Geoscience Reference
In-Depth Information
311
carbonated cement/lime binder has a similar appearance to
that of carbonated cement paste and it would be easy to
overlook the presence of lime if it were not for the sporadic
occurrences of small unmixed lime lumps. The presence
of relict Portland cement grains confirms the use of
Portland cement as a binder ingredient. In well mixed,
fully carbonated Portland cement:lime:sand mixes it is
difficult to detect the lime, and chemical analysis must be
relied upon to confirm its use.
Mortars for masonry jointing may use masonry cement
to produce a more workable and cohesive mortar than
using ordinary (CEM I or ASTM Type I) Portland cement.
Masonry cement comprises Portland cement finely
interground with limestone or another inert filler, often
used in combination with plasticizing or waterproofing
chemical admixtures. As a significant proportion of the
cement has been replaced with inert filler, mortar mixes
based on masonry cement should have a lower proportion
of sand compared with mixes made with other cements, in
order to achieve similar proportions of cement to sand.
Figure
314
shows the texture of masonry cement mortar,
notable for the frequent abundance of limestone dust filler
visible within the cement matrix.
311
Portland cement mortar coloured pink by the fine
aggregate. The fine aggregate comprises mainly quartz
particles (white) with a thin veneer of red iron oxide and
includes a proportion of iron-rich fines. An unhydrated
cement grain is also seen (centre); PPT, ×150.
312
312
Close view of an unhydrated cement grain
(centre) within a Portland cement-based mortar. It
comprises calcium silicates (white) and interstitial
phases (dark brown); PPT, ×300.
313
314
313
Portland cement-based mortar that has been
gauged with lime to improve workability, showing an
unmixed lump of lime (upper right) and carbonated
cement/lime matrix (light brown) that includes
sporadic unhydrated Portland cement grains (dark
brown). Quartz fine aggregate particles appear
grey/white; XPT, ×150.
314
Close view of a masonry cement blockwork
mortar, showing a frequent abundance of limestone
dust filler (pink/yellow) within the uncarbonated
cement matrix. There are natural quartzitic sand fine
aggregate particles (grey/white). An unhydrated
cement grain is seen centre right; XPT, ×300.
