Concrete is the single most widely used material in the world Essay
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Concrete a composite man-made material is the most widely used material in the construction industry. It consists of a rotationally chosen mixture of binding material such as lime or cement, well-graded fine and coarse aggregate, water and admixture. In a concrete mix, cement and water form a paste or matrix which fills the voids of the fine aggregate and binds them (fine and coarse) together. The mixture then placed in forms and allowed to cure and becomes hard like stone. The hardening of concrete is caused by chemical reaction between water and cement and it continues for a long time, and consequently, the concrete grows stronger with age.
The strength, durability and other characteristics of concrete depend upon the properties of its ingredients, the proportion of the mix, the method of compaction and other controls during placing and curing. Basically, concrete can be classified into two stages namely which is fresh concrete and hardened concrete. There are a few types of concrete likes polymer concrete, glass concrete, asphalt concrete and geopolymer concrete.
Geopolymers are formed by alkali-activating a variety of materials including fly ash, blast furnace slag, thermally activated clays etc. to produce a cement-like material. The three most common raw binders used in polymerization are slag, calcined clays (metakaolin) and coal fly ash. The binder materials should contain high levels of aluminum (Al) and silicon (Si) in amorphous form. The raw materials play a significant role in the geopolymer reaction and affect the mechanical properties and microstructure of the final polymeric products.
Generally, materials containing mostly amorphous silica (SiO2) and alumina (Al2O3) are the source for geopolymer production. Naturally available materials like kaolin , natural puzzolana and Malaysian marine clay , treated minerals like metakaolin and waste materials like fly ash ,Construction waste , red clay brick waste , fly ash and rice husk-bark ash, fly ash and blast furnace slag etc can be used. Many different materials have already been investigated and used as the binder in geopolymer concrete mixes, including:
Low calcium fly ash ( Class F fly-ash)
High calcium fly ash (Class C fly-ash)
Calcined kaolin or metakaolin
Natural minerals containing Al and Si
Geopolymer binders may be made from a variety of alumino-silicate sources. The engineering aspects of geopolymer concrete as later described in this document relate to geopolymeric materials based primarily on low calcium (or Class F) ﬂy ashes. Geopolymers incorporating significant quantities of calcium-rich materials such as slag, for instance, may have different properties to those based on low calcium ﬂy ash alone. While commercial availability of geopolymer concrete is a new phenomenon, not just in Australia but globally, geopolymer technology and its application in real projects is not new. Development of the technology has been undertaken in Europe for the entirety of the post-World War 2 era, predominantly in Ukraine during and following the Soviet rule, but significantly in France, Spain, Germany and other countries.
This era of research and development resulted in the construction of numerous structures including civil waterworks, railway sleepers, pipes, pavement, roads, fire resistance coatings, conventional precast products and even a twenty-story apartment building in Lipetsk,
Russia. Some of these structures are now over sixty years old and their durability has been proven in both the laboratory and most importantly, in the field. Despite this level of large-scale development, the commercial impetus to develop the technology into a business did not arise until the highly substantial carbon emissions from conventional OPC manufacture have become
2.1BACKGROUND OF STUDY
The study of the strength of geopolymer concrete by using oven curing was done by P. K. Jamade and U.R. Kawade. Geopolymer concrete is prepared by mixing the fly ash, sodium silicate and sodium hydroxide in this study case and cured at a different temperature which is 60℃, 90℃ and 120℃. The observation has been showing that geopolymer concrete gained a larger compressive strength at higher temperature. The curing time also affects the polymerization process which influences the compressive strength of geopolymer concrete. The polymerization process can be improved by increasing the period of the curing to increase the strength of geopolymer concrete.
Steenie Edward Wallah uses four different test specimen which has the different compressive strength to test the shrinkage of geopolymer concrete. The result was compared to the drying shrinkage value which was calculated by using Gilbert method. The result showed that the geopolymer concrete has a very low drying shrinkage. However, the value of drying shrinkage calculated by Gilbert method was 5 to 7 times higher than the value measured.
Monita and Hamid R. Nikraz studied the strength characteristics, water permeability, and water absorption of low calcium fly ash based geopolymer concrete. Geopolymer mix was tested with different water/binder ratio, aggregate/binder ratio, alkaline/fly ash ratio and aggregate grading. The results showed that reduce the water/binder ratio and aggregate/binder ratio can obtain a good quality of concrete; the water permeability does not affect by any factor; the water absorption increased by using well-graded aggregates, reducing water/binder ratio and increasing the content of fly ash.
Arya Aravind and Matthew M Paul had focused the study on the compressive strength and tensile strength of geopolymer concrete with the reinforcing steel fiber. Experiments were carried out in Box-Behnken experimental design which is a type of response surface methodology. From the result of the Box-Behnken design, it can be concluded that the compressive strength of geopolymer concrete is increased with an increase of the curing period. When the percentage of steel fiber increased, the tensile strength of geopolymer also increased. The strength obtained under the curing process with normal sunlight was 16 N/mm2.