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ADVANTAGES

The Polymer Concrete columns have a smooth finish, therefore not necessary to plaster.

The columns are hollow which makes transportation and positioning a pleasure to work with.

The columns may be used for aesthetics only or it can be filled with concrete should it be load bearing.

Specifications

Definition:
Polymer Concrete is made by bonding aggregates with a thermoset resin. In this application the most commonly used resins are unsaturated polyester resins and epoxies.

Principles:
Aggregate is coated with a catalyzed polyester resin and poured or vibrated into a mould and allowed to set. Since the resin is the most expensive ingredient the better the packing density of the aggregate; the less resin which will be required. Also the lower the surface area of the aggregate the better. This is achieved by using the largest aggregate possible governed by the fact that no particle diameter should exceed 1/3rd the thickness of the casting. The best blend of aggregator size appears to be five by Fulle's formula.

Mixers:
Batch mixers similar in principle to concrete mixers are used in smaller industries. Continuous mixers exist which feed at preset rates aggregates, resin and catalyst and deliver a ready-for-casting product. The best known of these is the Respect machine which is available in several sizes.

Vibration:
It is desirable that the vibrator has up and down as well as side to side motion. Drawing moderate vacuum on the mix also helps dispel the air. Vacuum should not exceed 70% otherwise the styrene vapour can cause cavities.

Additives:
The use of silanes improves the adhesion of the resin to the fillers and can improve the strength of the final product considerably. Air release agents can also be added to the resin. These both tend to be expensive options.

Resin:
The resin should be low viscosity and medium reactivity. This ensures good wet out of the aggregate and low exotherm. Because of the high levels of filler such reduce the exotherm, the accelerator and catalyst levels need to be somewhat higher than usual. The mixing procedure is to add the accelerator and catalyst to the resin followed by the powders and finishing with the coarsest fillers. This mixture is poured into the mould and vibrated and the G T should be sufficient to allow this to take place.

Property Polymer Traditional Concrete
Compressive Strength mPA 133 35
Tensile Strength mPA 10 2.5
Flexural Strength mPA 22 2.8
Bond Strength mPA 4.5 0.9
Young's Modulus (gPA) 35.6 10-40
Water Absorption 0.6 5.5

Source: Engineering Faculty, University of Kwa Zulu Natal. Howard College.

 

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