Conference reports 289

ated carbonation from the use of inappropriate coatings were discussed.

Methods for assessing in-situ strength and for analysing serviceability were presented. Bonded plate techniques for structural strengthening proved to have many cost and aesthetic advan- tages.

There were a number of well documented case studies. These included the telecommunication towers and housing blocks in the Netherlands, an experimental building in Motobu-Cho of Japan, the Hong Kong housing stock, a marine jetty in Malaysia and a variety of structures such as bridges, building facades, cooling towers and grandstand in Australia.

It was predicted that the business of concrete repair will continue to flourish, due to the increas- ing age of existing stock of structures worldwide and to inadequacy in the durability design of many new structures.

D.W.S. Ho E. C. Gray

7th INTERNATIONAL CONGRESS ON POLYMERS IN CONCRETE. 22-25 SEPTEMBER 1992, MOSCOW, RUSSIA

The congress was organized at Otradnoye-2, 143412 Moscow province, Krasnogorsk district. It is a place on the outskirts of Moscow city. The congress was attended by about 100 delegates, out of which 25 were foreign delegates. The con- gress was sponsored by Breton S.P.A., Trevisto, Italy. The congress was opened by Professor V. V. Paturoev (NI]ZhB, Russia), followed by an address by the director of NIIZhB, Professor R. Serykh, Dr A Ragolski, Director, Betecom Ltd, Russia, and Mr James T. Dikeou, President ACI.

In the plenary session review papers were pre- sented on the following topics: Applications of polymers in concrete in Russia; Precast polymer concrete in the construction industry in Australia; Polymer concrete floor and bridge overlays in USA; Polymer mortars for underwater concreting in Japan, US. Other specifications and standards for polymer concretes and concrete sealers for hydraulic applications were also presented. In polymer concrete using polyester resins, normal shrinkage is 3-5 mm/m (0.3-0-5%). It was shown by Mr Mathews, of Polycrete Australia, that by combining isophthalic polyester resins with

special thermoplastic additives, it is possible to eliminate shrinkage in the PC to acceptable levels (less than 0.15%). Mechanical properties are affected only marginally and well within accept- able limits. This allows for the addition of re- inforcement. Further, it was shown that, by using special resins, flammability and fire rating of the concrete is substantially improved. This property is of extreme importance in the building industry for all the materials used in the construction of high rise buildings. The properties of sealing materials have been defined. As there, are dif- ferent types of application, the function of sealers and the specific requirements for each type of application vary accordingly. A sealer specified for use in the building industry may not be suit- able for a highway bridge deck or for use on hydraulic structures. Selection criteria for sealers and the problems related to testing were dis- cussed. For underwater concreting PMMA mortars were shown to have better properties compared with epoxy (EP) and unsaturated poly- ester (UP) mortars. Further, it was shown that treating the sand with silane coupling agents, rather than adding the agent to the binder system, is much more effective.

Development of a special type of cement called a biocidal polymer cement has been reported. These cements can be made by applying acrylo- nitrile rubber latex with a biocidal group of tin organic compounds added to it. It will protect concrete from microorganisms. It is specially important for the concretes intended for use in industrial buildings for food, meat and milk pro- cessing. It is shown that the acrylic latexes give better protection against chloride ingress than the PCC made using SBR and plain mortars. Com- parison of two methods for testing chloride ion diffusion in polymer cement concrete was dis- cussed. The methods used were forced diffusion test and free diffusion test. It was shown that the forced diffusion test has many advantages, because it is less time consuming, and needs only a few samples. Furthermore, it has a good resolu- tion and is reproducible, which is very important.

Concrete is a heterogenous material and the strength at two places of the same concrete can vary considerably, especially when making super- high-strength concretes using very low water-to- binder ratios. The uniform dispersion of water in this case can be problematic. Consequently, the hydration can be different at different places. It can be one of the causes of localized damage. A new technique of using solid water was presented

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by Chandra, Sweden. Water is absorbed into super-absorbing polymer particles which are later added to the concrete mix. It has produced better homogeneity in the concrete mix. The variations in the compressive strengths have been substanti- ally reduced. Drying rate is controlled. It can also be useful in concretes using high water-to-binder ratios as it will decrease bleeding. It is a new approach in the use of polymers and is very promising.

The influence of polymeric phase distribution on the mechanical properties of premix PCC material was discussed. It was shown that the flexural strength increase in PCC can be related to the build-up of a coherent polymeric phase and to its morphological features. The morphology of the coherent frame strongly depends on water dis- persibility characteristics of the polymer. Further, the compression behaviour of premix PCC mortar is affected by the intrinsic strength of the poly- mers. A microstructural approach to an evalua- tion of factors affecting the performance of polymers and mortars has been discussed.

Dielectric properties of MDF cement pastes made with OPC, HAC, polyacrylamide and poly(vinyl alcohol) were discussed. It was con- cluded that the dielectric permittivity and loss factor were lower for MDF cement pastes based on HAC than those based on OPC. These

decrease with increase of W/C and P/C. Further, the lowest dielectric permittivity and loss factor and the highest flexural strength were reported for hot-pressed HAC-PVA, MDF cement pastes.

Mass production of polymer concrete and its properties were discussed. A polyester/cement composite for electrical insulators was reported which uses unsaturated polyester resin with cement and sand. Chemical and mechanical resistance of industrial floors was also discussed. Its use in piling structures has also been reported.

Repair of concrete in structures with low vis- cosity polymerizing compositions and evaluation of surface repair mortars for erosion damaged concrete were discussed.

Sulphur polymer concrete was a new session included in this congress. Production techniques of sulphur polymer concrete and its field of appli- cation were reported, especially the problem of stabilizing the polymorphous phases of sulphur.

This congress was followed by the RILEM Committee TC 113 CPT; 'Test Methods for Con- crete Polymer Composites'. The meeting was con- ducted by Dr K. Demura of Nihon University, Koriyama, Japan in the absence of Professor Y. Ohama, Chairman of the committee, who could not come owing to illness.

Satish Chandra