The right cement for your house
G. S. Dhillon

THESE days cement has received attention of the publicity and advertisement agents and we find it being given a priority equal to other items such as cosmetics and consumer durables etc. The products are being marketed under attractive labels and slick advertisements.

The customer is bound to get attracted by the alluring labels and there is nobody to give correct advice Consequently, many builders have had bad experiences with many cements being marketed but it too late for them. With a view to providing some guidance on the matter, a market survey was carried out and a review of the products being sold is done. In this review, the test reports available or being supplied by the agents selling the cement have been used.

In the market the following cements dominate:-

Ordinary portland cement (OPC)

“Grade 43”, OPC: “Grade 53” and Portland Pozzolana Cement (PPC) and these are reviewed next.

The market survey indicated that more than 75% of customers ask for the Birla Samrat, in spite of the fact that this belongs to the family of “Pozzolana Cements” which had inherent drawbacks some years earlier.

The Grade 53 cement was not available in the market, and the reason given was that this type of cement had difficulties in its storage. After two to three weeks of storage, small nodules get formed in the cement bags and the customers hesitate to buy such cements.

The price difference between the OPC Grade 43 sold at Rs 147/- to 149/- per bag and the Birla Samrat and also the Grade 53 cement is a mere Rs 2 per bag.

The rate of development of strength of three cements discussed above is shown in the Figure 1 attached and some important characteristics are indicated in Table 1.

Comparison Grade 53 and Grade 43 types of cement have nearly identical chemical composition, and main difference is between the degree of fineness. The Grade 53 is ground to a greater degree of fineness compared to Grade 43. The former type has a fineness index (m2 /kg) of 329 compared to 293 for the latter. This renders the finer cement (Grade 53) to be quick setting type as its initial setting time is found to be 120 minutes compared to 155 minutes for the coarser variety (Grade 43). It takes 30 minutes for the Grade 43 cement to finally set after initial set but the time taken by the Grade 53 cement is 35 minutes.

In addition, the rate of development of strength of cement mix is found to be higher at all the three levels of 3 days, 7 days and 28 days. The strength (measured in MP for the three intervals for Grade 53 are, 38, 48 and 59 compared to 31, 41 and 56 for the Grade 43. Generally, it is found that strength at one-year interval in the two types becomes equal. But one-year data is not available.

Birla Samrat & Grade 43

The Birla Cement is obtained by adding 23% flyash to the OPC Grade 43. The details of the flyash used are not available but it falls in the requirements of I.S. 1489 (Part I) - 1991. The product obtained has rate of development lower than the Grade 43 cement in spite of the fact that the former type of cement is finer i.e. having fineness index of 350 (m2/kg) compared to the value of 293 for the Grade 43 (see Figure 1).

The three values of strength after 3 days, 7 days and 28 days are 28, 35 and 48 MPa for the PPC Birla Samrat compared with the already cited values for Grade 43 of 31, 41 and 56 MPa.

The setting time for initial set for the Birla Samrat (PPC) is 140 minutes compared to 155 minutes for the Grade 43 cement which means there would be some problems during the storage of PPC cement of Birla Samrat compared to the OPC Grade 43 but these would be lesser compared to those encountered with OPC Grade 53 cement.

The final set in the case of the Birla Samrat (PPC) occurs in 175 minutes and in 185 minutes for the Grade 43 cement but is 155 minutes in the case of Grade 53 cement. So the Grade 53 cement allows minimum placement time compared to the other two cements under consideration.

Conclusions that could be reached from the data given above are that for use in the foundations, for cement mortar for building work and plaster, the use of Birla Samrat can be given preference, but for use in the RCC (Reinforced Cement Concrete) work, the choice should fall for OPC Grade 43 cement. Grade 53 cement will also involve problems during site storage.

NEW PRODUCTS & DISCOVERIES
500-channel Internet Radio

TECHNOLOGY has a funny way, sometimes, of reinventing some of the great pioneering products of human ingenuity. At the Demo 2000 Technology Conference in Indian Wells, California, just such a product was unveiled which will radically change how people think of radio. Developed by a Silicon Valley start-up (where else!) founded by former executives from Apple Computer and Power Computing Corporation, the Kerbango Internet Radio is the first true, standalone radio that allows you to listen to audio streams being broadcast through the Internet.

In other words, the Kerbango radio allows you to “tune in” broadcasts ranging from those originating from local radio stations, to those being broadcast from across the country, and across the oceans to international programmes in foreign languages.

The setup is relatively simple: all one needs to do is connect the “retro box”, radio that is, to a standard dial-up, cable modem, DSL, or network.

Press the “ON” button, and the radio automatically connects to the Internet and displays available stations on a medium sized LCD display by category. These include: rock & roll, classical, talk radio, country & western, jazz, and about a dozen more.

By using the tuning knob on the face of the radio, you select the desired category and then individual stations or streams will be displayed to you. Press “SELECT” and you have the desired stream automatically being broadcast to and played over the radio.

Using an embedded version of the RealNetworks RealPlayer G2, the Kerbango radio tuner always stays up to date with the latest stations available over the Internet through an extensive database, termed the “Kerbango Tuning Service”, which stores information about all stations which the device finds on the Internet. Each audio stream is screened to ensure acceptable broadcast quality. Once added to the Kerbango station library, special automated programmes, called “StreamBots”, continuously check the station’s transmission quality and reliability to confirm suitability.

Personal Therapy Manager

Doctors sometimes let patients suffering from chronic pain self-administer prescribed doses of intravenous drugs. But those patients have always had to be tethered to an IV and drug bag. A new device that works with the world’s first and only implantable and programmable drug pump could change all that. Here’s how it works: morphine is stored in a pager-size pump just under the skin of the abdomen.

A small tube, or catheter, connected to the pump carries the medication to the fluid-filled space surrounding the spinal cord, where pain signals travel on their way to the brain. In response to breakthrough pain, the patient presses a button on a handheld remote that activates the pump to deliver a programmed dose of additional medication.

According to its maker, the SynchroMed infusion system works better and requires much smaller doses than intravenous methods because the pump delivers the medication directly to the place where it can be most effective. Availability: In 2003, for $1,800.To Learn More: www.medtronic.com

Colour wrist camera

This new model features a colour display that enable the wearer to view colour images right on his/her wrist. It has a STN colour liquid crystal display with 4096 colours.

Up to 100 full-colour images using 16.77 million colours can be stored in the memory, and a Visual Databank feature lets you attach up to 24 characters of text to each image for storage of names, phone numbers, and other information. The camera’s 4,096-colour LCD monitor screen lets you view images on the spot, as soon as you record them (in colour).

Other features include 2x digital zoom, a camera timer that can be set for 2, 5, or 10 seconds, and much more. Of course, it also provides standard timekeeping, plus a full-month calendar display with variable colouring for special dates, five alarms, a 1/10-second stopwatch, and a choice of six different display colour patterns.

Another cool feature is the thumbnail display, which can combine four images on display for simultaneous viewing. Page numbering of images has been added for simplified image searching. The metal parts of the case create sharp lines and an image of high-tech elegance. All of this makes this cool gadget an essential wrist gear item for the modern lifestyle. Sells for 245 pounds.

Blue Sapphire light

The blue Sapphire Crystal, which is semiconductor based, produces a high efficiency, non-deteriorating, solid state beam. There is minimal heat generation from the soft illuminating light, and the manufacturer is so confident in the design and durability, that they guarantee it for life.

It’s light source that can be seen for over a mile at 180 degree viewing radius, and being only 6.7cm long, it’s small and compact enough for you to take anywhere. Sells for about 12 pounds

Damning report

Earth’s population will be forced to colonise two planets within 50 years if natural resources continue to be exploited at the current rate, a damning report reveals.

A study by the World Wildlife Fund (WWF), released on Tuesday, warns that the human race is plundering the planet at a pace that outstrips its capacity to support life. In a damning condemnation of western society’s high consumption levels, it adds that the extra planets (the equivalent size of earth) will be required by the year 2050 as existing resources are exhausted.

The report, based on scientific data from across the world, reveals that more than a third of the natural world has been destroyed by humans over the past three decades.

SCIENCE & TECHNOLOGY CROSSWORD

Clues

Across:

1. Number system based on 2.

7. Substance possessing a degree of hardness but having no definite crystalline form.

8. Computer language used in artificial intelligence.

9. A plumbing special.

12. Rock produced by volcanic action.

16. A time system having a tropical year as its unit.

17. A graph in which number of protons is plotted against number of neutrons.

19. Symbol for Titanium.

20. Circular coloured membrane behind cornea of eye.

21. Prestigious open university of India.

22. Abbr. for Computer aided mail service.

23. Short for Chief Engineer.

24. A spacecraft that provided wealth of information on solar phenomena, was named so.

26. A research institute for government industry and other science undertakings (abbr.)

27. Symbol for Cadmium.

Down:

1. Branch of science dealing with study of motion of projectiles.

2. First software company to introduce engg. Export systems in India.

3. Overhanging edge of a stair tread.

4. A govt. programme to provide accelerated rural water supply.

5. Inflamed swelling in groin or armpits as symbol of plague.

6. Phenomenon under which some molecular formula represents two or more compounds.

10. Units of power.

11. A small kind of male deer.

13. A counter used to detect and measure radioactivity.

14. A quantum of energy of an oscillator.

15. A mass of material surrounding a nuclear reactor for protection from radiation.

18. Upper limbs of body.

25. Symbol for Molybdenum.

Solution to last week’s Crossword: