| الملخص | Abstract
Kaolinitic claystone from Al-Amij and Al-Hussayniat regions in the Western Desert were evaluated for the preparation of pozzolan material. The raw claystone, were calcined at (600, 900 ˚C) for (45-90 minutes). The chemical and physical examination of all calcined materials were proved to be a good pozzolan material, as they conform to ASTM specification C618, however, Al-Amij claystone showed better strength activity index. Economically, the pozzolana that prepared from the calcination of Al-Amij claystone at 600 ˚C for 45 min is considered more economical due to the low energy and time consumed. Therefore it is recommended for the preparation of the pozzolanic Portland cement.
Introduction
According to the ASTM C618, a pozzolana is defined as: a siliceous or siliceous and aluminous material which in itself possesses little or no cementitious value, but will, in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperature to form compounds possessing cementitious properties. According to C618 the requirements to chemical composition of natural pozzolana are approximately 70 % for the sum of SiO2, Al2O3 and Fe2O3 of the total compounds that constitutes the material.
Calcined clays, however, seems to have great potential for producing artificial pozzolan.Mineralogically; clays are varied a lot and the calcining temperature (to convert kaolinite to metakaoline) is crucial and affects the pozzolanic reactivity of the resultant product. It was stated that, the calcining temperature that, produces the active pozzolanic is usually in the range of 600-800◦C, and it can be approach 900◦C too (Sabir et al., 2001 and Paul et al., 2001). Thereafter the increase in temperature resulted in recrystalization of kaolinite with the beginning of the nucleation of mullite phase (Al6Si2O13) and the reactivity would be expected to decrease sharply (Grim 1968-1962).
Experimental work
The kaolinitic claystones of Al-Amij and Al-Hussainiyiat (located in the Western Desert of Iraq) are of low grade and red in colour due to the presence of appreciable amount of iron oxide (Mahdi et al., 1990 and Mahdi and Al- Delaimi., 1999). The chemical and mineralogical analysis of a representative claystones samples were determined by X-ray fluorescence and X-ray diffraction (XRD).The results are shown in table (1) and Fig (1).In this work ordinary Portland cement and sand were used too. Sand sample was graded between ASTM 30mesh (600 micron) sieve and 100mesh (150 micron) sieve and each fraction was washed with HCl to dissolve the carbonate, and then carefully washed with water to remove the acid and clays.
Discussion and Conclusions
The chemical analysis results (Table 1) of the raw claystones samples indicated that claystones have silica (SiO2) contains of 45 and 42% and (Al2O3) of 28 and 24% with about 7% and 13% (Fe2O3) for Al-Amij and Al-Hussayniat respectively. The sum of these oxides however, is greater than 70%, therefore, these claystones could produce good pozzolans, if they are properly calcined to covert the kaolinite (shown in Fig 1) to metakaoline. The XRD analysis of the calcined claystones at the temperature range indicated the formation of the metakaoline (the pozzolanic material).The pozzolana activity index tests indicated that both claystones which were calcined between 600 and 800 ◦C gave good results. The produced pozzolana, however, is chemically and physically conform to the requirements of the ASTM C618 type (N).For economical reason the claystone that calcined at 600 ◦C for 45 min was used in the preparation of the blended – hydraulic cement (Portland pozzolana cement ). The optimum pozzolan added to the cement to get the best results was 20% by weight.
Table (1) chemical composition of the studied raw (Al-Amij and Al-Hussainiyiat) claystones (in wt %)
Material
SiO2 Fe2O3 Al2O3 TiO2 CaO MgO SO3 L.O.I Na2O K2O Cl
Al-Amij 45.32 7.81 28.07 1.34 1.44 0.92 0.29 12.65 0.62 0.81 0.65
Al-Hussainiyiat 42.77 13.6 24.53 1.59 0.86 1.88 0.21 12.53 0.34 0.54 0.15
Ө 2
Ө 2
Fig -2 -XRD pattern of raw Al-Amij and Al-Hussainiyiat claystone,
K: Kaolinite, Q: Quartz, An: Antase, G: goethite, and H: Hematite
REFERENCES
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2-Al-Rawas, A. A., and Hago, A.W., 2006. Evaluation of field and laboratory produced burnt clay pozzolans. Applied Clay Science., Vol. 31, p 29-35.
3-Barger, G. S., Hansen, E. R., Wood, M. R., Neary, T., Beech, D.J., and Jaquier, D., 2001. Production and use of calcined natural pozzolans in concrete. Journal of Cement, Concrete and Aggregates. Vol. 23, Issue 2. | en_US |
