THE EFFECTS OF STEAM CURING PROGRAM ON HYDRATION AND PORE STRUCTURE OF FLY ASH MORTAR

Abstract

This paper reports the results of an investigation of effects of steam heat-curing cycles on hydration and pore structure of fly ash cement for the raising efficiency of precast concrete production. The steam heat-curing conditions for the investigation were varied by changing the steam-heat curing processes of daily one-cycle to daily two cycles. The hydrate composition was measured by thermo-gravimetric/differential thermal analyzer（TG-DTA）, selective dissolution method and X-ray diffraction（XRD）Rietveld method to clarify the influence of steam heat-curing on fly ash cement hydration. The pore structure composition was measured by mercury instruction porosimetry. Compared with normal temperature curing, daily one-cycle steam-heat curing of processes lowered the cumulative pore volume at the age of 7 days and later. Compared with normal temperature curing, daily two-cycle steam-heat curing of totally shortened steam-heat curing processes made the cumulative pore volume about equal at the age of 91 days. The relation between compressive strength and total pore volume was formulated as a linear equation. However, this relationship was different for each steam curing program. The relation between amount of Calcium-silicate-hydrate (C-S-H) and pore volumes at 0.03 to 0.3μm was formulated as a linear equation. This relationship was same for each curing program.本研究は、フライアッシュを混和したプレキャストコンクリート製品用セメントモルタルを蒸気養生した場合の養生工程の短縮がセメント硬化体の水和反応と細孔構造に及ぼす影響について、XRD/リートベルト法と水銀圧入式ポロシメータを用いて検討した。材齢7日以降の細孔構造は、常温養生に比較して、1日1サイクル工程の蒸気養生では材齢7日以降から殆どの細孔径で細孔量が減少した。1日2サイクル工程の蒸気養生では材齢28日までは殆どの細孔径で細孔量が多いが、材齢91日では同等となった。細孔構造と圧縮強度には養生条件ごとに相関関係が認められた。毛細管空隙である細孔直径0.03～0.3μmの範囲の細孔量とC-S-H生成量に高い相関関係が認められた。