Microstructure of Concrete
Residual portland cement particle - Thin-section photomicrographs of a concrete showing a residual portland cement particle, hydration rim around it, and some patchy calcium hydroxide component of cement hydration in paste. Left photo is in plane polarized light and the right photo in crossed-polarized light mode in a petrographic microscope. The width of the particle is 30 microns.
Secondary Deposits - Photomicrograph of some common secondary deposits in an air void - fine needle-like crystals are secondary ettringite and large hexagonal platy crystals are secondary calcium hydroxide.
Air-voids - Thin-section photomicrograph
of a concrete showing small, spherical, entrained air voids
in paste, one large
rounded gravel coarse aggregate particle (left) and numerous small, angular,
fine aggregate particles. The air voids are highlighted by blue dye mixed
epoxy, which was used in impregnating the concrete prior to thin-section
preparation.