Masashi Soeda

MECHANICAL PROPERTIES, DRYING SHRINKAGE AND RESISTANCE TO FREEZING AND THAWING OF CONCRETE USING RECYCLED AGGREGATE

This paper presents the results of an investigation to determine the performance characteristics of concrete made with recycled coarse aggregate from a plant. Slump and air content of fresh recycled aggregate concrete are studied. The compressive strength, drying shrinkage and resistance to freezing and thawing were investigated experimentally when the types and combinations of coarse aggregate, admixture, air content and so on were varied. It was found that the recycled aggregate concrete decreased the compressive strength at 7 to 28 days as compared with those properties of the control concrete. The decrease in strength can be suppressed low by partial use of recycled coarse aggregate. Drying shrinkage of recycled aggregate concrete showed larger value than conventional crushed aggregate concrete. The use of shrinkage reducing agent can reduce the drying shrinkage of recycled aggregate concrete. The resistance to freezing and thawing of recycled aggregate concrete was lower than that of control concrete of similar composition. The decrease in resistance to freezing and thawing can be suppressed low by partial use of recycled aggregate, reducing the water cement ratio and increasing entraining air.

Mechanisms for the Aging-Induced Reduction of Lead Solubility in Scrubber Residues from Municipal Solid Waste Combustion

This manuscript elucidates the mechanisms responsible for aging-induced reduction in lead leaching from scrubber residues. Leaching tests (JLT13) were conducted on 48 types of scrubber residues and lead solubility was found to be significantly reduced independent of incinerator type or type of gas treatment method. Reaction kinetics that result in lead solubility reduction were shown to be proportional to carbon dioxide partial pressure and in many cases were limited by mass transfer to the residue. With forced gas convection through the residue and a CO2 partial pressure of 0.3%, the concentration of lead in leachate was reduced from 84 mg L-1 to < 0.5 mg L-1 in two days. Ettringite analogs (Ca6Al2(SO4)3(OH)2•26H2O) were identified by X-Ray Diffraction in the wetted scrubber residues early in the aging process; these appear to have been converted into gypsum (CaSO4•2H2O) and vaterite (CaCO3) in the aged material. All of these solid phases are believed to substitute lead into their crystal structure and evidence for this attenuation mechanism is presented.

FROST DURABILITY OF HIGH-PERFORMANCE CONCRETE INCORPORATING SLAG OR SILICA FUME

This paper presents the results of laboratory studies conducted to determine freezing and thawing and scaling resistance of high-performance concrete. High-performance concretes were made using a combination of different cementitious materials (blast-furnace slag and silica fume). The water-to-cementitious materials ratio was 0.27, and the bulk volume of coarse aggregate and fine aggregate per unit volume of concrete were fixed at 0.50 and 0.60, respectively. All mixtures used a superplasticizer and were non-air-entrained. Test cylinders were cast for testing in compression at 1 and 28 days, and test prisms were cast for determining resistance to freezing and thawing cycles in accordance with ASTM C 666, Procedure A, and for resistance to scaling from deicing chemicals according to ASTM C 672. The curing methods were water curing and steam curing. The air-void parameters of the hardened concrete were determined on the sawn sections. The test results indicate that non-air-entrained, high-performance concrete with steam curing showed low durability factors. High-performance concrete with water curing performed satisfactorily when subjected to up to 1500 cycles of freezing and thawing. Water-cured, high-performance concrete showed no appreciable scaling after 100 freezing and thawing cycles, showing high resistance to scaling.

DEVELOPMENT OF SIMPLE FREEZING AND THAWING TEST USING LIQUID NITROGEN

In this research, an apparatus for a simple freezing and thawing test using liquid nitrogen that enables measurement to be carried out even in actual structures has been developed based on existing research studies as a new testing method replacing the freezing and thawing test of concrete defined in the Japanese Industrial Standards (JIS), and a reviews was made of its practicality. The results indicated that, when used in conjunction with ultrasonic measurement equipment, the apparatus for a simple freezing and thawing test using liquid nitrogen was capable of evaluating the degradation of concrete surfaces part after only a small number of cycles and was greatly effective in practical application.

FREEZING-AND-THAWING RESISTANCE OF HIGH STRENGTH CONCRETE

This paper presents the results of a series of laboratory studies conducted to determine the freezing-and-thawing resistance of high strength concretes containing superplasticizer when tested in accordance with ASTM C 666, Procedure A. Three superplasticizers were used in these studies, which are compounds of poly-condensed aromatic sulfonate, sulfonated melamine sulfonic acid-formaldehyde condensates and sulfonated naphthalene formaldehyde.