page 1
page 2 page 3
page 4
page 5
page 6
< prev - next > Construction Cement and binders KnO 100074_Alternatives to portland cement An introduction (Printable PDF)
Alternatives to Portland cement
Practical Action
That lime is an appropriate and durable binding material, especially when mixed with
pozzolana, is well proven. The Pont du Gard at Nimes in France, a Roman aqueduct built in
AD 18 with hydraulic lime-based mortar, is still waterproof; the excellence of the mortar is
attributed to the selection of the materials and to the time spent tamping the mix into place
during construction.
The rebuilding of the Eddystone lighthouse in the English Channel by John Smeaton in 1756
is a more recent development in ‘lime technology’. It was achieved through Smeaton
recognizing the hydraulic properties of lime that result from the burning of a clayey limestone.
To make the highly water-resistant mortar needed for bonding the courses of stone, he
thoroughly mixed this already hydraulic lime with an equal proportion of imported Italian
pozzolana (so adding extra ‘hydraulicity’ to the mortar).
Why continue to use alternative cements
Major advantages of alternatives
to Portland cement are that they
are usually cheaper to produce,
needing much lower or even
negligible capital inputs to get
started, and requiring far less
imported technology and
equipment. They can also be
produced on a small scale to
supply a local market resulting
in greatly reduced transportation
costs and a much greater degree
of local accountability in the
supply of building materials.
From an environmental angle
lime-pozzolana cements can be
produced with lower energy input
than either lime by itself or
Figure 2: Medium-scale Portland cement plant, India
Photo: Practical Action
Portland cement giving a half
to one third consumption in use compared with Portland cement and about one fifth
compared with lime by itself. Low energy consumption is particularly prevalent with naturally
occurring pozzolanas, or those from waste materials, which might need little additional
processing other than drying. The use of clay as a binder, of course, results in negligible
energy consumption in production.
Lower production costs mean lower prices for the consumer, enabling those who could not
afford Portland cement to purchase and use a quality binding material.
Pozzolanic cements additionally have numerous other technical advantages to the user:
Improved workability
Improved water retention/reduced bleeding
Improved sulphate resistance
Improved resistance to alkali aggregate reaction
Lower heat of hydration
In many large civil engineering programmes involving mass concrete works, Portland cement-
pozzolana mixes are specified due to these technical advantages as well as to save money.
Social advantages of alternative cements to Portland cement include the potential for
affordable quality housing and the opportunity for local employment generation.