Interest in polymer-cement composites has increased considerably in recent years with systems finding widespread use in the concrete repair and main- tenance sector and speciality applications such as bridge deck overlays. In these cases, improved properties such as flexural strength, bond to existing material and durability are paramount. Some sectors which currently have a small market should grow and these include areas such as factory-produced pre-cast units, materials that incorporate general wastes or encapsulate hazardous wastes, and materials that, by saving resources, result in a more sustainable environment. High cost tends to preclude their use for more general, high volume applications and the inability to maintain their properties at high temperatures adds a further restriction. Since odour and toxicity of the polymer systems can be a problem, albeit short-term, it would seem prudent to anticipate more stringent restrictions through enhanced environmental legislation.
Relatively small incremental improvements in properties have been made over the years and there is much knowledge and experience available with regard to the various systems and their applications. However, even in established markets, further improvements in properties and reliability are desirable and, for new markets, the improvements would probably have to be substantial to justify cost and environmental considerations. Some questions that come to mind include the following:
· Can we find ways to improve the performance of polymer latexes in both liquid and powder forms (and especially the latter which is more desirable from environmental and quality control points of view)?
· How do the various monomer and polymer systems interact with the cement phases to influence rheology, hydration kinetics and microstructure develop- ment under various curing regimes?
· What determines, especially long-term, the bond between polymer modified cement, silanes and polymer coatings to existing (porous) concrete and aggregate substrates?
· How can we identify the true polymer-cement interface in these complex systems?
The answers to these, and other, questions will only be achieved by research, in particular research that utilises the latest techniques in polymer and cement chemistry and sophisticated instrumental methods of analysis. Procedures in the concrete laboratory should become more scientifically based. Even then this will probably only work if there is good collaboration between the researchers and those supplying the various components of the systems, applying the materials in the field and monitoring their life. A start has been made on standards but more needs to be done so that the properties of materials, as defined in the laboratory, are achieved by recognised application procedures in the field.
