Hi Building: What Is Concrete? Concrete for building is made by binding together, with cement and water, particles of fine aggregate and coarse aggregate. Fine aggregate is usually sand, the particles of which are less than 3/16 in. diameter, but it may consist of fine particles of crushed stone. Coarse aggregate consists of particles larger than 3/16 in. up to perhaps 2 in. diameter, consisting of gravel, crushed stone, brick, slag, etc.
These materials mixed together form a plastic mass, which sets as hard as stone, as a result of chemical action called the hydration of the cement whereby the water and cement combine. This hardening process continues for several months, even years, so that building concrete becomes stronger with age. The correct proportions in which to mix the cement and water, depend on the nature of the building work for which the concrete is intended. The resulting strength of the concrete and also its 'water-tightness' depend mainly on the amount of water used with a given amount of cement as long as the mixture is plastic and workable. This can be easily understood if the mixture of cement and water is considered as a paste holding the aggregates together; increasing or decreasing the proportion of water will dilute or thicken the paste and weaken or strengthen its cementing properties. To make concrete any well-known brand of cement may be used. It should be stored off the ground in a dry place and should not be used if it has begun to air-set from absorption of moisture. Cement is sold in packets containing approx. 94 lb. equivalent to 1 cubic foot. The sand (fine aggregate) should be clean, free from earth, clay or other foreign matter and should preferably be rather coarse and well graded from the largest particles down to the finest, with the larger sizes predominating. An excess of fine sand means that more cement has to be used to coat the particles and to fill the voids. A rough test for cleanliness is to put some sand in a glass of water and shake well. If the water becomes only slightly cloudy, the sand is fit to use, but if it is dirty, the sand should be washed. Crushed stone, in sizes from ΒΌ in. diameter down, is sometimes used in place of sand. It is satisfactory, provided it does not contain a large percentage of very fine particles of dust. If the particles are sharp, flat and elongated, they do not pack together as well as the more rounded particles of sand and so do not make as workable a concrete. Sand is usually sold by the cubic yard. It has the property of swelling or bulking with the addition of water up to a certain point, beyond which, if more water is added, the volume of sand will decrease to that occupied when perfectly dry. This bulking may amount to as much as 30% with only 5% of moisture present. As sand is often more or less damp, a cubic yard of damp soil will always contain less than a cubic yard of dry sand. If specified proportions are based on dry materials, it is necessary to increase the sand by the amount lost in bulking. For most concrete work, crushed stone or screened gravel is recommended. It should be clean, hard and durable, free from dust and foreign matter. It should be uniformly graded from the maximum size down to 3/16 in. sizes; smaller than this is classed as sand. Bank gravel, a natural mixture of sand and pebbles, is seldom used in good building concrete work without screening out sand, which usually occurs in excess quantity and then re-mixing the sand and pebbles in the specific proportions. One final point on good building concrete is the use of water. A good rule is that water must be fit to drink. It should be free from strong acids or alkalis and organic matter. Salt water may be used in plain concrete, although it retards the rate of hardening of the concrete, but should never be used in reinforced building concrete. ********************************************************************** This message and its attachments may contain legally privileged or confidential information. If you are not the intended recipient, you must not disclose or use the information contained in it. If you have received this e-mail in error, please notify the sender immediately by return e-mail and delete the e-mail. Any content of this message and its attachments which does not relate to the official business of Eraring Energy must be taken not to have been sent or endorsed by Eraring Energy. No warranty is made that the e-mail or attachment(s) are free from computer virus or other defect. ********************************************************************** [Non-text portions of this message have been removed] To listen to the show archives go to link http://acbradio.org/handyman.html or ftp://ftp.acbradio.org/acbradio-archives/handyman/ The Pod Cast address for the Blind Handy Man Show is. http://www.acbradio.org/news/xml/podcast.php?pgm=saturday The Pod Cast address for the Cooking In The Dark Show is. http://www.gcast.com/u/cookingindark/main.xml Visit The New Blind Handy Man Files Page To Review Contributions From Various List Members At The Following Address: http://www.jaws-users.com/handyman/ Visit the new archives page at the following address http://www.mail-archive.com/blindhandyman@yahoogroups.com/ For a complete list of email commands pertaining to the Blind Handy Man list just send a blank message to: [EMAIL PROTECTED] Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/blindhandyman/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/blindhandyman/join (Yahoo! ID required) <*> To change settings via email: mailto:[EMAIL PROTECTED] mailto:[EMAIL PROTECTED] <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
