POLYCARBOXYLATE ETHER SUPERPLASTICIZER (PCE)

Superplasticizers (SPs) are recognized as important admixtures for their applications in modern concrete technology. Efforts have long been made by scientists and technologists to keep fresh concrete fluid to provide homogeneous transport of all particles in the building industry. Traditional techniques which use the superplasticizers such as sulfonated melamine formaldehyde condensate (SMF) and sulfonated naphthalene formaldehyde condensate play a positive role in maintaining high fluiding concrete. The superplasticizers interact with the surface of cement particles and involve dispersion and decreasing of the natural tendency to coagulate in concrete. Polycarboxylates (PC) are recently commonly used as superplasticizers to disperse cement particles in concrete and mortar. However, it has been known that the dispersing force of PC for cement and its time variation are significantly affected by even slight differences in concrete components or mixing conditions. Such instability of the dispersing force is explained by the incompatibility between cement and PC. Moreover, the side chain of the copolymer-type PC is composed of polyethylene oxide units. The methyl oxide bonds are easy to break under heat and oxygen. Furthermore, as a new generation water-reducing agent, the PC water-reducing agent would face the problem of short resources in the near future for nonregenerate ability of crylic acid derived from petroleum, so melamine superplasticizer has shown great advantage. Melamine superplasticizer is one of the most commonly employed due to its colorless, nontoxic, and good thermal stability. However, the application of traditional melamine water reducing agent is becoming less and less due to the complex production process, high cost, and relatively inferior slump loss. Along with the architecture industrial development and on the concrete performance requirements to improve, the development of high performance superplasticizer is imperative.

Water-reducing admixtures or plasticizers are all hydrophilic surfactants which, when dissolved in water, deflocculate and disperse particles of cement. By preventing the formation of conglomerates of cement particles in suspension, less water is required to produce a paste of a given consistency or concrete of particular workability. Maintaining low water contents whilst achieving an acceptable level of workability results in higher strengths for given cement content as well as lower permeability and reduced shrinkage. An important consequence of the reduction in the permeability is a major enhancement of its durability. The permeability of concrete to gases (oxygen, CO2), and water (carrying chlorides, sulfates, acids and carbonates) is of major importance with respect to its durability.

Retarding admixtures, which extend the hydration induction period and thereby lengthening the setting times, are often treated together with plasticizing admixtures as the main components used for retarding mixtures are also present in water-reducing admixtures. As a result, many retarders tend to reduce mixing water and many water reducers tend to retard the setting of concrete.

A much greater reduction in the volume of mixing water can be achieved using socalled superplasticizers or high-range water-reducing admixtures in case of concretes of normal workability. Normal water reducers are capable of reducing water requirement by about 10-15%. Further reductions can be obtained at higher dosages but this may result in undesirable effect on setting, air content, bleeding, segregation and hardening characteristics of concrete. Superplasticizers are capable of reducing water contents by about 30%.

Plasticizers (UK: plasticisers) or dispersants are additives that increase the plasticity or viscosity of a material. The dominant applications are for plastics, especially polyvinyl chloride (PVC). The properties of other materials are also improved when blended with plasticizers including concrete, clays, and related products. According to 2014 data, the total global market for plasticizers was 8.4 million metric tons.

Plasticizers or water reducers, and superplasticizer or high range water reducers, are chemical admixtures that can be added to concrete mixtures to improve workability. Unless the mix is “starved” of water, the strength of concrete is inversely proportional to the amount of water added or water-cement (w/c) ratio. In order to produce stronger concrete, less water is added (without “starving” the mix), which makes the concrete mixture less workable and difficult to mix, necessitating the use of plasticizers, water reducers, superplasticizers or dispersants.

Plasticizers are also often used when pozzolanic ash is added to concrete to improve strength. This method of mix proportioning is especially popular when producing high-strength concrete and fiber-reinforced concrete.

Adding 1-2% plasticizer per unit weight of cement is usually sufficient. Adding an excessive amount of plasticizer will result in excessive segregation of concrete and is not advisable. Depending on the particular chemical used, use of too much plasticizer may result in a retarding effect.

Plasticizers are commonly manufactured from pop lignosulfonates, a by-product from the paper industry. Superplasticizers have generally been manufactured from sulfonated naphthalene condensate or sulfonated melamine formaldehyde, although newer products based on polycarboxylic ethers are now available. Traditional lignosulfonate-based plasticisers, naphthalene and melamine sulfonate-based superplasticisers disperse the flocculated cement particles through a mechanism of electrostatic repulsion (see colloid). In normal plasticisers, the active substances are adsorbed on to the cement particles, giving them a negative charge, which leads to repulsion between particles. Lignin, naphthalene and melamine sulfonate superplasticisers are organic polymers. The long molecules wrap themselves around the cement particles, giving them a highly negative charge so that they repel each other.

Polycarboxylate ether superplasticizer (PCE) or just polycarboxylate (PC), work differently from sulfonate-based superplasticizers, giving cement dispersion by steric stabilisation, instead of electrostatic repulsion. This form of dispersion is more powerful in its effect and gives improved workability retention to the cementitious mix.