Enhancing Durability Of Everyday Concrete
Amol Anand Patil, Product Manager-Admixture System, BASF India Limited
Self consoliditated Concrete (SCC) has tremendous
benefits over traditional vibrated concrete to increses
overall efficiency and durability of concrete. To design
SCC as per EFNARC guidelines requre miminum 500 – 650 Kg/
m3 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% of the traditional vibrated concrete classes are between
M20 to M35 MPa. To convert these strength classes to classical
SCC is a big challenge, especially to maintain balance between
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. Smart
Dynamic Concrete (SDC) is an innovative concept in concreting
and it is possible to achieve self-consolidation properties using
a lower amount of cementatious material without detrimental
effect in everyday concrete.
It is essential that every concrete structure should continue
to perform its intended function that is maintaining its required
strength and serviceability, during the specified or traditionally
expected service life. It follows that concrete should be able to
withstand the processes of deterioration to which it is expected
to be exposed. Such concrete is said to be durable.
Cause of Inadequate Durability
Inadequate durability manifests itself by deterioration, which can be due to either external factors or internal causes within the concrete itself. 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 sometimes difficult to assign deterioration to a particular factor, but quality of concrete in the broad sense of the word, though with a special reference to permeability, nearly always enters the pictures. Indeed, with the expectation of mechanical damage, all the adverse influences on durability involve the transportation of fluids through the concrete. For this reason, the consideration of durability requires an understanding of the phenomena involved.
Transportation of Fluid in Concrete
There are three fluids, particularly relevant to durability, which can enter concrete; water, pure or aggressive ions, carbon dioxide and oxygen. They can move through the concrete in different ways, but all transportation depends primarily on the structure of the hydrated cement paste. As stated earlier, the durability of concrete largely depends on the ease with which fluids, both liquids and gases, can enter into, and move through, the concrete; this is commonly referred to as permeability of concrete. Now, strictly speaking, permeability refers to flow through the porous medium. The movement of various fluids takes place not only by flow through the system but also by diffusion and sorption. Nevertheless, the commonly accepted term ‘permeability’ will be used for the overall movement of fluids into and through concrete excepted where, for clarity, distinctions between the various types of flow to be made.
Challenges in Day to Day Concrete
It is not enough that a concrete mix is correctly designed, transportation, placing and compaction, it is of utmost importance that the concrete must be placed in a systematic manner to yield optimum results. As stated earlier the permeability is a major factor for durability of concrete and it is related to density of concrete. The density of the concrete is majorly affected due to the improper compaction of concrete. The creation of durable concrete structure requires adequate compaction by skilled workers. However, a gradual reduction in skilled workers and the availability of workers in a construction industry has led to reduction of quality of construction. One solution for the achievement of durable concrete structure independent of construction of quality of work is the use of selfconsolidate concrete, which can be compacted into every corner of formwork, purely by means of its own weight and without the need of vibrating compaction. The necessity of these typesof concrete is proposed by Prof. Okamura in 1986. Studies to develop self-compacted concrete, including fundamental study of workability of concrete have been carried out by Ozawa and Meakawa at university of Tokyo (Ozawa 1989, Okamura 1993 and Meakawa 1999). Self consolidated Concrete (SCC) has tremendous benefits over traditional vibrated concrete as it increases overall efficiency and durability of concrete. But the picture is quite different in a day to day concrete requirement. Why this big difference? In today’s context of everyday concrete, almost 70 -80% of the traditional vibrated concrete classes are between M20 to M35 MPa. The usage of SCC in day to day concrete requirement is limited because of several reasons as follows.
I. The increase the initial cost since SCC has a higher unit content of powder compared to the traditional concrete.
II. The sensitivity of SCC to variation in the mix proportion can lead to higher production cost. The variation in moisture content of the aggregate, especially of the sand cans significantly the stability of SCC.
When concrete producers have to supply self consolidated concrete, they deliver much higher strength than ordered. This is due to higher fine content necessary for achieving the particular properties of SCC. Those fines are usually provided by cement and pozzolanic material that is readily available at batching plants. The excess of cement content and extra amount of fines required for SCC requirement compliances as per EFNARC guidelines increase production cost. The reduction of total fine content and of cement content would lead to decrease in unit cost of SCC as long as self-compaction properties are maintained. SCC is used for conditions, where a high density of reinforcement is used and high strength is required. The use of SCC goes through the designer specification, when the reliability of design characteristics and durability has to be assured in the concrete structure. The high fines content SCC has a higher plastic viscosity and which are suitable for heavily reinforced structure, and they have more than 350 Kg/m3 of steel as per JSCE recommendation. In today’s context of everyday concrete, almost 70 -80% of the traditional vibrated concrete classes are between M20 to M35 MPa. To convert these strength classes to classical SCC is a big challenge, especially to maintain balance between stability and fluidity of the concrete. Smart Dynamic Concrete (SDC) is an innovative concept in concreting and it is possible to achieve self-consolidation properties using a lower amount of cementatious material (fine) without detrimental effect in everyday concrete. Smart Dynamic Concrete is characterized by higher yield value and lower plastic viscosity and is suitable for light reinforced structure, where the amount of reinforcement is less than 100 kg/m3 and classified as Rank 3 in JSCE recommendation. This type of concrete is typically of a structure, where concrete of strength M20 to M35 is used - this is a major grade used in construction sites. Therefore, this diffusion of self compacted concrete should be increased; it is in this sector that the industry should focus its resources to find innovative approach to increase durability of day to day concrete. Concept of Smart Dynamic Concrete The Smart Dyanamic concept is suitable to upgrade high slump concrete to a higher performance level with selfcompacting characteristics and is as easy to produce as standard concrete. It allows the ready mix industry to reach better construction process economy, higher concrete durability and increased energy efficiency in order to save time and money and reduce CO2 emissions. MasterMatrix is the essential component of the Smart Dynamic Concrete concept. It consists of water soluble polymer witch modifies the rheological properties of concrete mix. Tailored-mode of action when used in conjunction with one of our MasterGlenium product, MasterMatrix brings a level of viscosity to the mix that allow the right balance between fluidity, passing ability and resistance to segregation apparently opposing properties to be achieved.
Mechanism of Action
Comparison of Traditional Vibrated Concrete versus Smart Dynamic Concrete.
– Smart Dynamic Concrete is designed to upgrade high slump concrete to become self-compacted concrete
– The centerpiece of this concept is MasterMatrix, a high performance viscosity modifying agent (VMA) which allows for a quantum leap in concrete robustness.
– Smart Dynamic Concrete combines the advantages both traditional vibrated and self-compacting concrete.
– Smart Dynamic Concrete improves durability criteria over traditional vibrated concrete.
– This concept makes unique mix design optimization (by reducing fines) possible.
– Smart dynamic Concrete adds economical, ecological and ergonomic values to concrete and has the potential to move the market up to the next level of advanced construction practice. (Amol Anand Patil, Business Development manager in BASF India limited, more than 14 years of experience in the concrete industry and has worked for development of high performance concrete, Geopolymer concrete and reactive powder concrete.)
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