• 沒有找到結果。

9 混凝土版受熱面之破壞情形

第五章 輕質骨材混凝土之防火隔熱性質探討

照片 5- 9 混凝土版受熱面之破壞情形

(b) 輕質骨材混凝土 (L40)

L40-1

L40-2

第六章 結論

本研究利用水庫淤泥輕質骨材混凝土,進行其構件行為與隔熱防火性 能研究,並與常重混凝土進行比較。由目前的試驗結果,可初步得到以下 幾點結論:

1、 本研究採用以石門水庫淤泥為原料所燒製成的造粒型輕質骨材拌製輕 質骨材混凝土,所燒製而得之三個骨材粒群(3/4"~1/2"、1/2"~3/8"

和 3/8"~#4),其單位重介於 1300~1460 kg/m3間,三十分鐘吸水率 均小於9%,可作為結構與非結構用之輕質混凝土粒料。

2、 輕質與常重混凝土的標稱握裹強度,在添加箍筋後約可提升 20%,而 添加箍筋的握裹試體,其破壞型式將由側向劈裂破壞,趨向為滑動握 裹破壞。

3、 當混凝土強度在 40 MPa 等級以上時,輕質骨材混凝土的握裹強度將比 常重混凝土高,此乃由於同強度輕質混凝土中的水泥漿,其水灰比較 低而使得握裹強度較高。20 MPa 等級輕質骨材混凝土之握裹力則略低 於常重混凝土約15%以內。

4、 輕質樑試體極限剪力強度隨剪力比變化之範圍介於 21.00~90.00 kN,

常重樑試體介於22.35~95.37 kN。相較於 ACI code 理論值, VC,LC/VC, ACI介於 1.49~5.25, VC,NC/VC, ACI介於 1.46~5.35。結果顯示輕質樑與 常重樑之剪力表現相當,ACI code 對於剪跨比較小之構件剪力預估值 則明顯趨於保守。

5、 ACI 規範以 fct/6.7 取代 fc'計算剪力,而輕質混凝土 fct/6.7 約為 0.75 fc',輕質樑較常重樑更形保守。

6、 輕質混凝土樑之 P-△曲線與常重混凝土樑相似,惟輕質混凝土較低之 彈性模數,使輕質混凝土樑試體之勁度較低,使加載初期之斜率略低 於常重混凝土樑。

7、 輕質混凝土樑與常重混凝土樑之極限剪力強度皆會隨剪跨比之降低而 大幅增加。剪跨比對極限剪力強度之曲線斜率幾乎相同(-33),表示

剪跨比對極限剪力強度之曲線斜率,主要來自於樑本身之試體尺寸,

而與混凝土之種類及強度等特性並無明顯之關聯。

8、 輕質混凝土樑與常重混凝土樑之極限剪力強度皆會隨混凝土抗壓強度 之增加而提升。但是輕質混凝土剪力破壞之模式由骨材劈裂,與常重 混凝土並不相同,故對於相同強度等級之混凝土,試驗結果大部分輕 質混凝土樑之極限剪力強度會略低於常重混凝土樑。

9、 20 MPa 強度等級輕質混凝土之等值應力塊深度參數β約為 0.77,高於 PCA 對輕質混凝土之等值應力塊深度參數β=0.76,當輕質混凝土強 度高達 40MPa 時,計算所得之輕質混凝土等值應力塊深度參數β約 為 0.73,乃高於 PCA 對輕質混凝土建議值 0.70,因此 PCA 對輕質混 凝土之等值應力塊深度參數β尚屬保守可行,不需對輕質混凝土做特 別的修正。

10、 中低強度輕質骨材混凝土的熱傳導係數介於 0.690 kcal/m.hr.℃~0.750 kcal/m.hr.℃之間,而常重混凝土則介於 1.330 kcal/m.hr.℃~1.425 kcal/m.hr.℃之間,當混凝土強度由 20MPa 等級提高至 40MPa 等級時,

混凝土熱傳導係數增加有7~8%,且輕質混凝土熱傳導係數僅佔常重 混凝土者的53%左右,相當有利於混凝土節約隔熱的性能。

11、 由日曬試驗與數值模擬分析可以發現,在台灣地區九月平均溫度、6 小時日曬條件下,輕質混凝土房屋相較同條件下之常重混凝土房屋的 內溫降低約3~5℃,比常重混凝土更有利於混凝土房屋保溫取涼的功 能。

12、 輕質混凝土版試體與樑試體在進行防火試驗時,若試體未進行完全烘 乾,將會因蒸汽壓力而發生表面剝落的情形,甚至導致樑或版的破壞。

常重混凝土樑或版試體則較不會發生表面剝落的情形。若為乾燥試 體,則輕質骨材混凝土防火性能優於常重混凝土。

13、 由於輕質混凝土的熱傳導係數較低,在進行混凝土版試體的防火試驗 時,其背部溫度上升的速率較慢,此為其優勢之一。輕質與常重混凝 土版試體的防火時效均可達1 小時以上。

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附件一 期初簡報會議記錄及處理情形

1、建議朝「標準設計斷面」、「標準跨度」的 選定入手,進行深入的結構性能測試,「標 準輕質樑」之選定以不超過三種為限,設 計強度一種,如此應可在期末獲致可立即 應用之研究成果。

謝謝委員意見。本文針對輕質混凝土 材料行為進行研究,未涉及斷面尺寸 形狀等因子。

詹 教 授 穎 雯

2、關於握裹力之量測另有束制條件與上筋效 應未納入探討範圍,建議考慮朝向「標準

2、關於握裹力之量測另有束制條件與上筋效 應未納入探討範圍,建議考慮朝向「標準