Zhuguo Li

Development of a Reference Material for the Calibration of Cement Paste Rheometers

Rheometers for measuring the properties of fluids are usually calibrated using a standard reference oil. However, a rheometer used for concrete cannot be calibrated using an oil, because of the unusual geometry and size. It would be advantageous to have a granular reference material. A material that can simulate a Bingham fluid, such as cement paste, was developed in this study as a mixture of corn syrup, water, and fine limestone. This reference material will form the basis of future mortar and concrete reference materials containing fine and coarse aggregates. This paper illustrates the various aspects of the development and shows data obtained using various geometries of rheometers.

Development of Paper Sludge Ash-Based Geopolymer and Application to Treatment of Hazardous Water Contaminated with Radioisotopes

Ambient temperature geopolymerization of paper sludge ashes (PS-ashes) discharged from paper mills was studied by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), induction coupled plasma atomic emission spectrometry (ICP-AES), and X-ray absorption near edge structure (XANES). Two varieties of alkaline liquors were used in the PS-ash based geopolymers, corresponding to aqueous Na-metasilicate and Na-disilicate compositions. PS-ashes were found to be semi-crystalline and to have porous structures that make it possible to absorb much liquor. Flexural strengths of PS-ash-based geopolymers with liquor/filler ratios (L/F) of 1.0–1.5 ranged from 0.82 to 1.51 MPa at 4 weeks age, depending on PS-ashes and liquors used. The reaction process of the constituent minerals of the PS-ash is discussed. Furthermore, we attempted to solidify hazardous water contaminated with radioisotopes. Non-radioactive strontium and cesium nitrates were added as surrogates at a dosage of 1% into the PS-ash-based geopolymers. Generally, high immobilization ratios up to 99.89% and 98.77% were achieved for Sr2+ and Cs+, respectively, depending on the source of PS-ashes, alkaline liquors, and material ages. However, in some cases, poor immobilization ratios were encountered, and we further discussed the causes of the instability of derived geopolymer gels on the basis of XANES spectra.

Development and Application of Eco-Friendly Concrete

Concrete is the most popular construction material. In its lifetime, natural resources such as limestone and aggregate are consumed. Meanwhile, emission of air pollutants and discharge of waste concrete in large quantities are of great concern. However, in recent years, high performance concrete and new types of concretes have been developed to decrease the environmental burden in its lifespan or in production phase, to utilize a substantial amount of recycled industrial waste, and to improve local environment. These eco-friendly concretes are classified into environmental protection type such as high performance concrete and recycled concrete, and environmental creation type such as porous concrete used for planting and air-purifying concrete with TiO2 coating. This paper introduces the concept of eco-friendly concrete and summarizes present technologies and application.

Treatment Technology of Hazardous Water Contaminated with Radioisotopes with Paper Sludge Ash-Based Geopolymer—Stabilization of Immobilization of Strontium and Cesium by Mixing Seawater

Long-term immobilization ratios of strontium (Sr2+) and cesium (Cs+) in paper sludge ash-based geopolymer (PS-GP) were investigated in one year. PS-GP paste specimens were prepared in the conditions of 20 °C and 100% R.H., using two kinds of paper sludge ash (PS-ash). Two kinds of alkaline solution were used in the PS-GP as activator. One was prepared by diluting aqueous Na-disilicate (water glass) with seawater. Another was a mixture of this solution and caustic soda of 10 M concentration. When seawater was mixed into the alkaline solution, unstable fixations of Sr2+ and Cs+ were greatly improved, resulting stable and high immobilization ratios at any age up to one year, no matter what kind of PS-ash and alkaline solution were used. Element maps obtained by EPMA exhibited nearly even distribution of Cs+. However Sr2+ was biased, making domains so firmly related to Ca2+ presence. The mechanism that seawater stabilizes immobilization of Sr2+ and Cs+ was discussed in this study, but still needs to further investigation. Chemical composition analyses of PS-GP were also conducted by SEM-EDS. Two categories of GP matrix were clearly observed, so called N-A-S-H and C-A-S-H gels, respectively. By plotting in ternary diagrams of SiO2-(CaO + Na2O)-Al2O3 and Al2O3-CaO-Na2O, compositional trends were discussed in view of ‘plagioclase gels’ newly found in this study. As a result, it is suggested that the N-A-S-H and C-A-S-H gels should be strictly called Na-rich N-C-A-S-H and Ca-rich N-C-A-S-H gels, respectively.

Concrete Mix Design Incorporating Additional Consideration of Environmental Performance

In this paper, we gave a clear concept of environmental performance (EP), and proposed an estimating method of environmental performance indicator (EPI) for concrete, based on an integrated life cycle impact assessment. The environmental burden (EB) factors of concrete were also discussed. In order to well evaluate the environmental benefits of waste utilization, land use change and nature environmental resource loss caused in the production stage of concrete were also taken as the EB factors and their estimating methods were given, besides air emissions, waterborne releases, and exhaustible resource consumption. Furthermore, An EB intensity database was constructed for concrete’s raw materials and processes such as transportation. An environment-conscious mix design method was suggested for maximizing EP of concrete, while still meeting the usual property requirements such as consistency, strength and durability. Finally, as an application example, mix proportions of a retaining wall concrete were designed.