Reducing the Environmental Impact of Concrete

The ability to design and build structures that last for 500 years or more instead of 50 will in the long run increase the concrete industry’s resource productivity by tenfold. Meanwhile substituting recycled materials for natural materials as described in this article it should be possible to substantially improve the resource productivity of the concrete industry immediately. Unquestionably the greatest challenge that the concrete industry faces during the 21st century is to achieve a sustainable pattern of growth. The task is formidable but the ideas and examples cited in this article show that it can be accomplished provided we make a paradigm shift from the culture of accelerating construction speeds to a culture of conservation of energy and material.

Technical Report Author: P. K. Mehta

Concrete Technology for Sustainable Development

In this article the author identifies what he sees as essential elements that are crucial to lay the foundation upon which the structure of an environmentally-friendly concrete technology can be built. The three essential elements of the foundation are: conservation of concrete making materials enhancement of durability of concrete structures and a paradigm shift from a reductionistic to a holistic approach in concrete technology research and education. Mehta argues that sustainable development for the cement and concrete industries can be reached if we make an effort to use the cementitious and pozzolanic byproducts produced by power plants and mettallurgical industries. Further concrete mixtures containing slag or fly ash are less prone to cracking and have increased structural durability through prolonged watertightness through service life.

Technical Report Author: P. K. Mehta

Greening of the Concrete Industry for Sustainable Development

The concrete industry is energy intensive and produces a large volume of carbon dioxide emissions. To reduce the environmental impact of the industry we must practice industrial ecology by recycling the waste products of one industry by substituting them for the raw materials of another. Blended portland cements containing fly ash from coal-fired power plants and ground granulated slag from the blast-furnace iron industry provide excellent examples of industrial ecology because they offer a holistic solution for reducing the environmental impact of several industries. High speed construction building codes that are prescriptive rather than performance based and the lack of a holisitic approach in engineering research and education lead to the construction of concrete structures with cracking and durability problems. Greening of the concrete construction industry will have to proceed before green concrete replaces conventional concrete as the material of choice for general construction.

Technical Report Author: P. K. Mehta

Monolith Foundation: Built to Last a 1000 Years

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

Heavily Reinforced Shearwalls and Mass Foundations Built With Green Concrete

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