Study On The Absorption And Keeping Fluidity Of Poly-naphthalenesulfonates

Concrete admixture is an essential ingredient in modern concrete. In the early sixties of the 20th century, three types of high range water reducers began to be used in concrete, they are poly-naphthalenesulfonates, poly-melaminesulfonates and poly-multi-ring anime sulfonates. The use of superplasticizers in concrete has dramatically improved the performance of concrete, and the water reduction levels can achieve 10~20percent. Superplasticizers can be used at minimal dosages to place high strength concrete and high fluid concrete, they can achieve remarkable effects on concretes. They can either yield a gain in strength by allowing less water to be used ,while maintaining workability; or, they allow a reduction of the quantities of both water and cement used, to obtain a given strength and workability.Among the superplasticizers used in concrete, poly-naphthalenesulfonates are the most welcomed in the world. Because they can reduce high-range water, entrain less air and less retard the concrete. Compare to other superplasticizers, they are less costly. But ,there are some incompatibility problems when poly-naphthalenesulfonates are used in the concrete industry, especially the property of keeping fluidity of fresh concrete. At present, there are not any theoretic explaination about the property of poly-naphthalenesulfonates's keeping fluidity. Most of the researchers only mix poly-naphthalenesulfonates with other admixtures, and then test the fluidity of cement paste or the slump of concrete. It's hard for them to give any theoretic and systematic analyses or studies.When poly-naphthalenesulfonates make their entry in the concrete, they are absorbed by the cement particles. The result of absorption is the decrease of surface energy, and then brings about a series of surface actions: (1)reduction of the surface tension of water; (2)induced electrostatic repulsion between particles; (3)"lubricating" film between cement particles; (4) dispersion of cement grains, releasing water trapped within cement floes; ﹊nhibition of the surface hydration reaction of the cement particles, leaving more water to fluidify the mix; ?induced steric hinderance preventing particle to particle contact. There is a broad agreement that the superplasticizers molecules absorb strongly onto the surface of the cement grains. TheABSTRACTabsorption of charged polymers conveys a high surface charge to all cement particles; these charges contribute important repulsive forces between the particles, and most certainly play a role in deflocculating and dispersing cement particles in water. This action will last as long as sufficient superplasticizer molecules are available at the particle/solution interface, i.e, the quantity of available superplasticizer will progressively decrease as the polymers become entrapped in hydration product.In this paper, our main purpose is to study the absorption of poly-naphthalenesulfonates on the surface of cement grains. We try to make clear about the relationship between absorption and fluidity. At the same time, we also want to know the parameters of poly-naphthalenesulfonates that influence absorption and fluidity. Further more, we will study the influence of set retarder, hardening accelerating admixture, expanding admixture, fly ash etc on the absorption of poly-naphthalenesulfonates. Knowing the rules of absorption, then we will have enough knowledge to produce super fluid concrete admixtures.