Epoxy adhesives have been used for decades to repair concrete infrastructures. The durability or expected service life of a structural adhesive is of concern in any application. However, even today, the service life of a concrete joint bonded with epoxy adhesive under specific environmental conditions is not well known or even understood due to the variables at play. The objective of this editorial is to summarize the history of epoxy adhesives in concrete infrastructure applications and to provide some light on the requirements and expected service life of an epoxy adhesive for this type of application.

Commercially produced epoxy resin adhesives became widely available in the early 1950s. Initial laboratory tests using epoxies on concrete began in the late 1940s. Development was limited to the laboratory until about 1953, when confidence grew to allow field applications.

In the mid-to-late1950s epoxy resins began to be used as surfacing materials on highways. Favorable results encouraged the pursuit of this technology. In 1954, the U.S. California Highway Department became interested in epoxies as a bonding agent for raised traffic line markers on concrete highway.¹ This was the first wide-spread utilization of epoxy adhesives for concrete.

Tremper² investigated the use of epoxy resins by California Division of Highways for repairing concrete. The bond strength of a proprietary formulated and applied adhesive was shown by many tests to be greater that that of the concrete. There was, of course, little information on durability at this time, but Tremper mentions some highly stressed joints which had been in service for five years without failure of the bond.

The US Army Corps of Engineers published the first Federal specification for an epoxy resin system in 1959, and ASTM specification C881 was first published in 1978. The use of epoxy systems for concrete bonding, patching, coating, etc. has since expanded in many directions. A comprehensive review of applications involving the use of epoxy adhesive in civil engineering is given by Hewlet and Shaw³ , Tabor⁴ , and Mays and Hutchinson ⁵.

Mays and Hutchinson identified the principal requirements for bonding steel-to-concrete, and these are very similar for the case of bonding concrete-to-concrete or concrete to any other material. In summary these adhesive requirements are:

Johnson ⁶ provides a useful early review of epoxy (and other adhesives) for structural concrete. With regard to environmental durability, he makes several conclusions that appear to still hold true today. Nearly all of the limited data on the strength of concrete-to-concrete joints relates to laboratory made specimens and that poor joint preparation leads to serious loss of strength and durability. Thus, the position with respect to site work is comparable with that existing in the early days of welding; there is a need for first-class supervision and for tests on joints made under actual site conditions. It is clear that the ultimate tensile strength of a properly made joint exceeds that of concrete. The knowledge of resin strength is sufficient to enable joints loaded in compression to be used with confidence. It seems likely that the strength of joints in shear will be governed by the tensile strength of the concrete and will depend on the shape of the adherends and related stress factors.

In more recent times, the use of epoxy adhesives has been studied thoroughly for bonding fiberglass reinforced plastic to concrete for the purpose of strengthening. Although most of the studies were focused at the strength and aging characteristics of the FRP when exposed to long term outdoor elements, the properties of the adhesive and bond interface were also examined in many cases.

In view of the variety of epoxy adhesives available and the complexity of the joint, application, process, loading, and environmental effects, it is not surprising that few claims are made regarding the long-term behavior and stability of epoxy-concrete joints.

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References

1. ACI Committee Report 503R, Use of Epoxy Compounds with Epoxy, 1998.
2. Tremper, B., "Repair of Damaged Concrete with Epoxy Resins", Proceedings of American Concrete Institute, Vol. 57, 1960, pp. 173-182.
3. Hewlett, P. C. and Shaw, J. D. N., in Developments in Adhesives, ed. W. C. Wake, Applied Science, London, 1977, pp 25-75.
4. Tabor, L. J., "Adhesives in Construction", Int. J Adhesion Adhesives, April 1982, 73-76.
5. Mays, G. C. and Hutchinson, A. R., Adhesives in Civil Engineering, Cambridge University Press, Cambridge, 1992.
6. Johnson, R. P., "Glued Joints for Structural Concrete", The Structural Engineer, Vol. 10, No. 1, October 1983, pp. 313-316.