Mechanical properties cement based composites modified with nano-Fe 3 O 4 /SiO 2 Elzbieta Horszczaruk a,⇑ , Malgorzata Aleksandrzak b , Krzysztof Cendrowski b , Roman Je˛ drzejewski c , Jolanta Baranowska d , Ewa Mijowska b a West Pomeranian University of Technology Szczecin, Faculty of Civil Engineering and Architecture, Al. Piastow 50, 70-311 Szczecin, Poland b Nanomaterials Physicochemistry Department, Faculty of Technology and Chemical Engineering, West Pomeranian University of Technology, Szczecin, Al. Piastow 45, 70-311 Szczecin, Poland c Lukasiewicz Research Network – PORT Polish Center for Technology Development, ul. Stablowicka 147, 54-066 Wroclaw, Poland d Faculty of Mechanical Engineering and Mechatronics, West Pomeranian University of Technology Szczecin, Al. Piastow 19, 70-310 Szczecin, Poland highlights  FeO 4 /SiO 2 nanoparticles were incorporated to cement composites.  Fe 3 O 4 /SiO 2 increases the amount of CH/C-S-H phase in the cement matrix.  Inclusion of Fe 3 O 4 /SiO 2 improved the Young Modulus of cement composites. article info Article history: Received 25 February 2019 Received in revised form 11 March 2020 Accepted 29 March 2020 Keywords: Cement based composites Magnetite-silica nanostructures Mechanical properties Nanoindentation abstract The nanomaterials are being increasingly used for modification of the cement composites properties. The aim of the research was determination of optimum content of the core-shell type Fe 3 O 4 /SiO 2 nanoparti- cles in the cement paste for obtaining the tight structure of the high-strength paste. For this purpose, such investigation techniques as atomic force microscope (AFM) and nanoindentation were employed. The significant effect of the silica shell on the increase of the porous phase in the tested composite has been found. Also, an increase of amount of high-stiff C-S-H phase was observed, which is a result of using of the nanoadmixture. The AFM method turned out to be effective for determination of the limit amounts of the nanoadmixture for the further investigation. The nanoindentation has brought information about the changes in the quantity and quality (stiffness) of the particular C-S-H phases, caused by modification of the tested pastes with various amounts of nano-Fe 3 O 4 /SiO 2 . The use of 3% of nano-Fe 3 O 4 /SiO 2 admix- ture in the cement paste together with a superplasticizer for reduction of the excessive porosity appeared to be an optimum solution in the case of the tested composites, as it has been demonstrated in the further durability tests. Ó 2020 Elsevier Ltd. All rights reserved. 1. Introduction Construction industry is a significant area, in which the quickly developing nanotechnology keeps up with the growing require- ments of the consumers. The most modern application dedicated mainly to the building materials are developed on the construction market. Nanotechnology brings to this sector the extraordinary, improved properties, like mechanical strength, resistance to bacte- ria, self-cleaning ability, energy saving and thermal insulation, just to name a few. This leads to the revolution in the modern sustain- able construction: safe and inexpensive buildings, railroads, air- field pavements and roads [1–4]. Titanium dioxide, zinc oxide and carbon nanotubes are the most common materials commer- cialized in the construction sector [2,5–10]. Like the other fields, the construction industry desperately needs new solutions for diminishing the pollution and wastes formed during the produc- tion processes. In this regard, the nanotechnological objects are some panacea, thanks to which the construction industry is more environmental friendly. https://doi.org/10.1016/j.conbuildmat.2020.118945 0950-0618/Ó 2020 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail addresses: elzbieta.horszczaruk@zut.edu.pl (E. Horszczaruk), malgorzata. wojtaniszak@zut.edu.pl (M. Aleksandrzak), krzysztof.cendrowski@zut.edu.pl (K. Cendrowski), roman.jedrzejewski@zut.edu.pl (R. Je˛ drzejewski), jolanta. baranowska@zut.edu.pl (J. Baranowska), emijowska@zut.edu.pl (E. Mijowska). Construction and Building Materials 251 (2020) 118945 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat