Simple Test Method to Assess the Relative Effectiveness of Plasticising Chemical Admixtures

his paper proposes a simple test method capable of assessing the relative effectiveness of plasticising chemical admixtures. Using a hydrometer, the test measures the relative ability of different admixtures to disperse the individual particles of Portland cement (PC)/silica fume (SF) binder combinations. In a laboratory study carried out to examine the relative performance of three separate admixtures, the test clearly differentiated between PC/SF combinations containing no admixture, normal-range water-reducing admixtures, and high-range water-reducing admixtures. The two high-range water-reducing chemical admixtures considered showed identical dispersive effectiveness in the hydrometer test. This trend was mirrored in a concrete workability study, which indicated that equal dosages of each high-range water-reducing admixture were required to achieve 75-mm nominal slump for mixtures prepared using a range of SF dosages.