使用石灰石水泥之自充填混凝土收縮行為與預測 模型 研究

Abstract

近年來，全球面臨日益嚴重的氣候變遷與碳排放問題，各國積極推動節能減碳措施以邁向淨零碳排目標。水泥工業作為主要的碳排來源之一，其低碳轉型成為當前關鍵課題。其中，以卜特蘭石灰石水泥為主要替代方案，因具有較低之碳足跡而成為歐美主流趨勢，尤其是自充填混凝土中。然而，在台灣工程規範限制混合水泥與卜作嵐摻料併用的背景下，石灰石水泥實際應用尚不普及。自充填混凝土因其高流動性、免振動搗實之特性，廣泛用於高密集鋼筋結構，但其低水膠比、高粉體用量與高藥劑需求，造成其收縮變形行為較傳統混凝土有所差異，若直接以石灰石水泥取代I型水泥，其體積穩定性仍有待深入探討。 本研究旨在探討使用卜特蘭石灰石水泥於自充填混凝土中的應用表現，特別聚焦於其對混凝土收縮行為的影響，並與傳統卜特蘭I型水泥進行比較分析。本研究針對三種不同水膠比（w/b=0.32、0.4、0.48）與三種卜作嵐摻料取代量（純水泥、30%爐石、35%爐石+15%飛灰）進行共18組自充填混凝土配比設計，評估其新拌性質、抗壓強度、自體收縮與乾燥收縮表現，並進一步與現有的預測模型Model B4TW-SCC進行驗證與分析，以探討其適用性與預測精度。 實驗結果顯示，石灰石水泥在新拌性質上與I型水泥表現相當，強度發展在中高水膠比條件下亦無明顯劣化。然在收縮行為上，石灰石水泥對乾燥收縮無顯著改善，但在所有水膠比條件下之自體收縮普遍高於I型水泥，尤其在搭配爐石與飛灰時情況更為明顯。推測是因為石灰石粉的成核效應促進水化產物形成並加速礦物摻料的卜作嵐反應，導致更劇烈之內部耗水與自乾現象。整體而言，石灰石水泥在自充填混凝土中對體積穩定性的影響需審慎評估。

In recent years, the world has faced increasingly severe challenges related to climate change and carbon emissions. Countries around the globe are actively promoting energy-saving and carbon reduction strategies to achieve net-zero emissions. As one of the major sources of carbon emissions, the cement industry is undergoing a critical low-carbon transformation. Among various approaches, Portland Limestone Cement (PLC) has emerged as a key alternative due to its lower carbon footprint and has become a mainstream trend in Europe and North America, particularly in the application of Self-Compacting Concrete (SCC). However, under current Taiwanese engineering specifications that prohibit the simultaneous use of blended cement and supplementary cementitious materials (SCMs), the practical application of PLC remains limited. SCC, known for its high flowability and self-consolidating properties without the need for vibration, is widely used in structures with dense reinforcement. Nevertheless, its low water-to-binder ratio, high powder content, and high chemical admixture dosage lead to different shrinkage behaviors compared to triditional concrete. Thus, the volume stability of SCC using PLC as a substitute for ordinary Portland cement (OPC) warrants further investigation. This study aims to evaluate the performance of SCC made with PLC, focusing particularly on its effects on shrinkage behavior, and to compare it with that of SCC made with OPC. Eighteen mix designs were developed, covering three different water-to-binder ratios (w/b = 0.32, 0.40, 0.48) and three different pozzolanic replacement levels (pure cement, 30% slag, 35% slag + 15% fly ash). Each mix was evaluated for fresh properties, compressive strength, autogenous shrinkage, and drying shrinkage. In addition, the prediction accuracy of the existing B4TW-SCC model was examined to assess its applicability. Experimental results indicated that the fresh properties of PLC mixes were comparable to those of OPC mixes, and the strength performance under medium to high w/b conditions showed no significant degradation. However, in terms of shrinkage behavior, PLC did not significantly improve drying shrinkage and generally exhibited higher autogenous shrinkage across all w/b conditions, especially when combined with slag and fly ash. This increase is attributed to the nucleation effect of limestone powder, which accelerates the formation of hydration products and enhances the pozzolanic reactions of SCMs, leading to more intensive internal water consumption and self-desiccation. Overall, the influence of PLC on the volume stability of SCC should be carefully considered in practical applications.