Effect of RDP on the performance of modified ultrafine powder mortar

RDP, as the main admixture of dry-mix mortar, is a powdered thermoplastic resin prepared by spray drying and subsequent treatment of high molecular polymer emulsion, usually in the form of white powder. RDP can increase cohesion and improve construction performance in dry-mix mortar, and is widely used. The following introduces the effect of RDP on the construction performance and mechanical properties of dry-mix mortar.

?

China is a big consumer of steel. With the rapid growth of infrastructure, the output of steel has increased rapidly in recent years. A large amount of steel slag powder is generated in the process of steel production, which not only pollutes the environment but also occupies land resources. The treatment of steel slag is urgent. Adding steel slag powder to limestone powder for grinding can improve the performance of limestone and partially replace cement, which can save costs and protect the environment.

The 3d and 28d flexural strength of mortar increases with the increase of steel slag content, and the flexural strength reaches the maximum when 25% steel slag is added; the 3d and 28d compressive strength increases first and then decreases with the increase of steel slag content. When 15% steel slag is added, the 3d compressive strength reaches the maximum, with a maximum value of 21.9MPa and an activity index of 74.5%. When 20% steel slag is added, the maximum 28d compressive strength is 38.2MPa and the activity index is 70.7%. Considering the mechanical properties and cost accounting at the same time, 15% steel slag content is selected.

Effect of RDP on mortar properties：?

The content of RDP is gradually increased from 1% to 4%, and each group increases by 1% (as a percentage of cementitious materials). RDP?has a great influence on the construction performance and mechanical properties of mortar.

The consistency of freshly mixed mortar tends to increase first and then decrease with the increase of RDP dosage. This is because RDP gathers on the surface of hydrated or unhydrated products, reducing the friction between particles in the mortar. In addition, the surface of RDP contains active substances, which can introduce a large number of tiny bubbles into the mortar, play the role of ball lubrication, and increase the fluidity of the mortar. When the water volume is fixed, increasing the amount of RDP will gradually increase the cohesion of the mortar, make the mortar more viscous, and reduce the workability of the mortar; the water retention rate tends to increase first and then decrease with the increase of RDP dosage. RDP has water retention. After the water retention rate reaches a certain level, it no longer increases with the increase of dosage; with the increase of RDP dosage, the 7d and 28d cubic compressive strength of the mortar tends to increase first and then decrease. RDP meets water in the freshly mixed mortar to form a polymer emulsion, which is evenly dispersed in the mortar. The emulsion gradually loses water during the hydration process of the mortar to form a flocculent film, which fills the gaps and defects inside the mortar and improves the density of the mortar. At the same time, the flocculent film has the effect of "microfiber", which is beneficial to the strength of the mortar. When the RDP dosage is 2%, the 7d and 28d cubic compressive strength of the mortar reaches the maximum. However, as the amount of RDP continues to increase, the air entraining effect of RDP and the high viscosity after emulsification increase the bubble content in the mortar, and the large bubbles are not easy to break to form harmful holes, the effective compressive area of the mortar decreases, and the compressive strength of the mortar decreases; as the amount of RDP increases, the 14d tensile bond strength increases, and RDP forms an emulsion in the fresh mortar. During the cement hydration process, the polymer emulsion particles are deposited on the hydration products and unhydrated cement particles. With the hydration of cement and the evaporation of water, they gradually lose water and condense to form a film. The film has a high deformation capacity, so that the hydration products and aggregates are bonded to each other to form an interpenetrating grid, filling the pores of the hydration products, reducing the microcracks at the interface between the cementitious material and the aggregate, thereby improving the bonding strength of the mortar.

Conclusion：

With the increase of slag content, the flexural strength of mortar tends to increase; the compressive strength first increases and then decreases. When the slag content is 15%, the 3d compressive strength reaches a maximum value of 21.9MPa, and when the slag content is 20%, the 28d compressive strength reaches a maximum value of 38.2MPa; considering the mechanical properties and cost consumption, the 15% slag content is selected. With the increase of RDP content, the consistency first increases and then decreases, and the maximum value reaches 98mm; the 7d and 28d compressive strengths show a trend of first increasing and then decreasing. When the RDP content is 2%, the 3d compressive strength reaches a maximum value of 7.8MPa, and the 28d compressive strength reaches a maximum value of 10.5MPa. Within a certain content range, RDP is beneficial to the compressive strength of mortar cubes; with the increase of RDP content, the 14d tensile bond strength continues to increase, and RDP is beneficial to the tensile bond strength.