Micro-quiz

The CXI photo Library

Each month a new photograph showing microstructures of concrete will appear on this page. If you have any comments to the description or interpretation of the photographs please contact Ulla Hjorth Jakobsen by email uhj@concrete-experts.com

September 2003
Fluorescence light mode, 4x6 mm, exposed surface at the top

The photograph shows a concrete which have suffering from heavily bleeding (patchy structure) and later over finishing (loss of water, dark green band, and air voids, yellow round, in concrete surface ). The concrete was later covered by a thin mortar layer.

October 2003
Fluorescent light mode, 2x3 mm, exposed surface is towards the top

The photograph shows a concrete which is cracked from alkali silica reaction. The reactive aggregate (right) is porous flint (appears light green due to high porosity). The wide crack running from the porous aggregate into the cement paste is filled with alkali silica gel (dark green and cracked due to shrinkage).

November 2003
Fluorescent light mode, 2x3 mm

Laboratory made sample suffering from paste expansion. The result of paste expansion is the appearance of wide open gaps around the aggregates. The gaps are empty.

December 2003
Plane polarized light, 0.1x0.2mm

Appearance of the cement paste in a one day old concrete having a w/c ratio of 0.35. The Alite grains appear clear with angular shapes, Belite grains are more rounded and slightly orange and the Ferrite phase is dark brown. Very little inner hydration product is visible after one day.