Self-leveling compounds（cement based Self-leveling compounds or gypsum based Self-leveling compounds ） have the advantages of good fluidity, easy construction, fast leveling speed, time saving, thin leveling layer thickness, high ground flatness, and high compressive strength. They can effectively solve the problems of poor flatness and sanding caused by traditional floor materials plastering, greatly meet the high requirements of new buildings for the base, and are suitable for floor repair and decoration projects. At present, self-leveling materials have become ideal materials for floor paving in large supermarkets, shopping malls, parking lots, factory workshops, warehouses, etc., and are also a development direction for modern building floor construction, with great market potential. The key technology of cement-based self-leveling materials is to have excellent rheological properties under low water-cement ratio conditions; good cohesion under the premise of high fluidity, which can prevent water seepage and segregation. One of its main technical routes is to add high-efficiency water reducer to reduce the water-cement ratio, improve fluidity, and add suitable viscosity regulator to ensure the appropriate viscosity coefficient, so that the mixture has both self-compacting and self-leveling properties and the viscosity required to resist segregation.
High-efficiency water reducers, such as naphthalene-based high-efficiency water reducers (PNS) and melamine-based high-efficiency water reducers (PMS), are the most important admixtures used in the preparation of self-leveling materials. However, while they improve the fluidity of mortar, they also significantly increase its shrinkage. In addition, mortars simply mixed with these two water reducers require a composite retarding component to delay its fluidity loss, and the addition of the retarding component in turn delays the mortar setting time, which conflicts with the early strength requirements of self-leveling mortar. Polycarboxylic acid-based water reducers (FWD PC-01, FWD PC-02 & FWD PC-03) are the third generation of water reducers developed after naphthalene-based and melamine-based water reducers. Compared with the first two generations of water reducers, it has the advantages of low dosage, high performance, high water reduction rate, good fluidity retention ability, strong adaptability, green and pollution-free, and strong performance designability.
Effect of water reducer types and dosage on the fluidity and fluidity retention of self-leveling mortar
Three water reducers were used to prepare cement-based self-leveling mortars at different dosages, and their fluidity and fluidity retention were tested. Because the water-reducing effects of the three water reducers were significantly different, the water addition amount of the mortar was fixed at 24% (PC), 26% (PMS) and 28% (PNS) of the dry powder mass according to the type of water reducer when doing these three types of tests. The effects of the three different water reducers on the fluidity of the mortar increased with the increase of their dosage, and after reaching a certain dosage, the effect on the fluidity of the mortar gradually decreased after increasing the dosage. At the same time, under the same fluidity, the dosage of PC was the smallest, and the fluidity loss of the mortar was the smallest after 30 minutes; PMS was second; PNS had the largest dosage, and the fluidity loss of the mortar prepared by it was also the most serious. From the state of the self-leveling mortar after 30 minutes of placement, the bleeding phenomenon of PNS is the most serious, and the surface state after the flow stops is the worst, showing that it is not flat and uneven. When the self-leveling mortar with PC added reaches 0.04%, the fluidity is very good, there is no bleeding on the surface, and the surface state after leveling is good.
Compared with naphthalene-based high-efficiency water reducers and melamine-based high-efficiency water reducers, polycarboxylic acid-based water reducers can achieve a higher plasticizing effect at a smaller dosage, and can make the self-leveling mortar have better fluidity retention, while naphthalene-based high-efficiency water reducers and melamine-based high-efficiency water reducers need to be added at a higher dosage to achieve a better plasticizing effect, and must be compounded with retarders to obtain better fluidity retention.
