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Blast furnace slag (BFS) has been widely used as a mineral admixture in cement and concrete in the concrete industry in order to reduce CO2 emissions. In Japan, the replacement levels of BFS are categorized into type A (5~30 wt%), type B (30~60 wt%), and type C (60~70 wt%) according to Japanese Industrial Standard (JIS). However, only type B BFS blended cement is actually used in the construction industry, and is mainly used in foundations or underground structures, and not in main structural elements due to the low compressive strength at early age. In order to broaden the practical application of BFS blended cement in the construction industry, the mechanical property and hydration process need to be further discussed. Therefore, the purpose of this research is to investigate the BFS blended cement in cementitious composites affected by various replacement ratios, such as in compressive strength development methods, with combined deterioration of carbonation and frost damage. Moreover, the compressive strength development of BFS blended cement and the combined deterioration effects of accelerated carbonation and freeze?thaw resistance were investigated in this thesis. In Chapter 2, a calcium silicate hydrate (C-S-H) type accelerator that was developed to serve the purpose of increased production efficiency and streamlining of manufacturing secondary products of concrete shows an effect in all temperature ranges. Therefore, it is the purpose of this research to establish if a C-S-H type accelerator is able to be used as a BFS blended concrete strength development method. The C-S-H type accelerator was compared with the quality standard of the accelerator, and proved possible to be positioned not merely as a hardening accelerator. Moreover, the addition of C-S-H type accelerator to BFS cement type B did not see a close relationship between additive amounts of C-S-H type accelerator and strength development; thus, we tested the heat of hydration by conduction calorimeter and analyzed it by X-ray diffraction (XRD). This indicates the cement hydration of the promotion mechanism of the C-S-H type accelerator. In chapter 3, it was investigates the compressive strength development of blast furnace slag (BFS) blended mortar mixtures incorporating various mineral admixtures, namely BFS, limestone powder (LSP), and gypsum (CS). BFS replacement ratios of 15, 20, and 25 wt.%; LSP replacement ratios of 2, 3, 4, and 5 wt.%; and a CS ii replacement ratio of 2 wt.% are employed to improve the strength of BFS blended mortar mixtures. The hydration reaction and products resulting from the use of cement, BFS, and mineral admixtures are quantitatively examined with respect to the XRD/Rietveld method in order to investigate the relationship between the produced hydrates and the strength. In addition, the strength is found to be decreased as the BFS replacement ratio increases. At a BFS replacement ratio above 20 wt.%, LSP affects the strength improvement of BFS cement and CS affects the initial strength improvement of BFS cement. The effect of high early strength Portland cement (HPC). The investigation of each concrete sample includes two curing cases, which are cured in air 5℃ or 20℃ at 30, 90, 210, 840 and 2730 Maturity. The result of experiments shows that, in the case of BFS A type, it has the same performance as the OPC. In the case of BFS B type, considering the advantage that largely reduced from the amount of CO2, the mixture BFS35% + LSP 3% + CS2% is judged appropriate. In chapter 4, the durability performance of cementitious material is traditionally based on assessing the effect of a single degradation process. However, this study investigates the mechanical and coupled deterioration properties of mortar incorporating industrial solid waste - ground granulated blast furnace slag (BFS) and different mineral admixtures, such as calcium sulfate (CS) and limestone powder (LSP). The combined deterioration properties caused by carbonation and frost damage in the mortar sample were experimentally investigated with respect to accelerated carbonation and freeze?thaw tests. Different degrees of deterioration, i.e., after subjected to 12, 30 and 60 freeze-thaw cycles were induced in the freeze-thaw tests. Mercury intrusion porosimetry (MIP) was used to measure the pore structure distribution in the mortar samples to quantify the influence of the mineral admixtures and the replacement ratio on the change in pore structure volume, providing reasonable guidance to assess the durability. The experimental investigation revealed that the compressive strength, frost resistance and carbonation resistance decrease as the BFS replacement ratio increases by weight from 0 to 45%. Moreover, to achieve the same strength as ordinary Portland cement, 2 wt. % CS and 4 wt. % LSP in the BFS mortar are required. However, the data shows that incorporating LSP into the BFS mortar produces a lower frost carbonation resistance. The combined damage tests revealed that different deterioration degrees resulting from 12, 30 and 60 freeze?thaw cycles slightly decreased the iii carbonation resistance, which is related to the decrease in the inkbottle pore volume due to its water retention characteristics. Simultaneously, the pre-carbonation deterioration could effectively decrease the surface mass scaling of the freeze?thaw, indicating In Chapter 5, the frost damage resistance of BFS cement has an effect on the carbonation. Hence, this study investigates the carbonation properties of pastes incorporating BFS and different replacement ratios, at 15%, 45%, and 65% of replacement ratio on weight percentage. The replacement ratio properties caused by the Ca/Si ratio of C-S-H in the paste samples were experimentally investigated with respect to mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), and thermal analysis tests. Different degrees of curing age (2 week, 4weeks) were subjected to water curing. The experimental investigation of the pore structure indicated that the total porosity decreases after carbonation. Calcium carbonation (CC) is denser than calcium hydroxide (CH) due to the carbonation. We found vaterite through chemical composition analysis by XRD, which has a high expansion rate, and which influences the carbonation characteristic of BFS blended cement paste.
高炉スラグ微粉末（BFS）は，二酸化炭素の排出を削減するためにセメントやコンクリートに混合し使用する鉱物質混和材として広く使用されている。BFSを混合したセメントの使用量を高めるために，高炉スラグの欠点である初期強度低下の改善と凍結融解被害を受けるおそれがある寒冷地での中性化と凍結融解を同時に受ける複合劣化に対する検討が必要である。そこで，本研究ではBFSセメントの圧縮強度を改善する方法と中性化と凍結融解による複合劣化挙動を明らかにすることを目的とした実験と検討を行い，以下の結論を得た。1. コンクリート2次製品の迅速な脱型のために開発されたC-S-H早強剤は，初期強度の改善剤としての機能を有することから，BFSセメントの強度発現性状を改善するための一方法としてのC-S-H早強剤の使用の可能性を検討した。結果的に，BFS混入によりC3S量が低下したセメント複合体では，C-S-H早強剤の効果は低く，BFSセメントへの適用は困難であると判断された。2. BFSセメントに石灰石粉末（LSP）と石膏（CS）を少量混合成分として添加した場合の圧縮強度の改善について検討した。生成される水和物と強度との関係を把握するために，セメントおよびBFSと少量混合成分に起因する水和反応と水和生成物をXRD / Rietveld方法について定量的に分析した。定量化した水和生成物量を基準に算定した空隙量と強度との関係から強度の改善効果を検証した。その結果，BFS 15％，LSP 4％とCS 2％を調合したBFSモルタルは，普通ポルトランドセメントを用いたモルタルと同等程度まで強度発現性状が改善されることを示した。3. BFSの混入はセメント硬化体において重要な水和物であるC-S-HのCa / Si比に影響を及ぼす。そこで，Ca / Si比が中性化に及ぼす影響を確認するために中性化前後の成分と空隙構造を実験的に検討した。その結果，促進中性化で生成する炭酸カルシウムは水酸化カルシウムより体積が大きいことから，中性化によって水和組織が緻密になることを確認した。また，BFSを使用した場合に生成する炭酸カルシウムにはバテライトが高比率で含まれており，カルサイトを多く含む普通ポルトランドセメントの場合とは異なる傾向を示した。4. BFSセメントに少量混合成分としてCSとLSPを使用して強度向上が確認されたモルタルを対象として耐久性の検討を行った。その結果，中性化と凍結融解による複合劣化の性状について，凍害劣化の進行により中性化抵抗性がわずかに低下することと中性化の進行が凍結融解の繰り返しによる表面のスケーリング量を減少させて凍結融解抵抗性が向上することが明らかとなった。