Effects of addition of Al(OH) 3 on the strength of alkaline activated ground blast furnace slag-ultrafine palm oil fuel ash (AAGU) based binder Moruf Olalekan Yusuf a,c , Megat Azmi Megat Johari a,⇑ , Zainal Arifin Ahmad b , Mohammad Maslehuddin c a School of Civil Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang Malaysia b Structural Materials, Niche Area, School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia c Center for Engineering Research, Research Institute, King Fahd University of Petroleum and Minerals, 31261 Dhahran, Saudi Arabia highlights  This study investigated the effects of Al(OH) 3 on the alkaline-activated-binder.  The possibility of formation of different distinctive products is established.  Al(OH) 3 enhances Si–Al substitution, amorphousity and carbonation of the products.  The 3-day compressive-strength of 42–49.5 MPa with inclusion of 3–4 wt.% Al(OH) 3 . article info Article history: Received 28 August 2013 Received in revised form 19 September 2013 Accepted 24 September 2013 Available online 18 October 2013 Keywords: Alkaline-activated-binder Compressive-strength Palm-oil-fuel-ash Ground-blast-furnace-slag Alumina-hydroxide abstract Effects of Al(OH) 3 content on the compressive-strength of alkaline activated ground blast furnace slag (GBFS)-ultrafine palm oil fuel ash (UPOFA) based mortar (AAGU) were investigated. The mortar was acti- vated with combined activators (Na 2 SiO 3aq of silica modulus (Ms = SiO 2 /Na 2 O) of 3.3 and 10 M NaOH aq ). The Scanning Electron Microscope couple with energy dispersive X-ray (SEM + EDX) revealed the possi- bility of formation of distinctive products of calcium-silicate-hydrate (C-S-H) and Ca/Na-alumino-sili- cate-hydrate (C/N-A-S-H) while Fourier transform infra-red spectroscopy (FTIR) revealed the existence of higher degree of Si–Al substitution, amorphousity and carbonation as a result of inclusion of Al(OH) 3 in the mixture. The 3-day compressive-strength of AAGU Al mortar increased with Al(OH) 3 up to optimum value of 4 wt.% of PMs (GBFS + UPOFA) but started decreasing when the Al(OH) 3 is outside the optimum. The strength of 42–49.5 MPa could be achieved at the Al(OH) 3 dosage of 3–4 wt.% while the equivalent SiO 2 /Al 2 O 3 molar-ratio ranged from 6.72 to 8.94. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Alkaline activated binder is the process of activating prime materials that contained high Si + Al or Ca + Si system using differ- ent alkaline activators of hydroxyl or silicate of alkaline metals to form two group products of Me 2 O–MeO–Me 2 O 3 –SiO 2 –H 2 O and Me 2 O–Me 2 O 3 –SiO 2 –H 2 O identified with geopolymer and alkaline activated slag (AAS) system, respectively [1]. However, there are some solid waste materials that contained very higher Si and Ca but lower content of Al. It is expected that augmenting the alumina components of those materials may not only bring a safe environ- mental condition but also better the valorization of these wastes. A typical example is palm oil fuel ash (POFA) which have been iden- tified to be pozzolanic [2–4]. There is proliferation of these materi- als in Malaysia and Thailand, so much that about 0.1 million ton of POFA is generated annually in Thailand while 3 million tons of POFA was produced in Malaysia in the year 2007 [5]. In another vein, blast furnace slag contained high Ca and its performance as a good prime materials for AAS have been established [6–9]. Second, high Ca 2+ has been reported to contribute to the stabil- ity of aluminosilicate formation or contribute to the formation of additional products of Ca-aluminosilicate-hydrate existing simul- taneously with calcium silicate hydrate (C-S-H) [10–13]. Therefore, addition of Al is expected to improve the performance of the prod- uct and reduce the resulting Ca/Al or Si/Al ratio that are required for optimum strength performance. In the light of this, Chindapra- sirt et al. [14] have studied effects of Si and Al incorporation in high Ca-based fly-ash geopolymer system. They reported that additions 0950-0618/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2013.09.054 ⇑ Corresponding author at: School of Civil Engineering, Universiti Sains Malaysia, Engineering Campus, Nibong Tebal, 14300 Penang, Malaysia. Tel.: +60 45996208; fax: +60 45941009. E-mail addresses: moy12_civ023@student.usm.my (M.O. Yusuf), cemamj@ eng.usm.my (M.A.M. Johari), zainal@eng.usm.my (Z.A. Ahmad), muddin@kfupm. edu.sa (M. Maslehuddin). Construction and Building Materials 50 (2014) 361–367 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat