The use of fly ash in building materials diverts millions of tons of ash from the landfills each year, increases the constructability and durability of concrete and brick, partially replaces energy-intensive Portland cement, and is recognized by the U.S. Green Building Council’s LEED rating system as a post-industrial recycled material.
On the other hand, environmentalists question whether the industry has enough testing data to conclusively determine that this byproduct of power-producing coal combustion is environmentally safe….. Read more
from GreenBuilder Magazine.
Michel de Spot chair of the EcoSmart Concrete Project presented this paper at the US Green Buildings -USGBC- in Pittsburgh November 2003.
Concrete a material synonymous with strength and longevity is a leading and universal material that is used in all types of construction. However Portland cement a key constituent of concrete has a significant environmental impact: the making of every tonne of clinker the base for Portland cement produces a similar amount of carbon dioxide -CO2- a greenhouse gas as a by-product which is released into the atmosphere.
The EcoSmartâ„¢ Concrete Projectâ€™s objective is to minimize the greenhouse gas -GHG- signature of concrete by replacing Portland cement with supplementary cementing materials -SCMs- such as fly ash to the greatest extent possible while maintaining or improving cost constructability and performance. The Project is an innovative industry-government partnership that aims to increase awareness of the benefits and challenges of EcoSmart concrete through case studies applied research and communication to the point where the technology becomes common practice. EcoSmart has demonstrated through a number of case studies that replacement levels of 50% are achievable within the parameters of cost constructability and performance particularly when appropriate design methodologies and construction practices are used.
Implementation of this technology in the field is one of the biggest challenges for EcoSmart. The LEED rating system potentially offers an incentive to specifiers to increase the use of SCMs in development projects. However in order for the LEED system to realize this potential it must first recognize the full environmental benefit of SCMs within its credit system.
Presentation Author: Michel de Spot, P.Eng.
This article details the construction of a temple foundation on the island of Kaua i. The foundation consists of unreinforced concrete monoliths which are required to remain crack-free during their specified 1000 years service life. Because the structure is being erected on a bed of soft clay the concrete foundation will support 2000 tons -1814 metric tons- of stonework without any significant settling and without cracking; otherwise the granite roof beams would separate from the columns and fall. In addition to careful selection of materials and proportions for the concrete mixture including the replacement of a portion of the portland cement with fly ash thermal cracking during construction was controlled by constructing the slabs with one week intervals between the two castings. For the success of the project three items were singled out for special attention by the authors: enthusiastic support from the key personnel involved in construction; strict vigilance of the quality and uniformity of ready-mixed concrete at the time of placement; and extraordinary precautions for proper curing.
Technical Report Author: P. K. Mehta, W.S. Langley
The seismic retrofit of Barker Hall a six-story 40-year-old concrete building on the University of California Campus in Berkeley required the construction of a concrete belt foundation with bonded post-tensioned -PT- tendons at the top and bottom. The belt foundation supports the new exterior shearwalls and collector beams that strengthen the structure. The shearwalls are heavily reinforced and serve as the exposed facade of the building. A strong committment to green building prompted the structural designer to specify high volume fly ash concrete -HVFA- requiring at least 50% replacement of cement by fly ash. The article contains a description of the materials mixture proportions construction practices and properties of the HVFA concrete used for Barker Hall s foundations and shearwalls. The experience with HVFA concrete at Barker Hall was very positive. Mixture proportion formulation followed by field trial proved to be invaluable in developing HVFA concrete mixtures that met the designer s criteria and expectations and were also accepted by the contractor.
Technical Report Author: P. K. Mehta, Dushyant Manmohan
In terms of advancements in concrete technology the driving forces have been durability and speed of construction. However the environmental impact of construction materials is becoming an increasingly important driver. In this paper Mehta evaluates concrete technologies using the criteria of construction speed durability and environmental impact. One of the technologies he examines is high volume fly ash and slag concrete particularly in terms of their use in structural concretes roller compacted concrete dams concrete pavement for highways and base courses and embankments.
Technical Report Author: P. K. Mehta