In the combined degradation process of concrete by chloride penetration and carbonation, chloride ions bound by the cement hydrates become free after carbonation and concentrate at the carbonation front. Thus, it may cause more severe damage to reinforcing steel than in the case where chloride attack and carbonation occur independently. Standard mass transfer models cannot reproduce such a complicated behavior in the hardened cement caused by the combined degradation because the target of analysis in those models is either Cl or CO₂ penetration. The aim of this study is to develop a model which accurately reproduces the changes in phase composition of the hardened cement paste with the combined process of chloride attack and carbonation. The model to be described consists of a mass transfer model combined with a thermodynamic phase equilibrium model. The mass transfer model calculates the transfer of aqueous species in the pore solution and CO₂ in the gas phase in the concrete pores. The thermodynamic model provides the phase composition at each spatial position of the considered domain of the hardened cement using the PHREEQC program. By coupling the chemical module with the mass transfer part, temporal change in phase composition in hardened cement paste caused by the penetration and chemical action of the external deteriorating factors can be numerically reproduced. For the verification of the combined model, concrete specimens containing a given amount of chloride were carbonated under controlled conditions in the laboratory. The comparison of calculation results obtained by the model and the experimental results confirmed that the model was capable of reproducing the experimentally measured concentration profiles of chlorides.

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 The objective of this study is to estimate the mechanisms of strength development in cement pastes cured first at high temperatures and then in water at a room temperature of 20℃. In this study, pastes of ordinary Portland cement (OPC) and blended cement (containing 40% ground granulated blast furnace slag; BB) were used, and changes in microstructure were examined using backscattered electron images, while hydration products forming around cement grains were determined by EDX. Large voids called "hollow shells" were formed in the OPC pastes during the heat curing, and hydration products precipitated within the hollow shells during the subsequent curing in water. These voids partly remained unfilled; which was likely to be the cause of lower strength of cement pastes cured at high temperatures than that of those cured at 20℃. The formation of rims observed around cement grains in the OPC pastes was suppressed in the BB pastes during the heat curing. This resulted in less formation of hollow shells, and the voids were further reduced during the subsequent curing in water at 20℃ because the continued reaction of slag contained in the BB pastes allowed the hydrates to fill them. Consequently, higher strength gain was achieved in BB pastes cured first at high temperatures and then in water as compared to the OPC pastes.

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 This paper investigates autogenous shrinkage behavior of ultra-high-strength concrete containing silica fume-premix cement (SFPC^Ⓡ) with a water-to-binder-ratio of 0.13 to 0.20. The concrete mix was added with expansive admixture (EX), shrinkage reducing agent (SRA) or shrinkage-reducing type superplasticizer (SRSP) solely or in combination of EX and SRA or EX and SRSP, and effects of these admixtures in reducing autogenous shrinkage were examined.
　The ultra-high-strength concrete specimens subjected to high temperature to simulate actual temperature conditions in massive columns exhibited distinct differences from those cured at a constant temperature of 20℃ in autogenous shrinkage/expansion strain behavior and resultant stress induced. Significant reduction in autogenous shrinkage was noted in all specimens, irrespective of the temperature conditions. Further investigation revealed that the effect of combined use of EX and SRA, or of EX and SRSP, was greater than the sum of their individual effects.

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 Steel fiber reinforced concretes (SFRC) are typically prepared by adding the fiber along with the other concrete constituents (cement, aggregate and water) in the mixing operation. This premix approach allows to include up to about 2 volume percent of fiber into the concrete. SFRC contains short discrete fibers that are uniformly distributed and randomly oriented, and adding the fibers exceeding that percentage makes it difficult to mix and cast the concrete properly. Since fracture toughness improves with the increase in fiber content, this situation places a limit on the ultimate mechanical property development in SRFC.
　In this study, a new manufacturing technique was developed for SFRC with steel fiber contents increased up to 15 volume percent. The manufacturing procedure for high volume fiber cementitious material (HVFC) consists of two steps. Highly compactible steel fibers are filled in the forms in the first step, and slotted pipes are inserted there and low-viscosity grout is injected through them in the second step. The HVFC provides improvements in compressive strength, fracture mechanics properties (fracture energy and tension softening curve) and drying shrinkage from conventional SFRC. These improvements in concrete properties were found to be related to the fiber orientation in the HVFC. Strain distribution obtained by failure image analysis revealed that fracture of the HVFC was prone to be localized.

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 Research and development work has been in progress on concrete for pavement using high-strength concrete technology for the promotion of concrete pavement.
　Verification from the viewpoint of structural design revealed that the high-strength concrete technology would be greatly effective in increasing pavement life and reducing pavement thickness. Basic performance and ease of construction of the high-strength pavement concrete were examined. The results showed that the high-strength concrete technology successfully improved the pavement concrete performance while ensuring the ease of construction and adequate pavement performance. In addition, high-strength porous concrete was found to have enhanced mechanical properties as compared to traditional porous concrete, as well as increased porosity under the conditions in which a required level of flexural strength was ensured.

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 In cement manufacturing, the process of clinker sintering requires high temperatures of 1450 degrees Celsius or above which accounts for approximately 80% of manufacturing energy consumption. One of the energy saving approaches in clinker sintering involves the addition of mineralizers and fluxes to cement raw mix to lower the sintering temperature. This paper describes findings from our study of mainly overseas research on the addition of CaF₂ and CaSO₄ which are the most promising agents for practical application, its effect on lowering the clinker sintering temperature as well as its impact on the manufacturing procedures and cement quality. Cement clinker added with CaF₂ and CaSO₄ as a mineralizer and a flux can have the sintering temperature lowered by around 200 degrees Celsius, making this approach a highly practical energy saving technology for the sintering process. In Japan, adopting this approach would have to be on the premise of maintaining the current amount of waste disposal.

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