On functional signatures of bare and coated formwork skin surfaces

Abstract

The sticking of the concrete on metallic formworks during building construction generates many concrete wall defects. Several solutions have been proposed, among which surface lubrication and polymeric coatings are commonly applied. In this paper, the main functional signatures of a steel formwork skin and a polymeric coating were determined to understand their effect on the concrete sticking. The topographical, chemical and mechanical signatures of the surfaces were characterized at near-surface regions. The top of the steel formwork a 10 µm-thick layer is constituted of two oxides each one having specific tribological properties. Adding the polymeric coating on the formwork skin surface lowers its surface tension, which lowers the sticking by reducing the wettability. Moreover, the smaller roughness of the coating limits the susceptibility of mechanical anchoring. Nevertheless, scratch testing suggests a short durability of the polymeric coating due to its weak resistance to abrasion.

Characterizing tribological behavior of fresh concrete against formwork surfaces

“…The deep scratches observed on the coupons suggest an abrasive-dominated wear mechanism with damages induced by the fines and granulates. The ranking is indeed correlated with the measured hardness from a previous work for PMr1 (12 ± 2 GPa), PMr2 (12 ± 2 GPa), and RPa1 (4.3 GPa) [40].…”

“…The surface geometry is significantly altered during casting by the concrete movement against the formworks, especially for non-lubricated surfaces. Surface topography is a factor that significantly affects the performance of formworks [40,41,50]. This factor is used in this research study to probe and quantify the wear of formwork plates.…”

Designing metallic surfaces in contact with hardening fresh concrete: A review

“…However, it remains unclear whether or not the kinetics of diffusion in saturated calcium hydroxide solutions are representative of those in concrete. Low cost and wear resistant steels are the most common materials used in formwork and reinforced bar designs [52,88]. The K2 L8 M14 N2 structure of iron atoms indicates the presence of a lone pair of electrons on most external 4 th orbit that make the iron atoms very reactive.…”

“…Aluminum doping in the galvanized coating limit the calcium hydroxizincate formation due to the preferential reaction of OHand Ca(OH)2 with Al atoms [109,110] but the results highlight ambiguous effects on bonding strength improvement or deterioration [34,88,95]. Electrochemical bonding of concrete on steel [112,113] and others metals such as Al, Zn and Pb [14] may be limited by controlling the electronic interactions with the metallic substrate polarization [114,115].…”

“…In fact, polymeric skins have proven an efficient anti-adherence solution [8][9][10]24,93,94,98,[121][122][123][124] but have weak resistance to fresh concrete-induced abrasion [52,88]. The study of concrete friction on substrates was mainly investigated using the plane/plane tribometer [16,19,21,52,88,[143][144][145][146][147][148][149][150] and few rheological models [52,88,151]. The friction and wear behavior have highlighted the dependence of interfacial friction stresses of fresh concrete on a substrate with the demoulding agents [19,150,152], the aggregate contents [149], the paste volume [16] and the optional addition of superplasticizer [16,19,150].…”