(1) The fly ash of good quality has a water-reducing effect, so it can reduce the water demand of mortar; the morphological effect and micro-aggregate effect of mortar can improve the density, fluidity and plasticity of mortar and reduce bleeding and segregation, and can also extend the setting time of mortar. After adding fly ash, mortar becomes viscous and soft, not easy for bleeding and good for plastering, improving the operational performance of mortar.
In general, with the increase in the addition amount of fly ash (PFA), the decrease in the strength of mortar will be greater. Especially the decrease in the early strength is more significant but the long-term strength will be improved. The PFA replacing cement quantity is related to the coefficient of excess. By adjusting PFA coefficient of excess, the mortar strength can be made equivalent to reference mortar.
- Elastic Modulus
The elastic modulus of fly ash mortar is proportional to the compressive strength. Compared with ordinary mortar, the elastic modulus of fly ash mortar after 28d is not lower and even higher than that of ordinary mortar of the same compressive strength. The elastic modulus of fly ash mortar is the same as the compressive strength and will increase with the increase of age; if the water-reducing effect of fly ash has reduced the amount of water used in fresh mortar, then this growth rate is more obvious.
There is not much difference between the creep property of fly ash mortar and of ordinary mortar. Due to the better workability of fly ash mortar, the mortar is denser and may have lower creep to some extent. Comparatively speaking, since the early strength of fly ash mortar is lower, the degree to which various factors affect creep at the initial stage of loading may be higher than ordinary mortar.
Since fly ash has improved the workability of ordinary mortar, its shrinkage will be lower than that of ordinary mortar; since the unburned carbon of fly ash can absorb moisture, under the condition of the same workability, the higher the loss on ignition of fly ash is, the greater the shrinkage of fly ash mortar will be.
It is generally believed that since fly ash has improved the pore structure of mortar, its permeability resistance is better than that of ordinary mortar. With the increase in the amount of fly ash, the permeability resistance of fly ash mortar will be improved.
The existing research results have shown that fly ash mortar has better resistance to sulfate attack than ordinary mortar. It is generally believed that the excellent resistance to sulfate attack of fly ash mortar is the expression of both physical properties and chemical properties. First, the pozzolanic chemical reaction of fly ash has reduced the amount of Ca (OH) 2 and free calcium oxide in the mortar and concrete; second, fly ash usually reduces the water requirement of mortar and improves the workability of mortar. Meanwhile, the secondary hydration product fills the coarse pores and improves its permeability resistance.