Introduction by Nemkumar Banthia
Civil infrastructure – the set of interconnected structural elements such as roads, water supply, sewers, electrical grids, telecommunications networks, and the built infrastructure of domestic, commercial and public buildings – is the foundation of a community’s health, safety and prosperity. Unfortunately, most countries around the world are experiencing a rapid loss of serviceability and safety in their concrete infrastructure. This is primarily due to a combination of improper maintenance and important compounding factors, including:
- the use of non-durable construction materials,
- exposure to aggressive environments,
- poor construction practices,
- increases in the design loads, and
- global climate change.
The latter is accelerating carbonation-induced corrosion as a result of increasing atmospheric CO2 levels, severe cracking due to increased thermal stresses, and extensive foundation scour due to rising water levels.
Concrete is literally a building block of communities and their economic development, both in new construction activities and in strengthening existing structures. However, there are key concerns with the continued use of cement as a main ingredient in concrete. A grave concern is that cement production is an environmentally damaging process that generates 5-7 percent of global CO2 emissions. Nevertheless, the global demand for cement is expected to increase from 3.2 billion tons today to over 6.0 billion tons by 2025. Consequentially, the global construction industry is under pressure to dramatically reduce its CO2 emissions. Significant research has been directed at replacing cement with industrial by-products that have “cement-like” characteristics such as fly ash, silica fume, blast furnace slag, non-ferrous slags, and metakaolin.
A large portion of the GHG footprint of concrete also emanates from use of aggregates as filler and stabilizers that require quarrying, transportation and remediation. Here, a great opportunity exists to use Recycled Concrete Aggregate (RCA) that are derived from old concrete stemming from demolition sites. USA alone produces 325 million tons of waste concrete each year; however, less than five percent is recycled in new concrete as RCA.
Unfortunately, the attached high porosity mortar on the surface of RCA results in poor bond, inferior transport properties and a consequential loss of durability and strength. Furthermore, RCAs may introduce a number of contaminants that can harm concrete. Significant progress has been made in this regard and innovative cleaning and treatment processes including ultrasonics, controlled agitation, acid leaching, nano-impregnation, carbonation, etc. have been developed. In this volume two such papers are introduced.
The University of British Columbia