Microscopy techniques for determining water–cement (w/c) ratio in hardened concrete: a round-robin assessment

Abstract

Water to cement (w/c) ratio is usually the most important parameter specified in concrete design and is sometimes the subject of dispute when a shortfall in concrete strength or durability is an issue. However, determination of w/c ratio in hardened concrete by testing is very difficult once the concrete has set. This paper presents the results from an interlaboratory round-robin study organised by the Applied Petrography Group to evaluate and compare microscopy methods for measuring w/c ratio in hardened concrete. Five concrete prisms with w/c ratios ranging from 0.35 to 0.55, but otherwise identical in mix design were prepared independently and distributed to 11 participating petrographic laboratories across Europe. Participants used a range of methods routine to their laboratory and these are broadly divided into visual assessment, measurement of fluorescent intensity and quantitative backscattered electron microscopy. Some participants determined w/c ratio using more than one method or operator. Consequently, 100

Analysis of cement paste and aggregate content of concrete using micro X-ray fluorescence

“…Examples include the physicochemical method of BS 1881-124 (British Standards Institution, 2015 and petrographic methods such as fluorescence microscopy (Mayfield, 1990, Elsen et al, 1995, Sibbick et al, 2019 and backscattered electron microscopy (BSE) (Wong and Buenfeld, 2009, Wong et al, 2013, Yio et al, 2014. A recent round-robin assessment involving eleven laboratories in Europe (Wong et al, 2020) has demonstrated the viability of petrographic microscopy methods for determining w/c ratio in hardened concrete. The aggregate content and particle size grading can be determined by breaking down the cementitious matrix through mechanical, thermal or chemical (acid dissolution) treatments, followed by a sieve analysis of the remaining material (British Standards Institution, 2015).…”

Petrographically Quantifying the Damage to Field and Lab-cast Mortars Subject to Freeze-thaw Cycles and Deicer Applications

“…In addition to contrast enhancement for crack detection, FM shows the potential to illustrate the capillary porosity in the cement paste matrix of concrete [22,23]. One important application is to determine water to cement ratio (w/c) [23].…”

“…In addition to contrast enhancement for crack detection, FM shows the potential to illustrate the capillary porosity in the cement paste matrix of concrete [22,23]. One important application is to determine water to cement ratio (w/c) [23]. More generally, the sensitivity of fluorescent light intensity on capillary porosity makes it an indicator of the microstructural alteration along the depth in cementitious materials subject to chemical attacks such as microbially induced corrosion [24].…”

Petrographically quantifying the damage to field and lab-cast mortars subject to freeze-thaw cycles and deicer application

“…In addition to contrast enhancement for crack detection, FM shows the potential to illustrate the capillary porosity in the cement paste matrix of concrete [23,24]. One important application is to determine water to cement ratio (w/c) [24].…”

“…In addition to contrast enhancement for crack detection, FM shows the potential to illustrate the capillary porosity in the cement paste matrix of concrete [23,24]. One important application is to determine water to cement ratio (w/c) [24]. More generally, the sensitivity of fluorescent light intensity to capillary porosity makes it an indicator of the microstructural alteration along the depth of cementitious materials subject to chemical attacks such as microbially induced corrosion [25].…”