Лако-красочные материалы — производство

We have seen that structural adhesive bonding has been employed in the aerospace and other industries for several years, whereas its use in civil engineering is relatively recent. Adhesive bonding can present some very unfamiliar concepts to many engineers and, in particular, civil engineers and this may partially explain the extremely cautious embrace of the technology. Thus it is perhaps worth considering at this stage the applicability of the experience gained in industries such as aerospace and automotive to future applications in civil engineering.

Projects in the construction industry are distinguished from those

in other industries by the fact that they are generally unique, are specifically commissioned and are built in situ. Unlike motor cars and aeroplanes, civil engineering structures are not generally mass produced, they are not built first and sold later and, with the exception of pre-fabricated components, cannot be assembled economically under cover. These factors all have an influence on the relevance of previous adhesive research and practical experience.

At the design and specification stage there exist few design tools and recommendations available for general applications of adhesives.

The civil engineer often requires an adhesive to perform a gap­filling role as well as being a stress transfer medium, with the adhesive often being used in thick bondlines. Far lower levels of dimensional precision would also be anticipated in construction, which further compounds the problem. This immediately calls into question the validity of any existing design tools developed for engineering applications generally involving the use of adhesives in very thin or thin bondlines.

The choice and availability of adhesives for Civil Engineering applications is also somewhat limited, because manufacturers have naturally tailored their products to the needs of the aerospace and general manufacturing industries. Thus products developed specifically for bonding steel and concrete are currently few and far between.

The bonding operation itself can be fraught with difficulties. The outdoor nature and scale of construction projects means that surface treatment techniques need to be appropriate to the practical conditions. Simple grit blasting and degreasing methods may even be very difficult in remote locations or in adverse weather conditions. Any form of quality structural bonding requires close control and protection from the weather. It may be that pre-treated or pre­primed components (like coil-treated sheet aluminium) could be used which present a reproducible surface to adhesives. Alternatively the development of sacrificial pretreatment technology, used for underwater bonding, may have considerable merit for certain situations if heat-cured adhesive products cannot be used. The application of adhesive materials is unlikely to be possible by automated equipment, although automatic mixing and dispensing may be practical. In many instances products which cure at ambient temperature will have to be used, although at temperatures below 10 °С the rate of curing drops off very rapidly; this may imply the need for space heating. If the superior performance of heat-cured adhesives is required then it may be possible to provide the necessary curing regime over small areas by using electrical heating tapes and blankets, infra-red heaters or even induction heating methods.

Many civil structures are designed for lives in excess of one hundred years and during this time they will be subjected to extremes of temperature, moisture and probably sustained as well as cyclic loading. The operating conditions in other industries may be quite different, in particular the life span of a vehicle or aircraft is unlikely to exceed twenty years. The engineer will need to satisfy himself that the adhesive joint remains capable of performing its intended role for a specified time; for primary structural connections this will usually be the design life of the structure. In repair or strengthening applications a shorter time may be acceptable in the knowledge that the process can be repeated if necessary at periodic intervals. The ability to check the integrity of bonded joints is very important although non-destructive methods are not yet generally available or applicable for many current and potential bonded joint applications in civil engineering.