Setting of cement with controlled superplasticizer addition monitored by ultrasonic measurements and calorimetry

Daake, Henning von; Stephan, Dietmar

doi:10.1016/j.cemconcomp.2015.11.004

Cited by 43 publications

(13 citation statements)

References 26 publications

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“…During this acceleration period a rapid crystallization of CH (portlandite) and C-S-H (calcium silicate hydrates), corresponding to the main hydration of the PC, took place. Although the linkage of the heat evolution due to the chemical reactions (calorimetric curves) with the setting time (physical formation of the hardened structure) is not linear, the initial setting time corresponds to the time in which the rate of the reaction becomes intense whereas the final setting time would take place before the system reaches the maximum [30,31]. …”

Section: Resultsmentioning

confidence: 99%

The Effect of TiO2 Doped Photocatalytic Nano-Additives on the Hydration and Microstructure of Portland and High Alumina Cements

et al. 2017

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Mortars with two different binders (Portland cement (PC) and high alumina cement (HAC)) were modified upon the bulk incorporation of nano-structured photocatalytic additives (bare TiO2, and TiO2 doped with either iron (Fe-TiO2) or vanadium (V-TiO2)). Plastic and hardened state properties of these mortars were assessed in order to study the influence of these nano-additives. Water demand was increased, slightly by bare TiO2 and Fe-TiO2, and strongly by V-TiO2, in agreement with the reduction of the particle size and the tendency to agglomerate. Isothermal calorimetry showed that hydration of the cementitious matrices was accelerated due to additional nucleation sites offered by the nano-additives. TiO2 and doped TiO2 did not show pozzolanic reactivity in the binding systems. Changes in the pore size distribution, mainly the filler effect of the nano-additives, accounted for the increase in compressive strengths measured for HAC mortars. A complex microstructure was seen in calcium aluminate cement mortars, strongly dependent on the curing conditions. Fe-TiO2 was found to be homogeneously distributed whereas the tendency of V-TiO2 to agglomerate was evidenced by elemental distribution maps. Water absorption capacity was not affected by the nano-additive incorporation in HAC mortars, which is a favourable feature for the application of these mortars.

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Section: Resultsmentioning

confidence: 99%

The Effect of TiO2 Doped Photocatalytic Nano-Additives on the Hydration and Microstructure of Portland and High Alumina Cements

et al. 2017

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“…Moreover, it is known that the effectiveness of SPs can be enhanced by delayed addition [23,29,30]. In contrast to a direct addition, together with the mixing water, a delayed addition leads to an increased flowability but simultaneously to more pronounced retardation [23].…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2020

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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.

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“…It was reported that the delayed addition or secondary addition of PC is of help in the fluidity retention of fresh concrete because it helps prevent the fast consumption of PC molecules by the hydration products formed early, such as AFt . In other words, the delayed addition of PC provides a nonadsorbed PC molecule pool that continuously supplies PC molecules for further adsorption on hydration products, and that contributes to improving the fluidity retention of concrete over time Similar to the idea of the secondary addition of PC, a capsule‐type water‐reducing agent, in which a water‐reducing agent is the core and a water‐soluble membrane acts as the shell of the capsules, was developed .…”

Section: Introductionmentioning

confidence: 99%

Working mechanism of post‐acting polycarboxylate superplasticizers containing acrylate segments

Zhang

Kong

Xing

et al. 2017

J of Applied Polymer Sci

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Acrylate-containing polycarboxylate superplasticizers were synthesized by copolymerizing acrylic acid, a-methallyl-xmethoxy poly(ethylene glycol) ether, and acrylic esters [hydroxyethyl acrylate (HEA) or hydroxypropyl acrylate (HPA)]. Their dispersing effects and fluidity-retaining capabilities were evaluated by spread tests of cement pastes. The temperature sensitivity of the performance was especially focused upon. It was found by Fourier transform infrared spectroscopy and specific anionic charge density measurements that the ester groups in the acrylate-containing copolymers hydrolyze in alkaline conditions, and thus additional RACOO 2 groups are continuously produced. The gradual production of RACOO 2 leads to increasing charge density and hence increasing adsorption of the polymer on the cement surface. The hydrolysis of HEA units is slightly faster than of HPA units in the corresponding copolymers. By this mechanism, a post-acting, or delayed, dispersing effect is realized. Such post-acting polymers alone or formulated with normal polycarboxylate superplasticizer can be used achieve a long fluidity retention of fresh concrete, especially under elevated temperatures.

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Setting of cement with controlled superplasticizer addition monitored by ultrasonic measurements and calorimetry

Cited by 43 publications

References 26 publications

The Effect of TiO2 Doped Photocatalytic Nano-Additives on the Hydration and Microstructure of Portland and High Alumina Cements

The Effect of TiO2 Doped Photocatalytic Nano-Additives on the Hydration and Microstructure of Portland and High Alumina Cements

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

Working mechanism of post‐acting polycarboxylate superplasticizers containing acrylate segments

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