الفهرس 
INTRODUCTION & OBJECT OF INVESTIGATIONOnly 14 pages are availabe for public view
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Abstract
The subject of pozzolanic cements production has been of considerable scientific and technological interest because such cements increase the chemical resistance to sulphate and chloride attack, lowers heat of hydration, and improves both of hydraulic properties and fire resistance of blended cement. The use of pozzolanic cement is increasing world-wide because it needs less energy for production.
Metakaolin is a white ultrafine powdered form of anhydrous alumino-silicate derived from the calcination of raw kaolin at a specific temperature range. Condensed silica fume (SF) is a by-product of silicon or ferrosilicon alloys industries. It consists of ~ 99 % amorphous silica with very high surface area. These characteristics account for the pozzolanic activity of silica fume in terms of both its capacity of binding lime and rate of hydration reaction. Slag in general is a byproduct of steel extraction. Slag is generated at 3 different stages of processing and accordingly classified as: blast furnace slag, electric arc furnace slag and ladle slag, it is extremely necessary to have a complete knowledge about the behavior of construction materials before using in the structural elements.
This investigation is divided into three sections:
Section (A):
Section (A) aims to study the physicochemical and mechanical characteristics of some artificial pozzolanic cement pastes containing calcined nano metakaolin (NMK) fired at 750°C.
The OPC-NMK blends were prepared by the partial substitution of OPC by 4, 6, 10 and 15% NMK. Then each dry mixture mixed with water by using an initial water/solid ratio 0.27. The pastes were hydrated for various time intervals of 1, 3, 7, 14, 28 and 90 days. At each time interval, the hydrated pastes were tested for compressive strength and the other physico-chemical properties were investigated using the ground dried samples.
On the basis of the results obtained in this investigation, the following conclusions could be derived:
1. Paste made of 90% OPC + 10% NMK (mix M3) possesses the highest strength values at most hydration ages as compared to the other pastes containing 0, 4, 6 and 15% nano metakaolin (Mo, mixes M1,M2 and M4).
2. The variations of the combined water values (Wn, %) with age of hydration are agreed with the variations of the compressive strength values.
3. The free lime contents obtained for all admixed OPC-NMK pastes are lower than those of the neat OPC paste.
4. DSC thermograms and XRD difractograms obtained for the hardened pastes indicate the formation of: nearly amorphous 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), CH and CaCO3.
5. Scanning electron microscopy micrographs indicate the formation of more dense microstructure for the hardened different OPC-NMK pastes as compared to OPC pastes specially after 90 days of hydration.
Section (B):
Section (B) aims to study the physicochemical and mechanical characteristics of blended cement pastes containing electric arc furnace slag (EAFS).
The OPC-EAFS blends were prepared by the partial substitution of OPC by 4, 6, 10 and 15% EAFS. Then each dry mixture mixed with water by using an initial water/solid ratio 0.27. The pastes were hydrated for various time intervals of 1, 3, 7, 14, 28 and 90 days. At each time interval, the hydrated pastes were tested for compressive strength and the other physico-chemical properties were investigated using the ground dried samples.
On the basis of the results obtained in this study, the following conclusions could be derived:
1. The optimum replacement of OPC by EAFS that causes an improvement of compressive strength compared to the neat OPC paste is 6 %.
2. High replacement of OPC by EAFS (10 or 15%) causes a notable deterioration in the compressive strength during all ages of hydration.
3. The results of hydration reaction revealed that EAFS possesses low pozzolanic activity.
4. DSC thermograms and XRD difractograms obtained for the tested hardened pastes indicate the same components as discussed in section A the formation of: nearly amorphous 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), CH and CaCO3.
Section (C)
Section (C) aims to study the physicochemical and mechanical characteristics of some multi-blended cement pastes containing nano metakaolin (NMK), electric arc furnace slag (EAFS) and/or silica fume (SF).
Different blended cement mixes were prepared as the following: mix MS contains (90% OPC + 6% NMK + 4% SF), mix ME contains the (90% OPC + 6% NMK + 4% EAFS) and mix ES contains (90% OPC + 6% EAFS + 4% SF). Then each dry mixture mixed with water by using an initial water/solid ratio 0.27. The pastes were hydrated for various time intervals of 1, 3, 7, 14, 28 and 90 days. At each time interval, the hydrated pastes were tested for compressive strength and the other physico-chemical properties were investigated using the ground dried samples.
On the basis of the results obtained in this investigation, the following conclusions could be derived:
1. The results revealed that the replacement of OPC by 10% pozzolanic materials (NMK, EAFS, and SF) causes a slight decrease in the values of compressive strength as compared to that of the neat Portland cement paste.
2. The presence of silica fume causes a notable improvement for the mechanical properties for the hardened paste of Mix ES (90% OPC + 6% EAFS + 4% SF) as compared to Mix E3 (90% OPC + 10% EAFS); this reflects the higher pozzolanic activity of SF as compared with EAFS.
3. Mix MS (90% OPC + 6% NMK+ 4% SF) possesses the highest pozzolanic activity than the other multi-blended pastes.
4. DSC thermograms and XRD difractograms obtained for the pastes indicate the formation of: nearly amorphous 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), CH and CaCO3.
5. The hardened OPC-NMK-SF and OPC-EAFS-SF pastes possess a more dense microstructure as compared with the neat OPC paste.