EXPERIMENTAL RESEARCH ON IMPROVEMENT OF ACID RESISTANCE IN FLYASHED NANO-SILICA CONCRETE

摘要

Nano silica is the extremely fine silica that can be used as cement admixture in construction and civil engineering industries. Nano silica can be used to improve slurry impermeability and the mechanical properties of the hardened material. With the adoption of very fine silica particles in cement matrix, porosity and permeability were significantly declined to about 33.3% and 99% respectively and compressive strength grew. For conducting this experiment, blended cement has been used. The blended cement used here consists of ordinary Portland cement and fly ash replaced to some percentages of cement. The percentage of replacement of fly ash by cement is about 20%, 40%, 60% and 80% respectively. Fly ash is a fine, glass-like powdered substance obtained from gases created by coal-fired electric power generation. Fly ash is an inexpensive substance which is used for replacing ordinary portland cement in concrete, which thereby improves the segregation, strength and ease of pumping of the concrete. Fly ash is also used as a constituent in brick, block, paving, and structural fills. Consisting mostly of silica, iron and alumina Fly ash is a pozzolana substance containing aluminous and siliceous material which form cement in the presence of water. When it is mixed with lime and water they form a compound similar to Portland cement. The spherical structure of the particles reduces the internal friction thereby increasing the consistency and mobility of the concrete, allowing longer pumping distances. Increased workability means less amount of water is required, thus resulting in less segregation of the mixture. Even though fly ash is less dense than Portland cement, the produced concrete will be denser and results in smooth surface with sharper details. Class F of Fly ash, in which particles are covered in a kind of melted glass, greatly reduces the possibility of expansion due to sulfate attack, as may occur in fertilized soils or near coastal area. We have chosen Class F fly ash for replacing cement.