The Effect Of The Time Of Mixing And The Percentage Of Water On The Tensile And Compressive Strength Of Plain Concrete

Author : Kajima Kensetsu Kabushiki Kaisha
Publisher :
ISBN 13 :
Total Pages : 19 pages
Book Rating : 4.:/5 (39 download)

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Download or read book Effect of Mixing Method on Mechanical Properties and Pore Structure of Ultra High-strength Concrete written by Kajima Kensetsu Kabushiki Kaisha and published by . This book was released on 1992 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt: High-strength and ultra-high-strength cast-in-place concrete tend to contain excessive unit volumes of cement when compared with normal concrete, and because the improvement of workability relies largely on the efficiency of the air-entraining and high-range water-reducing admixture, the properties of workability (or consistency) are different from normal concrete. With high-strength concrete it was found that the method of mixing concrete influenced flowability, strength properties, and pore structure as follows. 1) Slump was affected mostly by the mixing sequences, viz. whether the cement and fine aggregate are mixed first (called the M method), or all materials are mixed simultaneously (the S method), or the cement and water are mixed first (the P method). 2) The rate of slump loss was the least with the P method, followed by the S method and the M method. 3) Compressive strength also varied with the mixing method. However, effects due to mixing time and mixing speed were not clearly established. 4) The relationship between the compressive strength (sigma)c (MPa) of ultra-high-strength concrete and effective pore volume (ETPV, mm3/g) can be expressed by an equation as follows. log10 (sigma)c = -0.77 x 10-2 ETPV + 2.25 5) As the effective pore volume is not influenced by the volume of aggregate in concrete, it can be considered as a useful index for predicting the strength of ultra-high-strength concrete. 6) The compressive strength, when viewed from pore radius, was the highest when mixing with the M method, followed by the S method, and was the lowest by the P method. 7) The bound water of hardened paste was 9.3 to 10.2% at the curing age of 7 days, about 11% at 28 days, and there was no increase thereafter. It can be said that this is because the progress of hydration was high at an early age. 8) The effective cementitious (cement + silica fume)-to-water ratio that was obtained after the hydration of the cement + condensed silica fume mixture was 2.9 to 3.3 at a compressive strength of about 100MPa. 9) The compressive strength of ultra-high-strength concrete may be predicted from the effective cementitious (cement + silica fume) to-water ratio obtained after hydration.