86 Civil Engineering Dimension, Vol. 19, No. 2, September 2017, 86-92 DOI: 10.9744/CED.19.2.86-92 ISSN 1410-9530 print / ISSN 1979-570X online Effect of the Use of Metakaolin Artificial Lightweight Aggregate on the Properties of Structural Lightweight Concrete Risdanareni, P. 1* , Choiri, A.A. 1 , Djatmika, B. 1 , and Puspitasari, P. 2 Abstract: This paper investigates the effect of using metakaolin Artificial Lightweight Aggre- gates (ALWA) as a substitute for coarse aggregates to produce structural lightweight concrete. A combination of 10M NaOH solution and sodium silicate solution was used as alkali activator. The ratio between the metakaolin binder and the alkali activator used in producing metakaolin ALWA is 48%:52%, by mass. It is shown that metakaolin ALWA has higher abrasion and water absorption, and lower bulk density values compared to normal aggregates. To determine the effect of using metakaolin ALWA as coarse aggregates in concrete, three variations of ALWA dosages were used, i.e. 0%, 50%, and 100% of the total coarse aggregates, by volume. The results show that the compressive strength of concrete decreased along with the increase of ALWA content in the mixture. However, concrete using 100% ALWA as coarse aggregates meets the requirements of compressive strength and density of structural light weight concrete. Keywords: ALWA; compressive strength; concrete density; geopolymer; lightweight concrete. Introduction Indonesia is a country in Asia that is prone to earth- quake [1]. Based on data from Team for Revision of Seismic Hazard Maps of Indonesia in 2010, the financial loss incurred by the nation due to this natural disaster has reached trillions of Rupiahs for rehabilitation and reconstruction [2]. In order to minimize the amount of loss, the earthquake’s load should be reduced. One promising method on mini- mizing earthquake hazards to buildings is by reducing the weight of the building, since the magni- tude of the seismic force is directly proportional to the weight of the building [3]. Applying lightweight concrete with a density of 1100 kg/m 3 as a replace- ment of conventional concrete is one way to reduce the weight of structural and non-structural compo- nents of buildings. Based on the classification of lightweight concrete according to the level of compressive strength and aggregate type by Mindess and Young [4], light- weight aggregate concrete using artificial light- weight aggregate (ALWA) or lightweight coarse sin- tered fly ash and foamed slag aggregates can pro- duce compressive strength values of 17-41 MPa with a density range of 1500-2000 kg/m 3 [4]. 1 Department of Civil Engineering, Faculty of Engineering, State University of Malang, Malang, INDONESIA. 2 Department of Mechanical Engineering, Faculty of Engineering, State University of Malang, Malang, INDONESIA. *Corresponding author; Email: puput.risdanareni.ft@um.ac.id Note: Discussion is expected before November, 1 st 2017, and will be published in the “Civil Engineering Dimension”, volume 20, num- ber 1, March 2018. Received 25 August 2017; revised 01 September 2017; accepted 11 September 2017. Thus, it is included in the category of lightweight structural concrete because the compressive strength is not less than 17 MPa. One of the alternative materials that serves potentially as the basic ingre- dient of ALWA is metakaolin. Metakaolin is a mate- rial resulting from the calcination of kaolin at a cer- tain temperature. The Ministry of Energy and Mine- ral Resources (KESDM) in 2015 stated that the avai- lability of kaolin in Indonesia was approximately more than one billion tons with a low utilization rate [5]. Triani et al. and Risdanareni et al.’s study on the use of metakaolin as a raw material for manufacturing geopolymer paste found that the compressive strength of metakaolin-based geopolymer paste reached more than 42 MPa [6,7]. Based on the chemical composition of metakolin, the total amount of SiO2 + Al 2O3 + Fe2O3 in metakaolin is very high, i.e. 93.99%, thus it can be categorized as natural pozzolan of class N [6]. Subsequent research con- ducted by Aineto et al. on the manufacture of meta- kolin ALWA found that sintering at a certain tem- perature was effective to reduce the unit weight of ALWA [8]. Further, Lauw and Buen showed that the transition from normal to lightweight concrete occurred after 50% of the total volume of the coarse aggregates in concrete was replaced by styrofoam ALWA [9]. Referring to this research finding, the present research investigated three coarse aggregate replace- ment percentages by metakaolin ALWA, i.e. 0%, 50%, and 100% from the total volume of coarse aggregate, to determine the optimum dosage of ALWA as a substitute of coarse aggregates in manu- facturing lightweight structural concrete.