Dear Dr.Abbas..I think Epoxy adhesive is applied in these joints for the following purposes according to International Road Federation (1977):

(i) It seals up the joints completely between precast concrete segments to protect the

prestressing tendons;

(ii) By filling voids and irregularities along the segment joints, it helps to reduce stress

concentrations otherwise it will be developed; and

(iii) It helps in transferring of shear between the joints in case a large single shear key is used

Well Dr Amjad