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  • ISTRA 40

    ISTRA 40 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 40 is composed of calcium aluminates with the following characteristics:

    • high early strength
    • refractoriness
    • high abrasion resistance
    • resistance to biogenic sulphuric acid corrosion

    ISTRA 40 meets the requirements of EN 14647 for Calcium Aluminate Cements and is controlled in accordance with EN 14647.

    ISTRA 40 has a shelf-life of approx. six (6) months when stored under dry conditions.



    ISTRA 40 is produced by melting selected raw materials (bauxite and limestone) in special kilns. After cooling, the 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 40 contains mainly monocalcium aluminate (CA). This mineral phase is responsible for the high early strength. When mixed with water ISTRA 40 forms calcium aluminate hydrates as its hydration products.

    Mineral phases of ISTRA 40

    main mineral phase: CA
    minor mineral phases: C4AF, C2AS, C12A7

    Chemical composition (%):

    SiO2 ≤ 6
    Al2O3 38–42
    Fe2O3 13–17
    CaO 36–40
    MgO < 1,5
    SO3 < 0,4

    Cement technical properties

    residue on sieve at: 90 mm < 5%
    fineness (Blaine) approx.: 3100–3700 cm2/g
    bulk density approx.: 1.15 g/cm3
    specific gravity: 3.2–3.3 g/cm3
    refractoriness in cement approx.: 1270 °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 40 in mixtures with a workable consistency. A mixture containing CEN-standard sand and using a water/cement ratio of 0.4 is produced for testing the mortar on the basis of EN 14647.


    Initial set 1–4 h
    Final set maximum 120 min after initial set
    Water demand 23 ± 2%

    Development of strength

    After setting, strength develops very rapidly. ISTRA 40 is a cement with very high early strength and high compressive strength. After one (1) day, the compressive strength is higher than that of high grade Portland cements CEM I 52.5 R after 28 days.

    Time 6 h 1 d
    Compressive strength >30 >50

    The tests are conducted with mortar prisms 4 x 4 x 16 cm produced according to DIN EN 14647 containing CEN-standard sand and and using a water/cement ratio of 0.4.

    Resistance to corrosion

    High resistance to waste waters in combination with extraordinary abrasion resistance and high resistance to biogenic sulphuric acid corrosion (BSAC) makes ISTRA 40 an ideal product for sewer systems and waste water plants. When ISTRA 40 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 40 slowly emit their hydrate water without destroying 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 40 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 40 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.