The Tribune, Chandigarh, India

Is flyash-blended concrete beneficial?
Amar Chandel and G.S. Dhillon

A huge mound of flyash near the
Ropar thermal plant

Use of flyash admixtured cements and the flyash itself as admixture to the cement concrete to be used in the reinforced cement concrete (RCC) structures, was not permitted till recently by the CPWD and other governmental organisations. It was considered that such use leads to increased corrosion of reinforced steel, thus shortening the lifespan of such buildings.

However, with the advancement of technology and research in the field of concrete and flyash utilisation, a change came, and in year 2000 the BIS permitted the use of flyash as mineral admixture from the consideration of “Durability criterion” (IS 456-2000). Still the CPWD stuck to the stand taken earlier.

Earlier this year, discussions started between the Department of Science & Technology and the CPWD on the topic and the CPWD softened its stand. A circular (CDO/SE/RR/FLY ASH (Main)/ 387) was issued on May 12, 2004 permitting use of flyash as “part replacement of OPC.

However, the permission is restricted to such structures which use ready-mixed concrete obtained from RMC plants and grade of concrete not below Grade 30. In case of the prestressed concrete structures, such use was not allowed in the case of bridges and flyovers. Other restraints were also imposed which related to the mode to be used for obtaining flyash from the power plants.

Flyash is to be obtained in dry form i.e. not from the ash ponds but from the ESP’s (Electro-Static Precipitators) and properly stored. But when the concrete is obtained from RMPs this aspect is ensured automatically. It may be mentioned here that barely 7 per cent of concrete of the total quantity used is supplied by RMPs.

So, over 93 per cent of the concrete users are left uncovered by the above “permission”. Also the most commonly used grade of concrete is M20.

Another restriction imposed is that the use is for concrete used in the superstructure (limited to 30 cm below ground level) and not in the foundation or basements.

The flyash to be used should conform to the requirements of IS 3812-1981, relating to Grade I flyash, which fixes the “Lime Reactivity Strength” to 60 kg / cm2.

It will not be possible for a common builder to obtain “flyash” in dry form, because no such facility is available at any of the thermal plants located in Punjab.

The Gujarat Ambuja Cement Ltd (GALL) is utilising eight lakh tonnes of flyash annually at Ropar. The utilisation by its plant located at Bathinda is not known. However, the GACL has captured over 12 per cent of the market share of PPC (Puzzolana Portland Cement) by its two units located in Punjab, but had hardly cared to make arrangements for supply of flyash to a common user at Ropar or Bathinda. The only alternative available to the common user is to utilise PPC if he wants to make his house more durable and in that direction hardly any demonstration structures have been put by GACL.

The specifications need be further relaxed so that the benefit is available to the common user and the cement manufactures should undertake “demonstration trials” to show that by using PPC in the RCC structures, the obtained structure would be more “durable” than if only OPC had been used.

Solar airconditioning
K. C. Singhal

Solar airconditioning can be the answer to energy crisis. Solar airconditioning units are based on the principle of vapour absorption cycle. They require practically no electricity in running the airconditioners, expect in running some small motors for running the cycle. Even the refrigerant used is water. As such it is totally different from vapour compression cycle airconditioners. Solar airconditioning is not possible in vapour compression refrigeration cycle.

A solar driven absorption cycle with storage is given below using lithium bromide solution from which steam is driven out by the heat provided by the fluid from the solar collectors. Evacuated/stationery type or parabolic trough/tracking type collectors are to be used with the system to give a temperature of 90°C are above. Flat plate collectors available in the market will not serve the purpose of providing heat to the lithium bromide solution in the generator. The rest of the diagram is self-explanatory. The system can also be used for hot air in winter. Thus heating and cooling is possible through this system. As such solar energy systems would be attractive since the payback period will not be very long, ideally, not exceeding five years.

Solar-powered airconditioning is potentially one of the most advantageous solar applications in big establishments like hotels, libraries, hospitals, malls, etc since its large-scale use would reduce peak electrical demand as well as huge electrical energy consumption required by vapour compression refrigeration systems. Besides, there are other advantages like low operating costs, ozone friendly, negligible maintenance, noiseless and vibration-free, units.

UNDERSTANDING THE UNIVERSE
WITH PROF YASH PAL

What is the origin of the gaseous matter comprising the stars and galaxies? Surely something cannot be created out of nothing.

I could write a book-length story about this question. The story will contain many definite truths. It will have a lot of extrapolation and it might still leave out several big holes. Let me begin by first stating some things we now understand rather well.

We have found out that the familiar world around us is made up of less than one hundred elements. Hydrogen, oxygen, nitrogen, iron, carbon, copper, zinc etc right up to uranium represent examples of elements. Elements are defined through the number of protons in their nuclei. This we learnt later. First we learnt to recognise them through their chemical properties. It is amazing that wherever we look, the earth, the moon, the stars or vast interstellar and intergalactic spaces, the same and only the same limited numbers of elements are found. The richness we see on our planet is all derived from the multitude of ways in which these elements combine. This includes oceans, rocks, sand, little hills and mighty Himalayas. Besides it also includes all things living — the fantastic world of plants and flowers as also of butterflies and babies. Tens of millions of species on earth are all ultimately made up of stuff we are familiar with. The magic comes from differences in structure and architecture. Much of this structure is the result of forces whose nature by now we understand reasonably well. This also includes the question “Why nature has been constrained to have only 92 elements and not just 20, or as many as 500”. There are no real exceptions to the rules that govern the world of things we have encountered. Perhaps that is not strictly true but almost so. Those we cannot fully understand do not pose an ultimate violation but only represents our inability to comprehend and calculate. So now let us move to your question: how did all these things come into being? The variety they represent does not appear to be arbitrary. There is a deep related-ness. Therefore, the process of creation also cannot be arbitrary. Our broad understanding in this regard is the following:

We know by now that given enough concentration of energy, various forms of matter, such as protons, neutrons, electrons etc can be created and can transmute into each other. Einstein proved that theoretically exactly one hundred years ago. This is now well established in a large number of experiments. The ratio of particles produced depends on the details of interactions and the subsequent decay interactions. We understand a great deal in this regard through decades of theory making and experiments. The question arises as to what are the conditions and sources of such concentrations of energy. One of the moments where such conditions might have existed was the moment of the big bang, hypothesised to exist in the “beginning” of the universe. It might also be possible under special conditions involving high concentrations of mass — this is the contention of some scientists who are not happy with the big bang hypothesis. One should not be too worried about the availability of energy for this, because it can be shown that the positive energy of the particles produced is balanced by the negative gravitational energy. There is no generally accepted theory about the reason for the universe deciding to exist. Some people think that it was due to a quantum fluctuation in space-time! If all this is a little baffling, do not feel too unhappy. Scientists are still struggling with some of these aspects. But a lot about evolution of matter and energy in subsequent epochs is well understood. We think that the light elements, like deuterium, helium, lithium and beryllium were produced in the super hot stage like the big bang. The heavier elements were synthesised through thermonuclear reactions inside stars and those heavier than iron during supernova explosions of these stars. Stars can be considered as element manufacturing factories; they also produce heat, light and other forms of energy as a byproduct. Our sun is one such element-manufacturing factory. All this is not just science fiction or a loose story. The interactions involved and other aspects of stellar structure and evolution are fairly well understood.

What is the basic principle of working of a helicopter?

One thing is obvious. A helicopter has large propellers — essentially wings that rotate in the horizontal plane. They push the air downwards and resulting reaction lifts the helicopter. The horizontal motion can be obtained by slight tilt in the direction of the rotor and direction of motion is managed by the fan that is fitted on a horizontal axis near the tail of the helicopter. The rest is detail through which the rotor speed, the tilt of the rotor blades and the upward thrust are regulated. It is clear that maintenance of a certain altitude would depend on the pressure difference across the top and bottom of the machine. Within the operating limits of the helicopter, means are available to ensure that.

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New products & discoveries

Planets like earth

Artist’s depiction of a newly discovered Neptune-size planet orbiting the red dwarf star Gliese 436, which lies 30 light-years from Earth. NASA

Astronomers have discovered the three lightest planets known outside the solar system, moving researchers closer to the goal of finding extrasolar planets that resemble earth. One of the new planets joins three others orbiting the same star, forming the first-known quadruple-planet system.

Each new orb weighs between 14 and 25 times the mass of earth, or roughly the mass of Neptune. Although the compositions of the newfound bodies aren’t known, their relatively low masses suggest that they could be the first discovered extrasolar planets with solid surfaces.

Nearly all of the other 135 or so planets detected beyond the solar system are about as heavy as Jupiter-about 300 times the mass of earth-and are assumed to be mostly gas.

“Up until now, the technology has limited planet detection to those in the Jupiter- and Saturn-mass range,” says R. Paul Butler of the Carnegie Institution of Washington (D.C.), a codiscoverer of two of the new planets. Finding lower-mass planets bodes well for finding earthlike planets sooner rather than later, he adds. The trio of newfound planets is probably too hot to support life.

Learning from fish

A humpback whale shows off its side flipper with its distinctive
scalloped edge.

Ship propellers have served humankind well for more than a century, enabling vessels to travel in relatively straight lines over great distances. But modern engineers want to design vessels for more nuanced tasks. They want vehicles that can hover at the ocean floor and instantaneously respond to the current to hold their positions. They want vessels that can quickly manoeuvre around small objects or in tight spaces. They want machines that can operate in the harsh turbulence that would destroy existing craft. And they want all these capabilities in an energy-efficient package. In all, they want to reinvent the penguin-or perhaps the whale or a fish.