International Concrete Abstracts Portal

Crushed limestone dust is a waste material from the production of concrete aggregate by crushing quarried limestone rocks. The dust is usually less tan 1% of the aggregate production. Although it is coarser than common cementing materials such as as Portland cement, coal fly ash and ground blast furnace slag, it is fine enough to cause many problems during materials handling and disposal. Laboratory results have indicated that crushed limestone dust can be used to produce self-consolidating concrete (SCC) with properties similar to those of SCC containing coal fly ash. . Due to the differences in morphologies and particle size distribution, the mix design has to be modified when crushed stone dust instead of fly ash or ground blast furnace slag is used. Fresh SCC mixtures containing limestone dust loses its flowability and sets faster than the mixtures containing fly ash due to the acceleration of the hydration of Portland cement by the limestone powder. SCC containing limestone dust exhibited strengths similar to that containing fly ash during the first seven days, but the former exhibited lower strength than the latter at 28 and 90 days due to the contributions from the pozzolanic reactions between coal fly ash and lime released from the hydration of Portland cement. The former also have lower autogenous and drying shrinkages than the latter.

Secondary markets for waste glass have been widely developed in Europe. In the United States, on the other hand, most post-consumer glass is still being land-filled, primarily because it is mixed-color. Also, the need to clean the often highly contaminated glass constitutes a barrier against its beneficial use. For several years, an ongoing research effort at Columbia University has explored the potential of waste glass as an aggregate for concrete. The primary technical problem, caused by alkali-silica reaction, can be solved with existing means. The economics of beneficiating recycled glass in large urban areas such as New York City constitutes a more formidable barrier, because the standard aggregate that the glass would replace, whether sand or gravel, is relatively inexpensive. However, if the esthetic potential of color-sorted glass is exploited fully, the economic picture changes, and glass processors are more likely to create the link between curbside collection and concrete producer. A number of architectural concrete applications have been explored to date, and design professionals and developers have shown keen interest in adding high-quality concrete products to their palette of options. Some of these are already produced commercially. By developing a promising secondary market for recycled glass as a value-added component of architectural concrete, it is possible to offer the concrete industry new directions to shed its image of being environmentally unfriendly and to actively embrace the principles of sustainable development.

Three series of flowable slurry mixtures were made, each series with three different sources of wood ash (W-1, W-2, and W-3). The series of mixtures were: low-strength (0.3 to 0.7 MPa), medium-strength (0.7 to 3.5 MPa), and high-strength (3.5 to 8 MPa) mixtures. Tests were performed for flow, air content, unit weight, bleeding, settlement, compressive strength, and water permeability. Wood ashes W-1 and W-3 caused expansive reactions in CLSM mixtures resulting in little or slight (average 1%) net shrinkage of CLSM. Wood ash W-2 caused either significant net swelling (15% for Mixture 2-L, and 21% for Mixture 2-M) or no shrinkage (Mixture 2-H) of CLSM. The 91-day compressive strength of low-strength, medium-strength, and high-strength slurry mixtures was in the ranges of 0.38 to 0.97 MPa, 1.59 to 5.28 MPa, and 4.00 to 8.62 MPa, respectively. Overall, the slurry mixtures showed an average increase in strength of 150% (range: 25% to 450%) between the ages of 28 days and 91 days. This was attributed to pozzolanic and cementitious reactions of wood ash. In general, water permeability of CLSM mixtures decreased with age.

The reduction and utilization of waste and by-products is one of many challenges facing mankind in the modern world. This paper consists of an overview of the handling of the world's concrete waste and is concerned with unbound applications of blended construction and demolition (C&D) rubble for pavement bases and sub-bases in road construction. The problems of recycling mixed wastes are considered and global perspectives are presented on the use of C&D rubble. The paper proposes that studies should be carried out in order to research the technical properties of blended C&D rubble, which the authors believe would be economically and environmentally justifiable in promoting the widest possible range of recycled products for road construction.

Recycled concrete aggregate (RCA), when used appropriately, is an excellent substitute for natural aggregates in highway construction. RCA has been used successfully in unbound applications such as base course and fill, and in bound applications as aggregate in new concrete. However, a significant amount of concrete debris is still disposed of in landfills. Barriers to concrete recycling include regulatory and policy issues, economic disincentives, environmental concerns and technical questions. This paper reviews current obstacles to concrete recycling and discusses recent developments and research that will help overcome these barriers.