CHH Cement Composite A. Cwirzen, K. Habermehl-Cwirzen, L.I. Nasibulina, S.D. Shandakov, A.G. Nasibulin, E.I. Kauppinen, P.R. Mudimela, and V. Penttala Abstract. The compressive strength and electrical resistivity for hardened pastes produced from nanomodified Portland SR cement (CHH- Carbon Hedge Hog ce- ment) were studied. The nanomodification included growing of carbon nanotubes (CNTs) and carbon nanofibers (CNFs) on the cement particles. Pastes having water to binder ratio of 0.5 were produced. The obtained hardened material was charac- terized by increased compressive strength in comparison with the reference speci- mens made from pristine SR cement, which was attributed to reinforcing action of the CNTs and CNFs. The electrical resistivity of CHH composite was lower by one order of magnitude in comparison with reference Portland cement paste. 1 Introduction Carbon nanotubes (CNTs) were first described in 1991 [1] and since that time an intensive research has been initiated in number of institutes around the world. CNTs are characterized by high tensile strength and elastic modulus as well as exceptional electrical and thermal conductivity. CNTs were incorporated into ma- trixes based on metals, ceramics and to a limited extend into Portland cement [2- 5]. The main problems while incorporating CNTs into any matrix is to obtain their uniform dispersion and sufficient bond with the binder matrix. Incorporation of CNTs into Portland cement-based matrixes was done mainly by water dispersion, [6, 7]. The main drawback of this method is the limitation of the maximum amount of the CNTs to around 1-1.5% (according to the cement weight, with water to binder ratio of 0.5). Higher additions usually deteriorate severely worka- bility, [6]. Some solution of this problem was to add surfactants, usually polycar- boxylated-based superplasticizers, which facilitated dispersion processes and enhanced the workability. Another solution is to chemically functionalize CNTs surfaces with “polar impurities” e.g. OH, COOH end groups [8, 9, 10] or oxida- tion, [11]. One of the main drawbacks of functionalization in the case of Portland cement-based binders is strong loss of workability due to absorption of surfactants A. Cwirzen, K. Habermehl-Cwirzen, and V. Penttala Helsinki University of Technology, Faculty of Engineering and Architecture L.I. Nasibulina, S.D. Shandakov, A.G. Nasibulin, E.I. Kauppinen, and P.R. Mudimela Helsinki University of Technology, NanoMaterials Group, Department of Applied Physics and Center for New Materials