DOI: 10.20350/digitalcsic/17087
title: Influence of DEIPA and TIPA on the hydration and microstructure of model cements

description: C3S and model cement pastes were prepared by mixing 10 g of the powder with 0.35 g and 0.4 g of ultrapure water, respectively. Pastes were initially mixed with a 2-bladed propeller stirrer (JANKE KUNKEL IKA-WERK RW 20) at 200 rpm for 30 seconds and 800 rpm for 3 minutes. Dosages of 0.02 wt% and 0.1 wt% of DEIPA and TIPA by weight of powder (bwp) were included into the water, being these dosages in range of those usually studied in the literature. An isothermal calorimeter TAM Air (TA Instruments) was used to measure the hydration kinetics of the both synthetic phases. Pastes were externally mixed as described above and 5 g of each paste was introduced in the device set at 25 oC. Data obtained during the first 30 minutes were not considered in the analysis, as this is the time needed for the equilibration of the devise after placing the sample. The reaction of C3S and model cement pastes was quenched after 8 h, 1, 2 and 7 days by solvent exchange. For this purpose, a suspension of 10 g of isopropanol and 1 g of paste was stirred for 1 minute and filtered afterwards through a nylon filter with a pore size of 0.45 µm. A X´Pert PRO MPD (PANalytical) diffractometer in a Θ-2Θ configuration, using a CuKα1 (1.5406 Å) radiation (monochromatized with a primary Ge (1 1 1) monochromator) and a detection system that consists of a X´Celerator RTMS (Real Time Multiple Strip) constituted by 128 Si detectors, have been used to collect the data to carried out the phase identification including Rietveld quantitative analysis. This equipment was located at Servicios Centrales de Apoyo a la Investigación (University of Malaga). A scan range between 5o and 70o and a step size 0.0167o were used in the measurement of the sample. Quartz (Silicon (IV) oxide, 99.5%, Alfa Aesar) was used as internal standard [27] to quantify the phase content. Rietveld analyses were done with TOPAS software (Bruker). Due to the different microabsorption of the different phases a Brindley microabsorption correction was done as previously explained in the literature [14], [24]. 27Al MAS NMR spectra were obtained with a Bruker AVANCE-400 spectrometer (9.4T magnetic field). A 4 mm (outer diameter) ZrO2 rotor was used at a spinning frequency of 10 kHz. The spectra were obtained at a resonance frequency of 104.3 MHz. π/6 pulses of 2 μs, a recycle delay of 5 s and 400 scans were applied during the measurements. Chemical shift values of NMR resonances were referred to 1 M solution of AlCl3 aqueous solutions. Thermogravimetric analysis (TGA) experiments were done by using a TGA-DCS-DTA Q600 (TA instruments) equipment. Around 40 mg of powder in an alumina (Al2O3) crucible was heated from 25 oC up to 1000 oC with a rate of 10 oC/min under a 100 ml/min flow of N2. Prisms of 1 x 1 x 0.5 cm3 of C3S and model cement pastes were prepared and hydrated during 7 days at 25 oC and 99% RH. The hydration was quenched by submerging the samples in isopropanol for 5 days. Sample were consequently kept at low vacuum in a desiccator. The samples were embedded in epoxy resin, polished and carbon coated and the microstructure of samples was measured by Energy dispersive X-ray (EDX) using an Oxford Instruments X-Max detector. Total porosimetry of C3S and model cement pastes at 7 days of hydration were determined by a Micromeritics AutoPore IV 9500 V porosimeter. 20 g of Ca(OH)2 (powder QP, Panreac) and 40 g of ultrapure water containing 0 wt% of admixture, 0.02 wt% DEIPA, 0.1 wt% DEIPA, 0.02 wt% TIPA and 0.1 wt% TIPA were stirred for 3 h at 25 oC to determine the adsorption of the admixtures on the Ca(OH)2 [28]. The suspensions were afterwards centrifuged at 4000 rpm during 10 minutes. The aqueous phase was filtered through a 0.45 μm membrane filter and the total organic carbon content was determined on a SHIMADZU TOC-VCSH/CSN total organic carbon (TOC) analyser. The amount of admixtures adsorbed on the Ca(OH)2 was measured after 3 h of hydration by by depletion method.
description: This study investigates the impact of diethanol-isopropanolamine (DEIPA) and triisopropanolamine (TIPA) on hydration kinetics, phase assemblage and microstructure of C3S and a model cement (which clinker only contains C3S and C3A) pastes. Results showed that DEIPA initially delayed C3S reaction, probably due to the formation of DEIPA-Ca2+ complexes that slow down the supersaturation required for the nucleation of hydrates and/or by adsorbing onto the hydrates. In contrast, TIPA did not significantly modify the hydration kinetics of both studied cementitious materials. Furthermore, DEIPA adsorbs onto Ca(OH)2 and has a relevant impact on the amount of portlandite and morphology and stoichiometry of C-S-H. In particular, DEIPA decreased the amount of portlandite and favored the formation of a C-S-H with a higher Ca/Si than the one formed in plain C3S pastes. DEIPA also favored the intermixing of portlandite and AFm phase with C-S-H in C3S pastes and model cement pastes, as well as the formation of greater plates of portlandite in the latter. In contrast, TIPA did not impact the C-S-H stoichoimetry and the amount of portlandite, but a higher intermixing of C-S-H with portlandite and AFm has been observed in both model cementitious systems. The observed low impact of DEIPA and TIPA on the reactivity of the C3A and the amount of early aluminate hydrates in model cements in comparison to previous studies done on Portland cement, highlights the relevance of the presence of Fe on the working mechanims of both alkanolamines and in particular on the enhancement of C4AF reactivity by the formation of Fe-amino complexes.
description: 16 Files: 27Al MAS NMR spectra of model cements after 7 days; Adsorption of DEIPA and TIPA on portlandite; Heat flow and cumulative heat of C3S and model cement; Mineralogical composition of C3S and model clinker; Particle size distribution of C3S and model clinker; Percentage of bound water at 1, 2 and 7 days of C3S and model cement pastes; Portlandite content (%) vs degree of hydration (%) for C3S and model cement pastes; Portlandite content of C3S and model cement pastes; Weight percentage of C3S and amorphous phase and C3A in model cement pastes; Weight percentage of C3S and amorphous phase in C3S pastes; XRD patterns of C3S and model cement; XRD patterns C3S 8h, 1d, 2d, 7d; XRD patterns model cement 8h, 1d, 2d, 7d; TGA curves at 8h, 1. 2 and 7 days of C3S pastes; TGA curves at 8h, 1. 2 and 7 days of model cement pastes