Case Study of Using Stress Wave Velocity to Evaluate In-Place Strength of Concrete

本論文主要目的是以前人研究建立之應力波波速與混凝土強度成長率關係性實際應用於在建工地現場做為推估現地混凝土強度之案例研究試驗，探討現場實際各齡期混凝土波速與強度成長率之關係，並以混凝土表面自然乾燥及預濕飽和兩種狀態對波速影響之關係辦理修正。在混凝土波速與強度成長關係採用面乾內飽和之圓柱試體，波速量測採用超音波法，現地試驗時波速量測採用敲擊回音法再以前人研究與超音波法彼此間之轉換關係做轉換，來針對不同齡期混凝土試體進行波速量測並以混凝土含水狀態對波速做修正，再來預估混凝土強度，最後與鑽心試體抗壓強度做比較。本研究現地混凝土試體配比之實際水膠比(W/B)為0.56，其中飛灰佔25％，爐石粉佔25％。 研究結果，顯示以圓柱試體所建立的波速與強度成長率迴歸關係曲線與前人研究以水膠比0.5與0.6公式建立之波速-強度預估成長率關係曲線預測公式相似度極高，驗證與混凝土配比中之粗粒料含量、膠結料含量或是不同膠結摻料(爐石或飛灰)及水膠比對於波速-強度成長率關係曲線造成的影響的確有限。 在現場混凝土強度評估方面，因本研究案例之板試體採用現成鋼模以垂直方式灌置混凝土，故有明顯的粒料沈降現象，使得下部之粒料含量較上部為多，而早齡期之波速因漿體尚在水化階段，易受粒料分佈影響波速強度很大，以致造成位於下部之波速均較位於上部之波速來得高的狀況。本研究如以圓柱試體所建立的波速與強度成長率關係曲線來推估現場板試體強度，因與現場板試體實際狀況之配比(尤其是粒料含量)已明顯差異，故強度預測時，所需之終端波速已不相同。故本研究另外以超音波對28天之鑽心試體檢測求得波速，搭配抗壓試驗求得強度，再依據波速與強度關係成長率曲線分別推求得到板試體上、下兩部分之終端波速，再據以推估現場板試體之強度。研究顯示以修正的終端波速推估各齡期現地板塊試體強度結果，除7天早齡期仍偏低外，餘14天及28天的預估強度均已在可接受的範圍內。The objective of the thesis is to practically apply the previously established growth rate relationship between stress wave velocity and concrete strength for estimate of in-place strength of concrete in a construction site. The research work includes verifying the established relationship between ultrasonic pulse velocity (UPV) and strength growth rate and investigating the effect of surface natural dry and pre-wetting status on stress wave velocity. Concrete cylinders with saturated surface dry (SSD) were used to verify the UPV-strength relationship. In field study, the impact-echo (IE) method was adopted to measure the wave velocity at various ages of concrete and a suggested factor was used to convert the IE velocity into UPV. Subsequently, the converted velocity was modified by the moisture content of concrete to a status of SSD. Then, the strength of concrete was estimated by the velocity in SSD status with the established UPV-strength relationship and the estimated strength was compared with the strength of the cores taken from the field specimen. The water-cementitious ratio (W/B) of field concrete was 0.56 and replacement ratios of cement with fly ash and slag both were 25%. The results obtained from the study show that the relationship between UPV growth rate and strength growth rate is almost the same as the previously established one. This once again reveals that the UPV-strength growth rate relationship is not affected significantly by the change in mixture proportion of concrete. In the field study, separation of aggregates was found in a erected steel mold due to the gravity effect. This results in a higher pulse velocity in the lower part of the specimen containing more aggregates. In such a case, the terminal strength would not be affected because the W/B did not change. However, the terminal velocity needed in strength estimate with the UPV- strength growth rate relationship must be different due to change in aggregate content. Thus, the UPV and strength of core specimen at an age of 28 days was used to deduce the terminal velocity. Finally, the strength of the field specimen was estimated with the deduced terminal velocity. The estimated results are in a satisfactory range with an error within 15% for concrete at ages of 14 and 28 days.第一章 緒論 1 1-1研究背景 1 1-2研究目的與方法背景 2 第二章 文獻回顧 3 2-1超音波法及敲擊回音法介紹 3 2-1-1超音波法 3 2-1-2敲擊回音法 5 2-2波速於混凝土非破壞檢測上的應用 9 2-3混凝土之波傳行為特性 10 2-3-1混凝土之材料組成與波傳特性 10 2-3-2孔隙含量 12 2-3-3混凝土之養護溫度、含水狀況與材齡 13 2-4混凝土含水狀態之量測與波速之關係 13 第三章 試驗儀器、原理及方法 16 3-1含水量測定 16 3-1-1試驗儀器 16 3-1-2建立導電值與飽和度關係式試驗步驟 16 3-1-3現地混凝土試驗步驟 17 4-2敲擊回音法 17 3-2-1試驗儀器 17 3-2-2實驗室試驗步驟 19 3-2-3現地試驗步驟 19 3-3超音波法 20 3-3-1試驗儀器 20 3-3-2試驗步驟 21 3-4抗壓強度試驗 22 第四章 研究規劃 23 4-1試體規劃與製作 23 4-2試驗流程與方法 25 4-3強度預估原理與方法 25 4-4研究案例工程簡介 26 4-5研究案例現地試體製作及量測照片 27 第五章 現地試驗結果與討論 30 5-1圓柱試體超音波波速與強度關係曲線 30 5-1-1圓柱試體之UPV與抗壓強度關係 30 5-1-2以波速-強度成長關係曲線預測公式結果 30 5-1-3圓柱試體波速與強度關係曲線與成長關係曲線預測公式比較 32 5-2自然風乾板塊試體強度預測 32 5-2-1以圓柱試體迴歸曲線(取W/B=0.5)預估板塊試體強度結果 34 5-2-2以修正終端波速(取W/B=0.5)預估板塊試體強度結果 37 5-3預濕板塊試體強度預測 42 5-3-1以圓柱試體迴歸曲線(取W/B=0.5)預估板塊試體強度結果 42 5-3-2以修正終端波速(取W/B=0.5)預估板塊試體強度結果 45 5-4自然風乾與預濕板塊試體強度預測結果彙整 48 5-5現地護岸強度預測 49 5-5-1以圓柱試體迴歸曲線(取W/B=0.5)預估現地護岸強度結果 49 5-5-2以修正終端波速(取W/B=0.5)預估現地護岸強度結果 51 第六章 結論與建議 53 6-1結論 53 6-2建議 54 參考文獻（REFERENCES） 5