Ceramics-Silikáty 46 (3) 110-116 (2002)

INFLUENCE OF PORTLAND CEMENT ADDITION TO SULPHOALUMINATE - BELITE CEMENT ON HYDRATION AND MECHANICAL PROPERTIES OF HARDENED MORTARS

I. Janotka, Ľ. Krajči, S. C. Mojumdar

Ordinary Portland cement (PC), calcium sulphoaluminate - belite (SAB) cement and a 85 wt. % SAB cement/15 wt.% PC blend were used for mortar manufacture (cement to sand weight ratio 1 : 3, w/c ratio 0.5) of 40×40×160 mm specimens kept in wet air cure (20°C, 100 % R.H. for 90 days), and used for the tests. The results reveal the influence of cement type on mortar pro-perties. The mortars, made from tested SAB cement have the worst mechanical properties. The replacement of 15 wt. % of SAB cement by PC contributes to the increase in dynamic modulus of elasticity (DME), flexural strength of the mortar by 15 % and compressive strength almost by 40 % compared to the SAB cement mortar. Such mortar behaves mechanically similar to PC mortar. Differences in mechanical properties of mortars are caused by differences in chemical composition of cements (in SAB/PC mortar content of CaO is increased by 6.4 %, contents of Al₂O₃ and Fe₂O₃ are decreased by 8.2 % and 7.0 %, respectively compared to SAB cement mortar, SO₃ content is 2.6 higher than that in the PC mortar), and mineralogical composition and hydration kinetics of cements. Differences in mineralogical composition, mainly ettringite formation, and consequent-ly hydration kinetics are the substantial reason of higher demands on batch water, rapid initial and final set of SAB cement and lower DME and strength of SAB cement mortar relative to PC and PC mortar, respectively. The 85 wt. % SAB cement/15 wt. % PC blend gains on hydration activity, DME and strength growth by the C₃S activator from PC supporting less-active SAB cement hydration. Utility properties of SAB/PC mortar are more similar to PC mortar than SAB cement mortar.

Keywords: Calcium sulphoaluminate-belite cement, Microstructure, Mortar