AAR is the cement of alkaline oxide (Na2O or K2O) and the aggregate of silica activity occurred in a chemical reaction, in the aggregate to generate the complex surface of the base - silica gel, the water will Significant expansion (volume can be increased more than 3 times), which have led to the expansion of the concrete cracks and damage. Alkali aggregate reaction, and so on the strength of concrete to make a significant change in the nature, reduce the tensile strength of about 3O% ~ 5O%. Due to lower the tensile strength of concrete cracks, on the bars with low concrete structure could lead to the loss of tensile capacity of steel caused by shear, the lower the bond strength, leading to the destruction of structures. AAR is the beginning of the age of 3O in the western region of the United States of dams, roads, bridges, and other concrete structures abnormal swelling, and cracks found. 7O into the 1990s, from Europe, South Africa and other places from alkali aggregate reaction caused by structural damage reports, alkali aggregate reaction, as a general world-wide problem was put forward. In the Sea of Japan coast, many of the Harbor Building, bridges and so on, was less than one year's time, the surface of concrete cracking, spalling and corrosion of steel bars exposed, mainly due to alkali aggregate reaction. Beijing's three overpass bridge pier, less than two years after the completion of individual places, "chevron" crack is the result of alkali aggregate reaction. By alkali aggregate reaction to the destruction of the structure of the patch-up difficult and the results would be relatively poor, so the best approach is to actively take preventive measures.

       In the concrete mixing in micro-silica fume, alkali aggregate reaction to the apparent role of prevention and control. Micro-adding amount of silicon powder 5% ~ 1O% when the expansion of the concrete can reduce the amount of 1O% ~ 2O%, under the control of its response materials and micro-bone and different types of silica fume. Experimental studies have shown that micro-silica fume on the AAR main role of the control in the following areas:

(1) A micro-silica fume, due to very small micro-particles of silica fume, mixing concrete when water consumption increases, the concrete results of the change in the void to ease the pressure on the local.

(2) micro-surface area silica fume, can be alkali ion adsorption, concrete reduces the pore solution in the concentration of hydrogen ions, generates high-calcium non-expansion of the gel. The hydrogen ion concentration dropped below a certain threshold when no alkali aggregate reaction.

(3) add micro-silica fume, because of its small size, its first response hydroxide and hydration, did not generate the base sclerosis - silica gel to fill the pore structure and reaction to consume a certain amount The alkali aggregate reaction needed calcium hydroxide, calcium hydroxide so that the uniform distribution, so as to control the harmful expansion.

       Micro-alkali aggregate reaction of silica fume the prevention and control, effectively improve the durability of concrete, to extend the service life of structures. At the same time reducing the production of concrete, reduce the burden on the environment to achieve an important way.