高氧化鈣含量飛灰對自養護混凝土之影響

Abstract

飛灰以往為造成空氣汙染之廢棄物，經眾多工程研究發現飛灰之再利用價值後，如今已廣泛運用於混凝土工程，飛灰之卜作嵐材料特性，可與氫氧化鈣產生卜作嵐反應生成C-S-H膠體填充混凝土中之孔隙，改善混凝土之品質。但因卜作嵐反應需時較長且需良好之養護條件才可充分進行，故自養護藥劑之研發與應用，有助於保有混凝土中之水分，以利卜作嵐反應之進行。 本研究以高氧化鈣含量飛灰取代部分水泥，探討自養護藥劑於摻有不同飛灰取代量之混凝土中的效果，更進一步探討高氧化鈣含量飛灰可能含有大量游離氧化鈣對自養護藥劑之影響。研究過程中使用氧化鈣粉取代飛灰重量，增加飛灰中之氧化鈣與游離氧化鈣含量，進行砂漿與混凝土試驗。 砂漿試驗著重於觀察氧化鈣含量多寡對摻有自養護藥劑之砂漿流度與凝結時間之影響。混凝土試驗則著重於F級飛灰與高氧化鈣含量飛灰之取代水泥量多寡對摻有自養護藥劑之混凝土工作性與各項工程性質之影響。結果顯示自養護藥劑適用於使用高氧化鈣含量飛灰之混凝土，可有效增進養護效果，提高抗壓強度與劈裂抗張強度，減少水分重量損失與收縮應變，並藉由測量表面電阻率得知其具有良好之耐久性，但當高氧化鈣含量飛灰取代水泥量過多時，須注意坍度損失、體積穩定性等問題。

Fly ash is a kind of pozzolans. It can react with calcium hydroxide to form the calcium silicate hydrate which fills the pores in concrete. Pozzolanic reaction can improve the quality of concrete, but it is slower than the hydration of cement. This makes curing more important to guarantee the effectiveness of pozzolans, so the development and applications of self-curing admixture (SCA) help for retaining the moisture in concrete and facilitating the pozzolanic reaction. In this study, fly ash with high calcium oxide content was used to replace a part of cement, which aims to discuss the results of SCA using in the different fly ash replacement concrete. A method to increase the calcium oxide and free lime content in fly ash was selected by adding lime powder to the original fly ash in order to vary calcium oxide and free lime content of the fly ash. The basic properties of mortar tests consisted of water requirement, fluidity, initial and final setting time. The mortar tests focus on observing the different amount of calcium oxide content in mortar mixtures with SCA how to influence their basic properties. The concrete tests focus on comparing the differences between using class F fly ash and using fly ash with high calcium oxide content to replace different part of cement in concrete mixtures with SCA. This research showed that SCA is suitable for the concrete with high-calcium oxide-content fly ash. SCA can effectively enhance the curing of the concrete. Using high-calcium oxide-content fly ash in concrete can increase the compressive strength and splitting tensile strength and reduce the water loss and shrinkage. Surface resistivity test showed that the concrete with high-calcium oxide-content fly ash and SCA has good durability. But when it is applied to the concrete with large amount high-calcium oxide-content fly ash replacement, which may cause slump loss or volume stability problems.