Abstract
This study presents the results of an experimental investigation of the effects of nanosilica (NS) on the strength development, transport properties, thermal conductivity, air-void, and pore characteristics of lightweight aggregate concrete (LWAC), with an oven-dry density <1000 kg/m3. Four types of concrete mixtures, containing 0 wt.%, 1 wt.%, 2 wt.%, and 4 wt.% of NS were prepared. The development of flexural and compressive strengths was determined for up to 90 days of curing. In addition, transport properties and microstructural properties were determined, with the use of RapidAir, mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM) techniques. The experimental results showed that NS has remarkable effects on the mechanical and transport properties of LWACs, even in small dosages. A significant improvement in strength and a reduction of transport properties, in specimens with an increased NS content, was observed. However, the positive effects of NS were more pronounced when a higher amount was incorporated into the mixtures (>1 wt.%). NS contributed to compaction of the LWAC matrix and a modification of the air-void system, by increasing the amount of solid content and refining the fine pore structure, which translated to a noticeable improvement in mechanical and transport properties. On the other hand, NS decreased the consistency, while increasing the viscosity of the fresh mixture. An increment of superplasticizer (SP), along with a decrement of stabilizer (ST) dosages, are thus required.
Highlights
Lightweight concrete (LWC), often utilized in structural and masonry elements, is a versatile construction material with reduced dry density and low thermal conductivity
Flexural and compressive strength of the produced lightweight concrete were measured at the age of 7, 28, and 90 days to compare the mechanical performance of LWCs with different NS contents
On the basis of the results presented above, it can be concluded that NS significantly modifies the plastic and hardened properties of lightweight aggregate concrete (LWAC)
Summary
Lightweight concrete (LWC), often utilized in structural and masonry elements, is a versatile construction material with reduced dry density and low thermal conductivity. Because of the lower thermal conductivity of LWC, compared with normal-weight concrete, LWCs with low densities are widely used as heat and acoustic insulating elements. LWC owes its properties to the presence of natural or artificial aggregates with low specific densities (so-called lightweight aggregate concretes—LWACs), or the induction of air-voids in concrete or mortar (so-called cellular concrete). Lightweight concrete is characterized by its low thermal conductivity because of numerous number of pores compared with normal-weight concrete. Both pores in the aggregate and the cement matrix affect thermal properties of lightweight concrete. Owing to its high thermal insulation characteristics, lightweight concrete can be effectively used to save energy in buildings and structures, which requires high thermal resistance
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