Alkali-Sulfate Activated Blended Portland Cements KRIVENKO Pavel 1,a , SANYTSKY Myroslav 2,b , KROPYVNYTSKA Tetiana 2,c 1 Scientific Research Institute for Binders and Materials, Kyiv National University of Construction and Architecture, Povitroflotskyi prospect 31, Kyiv 03037, Ukraine 2 Department of Building Production, Lviv Polytechnic National University S. Bandera str., 12, Lviv 79013, Ukraine a pavlo.kryvenko@gmail.com, b msanytsky@ukr.net, c tkropyvnytska@ukr.net Keywords: alkali-sulfate activation, blended Portland cement, early strength, hydration products supplementary cementitious materials, sodium sulfate Abstract. Early strength of the blended Portland cements containing granulated blast furnace slag and natural pozzolanas (zeolite tuff, etc.) can be enhanced by the alkali-sulfate activation. High early strength of the blended Portland cements as a result of alkali-sulfate activation can be attributed to acceleration of pozzolanic reaction at the early stages and formation of more quantities of ettringite at the early stages of structure formation. The results of the study showed that with high amounts of sodium sulfate in the alkali-sulfate activator, contents of gypsum dihydrate as a setting regulator of the blended Portland cements could be reduced. The effect of sodium sulfate activator on properties of the blended Portland cements was studied and the results are discussed. Introduction Portland cement industry is responsible for approximately 7% of global CO 2 emissions. The blended cement systems are considered as one of the most important solution to reduce CO 2 emissions associated with cement production due to partial substitution of Portland cement clinker by one or more supplementary cementitious materials (SCMs). Advantages of these cementitious systems are the lower CO 2 emissions and high energy saving in cement production in combination with the higher durability of the concretes based on these cements. Currently, substitution levels of SCMs in blended cement systems are limited due to slow strength development of the resulted cement systems arising from low reactivity of the SCMs compared to clinker phases. The use of natural pozzolanic materials as supplementary cementitious materials have been discovered to have a negative effect as its early strength development is normally decreased [1, 2]. Different approaches have been developed to overcome these disadvantages and to enhance the reactivity of major constituents of the blended Portland cements. Acceleration of hardening of the blended Portland cements can be achieved through the alkaline activation. The alkali-activated cements can be positioned at the epicentre of a new and necessary transition from today's Portland cement to new cements of the future [3]. Sodium carbonate and silicate are the most widely used alkaline activators. These alkaline compounds, due to their interaction with gypsum dehydrate, sharply accelerate the initial setting of Portland cement and workability goes down. For this reason, the gypsum-free Portland cements are of practical interest [4]. However, without modification such gypsum-free Portland cements are characterized by unacceptably short setting time, which restrict their application in practice. In order to solve this problem, neutral salts such as Na 2 SO 4 can be used to partially substitute the alkali activators. Materials and Methods A quaternary Portland-composite cement CEM II/B-M (S-P-L) 32.5 R (Manufacturer – JSC "Ivano-Frankivsk Cement", Ukraine) containing granulated blast furnace slag (S), natural pozzolana-zeolitic tuff (P) and limestone powder (L) as major components was used as a representative of the blended Portland cements in the experiments. Its chemical composition and major components are shown in Table 1. Contents of main clinker phases was as follows, mass. %: Solid State Phenomena Submitted: 2017-12-04 ISSN: 1662-9779, Vol. 276, pp 9-14 Revised: 2018-03-02 doi:10.4028/www.scientific.net/SSP.276.9 Accepted: 2018-03-07 © 2018 Trans Tech Publications Ltd, Switzerland Online: 2018-06-20 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (#612351173, Kyiv National University of Construction and Architecture, Ukraine, Kyiv, Ukraine- 02/03/23,11:50:12)