Akinori Nakamura

INFLUENCE OF SPECIFIC SURFACE AREA AND CALCIUM SULFATE OF BLAST-FURNACE SLAG ON ADDITION EFFECT OF CALCIUM HYDROXIDE POWDER TO THE CEMENT CONTAINING BLAST FURNACE SLAG

This paper describes the influence of the specific surface area of blast-furnace slag and the existence of calcium sulfate in blast-furnace slag on the effect of calcium hydroxide powder, which is considered to accelerate the reaction of blast-furnace slag in cement containing blast-furnace slag, for the purpose of improving a characteristic of cement containing blast-furnace slag, in order to use it effectively as general purpose cement. The physical properties of 4 types of blast-furnace slag cement, which was changed the specific surface area of blast-furnace slag and the existence of calcium sulfate in blast-furnace slag respectively, were assessed in the presence of calcium hydroxide powder. As a result, setting time of cement paste was accelerated by addition of calcium hydroxide powder regardless of the kinds of blast-furnace slag. Concerning compressive strength of mortar, in case of about 4,000cm²/g of slag’s specific surface area, strength was improved by addition of calcium hydroxide powder because of the acceleration of blast-furnace slag. Considering the result of the amount of calcium hydroxide measured by TG-DTA and the reaction ratio of blast-furnace slag by selective dissolution method, the existence of calcium sulfate in blast-furnace slag was guessed to improve the effect of calcium hydroxide powder in the early period of hydration.高炉スラグ含有セメントの性能改善を目的に、高炉スラグの比表面積および石こう含有の有無が、高炉スラグの反応刺激剤としての作用が考えられる水酸化カルシウム微粉末の添加効果に及ぼす影響について検討を行った。その結果、水酸化カルシウム微粉末の添加により、高炉スラグの種類に関わらず凝結は促進され、高炉スラグの比表面積が4,000cm²/g程度の場合に、高炉スラグの反応促進により強度が増進する傾向が確認された。また、高炉スラグに石こうを含有した場合、水酸化カルシウム微粉末による高炉スラグの反応が促進される時期が、石こうを含有しない場合より促進される傾向が確認された。

INFLUENCE OF GYPSUM AND LIMESTONE POWDER ON AUTOGENOUS SHRINKAGE OF HIGH-FLOW CONCRETE WITH GROUND GRANULATED BLAST-FURNACE SLAG

高炉スラグ微粉末を使用した粉体系高流動コンクリートの問題点として, 自己収縮の増大が指摘されている. 本研究では, 高炉スラグ微粉末に添加されたセッコウ及び石灰石微粉末が高流動コンクリートの自己収縮特性に与える影響を検討し, その機構について考察を加えた. セッコウの添加により, 自己収縮ひずみが低減し, 単位引張強度あたりの自己収縮ひずみが減少した. 自己収縮の低減は, エトリンガイトの生成による毛細管空隙量の増加によるものと推定した. 石灰石微粉末の添加により, 初期材齢において自己収縮ひずみの低減ならびに単位引張強度あたりの自己収縮ひずみの減少が認められた. しかし, 長期にわたり自己収縮が継続する傾向が認められた. 長期にわたる自己収縮の増加は, 石灰石微粉末の反応に起因するものと推定した.

Influence of KCl on the Hydration and Strength Development in Alite-KCl System(Special Issue on Structural Materials)

The chlorides by-pass process has been introduced to many cement plants in recent Japan, because of the increase of chloride content in cement raw materials when municipal wastes are used. The extracted dusts called bypass dusts, containing potassium chloride as the main component were formed in this process. It is necessary to utilize this byproduct; otherwise it will become new industrial waste. This paper discusses the influence of potassium chloride on the hydration of alite, the main component of portland cement, by means of XRD quantitative analysis to determine the phase composition of hydration products. And, the relations between pore structures and compressive strength of hardened pastes with or without potassium chloride has also been investigated.The compressive strength was decreased with the increasing quantity of potassium chloride after the hydration of 7 days. The strength decreased remarkably by the addition of the potassium chloride at 28 days hydration. The dependence of the strength on the porosity of hardened pastes with potassium chloride was larger than without potassium chloride. And the porosity of hardened paste with potassium chloride became larger at the same hydration ratio of alite. Then, the amounts of produced calcium hydroxide were decreased at the same hydration ratio of alite, by the addition of potassium chloride, and Ca/Si ratio of calcium silicate hydrate was increased. It is conceivable that the above mentioned difference of hydration products influences the microstructure and the strength characteristics of the hardened alite paste with or without potassium chloride.

Influence of Calucium Sulfate on the Fluidity of High-Flow Concrete Made with Ground Granulated Blast-Furnace Slag.

We discuss the influence of calcium sulfates on the fluidity of high-flow concrete made with ground granulated blast-furnace slag (BFS) and polycarboxylate-based superplasticizer (PC). Gypsum, hemihydrate and anhydrate were added to BFS and the effect of each was examined. Gypsum and anhydrate had no effect on the fluidity of high-flow concrete with BFS. By addition of hemihydrate, the fluidity of high-flow concrete is reduced at very early stages, but it is improved rapidly after 5 minutes. The amount of adsorbed PC, amount of ettringite and sulfate ion concentration in the aqueous phase of cement paste with BFS and PC were measured to clarify the mechanisms for the changing of fluidity. Fluidity was decreased linearly with the increase of sulfate ion concentration. The results of present study suggest that the change in fluidity of high-flow concrete with BFS and PC due to calcium sulfates in BFS caused by a change in the dispersion of particles by sulfate ions in the aqueous phase.