Abstract
Abstract Influence of nano-strengthening immersion on the properties of recycled aggregate (RA) and recycled aggregate concrete (RAC) and the microstructure of interfacial transition zones (ITZs) between mortar and aggregate were studied in this paper. Results showed that nano-strengthening immersion was helpful to reduce the crushing value and total pore area of RA, to significantly improve the mechanical strength of RAC, and to modify the bond strength between RAC and steel rebar and the structural properties of RAC beams. Mercury intrusion porosimetry (MIP), micro-hardness (MH) and scanning electron microscope (SEM) observation were conducted in order to reveal the enhancement mechanism of nano-strengthening immersion. Results showed that the density and mechanical properties in ITZs were obviously improved by nano-strengthening because the coating and penetration of nano-materials was helpful to block the pores and cracks in ITZs, to avoid the directed gathering of CH crystal, and to accelerate the hydration of cement and mineral additions.
Highlights
Concrete is the most widely used building material in construction industry
Results showed that the density and mechanical properties in interfacial transition zones (ITZs) were obviously improved by nano-strengthening because the coating and penetration of nano-materials was helpful to block the pores and cracks in ITZs, to avoid the directed gathering of CH crystal, and to accelerate the hydration of cement and mineral additions
In order to study the efficacy of nano-materials on the properties of recycled aggregate (RA), specimen A was immersed into the water as the reference RA while other specimens were placed under the nano-strengthening solutions
Summary
It is estimated that the production of concrete may achieve more than 6 billion tons per year in the world. This causes severe environmental problems including the increasing shortage of natural aggregates and the pollution on the process of concrete production. It is reported that the recycling level in Holland and Belgium reached almost 90% in the late of 1990s while it was still less than 50% in many other developed countries [2,3,4]. The problems from C&DW are increasing up because of the accelerating urbanization in the developing countries, especially in China, Brazil and India [5,6,7]. The recycling for C&DW has been conducted for more than 50 years, but till it only covers the use of coarse aggregates and their use is restricted due to the low strength and elastic modulus, bad workability, high water infiltration, high shrinkage and creep of RAC [8, 9]
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