subject: The Prevention Of Silica Fume On Alkali Aggregate Reaction Of Concrete [print this page] Alkali aggregate reaction refers to the chemical reaction between the alkaline oxide (Na2O or K2O) in concrete and the reactive silica in the aggregate. It generates complex alkali silica gel in the aggregate surface. After the absorbent, volume expansion (volume can be increased in more than three times) will emerges, resulting in concrete producing expansion cracks and damage. Alkali-aggregate reaction significantly changes the strength and natures of the concrete. The tensile strength is decreased by 3O% ~ 5O%. Due to the decreasing of tensile strength, the concrete cracks emerge. It may lead to loss of tensile strength for the concrete containing less gluten. It leads to steel shear, bond strength decreased, resulting in the destruction of structures.
The alkali-aggregate reaction occurs in the expansion of cracks in dams, highways, bridges and other concrete structures in the 30's western United States. At 1970s, there are constantly found in Europe and South Africa from the metal powder supplier. The report declares that structural damage is caused by alkali-aggregate reaction. Alkali-aggregate reaction as a global common problem was put out. Less than a year in the Sea of Japan coast, harbor construction, bridges, etc., after the completion of the concrete surface cracking, spalling, exposed reinforcement corrosion, mainly due to alkali-aggregate reaction. Less than two years in Beijing, China Sanyuan overpass pier, after the completion of the individual parts of the chevron crack, the results of alkali aggregate reaction. Repair structures damaged by alkali-aggregate reaction are more difficult, the effect is relatively poor, and therefore the best approach is to actively take preventive measures.
Significant role in prevention and control of alkali-aggregate reaction in concrete mixed with silica fume. Expansion of the concrete can be reduced by silica fume adding 5% to 1O% 1O% to 20%, control effect is different depending on the type of response of bone materials and silica fume. Experimental studies have shown that silica fume on alkali-aggregate reaction control mainly in the following areas: plus silica fume, silica fume particles are very fine, mixing concrete, the need to increase water consumption, changed as a result of concrete. The easing of the porosity in the partial pressure. Silica fume, large surface area and adsorption of alkali ions, reducing the concentration of hydroxide ions in concrete pore solution, to generate high-calcium, non-expansive gel. Hydroxide ion concentration drops below a certain limit does not occur when the alkali-aggregate reaction.
After adding silicon powder, because of its small particle size, so it firstly reacts with hydration hydroxide. The unhardened alkali silicate gel is filled in the pore structure. And the reaction needs to consume a certain amount of alkali bone material response, so it needs calcium hydroxides uniform distribution. It will control the harmful expansion. The prevention and controlling of silica fumes on alkali-aggregate reaction will effectively improve the durability of concrete and extend the life of the structure. They are also the main ways to reduce the production of concrete and the environmental load.Source:http://www.mhcmp.com
