Journal of American Science 2012;8(7) http://www.jofamericanscience.org 232 The effects of ZrO 2 nanopowders on compressive damage and pore structure properties of lightweight concrete specimens Farzad Soleymani Department of Metallurgical Engineering, Payame Noor University, P.O. 19395-4697, Tehran, Iran. E-mail: farzad.soleymani52@yahoo.com Abstract: Malaysia is the largest producer and exporter of palm oil in the world. However the palm oil refineries also produce tones of waste products known as palm oil clinker or POC. POC is normally disposed of in landfill or incinerated, incurring costs and causing negative environmental impact, such as pollution. Therefore the appropriate use of POC can help preserve the environment from undesirable effects, while at the same time contributes to cost reduction for the palm oil industry. Flexural of concrete containing ZrO 2 nanoparticles which were cured in saturated limewater have been optimized. ZrO 2 nanoparticles with partial replacement of Portland cement by 0.5, 1.0, 1.5 and 2.0 weight percent have been used as nano-fillers. The specimens were cured in water and saturated limewater for 7, 28 and 90 days after casting and then their strength was evaluated by flexural strength test. The results showed that replacement of Portland cement with ZrO 2 nanoparticles up to 1.0 weight percent for the specimens cured in water and 2.0% for the specimens cured in saturated limewater produces concrete with the best strength. It has been obtained that curing the specimens in saturated limewater for 28 days and then in water until 90 days, produces more strengthened concrete than those cured only in saturated limewater for 90 days. Excess Ca(OH) 2 crystals which forms after 28 days, when the specimens cured in limewater, reduces the effect of strengthening gels which form until the 90 days hence reduces the mechanical properties of the specimens. On the other hand, curing the specimens in water after 28 days produces more strengthening gel results in a concrete with higher strength. The pore structure of different mixtures was studied. The addition of nanoparticles improves the pore structure of concretes, the refined extent of pore structure increase with decreasing nanoparticles’ content. The pore structure of concretes which were cured in saturated limewater is better than that of concretes cured in water. [Farzad Soleymani. The effects of ZrO 2 nanopowders on compressive damage and pore structure properties of lightweight concrete specimens. J Am Sci 2012;8(7):232-239]. (ISSN: 1545-1003). http://www.jofamericanscience.org . 37 Key words: ZrO 2 nanoparticles; flexural strength; optimized properties; pore structure; palm oil clinker; lightweight concrete. POC produced in the boiler when the burning process of husk fiber and shell of palm oil. This burning process is the phase to generate the energy in order to generate the plant boiler in palm oil mill. According to Tay (1991) about 20 % by weight of ash and other residues (i.e. clinker) are produced after the burning process. The clinker turned as abundance of the factory compared to ash. Researches in palm oil industry had been discovered the uses of the palm oil fuel ash (POFA) either as commercial construction material or as fertilizer for the palm oil plant. Also, the ashes turn to potential usage as a detergent. Less of research of POC caused a large amounts of untreated waste and finally contribute of contaminate land, water and air. There are few reports on incorporation of nanoparticles in cement-based composites. Li et al. [1] investigated the properties of cement mortars blended with nanoparticles to explore their super mechanical and smart (temperature and strain sensing) potentials. Also useful applications of nano- SiO 2 are addressed by the Fuji Chimera Research Institute (2002). However, until now, research performed over the years has been mainly aimed at achieving high mechanical performance with cement replacement materials in micro level. Several researchers have demonstrated that the finer the SiO 2 particle sizes in micron level, the higher the compressive strength [2,3]. But there are few works on the effects of ultra fine and nano-size particles on cementitious composite’s properties. Lu and Young [3] achieved high strengths on compressed samples which contain SiO 2 nanoparticles. Richard and Cheyrezy [4] developed Reactive Power Concretes (RPCs) by SiO 2 nano- fillers. The development of an ultrahigh strength cementitious composite was made possible by the application of DSP (Densified System containing homogeneously arranged ultra-fine Particles) with super plasticizer and silica fume content [5]. Kuo et al. [6] investigated the properties of waterworks sludge ash cement paste incorporating SiO 2 nanoparticles. In their work, the flowability of the cement pastes has been considered and it has been shown that the flowability of the cementitious composite decreases by increasing the nanoparticle