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GEO Report No. 119
Report No. : GEO Report No. 119

Report Title : Petrographic Examination of Concrete Samples (2001), 63 p.

Author : R.J. Sewell & S.D.G. Campbell

Abstract

This GEO Report consists of three Geological Reports prepared by the Planning Division of the Geotechnical Engineering Office. The Geological Reports, which contain results of petrographic examination of thin sections of concrete from three different sites, are presented in three separate sections in this Report.

Section 1 : Petrographic Examination of Concrete Cores from Fanling Footbridge

Sixteen concrete thin sections and polished slabs were submitted to the Geological Survey Section of Planning Division for petrographic analysis in order to identify any potential Alkali-Aggregate Reaction (AAR) constituents. The thin sections and polished slabs were prepared from core samples taken from a footbridge near Fanling KCR Station which is suspected of having alkali-aggregate reaction. Since no details were given of the field characteristics of the concrete, the findings of this report are based solely on the petrographic observations.

Four concrete cores were used in the selection of samples. Two samples from each core were taken generally within 10-20 mm of the surface of the concrete, and two samples were taken at a depth of 90-120 mm from the surface.

Section 2 : Petrographic Examination of Concrete Samples from Feature Nos. 11SE-A/C83 and C724 North Point Government School

Five concrete thin sections and polished slabs were submitted to the Geological Survey Section of Planning Division for petrographic analysis in order to identify any potential Alkali-Aggregate Reaction (AAR) constituents. The thin sections and polished slabs were prepared from core samples taken from ground anchors suspected of having alkali-aggregate reaction at Feature Nos. 11SE-A/C83 and C724 at the slopes behind North Point Government School. Since no details were given of the field characteristics of the concrete, the findings of this report are based solely on the polished slab and petrographic observations.

No details regarding the depth of the samples from the wall surface of the concrete were provided. The samples were apparently collected from loose blocks and therefore are assumed to have been within 100 mm of the surface.

Section 3 : Petrographic Examination of Concrete Samples from Hill Road Flyover (H114) from Pok Fu Lam to Connaught Road West

Three concrete thin sections, and polished slabs of the same samples, were submitted to the Geological Survey Section of Planning Division by Materials Division for petrographic analysis in order to identify any potential Alkali-Aggregate Reaction (AAR) constituents. The thin sections and polished slabs were prepared from samples taken from the Hill Road Flyover (H114) from Pok Fu Lam to Connaught Road West. The findings of this report are based solely on the petrographic observations.


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