Michio Kikuchi

INFLUENCE OF ENVIRONMENTAL CONDITION ON SULFATE RESISTANCE OF HARDENED CEMENTITIOUS MATERIALS USING ADMIXTURES

Sulfate attack is known as one of the deterioration phenomena of concrete structures. Sulfates react chemically with hydration products of cement pastes and lead expansion or weakening of cement matrix. Deterioration cases of this phenomenon have been reported in a variety of environments all over the world. However, most of studies about sulfate resistance of hardened cementitious materials were mainly considered at 23 degrees Celsius in Na₂SO₄ solution immersion. Thus, this study was conducted to investigate the influence of environmental condition（submerged temperatures：20 and 40 degrees Celsius, and sulfate types：Na₂SO₄ and MgSO₄） on sulfate attack of cementitious materials containing Ordinary Portland Cement（OPC） with Blast Furnace Slag（BFS）, anhydrite（AH：CaSO₄）, lime stone powder（LSP：mostly CaCO₃）, fly ash（FA） and silica fume（SF）, and to design a cementitious material with resistance for Na₂SO₄ and MgSO₄. From the experimental results, the deterioration by both Na₂SO₄ and MgSO₄ solutions became severe when the temperature of solution was 40 degrees Celsius. Also, the deterioration due to Na₂SO₄ solution was mainly expansion of the paste specimens, while MgSO₄ solution mainly caused mass decrease and scaling of specimen surface. This was considered that hydration products in MgSO₄ solution were different from that of Na₂SO₄ solution because the pH of the sulfate solutions was influenced from the difference of sulfate types. In addition, the comprehensive sulfate resistance was improved by adding BFS, AH and LSP to OPC. The best sulfate resistance was found for BFS/OPC ratio＝70：30 with AH5～10％ - LSP10％.本研究は、普通ポルトランドセメント（OPC）に高炉スラグ微粉末（BFS）-無水せっこう（AH）-石灰石微粉末（LSP）、フライアッシュ（FA）-シリカフューム（SF）、およびBFS-SFを用いたセメント系材料について、硫酸塩種および温度条件が硫酸塩劣化機構に及ぼす影響を明らかにし、Na₂SO₄とMgSO₄、さらに高温条件を考慮した総合的な耐硫酸塩性に優れた材料設計を提案することを目的とした。その結果、硫酸塩種の違いは硫酸塩溶液のpHに影響を及ぼし、さらには水和生成物が変化することで劣化形態が異なるものと考察した。温度条件もpHを変動させる要因となり、高温条件下では劣化が激しくなると考えられた。またBFS置換率70％とした材料に、AH5～10％およびLSP10％を併用混和することで耐硫酸塩性が向上した。