音射(acoustic emission, AE)為材料內部結構受外界刺激發生改變，期間儲存應變能瞬間釋放產生暫態彈性波之現象。音射檢測法使用壓電感測器轉換材料表面微小振動為電子訊號，藉由分析訊號波形或經萃取之音射參數，辨別材料破壞特徵及損傷程度，為非破壞檢測法的一種。本研究目的為探討粗粒料效應對混凝土性質之影響，針對配比固定之砂漿，改變粗粒料尺寸與含量，於水中養護28天後進行單軸抗壓試驗，過程中同步擷取音射訊號，使用音射法常用之參數法分析，觀察混凝土加載過程開裂形式分布隨時間之變化，並以高斯混合模型(gaussian mixture model, GMM)協助分類裂縫模式。
由於本研究使用之水泥砂漿強度高，而粒料周圍的界面過渡區具有孔隙率較高之特性，被認為是混凝土中軟弱區域，因此添加粗粒料相當於為微結構緻密的砂漿增添弱面。研究結果顯示粗粒料含量增加，抗壓強度有所下降，且粒徑較小者強度下降趨勢較為明顯，相同粗粒料含量下，粒徑較小者粗粒料間距離較近，導致相鄰粗粒料界面之裂縫易於連結，較大裂縫形成後即發生破壞。音射參數可反映混凝土中缺陷發展，粒徑較大者偏轉裂縫之能力較佳，且裂縫路徑較為曲折，開裂過程產生大量振鈴計數與能量，累積振鈴計數與能量隨粗粒料含量提升、粒徑增大而增加。GMM分群結果顯示，抗壓過程各試體內部裂縫模式皆以張力為主，粗粒料含量較低試體，加載後期較大裂縫形成後，無法抵擋開裂面滑動而破壞，因此剪力裂縫分群結果靠近兩者混合區間，且範圍內沒有較高的機率密度；隨著粗粒料含量提升，剪力模式訊號分布較廣，其中粒徑較小者整體剪力訊號分布接近兩者混合區，由於內部裂縫易於連結，導致訊號分布於混合型過渡到剪力區不久即發生破壞，此結果與其較低的抗壓強度相呼應。

The purpose of this study is to investigate effects of coarse aggregates (CAs) in portland cement concrete using the acoustic emission (AE) technique. Concrete specimens with variations in CA content and size were made by identical proportions of cement mortar and cured for 28 days until testing. The uniaxial compression test was carried out and monitored throughout the test with an AE system. After collecting the AE data, we use parameter-based method to analyze data. We also use gaussian mixture model (GMM), which is a statistical approach, to classify AE data into two clusters: tensile and shear.
The result shows that increasing the CA content decreases the compressive strength of concrete; moreover, the phenomenon is more apparent for the smaller CAs. Because the cement mortar is relatively dense, adding CAs into concrete would increase the volume of interfacial transition zone (ITZ) which is generally regarded as plane of weakness. Furthermore, the smaller CAs reduce the spacing between CAs, making planes of weakness closer to each other. The higher CA content and the larger CA size are, the more tortuous cracking path is, the higher cumulative counts and energy are observed. With regard to the results of GMM analysis, tensile cracks dominate no matter what CA content and size are. The area of shear mode becomes wider as CA content increases. And that of smaller CAs is near the transition area between tensile and shear because premature failure occurs.

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