Ardavan Yazdanbakhsh

The Effect of Carbon Nanofibers on the Strength of Concrete with Natural and Recycled Aggregates

This work reports on an experimental investigation about the effect of carbon nanofibers (CNFs) on the compressive strength of: (1) hardened portland cement paste and (2) two types of concrete; with natural and recycled coarse aggregates. It was observed that the incorporation of nanofibers caused a slight increase in the compressive strength of cement paste. However, for each type of aggregate, the strength of CNF-incorporated concrete was lower than that of control plain concrete. Based on the SEM studies and visual observations of the hardened paste specimens, the reason for these different behaviors was found to be the different dominating mechanisms by which bleeding is controlled in paste and concrete mixes; in paste CNF clumps partially block the pores and bleed water channels, while in concrete a portion of free water is adsorbed on the surfaces introduced by aggregates.

A bi-level environmental impact assessment framework for comparing construction and demolition waste management strategies

Several pioneering life cycle assessment (LCA) studies have been conducted in the past to assess the environmental impact of specific methods for managing mineral construction and demolition waste (MCDW), such as recycling the waste for use in concrete. Those studies focus on comparing the use of recycled MCDW and that of virgin components to produce materials or systems that serve specified functions. Often, the approaches adopted by the studies do not account for the potential environmental consequence of avoiding the existing or alternative waste management practices. The present work focuses on how product systems need to be defined in recycling LCA studies and what processes need to be within the system boundaries. A bi-level LCA framework is presented for modelling alternative waste management approaches in which the impacts are measured and compared at two scales of strategy and decision-making. Different functional units are defined for each level, all of which correspond to the same flow of MCDW in a cascade of product systems. For the sole purpose of demonstrating how the framework is implemented an illustrative example is presented, based on real data and a number of simplifying assumptions, which compares the impacts of a number of potential MCDW management strategies in New York City.