Civil Engineering Reference
In-Depth Information
History
The use of lime-based materials for casting goes back a long time. Excavation of Neolithic
dwellings in Jericho in the Middle East has revealed an extensive use of concrete as a
floor material. The concrete is almost completely made of lime, used as both the cast
material and the fill. The technical quality can be compared with modern concrete in rela-
tion to its absorption of water and compressive strength, and it is so widespread that there
must have been a relatively well-developed production technique using high-temperature
kilns (Malinowski, 1987).
In Egypt there are solid structures that are 5000 years old and have gypsum as the
main constituent in the mortar, while Greece used lime mortar. In Mychae on the
Greek mainland, exposed lime mortar 3000 years old is still intact. The mortar was
made the 'modern' way by mixing burnt and slaked lime with sand in the proportions
1:1 or 1:2.
The Romans mixed finely ground volcanic stone with their lime mortar 2000 years ago.
They thereby produced a hydraulic mortar, which could withstand both saltwater and
freshwater. The volcanic stone was fetched from Pozzuoli, and named pozzolana. The
Romans later discovered other mineral substances which could be used as pozzolana,
e.g. ground bricks and pottery.
The introduction of different pozzolanas revolutionized the building of inner walls and
stronger arches and vaults. The Pantheon in Rome has a cassette vault cast in pozzolana
cement. These pozzolanas were also used to make baths, water pipes and aqueducts
watertight, and as a jointing material between roof tiles.
During the Dark Ages after the fall of the Roman Empire, the pozzolana technique seems
to have been forgotten. With very few exceptions, such as the Sophiysky Cathedral in Kiev
(1000-1100), builders returned to slaked lime. Certain places managed with clay, for exam-
ple the stone churches of Greenland (1100-1400), but this was rather disappointing for future
archaeologists - when the roofs had disintegrated, the rain washed the clay away, leaving
only a pile of stones!
During this period there were several efforts to put oxblood, casein and protein into
lime. This produced watertight, more elastic mortars with quicker setting times. The poz-
zolana mixture turned up again in England during the sixteenth century, and around 1800
James Parker from Northfleet made 'Roman cement' - a somewhat misguiding nomen-
clature - by firing broken up argillaceous limestone, which contains small amounts of fos-
sil meal found along the banks of the Thames.
In 1824 an Englishman by the name of Aspedin patented what he called Portland
cement, because it resembled rock quarried on the Portland peninsula in the south of
England. In 20 years it was developed into the mixture still in use today. Many more
cements similar to Portland cement have been developed since then, in which Portland
cement is often an important ingredient. These cements have different expanding, elastic
or quick-drying qualities.
In northern Europe there are approximately 35 different types of cement on the
market. In the industrial countries its use is of the order of 1.7 m
3
/year/per per-
son; in countres with low and middle industrialization it is approximately 0.3 m
3
.
Apart from the usual problems associated with centralized industry, such as
vulnerability to market forces and distance from the user, the cement industry
also has high transport costs because of the weight of the cement and extra care
is required because of cement's sensitivity to moisture.
