SPECIALSPECIAL CONCRETESCONCRETES THROUGHTHROUGH THETHE RMCRMC ROUTEROUTE DR. MANAMOHAN R KALGAL Sr. Vice President Head, Technical Services, UltraTech Cement Ltd., ItIt allall startedstarted withwith…….. Stone ! Stone was considered to be the most robust and durable construction material for centuries But stone had problems of, ¾Non-availability ¾Heavy weight ¾High cost ¾Inflexibility ThenThen camecame………….. ConcreteConcrete !!!! • Panacea for all problems • Was called “flowing stone” Concrete is, Sensitive – Needs care Robust – Takes huge loads Followed by …… SpecialSpecial ConcretesConcretes !!!!!! Special concrete is a concrete that has been specially designed to achieve one or more properties, behavior, composition or performance to be different, usually superior, compared to conventional concrete. ¾ With special concretes, possibilities are ENDLESS… ¾ Special concretes can even be designed and specified, specifically for a project or an application. ¾ Special concretes need special care and control to achieve the desired properties High Performance Concrete (HPC) HPC - something more than what is achieved on a routine basis and involves a specification that often requires the concrete to meet several criteria. The ACI definition -A concrete meeting special combinations of performance and uniformity requirements that cannot always be achieved routinely when using conventional constituents, mixing, placing and curing practices. A high-performance concrete usually has certain characteristics that are developed for a particular application and environment. Properties of HPC HPC may have performance that is superior with respect to one or more of the following properties, ¾Ease of placement ¾Placing without Compaction ¾Early age strength ¾Long-term mechanical properties - durability ¾Impermeability ¾Lesser Heat of hydration ¾High/Low Density ¾Toughness ¾Heat Resistance ¾Crack resistance ¾Long life in severe environments etc… HPC from RMC ¾ A high-strength concrete is always a high-performance concrete, but a high performance concrete is not necessarily always a high-strength concrete. ¾ High-performance concretes are more sensitive to changes in constituent material properties than conventional concretes. ¾ Variations in the chemical and physical properties of the cementitious materials and chemical admixtures need to be carefully monitored. ¾ Substitutions of alternate materials can result in changes in the performance characteristics that may not be acceptable for HPC. ¾ The mix proportions are location specific. ¾ Many trial batches are usually necessary before a successful mix is developed. ¾ This means that a greater degree of quality control is required for the successful production of HPC ¾ RMC plants are ideal to handle the above issues. Self Compacting Concrete (SCC) Definition SCC is defined as a category of High Performance Concrete that has excellent deformability in the fresh state and high resistance to segregation, and can be placed and compacted under its self weight without applying external compaction effort. Basic properties of SCC Flowability Passing Ability Segregation Resistance History of development of SCC SCC was first developed in Japan in mid 1980’s. Extensive application in reinforced concrete sections containing congested reinforcements. In 1988, Professor Okamura and his associates at the University of Tokyo succeeded in developing SCC for commercial use. About 90% of the concrete used in Pre-cast industry in Japan is said to be SCC. The European countries formed a large consortium in 1996 to promote the development of SCC for practical applications in Europe. SCC is now being adopted in many European countries in the construction of pre-cast and cast-in-place bridges and other structures. History of development of SCC SCC is expected to replace conventional concrete to promote innovations, lessen environmental impact, improve durability and reduce cost in almost all applications. The use of SCC in the U.S. picked up a little later than in Japan and Europe. The pre-cast concrete industry has been using SCC since 2000 to produce precast structural and non-structural elements, and architectural panels. The initial hiccups in ready acceptance have been limited experience in the workability, durability, constructability and the long term properties of SCC. Constant efforts will help SCC be used in pre-cast and cast-in- place construction in the US and all over the world. Properties of SCC SCC can ¾ Be placed from bottom to top ¾ Minimize manpower and equipment outlay for placing ¾ Make pumping easier and faster ¾ Flow into complex structures ¾ Occupy it’s place without any compaction ¾ Reach inaccessible points ¾ Be placed in congested reinforcement ¾ Give a superior surface finish ¾ Give a safer and less noisier site condition ¾ Improve early strength, hence reduce form stripping time. SCC from RMC RMC plants – the ideal source for SCC. Requires new systems for concrete design and manufacture A system by which SCC can be supplied by RMC manufacturers would involve testing of self compactability, mix-design method, acceptance testing method at job site and development/use of new type of powder or admixture suitable for SCC. Okamura and Ozawa (1995) had proposed a simple mix proportioning system assuming general supply from RMC plants. SCC – Acceptance SCC involves rigorous mix design approach and usage of extremely sensitive chemical admixtures such as super-plasticizers and Viscosity modifiers. Sampling is very critical – should be based on experience and should be job specific. A practical acceptance test criteria at site was proposed by Ouchi et al. Ouchi testing apparatus - installed between the agitator truck and the pump at the job site. ¾ The whole amount of concrete is poured into the apparatus. ¾ If the concrete flows though the apparatus, the concrete is said to be having sufficient self- compactability. SCC - Indian Scenario • Adopted in Indian research only in the 1990’s. • Was used in various projects in small scale without much of a success till 2000. • Later, research and application stabilized with increasing awareness about the product. • Designers have started to specify SCC mainly to be able to place concrete in congested reinforcement and in places where access to vibration is not available. • Pre-cast industry (which in itself is small in comparisons to the potential) has not readily adopted SCC yet, but it is expected to pick up very soon. • Indian standards – IS 456, has also adopted and introduced SCC in its latest amendment in 2007. • With increase in labour costs and reduction in ready availability of skilled man power to place and vibrate concrete, SCC has a great scope in Indian concrete structures. SCC - UltraTech Mix designs for various grades of SCC between M 25 and M 80 have been developed and stabilized. Demonstrations on the performance of SCC have been carried out to various clients in different cities, in both pre-cast and cast in-situ applications. Considerable volumes of commercial supplies have been made from our plants in Mumbai, Pune, Gurgaon, Noida, Chennai and Hyderabad. Recently, a successful landmark pour of 900 m3 of SCC of M 50 grade was carried out for M/S Indu Projects, Pune. SCC was poured into a densely reinforced Post Tensioned beam of dimensions said to be the largest ever made in Asia. Fibre Reinforced Concrete (FRC) Definition Fibre-reinforced concrete is conventional concrete to which discontinuous discrete fibres are added during mixing, so as to enhance the properties of the concrete, such as tensile and flexural strength, ductility, toughness and crack resistance Origin of FRC ¾ Improving properties of brittle materials ¾ Conventionally started with the idea of RCC ¾ Discrete Steel fibres were later used – 1960’s ¾ Polymeric and mineral fibres were used much later Critical properties of FRC Improvement of properties of concrete by addition of fibres, governed by three main factors: ¾ Physical properties of concrete matrix and fibres. ¾ Uniform distribution of fibre throughout the matrix & ¾ Bond strength between concrete and fibre. Different available fibres Synthetic SteelGlass fibresfibres fibres Benefits of adding fibre to concrete ¾ Improvement of pseudo-ductility of concrete ¾ Crack arrest and crack control ¾ Increase in deformability and hence ultimate strength of concrete. ¾ Improvement in tensile strength and stiffness. ¾ Better energy absorption properties ¾ Resistance to impact and fatigue loading. Problems with manual mixing of FRC • An extended mixing time. This may be necessary to achieve a homogenous mix. • A possible need for an unnecessarily more expensive mixer in order to achieve the desired homogeneity and the possible under-utilization of the capacity of such plant. • A substantial time consumption for the weighing and proportioning • An insufficient control of the whole batching process • A lack of documentation for the control of the quantity of fibres actually added. • These problems can be avoided by using FRC from RMC. FRC – other issues Placing and Finishing (with synthetic fibres) ¾ FRC is as good as conventional concrete, while placing ¾ All traditional methods work ¾ The finishing could be marginally delayed ¾ There is change in bleeding and segregation properties and a visual reduction in slump of concrete, but workability of the concrete is the same. FRC – where do we stand ¾ FRC has been used in our country, for preventing shrinkage cracks. ¾ The application of using it as complete or partial replacement