International Concrete Abstracts Portal

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.

CDEM, a group of four Dutch papermills, joined forces to develop a proprietary (patented) process that allows the production of a new type of admixture for use as building material. The process consists of a controlled thermal conversion of deinking paper residue in a fluidized-bed combustor. The resulting mineral product has both hydraulic and pozzolanic properties. The mineral product is mainly composed of metakaolin and calcium compounds. The mineral product composition depends upon the chemistry of the starting paper residue and the thermal conditions applied. When the raw paper residue is rich in kaolin and the thermal conversion preserves calcium carbonate, a very reactive pozzolan is obtained. When the calcium content increases and decomposition of calcium carbonate occurs, a self-cementing material appears which can replace normal cement in several applications like: masonry blocks, autoclaved products, and backfilling mortars.

This paper provides a brief historical perspective on the development of cement, a look at common problems and solutions, and a statement of the current status of cement production and applications, particularly in USA. The authors further give their assessment ofthe need for performance-based standards and offer a look forward to characteristics that the cements ofthe future will need to incorporate. As we step into the new millennium and portland cement crosses1 75 years ofage, global cement consumption is stretching towards the 1.5billionton mark. Although cement strength has increased significantly since the Aspdin era, new challenges for the cement industry loom as we enter the new millennium. One of hese is to abide by the Kyoto agreement to reduce atmospheric CO? emissions. Binary-, ternary-, and quaternary- component blended cements appear to offer viable solutions for achieving this environmental target. Since there is an imminent need to move away from prescriptive to performance-based cement specifications, provisions will have to be made for performance-oriented blended cements to deal with the key issue of the low-clinker-factor cement.

This paper evaluates the potential of crushed waste calcined clay brick 3s cement replacement material. The crushed waste was characterised physically, chemically and mineralogically through fineness test, density, chemical composition and X-ray analysis and the consumption of calcium hydroxide determined using differential thermal analysis. The influence of the partial replacement of portland cement by calcined clay on the strength development was eAtrated until the age of 365 days. The pcrcentagc of ccmcnt replacement, by weight, ranged from 20 to 42% whereas the water/cement ranged from 0.37 to 0.45. The CO? emissions associated with portland cement production were determined as well as the emissions that can be avoided replacing portland cement by the calcined-clay brick. The results show that the crushed waste presented a good pozolanic activity and that the compressive strength of the blended mortars was higher than that observed for the control mixture for all ievels of cement replacement. The reductions in CO2 emissions can be achieved if pozzolanic materials such as calcined-clay brick is adequately used as cement replacement.

A judicious use of resources. achieved by the use of by-products and waste materials. and a lower environmental impact. achieved through reduced carbon dioxide emission and reduced natural aggregate extraction from quarries, represent two main actions that meet sustainable building development. Recycled-aggregate concrete containing fly ash is an example of a construction material which is in harmony with this concept, whereby sustainable building development is feasible with satisfactory performance in terms of both safety and serviceability of structures. The structural properties of recycled-aggregate concrete containing fly ash were evaluated by means of compression tests, splitting tension tests and pull-out bond tests on concrete specimens, whereas structure serviceability was checked by means of drying shrinkage. Moreover, corrosion measurements with galvanized steel embedded in natural-aggregate concrete containing fly ash were analyzed in order to expect the use of galvanized steel reinforcement in fly-ash recycled-aggregate concrete.