Experimental investigation of the properties of self-compacting concrete (SCC) mixtures containing recycled aggregates modified with micro an‎d nano materials in both fresh an‎d hardened states

3/16/2027 12:00:00 AM

In recent years, the use of recycled aggregates has gained attention as an effective strategy for construction waste management. However, the presence of old porous mortar an‎d the weak interfacial transition zone (ITZ) in these aggregates lead to a decline in mechanical properties an‎d durability, as well as alterations in the rheological behavior of concrete. The main objective of this study is to modify the microstructure an‎d compensate for the mechanical an‎d permeability deficiencies of self-compacting concrete (SCC) containing 100% recycled aggregates. This is achieved by incorporating filler particles at two scales: micro (micro-silica, micro-titanium dioxide, an‎d micro-iron oxide) an‎d nano (nano-silica, nano-titanium dioxide, an‎d nano-iron oxide), an‎d eva‎luating their interactive effects on the stability, strength, an‎d durability of the concrete. To this end, 9 mix designs were prepared, including a reference concrete, concretes with 50% an‎d 100% recycled aggregate replacement, an‎d 6 modified recycled mixes (containing 10% micro-silica, 4% micro an‎d 2% nano TiO2, 4% micro an‎d 2% nano Fe2O3, an‎d 2% nano-silica by weight of cement). Fresh concrete tests (slump flow, J-ring, V-funnel, an‎d segregation resistance) an‎d hardened concrete tests (compressive strength, porosity, water absorption, electrical resistivity, an‎d rapid chloride penetration) were conducted. The summarized results indicate that the addition of nanomaterials, due to their high specific surface area, increases the apparent viscosity (resulting in longer V-funnel flow times), whereas microparticles (especially micro-oxides) exhibited better performance in controlling dynamic segregation an‎d maintaining the static stability of the mixture. Regarding hardened properties, nano-silica had the most significant impact on enhancing compressive strength (particularly at 90 days), bringing it close to the values of the reference concrete. Nevertheless, in terms of durability indicators, the best performance belonged to the mix containing micro-silica (10%). By densifying the concrete structure, this mix minimized porosity (13.96%) an‎d significantly reduced chloride permeability (1444 Coulombs). Another major finding of this research is that the enhancement of mechanical strength does not necessarily align with the improvement of durability indices. For instance, despite increasing strength, certain mixes containing nanomaterials (such as nano-silica) recorded a higher capillary water absorption coefficient compared to the unmodified mix. Overall, the present study demonstrates that the selec‎tion of the modifying agent in recycled SCC should be based on project requirements: microparticles are more favorable for corrosive environments (where high durability is required), while nanoparticles are more effective in providing structural strength.

بتن خودتراكم , سنگدانه بازيافتي , نانومواد , ميكرو مواد , خواص بتن تازه , خواص مكانيكي , دوام

Self-compacting concrete (SCC) , Recycled aggregate , Nanomaterials , Micromaterials , Fresh concrete properties , Mechanical properties , Durability

Amirali Rahmani

Dr.Ali Akbar Shirzadi Javid