الفهرس 
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Abstract
The work aims to study the pozzolanic activity of different types of silica such as microsilica (SF), nano-SiO2 (NS) and the silica obtained from the burning rice husk (rice husk ash, RHA). This comprises the activity of the reaction of each type with lime as a function of curing up to 90 days. The pozzolanic activity can be studied by mixing various contents of lime with silica sources in suspension with curing time up to 90 days. This is followed by the determination of the combined water, residual lime, and insoluble residue. The hydration products can be followed by using XRD, DTA, IR, SEM, and TEM techniques. The nano-size of each type of nano-silica can be determined by TEM technique. The pozzolanic activity was studied as suspension in bottles at the ratio water/solid ratio of 10. The hydration of each mix was investigated after 1, 3, 7, 28, and 90 days of hydration. Each mix of exactly 10g was introduced into air-tight-bottles containing 100 ml distilled water. The bottles were tightly stoppered and mixed with paraffin wax. Suspensions of SF, NS, and RHA were mixed with different ratios of lime (5%, 10%, 15%, 20% and 25%).The bottles were tightly stoppered and mixed with paraffin wax to avoid any carbonation from atmospheric air. The bottles were mechanically stirred from time to time, daily, with mechanical shaker, in order to attain complete homogeneity with water. After each time of hydration, the hydration was stopped by chemically method.The stopping solution was prepared (1:1by volume) of methyl alcohol and acetone, then filtered through sintered glass funnel (G4), washed three times with the stopping solution and finally dried at 60˚C, then kept in air tight containers using a desiccator until the time of testing was reached, for further investigations.Part A: Pozzolanic activity of silica fume:Part A aims to study the activity of silica fume. The different solid dry mixtures are hydrated in the suspension form using water/solid ratio of 10. The resultant suspensions are cured at room temperature for different time intervals of 1, 3, 7, 28 and 90 days.Thephysico-chemical properties studied are: hydration kinetics, X-ray diffraction analysis (XRD), differential scanning calorimetry (DSC), Fourier transform Infrared (FTIR) spectroscopy as well as scanning electron microscopy (SEM). Hydration kinetics was also studied by determining the chemically combined (non-evaporable) water and free lime contents of the dried pastes at the various ages of hydrationThe main conclusions derived from the results of part A are summarized as follows:The pozzolanic activity of the SF is the rate of the hydration of SF with lime as a function of curing time at room temperature. The mixes containing 95:5, 90:10, 85:15, 80:20 and 75:25 SF-CH in suspension form (mixes A.1, A.2, A.3, A.4 and A.5) cured up to 90 days1. The free lime contents of all mixes decrease sharply during the early hydration ages. Evidently, the mixes A.1 and A.2 possess lower values of free lime content than those of A.3, A.4 and A.5.SF has higher lime fixation ability especially at the early ages of hydration.2.The combined water contents increase gradually with curing time for all of the pasts, which is due to the progress of hydration process with curing time and the formation of C-S-H (I, II). The chemically combined water content appears to be reduced with time due to a release of water during polymerization of silicates.3. The results of free silica contents decrease continuously with curing time. As the hydration time increase, the rate of hydration accordingly, increases with the formation of more (C-S-H) hydrated products. Mix A.5 has a lower value of free silica contents up to 90 days.Part B: Pozzolanic activity of nano-silica:Part B aims to study the activity of nano-silica. The different solid dry mixtures were hydrated in the suspension form using water/solid ratio of 10. The resultant suspensions are cured at room temperature for different time intervals of 1, 3, 7, 28 and 90 days.The main conclusions derived from the results of part B are summarized as follows:1.The free lime contents of NS/CH decrease sharply during the early hydration ages, and almost are consumed after 1 day for all samples; indicating a high degree of reactivity at the early ages of hydration, NS acts as nucleating agent, which accelerates the rate of hydration, which reacts with CH forming (C-S-H). NS is an amorphous very active form of silica, which is higher than SF in reactivity.2. The chemically combined water values of NS/CH are higher than those values within SF system, indicating a higher reactivity of NS than SF, these results are mainly related to the relative pozzolanic reactivities and/or the types of hydration products and surface area formed at the different ages of hydration. 3.Mix N.5 has a lower value of free silica contents up to 90 days. 4.The area of the endothermic peak corresponding to C-S-H phase increases with curing time, and it is higher than those of SF system. There is no mass loss of endothermic peak located at 420-500°C, attributing to the dehydroxylation of CH, indicating a higher reactivity than NS.5.XRD diffraction patterns show that the intensities of the peaks characterizing CH decrease with increasing age of hydration; however, the peaks characteristic for free CH are completely disappeared after 1 day of curing in NS/CH suspension form6. SEM micrographs of NS/CH show a closely-packed structure was appeared, which composed mainly of nano-crystalline hydration products. The microstructure of the paste after 90 days of hydration displayed the formation of nearly nano-crystalline C-S-H products as well as rod-like crystals like. Part C: Pozzolanic Activity of Rice Husk Ash:The pozzolanic activity of the rice husk ash fired at differenttemperatures 500ºC, 700ºC, and 900ºC, can be studied by mixing various mixes of RHA/CH in suspension form with curing time to 90 days. The pozzolanic activity was determined from the combined water, free lime, and free silica contents. Some selected samples were examined by the aid of SEM, TEM, IR and DTA techniques1.The free lime contents of all mixes decrease sharply during the early hydration ages, and almost consumed (zero %) after 1 day. This is due to the higher surface area of the rice husk ash fired at 500ºC. Rice husk ash fired at 500-700°C is an amorphous active form of silica, which leads to form C-S-H, which is higher in its reactivity than SF, but lower than NS. RHA fired at 900ºC, is exhibiting a lower degree of amorphousness, indicating the low degree of reactivity at the early ages of hydration, which is similar to SF.2.The chemically combined water content of RHA fired at 500ºC/CH suspensions mixes showed the highest values as shown with SF/CH, but lower than NS/CH mixes, that indicates a comparable a higher rate of hydration, especially at the early age of hydration.3.The combined water values are the highest values, indicating the highest reactivity relating to RHA fired at 500 °C and 700°C as well as in the case of NS. The combined water values of RHA fired at 900ºC are similar to SF-CH, indicating a lower activity, relating to the relative pozzolanic reactivities.4.Evidently, the free silica contents decrease, since the amount of CH disappears, equal to that reacted with RHA to form calcium silicate hydrates, due to pozzolanic reaction. Mix Z.3 has a lower value of free silica contents up to 90 days than A.5 and R.5, but higher than X.3 and N.5.