International Concrete Abstracts Portal

The crushing of reclaimed concrete-based demolition waste in the production of recycled aggregate produces a large volume of fine material which is rich in hydrated cement paste phases, the coarser fraction being predominantly composed of aggregate. It is the coarse fraction which is of use in construction and the fine fraction which is destined for landfill. Heavy metal-bearing wastewater and sludge arise from a number of industrial processes including; electroplating, galvanising, metal finishing and battery production. Treatment procedures for aqueous heavy metal-contaminated waste streams include; precipitation, adsorption, ion exchange, membrane filtration and soliditication/stabilisation using cement or lime-based materials. The removal of heavy metal species from aqueous media by the cement-rich fraction of ordinary portland cement-based waste concrete is demonstrated herein. Crushed concrete waste in the particle size range 1 - 2 mm is shown to be effective in the exclusion of a range of heavy metal nitrates (Pb2’, Cr3+, Cu’+, NiZf and Zn*‘) from solution. The leaching characteristics of the metal-impregnated cement matrices are also reported.

The expansive and mechanical characteristics of blends of Ground Vitrified Blast Furnace (GVBF) slag and Circulating Fluidized Bed Combustion (CFBC) ashes have been investigated at different ages. The products of hydration, and their variations over a period of time have been identified by X-ray diffraction and differential thermal analysis. The results of this investigation show that the hydration of the slag can be optimally accelerated and reinforced’ by using about 1525% of CFBC ash. At this optimum level, according to the type of CFBC ash used, the flexural and compressive strength at 28 days can reach about 2.6-5.4 MPa and 30.7-54.0 MPa respectively. After 180 days, these values are about 4.3-6.5 IvIPa and 44.0-73.0 MPa respectively. This interesting development can be essentially attributed to the massive formation of C-S-H gel combined with certain quantity of ettringite, which produces a small amount of expansion.

SP-202 Alternative cementitious materials can play a major role in the concrete industry’s contribution to sustainable development by helping to reduce carbon dioxide emissions and ease the fly ash disposal problem. Some of the approaches to sustainable development are described in ACI SP-202, Third CANMET/ACI International Symposium on Sustainable Development of Cement and Concrete. Twenty-nine papers from international authors describe experiences with non-ferrous slag, steel slag, crushed waste calcined-clay brick, and rice-husk ash used as partial replacements for portland cement. Other topics include use of recycled concrete as aggregate, high-volume fly ash RCC for dams, and performance-based hydraulic cements.

Sustainable development in the concrete and cement industry is achievable in the near future. This paper proposes the viability of a factor 10 reduction in the negative environmental effects of current cement/concrete production through the use of cement blends with minimum portland cement and maximum pozzolanic loading. Such cement blends substantially extend the longevity of concrete and avoid the enormous cost of several repair and replacement cycles. ‘l’he transition to sustainable concrete technology will be driven not by environmental imperative but rather by market forces pursuing economic advantage through more durable concrete. Market driven economics already in place will soon prove that concrete durability is worth a high premium but is available at a bargain. There is enormous leverage in improving concrete quality as a doubling of the price of highest quality cement would add only 2% to overall construction project costs while the extended service life of the structure would offer a many-fold return on the additional investment. In coming years, the consideration of CO2 emissions regulations and increasingly valuable internationally traded CO2 credits will assume an economic importance equal to or greater than capital and operating costs among cement producers. Those who do not move to sustainable concrete technologies will run the risk of losing substantial market share or business failure.

In 1995 the German cement industry committed itself to a 20 % reduction in it’s specific fuel energy consumption between 1987 and 2005. In 2000, this commitment has been adapted to the international agreements, particularly to the Kyoto Protocol. Now the voluntary agreement includes a reduction of the specific energy-related CG2 emissions from 1990 to 2008/12 by 28 %. As the burning and grindrng facilities have been widely optimized during the past years, the German cement industry is planning to increase the sub-stitution of fossil fuels by waste fuels and to promote the marketing of blended cements. From 1987 to 1999 the German cement industry’s efforts have led to a reduction of the energy related CO, emissions by 3,6 million ton-nes per year. The share of waste fuels has been increased from 4 to 23 % and the clinker portion in cement has been decreased from 86 to 80.6 % by using more granulated blast-furnace slag and unburned limestone as the main constituents in cement. To what extent other instrument like emission trading, joint imple-mentation or clean development mechanism can be used in the future to achieve further reductions, will depend on mutual arrangements and implementation by the international community.