STUDIES ON MIXING BENTONITE TO PORTLAND CEMENT, PART I

Abstract

Recently there are many reports of studies on Japanese bentonite (e. g., Uchida, This Journal, 1933, 41, 181; 1934, 42. 65; 1935, 43, 21; Journ. Soc. Chem. Ind. Japan, 1935, 38, 1170, 1174; R. Isomatsu, This Journal, 1935, 43, 742; Journ. Soc. Chem. Ind., Japan, 1935, 38, 395; etc.). The present authors commenced the studies on effects of mixing bentonite to common Portland cement and reported some results in the present Japanese communication, which are briefly abstracted, as following:
(1) The two samples of bentonite from Niigata Prefecture were analysed by the methods of total analysis and soluble analysis, the latter being treated with 10% NaOH and then 5% HCl solutions on water bath. The results are shown in the following tables 1 and 2.
Table 1-Results of Total Analysis of Bentonite Samples
These bentonite samples contain not so much amounts of soluble components, silica, alumina, etc.
(2) By adding 5, 10, 15% of these bentonite samples to two samples of common Portland cement, the setting times of the cement were seen, the one retarded and the other accelerated.
(3) Two samples of clinker of common Portland cement and these two bentonite samples were mixed in proportions 90:10, 80:20 aud 60:40, two series and six samples of common and mixed Portland cements were prepared and tested on their chemical compositions, specific gravities, setting times, etc. The effect of addition of bentonite on setting time was seen to be retarding both initial and final setting times.
(4) These two series of cement samples were tested on their hardened strengths of cement-sand mortars by both of non-plastic and plastic mortars. Too much mixing of bentonite (e.g., 30-40%) does not give good results, showing the bentonite to be unsuitable as the common admixture.
(5) The plasticity of these mixed cements in pure cement paste was comparatively tested by falling cylinder of Vicat's tester degree of flow by a small flow table, Emley's plasticimeter defined in A. S. T. M. Designation: C6-31 for the hydrated lime for structural purposes, etc. Mixing about 20-40% of bentonite increased considerably the plasticity, which is seen to be suitable for the manufacture of plastic cement.
This study is now further being continued on every points, which will be reported in the future reports.