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Heavy damage due to alkali-aggregate reaction has been observed in concrete structure in and along the sea. An accelerated test is performed on mortar to evaluate effectiveness of fly ash for controlling alkali-aggregate reaction in the marine environment. Mortar bars using Pyrex as aggregate and cements with 0.6 and 1.1% of equivalent sodium oxide are made. The alkali content in the mixture is adjusted by adding NaOH or NaCl. Specimens are stored in distilled water, NaCl solution, and under more than 95% of relative humidity. The controlling effect of fly ash and the effect of internal and intruded chloride ion in mortar on alkali-aggregate reaction is studied by measuring the expansion of mortar. Expansion of mortar depends on the type of cement and chemical reagents used for alkali adjustment, the amount of fly ash used and the exposure condition. Even with the same equivalent sodium oxide in the mixture, mortar using NaCl for alkali adjustment shows higher expansion than mortar using NaOH. The highest expansion is revealed for mortar cured in NaCl solution. The controlling effect of fly ash also depends on the type of cement and the exposure condition.

Compressive strength, flexural strength, and fracture energy of ordinary portland cement concrete with and without fly ash have been determined over a 6-month period. Specimens were cured in water at various constant temperatures ranging from 7 to 80 C. Flexural strength and fracture energy were measured on notched specimens subjected to a constant rate of deformation. The influence of temperature on strength is complex, and does not always follow the trend of a higher initial rate and lower ultimate value as the curing temperature is raised. Compared with strength, fracture energy is less sensitive to curing temperature. For all concretes, general expressions are presented for relating flexural and compressive strengths, and facture energy and flexural strength. These expressions are independent of age and temperature, and suggest that approximate estimates of strength and fracture energy can be made only from a knowledge of strength of ordinary portland cement concrete cured at 20 C.

The results of a corrosion investigation of cement mortars immersed in different sulfate solutions of the same concentration are presented. Factors such as the type of cement, aggressive solution, and, in particular, size of specimens are studied. To study the degree of corrosion, several testing methods were used, including expansion, weight channels, compressive strength, dynamic modulus of elasticity, and the amount of bound compounds in the mortars. Previous results regarding the differences in the sulfate resistance of cements with different C 3A contents and the effect of blast furnace slag in blended cement were confirmed on the mortars where no silica fume was added. With silica fume addition, the corrosion resistance of the mortars was influenced markedly, depending both on the type of cement and the particular sulfate anion. The relative aggressiveness of the solutions for both plain and silica fume-modified, from weakest to strongest, was as follows: sodium sulfate < magnesium sulfate << ammonium sulfate. The effectiveness of silica fume in improving the sulfate resistance of cement mortars proved beneficial when combined with ordinary portland cement prior to portland blast furnace slag cement or sulfate-resistant portland cement, mainly in sodium sulfate solution.

A carbon fiber cement composite (CFCC) was developed to overlay old concrete. Three aspects of the CFCC mechanics, with varying silica fume (SF) dosages, were investigated through an experimental program: the amount of fracture energy of CFCC, the adhesion between the fiber and matrix, and the adhesion between CFCC and the old concrete. Five different matrixes were considered in which the percentage of SF is 0-5-10-15-20 of the cement content by weight. Some new types of tests for the aspects investigated are discussed. The results of this work establish that the incorporation of SF seems to be beneficial for the toughness of the composite, while not beneficial for the adhesion between composite and old concrete.

The fatigue life of reinforced concrete beams decreases generally when tested under the environment of water. Beams in which fatigue breaks main reinforcing bars in the room condition sometimes fail in shear compression of concrete under water. It is suggested that the development and propagation of cracks in shear span are accelerated by the existence of water. It can be predicted that silica fume concretes may be effective in increasing the fatigue life under the environment of water or seawater because of high density and low permeability. The effect of silica fume on the fatigue of reinforced concrete beams under the environment of tap water or chloride solution was investigated. Two types of beam were used. Type 1 is the sound beam without corroded steel bar, and Type 2 is the deteriorated beam with corroded steel bar. Through the incorporation of silica fume, the fatigue life of beams increased for both types. The effect of silica fume was also observed in the crack pattern in the shear span of concrete. It was almost the same as that tested in the room condition, while the diagonal cracks developed quickly, and its inclination was very steep in the beam without silica fume. When the deterioration due to chloride corrosion was relatively small, the influence of corroded steel bar on the fatigue life of reinforced concrete beam was not observed.