The damage to concrete due to alkali-aggregate reaction of chert has recently been discovered in several regions in Japan. Cherts are included in river and pit gravels and they are used in large quantities as concrete aggregate. In this paper, alkali reactivity of chert gravels was investigated with polarizing microscope, scanning electron microscope, X-ray diffractometer, and chemical (ASTM C289) and mortar bar (ASTM C227) test methods.
Results obtained are summerized as folows:
(1) The chert particles used were composed largely of cryptocrystalline to microcrystalline quartz, with some chalcedony. Especially, the amount of the chalcedony showed a considerable variation with the types of chert particles. Quartzite particles containing strained quartz with structural defect were also found in small quantities.(2) The texture of chalcedony under polarizing microscope was radiating fibers. They were embedded in the matrix of apparently non-fibrous silica (opal). Under scanning electron microscope, chalcedony showed still a fibrous texture at a low magnification, but appeared at a high magnification as an assemblage of rod-like particles with uneven surfaces and of different sizes. The rod-like particles were seen clearly after etching with hydrofluoric acid, which dissolved preferentially, but partly, the filling of opal.(3) The X-ray diffraction patterns of chalcedony were different in features from those of quartz: the 2.46 Å(110) peak of chalcedony was less intense and the 1.382 Å(212), 1.375 Å(203) and 1.372 Å(301) peaks were much less resolved than quartz. Such features of X-ray diffraction patterns could be utilized to establish the presence of chalcedony in some cherts.(4) Expansion of mortar bars was negligible when the alkali content (Na₂0 equivalent) was kept at 0.8%. Increasing the alkali content to 1.5 %, however, expansion occurred and its magnitude was in the order of white-> green-> dark gray-> reddish brown-colored cherts.(5) ASTM C289 chemical test revealed that cherts were deleterious or potentially deleterious aggregates, though mortar bars did not expand when normal Portland cement of about 0.8 % Na₂0 equivalent was used. The expansion of mortar bar made with chert in pit qravels changed remarkably upon the change of alkali content and curing temperature.(6) The crystals showing appearance of staurolite twin were observed around the reaction products in chert aggregate in damaged concrete bridge of eighteen years old.

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X-ray diffracation method was used to determine the mineral composition of landslide clays and tuffaceous rocks collected in the Kunimi landslide area. Results showed that the landslide clays contained smectite, quartz, and feldspars, with analcime and illite in addition in some samples. Mineral composition of the tuffaceous rocks was very similar to that of the landslide clays, except that analcime was found often in the former.
The smectite content in the landslide clays and in the bottom face of the tuffaceous rocks (the upper face of hard mudstone rocks) increased along a traverse from the sliding head toward the tail, i. e, from high altitudes downwards indicating that the smectite in the landslide clays in the study area was formed from zeolites in the tuffaceous rocks, under the influence of groundwater flowing down along the sliding plane, which conformed with the upper surface of the relatively fresh bedrocks.

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In Na-and Na/Al-montmorillonite pastes, two types of spaces accommodating water exist; interlayer space and inter-packet voids. The amount of water in the former was determined from the basal spacings (001) obtained by X-ray diffractometry. The amount of water in the latter was determined by subtracting the amount of interlayer water from the total amount of water in the pastes. In the montmorillonite pastes prepared, the proportion of interlayer water was about 90% at the water content from 0.61 to 1.2ml/g, and it decreased with increasing water content and reached 60% at the water content of 5.5 ml/g. The addition of Al³⁺resulted in the decrease in the proportion of interlayer water, which was influenced significantly by the amount of the Al³⁺ added. In a paste having water content of 5.5ml/g, for example, the proportions were 40, 30, and 7%, when the Al³⁺ added was 10, 20, and 30% of CEC, respectively. Furthermore, when the amount of water was fixed (2.2ml/g), the amount of interlayer water abruptly decreased at the Al³⁺ concentration of about 20% of CEC. From the comparison of the basal spacing influenced by the Al3+ concentration with that by the excess Na⁺, the effect of Al³⁺ itself was considered to appear at its concentration of about 20% of CEC, thereby the decrease in the amount of interlayer water decreased abruptly and greatly.

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