Studies on Mixed Portland Cements, XIV

Abstract

The authors report, in continuing their previous studies I-XIII on mixed Portland cements, the further results of comparative studies on expansion or contraction and corrosion of hardened mortars of various cements by curing in various salt solutions. The main points of the present communication are abstracted from the original Japanese paper.
(1) Two sorts of Portland cement clinker and 6 sorts of various admixture (2 sorts of spent shale, one of basic blast furnace slag, 3 sorts of natural siliceous earth containing large amount of soluble silica) are mixed in proportions 60:40 or 50:50, and ground to various cement samples (2 sorts of common Portland cement and 12 sorts of mixed Portland cements).
(2) The specific gravity, fineness, setting time and chemical analysis of these cement samples are compared in the following table 1.
It is seen from these results, that the mixed Portland cements 90, 91, 92, 102, 103, 104, 105, etc., obtained from clinker and various natural siliceous earths containing large amount of soluble silica in proportion of 60:40 or 50:50, contain very large amount of total silica 45-50% or over 50% and are to be called as silica cement.
(3) Nextly, these cement samples are compared on their mortar strengths by the following two methods, (a) Compressive strength of 7.07cm cubical test piece and tensile strength of 8-type test piece were tested by dry or nonplastic mortar of small water cement ratio (w/c×100=26-32%), which is the method specified in the Japanese Engineering Standard for Portland cement (JES 28) and that for blast furnace slag cement (JES 29), and (b) Bending and compressive strengths by 4×4×16 (or 4×4×20) cm prismatic test piece from wet or plastic mortar of large water cement ratio (60-70%), which is the newly proposed method by Prof. M. Rôs in Switzerland and Dr. G. Haegermann in Germany, and the present author (S. Nagai) took the lead in using the modified method to study various mixed Portland cements.
(4) This prismatic test pieces of plastic mortar were applied to compare the expansion or contraction in water curing for various ages. The results of the measurement of expansion or contraction measured by planimeter are compared in the following table 2.
From these results, it is seen that mixed Portland cements are of quite equally superior quality in expansion or contraction to common Portland cement.
(5) Moreover, these prismatic test pieces are equally conveniently used for the comparison of mixed and common Portland cements to study the expansion or disintegration and contraction of hardened mortar cured vertically half dipped in variour salt splutions for long ages, by measuring with planimeter the distances between two cross marks on platinum, pins bedded on the test pieces. And then the bending and compressive strengths were tested and compared the decrease or increase to that cured in water for same ages. The results are shown in the following table 3, which are the suitable measure to discuss the resistibility of mixed Portland cement to various solutions of aggressive salts of the components of sea water.
From these results, some special points of mixed Portland cements are clearly seen, (1) Reaction of sulphate solution is considerably severe to common Portland cement, especially 10% Na₂SO₄ solution is more reactive that 10% MgSO₄ solution, (2) Mixed Portland cements are more resistive to sulphate and chloride solutions than common Portland cement, (3) Among chloride solutions, 10% MgCl₂ solution is more reactive than 10% NaCl solution, (4) Bending and compressive strengths of Mixed Portland cement mortars cured in 10% NaCl and 10% Na₂SO₄ solutions are larger that those cured in water, (5) Strengths of Mixed Portland cements cured in water for 56 weeks are nearly equal or a little stronger than those of common Portland cement cured in the same