Energy and Buildings 58 (2013) 292–301 Contents lists available at SciVerse ScienceDirect Energy and Buildings j our na l ho me p age: www.elsevier.com/locate/enbuild Effect of nano-SiO 2 , nano-Al 2 O 3 and nano-Fe 2 O 3 powders on compressive strengths and capillary water absorption of cement mortar containing fly ash: A comparative study Meral Oltulu ∗ , Remzi S ¸ ahin Atatürk University, Engineering Faculty, Department of Civil Eng., 25240, Erzurum, Turkey a r t i c l e i n f o Article history: Received 14 October 2012 Accepted 18 December 2012 Keywords: Porous materials Nanostructured materials Hardening Composites Aging a b s t r a c t In this study, addition of both nano-SiO 2 (NS), nano-Al 2 O 3 (NA) and nano-Fe 2 O 3 (NF) powders and their binary and ternary combinations on the compressive strength and capillary water absorption of cement mortars containing fly ash (FA) were investigated. Powder amounts were used at ratios corresponding to 0.5 wt%, 1.25 wt% and 2.5 wt% of the binder for all mixtures. Results show that addition of any single type of oxide powders at 1.25% increased compressive strength of the mortars much further than the other proportions. The use of NS + NA powders at 1.25% improved the compressive strength by the most compared to the control specimen. For all binary powder combinations, the rate of increase in strength reached generally their peak on the 28th day and gradually decreased through aging. Among all groups, the best results were obtained from the mortars added with NS + NA + NF powders at 1.25%. For this par- ticular mortar, 7–32% increase in the compressive strength and 14% decrease in the capillary absorption were determined relative to the control specimen. Agglomeration formation due to excessive use of nano powders and their pozzolanic activity should be investigated in detail. The results were also compared with those obtained from Oltulu and S ¸ ahin (2011). © 2013 Elsevier B.V. All rights reserved. 1. Introduction Various mineral additives such as fly ash and silica fume have been traditionally utilized in cement composites not only for their environmental and economic advantages, but also for their tech- nical benefits such as the ability to fill in micro and macro voids and displaying partial binder effect. On the other hand, a signifi- cant increase is observed over the past few years in the number of studies about the utilization of nano-sized materials in cement composites. Nano-powders are expected to influence the kinet- ics and hydration of cement significantly and yield better results in filling of voids of cement-based composites compared to the mineral additives due to their larger surface area and greater elec- trostatic force [1–10]. Currently, the most widely used minerals as additives are silica fume and fly ash, while the most commonly utilized nano-powders are nano-SiO 2 (NS), nano-Al 2 O 3 (NA) and nano-Fe 2 O 3 (NF) in cement and/or concrete industry. Meanwhile, the effects of various other powders, such as nano-ZnO 2 and nano- TiO 2 , on the mechanical and physical properties of concrete were also investigated in a number of studies [8,11–14]. ∗ Corresponding author. Tel.: +90 442 231 46 15; fax: +90 442 236 09 57. E-mail address: mroltulu@atauni.edu.tr (M. Oltulu). Most of the previous studies (e.g. Refs. [13–16]) on the pro- duction of cement-based composites without addition of mineral additives involve the use of oxide nano-powder(s). Validity of the studies performed by the addition of nano-sized powders without the addition of micron-sized particles such as mineral additives in terms of compactness and strength enhancement of composites is highly controversial. On the other hand, contradictory results were obtained from the studies conducted on the optimal powder proportions that yield the best results concerning the physico- mechanical properties of cement-based composites. For instance, while Jo et al. [6] was able to escalate the proportion of NS addition to as high as 10%, Quing et al. [3] and Li [16] found that this ratio should vary between 1% and 5%. Besides, while the compressive strengths of composites were determined from specimens aged 7 or 28 days [4,6,17], with the exception of Li [16] and Quing et al. [3], the evolution of later aged strengths was not investigated in the literature. This study provides results from an extensive investigation con- ducted on cement mortars containing both nano-powders and fly ash (FA), and is a follow-up on the previous one [18] containing silica fume (SF) as the mineral additive. In this study, addition of both nano-SiO 2 (NS), nano-Al 2 O 3 (NA) and nano-Fe 2 O 3 (NF) pow- ders and their binary and ternary combinations on the compressive strength and capillary water absorption of early, standard and late aged cement mortars were investigated. The results were then 0378-7788/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.enbuild.2012.12.014