Key Engineering Materials ISSN: 1662-9795, Vol. 677, pp 53-56 doi:10.4028/www.scientific.net/KEM.677.53 © 2016 Trans Tech Publications, Switzerland Submitted: 2015-09-12 Revised: 2015-09-23 Accepted: 2015-09-24 Online: 2016-01-27 Multi-Functional High-performance Cement Based Composite BAŽANTOVÁ Zdeňka1, a, KOLÁŘ Karel1,2,b, KONVALINKA Petr2,c and LITOŠ Jiří1,d * 1 Faculty of Civil Engineering, Czech Technical University in Prague, Thákurova 7/2077, Prague 6, 166 29, Czech Republic 2 University Centre for Energy Efficient buildings, Czech Technical University in Prague, Třinecká 1024, 273 43 Buštěhrad, Czech Republic a email@example.com, firstname.lastname@example.org, email@example.com, d firstname.lastname@example.org Keywords: Strength development, rheology of fresh mixture, setting time, precast mixture. Abstract. The paper introduces development of new type of high-performance Portland cement based composite applicable for number of practical utilization. The fundaments of performed research was to design mixture with controlled process of hydration, easy production, suitable time of setting, good workability and rapid evolution of mechanical properties as well as satisfactory long-term stability of hardened composite. Selected mixture were evaluated by means of mechanical properties and volume changes determination. Introduction Application of commonly produced siliceous cement declared as pure Portland cements or blended and standardized cements according to CSN EN 197-1, or any other additional standards brings for the formulation of special cementitious composites number of difficulties resulting from basic standard requests for physic-chemical parameters of commonly produced cementitious binders. Reliable system of hydration regulation, hardening, suitable workability of fresh mixture, easy way of placing, volumetric stability and reaching of required resistance to the designed environment condition are the crucial parameters of the successful development of cement based composites. Various ways for the control of the above mentioned properties are documented is the research works [1, 2] for different binder siliceous systems. Gypsum or non-gypsum cements signify some specifics and necessity of adjustment or corrections for practical use in case of special cementitious composite [3, 4]. Varied possibilities of setting time regulation is described by use of plasticizers, retardants, accelerators and other types of admixtures and various regimes of mixing as well. It is necessary to pass the particular requirements for mixture homogeneity, reaching of final mechanical parameters and workability with respect to the used technical devices in the real time. Formulation of the Multi-functional Composite Current approach to the design and material formulation of the composite materials exploits both natural and artificial filler resources of granular or fibrous character, binding matrix usually based on the siliceous cement which ranks to the most popular binder system. It is presented by the pure Portland cement or so called blended cements containing various types of hydraulic or inert additives due to technical, environmental or economic reasons. Applied additives could be latenthydraulic, pozzolanic or inert ones and their suitable granularity could contributes to the optimal granulometry of the entire mixture and to increase total effectivity of particular components utilization [5, 6]. 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, www.scientific.net. (#103440547, Technische Universitaet Muenchen, Muenchen-13/11/17,09:06:30) 54 Special Concrete and Composites 2015 Natural or artificial resources of mineral additives such as micronized limestone, silica fume, fly ash, blast furnace slag, aluminosilicates are used to for the choose of fine or superfine parts of siliceous composites. It is necessary to respect their basic chemical and physical properties to prevent their potential negative impact on the final technical parameters such as setting time, sudden loss of workability. Modern commonly used admixtures like plasticizer often contain number of chemical substances to ensure sufficient resistance to variation in the chemical composition of used binder [4, 6, 7]. Additional fine components over 0.1 mm are often considered as inactive parts, toward binder system, and are usually represented by the pure silica sand however number of other rocks or mineral base could be used, such as chamotte, carborundum, basalt, corundum, glass, etc. [4, 8]. Their technical properties determined by their structural properties it is necessary to take into consideration during the mixture composition design [9, 10, 11]. Coarser fractions of aggregates, over 1-2 mm, are used for economic reasons. In case of porous natural or artificial aggregates is possible to reach interesting values of thermal conductivity and bulk density or increased resistance to thermal loading [12, 13]. The aim of present research work was to develop the precast multi-functional concrete mixture of easy application and high mechanical and basic physical properties. Binder system is controlled by the traditional cement technology and regulated by at least one type of plasticizer. Air-separator was incorporated together with fillers of optimized granularity. Granularity of studied mixture was developed to be compatible with high doses of fibers which ensure resistance to impact and shock loading [6, 14]. Experimental Binding components are the products of cement companies acting on the national market which are specific by their mineralogical composition: Čížkovice, Prachovice, Mokrá, Hranice na Moravě a Radotín. Admixtures in the powdered form was selected from the offer of companies Sika, Basf, Stachema, Chryso, Radka and others to cover the wide spectrum of products. Micro-fillers and coarser aggregates were selected on the base of their economic parameters. There are introduced results of selected recipes of the precast multi-functional concrete mixture which were prepared by the mixing in the slow-rotary mixer for 1.5 min. Final fresh mixture was prepared by adding water is dose 0.1 by mass. Setting time, workability and the flow test were performed according to traditional laboratory procedures used for cement. Prismatic specimens of dimension 40x40x160 mm were used. Evolution of mechanical properties was studied as well as the total volume changes. Flexural test and compressive strength determination was organized according to commonly used test [5, 15] and procedures developed on authors’ department . Volume changes determination is organized as a non-contact measurement by using laser sensor which allows data recording including the initial phases of hydration. Tested sample is inserted into the waved molding of vertical orientation. Upper surface is equipped by the reflex plate which is necessary to signal transfer. Three concrete mixtures with different setting time were chosen from the large experimental program to document process of composite development. Various setting time was obtained by using different way of regulation. Changes in the mixture rheology were reached by the application of super-plasticizer on the base of polycarboxylates in the combination with various proportions of regulation system. Present simple way of modification made possible wide range of setting time – from 10 minutes up to 5 hours. Obtained results are introduced in Table 1. Detailed results of the evolution of mechanical properties, compressive strength fc and flexural strength ft, are shown in Table 2. Record of volume changes is showed in Fig. 1, where is also mentioned setting time of particular mixtures. Key Engineering Materials Vol. 677 Flow test [mm] Setting time [minutes] 55 Table 1. Rheology properties of studied mixtures. Mixture 1 2 280 280 20 130 3 280 330 Table 2. Evolution of studied mechanical properties in time. Mechanical properties [MPa] Mix. 1 Mix. 2 Mix. 3 ft fc ft fc ft [MPa] 0.9 1.4 3.7 8.1 13.2 19.7 1 h. 2 h. 5 h. 10 h. 15 h. 1 day 7 days 28 days [MPa] 5.8 8.0 22.1 47.4 79.4 106.1 [MPa] 0.3 4.5 8.7 13.1 16.2 [MPa] 1.6 26.1 50.2 78.3 95.6 [MPa] 0.1 1.6 7.6 11.2 19.2 fc [MPa] 0.8 9.5 45.5 65.3 95.5 Results of mechanical properties well documented significant influence of the properties of fresh mixture and regulation of hydration process respectively on the final values. Volume changes [mm/m] 0.2 Mix. 1 - 20 min 0.0 -0.2 0.0 20.0 Mix. 2 - 130 min 40.0 60.0 Mix. 3 - 330 min 80.0 100.0 -0.4 -0.6 -0.8 -1.0 -1.2 -1.4 -1.6 Time [hod] Fig. 1 Record of volume changes of studied mixtures with different setting time. Conclusion The developed mixture was created by the combination of commonly used components what significantly increases its economic aspects. Mixtures exhibited high level of workability with respect to the very low water/cement ratio. 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