Portland Puzzolana Cement (IS: 1489 (Part I)
Portland Puzzolana Cement (IS: 1489 (Part I): It is manufactured by grinding Portland cement clinker and puzzolana (usually fly ash 10-25% by mass of PPC) or by intimately and uniformly blending Portland cement and fine puzzolana. Puzzolana (burnt clay, shale, or fly ash) has no cementing value itself but has the property of combining with lime to produce a stable lime-puzzolana compound which has definite cementitious properties. Free lime present in the cement is thus removed. Consequently, the resistance to chemical attack increases making it suitable for marine works. The hardening of Portland puzzolana cement consists in hydration of Portland cement clinker compounds and then in interaction of the puzzolana with calcium hydroxide released during the hardening of clinker. At the same time, calcium hydroxide is bound into a water-soluble calcium hydrosilicate according to the reaction with the effect that puzzolana Portland cement acquires greater water-resisting property than ordinary Portland cement.
Ca(OH)2 + SiO2 + (n - 1) H2O = CaO.SiO2.nH2O
Properties: These have lower rate of development of strength but ultimate strength is comparable with ordinary Portland cement.
72 ± 1 hr 16.0 N/mm2
168 ± 2 hrs 22.0 N/mm2
672 ± 4 hrs 33.0 N/mm2
The initial and the final setting times are 30 minutes (minimum) and 600 minutes (maximum), respectively. The drying shrinkage should not be more than 0.15% and the fineness should not be less than 300 m2/kg.
Uses: It has low heat evolution and is used in the places of mass concrete such as dams and in places of high temperature.
Copyright Â© 2018-2021 BrainKart.com; All Rights Reserved. (BS) Developed by Therithal info, Chennai.