1. Introduction .....3-4
2. Proportions and Strength 4-5
3. Admixtures .......5
4. Aggregate . ...6
5. Cement ...7
6. Curing 7
7. Workability 8
The Romans used concrete at least 500 years before the time of Christ, and they were probably not the only ones or the earliest ones. Although concrete technology has advanced a little since those remote days, it is still used in modern building projects - from foundations for giant structures, to nuclear power stations, to sky-scrapers in our cities, to garage and patio floors, roads and railway sleepers, shore protectors against wave action, dam walls, bridges etc.
Modern concrete, very much like its earliest form used by our ancestors, is a mixture of cement, or a cement-like substance, with sand, stones and water. The water is added to the dry components to initiate the chemical changes leading to hardening, after which the strength and durability of the material is comparable to some of the hardest rocks. But, unlike the ages-long geochemical processes involved in rock formation, concrete can be mixed in a few minutes, and will approach its final hardness within a few weeks - or even a few hours if certain chemical "accelerators" are added during the mixing stage.
The "heart" of concrete is of course the cement - the substance that, with water, does the chemical work, and binds the sand and stones into an astonishingly strong, composite material.
The sand and stones are referred to as "aggregate": stones are the "coarse aggregate" and sand the "fine aggregate". Though less important than the qua...
... middle of paper ...
...UPKE, M. 2010. Textbewehrter Beton als Kurrosionsschurtz. Hamburg: Diplomica Verlag. FIVE CUBITS. 2012. Factors affecting the durability of concrete. http://www.aggregatetesearch.com/articles/18272/factors-affectingdurabilityofconcrete.
PCA( PORTLAND CEMENT ASSOSIATION) ( (a). 2012. Cement & Concrete Basics: Chemical Admixtures. http://www.cement.org/basics/concretebasics_chemical.asp.
PCA (PORTLAND CEMENT ASSOSIATION) (b). 2012. Cement & Concrete Basics: Curing Concrete. http://www.cement.org/basics/concretebasics_curing.asp.
ROBERTSON, S (Dr.). 2002. Chemistry of Cement – PART II. http://www.scienceinafrica.co.za/2002/september/concrete.htm. Science in Africa.
SABS (SOUTH AFRICAN BEUREAU OF STANDARDS). 1976. SABS Method 863: Compressive strength of concrete. Pretoria: SABS. WIKIPEDIA. 2012. Concrete. http://en.wikipedia.org/wiki/Concrete
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