The influence of the cement paste microstructure on corrosion and the adherence of reinforcing bars as a function of the water–cement ratio

Abstract

Hardened cement paste is a heterogeneous system resulting from the grouping of particles, films, microcrystals and other solid structural elements bounded in a porous mass. The cement paste microstructure must be understood firstly due to its influence on concrete properties. The behaviour of concrete greatly depends on the conformation of localised special structures rather than on general structures found in the mass cement paste. The objective of this paper was to study the cement paste microstructure, as a function of the water–cement ratio, in order to interpret the variations of the steel–mortar bond strength and the developing of the corrosion process in steel–mortar specimens kept in tap water and 3 percent sodium chloride solutions for 1 year. A description of the steel–mortar interface was also provided.

Rebar corrosion in mortars with high limestone filler content

“…Rebars extracted from N1 specimens, stored in tap water, presented two well differentiated regions after SEM examination. The most widespread morphology was constituted by gels with filament like formations (Figure 6(a)) and was similar to others reported in the literature (Romagnoli et al , 2002). Spectral data showed that these formations were rich in hydraulic compounds (SiO 2 : 20‐25 per cent; CaO: 32‐40 per cent) with lower amounts of iron oxides (Fe 2 O 3 : 11‐19 per cent) and carbon dioxide (CO 2 : 8‐10 per cent).…”

“…The carbon dioxide content was a little higher than in samples cured in the air (CO 2 : ∼23‐33 per cent). Three different morphologies were observed in FC specimens: a cracked surface constituted by amorphous plates (Figure 9(a)), formations similar to those reported for OCP hydration products (Romagnoli et al , 2002) in certain zones of the rebars (Figure 9(b)) and, finally, the third one with high calcium oxide content and low levels of iron oxide (Figure 9(c)). All the formations were enriched in hydraulic compounds as it was revealed by the higher contents of SiO 2 and CaO.…”

“…The carbon dioxide content was a little higher than in samples cured in the air (CO 2 : ,23-33 per cent). Three different morphologies were observed in FC specimens: a cracked surface constituted by amorphous plates (Figure 9(a)), formations similar to those reported for OCP hydration products (Romagnoli et al, 2002) in certain zones of the rebars (Figure 9(b)) and, finally, the third one with high calcium oxide content and low levels of iron oxide (Figure 9(c)). Notes: Water/cement ratio: 0.50; electrolyte: tap water In the case of samples stored in 3% NaCl variable amounts of chloride were detected on the rebar surface; typically 0.7-2.0 per cent but, in certain cases, it increased up to , 7 per cent, particularly associated with high Al 2 O 3 contents.…”

Rebar Corrosion in Mortars Containing Calcareous Filler

“…Rebars extracted from specimens elaborated with OPC, stored in tap water, presented two well differentiated regions after SEM examination. The most widespread morphology was constituted by gels with filament-like formations (Figure a) and was similar to others reported in the literature. − Spectral data showed that these formations were rich in hydraulic compounds (SiO 2 : 20−25%; CaO: 32−40%) with lower amounts of iron oxides (Fe 2 O 3 : 11−19%) and carbon dioxide (CO 2 : 8−10%). The other morphology contained gels constituted by nonexpansive iron oxihydroxides (Figure b).…”