Investigation of the Incompatibilities of Cement and Superplasticizers and Their Influence on the Rheological Behavior

Abstract

The rheological behavior of cement paste and the improvement of its flowability takes center stage in many research projects. An improved flowability can be achieved by the addition of superplasticizers (SP), such as polycarboxylate ethers (PCE). In order to be able to use these PCEs effectively and in a variety of ways and to make them resistant to changes in the environment, it is crucial to understand the influence of SPs on cement hydration. For that reason, the topic of this paper was the incompatibility of a specific SP and an ordinary Portland cement (OPC). The incompatible behavior was analyzed using rheological tests, such as the spread flow test and penetration test, and the behavior was compared by means of an ultrasound technique and explained by the phase content measured by in-situ X-ray diffraction (XRD) the heat evolution measured by calorimetry, and scanning electron microscope (SEM) images. We showed that the addition of the SP in a high dosage led to a prevention of the passivation of the most reactive and aluminum-containing clinker phases, aluminate and brownmillerite. This induced the aluminate reaction to take place in the initial period and led to an immediate stiffening of the cement paste and, therefore, to the complete loss of workability. The results showed that in addition to the ettringite, which began to form directly after water addition, hemicarbonate precipitated. The fast stiffening of the paste could be prevented by delayed addition of the SP or by additional gypsum. This fast stiffening was not desirable for SPs, but in other fields, for example, 3D printing, this undesirable interaction could be used to improve the properties of printable mortar.

Utilization of Thermally Treated SiC Nanowhiskers and Superplasticizer for Cementitious Composite Production

“…Nonetheless, their main heat flow peak values were still higher than that of plain cement pastes. This agrees with previous reports [35][36][37][38], which observed delays in cement hydration when polycarboxylate-based SPs were added. According to some authors, this occurs because the molecules of SP adsorb on the cement particles' surface.…”

Early performances of cement paste in the presence of triethanolamine: Rheology, setting and microstructural development

“…It indicates the higher TEA dosage is harmful to the rheological retention ability. Considering the significant effect of the hydration of aluminate phase on the rheological performance of cement paste 29 and the acceleration effect of TEA on the aluminate phase reaction, 12 it is reasonable to deduce that the fast increase in the yield stress is caused by the rapid reaction of the aluminate phase accelerated by TEA, either by the formation of AFt (Figure 3(d)) or the transformation of AFt to AFm, which will be discussed elaborately later.…”

Fluorescence Microscopy of Superplasticizers in Cementitious Systems: Applications and Challenges

“…As mentioned above, the interaction of SPs with early hydrate phases can be crucial for their performance. As reported for example by Pott et al [ 41 ], the aluminum and silicon reaction of cement hydration can be affected by SPs in very different ways. Identifying particular clinker phases (C 3 A and C 3 S) prior to this laser microscopic investigation may lead to convincing in-situ results, especially if the possibility of using and imaging differently stained SP-types parallel is taken into account.…”

“…Early hydration products are known to have an important impact on the superplasticizer performance because they use to adsorb high amounts of SP-polymer due to positive surface charges and extension of the specific surface area [ 37 ] or even incorporate the molecules in their crystal structure [ 38 ]. The presence of specific minerals such as clay [ 39 , 40 ] or an unfortunate combination of SP and binder materials [ 41 ] may lead to a complete loss of the plasticizing effect of SPs. In this context, high-resolution fluorescence microscopy via confocal laser scanning microscopy [ 42 , 43 ] allow a precise detection of those phases and the adsorption of SPs on cement grains, as shown below.…”