以改良式混凝土質流儀量測新拌混凝土

Abstract

本研究開發改良式混凝土質流儀(MCR)，係依據現有的混凝土質流儀進行改良，其中外桶與葉片的間距為最大粗粒料粒徑的6.4倍以降低兩者互相的影響，並以數種低轉速(0.003 rev/sec以上)直接量測新拌混凝土的降伏扭矩。本研究量測40組新拌混凝土的降伏扭矩及黏度尤其是針對自充填混凝土(SCC)，並且與既有的混凝土工作性測試法進行比較，試驗結果顯示所量測的降伏扭矩皆為正值且再現性較單一轉速為佳。F級飛灰與水淬高爐爐石粉取代水泥量影響粉體系自充填混凝土的質流行為，含增黏劑的自充填混凝土因總粉體量小且水膠比較大，其黏度與降伏扭矩大部份比粉體系自充填混凝土略小且數值範圍較為集中，故工作性的穩定性較佳。而改良式混凝土質流儀不僅建立普通混凝土的坍度與降伏扭矩、黏度之關係，並且可區分大部份自充填混凝土之分佈範圍，因此可作為檢測新拌混凝土工作性之品管儀器。

The modified concrete rheometer (MCR) apparatus developed in this study is based on existing concrete rheometers, the main differences being the gap size and measurement method, and thus the interpretation of the results. The gap between the inner cylinder wall and the tip of the vane was set to 6.4 times the diameter of the largest coarse aggregate in order to reduce interaction between the aggregate and the wall and the friction force from the wall. The MCR apparatus was used to measure yield torque directly at different low rotational speeds (above 0.003 rev/sec). A study of the yield torque and viscosity of forty fresh concrete mixtures was also made, with a particular focus on self-compacting concrete or self-consolidating concrete (SCC), and the results were compared with those obtained using other workability tests. The test results showed that the MCR can differentiate between conventional concrete (CC), powder-type SCC and SCC with viscosity-modifying agents (VMA). The rheological behavior of powder-type SCC was found to be influenced by the composition of Class F fly ash and ground granulated blast-furnace slag (GGBFS), and this type of concrete exhibited a wider range of viscosity and yield torque values. Despite the lower powder content and larger water to binder ratio (w/b), the viscosity of VMA-type SCC was shown to be slightly lower than that of powder-type SCC, and the values were clustered together within a certain range; thus, the workability of SCC containing VMA is more easily controlled. In addition, the MCR apparatus can also be applied to CC of differing viscosity and yield torque, thus making this apparatus suitable for determination of the workability of all kinds of fresh concrete.