Study on the Alteration of Hydrogeological and Mechanical Properties of the Cementitious Material (III); Summary Report

Takei, Akihiko*; Fujita, Hideki*; Harasawa, Shuichi*

We experimentally investigated the influence of several phenomena at the disposal environment, to evaluate the long-term alteration of cementitious material. The results are shown below. (1)Hardened cement paste specimens were altered and characterized after artificial seawater permeation. The calcium dissolution was accelerated, and secondary minerals containing magnesium were deposited. The permeability became one to three orders of magnitude smaller than data from specimens altered by deionized water permeation. It was estimated that secondary mineral formations reduced the permeability. These results meant that seawater and pure water differ remarkably from each other in influence to alteration of cementitious material. (2)Two type mixture proportions concrete, two type mixture proportions mortar and a cement paste under same W/C ratio 55% were characterized, to apply the accumulated data of paste to concrete or mortar. Compressive strength of paste was lower than that of concrete and mortar. It was contrary to the previous report. The behavior of Young's modulus and Poisson's ratio could be explained well using amount of aggregate. The data of permeability meant that boundary between aggregate and cement paste didn't become path of water flow, and that aggregate disturbed permeation. (3)Self-sealing property of cracked specimen of cementitious material were investigated by the water permeation test using sodium bicarbonate solution. The permeability decreased in two orders of magnitude, and possibility of sealing was suggested. By the morphology, the deposits in the cracks might be portlandite and C-S-H, and be not calcium carbonate. (4)Alteration of characteristics of cementitious material in sodium-nitrate and ammonia solution was evaluated by the water permeation test. Alteration degree of the nitrate and ammonia solution case showed similar trend to that of the sodium nitrate solution case. This result meant that ammonia solution would not ...