Incompatibility phenomena of delayed hardening of concrete having specific combination of materials are studied from the viewpoint of mechanism and the countermeasures are presented. When higher replacement ratio of fly ash of ASTM Class C and chemical admixtures having strong retarding effects are used, significant delay of hardening for several to tens days was observed. When once strength development was restarted, the strength development is comparable with normal concrete. XRD and thermal analysis clarified the mechanism of this delayed hardening as the delay of hydration of C₃S accompanied by the abnormal hydration of C₃A. One characteristic point of fly ash of this problem is the high content of C₃A as much as 9 mass%, which caused the delayed hardening by the insufficient supply of sulfate and Ca ions under the combined effect of the chemical admixture that has a catching effect of Ca ions from solution phase. As countermeasures, restrain of the usage of chemical admixtures having retardation effects, increase in calcium sulfate in cement, and the addition of limestone powder are proposed. In order to detect the possibility of delayed hardening, when significantly high amount by Class C fly ash is used in concrete, prior measurement of heat generation by isolated calorimetry can be an effective method.

View full abstract

 Generally, the determination of dioxins takes much time and a lot of trouble. We studied the rapid determination technique of dioxins. Acceleration of an extraction process and simplification of a cleanup process was carried out. Moreover, a quantitative process of HRGC/HRMS was simplified.
　Dioxins concentrations of more than one bottom ash which is a by-product of incineration facilities were analyzed in the rapid determination method and the standard method. And dioxins concentrations of more than one fly ash and exhaust gases were analyzed also. As a result, a good correlation was found between the rapid determination method and the standard method.
　The rapid determination method of dioxins which is rational and good precision was established. We propose to use this rapid determination method as a screening for cement kiln and incineration facilities.

View full abstract

 Silica fume-premix cement (SFPC^Ⓡ), which enables to manufacture ultra-high-strength concrete (UHSC) with design strength of 100N/mm² over, has been newly developed July 2006. This report shows the experimental results regarding fresh properties, strength properties, and durability of SFPC^Ⓡ-used concrete with water-to-binder-ratio of 0.13-0.27. This report also demonstrates fluidity of fresh concrete and strength of concrete in structure of SFPC^Ⓡ-UHSC, produced at ready-mixed concrete plant practically.

View full abstract

 Fiber reinforced regulated set concrete has the feature of easily controlled setting time, and high initial strength. However it is possible that cracks may appear due to autogenous shrinkage and heat of hydration in its early age. This study investigates the practical use of expansive fiber reinforced regulated set concrete, prepared by mixing high responsive type expansive admixture and fiber reinforced regulated set concrete, to reduce autogenous shrinkage. This report grasps the various physical properties of expansive fiber reinforced regulated set concrete, standard mix proportion and process of manufacture was constructed based on those properties. This report also looks at the importance of heat curing at the low temperature and selection of setting retarders at high temperature for concrete with enough performance.

View full abstract

 TAIHEIYO CEMENT CORPORATION developed technology to reuse waste of high chlorine content as cement raw materials. At first, in "a chlorine bypass system", we succeeded in the development of a small probe having the ability for high chlorine removal by the change of the extraction gas cooling method. Furthermore, we succeeded in collecting it as salt for the industrial use (KCl) without disposing of high chlorine component dust (we call it K-powder) collected by a chlorine bypass system. As a result, we established the technology that could produce Portland Cement safely even if we used recycling resources equivalent to chlorine of 500mg per cement raw materials 1kg.
　This report mentioned a result of "Cement production technology development to use high chlorine component waste as recycling raw materials " that we examined as an NEDO project for four years from 2002.

View full abstract

 Cement-based material is not only economical and excellent for immobilizing heavy metals contaminated in the soil, but it also hardens and develops strength by hydration. However, it is difficult for the material to immobilize lead in high alkali atmosphere due to its amphoteric property and Cr(Ⅵ) which comes out of cement-based materials due to hydration inhibition in clay, especially loam in the Kanto district in Japan. Therefore, we have developed a new material for immobilizing heavy metals, DENITE, which is free from Cr(Ⅵ), and reviewed its immobilizing performance. As some results of the examination, the DENITE is effective to immobilize lead, Cr(Ⅵ) and fluorine due to lower pH(=10-11) and no chromium compounds included, and it is confirmed that heavy metals in soil immobilized by DENITE is stable in acid and alkali condition.

View full abstract