عنوان مقاله [English]
In this paper, the mechanical and physical properties, such as strength, water absorption, type of curing, failure mode and microstructure of expanded polystyrene (EPS) structural lightweight concretes modified by Micro-silica and Nano-silica, were investigated. In the specimens without EPS beads, replacement of Micro-silica and Nano-silica up to 15\% and 3\% wt of cement, respectively, led to the increase of compressive strength and decrease of water absorption; after that, these trends were vice versa. These amounts of the concretes containing EPS were 10\% and 2\%, respectively. By replacing nearly each 5\% of Micro-silica or each 1\% of Nano-silica, the compressive strength increased by approximately 10\% to 15\% and water absorption decreased by approximately 15\% to 20\%. These results showed that the effect of 1\% Nano-silica is almost equal to the effect of 5\% Micro-silica, though it is more costly. In concretes containing EPS without silica materials, EPS beads do not have sufficient adhesion with the cement paste, and the transition zone between EPS and cement paste has a relatively large width. Therefore, by adding Micro-silica and Nano-silica to the concretes containing EPS beads, proper adhesion between the EPS beads and other concrete components was formed as confirmed by the SEM images of the specimens. On the other hand, the use of EPS beads in the concrete mixture led to increasing the slump and workability of the concretes and significant reduction in their compressive strength, density, and water absorption. Therefore, the result indicated that the use of EPS beads in concrete changed the concrete's failure mode from diagonal lines, brittle mode to soft, and parallel lines mode. In addition, the effects of three curing methods with water, limewater and water steam on the strength and water absorption of concretes were investigated. The findings showed that 28-day limewater and 1-day water steam curing resulted in the highest strength and the lowest water absorption compared to other curing methods.