Cement Paste Pore Solution Research Articles

Corrosion shielding effect of polyaluminium sulphate on metallic aluminium during the solidification of radioactive incineration bottom ash by low alkalinity cement

Radioactive incineration bottom ash containing metallic Al is difficult to be directly solidified in the cement matrix due to the generation of hydrogen gas during the reaction of aluminium with alkali pore solution of cement paste. In this study, the simulated incineration bottom ash (SIBA) containing metallic Al was successfully and directly solidified by polyaluminium sulphate (PAS)-modified low alkalinity cement (LAC), and the mechanism of the corrosion shielding effect of PAS on metallic Al was characterized by a range of analytical techniques. The results indicate that the cement waste form containing 29.56 wt% SIBA achieved a compressive strength of 16.6 MPa at 28 days of hydration, which increased by 13.3 % and 36.1 % after freeze-thawing test and immersion test, respectively. The 42d cumulative fraction leached of Nd3+ and Ce3+ were 1.74×10−7 cm and 3.40×10−7 cm, respectively. The corrosion degree and corrosion rate of Al sheets in LAC with PAS addition was much lower than that without PAS at early and late age hydration, by transforming thick porous corrosion layer to thin dense one. The mineral phase of corrosion product remained as bayerite (Al(OH)3), regardless of whether PAS was added. The addition of PAS reduced the hydrogen gas generation and prevented the dissolution of Al(OH)4- from metallic Al sheet. The hydrolysis of PAS produced a large amount of Al(OH)4- in pore solution, which extended the pH range for Al(OH)3 passivation by preventing the transformation of Al(OH)3 protection layer on the Al sheet surface to Al(OH)4- in the pore solution, and accelerated the formation of ettringite to decrease the pH of pore solution. This study cast the light on the direct solidification of metallic-aluminium-containing incineration bottom ash or Al bulks by cement-based materials without the need for complex pretreatment processes.

Unraveling polycarboxylate superplasticizer (PCE) compatibility in muscovite-blended cement paste through aggregation mechanisms

Muscovite is a common harmful mineral in manufactured sand, and has always led to the poor compatibility of superplasticizers in fresh concrete. Currently, the failure mechanism is usually explained by competitive adsorption and interlayer adsorption. In addition to the adsorption point of view, as a kind of surfactant, the self-aggregation conformation of superplasticizers in solutions also requires attention. This study explored the compatibility of polycarboxylate superplasticizer (PCE) in cement paste containing muscovite and explained the failure mechanism from the PCE aggregation point of view. Results showed that at the saturated dosage of PCE (0.14 wt%), the introduction of 6 wt% muscovite resulted in a complete loss of fluidity. In the pore solution of cement paste blended with muscovite, the PCE exhibited a lower critical micelle concentration (CMC) and larger aggregation size. The aggregation of PCE is due to the high ionic concentration in cement paste with muscovite, which increases the hydrophobic interaction between PCE and counter ion.

Effect of Poly(ethylene glycol)–Poly(propylene glycol) Triblock Copolymers on Autogenous Shrinkage and Properties of Cement Pastes

This study investigates the hydration, microstructure, autogenous shrinkage, electrical resistivity, and mechanical properties of Portland cement pastes modified with PEG-PPG triblock copolymers with varied molecular weights. The early age properties including setting time and hydration heat were examined using the Vicat test and isothermal calorimetry. The hydration products and pore size distribution were analyzed using thermogravimetric analysis (TGA) and nitrogen adsorption, respectively. Mechanical properties and electrical resistivity were evaluated using the compressive strength test and electrochemical impedance spectroscopy (EIS). It was shown that the addition of the copolymers reduced the surface tension of the cement paste pore solution due to the presence of a hydrophobic block (PPG) in the molecular structure of the copolymers. The setting time and hydration heat were relatively similar in the control paste as well as the pastes modified with the copolymers. The results showed that copolymers were able to reduce the autogenous shrinkage in the paste due primarily to a reduction in pore solution surface tension. TGA showed a slight increase in the hydration degree of the paste modified with the copolymers. The compressive strength was reduced in the pastes modified with the copolymers that showed an increased volume of air voids. The addition of copolymers did not affect the electrical resistivity of the pastes except in the case where there was a large volume of air voids, which acted as electrical insulators.

Alkali metal distribution in composite cement pastes and its relation to accelerated ASR tests

Accelerated testing of alkali silica reaction (ASR) in concrete at elevated temperatures of 38 and 60 °C has an unknown impact on the alkali metal distribution in the cement paste. This paper investigates how the alkali metals released from hydrating Portland cement, limestone, and SCMs distribute between non-reactive and unreacted phases, C-A-S-H, and the pore solution. The SCMs investigated were fly ash and a volcanic pozzolan. The hydrate assemblage and pore solution of cement pastes cured at 20, 38 and 60 °C were analysed and related to the expansion of concrete prisms. There is little difference in alkali metal distribution at 20 and 38 °C, whereas curing at 60 °C has a large impact for the SCM containing blends. At alkali metal concentrations in the pore solution below 0.5 mol/L (Na + K) expansion of concrete was suppressed. Pore solution analysis could be used to screen new SCMs for ASR mitigation.

Effect of low temperature calcined electrolytic manganese residue on the early-age hydration of cement paste

Low temperature calcination is an appropriate method to pretreat the electrolytic manganese residue (EMR). 180℃ is selected as an optimal temperature to apply to the present study, since the hemihydrate gypsum formed at 180℃ can improve the reactivity of EMR at no expense of considerable energy consumption and environmental pollution. This study examines how 180 °C-calcined EMR affects the composition of the pore solution and solid phases of cement paste as well as the hydration kinetics at early ages. The results indicate that the inhibition of EMR on the early-age hydration of cement paste mainly results from the dissolution behavior of hemihydrate gypsum in 180℃-calcined EMR during the 6 h-12 h period. A large-scale dissolution of hemihydrate gypsum after 6 h, released from EMR, leads to an increased Ca and S concentrations at the expense of a postponed consumption of gypsum, thus a reduced C3A reaction and a lower ettringite formation rate. In addition, the adding EMR significantly decreases the degree of pore solution in supersaturated state concerning portlandite (CH) and calcium silicate hydrate (C-S-H) gel during the 6 h-12 h period, thus hindering the early formation of hydration products by an inhibited C3S reaction. Moreover, the inhibition mechanism of 180℃-calcined EMR during the 6 h-12 h period is further emphasized on the early-age hydration.

How to Measure the Absorption and Desorption Curves of Superabsorbent Polymers in the Presence of Calcium Ions

The absorption and desorption curve of superabsorbent polymers (SAP), which reflects key information of the maximum absorbency and retention capacity, is crucial for the mix designs of internally cured concretes. In this paper, the effect of amount of Ca2+ on the absorption and desorption curve of SAP is studied. Results show that the proportion between amount of Ca2+ and SAP mass has a notable influence on the absorption and desorption curve of SAP, whether in tap water or mimicked pore solution of cement paste. Considering the important effect of amount of Ca2+, it is suggested that researchers need to determine the relationship between the retention capacity and the ratio of amount of Ca2+ to SAP mass in advance before formal measurement using classic tea bag method or filtration method. Furthermore, from the view of the ion exchange equilibrium between SAP and Ca2+, we discussed the mechanism that amount of Ca2+, concentration of Ca2+, SAP type, alkalinity, etc. have decisive effect on the absorption and desorption curve.

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

AbstractThe effect of triethanolamine (TEA) at various dosages on the early performance of cement paste was systematically evaluated through the techniques of rheological measurements, penetration tests, and ultrasonic pulse velocity. The correlation of early performance to the chemical hydration process was analyzed by calorimetry, zeta potential, in situ XRD, and pore solution analysis. It is found that the effect of TEA on the early performance of cement paste is strongly dependent on its dosage. With the TEA dosage below 0.1 wt%, the setting and microstructural development of cement paste are retarded. Meanwhile, the yield stress of fresh paste is decreased due to the increasing zeta potential of cement grains. The promoted formation of ettringite (AFt) and monosulfate (AFm) caused by TEA decreases the rheological retention ability. At dosages ≥0.2 wt%, the reaction of aluminate‐containing phases is greatly accelerated and a flash setting is observed. Besides, the importance of ferric phase on the reaction of cement with TEA is highlighted. At a low dosage, TEA prefers to accelerate the dissolution of tetracalcium aluminoferrite (C4AF) first and increases the [Fe] in the pore solution of cement paste. In cement without C4AF, the retardation of TEA on silicate phase hydration is significantly alleviated.

Chemical properties of pore solution of hardened cement pastes with mineral additions

This paper presents the influence of mineral additions in blended cement, or ‘green’ concrete, on the divalent ions of the cement paste pore solution. Because of the lack of data concerning the direct comparison between the pore solution of cement and mineral additions-based material, six types of hardened cement pastes were tested. For this purpose, Portland cement (CEM I or CEM V) and mineral additions (limestone filler, fly ash, blast-furnace slag and silica fume) were used. Results from chemical analyses by ionic chromatography show significant concentrations of divalent ions, such as sulfates and calcium, in the pore solution. In fact, the reference cement paste based on CEM I contains about 1.8 mmol/l of calcium and 1.6 mmol/l of sulfates. However, the use of mineral addition significantly modifies the pore solution. In particular, a substitution of cement by 10% of silica fume increases the calcium and sulfates concentrations to 12.2 mmol/l and 6.7 mmol/l, respectively. This change in the chemical composition, the pH and the ionic strength should be taken into account in multispecies transfer modelling and the thermodynamic equilibrium. The time evolution of the chemical composition, pH and ionic strength of the pore solutions was also investigated.

Compatibility between thermochromic pigments and Portland cement-based materials

Encapsulated reversible thermochromic (ERTC) pigments with optical properties that change reversibly with temperature have been used in building coatings to improve energy efficiency and reduce environmental impact of buildings. This work presents a detailed characterization of commercial ERTC pigments useful for this application and an analysis of their compatibility with the aggressive cementitious matrix. Chemical reactions involving the pigment are identified through the analysis of the solid phase and pore solution of a white Portland cement paste and a mortar with calcareous aggregate during the first 3 h of hydration. The results indicate that a low concentration of potassium ions in the aqueous phase is necessary with respect to the concentration of pigment microcapsules to achieve a proper stability of the thermochromic response. This condition is fulfilled in the case of mortar formulations used for building coatings, thus ensuring the viability of developing a chemically stable thermochromic mortar coating.

Effects of leaching and chloride migration on the microstructure and pore solution of blended cement pastes during a migration test

This paper investigates the influence of the multispecies diffusion and leaching phenomena on the thermodynamic equilibrium and microstructure of cementitious materials containing mineral additions during a chloride migration test. Because of a lack of data on these effects, the aim of this study was to quantify changes in the material’s microstructure during an experimental program based on mercury intrusion porosimetry before and after chloride exposure, scanning electron microscopy and chemical analyses of the materials. The experimental results highlight a modification of pore size distribution and a reduction of up to 60% in total porosity after chloride transfer. This was due to chloride interactions which led to the formation of new compounds in the porosity range of 7–70 nm. These compounds were investigated by elemental analyses and quantified.Moreover, a chloride migration test was performed in order to investigate the leaching of pore solution ions in the two compartments of the migration cell. The results enabled us to: (i) quantify the concentration of ions that diffused into/from the material, and (ii) estimate the kinetics of calcium release and the quantity of portlandite dissolved in the material. The chloride diffusion coefficient of the materials ranged between 2.38 × 10−12 and 5.96 × 10−12 m2/s, the kinetics of calcium, expressed as a flux, were between 1.8 × 10−2 and 1.2 × 10−1 mmol.m−2.s−1.

The significance of dispersion of nano-SiO2 on early age hydration of cement pastes

Nano-materials have various promising properties to concrete material. However, the poor dispersion of nano-materials remains to be a big challenge which impairs the target performances and thus increases the economic cost. In this study, we focused on one of the most widely used nano-materials, nano-SiO2 and investigated the influence of its dispersion on the early age hydration of cement pastes. A recently developed method was applied to chemically graft polycarboxylate superplasticizer onto nano-SiO2 particles to produce well dispersed particles with the shell core structure (nano-SiO2@PCE). Dispersity of nano-SiO2@PCE in deionized water (DI water) and in simulated pore solution of cement pastes was carefully characterized by Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM), and Fourier Transform Infrared Spectrometer (FTIR) techniques. The effects of nano-SiO2 dispersion on the early age hydration of cement pastes were investigated. The results showed that with good dispersion only 0.5% by mass of nano-SiO2 can significantly accelerate hydration. The retarding effect unintentionally caused by PCE was observed to influence particularly on the length of induction period rather than other stages of hydration. BNG model was used in the end to quantitatively analyze and shed more lights on the influence of nano-SiO2 on the kinetics of C3S hydration.

A Study on the Effect of Ceramic Polishing Powder on the Nucleation and Growth of Hydrates in Cement Paste

The production of cement leads to a large amount of CO2 emission. Using industrial waste slag, such as ceramic polishing powder (PP), to replace part of Portland cement can reduce the pollution caused by the cement industry and solid waste disposal. In order to use PP as a replacement for cement, its effects on the properties of cement paste need to be clarified. In this study, the effect of PP on the nucleation and growth of hydrates in cement paste at very early ages was investigated. Quartz was used as a reference. The interactions of their surface with various ions in cement paste solution, which has an important effect on the nucleation and growth of hydrates, were studied by using the zeta potential test. The morphology of the nucleus and crystal of hydrates was investigated by using SEM. The zeta potential measurements showed that the affinity of the surface of PP and quartz to ions in the pore solution of cement paste is similar. The image of SEM indicated that there is also not much difference in the crystallization of hydrates on the surfaces of PP and quartz. These evidences suggested that PP has similar surface charge properties as quartz, and its effects on the properties of cement paste are the same as that of quartz. From the viewpoint of the effect on very early hydration, PP can be used in cement paste, similar to quartz power.

Microstructural evolution/durability of magnesium phosphate cement paste over time in neutral and basic environments

This study investigates the evolutions of the mineralogy, pore solution and porosity of magnesium potassium phosphate cement pastes (MKPC) over time in neutral and basic environments, media that MKPC pastes might encounter when used as patch repair materials or as stabilization materials for hazardous wastes. Mineralogy evolutions were characterized by X-ray diffraction/Rietveld (XRD) and thermogravimetric analyses (TGA) and completed with scanning electron microscopy (SEM/EDX) microanalyses. Pore solution compositions (ICP-OES, IC) and the porosity of the materials were also analyzed. The results showed an amorphization of MKPC pastes over time that might be related to structural changes for the K-struvite phase. Achieving chemical equilibrium between the cementitious waters and the MKPC pore solution can result in porosity evolutions within the materials. Transport and mechanical changes might be expected, especially for MKPC pastes kept in basic media, since K-struvite [MgKPO4·6H2O], could be partially dissolved, leading to a higher total pore volume.

“ACEME”: Synthesis and characterization of reactive silica residues from two stage mineral carbonation Process

In this experimental work we synthesized, characterized, and investigated the reactivity of silica‐enriched residue materials produced from low pressure, low temperature dissolution applicable to a two stage mineral carbonation process. XRF and XRD analysis indicated that 66 wt % of silica‐enriched residue (SER) produced from dissolution of heat activated lizardite comprised amorphous silica. We also treated SER with nitric acid to produce amorphous acid treated silica‐enriched residue (ATSER) with over 88 wt % silica. Dissolving these synthesized materials in highly alkaline solution with pH similar to cement paste pore solution for 28 days showed that all synthesized materials displayed some level of Si solubility. ATSER showed the most rapid rate of Si extraction, higher than silica fume (a commercial pozzolanic cement substitute), followed by silica‐enriched residue (SER) which had a faster rate of Si extraction compared with Portland cement as a standard. © 2018 American Institute of Chemical Engineers Environ Prog, 38:e13066, 2019

The influence of air cooled blast furnace slag (ACBFS) aggregate on the concentration of sulfates in concrete’s pore solution

This study evaluates changes in chemical composition of artificial pore solutions (APSs), representing the actual pore solutions of plain, binary, and ternary cementitious systems, resulting from contact of APSs with air cooled blast furnace slag (ACBFS) aggregate. The maximum increase in the sulfate concentration of APSs was 12.23 and 16.87 mmol/L for, respectively, the coarse and crushed ACBFS aggregate. More than 40% of the total sulfate released by ACBFS aggregate occurred within the first 3 days of contact with APSs. After 28 days of contact with ACBFS aggregates, the pore solution of plain cement paste had the highest sulfate concentration.

Study of the pore solution and the microstructure of mineral additions blended cement pastes

In this paper, the influence of mineral additions on the microstructure and the chemical composition of the pore solution of cementitious materials is investigated. For this purpose, hardened cement pastes based on Portland cement CEM I are used. In order to study the influence of the cementitious materials composition on their microstructure and pore solution, a part of the cement is substituted by different mineral additions (limestone filler, fly ash, blast furnace slag and silica fumes). Experimental tests covered measurement of chloride diffusion coefficient by migration test and water and mercury porosimetry. Furthermore, pore solutions are extracted by pressing from cement pastes and analyzed by ionic chromatography. Results show that the substitution of cement by mineral addition modifies the total porosity and the pore sizes distribution of the blended cement pastes tested. Chemical analyses showed that all the tested pore solutions are mainly composed by sodium and potassium. A significant concentration of divalent ions, such as sulfates and calcium, is also noticed. The substitution of cement by mineral addition also significantly modifies the pore solution of cement pastes. In fact, a substitution of cement by 10% of silica fume decreases the alkalis concentrations and increases the sulfates and calcium ones. Thus, the divalent species (Ca2+ and SO42-) should be taken into account for the chloride diffusion modelling unlike the current models of the literature. Results of this chemical investigation could be used as initial and boundary conditions in the modeling of aggressive species transport through porous construction materials.

Influence of lead and vanadium on the setting of Portland cement CEM I 52,5N SR3/NA

Lead and vanadium are known retarder of cement setting. However, during the tests conducted in the laboratory, it was discovered the uncommon effect of this metals, i.e., they accelerated cement to set. This was caused by ettringite crystallization, because the alite was covered by an impermeable layer formed probably the amorphous hydroxides of these metals. The examination was shown that the used industrial cement containing natural anhydrite as cement set regular and the clinker in this cement had very low content of sulfates. The determination of the concentration of sulfate ions in the cement paste pore solution has shown that it was very low at the beginning of hydration, because of the low rate of anhydrite dissolution. The conclusion of this study was that the influence of these two heavy metals is dependent on the sulfate ions concentration in the cement paste pore solution. The addition of 0.5% mass of hemihydrate to the cement caused the normal retarding effect of lead and vanadium.

Extraction and analysis of pore solution of cement paste: desaturation and resaturation cycles using a non-destructive method by gas injection

The aim of the present study is to extract the pore solution from cement pastes and mortars with high W/C ratio by a non-destructive method. The sample is placed in a hydrostatic cell under a confining pressure and an inert gas under high pressure is applied at one end to force a movement of interstitial water. As a result of the non-destructive nature of this method, successive extractions were carried out on cement pastes with W/C ratio equal to 0.7: the first one is directly performed on three initially saturated samples and the second one after drainage and resaturation by two chemically different solutions to observe the exchanges between the saturating solution and cementitious matrix. The chemical analysis results of K+, Na+, SO42−, Mg2+, Ca2+, Li+ and Sr2+ show that the volume of extracted water is representative of concentrations of the various ionic species present in a pore solution of cement pastes.

Coupled effect of viscosity enhancing admixtures and superplasticizers on rheological behavior of cement paste

The coupled effect of viscosity enhancing admixtures (VEA) and superplasticizer (SP) on the rheological behavior of cement paste was investigated in this work. Two types of VEAs, including hydroxypropyl methylcellulose (HPMC) and Welan gum, and two types of SPs, i.e. polycarboxylate (PCA) and polynaphthalenesulfonate (PNS) were used as admixtures for cement paste. Rheological curves of cement paste and simulated pore solution containing VEA and SP were tested. Simulated pore solution test results show that molecules of different SPs may generate different effects on the viscosity of VEA solutions. Hershel-Bulkley (H-B) model was used to fit rheological curve of cement paste. Strong interaction between PNS and HPMC was observed in this work.

Insights into the mechanisms of nucleation and growth of C\u2013S\u2013H on fillers

A complete understanding of the mechanisms upon which a filler acts in a cement-based material, e.g. as a C–S–H nucleation and/or growth-inducing factor, is of high importance. Although various studies report on accelerated cement hydration in the presence of fillers, the reason behind these observations is not completely understood yet. This work contributes to this subject, by providing an experimental evidence on the (electro) chemical aspects of the filler surface modification in the model solution, simulating the pore solution of cement paste. The nature of the various interactions with regard to the affinity of a filler surface towards C–S–H nucleation and growth was discussed in detail in this work with regard to zeta potential measurements of micronized sand and limestone particles in the model solutions. These results are further supported by microscopic observations of morphology and distribution of hydration products on the filler surfaces, together with considerations on thermodynamic principles in view of hydration products formation and distribution. The C–S–H nucleation and growth appeared to be due to the interactions between a filler surface and calcium ions in the pore solution. These interactions were determined by the chemical nature of the filler surface. The interaction mechanisms were found to be governed by relatively weak electrostatic forces in the case of micronized sand. This was reflected by a non-significant adsorption of calcium ions on the filler surface, resulting in non-uniformly distributed and less stable C–S–H nuclei. In contrast, the nucleation and growth of C–S–H on limestone particles were predominantly determined by donor–acceptor mechanisms, following moderate acid–base interactions. Consequently, a strong chemical bonding of calcium ions to a limestone surface resulted in a large amount of uniformly distributed C–S–H nuclei.