Fluorescence Microscopy of Superplasticizers in Cementitious Systems: Applications and Challenges

Abstract

In addition to the desired plasticizing effect, superplasticizers used in high and ultra-high performance concretes (UHPC) influence the chemical system of the pastes and for example retardation of the cement hydration occurs. Thus, superplasticizers have to be chosen wisely for every material composition and application. To investigate the essential adsorption of these polymers to particle surfaces in-situ to overcome several practical challenges of superplasticizer research, fluorescence microscopy is useful. In order to make the superplasticizer polymers visible for this microscopic approach, they are stained with fluorescence dyes prior the experiment. In this work, the application of this method in terms of retardation and rheological properties of sample systems is presented. The hydration of tricalcium oxy silicate (C3S) in combination with different polycarboxylate ether superplasticizers is observed by fluorescence microscopy and calorimetry. Both methods can identify the retarding effect, depending on the superplasticizer’s chemical composition. On the other hand, the influence of the superplasticizers on the slump of a ground granulated blast furnace slag/cement paste is correlated to fluorescence microscopic adsorption results. The prediction of the efficiency by microscopic adsorption analysis succeeds roughly. At last, the possibility of high-resolution imaging via confocal laser scanning microscopy is presented, which enables the detection of early hydrates and their interaction with the superplasticizers.

Adsorption of PCE in alkali‐activated materials analysed by fluorescence microscopy

“…18,19 The superplasticizers were synthesized by the department of chemistry at the TU Munich. The superplasticizers were stained with aminofluorescein as described in Arend et al 18,19 For the alkali-activation potassium, waterglass and potassium hydroxide solutions were used. As particles, a Si-rich fly ash and a ground granulated blast furnace slag were used.…”

“…Two different PCE were used: 7APEG2 and 45PC2 (MPEG) (for further description please see. 18,19 The superplasticizers were synthesized by the department of chemistry at the TU Munich. The superplasticizers were stained with aminofluorescein as described in Arend et al 18,19 For the alkali-activation potassium, waterglass and potassium hydroxide solutions were used.…”

“…Two different PCE were used: 7APEG2 and 45PC2 (MPEG) (for further description please see 18,19 . The superplasticizers were synthesized by the department of chemistry at the TU Munich.…”

“…[15][16][17] An analytical method has been developed in the past few years which, based on fluorescence microscopy, enables the observation of the adsorption behaviour of organic concrete admixtures on solid surfaces. [18][19][20] In particular, in situ investigations limit the possible analysis methods to light microscopy for preparative reasons, the resolution is not sufficient to detect the admixtures. This problem can be solved by means of fluorescence microscopy, in which dyes previously bound to the additives are excited to fluorescence, which serves the actual imaging.…”

“…By coupling admixtures with fluorochromes, admixtures in mineral‐bound systems can be localised by fluorescence microscopy 15–17 . An analytical method has been developed in the past few years which, based on fluorescence microscopy, enables the observation of the adsorption behaviour of organic concrete admixtures on solid surfaces 18–20 . In particular, in situ investigations limit the possible analysis methods to light microscopy for preparative reasons, the resolution is not sufficient to detect the admixtures.…”