Journal of Materials in Civil Engineering

The suitability of crushed building and demolition waste as a raw material for the production of calcium silicate products has been determined. Therefore calcium silicate bricks have been produced by replacing the natural sand with crushed building and demolition waste of different sources. The mechanical properties of the bricks made with these wastes are comparable or, in some cases, even better than those of bricks with natural sand. The green shear strength of the bricks is higher. The amount of quartz and reactive SiO₂ in the waste materials is high enough for the formation of tobermorite as a cementitious material between the grains. A negative aspect is the appearance of brown stains on the surface of the bricks when the waste materials are slightly contaminated with organic substances. This risk can be reduced when, besides the crushing of the waste, a washing process is also included.

A new recycled material derived from waste concrete using a CO₂-activated hardening process is proposed. Waste autoclaved lightweight concrete powder was used as the starting material. The powder was mixed with water, compacted by pressing, and cured in high CO₂ concentrations. The bending strength and the specific surface area of this hardened material increased as the degree of carbonation was increased. The hardened material had a high moisture absorption and desorption performance, suggesting potential application to the interior wall having a moisture control function.

Pressurized fluidized bed combined-cycle (PFBC) ashes have proved favorable for utilization in a variety of applications. The Swedish Geotechnical Institute has previously carried out comprehensive testing on ashes from ABB Carbon's pilot plant in 1988–1989, with complementary tests on ashes from the commercial plants in Värtan, Tidd, and Escatron. The scope of the tests was expanded in 1997–1998 to include fuel mixtures based on oil shale from ABB Carbon's test plant. While providing a historical and commercial perspective for the applications for PFBC residues, the focus of this paper is upon the result of investigations performed on ashes from oil shale fuel combinations.

In order to use waste materials effectively, a possibility of simultaneous solidification of inorganic waste materials and fixation of alkaline ions and heavy metal through formation of zeolite by using hydrothermal processing, was investigated. Fly ash, cinder of sewage sludge, and cinder of rubbish were used as the starting materials. Ca/Si and 2Na/Si molar ratios of the specimens were changed by the addition of CaO and Na₂CO₃. These mixtures were formed and hydrothermally processed at 200°C. Various zeolites, such as analcime, Linde B₁ zeolite, cancrinite, zeolite P-C, and hauyne, were formed at Ca/Si = 0.3 or 0.5 and 2Na/Si = 0.1–1.0. In the case of the fly ash system, although only the zeolite minerals were formed, the flexural strength reached up to 17 MPa when Ca/Si = 0.3 and 2Na/Si = 0.1, and the fixing ratio of Na⁺ ion reached a maximum value of 85% by the formation of zeolites. When cinder of rubbish was used, dissolution of heavy metals from the solidified specimen was scarcely observed. The microstructure and the variation of pore size distribution were also discussed.

New binder alternatives based on industrial by-products were studied for stabilization of clayey soils. The main emphasis was on pulverized, granulated blast-furnace slag activated in different ways, and on binder combinations based on fly ash and waste from desulfuration units. Cement was used as the control binder. The aim of this study was to evaluate the stabilization characteristics of new binder alternatives with different mixture combinations and to understand the effects of geotechnical index properties of clay and chemical/mineralogical composition on stabilization characteristics. The results of the laboratory tests indicate that the strength of stabilized clay is strongly dependent on the water-binder ratio, and that the strengthening effect is minimal at water-binder ratios below a certain threshold value. For the clay types examined in this study, blast-furnace slag activated with cement generally gives higher strengths than cement alone after the relatively long hardening periods usually employed in stabilization. It is possible to predict final strengths by accelerating the hardening with heat treatment. A temperature of 60°C seems to be suitable for this acceleration.

Recent efforts to actively recycle paper have caused the amount of papermaking sludge to increase steadily each year, with current estimates of over 3,000,000 tons discharged annually throughout Japan. The Nippon Telegraph and Telephone Corporation has achieved success in converting ash derived from incinerated papermaking sludge into a new porous material with high cation exchange capacity by reacting this ash in an alkali solution. This paper reports some application of the new material to environmental conservation, such as improvement of water quality and admixture in concrete.

Fiber reinforcement can effectively improve the toughness, shrinkage, and durability characteristics of concrete. The use of recycled fibers from industrial or postconsumer waste offers additional advantages of waste reduction and resources conservation. This paper reviews some of the work on concrete reinforcement using recycled fibers, including tire cords/wires, carpet fibers, feather fibers, steel shavings, wood fibers from paper waste, and high density polyethylene. This paper also provides a summary of the properties and applications of concrete reinforced with these fibers.

The problems dealt with by the cement and concrete industry and the future direction of technical development such as recycling of wastes as raw material and fuel for cement manufacturing; development of Ecocement using wastes; environmental load-reducing cement emitting less CO₂ and NO_x during manufacturing; up-grading of the performance of concrete aiming at energy-, resources-, and manpower-savings; utilization of wastes for concrete raw materials; and recycling of concrete wastes from obsolete concrete structures are described and discussed.