Effect of fly ash on the performance of concrete


Release time:

2020-08-03

Author:

Source:

Effect of fly ash on the performance of concrete

(1) Working performance

Fly ash can improve the particle gradation of cementitious material system, reduce the porosity, release the "filling water" between cement particles, and improve the workability of concrete.
Fly ash contains a large number of spherical glass, play a "ball, bearing" lubrication effect, reduce the friction between particles, improve the workability of concrete.
The activity of fly ash is much lower than that of cement, which can reduce the slump loss of concrete. The adsorption of high-quality fly ash on admixtures is lower than that of cement, and the use of high-quality fly ash is equivalent to increasing the amount of admixtures, and the initial slump and retention capacity of concrete are improved.
The density of fly ash is less than that of cement. After replacing cement in equal amount, the slurry volume in concrete increases, which improves the cohesion of concrete, improves the anti-segregation ability, reduces water bleeding, improves the working performance of concrete, makes concrete have better fluidity, compactness and homogeneity, and facilitates the construction of concrete.


(2) Mechanical properties

Fly ash itself can not carry out hydration reaction, can only be secondary hydration with cement hydration products, therefore, with the same amount of fly ash instead of cement, the early strength will be reduced, with the secondary hydration, the middle and late will reach or even exceed the concrete without fly ash.
With the increase of the amount of fly ash instead of cement, the early strength decreases gradually, but the later strength of concrete mixed with fly ash increases rapidly, and within a certain range (<50%) increases with the increase of fly ash content.

(3) Durability

Replacing part of cement with fly ash, reducing the water-cement ratio or increasing the amount of fly ash under the premise of keeping the water-cement ratio unchanged can improve the impermeability of concrete.
The early carbonation depth of fly ash concrete increases rapidly, and the later growth of carbonation depth is relatively slow. With the increase of fly ash content, the carbonation rate increases and the alkalinity of concrete decreases, which will induce corrosion of steel bars. Therefore, the amount of fly ash should be controlled and a reasonable concrete mix ratio should be designed.


Key words: