الفهرس 
INTRODUCTION AND OBJECT OF INVESTIGATIONOnly 14 pages are availabe for public view
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Abstract
The objectives of the present investigation are to study the main hydration characteristics of autoclaved building products derived from ordinary Portland cement clinker (PCC) gronnd granulated blast furnace slag (GGBFS) metakaolin (MK) nano- metakaolin (NMK) cement kiln dust (CKD) hydrated lime (CH) and gronnd sand (S).
Different hydrothermal reactions were studied by the hydrothermal treatment in an autoclaved at a pressure of 8 atm. of saturated steam for different time intervals of 0.5,2,6,12 and 24hours. Various hydrothermal reactions were studied with respect to hydration kinetics, compressive strength and phase composition of the formed hydration products and the following autoclaved systems were investigated:
1.PCC
2.PCC – GGBFS
3.PCC – GGBFS –S
4.PCC – GGBFS – MK
5.PCC – GGBFS – MK – NMK
6.CKD –S
7.CKD – GGBFS –S
8.CH –S
9.CH – GGBFS –S
Various blended cement pastes were prepared from the different dry mixtures by mixing each dry mixture with water (Water/Solid ratio = 0.27 – 0.28) and the cylindrical specimens having 2cm diameter and about 2cm height were mounded under a hydraulic pressure of 50kg/cm2. The specimens of each mixture, thus obtained, were first cured at 100% relative humidity at room temperature for 24 hours and cured under hydrothermal conditions in an autoclave at a pressure of 8 atm of saturated steam for ( 0.5, 2 , 6 , 12 and 24 hours. At the end of each autoclaving period, the specimens were removed from the autoclave for dried a overnight at 1050C to remove the free water.
The dried specimens, obtained after each autoclaving time, were tested for their compressive strength; then, the following studies were carried out on the ground dried specimens:
1-Kinetics of hydration products were studied by the determination of chemically combined (non-evaporable) water (Wn , %) and free lime (CaO,%) content at the different autoclaving times.
2-Phase composition of the formed hydration product was investigated by means of x-ray diffraction (XRD) and differential scanning calorimetry (DSC).
3-Morphology and microstructure of the hydrothermally hardened specimens were studied using scanning electron microscopy (SEM).
The results of physicochemical and mechanical studies obtained from this investigation were divided into four parts; these are:
In part A, the results of the main physicochemical and mechanical characteristics of the autoclaved specimens made of PCC (mix A0) , PCC – GGBFS (mix AI) , PCC – GGBFS – S (mix AII, AIII and AIV) blends indicated the following:
1-The autoclaved specimens made of PCC (50%) – GGBFS(50%) blend (mix AI) possess of lower compressive strength values than those of the specimens made of the neat PCC(mix A0) at all ages of hydration. However, the incorporation of ground sand (S) at the expense of GGBFS and /or PCC leads to an enhancement in the compressive strength values at all autoclaving ages for the specimens made of PCC – GGBFS –S blends (mixes AII, AIII and AIV).
2-The decrease in the strength values of the specimens made of PCC – GGBFS blend of mix AI is mainly due to the formation of hydration products having weaker hydraulic properties, mainly as hydrogarnet – like hydrate (C3ASH4), at the expense of calcium silicate hydrates (CSH) which possess stronger hydraulic character. This conclusion is also confirmed from the results of XRD, SEM and DSC studies reported in this investigation.
3-The results of hydration kinetics, as obtained from non – evaporable water (Wn,%) and free lime (CaO,%) contents are in agreement with the result of compressive strength development of the autoclaved PCC – GGBFS pastes.
4-The higher strength values of the hydrothermally hardened specimens made of autoclaved PCC – GGBFS – S blends (mixes AII, AIII and AIV) are mainly attributed to the formation of CSH hydrates at all ages of autoclaving as confirmed by the results of XRD, DSC and SEM studies.
In part B, the results of the main physicochemical and mechanical characteristics of the autoclaved specimens made of PCC- GGBFS - MK (mixes BI, BII & BIII) and PCC- GGBFS – MK-NMK (mix BIV) blends indicated the following:
1-In case of PCC- GGBFS – MK blends, the compressive strength values increase with increasing GGBFS content and decreasing MK content at all autoclaving ages , where the autoclaved specimens made of mix BI possess of the highest compressive strength values as compared to these made of mixes BII and BIII.
2-The results of the hydration kinetics , as obtained from the values of non – evaporable water (Wn,%) and free lime (CaO,%) indicated the same variations observed in the compressive strength values with increasing time of autoclaving .
3-The results of the phase composition, determined by XRD analysis
and DSC thermograms, indicated that the main phases in identified are CSH ,CH and quartz.
4-The PCC(50%) – GGBFS (45%) – MK (5 %) blends of mix BI represent the optimum composition which possess reasonable physicochemical and mechanical characteristics of the autoclaved specimens made PCC- GGBFS – MK blends .
In part C, the results of the main physicochemical and mechanical characteristics of the autoclaved specimens made of CKD –S (mixCI) , CKD –S – GGBFS – (mixes CII, CIII and CIV) and CKD –S –GGBFS – NMK (mix CV) blends indicated the following:
1. The utilization of CKD as an alkaline activator for GGBFS and S hydration in autoclaved CKD –S and CKD–GGBFS-S blends is associated with relatively low compressive strength values for the specimens made of these blends.
2- The incorporation of NMK in CKD – GGBFS –S – NMK blend (mix CV) is accompanied by a slight increase in the compressive strength results of the autoclaved specimens made of this blend.
3- The results of phase composition, as obtained from XRD and DSC studies, indicated the presence of CSH, CH, CASH, and quartz.
4- Almost all of the free lime content, present in CKD, is almost consumed at all ages of the hydrothermal process.
In part D, the results of the main physicochemical and mechanical characteristics of the autoclaved specimens made of lime –S (mix DI)
and lime - GGBFS –S (DII , DIII and DIV) blends indicated the following:
1-The utilization of hydrated lime (CH) as an activator for S and GGBFS hydration in autoclaved lime - S and lime –S – GGBFS hydrothermal reactions is associated with relatively low compressive strength values for the specimens made of these blends.
2-The main phases identified are CH,CSH and quartz as obtained from the results of XRD analysis .The intensities of peaks characteristic for quartz and calcium hydroxide (CH) phases decrease with increasing age of autoclaving ; while the intensity of the peaks characterizing calcium silicate hydrates (CSH) increase with the increase age of autoclaving .
3- The results of non – evaporable water content showed the same parallel variations observed in the compressive strength with increasing age of autoclaving.