The Scientific Bulletin of VALAHIA University MATERIALS and MECHANICS –Vol. 17, No. 17 DOI 10.2478/bsmm-2019-0016 PROPERTIES AND STRUCTURE OF LOW-CEMENT CONCRETE ACCORDING TO ITS COMPOSITIONAL PARAMETERS Dan Nicolae UNGUREANU, Elena Valentina STOIAN, Florin TOMA, Daniel ANCULESCU, Alexandru Gabriel COLȚA, Nicolae ANGELESCU, Vasile BRATU Faculty of Materials Engineering and Mechanics, Valahia University of Targoviste, 13 Aleea Sinaia Street, Targoviste, Romania E-mail: elenastoian22@gmail.com Abstract: Refractory concretes with the usual cement content (about 20%) present, besides their well-known advantages, several important disadvantages which make such concretes unfit for certain applications. The relatively high CaO content in concretes, the presence of even small amounts of SiO 2 and Fe 2 O 3 in cement reduce in the first place the concretes refractoriness; if their relatively high porosity is also taken into account, the concretes behavior is further damaged in regard to the structural and thermal-chemical stability. especially at their high operating temperatures. This work is an attempt to correct the shortcomings shown by reducing the cement dosage and using appropriate admixtures in the technological process of concrete making. Keywords: cement dosage, admixtures, aluminous cement, different aggregates, mechanical and structural properties, refractoriness 1. INTRODUCTION A possible way to avoid the disadvantages encountered in refractory concrete with normal cement dosage (20%) is to decrease the cement content, using at the same time such admixtures whose effects would make up for the decrease of the cement ratio; this requirement would be accompanied, at the same time, by an improvement of the mechanical properties of the high cement concrete. The desirable effects of the mentioned additives could be essentially achieved by: - their dispersing action, with an increase of the specific volume of the products of hydration, having positive consequences on the gel/space ratio and on the paste- aggregate adherence [1-8]; - their action on the hardening process in relation with their dispersing influence; by modifying the chemical- morphological nature of the hardening products, such additives improve the paste texture of the concrete and influence its physical-mechanical characteristics (certain additives of this kind can also act as hardening agents of the oxide-acid type as in the case of the Cr +6 substances [6 - 14]. 2. EXPERIMENTAL CONDITIONS A CA2 type (R 006 =20%) cement and three aggregate types: tabular alumina (99.5% Al 2 O 3 ), fire-clay (49,37% Al 2 O 3 and 47,6% SiO 2 ) and sintered magnesite have been used in order to obtain the concrete mixture under investigation. From a granulometric point of view the mixture have been calculated taking as a model the Boloney granulometric curve. The Calcium Lignosulphonate (LSC) and a phosphatic compound (TFS) have been used as additives. Table 1 shows the composition of the concretes under investigation. Table 1. Composition of conceres Agregate Aditives Concrete Index Cement Contents Nature Maximum Grain Size [mm] LSC TFS Water Gravimetric Ratio in the Concrete [%] Refractoriness [ 0 C] 1 20 Tabular alumina 3 - - 10.8 1820 2 15 Idem 3 - - 9.8 1840 3 12.5 Idem 3 - - 9.4 1850 4 10 Idem 3 - - 9.2 1850 5 7.5 Idem 3 - - 8.9 1850 6 5 Idem 3 - - 8.7 1850 33