Energy and Buildings 35 (2003) 1155–1159 Thermal conductivity and compressive strength of expanded perlite aggregate concrete with mineral admixtures Ramazan Demirboˇ ga ∗ , Rüstem Gül Department of Civil Engineering, Atatürk University, 25240-Erzurum, Turkey Received 20 July 2003; received in revised form 3 September 2003; accepted 12 September 2003 Abstract This paper studies the influence of two admixtures on expanded perlite aggregate concrete. Both silica fume and fly ash were added as replacement for cement by decreasing the cement weights in the ratios of 10, 20 and 30% by weight. The binder dosage was kept constant at 200 kg/m 3 throughout this study. Superplasticizer was used 1.5% by weight of Portland cement to reduce w/c ratios. The obtained results showed that: the thermal conductivity decreased with the increase of silica fume and fly ash as replacement for portland cement up to 14 and 18%, respectively. Densities of all samples decreased from 522 to 483kg/m 3 with the increase of both admixtures. Silica fume and fly ash decreased the density of samples. The compressive strengths decreased 12, 19, 29 for 7 days, and increased 9, 13%, 4%, for 28 days due to 10, 20 and 30% silica fume, respectively. Fly ash induced to reductions in the compressive strength up to 36% at 7 days and 27% at 28 days. © 2003 Elsevier B.V. All rights reserved. Keywords: Silica fume; Fly ash; Expanded perlite aggregate; Compressive strength; Thermal conductivity 1. Introduction Thermal behavior of concrete is relevant to any use of concrete, especially in relation to structures where it is desir- able to have low thermal conductivity, dimensional stability, high specific heat, and little or no decrease of stiffness upon heating. Although much work has been done on the effect of admixture and the mechanical properties of concrete, rela- tively little work has been done on the thermal conductivity [1–4]. Thermal conductivity of concrete increases with increas- ing moisture content. Since water has a conductivity about 25 times that of air, it is clear that when the air in the pores has been partially displaced by water or moisture, the concrete must have greater conductivity [5–9]. Steiger and Hurd [10] reported that when unit weight of concrete increased 1% due to the water absorbsion, the thermal con- ductivity of these specimens increases 5%. Bouguerra et al. [11], reported that the thermal conductivity of lightweight concrete chages considerably with porosity. ∗ Corresponding author. Tel.: +90-442-231-4768; fax: +90-442-236-0959. E-mail addresses: ramazan@atauni.edu.tr, rdemirboga@yahoo.com (R. Demirboˇ ga). Thermal conductivity of concrete increases with increas- ing cement content [2,12], and thermal conductivity of aggregate [7,8]. SF causes a decrease in the thermal con- ductivity and an increase in the specific heat of cement paste [1]. SF also causes an increase in the electrical resis- tivity [4]. However, the effect of SF and FA on the thermal conductivity of expanded perlite aggregate concrete (EPAC) has not been previously reported. In view of the global sustainable development, it is im- perative that supplementary cementing materials be used in replace of cement in the concrete industry. The most world- wide available supplementary cementing materials are silica fume, a by-product of silicon metal, and fly ash, a by-product of thermal power stations. It is estimated that approximately 600 million tons of fly ash is available worldwide now, but at present, the current worldwide utilization rate of fly ash in concrete is about 10% [13]. Due to the rapid economic de- velopment and the growth in the world population consump- tion of the energy over the world, the fly ash has significantly increased. Thus, air and environment pollution became a problem, then, the idea of using waste material has gained popularity. FA and SF are two of the most common concrete ingredients due to their pozzolanic properties [13,14]. Lightweight concretes, made up of lightweight aggre- gates, have superior properties such as lightness, thermal iso- lation, freeze–thaw resistance, and fire protection but have 0378-7788/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2003.09.002