Experiment on long term seepage corrosion stability of plastic concrete

Abstract: In order to evaluate long-term seepage stability and service life of plastic concrete that are made of bentonite, clay, cement, soil aggregate, water, superplasticizer, etc., we studied incomplete or contain holes of plastic concrete's long-term seepage stability and service life. Specimens of plastic concrete were molded after many times of tests, and their compressive strength of 28 days was 1.25 MPa, and meet requirements impermeability grade was S1 which was test code for hydraulic concrete because water pressure measured was 0.2 MPa by step by step method. The preparation of plastic concrete permeability test required to a round-shaped specimen (top diameter is 175 mm, basal diameter is 185 mm, height is 150 mm). Type I was complete specimens of concrete impermeability; and Type II specimens were high in the direction parallel to the reserved five through holes with a diameter of 3.5 mm, plum-shaped layout was on the plane. It was found after long-term corrosion test plastic concrete can produce shear cracks and tensile cracks and even had lager plastic deformation after long-term seepage dissolution by pure water, which led to damage of the plastic concrete. This resulted in an increase of maximum displacement values of top surface of the specimen by 38.5 mm on average. The permeability coefficient was changed in the early (30 to 40 days) penetration test, but they were in 10-7 cm/s orders of magnitude. The permeability coefficient was increased to 3.0×10-7 cm/s and then tended to be stable during 150-180 days. Ca2+ were dissolved from the concrete and leached out after long-term seepage dissolution, the amount of Ca2+ removed from concrete specimens were linearly decreasing as dissolution time (<150 days). The concentration of Ca2+ in the specimen water seepage fell below 110 mg/L after 180 days of dissolution. Through dissolution experiment, calculating plastic concrete's coefficient of permeability and content of CaO were done based on the formula of diaphragm wall's durable years, the calculated service life was 37.1-60.7 years. Drench experiment showed that flows may create preferential erosion in holes in concrete, and Ca(OH)2 in concrete were dissolved and carried away by the flow which led to decrease in weight of plastic concrete. The flow of constant pressure through holes of concrete was relatively weak, and few Ca in concrete were dissolved and carried away. Even after drench 197 d, there was less quality loss compare with the original, the relative loss was not more than 1%. However the concrete strength loss was larger (up to 25.4%). The white precipitates in the hole were CaCO3, and some Na+, trace clay and bentonite particles after laboratory analysis. The studies showed that the features of plastic concrete made of clay and bentonite had a low-intensity, high impermeability and long service life which met the requirement of impervious wall of earth-rock fill dam. Thus, it can be used for embankment dam for seepage prevention.