Recycled Building Materials Research Articles

Toward a Mechanistic Approach for Analysis and Design of Asphalt Pavements

Most current analysis and design methodologies of asphalt pavements rely on experience and empirical relationships. These relationships were developed on the basis of results of laboratory tests and by monitoring the performance of actual pavements and sections in accelerated loading experiments. The empirical relationships are limited in accounting for the fundamental properties of the materials, loading configuration, distribution of loads, and variable environmental conditions. In spite of these limitations, fairly good pavements could be constructed until recently, primarily because the lack of appropriate models could be backed up by practical experience. Relying on experience is, however, not acceptable any more because of the rapidly changing conditions of the road network. First, the significant increase in the capital investment in road construction and the need for maintenance-free roads encouraged the design of improved pavement materials modified binders, aggregate treatment, layer stabilization, and new designs of asphalt mixes . In addition, economical and environmental factors have put more emphasis on the use of local and secondary recycled building materials. Advancing the material properties and the use of locally available materials should be accompanied by developing experimental and analytical approaches that can accurately determine the effect of these materials on the design of long-lasting pavements and life-cycle cost. Second, the number and loads of trucks have increased beyond expectation as a consequence of the need to increase road transport efficiency. Furthermore, the expected introduction of aramide-reinforced truck tires in combination with foreseeable changes in wheel configurations will result in extremely high wheel pressures. Recently, a significant change in design philosophy has occurred through the development of the empirical-mechanistic design guide. The mechanistic part refers to the use of layered elastic analysis and viscoelastic material properties in some parts of the guide to determine the pavement response. Empirical relationships are used to link the calculated pavement elastic response at critical points within the structure and damage mechanisms such as permanent deformation and cracking. The empiricalmechanistic design guide includes approaches to account for traffic distribution over time and for the influence of environmental conditions on material properties. Although the empirical-mechanistic approach is considered a major step, the constitutive material models in this approach are still considered to be oversimplified because they are not able to accurately determine all aspects of the inelastic triaxial and

Release of Substances from Secondary Materials in Field Conditions

The objective of this investigation was to determine the concentrations in the seepage water from recycled building materials under field conditions and the influence of the passage through the soil on these concentrations. Using suction cups and lysimeter determinations seepage water was collected from locations with recycled materials and tested for the inorganic parameters: pH, conductivity, sulfate, copper, nickel, arsenic, chromium, and vanadium. The sulfates in the seepage water originate, in particular, from gypsum-containing components of the building materials, and to a lesser degree from brick materials. Increased pH values of up to pH 12 and increased conductivity occur to greater degrees in seepage water from concrete-containing materials due to the release of Ca(OH)2. In the building material layer the lower availability of CO2 means that the carbonatization of the leached calcium hydroxide is delayed. As the pH values increase, more copper and nickel is released due to the formation of water-soluble complexes with ammonia. At some locations the seepage water concentrations of copper, arsenic, and chromium increased likewise with increasing pH values due to the amphoteric character of these heavy metals. The formation of water-soluble compounds under reductive conditions within the water-saturated pieces of building materials means that there is an increased release of arsenic and vanadium into the seepage water. During the passage through the soil the carbonization and oxidizing conditions mean that the concentration of most parameters decreased. The most common contamination of the seepage water is through increased sulfate concentrations.

Deconstruction of structures: an overview of economic issues

As federal, state and municipal governments strive to reduce the volume of solid waste that is buried or incinerated, salvaging reusable and recyclable building materials through 'deconstruction' is rapidly becoming an attractive alternative. Until recently, most contractors and developers have relied primarily on business profitability considerations when making the 'demolition vs. deconstruction' decision which, not surprisingly, have favoured demolition because demolition is often faster, less labour intensive, and usually more convenient. Slowly but surely, the balance is shifting – an increasing number of deconstruction projects have shown that deconstructing buildings can be economically and technically viable. The lessons of these projects as well as public policies aimed at providing the appropriate incentives (as well as disincentives) can help in the maturation of a market-based deconstruction industry as part of the larger construction industry cluster.

Development and application of knowledge-based source-term models for radionuclide mobilisation from contaminated concrete

ABSTRACTConcrete materials in nuclear facilities may become activated or contaminated by various radionuclides through different mechanisms. Consequently, decommissioning and dismantling of these facilities produce considerable quantities of these materials (e.g. concrete structures, rubble), which are at least potentially contaminated with radionuclides and which must be managed safely and cost-effectively. In this paper, we present results from a research project that aims at the development of source-term models for the mobilization of radionuclides from contaminated concrete. The objective of this task was to clarify whether a more realistic source-term description could be beneficial for optimization of the management of decommissioning wastes by reducing the amount of material for disposal as radioactive waste as well as by saving natural resources due to the recycling of building materials.To identify important parameters and processes that affect the release rates of radionuclides, we evaluated the chemical behavior and the solid speciation of radionuclides in concrete materials and the influence of factors like concrete properties, source/pathway of contamination, and the scenario-specific chemical environment and hydraulic regime. Furthermore, concrete degradation processes and their influence on contaminant mobilization were addressed. On this basis, source-term models were developed to describe the radionuclide release by (i) the dissolution of radionuclide containing solid phases, (ii) the desorption of radionuclides from surfaces, and/or (iii) the leaching of radionuclides from a solid matrix without disrupting its structure. These source-term models were parameterized for probabilistic simulations of various release options, including the reuse of recycled building materials, the disposal of rubble in inert and municipal landfills as well as the on-site disposal of concrete materials (e.g. foundations remaining in the ground, in situ burial of rubble). For some scenarios and radionuclides, the calculated release rates were between one and two orders of magnitude lower than those used in former generic calculations. Based on the results of stochastic simulations, the consequences of the use of a more realistic source-term for dose assessments with respect to clearance/recycling of contaminated concrete will be illustrated and discussed.

リサイクル建築資材製造時の環境負荷原単位に関する研究

This study aims at contributing to life Cycle Assessment Analysis of resource recycling building and shows how to calculate environmental load units from manufacturing of recycled building materials. The results are as follows. 1) The environmental loads of 31 recycled building materials became clear by a reference investigation and a questionnaire performed to the makers. 2) We presented the method of incorporating the environmental loads which were calculated by accumulation method into Life Cycle Assessment Analysis with environmental load units by Input-Output table. And we made the environmental load units of recycled building materials at the time of building materials manufacture.

U.S. building-demolition wastes: Quantities and potential for resource recovery

The economic and technical potential for recycling building materials from demolished buildings in the United States has been assessed. The first section of the study is a comprehensive analysis of the type and quantity of demolished building materials available nationwide, based on data collected from 27 cities and towns. The flow of demolition debris for the U.S. is estimated at 31 million metric tons (31 Mt, 34-million U.S. tons) for the mid-1970s. The factors correlated with the demolition-debris flow are studied to develop a model of the flow. Potential markets for the processed debris are examined, and options for the processing equipment for a central reclamation plant are evaluated. Such plants seem likely to be economical in most of the larger cities of the U.S. (>400 000 population).