AMOL ANAND PATIL elaborates upon the concept of Smart Dyanamic ConcreteTM. Self-consolidated concrete (SCC) has tremendous benefits over traditional vibrated concrete to increase overall efficiency and durability of concrete. Designing SCC according to European Federation of National Associations Represening (EFNARC) guidelines require a miminum of 500-650 kg per cu m fines in the mix, which is not available in M20 to M30 grade of concrete.
In today´s context of everyday concrete, almost 70-80 per cent of traditional vibrated concrete classes are between M20 and M35 MPa. To convert these strength classes to SCC is a big challenge, especially to maintain the balance between the stability and fluidity of the concrete. This paper is about smart materials that can be used to enhance the concreting process and achieve maximum durability of everyday concrete.
It is essential that every concrete structure should continue to perform its intended function - to maintain its required strength and serviceability during the specified or expected service life. This means concrete should be able to withstand the processes of deterioration to which it is expected or exposed. The concrete is then said to be durable.
Cause of inadequate durability
Inadequate durability manifests itself by deterioration, which can be either owing to external factors or internal causes within the concrete. The various actions can be physical, chemical or mechanical. It should be observed that the physical and chemical processes of deterioration can act in a synergistic manner. For these reasons, it is difficult at times to relate deterioration to a particular factor. However, the quality of concrete, in particular its permeability, has a strong influence on its durability. Most damages and deterioration can be traced to the adverse influence of the transport mechanism of fluids through the concrete. Thus, an understanding of the impact of the movement of fluids on the durability of concrete is required.
Transportation of fluid in concrete
There are three fluids particularly relevant to durability that can enter concrete û water, pure or carrying aggressive ions; carbon dioxide; and oxygen. They can move through concrete in different ways, but all transportation depends primarily on the structure of the hydrated cement paste. As stated earlier, durability of concrete largely depends on ease of how fluids, both liquids and gases, can enter into and move through the concrete; this is commonly referred to as permability of concrete. In another words, permeability refers to flow through the porous medium. Now, the movement of various fluids takes place not only by flow through the system but by diffussion and absorption as well. Nevertheless, the commonly accepted term ´permeability´ will be used for the overall movement of fluids into and through concrete except for where, for clarity, distinctions between the various types of flow are to be made.
Challenges in day-to-day concrete
Having a correctly designed concrete mix is not enough. Transporting, placing and compaction are of utmost importance for the concrete to yield optimum results. As mentioned above, permeability is a major factor for durability of concrete and it is related to the density of concrete.
The creation of a durable concrete structure requires adequate compaction by skilled workers. However, a gradual reduction in skilled workers and the availability of workers in the construction industry has led to reduction of quality in construction. One solution to achieve durable concrete structures to compensate for limited resources but maintain quality of work is the use of SCC, which can flow into every corner of formwork, purely by means of its own weight and without the need to vibrate or compact. The foundation of SCC was proposed by Prof Okamura in 1986. More studies to develop SCC, including a fundamental study of workability of concrete, have been carried out by Ozawa and Meakawa at the University of Tokyo (Ozawa 1989, Okamura 1993 and Meakawa 1999).
SCC has tremendous benefits over traditional vibrated concrete to increase the overall efficiency and durability of concrete. But the picture is quite different in day-to-day concrete requirement. Why this big difference? In today´s context of everyday concrete, almost 70-80 per cent of traditional vibrated concrete classes are between M20 and M35 MPa. The usage of SCC in day-to-day concrete requirement is limited because of the following reasons:
Concept of Smart Dynamic ConcreteTM
BASF Smart Dynamic Concrete (SDC) is an innovative concept in concreting and it is possible to achieve self-consolidation properties using a lower amount of cementitious material (fines) without detrimental effect in everyday concrete. SDC is characterised by higher yield value and lower plastic viscosity and is suitable for light reinforced structures where the amount of reinforcements are less than 100 kg per cu m and classified as rank three in JSCE recommendations. This type of concrete is suitable for structures where concrete of strength M20 to M35 is used; this is also the major grade used in construction sites.
The SDC concept is suitable to upgrade high slump concrete to a higher performance level with self-compacting characteristics and it is also easy to produce as standard concrete. It allows the ready-mix industry to achieve a better construction process, higher concrete durability and increased energy-efficiency to save time and money and reduce CO2 emissions.
MasterMatrixTM is the essential component of the SDC concept. It consists of water-soluble polymer that modifies the rheological properties of the concrete mix. A tailored mode of action when used in conjunction with MasterGlenium®, MasterMatrixTM brings a level of viscosity to the mix that allows the right balance between fluidity, passing ability and resistance to segregation apparently opposing properties to be achieved.
Mechanism of action
The unique mix design optimisation allows the substitution of concrete paste quantity by concrete paste quality to achieve self-compacting properties and concrete stability at the same time. MasterMatrixTM is based on BASF proprietary, intelligent (smart), high molecular weight ionic polymers that interact among themselves and mainly with water molecules, generating a water envelope, therefore building up a highly structured cement paste.
An additional mechanism of action that strengthens the effectiveness of the system is the simultaneous absorption of MasterMatrixTM molecules in more than one fine particle of cement or fine sand, leading to a bridging phenomenon that generates an even more powerful molecular network.
Traditional vibrated concrete vs smart dynamic concrete
Data has been generated on one of the sites where we have compared traditional vibrated concrete to SDC. This is an M35 grade of concrete evaluated on the physical and mechanical properties of concrete. Over and above, we have conducted durability parameter in terms of water permeability, water penetration and rapid chloride ion penetration test.
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About the authors:
Amol Anand Patil, Product Manager-Admixture System, BASF India, has more than 14 years of experience in the concrete industry and has worked in the development of high performance concrete, Geopolymer concrete and reactive powder concrete.
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