Effect of compounding of sodium tripolyphosphate and super plasticizers on the hydration of α-calcium sulfate hemihydrate

Abstract

The inhibition and its mechanism of sodium tripolyphosphate (STP) composited with super plasticizers (SPs) on hydration of α-calcium sulfate hemihydrate were studied by setting time, strength, hydration heat, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electronic probe micro analysis (EPMA), scanning electron microscopy (SEM) and differential scanning calorimeter (DSC) measurements. The experimental results show that compared with STP addition, compositing STP with polycarboxylate (PC) plasticizer, the fi nal setting time is prolonged from 0.5h to 2hs. While formulating STP with naphthalene-based plasticizer (NAP) or sulfonate melamine formaldehyde plasticizer (SMF), the fi nal setting time is reduced to quarter of an hour. Similar changes can also be found in the rate of exothermic hydration and hydration degree. Formulating STP with suitable addition of PC can enhance the strength, while compositing STP and NAP or SMF weakens the strength. Besides, adding STP or STP and SMF, obvious movement (more than 1ev) of binding energy of Ca2p1/2 and Ca2p3/2 is detected. Compared with STP addition, content of the characteristic element (P) of STP is cut down form 1.1% to 0.49% by compositing STP with SMF. Furthermore, as hydration age increases, hydration inhibition in the presence of admixtures weakens and even disappears within 56 h.

Effect of superplasticiser and sodium tripolyphosphate on fluidity of cement paste

“…When the dosage of STPP is 0 . 025%, it significantly prolongs the setting time of gypsum (Pan and Wang, 2011). In cement hydration, STPP reacts with calcium ions in solution to inhibit the formation of hydration products and thus delay hydration.…”

Fluoro​an​hydrite Compositions Plasticized by Polycarboxylate Esters

“…Polycarboxylate superplasticizer is considered the most effective dispersant of cement-based materials and also demonstrates excellent ability to disperse gypsum particles (Tan et al, 2018;Neuville et al, 2012;Guan et al, 2010). Adding an aqueous solution of polycarboxylate esters increases the strength (Sakthieswaran & Sophia, 2018;Pan & Wang, 2011), reduces water demand (Martin, 2015) and increases the consistency of mixtures (Müller & Hampel, 2018). High workability of mixtures modified with polycarboxylate esters can significantly expand their field of application and makes them suitable for self-leveling floor screeds.…”