新拌水泥漿體為控制混凝土流動性之最重要因素，水泥漿體所承受之剪應力及其剪切速率之關係會直接影響整體流動行為。為改善水泥漿體的流動性質，本文研究不同高速拌合與不同施加剪應力之影響。從流變儀試驗分析，可得知拌合速度越高與施加剪應力越大，水泥漿體黏滯性隨之變小。再利用高速拌合之純漿體進行抗壓試驗，可得水泥絮凝顆粒在高轉速拌合下越均勻分散，抗壓強度也隨之明顯提升，特別是早期強度。兩段式拌合水泥砂漿抗壓強度較同水灰比之水泥漿體抗壓強度低，猜測細骨材顆粒與漿體間過渡區性質較弱所造成。本研究為水泥漿體之流變特性提供試驗方法，實驗結果提供拌合速度對流動性與抗壓強度之影響的參考依據。

Fresh cement paste is the most essential factor controlling the flow property of concrete. The relation between shear stress and shear rate in cement paste can directly influence the overall flow behavior of concrete. To modify the flow property of cement paste, this study investigates the influences of different high mixing speeds and applied shear stresses on the flow property. From the experimental analysis of the dynamic shear rheometer, we know that the higher the mixing speed, the lower the viscosities of the cement paste. Similarly, the higher the applied shear stress, the lower the viscosities. This study further conduct the compression test of pure cement paste mixed at high speeds. As flocculated cement particles were separated evenly by high mixing speeds, the compressive strength of the cement paste is improved significantly as well, especially at the early stage. The compressive strength of cement mortar undergoing the two-stage mixing approach is lower than that of pure cement paste at the same water-cement ratio. This could be attributed to the weaker property of the transition zone between fine aggregate particles and paste. This study provides a method for testing the rheological properties of cement paste, and the references of how mixing speed affects the rheology and the compressive strength of cement paste.

[1] G.H. Tattersall and P.F.G. Banfill, “The Rheology of Fresh Concrete,” Pitman, London (1983).
[2] A.T. Hoissam, and E.K. Tahar, “The influence of Silica Fume on the Compressive Strength of Cement Paste and Mortar,” Cement and Concrete Research, Vol. 25, No. 7, pp.1591-1602 (1995).
[3] S. Kawashima, M. Chaouche, D.J. Corr, S.P. Shah, “Rate of thixotropic rebuilding of cement pastes modified with highly purified attapulgite clays,” Cement and Concrete Research, Vol. 53, pp.112–118 (2013).
[4] A. Chougnet, A. Audibert, M. Moan, “Linear and non-linear rheological behaviour of cement and silica suspensions. Effect of polymer addition,” Rheological Acta, Vol. 46, No. 6, pp.793–802 (2007).
[5] C.K. Park, M.H. Noh, T.H. Park, “Rheological Properties of Cementitious Materials Containing Mineral Admixtures,” Cement and Concrete Research, Vol. 35, pp.842-849 (2005).
[6] C. Jayasree, J.M. Krishnan, R. Gettu. “Influence of superplasticizer on the non-Newtonian characteristics of cement paste,” Materials and Structures Vol. 44, pp.929–942 (2011).
[7] T.D. Rupnow, V.R. Schaefer, K. Wang, B.L. Hermanson, “Improving Portland Cement Concrete Mix Consistency and Production Rate through Two-Stage Mixing,” National Concrete Pavement Technology Center, Final Report, September 2007.
[8] H. A. Barnes, “A Handbook of Elementary Rheology,” University of Wales, (2000).
[9] V.A. Hackley, C.F. Ferraris, “The Use of Nomenclature in Dispersion Science and Technology,” NIST Recommended Practice Guide, Special Publication 960-3, August 2001.
[10] R. Alfani, N. Grizzuti, G.L. Guerrini, G. Lezzi, “The use of the capillary rheometer for the rheological evaluation of extrudable cement-based materials,” Rheological Acta, Vol. 46, No. 6, pp.703–709 (2007).
[11] Brookfield DV-II+ Pro Programmable Viscometer Operating Instructions, Manual No. M/03-165-C0508. Retrieved June 15, 2015, from http://www.brookfieldengineering.com/
[12] C. Jayasree, R. Gettu “Experimental study of the flow behaviour of superplasticized cement paste,” Materials and Structures Vol. 41, pp:1581–1593 (2008).
[13] M. Cyra, C. Legrandb, M. Mouretb “Study of the shear thickening effect of superplasticizers on the rheological,”behaviour of cement pastes containing or not mineral additives,” Cement and Concrete Research, Vol. 30, pp.1477-1483 (2000).
[14] W.N. Findley, J.S. Lai, K. Onaran, “Creep and Relaxation of Nonlinear Viscoelastic Materials,” North Holland (1976).
[15] M.A. Schultz and L.J. Struble, “Use of Oscillatory Shear to Study Flow Behavior of Fresh Cement Paste,” Cement and Concrete Research, Vol. 23, pp.273-282 (1992).
[16] M.A. Schultz and L.J. Struble, “Using creep and recovery to study flow behaviour of fresh cement paste,” Cement and Concrete Research Vol. 23, pp.1369–1379 (1993).
[17] K.S. Rejeb, “Improving compressive strength of concrete by a two-step mixing method,” Cement and Concrete Research Vol. 26, No. 4, pp.585–592 (1996).
[18] A.K. Mukhopadhyay and S. Jang, “Using Cement Paste Rheology To Predict Concrete Mix Design Problems,” Final Report, July 2009.
[19] S. Mindess and J.F. Young, “Concrete,” Prentice-Hall, Englewood Cliffs, (1981).
[20] J.P. Ollivier, J.C. Maso, and B. Bourdette, “Interfacial Transition Zone in Concrete,” Journal of Advanced Cement Based Materials, pp.30-38 (1995).
[21] A. Elsharief, M.D. Cohen, J. Olek, “Influence of Aggregate Size, Water Cement Ratio and Age on the Microstructure of the Interfacial Transition Zone,” Cement and Concrete Research, Vol. 33, pp.1837-1849 (2003).
[22] S.M. Palmquist, E. Kintzel, K. Andrew, “Scanning Electron Microscopy to Examine Concrete with Carbon Nanofibers,” 5th Pan American Conference for NDT, October (2011).