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Abstract
CHAPTER V
SUMMARY AND CONCLUIONS
The pozzolanas are silicieous and aluminous materials, either natural or artificial which in itself possess little or no cementing properties, but will in a finely divided form and in the presence of moisture react with Ca (OH)2 or with materials that can release Ca(OH)2 such as Portland cement clinker at ordinary temperatures to form compounds possessing cementitIous properties.
Fillers are usually fine chemically inert natural and industrial materials which have no hydraulic activity but have microfilling effect results in beneficial effects on desirable properties of concrete. High filler content reduces strength of concrete through the porosity of cement matrix is reduced.
Pozzolanic cements are usually blends of less than 95% Portland cement clinker with other finely ground pozzolanic materials such as dealuminated kaolin, silica fume, homra and fly ash as well as latent hydraulic materials such as ground granulated blast- furnace slag. Blended cements have attracted considerable interest, from both scientific and technological points of view, since the beginning of this century.
In pozzolanic cements, the addition of pozzolana to Portland cement can include the following benefits:
i- Pozzolana improves the ultimate strength of hardened cements by transforming lime into calcium silicate and calcium aluminosilicate hydrates.
ii- Pozzolanic cements may also show enhanced resistance to firing because pozzolana improves the mechanical properties of cement.
Basalt is an aluminosilicate material and can be used as filler by adding to the Portland cement. Also, basalt acts as filler and nucleating agent, which accelerates the hydration of Portland cement and improves the firing resistance of hardened cement pastes.
Dealuminated kaolin is an industrial by- product produced from the preparation of aluminium (alum) and obtained from Egyptian Shabba, Company, Egypt. The alum is produced from calcined kaolin fired in the range 800-850ºC and treated with concentrated sulphuric acid. The filtrate is aluminum sulphate whereas the precipitate is the dealuminated kaolin.
The starting materials used in this work were OPC from Suez cement Company and fresh basalt provided from (Abou- Zaabal, Cairo, Egypt) and dealuminated kaolin provided from Shabba, Company, Eygpt.
The aim of the present study is to investigate the pozzolanic activity of (dealuminated kaolin) with lime. Also, the effect of substitution of OPC with basalt and substitution of basalt with dealuminated kaolin on the physico- chemical properties of pozzolnaic- filled cement pastes was studied. It was suggested that dealuminated kaolin accelerates the rate of hydration of pozzolnic- filled cement by the reaction with the liberated Ca(OH)2 forming hydration products precipitated in some of open pores of the cement paste.