| 摘要: | 瀝青混凝土由具膠結特性之瀝青膠泥，混合粗細粒料結合而成，其中瀝青膠泥具溫感性，隨著周遭溫度高低而產生硬固或流動現象，也因此種特性使得瀝青混凝土整體勁度必隨著溫度變化而有顯著差異，進一步左右柔性鋪面之勁度與承載力，影響鋪面服務品質。瀝青混凝土鋪面受到外在大氣溫度影響，實際上鋪面表面至內部之間存在溫差變化與溫度分佈，瀝青鋪面因溫度而導致回彈模數隨著瀝青層深度呈現非均值之分佈，因此鋪面破壞分析中若忽略柔性鋪面回彈模數受溫度分佈之影響而採用瀝青層回彈模數定值進行分析，必高估鋪面服務年限與耐久性。透過實際量測台灣高速公路柔性鋪面之溫度分佈，深入分析鋪面內部溫度之變化對柔性鋪面應變之影響，研究結果顯示柔性鋪面溫度分佈隨著季節氣候變化而不同，隨著鋪面溫度與深度之分佈趨勢分為正負溫度分佈曲線兩種型態，全年度鋪面溫度分佈以此兩種型態為主。再者，透過柔性鋪面熱學參數與溫度分析顯示，太陽輻射為主要影響瀝青鋪面溫度之來源，透過放射輻射、熱對流與熱傳導之分析可瞭解太陽輻射對柔性鋪面造成之溫度變化，進一步藉由熱傳導能之計算可瞭解鋪面進入升溫與降溫期之時間點。 由於高速公路瀝青層厚度較大，使AC與BTB層溫度分佈型態有所不同，一天中AC層溫度隨時間變化情形近似sine函數曲線，而BTB層溫度隨時間之變化呈現平緩，因此溫度預測模式考量分佈型態而分別加以建立。鋪面各層應變隨著一天24小時溫度分佈而變化，由於最大水平應變為BTB層底部控制，因此其溫度於清晨7~9點與下午16~18點時段溫度達到一天中最低與最高的同時，鋪面應變反應也呈現同樣情形，並非中午高溫時段為最高。 AC與BTB的溫度分佈特性亦影響高速公路鋪面有效溫度位置，利用鋪面模型分析得1/2 AC 層深度位置與BTB 層頂部以下2cm 處之溫度代表整體柔性鋪面，所呈現鋪面反應近似鋪面實際狀況且誤差最小，故進行鋪面結構分析時，高速公路瀝青層應視為AC與BTB兩層結構，並各取有效溫度進行分析，較能符合現地鋪面力學反應。再者，高速公路柔性鋪面考量鋪面溫度梯度24 小時變化與交通量軸重作用下得知，每軸次損傷程度隨著白天鋪面升溫而逐漸提高，至夜晚鋪面散熱降溫後損傷程度逐漸降低，顯示一天鋪面的溫度循環左右著重車對鋪面的破壞程度，鋪面破壞比亦呈現相同結果。此外，高速公路受到溫度效應影響，透過每軸次損傷程度分析顯示各月份以疲勞破壞機制較車轍破壞機制明顯，顯示高速公路高厚度結構伴隨著實際溫度梯度分佈與交通量作用下疲勞裂縫較車轍變形早發於柔性鋪面。 探討不同時間區間之鋪面均溫與交通量對鋪面破壞比與服務年限之影響，選擇時間區間由每小時擴大至一年，研究結果顯示1hr 時間區間可模擬鋪面經歷每日升溫與降溫之影響，及交通量尖離峰時段的作用，其鋪面破壞機制之反應近似高速公路實際狀況，所得破壞比高於年平均溫度結果，顯示高速公路鋪面破壞損傷程度更為嚴峻，求得鋪面服務年限比年平均溫度之服務年限為短，鋪面年平均溫度狀態與實際鋪面狀況之間存在顯著差異，本研究為兩者之間透過鋪面服務年限調整係數確立彼此關係。鋪面服務年限調整係數的建立以1hr 時間區間之預估鋪面服務年限為準，進一步為各時間區間確立相對關係，當中主要以年均溫區間為調整目標，可為高速公路鋪面設計者提供兩者時間區間條件下確切的關係，為鋪面厚度設計與殘餘服務年限評估進行修正，有助於掌握鋪面實際服務成效。 Asphalt concrete (AC) is a sensitive material with temperature, its stiffness is greatly influenced by ambient temperature. As the temperature of the asphalt concrete increases, its stiffness decreases that may lead to rut occurring on the asphalt pavement from wheel loads. A decrease in asphalt concrete stiffness results in lower structural capacity to support vehicle loads. Therefore, the mechanical property of flexible pavement is affected by temperature deeply. In this study, based on field temperature measurements obtained from a test site simulating actual pavement structures of freeways, the pavement temperature distribution in Taiwan’s freeway were discussed in details. The results indicated the temperature of pavement changes with the climate within a year. Since the thickness of freeway pavements in Taiwan is relatively thick, the temperature distribution of the AC and bituminous treated base (BTB) layers was found to be different. Thus, separate temperature prediction model was established according the characteristic of each asphalt layer. Based on the test results, the effective temperature depth of pavement was affected by the temperature distribution of AC and BTB. Through the analysis on pavement structural responses, it is indicated that the 1/2 depth of AC layer and the 2 cm under the top of BTB layer are considered appropriate depth as effective temperature for strautural analysis of pavements. Also, separate temperature prediction model were established for AC and BTB layers, respectively. Besides, considering the pavement temperature variation within 24 hours and traffic loads applied on freeway pavement, the damage per pass of each load axle was calculated for different times in a day. It was found that the damage increases as pavement temperature increases in the daytime and reduces as the temperature decreases in nighttime. In other words, the temperature cycle within a day has a great effect on the damage level caused by traffic loads in flexible pavement. Moreover, with the thick pavement structure used by Taiwan’s freeway, it was found that the fatigue damage will occur earlier than permanent deformation. Various time-durations, ranging from 1-hour to 1-year, for average temperature input to predict pavement service life and/or design ESAL were evaluated carefully. The effects of pavement average temperature of various time periods and traffic loads on pavement damage ratio and service life were determined. It was found that the 1-hr time period with average pavement temperature could simulate the actual response of freeway pavement under the pavement temperature cycle and traffic loadings. Segmentation of the pavement temperature and traffic loading into 1-hr period will produce a pavement damage ratio greater than that into 1-yr period. This indicates that the actual damage of freeway pavement is more severe than that expected by considering the yearly average temperature only. The adjustment coefficient of pavement service life established the relationship for the apparent difference between the yearly based average temperature and the real situation of in-situ pavement temperature. Using the pavement service life calculated using 1 hr period as the basis, a correlation is established for different time periods for average temperature. It provides an exact relationship obtained from the average temperature of 1 hr period and a yearly period for pavement structure design and the estimation of remaining pavement service life. |
