indicates greater flow ability. The Brite EuRam research suggested that a time of 3-7 seconds is acceptable for civil engineering applications, and 2-5 seconds for housing applications. In case of severe segregation most coarse aggregate will remain in the centre of the pool of concrete and mortar and cement paste at the concrete periphery. In case of minor segregation a border of mortar without coarse aggregate can occur at the edge of the pool of concrete. If none of these phenomena appear it is no assurance that segregation will not occur since this is a time related aspect that can occur after a longer period.

2.4.2 V funnel test and V funnel test at T 5 minutes Introduction: The equipment consists of a v shaped funnel as, show in Fig. An alternative type of V-funnel, the O funnel, with circular. The test was developed in Japan and used by Ozawa et al. The equipment consists of Vshaped funnel section is also used in Japan. The described V-funnel test is used to determine the filling ability (flow ability) of the concrete with a maximum aggregate size of 20mm. The funnel is filled with about 12 liter 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 increases significantly. Assessment of test: Though the test is designed to measure flow ability, 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 interparticle 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. Equipment: • V-funnel • Bucket (±12 liter) • Trowel • Scoop

•

Stopwatch

Fig 2.4.2 V Funnel test Apparatus Procedure flow time: About 12 liter of concrete is needed to perform the test, sampled normally. Set the V-funnel on firm ground. Moisten the inside surface of the funnel. Keep the trap door to allow any surplus water to drain. Close the trap door and place a bucket underneath. Fill the apparatus completely with the concrete without compacting or tamping; simply strike off the concrete level with the top with the trowel. Open within 10 sec after filling the trap door and allow the concrete to flow out under gravity. Start the stop watch when the trap door is opened, and record the time for the complete discharge (the flow time). This is taken to be when light is seen from above through the funnel. The whole test has to be

performed within 5 minutes. Procedure flow time at T5 minutes: Do not clean or moisten the inside surface of the funnel gain. Close the trap door and refill the V-funnel immediately after measuring the flow time. Place a bucket underneath. Fill the apparatus completely with concrete without compacting or tapping, simply strike off the concrete level with the top with the trowel. Open the trap door 5 minutes after the second fill of the funnel and allow the concrete to flow out under gravity. Simultaneously start the stop watch when the trap door is opened and record the time discharge to complete flow (the flow time at T5 minutes). This is to be taken when light is seen from above through the funnel.

Interpretation of result: This test measures the ease of flow of concrete, shorter flow time indicates greater flow ability. For SCC a flow time of 10 seconds is considered appropriate. The inverted cone shape restricts the flow, and prolonged flow times may give some indication of the susceptibility of the mix to blocking. After 5 minutes of settling, segregation of concrete will show a less continuous flow with an increase in flow time.

2.4.3 L Box Test Introduction: This test is based on a Japanese design for under water concrete, has been described by Peterson. The test assesses the flow of the concrete and also the extent to which it is subjected to blocking by reinforcement. The apparatus is shown in the figure. The apparatus consist of rectangular section box in the shape of an ‘L’, with a vertical and horizontal section, separated by a movable gate, in front of which vertical length of reinforcement bar are fitted. The vertical section is filled with concrete, and then the gate lifted to let the concrete flow into the horizontal section. When the flow has stopped, the height of the concrete at the end of the horizontal section is expressed as a

proportion of that remaining in the vertical section. It indicates the slope of the concrete when at rest. This is an indication passing ability, or the degree to which the passage of concrete through the bars is restricted. The horizontal section of the box can be marked at 200mm and 400mm from the gate and the times taken to reach these points measured. These are known as the T20 and T40 times and are an indication for the filling ability. The section of bar con be of different diameters and are spaced at different intervals, in accordance with normal reinforcement considerations, 3x the maximum aggregate size might be appropriate. The bar can principally be set at any spacing to impose a more or less severe test of the passing ability of the concrete. Assessment of test: This is a widely used test, suitable for laboratory and perhaps site use. It asses filling and passing ability of SCC, and serious lack of stability (segregation) can be detected visually. Segregation may also be detected by subsequently sawing and inspecting sections of the concrete in the horizontal section. Unfortunately there is no arrangement t on materials or dimensions or reinforcing bar arrangement, so it is difficult to compare test results. There is no evidence of what effect the wall of the apparatus and the consequent ‘wall effect’ might have on the concrete flow, but this arrangement does, to some extent, replicate what happens to concrete on site when it is confined within formwork. Two operators are required if times are measured, and a degree of operator error is inevitable. Equipment:

• L box of a stiff non absorbing material • Trowel • Scoop • Stopwatch

Fig.2.4.3 L Box test Apparatus Procedure: About 14 liter of concrete needed to perform the test, sampled normally. Set the apparatus level on firm ground, ensure that the sliding gate can open freely and then close it. Moisten the inside surface of the apparatus, remove any surplus water, fill the vertical section of the apparatus with the concrete sample. Leave it stand for 1 minute. Lift the sliding gate and allow the concrete to flow out into the horizontal section. Simultaneously, start the stopwatch and record the time for the concrete to reach the concrete 200 and 400 marks. When the concrete stops flowing, the distances ‘H1’ and ‘H2’ are measured. Calculate H2/H1, the blocking ratio. The whole has tom performed within 5 minutes.

Interpretation of the result: If the concrete flows as freely as water, at rest it will be horizontal, so H2/H1=1. Therefore the nearest this test value, the ‘blocking ratio’, is unity, the better the flow of concrete. The EU research team suggested a minimum acceptable value of 0.8. T20 and T40 time can give some indication of ease of flow, but no suitable values have been generally agreed. Obvious blocking of coarse aggregate behind the reinforcement bars can be detected visually.

2.4.4 U box test method Introduction: The test was developed by the Technology Research Centre of the Taisei Corporation in Japan. Some time the apparatus is called a “box shaped” test. The test is used to measure the filing ability of self compacting concrete. The apparatus consists of a vessel that is divided by a middle wall into two compartments; an opening with a sliding gate is fitted between the two sections. Reinforcing bar with nominal diameter of 134 mm are installed at the gate with centre to centre spacing of 50 mm. this create a clear spacing of 35 mm between bars. The left hand section is filled with about 20 liter of concrete then the gate is lifted and the concrete flows upwards into the other

section. The height of the concrete in both sections is measured. Assessment of test: This is a simple test to conduct, but the equipment may be difficult to construct. It provides a good direct assessment of filling ability-this is literally what the concrete has to do- modified by an unmeasured requirement for passing ability. The 35 mm gap between the sections of reinforcement may be considered too close. The question remains open of what filling height less than 30cm is still acceptable. Equipment: • U box of a stiff non absorbing material • Scoop • Trowel • Stopwatch

Fig 2.4.4 U box test Apparatus Procedure: About 20 liter of concrete is needed to perform the test, sampled normally. Set the apparatus level on firm ground, ensure that the sliding gate can open freely and then close it. Moisten the inside surface of the apparatus, remove any surplus water, fill the vertical section of the apparatus with the concrete sample. Leave it stand for 1 minute. Lift the sliding gate and allow the concrete to flow out into the other compartment. After the concrete has come to rest, measure the height of the concrete in the compartment that has been filled, in two places and calculate the mean (H1). Measure also the height in

the other equipment (H2). Calculate H1-H2, the filling height. The whole test has to be performed within 5 minutes. Interpretation of the result: If the concrete flows as freely as water, at rest it will be horizontal, so H1H2=0. Therefore the nearest this test value, the ‘filling height’, is to zero, the better the flow and passing ability of the concrete.

2.4.5 Fill box test method Introduction: This test is also known as ‘Kajima test’. The test is used to measure the filling ability of self compacting concrete with a maximum aggregate size of 20 mm. the apparatus consists of a container (transparent) with a flat and smooth surface. In the container are 35 obstacles are made of PVC with a diameter of 20mm and a distance centre to centre of 50mm, see figure. At the top side is a put filling pipe (diameter 100mm height 500mm) with a funnel (height 100mm). The container is filled with concrete through this filling pipe

and difference in height between two sides of the container is a measure for the filling ability. Assessment of test: This is a test that is difficult to perform on site due to the complex structure of the apparatus and large weight of the concrete. It gives a good impression of the self compacting characteristics of the concrete. Even a concrete mix with a high filling ability will perform poorly if the passing ability and segregation resistance are poor. Equipment • Fill box of a stiff non absorbing material • Scoop 1.5 to 2 liter • Ruler • Stopwatch

Fig.2.4.5 (b) Detail dimensions & c/s of fill box

Fig.2.4.5 (b) Detail of fill box empty & filled with concrete

Procedure:

About 45 liter of concrete is needed to perform the test, sampled normally. Set the apparatus level on firm ground, ensure that the sliding gate can open freely and then close it. Moisten the inside surface of the apparatus, remove any surplus water, fill the apparatus with the concrete sample. Fill the container by adding each 5 seconds one scoop with 1.5 to 2 liters of fresh concrete into the funnel until the concrete has just covered the first top obstacle. Measure after the concrete has come to rest, the height at the side at which the container has filled on two places and calculate the average (H1). Do this also on opposite side (H2). Calculate the average filling percentage: average filling percentage F= {(H1+H2)/2*H1}*100%. The whole has to be performed within 8 minutes. Interpretation of the result: If the concrete flows as freely as water, at rest it will be horizontal, so average filling percentage = 100%. Therefore the nearest this test value, the filling height’, is to be 100%, the better self compacting characteristics of the concrete.

CHAPTER 3

MIX DESIGN OF SCC Before any SCC is produced at a concrete plant and used at construction site the mix has to be designed and tested. During this evaluation the equipments and the local Materials used at the plants have to be tested to find new concrete mixes with the right mixing sequences and mixing times valid for that plant and material used and also suitable for the element to be cast. Various kinds of fillers can result in different strength, shrinkage and creep but shrinkage and creep will usually not be higher than for traditional vibrated concrete. A flow-chart describing the procedure for design of SCC mix is shown in Figure 2 below,

Figure 2: SCC mix design procedure 3.1 General Requirements in the mix design

A high volume of paste: the friction between the aggregate limits the spreading and the filling ability of SCC. This is the why SCC contains a high volume of paste (cement + additions + efficient water + air), typically 330 to 400 l/m³, the role of which is to maintain aggregate separation. A high volume of the particles (<80µm): In order to ensure sufficient workability while limiting the risk of segregation or bleeding, SCC contains a large amount of fine particles (around 500 kg/m³). Nevertheless, in order to avoid excessive heat generation, the Portland cement is generally partially replaced by mineral admixtures like fly ash (cement should not be used as a filler). The nature and the amount of filler added are chosen in order to comply with the strength & durability requirements. A high dosage of super plasticizer: Super plasticizers are introduced in SCC to obtain the fluidity. Nevertheless a high dosage near the saturation amount can increases the proneness of the concrete to segregate. The possible use of viscosity agent (water retainer): these products are generally cellulose derivatives, polysaccharides or colloidal suspensions. These products have the same role as the fine particles, minimizing bleeding and coarse aggregate segregation by thickening the paste and retaining the water in the skeleton. The introduction of such products in SCC seems to be justified in the case of SCC with the high water to binder ratio (for e.g. residential building). On the other hand, they may be less useful for high performance SCC (strength higher than 50 MPa) with low water to binder ratio. For intermediate SCC, the introduction of viscosity agent has to be

studied for each case. Viscosity agents are assumed to make SCC less sensitive to water variations in water content of aggregates occurring in concrete plants. Because of he small quantities of viscosity agents required, however it may be difficult to achieve the accuracy of dosage. A low volume of coarse aggregate: it is possible to use natural rounded,

semi crushed or crushed aggregate to produce SCC. Nevertheless, as the coarse aggregate plays an important role on the passing ability of SCC in congested areas, the volume has to be limited. On the other hand the use of coarse aggregate allows optimizing the packing density of the skeleton of the concrete & reduction of the paste volume needed for the target workability. Generally speaking, the maximum aggregate size (Dmax) is between 10mm &20mm. the passing ability decreases when Dmax increases, which leads to decrease of the coarse aggregate content. The choice of a higher Dmax is thus possible but is only justified with low reinforcement content. Admixtures added to SCC can have a retarding effect on the strength and the temperature development in the fresh concrete, & this will have to be borne in mind in the construction process. Suppliers of admixture can produce various admixtures suitable for different weather conditions & temperatures. 3.2 Mixing procedure

The coarse and fine aggregate contents are fixed so that self compatibility can be achieved easily by adjusting the water/powder ratio and super plasticizer dosage only. Procedure: The following sequence is followed • Determine the desired air content • Determine the coarse aggregate volume • Determine the sand content • Determine the paste composition • Determine the optimum water to powder ratio & super plasticizer dosage in mortar • Finally the concrete properties are assessed by standard test (Explained in section 2.4) Air content: Generally air content may be assumed to be 2%. In case of freeze/thaw condition in cold weather concreting higher percent of air content may be specified. Determination of coarse aggregate volume: Coarse aggregate volume is defined by bulk density. Generally coarse aggregate (D>4.75) should be between 50% & 60%. Optimum coarse aggregate content depends on the following parameters. • The lower the maximum aggregate size, the higher the proportion.

• The rounded aggregate can be used at higher percentage then crushed aggregates. Determination of sand content: Sand, in the context of mix design procedure is defined as all particles bigger than 125 microns & smaller than 4.75mm. Sand content is defined by bulk density. The optimum volume content of sand in the mortar varies between 40-50% depending on the past properties. Design of paste composition: Initially the water/powder ratio for zero flow (ß) is determined in the paste, with chosen proportion of cement & additions. Flow cone test with water/powder ratio by volume are performed with selected powder composition. Fig. 2.1 shows the typical results. The point of intersection with “Y” axis is the ß value. These ß value is used mainly for quality control of water demand for new batches of cement & fillers.

Fig.3.2 Determination of water/powder ratio ß for zero slump flow

Determination of optimum volumetric water/powder ratio & super plasticizer dosage in mortar: Test with flow cone & V-funnel for mortar are performed at varying water/powder ratio in the range of (0.8 to 0.9) ß & dosage of super plasticizer is used to balance the rheology of the paste. The volume content of the sand in mortar remains the same as determined above. The target values are slump flow of 24 to 26 cm & V-funnel time of 7 to 11 seconds. At target slump flow, where V-funnel time is lower than 7 secs, then decrease the water/powder ratio. For largest slump flow & V-funnel time in excess of 11 seconds water/powder ratio should be increased. If these criteria cannot be fulfilled, then the particular combination of material is inadequate. One can also change the type of super plasticizer. Another alternative is a new additive, and as a last resort is to change the cement.

CHAPTER 4 TRANSPORTATION, CASTING ON SITE & FORM SYSTEM 4.1 Transportation SCC can be delivered either by truck mixer or truck agitator. The mixing/agitating bowl should be free from remains of the previously delivered concrete and remains of wash-out water, and it should not be dry. Truck mixers should be distinguished from truck agitators. In simple words, truck mixers are able to adequately produce, deliver, and discharge concrete while truck agitators can not adequately produce concrete. Often properties of SCC need to be adjusted on the job site and for some SCC producers this is a part of production/delivery process. At such circumstances truck agitators shall not be used. Great care should be taken if SCC is to be delivered by tip trucks due to the risk of static segregation. The limitations to the delivery load size would be only dictated by the road conditions, i.e. driving uphill. SCC can be safely transported over the reasonably hilly roads if the load size of SCC is not exceeding 80% of the full capacity. • But before the drum actually delivers the SCC at site it has to rotate at full speed (10-20 RPM) • Care must be taken for long haul delivery sites. • The driver must not add admixtures or any kind of fibers on his own.

• However if the mix is too hard super plasticizer can be added on site at the time of delivery by the driver after obeying the note of instructions given to him. • Also this has to be handed over to the site engineers about the report of how the SCC has been handled before, during the haul duration n the expected handling after the mix has been delivered. • The addition of water has to be avoided in order to avoid segregation. The addition of water is a very usual n cheap practice to make the mix workable. • A Slump test can be worked out at the site to check the workability if the mix, also to check that there is no segregation. • In addition to the basic information provided, the following details will add to the perfection of the work carried out 1. Slump Flow – target value and acceptance range 2. Production time (Time when it was produced) 3. Remarks if any admixture that shall be added at site

4.2 Casting on site It is divided into 4 following sections, 4.2.1 Planning 4.2.2 Filling of formwork 4.2.3 Finishing 4.2.4 Curing 4.2.1 Planning: The process of casting SCC can be mechanized to a great extent. Increased productivity, lower cost and improved working environment is achieved. A minimum of manual interaction in the process is however necessary. Based on formwork configuration, reinforcement, temperature, casting equipment,

casting speed etc., the persons in charge of the concrete supply and the form filling respectively have to plan and jointly agree on SCC workability data, including accuracy, open time, casting speed etc. In more complex industrialized casting operations, the planning of flow of concrete can be computer modeled in order to optimize the rheological material data to the specific formwork, the reinforcement configuration and the sequence and methods of casting. The planning also includes agreement on the quality assurance procedure, test methods, frequency of test as well as of actions taken as results of tests. The planning should also address the corrections of the mix that might be done at the casting site through extra dosage of plasticizer. Even if there will always be options of buying SCC off the shelf as standard products, the strongest benefits and highest profits will come from optimizing the fresh concrete as an integral approach in an industrialized process designed for the specific situation at hand. Even if there is a significant reduction in the needed skill for the actual casting when SCC is applied, the need for skills in planning, preparation and quality assurance is raised. 4.2.2 Filling of Formwork: SCC is a liquid suspension following the rules of fluid mechanics while vibrated concrete is a granular mass requiring vibration to be compacted. SCC is well suited for pumping and can be fed through valves under pressure into vertical formwork. This technique is frequently used when casting complex enclosed volumes where release from above is not possible or no limited entrance to the interior of the form work is possible, nor vibrating it by hand tools. Pumping SCC into the form work from underneath has proven to be

beneficial when high demands of aesthetics are of importance. The problem with pores and pot-holes also tends to be less when the concrete has been fed from underneath through valves. Experience from pressurized castings of 30+ vertical meters exists from practice. If the pipe-based feeding system used includes furcating, the concrete flow chooses the easiest way through the piping system. This may result in parts of the concrete not moving, thereby preventing the concrete to fill the form work uniform and symmetrically Vertical formwork can also be cast by dropping from above using pumps or crane skips. Experience from dropping heights of 8 meters exists but 1-3 meters will be more common. Flat and shallow formwork such as slab and decks are most often filled from above even if in certain situations, e.g. in industrial production, casting through valves by pumping might be an attractive option. For flat and shallow structures the dropping height is about 0.5-0.8 meters. High dropping heights require a stable mix to counteract the risk of segregation and damage of the air pore system. To release the SCC from a pump hose submerged some decimeters under the concrete upper surface tends to reduce the coarser air pore structure. The results are not fully consistent depending probably on the fact that the specific workability features of used SCC have differed. The layer thickness should be kept as thin as possible, in order to prevent larger air bubbles to get trapped in the concrete or at the form surface. It is also beneficial to let the concrete flow horizontally some distance (how long is depending on the mix and local circumstances as form work geometry, denseness of reinforcement etc.). On the other hand, the concrete has to be prevented to flow a very long distance in the form. If this is not taken care of,

separation at the front might occur. This is the reason why the concrete should be released at fixed distances along the form work. These points of release should be at a maximum distance from each other of about 5-8 meters depending on the geometry of the form and density of the reinforcement and other obstacles. Due to the high amount of fines, SCC is suitable for pumping. The usually high viscosity of SCC may require a slower pumping rate, in order to avoid high pressure built up in the piping system. High pressure may cause aggregate separation and pump stops. A possible negative effect of too high a feeding rate is a significant drop in slump flow (and mobility) after the pump. The openings should be large enough to allow the pump hose to pass inside the form in an inclined position and when the concrete level has reached the opening (openings) the pump hose (hoses) is pulled out and moved to the next opening above. The lower openings are thereafter closed. Horizontal distances of 4-6 meters between the openings and correspondingly 2-3 meters in vertical direction, have been proven successful. Practical experiences have shown the importance of operating with several valves or pipes, in order to fill the formwork evenly and symmetrically, and to prevent the concrete from traveling a long horizontal distance in the formwork. The most common procedure is to pump the concrete through two or more valves or pipes simultaneously. It is important to visually observe the flowing concrete in the formwork. Especially important is to notice its flow around obstacles, reinforcement bars and other objects in the form. Even in sections with dense reinforcement, the

surface of the flowing concrete should be fairly even, without any significant differences between the levels of the upper surfaces that might indicate blocking. Coarse aggregate should be visible on the upper surfaces. Foam on the upper surface is likely to indicate segregation. It is important to plan the casting sequence. Layers of fresh SCC should be given some time for the release of air through the surface while on the other hand following layers should not come too late, which might make an integration of the layers difficult. SCC is not necessarily self-leveling. SCC can be so designed that it can be built up in a slope of a few degrees from the release point. This is an important possibility when casting e.g. a bridge slab requiring a limited slope from the centre to the edges. 4.2.3 Finishing: Finishing operations can be more difficult for SCC due to the thixotrophy, sometimes sticky behavior. The absence of bleeding makes it even more difficult and the finishing operations should be related to the setting time of the mix in actual conditions. It is advisable to perform an appropriate field trial in advance to improve planning and timing of finishing. The characteristics of the SCC mix, and the skill and timing of the finishers during placement affect the quality of the surface of slab cast. The general experience seems to be that conventional tools and ways to finish the upper surface can be used working with SCC but sometimes finishing tools with other surface materials are used. It is wise to expect this operation to take a little longer in comparison with the finishing of conventional vibrated concrete.

4.2.4 Curing: SCC mixes are characterized by a moderate to higher amount of fines in the formulation, including various combinations of powders such as Portland cement, limestone filler, fly-ash or ground granulated blast furnace slag. Thus, there might be very little or no bleeding and the concrete will sometimes be more sensitive to plastic shrinkage cracking. The tendency of plastic shrinkage increases with the increase in the volume of fines. This situation is sometimes more complicated if the setting time is delayed because of the admixture effect, and the concrete remains many hours in the fresh state. Curing to counteract longer term shrinkage is to be handled like what is done for vibrated concrete. It should be observed that due to a lower permeability of SCC, the drying rate and following from that also the shrinkage rate might be slower. 4.3 Form system

Fig. 4.3.1

SCC Definition: Self Compacting Concrete is an innovative concrete that does not require vibration for placing and compaction. It is able to flow under its own weight, completely filling formwork and achieving full compaction, even in the presence of congested reinforcement. The hardened concrete is dense, homogeneous and has the same engineering properties and durability as traditional vibrated concrete. Formwork: • When a contractor opts to use SCC on a project there will be an immediate impact on the type of formwork system that can be used. This is primarily due to the higher pressures that will occur during the casting period. • If SCC is to be utilized this will generally negate the option for the contractor to use traditional hand-built timber and plywood columns or walls as is sometimes still seen on sites • Due to the considerably higher design pressures created when SCC, as opposed to traditional concrete, is poured into vertical forms, the contractor is advised to use high quality system formwork • SCC requires a very accurate assembly of the formwork, with no openings left and 100% tightness to avoid possible leaks • SCC easily flows around obstructions with no vibration needed.

Fig. 4.3.2 • Formwork should be designed for full liquid head. This means that there will be another 220 kg of pressure for each meter of height of the forms. This is a danger for SCC since it places so rapidly and can develop pressures leading to blowouts. • Steel and plywood are used as formwork materials for SCC. • In winters or in colder areas there is a need to maintain the temperature of the SCC. In such cases the temperature is maintained by providing insulations to the formwork itself before actually pouring the concrete into the formwork. •

Due to the cohesiveness of SCC, the formwork does not need to be tighter

than that for conventional vibrated concrete.

CHAPTER 5 ECONOMICS OF SCC Savings in labor costs might offset the increased cost related to the use of more cement and super plasticizer, and the mineral admixtures, such as pulverized fuel ash (PFA), ground granulated blast furnace slag (GGBS) or lime stone powder (LSP), could increase the fluidity of the concrete, without any increase in the cost. These supplementary cementing materials also enhance the rheological parameters and reduce the risk of cracking due to the decreased heat of hydration, and therefore, improve the durability 5.1 Advantages of SCC Why SCC should used? Self compacting concrete that is able to flow under its own weight and completely fill the form work, even in the presence of dense reinforcement, without the need of any vibration, whilst maintaining homogeneity. Financial & Environmental Benefits • Minimal labor involved • Rapid construction without mechanical vibration • Low noise-level in the plants and construction sites

• Overcome problems arise with vibration. • Safer working environment • Accelerated project schedules • Reduced equipment wear • Allows for innovative architectural features • Greater Range of Precast Productions Engineering Benefits • Better surface finishes • Easier placing • Improved durability • Greater freedom in design • Thinner concrete sections • Ease of filling restricted sections and hard to reach areas • Encapsulate congested reinforcement • Allows for innovative architectural features • Homogeneous and uniform concrete • Better reinforcement bonding

5.3

SCC v/s NCC • One of the practical advantages of SCC over NCC is its lower viscosity and, thus, its greater flow rate when pumped. As a consequence, the pumping pressure is lower, reducing wear and tear

on pumps and the need for cranes to deliver concrete in buckets at the job site. • This also reduces significantly the construction period and the amount of personal necessary to accomplish the same amount of work. • SCC gives designers and contractors a solution for using concrete in special problems, like casting of complicated shapes of elements, heavily congestion of reinforcement, or casting of areas with difficult access. Compaction of NCC is tedious and costly in such congested structures. Also the use of vibrators is time consuming. • In all these cases, the use of NCC compromises the durability of the structure due to poor consolidation. SCC is also called a “healthy” and “silent” concrete as it does not requires external or internal vibration during and after pouring to achieve proper consolidation. • Where the mechanical vibration is a noisy and demanding task for the members of the casting team the reduction or total elimination of this assignment diminishes the environmental impact as well as the overall cost.

CHAPTER 6 CASE STUDY

CASE STUDY Use of self compacting concrete for domes in Rajasthan Atomic Power Project. (Carried out by HINDUSTAN CONSTRUCTION COMPANY LIIMITED) The following trials were conducted: TRIALS OF SCC AT RPP – M45 GRADE Ingredients (kg/m³)

Present Mix

Proposed SCC Mix Cement

400

Fly ash

0

300

200(40%) W/CM

0.37

0.36

Water

148

180

20mm

526

290

10mm

526

436

Coarse Sand

479

331

Fine Sand

305

539

Super plasticiser

8.5

4.0

VMA

0

0.75

Retarder

0

0.5

Present Mix Proposed SCC Mix Fresh Concrete Properties Conforming to criterion given in EFNARC

Hardened Concrete Properties 3 days

32MPa

26MPa

7 days

45MPa

38 MPa

28 days

60MPa

57 MPa

56 days

62 MPa

64 MPa

Trials of SCC AT RAPP-M25 Ingredients (kg/m³)

Proposed SCC Mix

Present Mix

Cement

320

225

Fly ash

0

225

W/CM

0.5

0.4

Water

160

180

20mm

511

250

10mm

219

374

Natural sand

627

426

Crushed sand

5.2

562

Superplasticiser

-

3.8

VMA

-

0.45

(40%)

Retarder

0.45

Present Mix Proposed SCC Mix Fresh Concrete properties Conforming to criterion given in EFNARC Hardened Concrete Properties 3 Days

-

11.5

7 Days

31

19.5

28 Days

43

35.0

56 Days

41.5

41.5

USE OF SELF COMPACTING CONCRETE FOR PIERS IN BANDRA WORLI SEA LINK PROJECT TRIALS OF SCC AT BWSL – M60 Ingredients (kg/m³)

PROPOSED SCC

Mix Cement

345

Fly ash

150

Micro silica

49.5

W/Cm

0.30

Water

165

Coarse aggregate

540

Fine aggregate

1160

Super plasticizer

5.5

Retarder

1.0

VMA

2.0

PROPOSED Mix Fresh Concrete Properties Conforming to criterion given in EFNARC Hardened concrete properties 3 days

34.3

7 days

52.8

28 days

71.8

Permeability (DIN)

0

TRIALS CARRIED OUT AT RMC INDIA LMT. FOR SCC

SCC

TRIALS FOR SCC (ELKEM)

M35

TM NO. 2437 OPC 225 (Coramandal) PFA (Dirk 63) 225 Micro silica 35 (Elkem) Total Cemetitious 485 10mm (Elkem) 634 SAND (Elkem) 1009 TOTAL AGG 1643 % Fines 61.4 HWRA 1.5% (supaplast) WATER 176 DPD 2304 APD 2339 F W/C RATIO 0.33 FLOW (mm) 700 STR – 3DAY 10.6 7 DAYS 20.33/2367 28 DAYS 40.54 28 DAYS 41.36 AVE.28 DAYS 40.95

M35

M35

M35 (With RMC aggs) 2440 320

2438 280

2439 445

165 35

0 35

180 0

480 634 1009 1643 61.4 1.2%

480 634 1009 1643 61.4 1%

500 634 1009 1643 61.4 1%

176 2299 2316 0.33 700 11.21 22.41/2331 44.18 42.26 43.22

175 2298 2252 0.33 700 22.09 27.94/2291 43.37 46.17 44.77

227 N.T. 0.33 600 20.93* 26.86/2330 46.47 47.46 46.965

*: 4 day strength

CHAPTER 7 CONCLUSIONS

SCC mixes requires superior quality material, admixtures, methods & supervisions. SCC eliminates the requirement of compaction which reduces the time & cost of construction, hence bringing a new phase in concrete manufacturing. Country to country even the normal concretes are defined differently. From time to time even the definition of normal concrete keeps changing in the same country. It is likely that concrete such as SCC will also be regarded as normal & will be redefined in future. The compressive strength of SCC specimens increased with the time of curing. A considerable increase in the compressive strength of concrete specimens exposed to thermal variations was noted compared to specimens exposed to wet-dry and normal exposures. Further, compared to the compressive strength of specimens under normal Exposure, the compressive strengths of specimens under wet-dry was higher. The SCC specimens displayed better performances with regard to water absorption. The chloride permeability of SCC was very low for all the specimens exposed to all the conditions investigated in this study. The chloride permeability values obtained in this study are in agreement with those reported in the literature. Concrete technology is dynamic & always displaying new, interesting & often exciting phases. The traditional approach to durability, i.e., minimum cement content, maximum w/c ratio & type of cement is being questioned by researchers & technologists. Toda studies are being done on concrete durability & new dimension such as particle packing, transport mechanism, binding capacity are the hot topics being looked into.