Investigations on the preparation and mechanical properties of the nano-alumina reinforced cement composite Zhenhua Li a, ⁎ , Huafeng Wang a , Shan He a , Yang Lu a , Miao Wang b a Department of Mechanics Zhejiang University, Hangzhou 310027, China b Department of Physics Zhejiang University, Hangzhou 310027, China Received 8 May 2005; accepted 27 August 2005 Available online 26 September 2005 Abstract In order to investigate the effect of nano-alumina on the elastic modulus and compressive strength of cement composite, cylindrical specimens (Φ20 × 40 mm) with different volume fractions of nano-alumina at different curing days (3 days, 7 days, 28 days) were cast and tested. Based on experiment, the compressive strength and elastic modulus of mortars were all increased by incorporating nano-alumina into matrix. When the fraction of nano-alumina was 5%, the elastic modulus of composites increased by 143% at 28 days; when the fraction of nano-alumina was 7%, the compressive strength of composites increased by 30% at 7 days. The compactness of interfacial transition zone increased and porosity of cement decreased by incorporating nano-alumina into mortars, and as a result, the elastic modulus and compressive strength of mortar with nano- alumina increased. © 2005 Published by Elsevier B.V. Keywords: Mortars; Nano-alumina; Elastic modulus; Compressive strength 1. Introduction Mortar and concrete are composite whose overall me- chanical properties are affected by properties and arrangement of each constituent (cement, aggregate) in it. By incorporating nano-materials into matrix to improve mechanical properties emerged as a promising research field of nano-composite. Compared with the case of dense structure matrix such as polymer, the situation is quite different in the area of cement- matrix composites, because cement-matrix has relative loose structure. Between the cement and the aggregate there are nano- sized air voids which may have significant effect on the nano- composite's mechanical properties. There exists much room for improvement of cement composites by incorporating nano- materials into the cement-matrix [1]. Super fine inorganic materials including active composite (SiO 2 , Al 2 O 3 ,CaO) such as slag, zeolite and coal ash were proved to be indispensable ingredient of some high-strength cement. According to some research results, silica fume is valuable for improving mechanical properties, and enhancing the freeze–thaw dura- bility, the vibration damping capacity, the abrasion resistance, the bond strength with steel rebars, the chemical attack resistance and the corrosion resistance of steel rebars. Furthermore, silica fume decreases the alkali-silica reactivity, the drying shrinkage, permeability, creep rate and thermal expansion[1–3]. There have been a lot of researches on silica fume enhanced mortars, but the situation is different in the area of nano-alumina incorporated cement, where little researches have been made on this up to now. So in this paper, the enhancing effect and the mechanism of nano-alumina were addressed. 2. Experiment 2.1. Raw materials In this study, ordinary 325# Portland cement, standard sand and nano-alumina produced by Zhoushan Mingri. Nanometer Materials Letters 60 (2006) 356 – 359 www.elsevier.com/locate/matlet ⁎ Corresponding author. Tel.: +86 571 87952024. E-mail address: zhhli@zjuem.zju.edu.cn (Z. Li). 0167-577X/$ - see front matter © 2005 Published by Elsevier B.V. doi:10.1016/j.matlet.2005.08.061