Effect of metakaolin on the chloride ingress properties of concrete

Abstract

Research and practical experience have shown that partial replacement of cement by metakaolin improves concrete durability as a result of the refinement of the pore structure. While much research has been presented on concrete performance with metakaolin, it is scarce concerning the transport properties of chlorides in concrete with metakaolin, in natural conditions (i.e., un-accelerated). This study determines the chloride diffusion coefficients for several concretes with vary levels of cement replacement with metakaolin, and compares these results with chloride migration coefficients obtained from accelerated laboratory testing. In this study, two cement types (CEM I 42,5R and CEM IV/A 42,5) and two cement contents levels where used with metakaolin replacement levels varying from 10-20%. Concretes where tested for fresh properties, compressive strength, electrical resistivity, chloride ingress characteristics (natural diffusion and migration), and mercury intrusion porosimetry. The results show improved strength, durability properties and chloride penetration resistance of concretes with metakaolin. Furthermore, the use of metakaolin in fly ash concrete improves the early age performance of the concrete (<90 days), counteracting the delay in strength and durability gain typically associated with fly ash concrete. The results obtained from this study fulfil the lack of critical input for service life design models of reinforced concrete structures in chloride environments, with emphasis on concretes with metakaolin replacement.

Relationship between pore structure and chloride diffusion in cementitious materials

“…Table 1 lists the literature used in this study. Ferreira et al [16] Zhao [17] reported the derivative of pore size distribution and the intrusion steps were shown; however, each plot was not clear because there are many plots. Therefore, these were omitted in this study.…”

Procedimento para detectar a penetração de cloretos com nitrato de prata em concreto carbonatado

“…The colorimetric method of spraying silver nitrate is widely used in experimental works in which the tested concrete is found in saturation conditions and free from the carbonation process. Many works published in recent years in high-impact magazines (such as : Ferreira et al, 2016;Weiss et al, 2017;Wei et al, 2018;He et al, 2018;Slomka-Slupik et al, 2018;Fernández-Ruiz et al, 2018;Lau et al, 2018;Azarijafari et al, 2018) confirm its frequent use in current research. However, some studies (França, 2011;Real et al, 2015) point out that the silver ions (Ag+) in the silver nitrate solution react with the carbonation product CO3, forming Ag2CO3, which also gives a whitish color to the concrete.…”

Analysis of Hydration-Mechanical-Durability Properties of Metakaolin Blended Concrete

“…The reaction products of metakaolin include calcium silicate hydrate (CSH), C 4 AH 13 , C 3 AH 6 , and C 2 ASH 8 [18]. Dunster et al [18] designed trimethylsilylation studies of the hydration of metakaolin-calcium hydroxide paste.…”

“…Güneyisi et al [4] and Wong [5] pointed out that the compressive strength was improved in MK blended concrete due to the pozzolanic reaction of MK. Ferreira et al [6] and Poon et al [7] stated that chloride diffusivity decreased as MK replacement levels increased. Ramezanianpour [8] and Duan et al [9] indicated that durability aspects, such as the resistances about sorptivity, water penetration, salt ponding, and carbonation, were improved due to MK additions.…”

“…Considerable experimental studies have been performed regarding material characteristics, hydration, and the mechanical and durability properties of metakaolin (MK) blended concrete [2][3][4][5][6][7][8][9][10]. Bai et al [2] reported that MK blended concrete had a lower slump than control concrete because MK has a higher specific surface than cement.…”