Dr. P. Muthupriya, Associate Professor, School of Civil Engineering, Karunya University, Coimbatore
V. Manjunath, Assistant Professor, Department of Civil Engineering, Bannariamman Institute of Technology, Sathyamangalam.
B. Keerdhana, Assistant Professor, Department of Civil Engineering, Dr.NGP Institute of Technology, Coimbatore
Abstract: In this Investigation, the strength studies of fibre reinforced self-compacting concrete is made. The mix proportion is obtained as per the guidelines given by European Federation of producers and contractors of specialist’s products for structure (EFNARC). SCC mixes are produced by replacing the cement with 30%, 40% and 50% of Fly ash and with addition of polypropylene synthetic fibre of 0.05% and 0.10% to the SCC concrete. The w/p ratio used in this investigation is 0.4. Superplasticizer used in this study is Glenium B233 and its dosage is 2% to obtain the required SCC mix. Fresh concrete properties are checked by conducting the workability tests such as Slump Flow, T50, L-Box, U-Box, V-Funnel tests. Specimens such as cubes, cylinders and prisms were tested for various mix proportions to study the mechanical properties such as compressive strength, split tensile strength and flexural strength at different ages of concrete such as 7 days, 14 days and 28 days. While there is abundant research information on ordinary confined concrete, there are little data on the behavior of Self-Compacting Concrete (SCC) under such condition. Due to higher shrinkage and lower coarse aggregate content of SCC compared to that of Normal Concrete (NC), its composite performance under confined conditions needs more investigation. This project has been devoted to investigate and compare the mechanical behavior of confined concrete circular columns cast with SCC and NC under axial loading. The parameters affecting are including concrete compressive strength and confinement configuration. Six column specimens were tested using two confinement techniques Glass fiber wrap, FRP (aramid fiber) tube. The performance of the tested column specimens is evaluated based on mode of failure, load–displacement curve, ultimate strength, ductility factor, energy absorption, toughness index and percentage of enchancement due to confinement.
Self-Compacting Concrete (SCC) is a relatively new concrete type therefore, limited experience is provided by its appropriate composition. Construction quality of normal concrete structures highly depends on the vibrating time during casting, and in a liquid vibration, this may lead to inferior quality of concrete. However, this drawback can be overcome if SCC is employed. SCC is a highly performance concrete that can flow into place under its own weight and achieve good consolidation without internal or external vibration and without exhibiting defects due to segregation and bleeding. A lack of conformation regarding in-place properties and structure performance of SCC is one of the main barriers to its recognition in the construction industry.
Method of Producing SCC
SCC can be made in three ways. They are:
- Powder type
- VMA type
- Combined type
Scope and Objective of the Project
In this project, it is proposed to study
- Mix proportion for high strength self-compacting concrete by Trial and error method
- To determination of optimum dosage of chemical admixture in concrete using marsh cone
- To determination of partial replacement of Fly ash and addition of polypropylene fibres by weight tend to improve the compressive strength, tensile strength, and impact resistance of hardened SCC. Fibers increase the ductility of the concrete.
- To Study of strength characteristics on SCC
- Compressive strength
- Flexural strength
- Split tensile strength
- To Study the behaviour of confined self-compacting reinforced concrete circular columns under axial load with various confinements Fiber Reinforced Polymers (aramid fiber) and Glass fiber mat
- To find the load deformation behaviour of short column
- To find energy absorption capacity, load carrying capacity, toughness index, ductility factor of the column short column
In the field of Civil Engineering many applications of Self-Compacting Concrete spread throughout the world ranging from the making of industrial floors, nuclear power projects to high rise infrastructure buildings and water retaining structures. Many research works are still under progress in the field of SCC so as to meet the likely demands of the fast growing construction industry and performance requirements. The definition of SCC was also expanded to encompass both durability and strength of structural components.
Hajime okamura and Masahiro Ouchi (2003) investigated the properties of self compacting concrete and concluded that self compacting concrete is durable and reliable and have very little maintenance work. When self compacting concrete is so widely used it is seen as ordinary concrete rather than “special concrete. Bouzouba N, Lachemi M (2011) carried on Self-compacting concrete incorporating high volume of class F fly ash: Preliminary results and concluded that in recent years, Self-compacting concrete (SCC) has gained wide use for placement in congested reinforced concrete structures with difficult casting conditions. The use of fine materials such as fly ash can ensure the required concrete properties. The SCCs developed 28-day compressive strengths ranging from 26 to 48 MPa. The results show that an economical SCC could be successfully developed by incorporating high volumes of Class F fly ash. Frances Yang (2004) studied on Self-Consolidating Concrete and concluded that this paper investigates the technology behind creating SCC, including its components and mix proportioning techniques. The highly flowable nature of SCC is due to very careful mix proportioning, usually replacing much of the coarse aggregate with fines and cement, and adding chemical admixtures. While there is no set definition for SCC yet, for now the concrete construction industry generally follows certain methods of measuring mix properties to define an SCC. Bouzouba N,. Noratan M D and Hanizamawang (2011) investigated on the Compressive And Flexural Strengths Of Self-Compacting Concrete Using Raw Rice Husk Ash and concluded that raw rice husk ash can be used to replace cement in self-compacting concrete.15%replacement of OPC with RRHA, 30% replacement with two mineral additive components and 45% replacement with three mineral additive components produce comparable compressive strength as the control mix and improved flexural strength. 30% replacement of OPC with two mineral additive components and 45% replacement with three mineral additive components produce comparable compressive and flexural strengths as the control mix.
- Cement-Ordinary Portland cement, 43 Grade conforming to IS: 12269 – 1987.
- Fine Aggregate-Locally available river sand confined Grading zone II of IS: 383-1970
- Coarse Aggregate-Locally available crushed blue granite stones conforming to graded aggregate of nominal size 12.5 mm as per IS: 383 – 1970.
- Mineral Admixture-Dry Ground Granulated Blast Furnace Slag (GGBFS)
- Fibers-Synthetic fibres-Polypropylene fibre
- Chemical Admixture-Super plasticizer Glenium- B233as per EN 934-2 T3.1/3.2,Viscosity modifying agent Glenium stream -2 as per ENC 180VMA r13, 22/10/06.
- Water-Potable water as per IS 456-2000
- Confinement materials-Fiber Reinforced Polymers, Glass fiber mat
For making SCC maximum size of aggregates is 12.5 mm. The aggregates used is sound; free from deleterious materials and hacking crushing strength, at least 1.5 times that of concrete. Crushed blue stone angular shaped aggregate is used.
Fly ash is finely divided residue resulting from the combination of ground or powered coal. They are generally finer then cement and consist mainly of glassy spherical particles as well as residue of hematite and magnetite, char and some crystalline phases formed during cooling. Table 1 shows the chemical properties of fly ash.
Super Plasticiz.ers GLENIUM B233
Glenium B233 is an admixture of a new generation based on modified poly carboxylic ether. The product has been primarily developed for applications in high performance concrete where the highest durability and performance is required. It is free of chloride & low alkali. It is compatible with all types of cements. The hyper plasticizer shall be Glenium B233, high range water reducing, Super plasticizer based on polycarboxylic ether formulation. The product shall have specific gravity of 1.09 & solid contents not less than 30% by weight. Optimum dosage of Glenium B233 should be determined with trial mixes. As a guide, a dosage range of 500 ml to 1500ml per 100kg of cementitious material is normally recommended.
Portable water confirming to the requirements of IS: 456 is used for making of SCC.
Structural Applications of FRP
FRP can be applied to strengthen the beams, columns, and slabs of buildings and bridges. It is possible to increase the strength of structural members even after they have been severely damaged due to loading conditions. In the case of damaged reinforced concrete members, this would first require the repair of the member by removing loose debris and filling in cavities and cracks with mortar or epoxy resin. Once the member is repaired, strengthening can be achieved through wet, hand lay-up of impregnating the sheets with epoxy resin then applying them to the cleaned and prepared surfaces of the member.
Glass fiber (also spelled glass fiber) is a material consisting of numerous extremely fine fibers of glass.
Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the invention of finer machine tooling. In 1893, Edward Drummond Libbey exhibited a dress at the World’s Columbian Exposition incorporating glass fibers with the diameter and texture of silk fibers. This was first worn by the popular stage actress of the time Georgia Cayman. Glass fibres can also occur naturally, as Pele’s hair. Glass wool, which is commonly known as “fiberglass” today, however, was invented in 1938 by Russell Games Slayter of Owens-Corning as a material to be used as insulation. It is marketed under the trade name Fiberglas, which has become a generalized trademark. Glass fiber is commonly used as an insulating material. It is also used as a reinforcing agent for many polymer products; to form a very strong and light fiber-reinforced polymer (FRP) composite material called glass-reinforced plastic (GRP), popularly known as “fiberglass”. Glass fiber has roughly comparable properties to other fibers such as polymers and carbon fiber. Although not as strong or as rigid as carbon fiber, it is much cheaper and significantly less brittle.
The mix composition is chosen to satisfy all performance criteria for the concrete in both the fresh and hardened states. There is no standard method for SCC mix design and many academic institutions, admixture, ready-mixed, precast and contracting companies have developed their own mix proportioning methods. However, to obtain the required properties of fresh concrete in SCC, a higher proportion of ultra fine materials and the incorporation of chemical admixtures are necessary. The components shall be coordinated one by one so that segregation, bleeding and sedimentation are prevented. A rational mix design process should be used, to reduce the number of trial tests in laboratory.
Further information on mix design and on methods of evaluating the properties of SCC can be found in the European Federation of National Associations Representing for Concrete EFNARC Guidelines for SCC.
Mix Design Principles
To achieve the required combination of properties in fresh SCC mixes:
- The fluidity and viscosity of the paste is adjusted and balanced by careful selection and proportioning of the cement and additions, by limiting the Water/Powder ratio and then by adding a superplasticiser and (optionally) a viscosity modifying admixture. Correctly controlling these components of SCC, their compatibility and interaction is the key to achieving good filling ability, passing ability and resistance to segregation.
- In order to control temperature rise and thermal shrinkage cracking as well as strength, the fine powder content may contain a significant proportion of type I or II additions to keep the cement content at an acceptable level.
- The paste is the vehicle for the transport of the aggregate; therefore the volume of the paste must be greater than the void volume in the aggregate so that all individual aggregate particles are fully coated and lubricated by a layer of paste. This increases fluidity and reduces aggregate friction.
- The coarse to fine aggregate ratio in the mix is reduced so that individual coarse aggregate particles are fully surrounded by a layer of mortar. This reduces aggregate interlock and bridging when the concrete passes through narrow openings or gaps between reinforcement and increases the passing ability of the SCC.
These mix design principles result in concrete that, compared to traditional vibrated concrete, normally contains:
- Lower coarse aggregate content
- Increased paste content
- Low Water/Powder ratio
- Increased superplasticiser
- Sometimes a viscosity modifying admixture.
Mix Design Approach
Laboratory trials should be used to verify properties of the initial mix composition with respect to the specified characteristics and classes. If necessary, adjustments to the mix composition should then be made. Once all requirements are fulfilled, the mix should be tested at full scale in the concrete plant and if necessary at site to verify both the fresh and hardened properties.
The mix design is generally based on the approach outlined below:
- Evaluate the water demand and optimize the flow and stability of the paste
- Determine the proportion of sand and the dose of admixture to give the required robustness
- Test the sensitivity for small variations in quantities (the robustness)
- Add an appropriate amount of coarse aggregate
- Produce the fresh SCC in the laboratory mixer, perform the required tests
- Test the properties of the SCC in the hardened state
- Produce trial mixes in the plant mixer.
- Mix Design Procedure
- Adjust the Water/Powder ratio and test the flow and other properties of the paste
- Try different types of addition (if available)
- Adjust the proportions of the fine aggregate and the dosage of superplasticiser
- Consider using a viscosity modifying agent to reduce sensitivity of the mix
- Adjust the proportion or grading of the coarse aggregate.
Efnarc Guide Lines
- There is no standard method for SCC mix design and many academic institutions, admixture, ready-mixed, precast and contracting companies have developed their own mix proportioning methods.
- Further information on mix design and on methods of evaluating the properties of SCC can be found in the EFNARC Guidelines for SCC.
- These Guidelines are not intended to provide specific advice on mix design but Table 2 is an indication of the typical range of constituents in SCC by weight and by volume. These proportions are in no way restrictive and many SCC mixes will fall outside this range for one or more constituents.
For the above mix proportion that is M35 various replacement of mineral admixture like Fly ash is replaced with cement for various percentage like 30%,40%,50% and synthetic fibres like Polypropylene fibres are added in 0.05% and 0.10% ratio to gain better strength in SCC.
General (Marsh Cone)
It has been noticed that all super plasticizers are not showing the same extent of improvement in fluidity with all types of cements. Some super plasticizers may show higher fluidizing effect on some type of cement than other cement. There is nothing wrong with either the super plasticizer or that of cement. The fact is that they are just not compatible to show maximum fluidizing effect. Optimum fluidizing effect at lowest dosage is an economical consideration. Giving maximum fluidizing effect for a particular super plasticizer and cement is very complex involving many factors like composition of cement, fineness of cement.
Although compatibility problem looks to be very complex, it could be more or less solved by simple rough and ready field method. Incidentally this simple field test shows also the optimum dose of the super plasticizer to the cement.
Marsh Cone Test
In the marsh cone test, cement slurry is made and its flow ability is found out. In concrete, really come to think of it, it is the cement paste that influences flow ability. Although, the quantity of aggregates, its shape and texture etc. will have some influence, it is the past that will have greater influence. The presence of aggregate will make the test more complex and often erratic. Where as using of grout alone will make the test simple, consistent and indicative of the fluidifying effect of superplasticizer with cement.
Workability requirements of successful casting of SCC include high deformability, passing ability, filling ability and resistance to segregation. Deformability refers to ability of SCC to flow into and completely fill all spaces within the formwork, under its own weight. Deformability is the property most commonly associated with SCC and provides the justification of acceptance of technology. Optimum mix water/cement ratio of 0.45 is chosen from EFNARC guidelines and following workability studies slump flow, V-funnel, L-Box test, T50 were carried out to assess the workability characteristics.
Slump Flow Test
The slump flow test is used to assess the horizontal free flow of SCC in the absence of obstructions. The test method is based on the conventional slump test. The diameter of the concrete circle is a measure for the filling ability of the concrete. 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. The higher the slump flow value, the greater is its ability to fill formwork under its own weight. Acceptable range for SCC is from 650 to 800 mm.
T50 Slump Flow Test
The procedure for this test is same as for slump flow test. When the slump cone is lifted start the stop watch and find the time taken for the concrete to reach 500mm mark. This time is called T50 time. This is an indication of rate of spread of concrete. A lower time indicates greater flow ability. It is suggested and T50 may be 2 to 5 sec.
This test is used to determine the filling ability (flow ability) of the concrete with a maximum aggregate of 20 mm. The funnel is filled with about 12 liters of concrete and the time taken for it to flow through the apparatus is measured. The test measures the ease of flow of the concrete; shorter flow times indicate greater flow ability. For SCC, a flow time in the range of 6 to 12 second 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.
L -Box Test
The L – Box test apparatus consists of a vertical and horizontal section. Reinforcing bars are placed at the intersection of two sections of the apparatus. In general, the gap between the reinforcing bars kept at 35 and 55mm for 10mm and 20mm coarse aggregate respectively. The time taken by the concrete to flow a distance of 200mm and 400mm in the horizontal section of the apparatus after the opening of the gate from the vertical section is measured. The L – Box test gives an indication of the filling, passing and segregation ability of the concrete.
This test is used to measure the filling ability of SCC. The apparatus consists of a vessel that is divided by a middle wall into two compartments. It provides a good direct assessment of filling ability. For conducting the U-box test, one of the compartments of the apparatus is filled with the concrete sample and filled concrete is left to stand for 1 minute. Then the sliding gate is lifted to allow the concrete to flow out into the other compartment. After the concrete comes to rest, the height of the concrete in the compartment that has been filled is measured in two places and the mean height (H1) is calculated. Also the height in the other compartment (H2) is measured. The filling height is then calculated as H1- H2. The whole test has to be performed within 5 minutes. If the concrete flows as freely as water, at rest it will be horizontal, so H1- H2 = 0. Therefore, the nearer this test value, i.e., the ‘filling height’, is zero, the better the flow and passing ability of SCC.
Compressive Strength Test
Compression test is the most common test conducted on hardened concrete, partly because it is easy test to perform, and partly because most of the desirable characteristic properties of concrete are qualitatively related to its compressive strength. The compression test is carried out on specimens cubical or cylindrical in shape. The cube specimen is of the size 150 x 150 x 150mm. Due to compression load, the cube or cylinder undergoes lateral expansion owing to poisons ratio effect.
Split Tensile Strength Test
It is a method of determining the tensile strength of concrete using a cylinder which splits across the vertical diameter. It is expressed as the minimum tensile stress (force per unit area) needed to split the material apart. A cylindrical specimen of size 150×300 mm is used. The specimen if loaded until failure occurs and failure load is noted. The main advantage of this method is that the same type of specimen and the same testing machine as are used for the compression test can be employed for the test. The splitting test is simple to perform and gives more uniform results than other tension tests. Strength determined in the splitting test is believed to be closer to the true tensile strength of concrete, than the modulus of rupture. Splitting strength gives about 5 -12% higher value than the direct tensile strength.
Flexural Strength Test
A beam specimen is cast to test the flexural strength of the concrete. The standard specimen size is 100x100x500 mm. A UTM machine is used for the testing of these specimens. The testing machine shall be set to any reliable type of sufficient capacity for the test. Permissible errors should not be greater than ±0.5%. The bed of the machine should be provided with two steel rollers, of 38 mm diameter, on which the specimen is supported. The test specimen should be cast and cured for 28 days and tested for maximum load.
Concrete columns are important structural elements which are vulnerable for exceptional loads. In older structures, columns often have insufficient transverse reinforcement which is unable to provide sufficient confinement to the concrete core or to prevent buckling of the longitudinal reinforcement. This can lead to unacceptable premature strength degradation. Confinement is required to delay the softening of concrete under ultimate load conditions and to allow a ductile response of the column. Numbers of retrofit techniques have been developed for strengthening columns which have led to improvement in both axial strength and ductility and to prevent buckling of the longitudinal reinforcement.
Confined Short Column Detailing
Totally six identical circular column specimens were tested in this study. The investigated specimens were classified into two groups. Three of the specimens were made with NC (slump less than 200 mm), whereas the others were made using FRSCC (Fiber Reinforced Self-Compacting Concrete). All studied columns had a circular cross-section with diameter of 150 mm, height of 600 mm and were reinforced by 6Ø of yield strength fy= 360 MPa and with reinforcement ratio g= 3.5%. In this context, Aramid Fiber Reinforced Polymer tube (FRP tube), Glass Fiber Reinforced Polymers wrap (GFRP tube), two confinement techniques which were used for both columns made with SCC or NC. Totally six columns were cast and tested.
Test Setup for Column Testing
The columns were taken out after the 28 days curing and cleaned for testing. The column was supported with steel circular box at top and bottom establishing partial fixity condition and to prevent the local crushing. The column specimens are adjusted in such a way that the center line of the axial load coincides with the longitudinal axis of the column. The compressometer was fixed in the middle region to observe the axial deformation. All the columns were tested for axial compression ine1000 kN universal testing machine.
Results and Discussion
In this chapter the test results of Marsh cone test ,workability, strength and behavioural studies of circular short column are discussed and its influence on various constituents of SCC.
Marsh Cone Test
The test results concluded that the mixes that contain higher powder content and lesser coarse aggregate attained quicker reach of 500 mm slump at a lesser time.
The test results concluded that the higher replacement of the mix with highly fine powdered materials have given higher value of slump as shown in the Fig 10 and achieved self-compaction.
The test results of V-funnel showed that the flow time was minimum for the mix containing lesser coarse aggregate and finer powder materials.
The test results of L-box apparatus concluded that the blocking was minimum for mix containing minimum coarse aggregate and the ratio was nearing 1.
The results showed that the U-Box difference in values decreased for the mix containing lesser coarse aggregates and more powder materials
Behaviour of Circular Short Column
The load was applied gradually and the deformation readings were taken at regular intervals of 50 kN. The column was gradually loaded upto the ultimate load level. As the load level was increased in each interval , the observed deflection in compressometer was greater then that of the in earlier interval. The results of the axial load and corresponding deformation have been recorded in Table 10.
The load carrying capacity of the column is defined as the load at which the column fails by crushing and load retrieve from peak load.
The ductility value has been calculated as the ratio of ultimate or maximum deformation (Du) to the yield deformation (Dy). The yield deformation can be determined from the load – deformation curve by assuming bilinear behaviour of the column specimen. The ductility factor for all columns are shown in Table 12.
Energy Absorption Capacity
The energy absorption capacity was calculated as the total area under the load deformation curve. The relative energy absorption capacity of all types of column is tabulated.
Toughness index is defined as the ratio of ultimate energy to energy at yield from the load deformation curve. The toughness index values for all types of columns are tabulated.
Based on the experimental the following conclusion is drawn within the limitation of test result.
- From the above experimental work, it is concluded that when the coarse aggregate content is reduced better flow in SCC can be achieved due to the less blocking effect. The volume of coarse aggregate content was reduced to 46% instead of 50% to avoid segregation.
- In this study it has been found that with increase in superplasticizer dosage the workability is increased. So that the required slump value can be obtained thus full filling the criteria of EFNARC.
- For 50% fly ash replacement and 0.05% fibres added, the fresh properties observed were good as compared to other mix proportions replacement.
- For 30% fly ash replacement and 0.1% of fibres added considerably gave high mechanical properties than other various mix proportions
- The entire rheological test can be concurrently used to predict the flow behaviour of the concrete made with different composition.
- Suitability of self-compacting concrete mixture proportion was verified through displacement trials in a complicated mould and field trials.
- Fly ash substitution generally results in favourable outcomes and is highly recommended for all SCC mixes.
- The load carrying capacity of the circular short column increased with the addition of synthetic fibres and provision of confinement.
- The ductility of FFSC4-F (value) is greater than all other columns.
- There is is a marginal improvement in the energy absorption capacity of the RC columns with inclusion of fibers and provision of confinement.
- The toughness index of the short column confined with aramid fiber is more then other specimens.
- In general it is conclude that Fiber reinforced self-compacting concrete short column confined with aramid fiber FRP provides good results in this experimental investigation.
- ASTM C 143-03, “Standard Test Method for Slump of Hydraulic Cement Concrete”, Annual Book of ASTM Standards, pp. 1-8, 2003.
- ASTM C 494, (1992), “Standard Specifications for Chemical Admixtures for Concrete”, Annual Book of American Society for Testing Materials Standards.
- BIS: 383-1970 (reaffirmed 1997), “Specification for Coarse and Fine Aggregates from Natural Source for Concrete”, New Delhi.
- BIS: 12269-1987 (reaffirmed 1999), “Specification for Ordinary Portland Cement”, New Delhi.
- Das,D., VGupta,V.K. and kaushik,S.K., “Effect of maximum Size and Volume of Coarse Aggregate on properties of SCC”. The Indian concrete journal, vol80, no 3, March 2006, pp 13-20.
- EFNARC, European guidelines for Self-compacting Concrete, Specification, Production and Use. (May-2005).
- Gambhir M.L., (2005), ‘Concrete Technology’ Tata McGraw Hill Publications Co.Ltd. New Delhi.
- IS 383: 1970, “Specification for coarse and fine aggregates from natural sources for concrete” Bureau of Indian Standards, New Delhi, India.
- IS 456 – 2000, “Plain and Reinforced Concrete – Code of Practice” (Third Edition), Bureau of Indian Standards, New Delhi, India.
- IS 3812: 1981 Specification for fly ash for use as pozzolana and admixture Bureau of Indian Standards, New Delhi, India.
- IS 12269: 1987 “Specification for 53 grade ordinary Portland cement” Bureau of Indian Standards, New Delhi, India.
- Vengala,J., Sudarsan,M.S., and Ranganath,R.V., “Experimental Study for obtaining Self-compacting concrete”. Indian concrete journal, Vol. 77, August 2003, pp. 1261-1266.