Hybrid effect of carbon nanotube and nano-clay on physico-mechanical properties of cement mortar M.S. Morsy * , S.H. Alsayed, M. Aqel King Saud University, College of Engineering, Specialty Units for Safety & Preservation of Structures P.O. Box 800, Saudi Arabia article info Article history: Received 7 March 2010 Received in revised form 5 May 2010 Accepted 19 June 2010 Available online 15 July 2010 Keywords: Carbon nanotube Nano-clay Cement mortar Thermal analysis Compressive strength Microstructure abstract In this work, several nanomaterials have been used in cementitious matrices: multi wall carbon nano- tubes (MWCNTs) and nano-clays. The physico-mechanical behavior of these nanomaterials and ordinary Portland cement (OPC) was studied. The nano-clay used in this investigation was nano-kaolin. The metakaolin was prepared by thermal activation of nano-kaolin clay at 750 °C for 2 h. The organic ammo- nium chloride was used to aid in the exfoliation of the clay platelets. The blended cement used in this investigation consists of ordinary Portland cement, carbon nanotubes and exfoliated nano metakaolin. The OPC was substituted by 6 wt.% of cement by nano metakaolin (NMK) and the carbon nanotube was added by ratios of 0.005, 0.02, 0.05 and 0.1 wt.% of cement. The blended cement: sand ratio used in this investigation was 1:2 wt.%. The blended cement mortar was prepared using water/binder ratio of 0.5 wt.% of cement. The fresh mortar pastes were first cured at 100% relative humidity for 24 h and then cured in water for 28 days. Compressive strength, phase composition and microstructure of blended cement were investigated. The results showed that, the replacement of OPC by 6 wt.% NMK increases the compressive strength of blended mortar by 18% compared to control mix and the combination of 6 wt.% NMK and 0.02 wt.% CNTs increased the compressive strength by 29% than control. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction The mechanical behavior of concrete materials depends on structural elements and phenomena that occur in a micro and a nano scale. As a result, nanotechnology can modify the molecular structure of concrete which leads to improvement in the material’s bulk properties. Nanotechnology can also improve the mechanical performance, volume stability, durability, and sustainability of concrete. The revolutionary effects accompanying nanotechnology allows the development of cost-effective, high-performance, and long-lasting products of cement and concrete which can lead to unprecedented uses of concrete materials. One of the most desired properties of nanomaterials in the construction sector is their capability to confer a mechanical rein- forcement to cement based structural materials. When using nanomaterials three main advantages are considered. The first advantage is the production of high-strength concrete for specific application. The second advantage is to reduce the amount of ce- ment needed in concrete in order to obtain similar strengths and decreasing the cost and the environmental impact of construction materials. The third advantage is reducing the construction periods as nanomaterials can produces high-strength concrete with less curing time. Carbon nanotubes (CNTs) are hollow tubular channels, formed either by one single walls carbon nanotube (SWCNTs) or malty walls carbon nanotube (MWCNTs) of rolled graphene sheets [1,2]. They have received an increasing scientific and industrial interest due to their physical and chemical properties that is suit- able for different potential applications ranging from living matter structure to nanometer-sized computer circuits and composites [3,4]. Since CNTs exhibit great mechanical properties along with extremely high aspect ratios (length-to-diameter ratio) ranging from 30 to more than many thousands, they are expected to pro- duce significantly stronger and tougher cement composites than traditional reinforcing materials (e.g. glass fibers or carbon fibers). In fact, because of their size (ranging from 1 nm to 10 nm) and as- pect ratios, CNTs can be distributed in a much finer scale than com- mon fibers, giving as a result a more efficient crack bridging at the very preliminary stage of crack propagation within composites. However, properties and dimensions of CNTs are strongly depend on the deposition parameters and the nature of the synthesis method, i.e., arc discharge [5], laser ablation [6], or chemical vapor deposition (CVD) [6,7]. Carbon nanotubes used in this investigation were produced by arc discharge technique with diameters from 3 up to 8 nm and different length. The high specific strength, chem- ical resistance, electrical conductivity and thermal conductivity of 0950-0618/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2010.06.046 * Corresponding author. Tel.: +966 14670631; fax: +966 14673600. E-mail address: msmorsy@yahoo.com (M.S. Morsy). Construction and Building Materials 25 (2011) 145–149 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat