Recently, due to the skyrocketing price of upstream epoxy resins, the price of reinforcing adhesives has also risen accordingly, causing many manufacturers and customers to complain. At this time, there are also many voices in the market, such as whether it is possible to use lower-priced unsaturated polyester resin instead of epoxy resin as the adhesive...

wake up! 

wake up! 

wake up!

The answer is obviously: no!

According to the provisions of GB 50367-2013 "Specifications for the Design of Reinforcement of Concrete Structures": "It is strictly forbidden to use unsaturated polyester resins and alkyd resins as adhesives in the reinforcement of load-bearing structures."

Adhesives used in load-bearing structures must be tested for bond shear strength. During the inspection, the standard value of the bond shear strength should be determined according to the requirement that the confidence level is 0.90 and the guarantee rate is 95%.

Unsaturated polyester resins and alkyd resins are poor due to their hydrophilicity, moisture resistance and resistance to damp heat aging. The use of structural adhesives in load-bearing structures will not only leave safety hazards, but also some reinforcement projects have caused safety accidents due to the use of such adhesives. Therefore, its use in the reinforcement of load-bearing structures must be strictly prohibited.

Then why can epoxy resin be used with confidence?

Because after decades of practice, it is now recognized that the specially developed modified epoxy resin adhesive is the first choice for reinforcing concrete structures.

Compared with unsaturated polyester resin, epoxy resin has the following five advantages:

1. High mechanical properties

Epoxy resin has strong cohesion and compact molecular structure, so its mechanical properties are higher than general-purpose solid resins such as phenolic resin and unsaturated polyester.

2. Strong adhesion

The epoxy resin curing system contains extremely reactive epoxy groups, hydroxyl groups, and polar groups such as ether bonds, amine bonds, and ester bonds. The epoxy cured product has excellent adhesion to polar substrates such as cermet, glass, concrete, and wood.

3. Small curing shrinkage

It is generally 1%-2%, which is one of the varieties with the smallest curing shrinkage rate among thermosetting resins.

4. Good craftsmanship

The epoxy resin basically does not produce low molecular volatiles when it is cured, so it can be molded under low pressure or contact pressure. It can be combined with various curing agents to produce environmentally friendly coatings such as solvent-free, high-solid, powder coating and water-based coatings.

5. Excellent resistance to chemicals

The epoxy cured product has excellent chemical stability. Its corrosion resistance to various media such as alkali, acid and salt is better than thermosetting resins such as unsaturated polyester resin and phenolic resin.

Especially for bonding fiber composite materials and steel materials, no matter from the perspective of anti-peeling performance, environmental resistance performance, long-term stress resistance performance, or impact resistance and fatigue resistance, it is unmatched by other types of adhesives.

It should be noted that these good adhesive properties are obtained through modification and screening with high-performance curing agents and other modifiers, thus eliminating the inherent brittleness defects of epoxy resins. Therefore, it must be inspected and appraised according to the current national standard GB 50728-2011 "Technical Specification for Safety Appraisal of Engineering Structure Reinforcement Materials" before use.