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  • ISTRA 50

    ISTRA 50 is a normal setting, rapid hardening Calcium Aluminate Cement (CAC) with high early strength. It differs substantially from the usual calcium silicate cements (Portland cements) in its manufacturing process, chemical composition and rapid strength gain.


    ISTRA 50 is composed of calcium aluminates with the following characteristics:

    • high early strength
    • refractoriness
    • high abrasion resistance
    • resistance to biogenic sulphuric acid corrosion (BSAC).

    ISTRA 50 meets the requirements of EN 14647 for Calcium Aluminate Cements and is controlled in accordance with EN 14647.

    ISTRA 50 has a shelf-life of approx. six (6) months when stored under dry conditions.



    ISTRA 50 is produced by melting selected raw materials (bauxite and limestone) in special kilns. After cooling, the crystallised clinker is ground using ball mills.

    Technical data

    The following information represents typical values for the quality control carried out in our plant.

    Mineralogical composition

    ISTRA 50 contains mainly monocalcium aluminate (CA). This mineral phase is responsible for the high early strength. When mixed with water ISTRA 50 forms calcium aluminate hydrates as its hydration products.

    Mineral phases of ISTRA 50

    main mineral phase: CA
    minor mineral phases: C2AS, CT, C12A7

    Chemical composition (%):

    SiO2 ≤ 6
    Al2O3 50–53
    Fe2O3 ≤ 3.0
    CaO ≤ 40
    MgO ≤ 1.5
    SO3 ≤ 0.4

    Cement technical properties

    residue on sieve at 90 μm < 3%
    fineness (Blaine) approx. 3300–3800 cm²/g
    bulk density approx. 1 g/cm³
    specific gravity 3.0–3.1 g/cm³
    refractoriness in cement approx. 1440 °C

    Setting time and water demand

    The testing of the setting time is performed using the mortar in order to describe the behaviour of the ISTRA 50 in mixtures with a workable consistency. A mixture containing CEN-standard sand and using a water/cement ratio of 0.40 is produced for testing the mortar on the basis of EN 14647.


    Initial set 1:30 – 4:30 h
    Final set maximum 120 min after initial set
    Water demand 26 ± 2%

    Development of strength

    After setting, strength develops very rapidly. ISTRA 50 is a cement with very high early strength and high compressive strength. After one (1) day, the compressive strength is higher than of high grade portland cements CEM I 52.5 R after 28 days.

    Development of strength [N/mm²]

    Time 6 h 1 d
    Compressive strength >18 >60


    The tests are conducted with mortar prisms 4 x 4 x 16 cm produced according to DIN EN 14647 con-taining CEN-standard sand and and using a wa-ter/cement ratio of 0.40.

    Resistance to corrosion

    High resistance to waste waters in combination with extraordinary abrasion resistance and high resis-tance to biogenic sulphuric acid corrosion (BSAC) makes ISTRA 50 an ideal product for sewer sys-tems and waste water plants. When ISTRA 50 is mixed with water, the hydration products of calcium aluminate are formed.

    They are extremely resistant to aggressive, slightly acid waters (pH factor > 3) including water soluble sulphates.


    After drying out, mortars and concretes made from ISTRA 50 slowly emit their hydrate water without de- stroying the matrix. At high temperatures (> 1000 °C), ceramic bonding occurs between the high alumina cement parts and the refractory aggregates. These ceramic bonds make ISTRA 50 an excellent binder in refractory concretes and other refractory mortars or gunning mixes.

    Safety instructions

    The normal safety measures for cement must be followed. You will find further information in our safety data sheet.


    Like all other Calucem products, the production of ISTRA 50 is subject to stringent quality control. Constant monitoring of all components ensure a consistent quality. The production plant is certified according to EN ISO 9001 – certificate number CH99/0297 and the Environmental Management System EN ISO 14001 – certificate number CH02/0862.