Redispersible polymer powder added to cement mortar has a certain water-reducing effect, and the water-reducing rate increases with the increase of the polymer-cement ratio. Moreover, since the polymer and cement form an interpenetrating network structure, the bonding between aggregates is strengthened and some pores in the mortar are blocked, so the various properties of the hardened polymer-modified mortar are better than those of ordinary mortar.
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Flexural strength and compressive strength
The flexural strength and compressive strength tests are carried out according to GB/T 17671-1999 "Test Method for Cement Mortar Strength" (ISO method), and the polymer-cement ratio is 0~0.1. See Table 1 for details of the compressive and flexural strength of polymer powder modified mortar.
Table 1
It can be seen from Table 1 that under the condition of fixed mortar fluidity, due to the water-reducing effect of the redispersible polymer powder, as the polymer-cement ratio increases, the water-cement ratio decreases, and the flexural strength and compressive strength both show an increasing trend.
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Bond strength
The test selected P•O32.5 cement and river sand, m (cement) ∶ m (sand) ∶ m (water) = 1∶2∶0.4. The effect of redispersible polymer powder on the bond strength of modified mortar is shown in Table 2.
Table 2
It can be seen from Table 2 that as long as a small amount of redispersible polymer powder is added to the mortar, the bond strength of the mortar can be significantly improved. When the poly-cement ratio is 0.01, the bond strength of 7 days is higher than that of the blank mortar at 28 days. With the increase of poly-cement ratio and the increase of age, the bond strength continues to increase. Moreover, when the VAE emulsion dosage is 0.073 poly-cement ratio (converted to solid content of 0.04), the bond strength is close to that of the mortar with a poly-cement ratio of 0.04; and because of the selection of a suitable protective colloid, although the effective content of VAE in the redispersible polymer powder is reduced, the bond strength is not reduced compared with the VAE emulsion.
