POLYMER-CEMENT CONCRETE

Polymer-Cement Concrete

Polymer-cement concrete (PCC), also called polymer-Portland-cement concrete (PPCC) and latex-modified concrete (LMC), is made by Portland cement and aggregate just like ordinary concrete but organic polymers dispersed in water (latex) are added at the time of mixing. The organic polymer is a substance composed of thousands of simple molecules, called monomers, combined into large molecules in a process called polymerization. The polymer is called a homopolymer if it is made by the polymerization of one monomer, and a copolymer if two or more monomers are polymerized. By adding polymer dispersions to the concrete mixtures, bond strength to concrete substrates, flexibility and impact resistance, resistance to penetration by water and by dissolved salts, and resistance to freezing and thawing are improved. Polymers made by emulsion polymerization are the most widely used. Styrene butadiene and acrylic latexes are the most effective and widely used materials for concrete restoration, but vinyl acetate is also used. Generally, 10 to 20% of polymer solids are usually added with respect to the mass of cement and typical w/c for workable materials used for repair range from 0.30 to 0.40 for mixes with latexes, and 0.25 to 0.35 for mixtures with epoxies.

Following points are considered for use of polymer cement concretes:

1. PCC overlays have excellent long-term performance.

2. Mixing of PCC must be done in a concrete mobile mixer.

3. Handling, placing, and finishing of PCC is to be completed in less than 30 min.

4. PCC requires one to two days of moist curing followed by air drying.

5. It has good workability and ease of application.

6. Styrene-butadine PCC has excellent durability for exterior exposures or environments where moisture is present.

7. Surface discoloration occurs when the concrete is exposed to UV light, except for acrylic polymers.

8. It is used as overlay of bridge decks, floors, and patching of any concrete surfaces ranging in thickness from 4 to 100 mm for concretes.

9. Acrylic latexes are used for floor repair and patching and in cases where color retention is important.

10. These overlays produce high-strength wearing surface that is very durable against weathering.

11. PCC is also used as an effective patching material.

12. PCC must be placed and cured at 7 to 30 °C.

13. Mobile, continuous mixers, fitted with an additional storage tank for the latex must be used for large applications of polymer modified concrete.

14. The mixing time is limited to 3 min for small batches or for mortar mixers.

15. PMC has a tendency for plastic shrinkage cracking during placement and special precautions are necessary when the evaporation rate exceeds 0.5 kg/m2/h.

16. The modulus of elasticity is generally lower compared to conventional concrete and hence its use in axially loaded members must be evaluated accordingly.

17. Polyvinyl acetate mixtures must not be exposed to moisture.

18. Epoxy emulsions are more expensive.

The rate of 15% latex solids to Portland cement by mass has been most commonly used in bridge and parking deck overlays. The water in the latex constitutes part of the water required to hydrate the cement, and the latex provides supplementary binding properties to produce a concrete with a low w/c, good durability, good bonding characteristics, and a high degree of resistance to penetration by chloride ions. Mixing, placing, and finishing should be completed within 30 min. Mixing the LMC must be done in a mobile mixer. Concrete mixed in a concrete truck or drum-type mixer must be limited to 3 min of mixing after the latex has been added. Longer periods of mixing entrap air and subsequently increase the total air content. The result can be significant reductions in compressive strength and abrasion resistance. LMC overlays are generally used as wearing and protective barriers on bridge and parking garage decks and in damp-proofing or decorative systems on plaza decks and parking garages. Hot weather and wind cause rapid drying which makes finishing difficult increasing the chances of shrinkage cracking.