Many special cements and concretes have been developed for a wide range of applications. Most are more expensive than ordinary Portland cement. Some examples of these materials are given in this section. The list is by no means comprehensive and only an outline will be given of the produc­ tion and properties of these materials. The systems to be described include:

• high alumina cement used as a construction material in concrete; • high alumina cement used as a refractory castable; • fast-setting cements based on high alumina cement; • polymer-modified cements and concretes and high-strength polymer

mortars (Macro Defect Free) based on Portland cement or high alumina cement;

• supersulphated cement which is resistant to sulphate attack; • modifications to Portland cement based materials; these include the

production of coloured cement and concrete by the control of impu­ rities in the raw materials and by the use of pigments; concrete used for nuclear radiation shields produced by the additions of special aggregates and cements and concretes which expand during the setting reactions;

• non-calcareous cements for refractory applications, for use in acidic or salt environments and for dental applications.