STUDIES ON MIXED PORTLAND CEMENTS, XVIII

Abstract

The author reported, in continuing the previous studies (This Journal, 1933, 41, 623; 1934, 42, 273, 628, 688; 1935, 43, 215, 572; 1936, 44, 22, 617; 1937, 45, 8), the results of further studies on mixed Portland cements. The report of the present paper is the continued tests of high silica mixed Portland cements, which were already studied on their common physical properties and chemical compositions. The brief summary is abstracted from the original Japanese paper, as following:(1) The paste of neat cement was kneaded with the amount of water of normal consistency for determining the time of setting, and moulded to small cylindrical test pieces (Dia.: 5cm and Ht.: 10cm). These test pieces were cured in four serie-(a) in water for 7 days, (b) in water for 28 days, (c) in water for 7 days and then in warm (50°C) water for 7 days, and (d) in water 7 days and then in warm (50°C) water for 28 days. The compressive strengths of these four series of cured specimens, were tested and the hardened samples were quickly taken from the fresh part of the crushed pieces after strength tests and dried in desiccator. The chemical compositions were determined and the amounts of free lime or hydrated lime were specially determined and compared for these four series of curing (a), (b), (c) and (d), which are tabulated in the table 1.Table 1 Amounts of Free Lime in Hardened CementsFrom these results, it can be clearly observed that the amount of free calcium hydroxide increses in Portland cement and on the contrary decreases in mixed Portland cement. This fact shows that the high siliceous admixture used in mixed Portland cement combines with calcium hydroxide set free by the hydration, which owes to clinker part 60-75% of cement.(3) The strengths of dry (or non-plastic) and wet (or plastic) mortars of these cements were tested in the longer curing ages (3, 6 and 12 months) than the standard curing ages 3, 7 and 28 days, which strengths were already reported in the foregoing report (This Journal, 1937, 45, 8). The increase of strength is greater in high silica mixed Portland cements than in the common Portland cements, which owes to the same reason with the combination of siliceous admixture and calcium hydroxide produced in set cement.(4) The expansion or contraction of mortars were tested by the prismatic (4×4×16cm) test pieces moulded by wet mortars and cured in water for 3, 7, 28, 91 (3 months), 182 (9 months) and 364 (12 months) days. The results show the fact that the contraction or expansion was not greater in the case of high silica mixed Portland cement than in the case of common Portland cement, which is quite contrary in air curing.(5) The corrosion, expansion or contraction, and decrease or increase of strength by curing in water, 10% NaCI solution and 10% Na2SO4 solutions were fully studied by using the prismatic test pieces of wet mortar, which were vertically dipped in water or salt solutions for 4, 8, 12, 16, 20 and 24 weeks. The expansion crack and then disintegration were seen in the test pieces dipped in 10% Na2SO4 solution and especially considerable in common Portland cement and blast furnace slag cement. This result owes to the large amount of alumina in the cement, and the formation of xCaO⋅yAl2O3⋅zCaSO4⋅nH2O (so-called cement bacillus). This results were clearly shown by the photographs of the disintegrated test pieces, and coincide quite well with those recently reported by G. Haegermann (Zement, 1937, 26, 210).(6) The strengths were tested b these corroded test pieces after expansion test for 24 weeks curing above described. The decrease of strength was most remarkable in the specimens cured in 10% Na2SO4 solution, and then followed by those cured in water and 10% NaCl