SELF COMPACTING CONCRETE: SELF COMPACTING CONCRETE SUBMITTED BY: ISHA ROLL NO- 3130609 M.TECH. Ist year INTRODUCTION-: INTRODUCTION- It is a highly flowable , non segregating concrete that can spread into place , fill the formwork and encapsulate the reinforcement without any mechanical vibration. It is the concrete which flows to a virtually uniform level under the influence of gravity without segregation due to which it completely fill the spaces between reinforcement. It is able to consolidate under its own weight. DEVELOPMENT: DEVELOPMENT Problem of durability of concrete structures in japan. Creation of durable structures require adequate compaction by skilled workers. Solution for achievement of durable concrete structures independent of quality of construction work is employment of self- compacting concrete. The first usable version of self-compacting concrete was completed in 1988 and was named “ HIGH PERFORMANCE CONCRETE ”, and later proposed as “ SELF COMPACTING HIGH PERFORMANCE CONCRETE ”. The method for achieving self-compacting ability involves : The method for achieving self-compacting ability involves Limited aggregate content Low water-powder ratio Employment of superplasticizer 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 when concrete flows through the confined zone of reinforcing bars. PowerPoint Presentation: Limiting the coarse aggregate content, whose energy consumption is particularly intense, to a level lower than normal is effective in avoiding kind of blockages near obstacles. Highly viscous paste is also required to avoid blockage of coarse aggregate when concrete flows through obstacles. High deformability can be achieved only by use of superplastisizers , keeping the water –powder ratio to a very low value. Comparison of mix proportioning of SCC with other type of conventional concrete MATERIALS: MATERIALS It has more powder content and less coarse aggregate. incorporates high range water reducers (HRWR, superplasticisers ) in larger amounts a viscosity modifying agent (VMA) in small doses POINTS TO BE NOTED: (i) limits on the amount of marginally unsuitable aggregates, that is, those deviating from ideal shapes and sizes, (ii) choice of HRWR, (iii) choice of VMA, (iv) interaction and compatibility between cement, HRWR, and VMA. AGGREGATES: AGGREGATES Give dimensional stability to concrete. The important properties of aggregates is Shape and Gradation. self- compactability is achievable at lower cement (or fines) content when rounded aggregates are used. Rounded aggregates would provide a better flowability and less blocking potential for a given water-to-powder ratio. the presence of flaky and elongated particles may give rise to blocking problems in confined areas, and also increase the minimum yield stress. Fillers can be used with aggregates having poor gradation. Admixtures: Admixtures SCC invariably incorporates chemical admixtures. High range water reducers:with or without viscosity modifying agents HRWRAs that work on ‘steric hindrance’ require low dosage as compared to those based on ‘electrostatic repulsion’. acrylic copolymers (AC) and polycarboxylate ethers (PCE) are effective at lower dosages compared to sulfonated condensates of melamine (SMF) or naphthalene (SNF) formaldehyde . Viscosity modifying agents: : Viscosity modifying agents: use to improve the stability. used for underwater concreting in the past. VMAs have polysaccharides as active ingredient. VMA should be added after the superplasticizer . VMA is packaged in water-soluble bags that can be added directly at the concrete mixer. PRODUCTION: PRODUCTION Fresh Properties of SCC: Fresh Properties of SCC These are most important properties of SCC which are always determined while making its mixtures. Fresh properties means properties when concrete remains is in plastic state. In Fresh properties we determine Slump flow , passing ability and filling ability of SCC. TESTS FOR SCC:: TESTS FOR SCC: SLUMP FLOW TEST J-RING TEST L BOX TEST Slump flow test of SCC: Slump flow test of SCC Slump cone of 300mm height , 100 mm upper dia and 200 mm bottom dia is taken on a horizontal plate SCC is filled in the cone without any compaction. Then cone is lifted and concrete is allowed to spread. The dia. of spread should be between 650mm-800 mm as per IS 456:2000 J ring test of SCC: J ring test of SCC It determine the passing ability of SCC. J ring consist of a ring of reinforcement bars that will fit around the slump cone. Slump cone is filled with concrete and lifted up as in slump cone test. Final spread is measured. Diff. between above and normal slump is measured and it should not be more than 50mm. L box test of SCC: L box test of SCC It measure passing ability. L ring apparatus has a vertical channel and a horizontal channel separated by trap door. There is obstacle of 3 reinforcing bar in the horizontal part Vertical part is filled with SCC. Door is opened and concrete allow to pass through blocking bars. Height of concrete left in vertical section and end of horizontal section is measured. Settlement and stability tests: Settlement and stability tests Tendency for settlement was assessed using visual analysis of plane surfaces cut out of hardened concrete. settlement column test, sieve stability test, and penetration test were carried out. Settlement column test: a mould of height 400-500 mm, into which fresh SCC is poured. The test involves the collection of concrete samples from the top and bottom parts of this column after a controlled agitation and settlement period. The segregation potential is expressed as the ratio of the mass of coarse aggregates in the top and bottom parts . PowerPoint Presentation: Sieve stability : test a fresh SCC sample is left undisturbed (static condition) for 15 minutes in a bucket. The top layer of the sample is then poured onto a 5 mm sieve, and the mass of the mortar passing through the sieve is determined. Segregation potential is expressed as the ratio between the mass of mortar collected through the sieve and the original mass collected from the top portion . Penetration test : measures the segregation potential as the depth of penetration of a standard mass (54g) into the concrete. If segregation is high, then the top part of the concrete would be mainly mortar, and the resultant depth of penetration would be high. For good SCC, penetration should not be more than 8 mm Hardened properties of SCC: Hardened properties of SCC These properties are same as ordinary concrete as mentioned below: Compressive strength Tensile strength Exposure to fire Durability Differences in performance of SCC and normally-vibrated concrete: Differences in performance of SCC and normally-vibrated concrete Property of SCC Expectation Reality Variation in strength across depth of structure Can take place for SCC No difference (between SCC and vibrated concrete) Creep and drying shrinkage Higher for SCC No significant difference Early age shrinkage and cracking Higher for SCC Higher for SCC Strength and elastic modulus No difference for same grade of concrete No difference Durability Better for SCC Better for SCC Advantages of SCC: Advantages of SCC Faster and more efficient placement of fresh concrete is achieved. Total concreting time is reduced. High quality of placed concrete is achieved, regardless the skill of the workers. No vibration of fresh concrete is necessary during placement into forms. Good bond between concrete and reinforcement is obtained, even in congested reinforcement. High quality of concrete surface finish is obtained with no need for subsequent repair. • With a better final appearance of concrete surface, smooth wall surfaces and flat floor surfaces that need no further finishing are obtained. • Improved durability of structures is achieved and Maintenance costs are reduced. APPLICATIONS: APPLICATIONS Self-compacting concrete has been used in bridges and even on pre-cast sections. One of the most remarkable projects built using self-compacting concrete is the Akashi- Kaikyo Suspension Bridge, Japan In this project the SCC was mixed on-site and pumped through a piping system to the specified point, located 200 meters away . On this particular project the construction time was reduced from 2.5 years to 2 years. Construction Issues: Understanding the limit of flow distance of the concrete, in order to avoid segregation of coarse aggregate. Results from Japan indicate that for distances less than 10 m, segregation does not occur. Arima et al proposed the use of automatic gate valves for discharging the concrete at many different points, at intervals of 6-20 m. Another issue is that of lateral pressure of the SCC on the formwork, due to the highly fluid nature of SCC. Higher rates of casting with SCC could compound the problem of excess formwork pressure Construction Issues References: References http:// en.wikipedia.org/wiki/Self-consolidating_concrete theconcreteportal.com Okamura H., Ouchi M., SELF COMPACTING CONCRETE , Concrete Library of Japanese Society of Civil Engineers, march 30, 2003.