|SCIENCE TRIBUNE||Thursday, August 17, 2000, Chandigarh, India|
For stronger, wider, durable roads
Paints that change colour
For stronger, wider, durable roads
INDIA has a vast road network of 2.4 million kilometres. However, the condition of most of the roads is deplorable. Potholes, deep enough to break the axles of vehicles, stretches, washed away by rains and berms poorly maintained and often becoming death-traps for scooterists constitute integral parts of many of our roads and highways. Not that the road construction technology has not seen growth. The tragedy is that we have not fully adopted the new developments and are resigned to whatever condition of roads is provided to us.
No doubt there has been an unprecedented growth in road traffic in India. Suddenly we have lost count of the car makes. Cargo transport has grown by 60 times during the last 50 years. Passenger traffic has risen by 65 times and number of vehicles by 80 times. Road network, however, has not grown in proportion. And this is despite the fact that a host of new methods and machinery have been invented for road construction — the ones that can give stronger, wider and durable roads !
Be it the improvement of soil conditions to provide a strong sub-base before the laying of road, be it the compaction of sub-grade, be it the construction of top paving or be it the requirement of utmost precision in road camber and longitudinal level, highly effective, fully automatic and sophisticated machinery has been developed and even put to use in cases where the authorities have maintained a stringent control over quality of work. That the number of such cases is small is, however, a different story.
Most of Indian roads are flexible pavements, the ones having asphalt-toppings. These days, a little switch-over to rigid pavements, that is concrete roads, has begun. Each type of pavements have their own advantages and disadvantages. Flexible pavement have a great advantage that these can be strengthened and improved in stages with the growth of traffic. Another major advantage of these roads is that their surfaces can be milled and recycled. These are less expensive also. Concrete roads, on the other hand, offer better skid resistance, need lesser maintenance, allow better vehicle-mileage to road users and do well when subjected to freezing and thanking conditions.
In addition to giving due consideration to various advantages of each type of paving, selection depends on additional factors such as local availability of materials, availability of funds and climatic conditions. Certain factors change with time. Earlier, there used to be scarcity of cement and India went for asphalt-top roads. These days, asphalt that is generated during the refining process of petroleum — a diminishing product, tends to become scarce while cement is available in abundance. The present situation reveals that both type of roads shall be adopted by India in future with a tilt towards concrete roads.
While the vehicular and passenger traffic is bound to rise further in India in an unabated manner, there is an immediate need to adopt the latest techniques for road construction and to maintain and widen the existing roads. Forgetting whatever has been done in the past and taking cue from "it is never too late", it is time now to look into the following developments and adopt them to maximum possible extent.
Machinery for compaction: Heavy weight has no more remained the necessity for the compaction of the soil. Vibratory rollers have now been developed and seen a great improvement during the last few years. They can be used for compaction of soil as well as asphalt surfaces. They act on the principle of eccentricity. Their main components are an ecentric weight and a rolling drum. The eccentric weight is made to rotate by a motor. Its connection to the roller drum produces vibration in the drum which repeatedly lifts itself and bounces against the base sending impact-waves through it and thus compacting it to a greater depth. Such rollers have proved highly effective in sandy soils.
Many Indian companies of Delhi, Bangalore, Patna, Nasik, Faridabad and Ahmedabad are producing such rollers with a variation in width, weight, vibration frequency and the number of drums. A very limited use, however, has been made so far.
Oscillatory rollers are a further improvement over vibratory rollers. In these rollers, there are two eccentic weights instead of one as in vibratory rollers. These two eccentric weights cancel the vertical vibrations of each other and thus cause horizontal vibrations only. Due to the cancellation of vertical vibrations, the drum does not lift above the ground but causes oscillations in it resulting in better compaction of upper layers of soil. Experiments have proved that such rollers even if 25-30% lighter than vibratory rollers give better and smooth compaction. Their fuel consumption is also lesser. Such rollers are quite useful when an under-laid sewer or a near by foundation is to be saved.
Machinery for paving: In order to have best road surface, excellent finish and excellent riding quality, use of pavers has become mandatory in developed countries. Though India has begun producing pavers, very little use of them has been made so far. Pavers are wonderful machines that can give utmost accuracy in road construction. They can be used both for concrete as well as bituminous roads. They are both crawler type and wheel mounted, the former used for larger road width.
Pavers can handle up to 300 cubic-metre of concrete per hour even if the thickness of pavement is as little as 30 cm. Earlier, the pavers used to be run on rails but now they have given way to slip-form pavers which are capable of bringing a revolution on road construction front. The pavers being produced in India can lay road width varying from two metre to 17 metres in a single pass. Indian slip-form pavers are highly versatile and many optional equipments can be attached to them. While the MES, IRCON and a few other departments have built some roads with pavers, a more frequent use needs to be made wherever possible.
Systems for accuracy: Automatic controllers have been developed to control longitudinal level and transversal slope of roads. Electronic level sensors are mounted on the pavers for longitudinal level checking and these continue to check the material thickness with respect to a fixed datum. Transversal slope controllers are mounted on the cross beams and send signals as an when there is a change in slope. In addition to these electronic controllers, manual controls are kept stand-by. Now-a-days, microwave technology and laser systems are being inducted in road-construction-equipment-control.
Recycling equipment: Recycling of road material is an aspect extremely important to a country like India which can not spend heavily on relaying altogether new roads along the worm out ones. Patch-work is of no use in India. After one shower or two, roads regain their deteriorated condition. Laying of a seal coat over the worn out road again proves useless as it is unable to provide strength and stability to the road. Moreover, relaying of seal coats not only proves expensive but raises the level of the roads thus disturbing the drainage system, side-walks and the berm-position.
Cold recyclers have now been developed which mill the broken road surface, add cement or bitumen emulsion to it and relay the course in a single cylce. A lot of saving is thus achieved and road level is also maintained. Mumbai Municipal Corporation recently used the cold recyclers to repair their asphalt roads and results were quite satisfactory. India must respond fully to recycling of road materials instead of resorting to patch-work as most of its roads are asphalt-topped.
In addition to above
developments, a lot of experimentation is under progress. Use of
Fibre-reinforced concrete, pre-stressed concrete, roller compacted
concrete and vacuum processed concrete is being tried. Even the
pavement design methods are undergoing a significant change as the
engineers want to get rid of age-old empirical formulae. Need of the
hour is to reframe our road specifications, induct compulsory use of
machinery in road construction, recycle the used material by milling
the existing roads so as to bring savings and to free the country of
all the criticism that the pathetic condition of its roads invites.
Paints that change colour
by G.V. Joshi
IN a hot country like ours, there is always a danger that most vaccines may lose their potency due to exposure to high temperature either during transit or due to poor storage facilities.
It is not possible for a common man or even a doctor to know whether a vaccine or medicine has lost its potency due to exposure to high temperature. Some researchers have also started questioning whether the much publicised polio vaccine is really effective in rural areas because it may not be stored or transported at the desired low temperature.
Now scientists at the Indian Institute of Chemical Technology (IICT) in Hyderabad have developed a new type of temperature sensitive warning labels for vaccine vials. These labels change their colour if the vaccine or medicine contained in the vial is exposed to temperature higher than the prescribed one.
According to K V Raghavan, director of IICT, the institute is ready to transfer the technology and is looking for industrialists to take up commercialisation. Such labels are compulsory in developed countries.
One of the simplest and certainly most colourful of the procedures to indicate the temperature of surfaces is based on colour changes that certain materials undergo when they are heated.
Coatings of these substances which can be applied to metal, glass, ceramic bricks or practically any other surface, change their shade completely at specific temperatures. The resulting hue in most cases does not change when the material cools, but remains as a permanent visual record.
Temperature indicating paints known as thermo-colours were developed before World War-II by German chemists in connection with its fuel research and aircraft engine efficiency studies.
Mixtures of indicators may be used for colour changes at more than one temperature. The thermal indicators are easy to use. One hundred parts of a coloured powder are stirred with 60 to 80 parts of alcohol and the resulting paint spread thinly up on the surface to be tested.
At present, powders are available which change colour at temperatures ranging from 40 to 1000 degrees celsius, some of them passing through as many as four distinct changes at progressively higher temperature.
The ability of thermo-colours to indicate thermal conditions of an entire surface — not merely a few isolated points —and the value of enduring record suggests industrial potential.
Their uses include supervising the heat of reactors, studying heat distribution and heat transfer in processing equipment, pointing insulation failures or flaws in castings, and signaling thermal strains and overheating.
For best results, a few requirements and limitations must be kept in mind when any of these paints are used.
Any material with which the pigments are mixed must withstand the temperature the thermo-colours will be exposed to. When the oil is in contact with the coating, a layer of protective lacquer over it is recommended.
If the foul smelling gas — hydrogen sulphide — is present in concentration of two per cent or more, only three of the colours are affected adversely by ammonia and sulfur dioxide.
For all but one of the colours, the colour change is also influenced by the length of time the paint is exposed to high temperature. For example, a thermo-colour rated for 440 degrees celsius on 30 minutes exposure will change colour in ten minutes at 445 degrees celsius. A chart provided with the colours enables the user to determine the actual temperature of the surface by these known time-temperature relationships.
Thermo-colours are just one of a number of somewhat novel methods for applying physical and chemical changes to determine temperature.
Recently technologists have used a black strip of paper covered with a white coating which on heating melted and was absorbed into the paper backing. A visual change in the test strip from white to black at a specified temperature has been reported.
One well known line of materials with specific melting points is marketed in the form of sticks, pellets or liquids that may be applied as surface marks or coatings. By observing the melting point, the temperature of the surface on which the indicating material has been placed can be estimated over a range from 45 to 1370 degrees celsius temperatures.
Some day not too far
away, it may be possible to have colour changing labels so sensitive
as to indicate body temperature from 36 to 42 degrees celsius when
applied to the forhead of any patient will indicate whether he has
fever or not. For children, they will be a boon because the danger of
swallowing mercury by accidental breaking of a thermometer under the
tongue will be a thing of the past.(PTI)
Not so plain sail
The Norwegians call it the "Plain Sail". But there is nothing plain about this sailboat, which has taken sailing to new heights. The 16-metre (57-foot) state-of-the-art Timarand Vacht is powered by three giant wings attached to roller bearings.
Unlike the conventional sailing boat, these wings hoist the boat much like a hovercraft and enable it to achieve great speeds.
But veteran seafarers say that it is more fun sailing at normal speeds on the "Plain Sail" because it not only gives excellent manoeuverability but also has plenty of space to move around and you can go deep sea fishing as well.
Mini medical robots
Robots the size of the punctuation mark in this sentence could one day be used to move single cells or capture bacteria, say Swedish inventors.
The tiny robots are shorter than a hyphen and no wider than the period at the end of this sentence, according to Edwin W.H. Jager of Sweden’s Linkoping University.
The robots might be used as microsurgical instruments, explained Jager.
Or, he added, these microrobots might be used to build other microdevices, just as cars are built by robots. In medicine, the robots could move a single cell from one point to another, he said.
In experiments the team has used the robots to pick up and move tiny glass beads invisible to the unaided eye, the scientists reported in Science.
The microrobots are made of layers of polymer and gold and somewhat resemble a human arm. The robots have flexible elbow and wrist joints and the research team made them in various forms with hands made up of two to four fingers.
Importantly, Jager noted, these devices can work while submerged in such liquids as blood, urine and cell-culture medium, suggesting possible uses in biotechnology. Stuck on the end of a catheter, the microrobots might increase the range of surgeons.
To make the microrobots move, the team used
conducting polymers in the joints. These polymers absorb charged particles
called ions from the surrounding liquid, or shed them, depending on the
electrical charge applied through tiny wires connected to the robot.