The effects of early hydration reactivity of cement on the dispersing force of a polycarboxylate type superplasticizer (PC) were investigated by using normal Portland cement (NPC) and belite-rich low heat Portland cement (LHC). Early hydration reactivities were controlled for both NPC and LHC by exposing them to a condition of 80%RH and 20℃. Regardless of the differences in the cement type and in early hydration reactivities of cements, the fluidity of PC-added paste was positively related to PC adsorption amount per BET specific surface area of the solid phase of the paste, Adpc/BET. The dispersing force of a PC was determined by the amount of PC adsorbed on the unit surface area of the solid phase. In each case of NPC or LHC, Adpc/BET corresponded to the variation of BET specific surface area of the solid phase of the paste, SSApc. The variation of SSApc was caused by the variation of early hydration reactivity of cement. Adpc/BET was also affected by the sulfate ion concentration in the solution phase of the paste because sulfate ions act as competitive adsorbates with PC. Adpc/BET for LHC was larger than Adpc/BET of NPC at the same SSApc because of the lower alkaline sulfate content of LHC.

View full abstract

 Relationship between chemical indexes of Eco-cement and unit weight of municipal waste incinerator ash for raw material was investigated. Raw material with low SM enables to utilize much amount of incinerator ash and takes advantages in burnability and grindability without undesirable influences on process and properties. Burnability also depends on nature of raw materials. Raw material that contains incinerator ash has higher burnability than that contains natural resources such as clay. Eco-cement contributes to reduce consumption of energy and natural resources by optimization of mineral composition and utilization of incinerator ash.

View full abstract

 The control of drying shrinkage in concrete as well as autogenous shrinkage in high-strength concrete is an important issue to avoid cracking and improve durability of concrete structures. In this report, the effect of shrinkage-reducing agent (product name: TETRAGUARD AS₂₁), which has been in use since 1996, on various properties of concrete, such as drying/autogenous shrinkage, setting time, compressive strength and adiabatic temperature rise is investigated. The concrete mixtures investigated in this study were proportioned with a W/C ranging between 0.30-0.55.

View full abstract

 For the purpose of improving a durable plant, retaining soil and so on, we developed green roof systems which makes plants grow using vegetation blocks. These concrete blocks are made of artificial light-weight aggregate and vegetational substrate is put into the porous voids. This system was installed on the roof of a dormitory in Kumagaya-City, Saitama Prefecture, and the temperature was measured in the summer of 1999 and in winter of 2000 in order to investigate how this system affects the indoor thermal environment of the lower floor. As a result of this, it wascomfirmed that the indoor temperature of the lower floor in summer and winter could be moderated, heating and cooling energy could be reduced by installing the green roof system with light-weight porous concrete.

View full abstract

 Rapid analytical methods for the concentration of dioxins in flue bypass gas at Eco-cement demonstrated plant have been investigated in this experiment. As a result of the investigation, it is confirmed that there are some correlations between dioxins concentration and TOX concentration in the flue bypass gas. TOX is one of the substituted index for regulating dioxins concentration. The dioxins concentration simultaneously measured was about 0.01～1ng-TEQ/m³N. The regulated TOX concentration value was 100μg/m³N for the strictest dioxins environmental quality standard. This strictest emission standard of dioxins concentration of flue gas is 0.1ng-TEQ/m³N. It takes about 1 hour to measure TOX concentration.
　Besides the result of TOX, it is also confirmed that there is a similar correlation between the dioxins concentration and the chlorobenzene concentration in the same gas. Especially the chlorobenzene that 5 or 6 hydrogens of benzene are chlorinated are striking for that tendency. So it is judged that chlorobenzene can also be used for the substituted index for the dioxins concentration in the flue bypass gas.
　CO and EIA were judged to be not suitable for the substituted index being used as the dioxins regulation concentration.

View full abstract

 Cement is one of the constituent materials of concrete. Cement is mixed with other materials into fresh concrete in concrete-mixing plants and then concrete is transported to construction sites. Under the effects of environmental conditions such as temperature, humidity, intruding and extruding movement of water, etc., a special microstructure is formed in concrete. After placement, the microstructure of concrete continues to develop. Besides this reaction, the deteriorating reaction of concrete also starts simultaneously. Recently, the durability of concrete structure has been recognized again to be very important. This trend leads to the change of requirements in performances and diversity in concrete as well as its constituents. The microstructures and mass transfer of concrete in nanometer scale is markedly related to durability. In order to understand durability, it is necessary to understand microstructures of hardened concrete that is affected by various mixing proportions and environmental conditions. It is also important to clarify the relationship among the durability of concrete structure, the microstructure, and environmental conditions. Present or future, nano-technology is going to be an inevitable subject for the cement-concrete industry because the mechanical strength and the life of concrete structures are determined by the micro-structure and by the mass transfer in nano-scale, no matter how the structure is huge and gigantic. In this review, the control of cement powders, the dispersion of constituent materials of concrete, and the microstructure of hardened concrete are discussed as phenomena in nano-meter scale from the point of view of cement-concrete material science.

View full abstract