A Study on the Adhesion of Cementitious Fireproofing Coatings to the Metal Structures With Different Types of Anticorrosive Primers

The steel building lifecycle in fire condition can be enhanced through application of some well-known Cementitious and/or Intumescent based fireproof coatings, providing sufficient time for the safe evacuation of people from the fired building. In the presence of the fireproofing coating the steel building structure collapse and/or failure in fire condition (at around 550°C) can be delayed due to the thermal insulating properties of the coating. There are a large number of reports on the development of new and advanced fireproofing materials with better thermal insulating properties. The most important challenge regarding the application of the fireproofing coatings on the steel structures is their insufficient adhesion properties mainly in the case of the metals coated with a primer layer. Most of the time the steel building structure is covered with an anti-corrosive primer layer based on the epoxy or alkyd for corrosion protection in wet/corrosive condition. In case of poor adhesion of the fireproofing coatings to the substrate, all other properties like thermal insulating properties are rendered useless. One way for overcoming this shortcoming is the application of an adhesive intermediate layer on the un-coated or coated steel structures. Howevere, findig a proper ype of adhesive layer is still the topic of the recent resercahes. According to literature there is no systematic report/study on the effect of the type of primer on the adhesion of the cementitious and/or Intumescent coatings to the steel structures.In the present study, for the first time we endeavor to find a correlation between the adhesion characteristics of a cementitious fire retardant coating and steel structures coated with some well-known corrosion protective primers. To this end, four types of anti-corrosive primers including epoxy zinc phosphate, epoxy zinc chromate epoxy, iron oxide and zinc chromate alkyd primers were selected and applied on the shot blasted mild steel sheets. A cementitious fireproofing coatings with and without adhesive primer (for improving the adhesion between the anti-corrosion primer and cementitious) were applied on the primed substrates. The cohesion/adhesion forces of the coatings were studied through the ASTM E 736. It was found that the adhesion force of the cementitious coating exactly correlate with the primer properties. The cementitious coatings showed higher adhesion to the epoxy based primers than the alkyd based ones.The interaction between the fire retardant coating and primer was characterized by SEM, FT-IR and DSC analyses.