الفهرس 
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Abstract
SUMMARY AND CONCLUSIONS Admixtures used for concrete are defined as materials other than hydraulic cements, water or aggregates that are added immediately before or during mixing but don’t take part in the hydration reactions and don’t make a substantial contribution to the hydration product. Chemical admixtures are one of the essential components of concrete in recent years. Different chemical admixtures with different composition have been offered to the users today in response to the needs of the construction market.
The major types of admixtures which used in concretes are: plasticizers (normal water reducers), superplasticizers (high range water reducers).
In this investigation the main mechanical and physico-chemical properties of the neat ordinary Portland cement and ordinary Portland cement pastes admixed with 0.25, 0.50, 0.75 and 1.00 percentage by weight of two types of admixtures namely Melamine Formaldehyde Sulphanilate (MFS), and Cyclohexanone Formaldehyde Sulphonate (CFS) were studied. The pastes were prepared using the values of standard water of consistency (W/C) ratio with different additions of each admixtures. The pastes were hydrated for various time intervals of 1, 3, 7, 28, 90 and 180 days. At each time interval, the specimens were tested for compressive strength, hydration kinetics, phase composition by X-ray diffraction analysis (XRD) and differential scanning calorimetry (DSC). Hydration kinetics were studied by determining the chemically combined (non-evaporable) water and free lime contents. Also the effect of different percentage additions of each admixture on the rheological characteristics of Portland cement was investigated via determintion the values of mini-slump of the prepared pastes.
On the basis of the results obtained in this investigation, the following conclusions could be derived:
1. The results of compressive strength values obtained for hardened OPC pastes admixed with different weight percentage of MFS or CFS admixture indicate a notable lower values as compared to the values obtained for pastes made from neat OPC (Mix Ao), especially during the early ages of hydration. These results explained in terms of the retardation effect of both MFS and CFS beside their water reducing effect.
2. The combined water contents and free lime values for all admixed hardened OPC pastes are lower than the values obtained for neat OPC hardened pastes.
3. DSC thermograms and XRD difractograms obtained for neat and admixed OPC hardened pastes indicate the formation of: nearly amorphous and illcrystalline calcium silicate hydrates (mainly as CSH-I and CSH-II), calcium sulphoaluminate hydrates (ettringite and monosulphate hydrates), calcium aluminate hydrates (mainly as C4AH13), hydrogarnet (mainly as C3ASH4 and C2ASH8), Portlandite (CH) and CaCO3.
4. Rheological measurement indicated that the mini-slump values of cement pastes admixed with different doses of CFS and MFS are higher than that of neat OPC. Also; increase the amount added of each admixtures; increase the values of mini-slump. These results are mainly due to increase the fluidity of these cement pastes.
5. The obtained results of mini-slump values indicated that CFS admixture has higher efficiency in improving the rheological properties of