الفهرس يوجد فقط 14 صفحة متاحة للعرض العام
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المستخلص
The linear expansion of mortar bars containing 0 and CO aggregates admixed with 1.S% Na20 equivalent at 100% R.H. or immersed in 1 N NaOH solution at SO°C has been determined. The mortar expansion values in case of both aggregates have been found insignificant. Consequently, the investigation concentrated on declaring the variations in the mechanical properties of the mortar as affected by the different exposure conditions as well as the accompanying variations in the mortar structure. Then, some preventive measures for controlling the ACR have been adopted. Compressive strength measurements revealed ’that the mortar incorporating dolomite aggregate retains higher strength levels than that incorporating calcitic dolomite aggregate. Compressive strength development of both mortar types could not resist the hot alkali migrating from the surrounding medium for more than 60 days, then, continues to decrease. Such behavior urged to follow the variations in the aggregate structure that could lead to strength reduction. X-ray diffraction analysis revealed the intense effect of migrating alkali - Na2S04 in particular - as well as elevated temperature on aggravating the dedolomitization process. Also, the effect is intensified as the curing duration is extended. This behavior has been confirmed by microscopic investigations. The effect of exposure to saline media on the ACR has been investigated. Mortar cubes with dolomite aggregates have been exposed to aggressive chloride and sulfate media, namely, 1 N of each of Na2S04, NaCI, Mg S04 and MgCI2 solutions at 80°C as well as hot water. The effect of subjecting mortar samples to these aggressive media on the compressive strength of mortar has been investigated and the concomitant effect on the dedolomitization process has been microscopically identified and through X-ray diffraction analyses. It has been found that, sulfate ion - particularly Na2S04 - is the highly effective in suppressing the mortar strength. This fact has been
assured through microscopic and X-ray identifications. This part of the study
has declared that, dedolomitization is accompanied by growth and
rearrangement of the reaction products into a confined space, thus, causing
expansion and internal pressures to the extent of yielding transgranular
cracking with a significant reduction in mortar strength. The efficacy of some mineral admixtures in controlling ACR has been evaluated through X-ray
diffraction analyses as well as effect on compressive strength of calcitic
dolomite mortar. Mineral admixtures could be arranged according to their dual effect on developing mortar strength and the degree of ACR prevention in the following order: 20% fly ash> 10% silica fume> 20% silica fume> slag cement (35-40% slag) replacing O.P.C. > 30 ground slag> 20% ground slag> 30% fly ash.