Technical Note on Research of Nano Concrete (NAC)
Background of Research on Nano Concrete:
Though stone is the strongest constituent of concrete the strength of stone is not evident in compressive strength. It is the bond-strength at transition zone which reflects as the grade strength of concrete. This is evident where, cement is normally increased to upgrade the strength of concrete but not the input of stone. Here the research dimension came into question: “Since stone is the constituent of concrete transition zone do develop surrounding the stone that pronounces the grade strength of concrete. Why not avoid stone so much so the transition zone?” The pursuit of this research though paid dividends where if the control concrete with 350 kg of cement input gives strength of M25-M30, for the same input of cement Nano Concrete has given a strength of over M60.
This wonder product is called No-Aggregate Concrete (NAC), which means a concrete without sand and stone. It is also christened as Nano Concrete since the pore structure in NAC does refined to nano pores as against micro pores common with matrix of the control concrete. The detailed technical note is given below:
Sacred Pillar of Balaji Temple installed using Nano Concrete
The Dhwaja Sthambham (the sacred post in front of the temple) of Lord Venkateswara Swamy Temple on the hill, opposite to BHPV Township in Visakhapatnam, has deteriorated due to ingress of moisture that facilitated development of pest. Hence the Punah-Pratishta of this sacred pillar was conducted on 3rd-5th February 2014. This time, the temple authorities desired to make it resistive to pest attach and approached the scientists. the pit, holding the Pillar, is filled with Nano Concrete (NAC) for its characteristic ability in rendering absolute impermeability (27-100 Coulombs) associated with high strength (60 MPa at 28-day and 100-120 MPa at 1-year).
The idea for this invention stems out of the practice prevalent at Bangladesh where, in order to meet the need for aggregate of concrete in the absence of hillocks, they break clay bricks in jaw crushers. The research thought emerged at this point: “while 15-20 MPa strength of clay bricks could be crushed to aggregate and structures are executed at Bangladesh, why not NAC boulders with their strength of over 60 MPa?
Exactly at this point of time NTPC announced the National Grand Challenge (2019) seeking practical ideas for mass scale fly ash utilization where NACA has bagged the 1st prize. Now came the question of translating this idea to a demo project. Inventors have cast over 90 tons of NAC boulders, sent to commercial crusher and supplied the derived product of 20 mm and 10 mm aggregate to NTPC. They have constructed a demo building at their town ship, Deepanjalinagar, Simhadri Power Plant, Visakhapatnam.
The strength of various natural stones right from limestone to granite ranges at 60-150 MPa. But the concretes made out of such stones are targeted with 20-40 MPa strength in almost 85% of the structures nationwide. Thus NACA is comfortably positioned to meet 85% of the concrete requirements. More over, NACA concrete with its density of 2.0 to 2.1 tons/cu.m weighs over 25% lesser than control concrete saving on dead loads and, in turn, on structural steel. This is to be proved further by Structural Engineering studies by various engineering institutes in near future.