Portland Cement Samples Research Articles

Simultaneous adsorption at 25 °C and the peculiarities of gyrolite substituted with heavy metals

The simultaneous adsorption kinetic parameters of synthetic gyrolite (200 °C, 48 h) for heavy metals ions (zinc, copper, manganese, nickel, iron and cobalt ions) as well as the influence of this compound on the hydration of ordinary Portland cement were studied. The examination revealed that the intercalation of heavy metal ions into the crystal structure of gyrolite proceeds intensively at the beginning of the process, because after 30 s the amount of adsorbed ions reaches 93 %. It was estimated that the reactions of simultaneous adsorption are not reversible, i.e., almost all heavy metal ions are chemisorbed by gyrolite. The experimental data were adequately described by pseudo-second Ho kinetic model: The largest adsorption rate constant is typical for iron ions (1.65 g min−1 mg−1), while the minimum value—for cobalt ions (0.45 g min−1 mg−1). It was found that gyrolite with impure heavy metal ions retained very good adsorption properties for the alkaline and alkaline earth ions by accelerating the early hydration of ordinary Portland cement samples. Meanwhile, at later stages of hydration, this compound affects as the usual pozzolanic additives because the amount of cumulative heat grew with the increasing amount of gyrolite in the samples: from 282 J g−1 in pure ordinary Portland cement samples to 301 J g−1 in samples with 15 % of gyrolite with impure heavy metal ions. It was determined that the additive of gyrolite with impure heavy metal ions do not have a significant effect on the properties of cement stone.

Effects of triisopropanol amine, sodium chloride and limestone on the compressive strength and hydration of Portland cement

The effect of triisopropanol amine (TIPA), sodium chloride (NaCl) and limestone (LS) on compressive strength and hydration of Portland cement were studied using Design of Experiment (DoE) and isothermal calorimetry, respectively. The results showed that combination of TIPA and NaCl could increase both early age and later age compressive strength of Portland cement mortars and Portland cement–limestone mortars. No major interactive effects on strength enhancement were observed for these three additives. However, the results of isothermal calorimetry showed clear interaction between TIPA and NaCl. It was found that NaCl increased the effectiveness of TIPA through promotion of two transitions: (i) conversion of AFt to AFm for Portland cement sample, (ii) conversion of carboalumiante phases for Portland–limestone cement sample.

A COMSOL–GEMS interface for modeling coupled reactive-transport geochemical processes

An interface was developed between COMSOL MultiphysicsTM finite element analysis software and (geo)chemical modeling platform, GEMS, for the reactive-transport modeling of (geo)chemical processes in variably saturated porous media. The two standalone software packages are managed from the interface that uses a non-iterative operator splitting technique to couple the transport (COMSOL) and reaction (GEMS) processes. The interface allows modeling media with complex chemistry (e.g. cement) using GEMS thermodynamic database formats. Benchmark comparisons show that the developed interface can be used to predict a variety of reactive-transport processes accurately. The full functionality of the interface was demonstrated to model transport processes, governed by extended Nernst–Plank equation, in Class H Portland cement samples in high pressure and temperature autoclaves simulating systems that are used to store captured carbon dioxide (CO2) in geological reservoirs.

Geochemical alteration of wellbore cement by CO2 or CO2 + H2S reaction during long‐term carbon storage

AbstractCement samples were reacted with CO2‐saturated synthetic groundwater, with or without added H2S (1 wt.%), at 50°C and 10 MPa for up to 13 months (CO2 only) or for up to 3.5 months (CO2 + H2S) under static conditions. After the reaction, X‐ray computed tomography (XCT) images revealed that calcium carbonate (CaCO3) precipitation occurred extensively within the fractures in the cement matrix, while micro‐fractures with aperture size <∼50 μm at the cement‐basalt interface were completely sealed by CaCO3 precipitation. Exposure of a fractured cement sample to CO2‐saturated groundwater (50°C and 10 MPa) over a period of 13 months demonstrated progressive healing of cement fractures by CaCO3 precipitation. After reaction with CO2 + H2S‐saturated groundwater, CaCO3 precipitation also occurred within the cement fracture as well as along the cement‐basalt caprock interfaces. X‐ray diffraction analysis showed that major cement carbonation products of the CO2 + H2S‐saturated groundwater were calcite, aragonite, and vaterite, all consistent with cement carbonation by CO2‐saturated groundwater. While pyrite is thermodynamically favored to form, due to the low H2S concentration it was not identified by XRD in this study. The cement alteration rate into neat Portland cement samples by CO2‐saturated groundwater was similar at ∼0.02 mm/d based on XCT images, regardless of the cement‐curing pressure and temperature (P‐T) conditions, or the presence of H2S in the groundwater. The experimental results imply that wellbore cement with micro‐fractures within the cement matrix or along the cement‐caprock interface (<∼200 μm aperture under current experimental conditions) is likely to be healed by CaCO3 precipitation during exposure to CO2‐ or CO2 + H2S‐saturated groundwater. Published 2016. This article is a U.S. Government work and is in the public domain in the USA

White Ordinary Portland Cement blended with superfine steel dust with high zinc oxide contents

The addition of steel waste in the form of slags and dust to cement is beneficial to the environment because waste can be immobilized, and thus, decreasing the waters contamination. In this paper, paste and mortar-based Portland cement samples with up to 70.0wt% of steel dust were investigated. Since it is known that for one ton of Portland cement fabricated 900kg of CO2 are emitted to the environment, the addition of steel waste to cement is very beneficial. Moreover, since steel dust reduces the amount of needed cement in concrete, it reduces the final cost of concrete significantly. Additionally, the manufacturing processing was conducted entirely at room temperature; therefore, the negative impact of cement in the environment is reduced.Scanning electron microscopy and X-ray diffraction characterization were conducted in order to investigate the microstructure of the samples. In addition, compression, density, and flow table tests were done over all samples. Thermo-gravimetric tests were performed to analyze the waste thermal stability. The effect of the potential hazardous components of this waste in water was analyzed through leachability tests. For all samples, compressive strength ranged from 73 to 2.5MPa. The lowest strength value corresponded to 70wt% of waste. Results show a solution for using this waste as admixture in cements and concrete, and therefore as a method for reducing cement paste in buildings and infrastructure.

Deconvolution of the particle size distribution of ProRoot MTA and MTA Angelus

Objective Mineral trioxide aggregate (MTA) cements contain two types of particles, namely Portland cement (PC) (nominally 80% w/w) and bismuth oxide (BO) (20%). This study aims to determine the particle size distribution (PSD) of PC and BO found in MTA.Materials and methods The PSDs of ProRoot MTA (MTA-P) and MTA Angelus (MTA-A) powder were determined using laser diffraction, and compared to samples of PC (at three different particle sizes) and BO. The non-linear least squares method was used to deconvolute the PSDs into the constituents. MTA-P and MTA-A powders were also assessed with scanning electron microscopy.Results BO showed a near Gaussian distribution for particle size, with a mode distribution peak at 10.48 μm. PC samples milled to differing degrees of fineness had mode distribution peaks from 19.31 down to 4.88 μm. MTA-P had a complex PSD composed of both fine and large PC particles, with BO at an intermediate size, whereas MTA-A had only small BO particles and large PC particles.Conclusions The PSD of MTA cement products is bimodal or more complex, which has implications for understanding how particle size influences the overall properties of the material. Smaller particles may be reactive PC or unreactive radiopaque agent. Manufacturers should disclose particle size information for PC and radiopaque agents to prevent simplistic conclusions being drawn from statements of average particle size for MTA materials.

Indicator of carbonation front in concrete as substitute to phenolphthalein

A method to substitute the recognized toxic phenolphthalein in mortars and concretes is proposed. It comprises putting a portland cement sample in contact with an innocuous solution, curcumin-based, which acts as an indicator yielding a red color in areas where there is alkaline reserve (pH ~12) and yellow in carbonate zones (pH ≤9).Solutions containing curcumin extracted from commercial turmeric powder and from the rhizomes of the turmeric plant were prepared by using ethanol as a solvent. Subsequently it has been experienced with solutions in which curcumin has been used with a purity of over 95%.The dissolution of curcumin can be used with the same reliability as phenolphthalein in the carbonation process with the advantage that it is safe and presents no health risks.

Effect of different mixing methods on the physical properties of Portland cement.

BackgroundThe Portland cement is hydrophilic cement; as a result, the powder-to-liquid ratio affects the properties of the final mix. In addition, the mixing technique affects hydration. The aim of this study was to evaluate the effect of different mixing techniques (conventional, amalgamator and ultrasonic) on some selective physical properties of Portland cement.Material and MethodsThe physical properties to be evaluated were determined using the ISO 6786:2001 specification. One hundred sixty two samples of Portland cement were prepared for three mixing techniques for each physical property (each 6 samples). Data were analyzed using descriptive statistics, one-way ANOVA and post hoc Tukey tests. Statistical significance was set at P<0.05.ResultsThe mixing technique had no significant effect on the compressive strength, film thickness and flow of Portland cement (P>0.05). Dimensional changes (shrinkage), solubility and pH increased significantly by amalgamator and ultrasonic mixing techniques (P<0.05). The ultrasonic technique significantly decreased working time, and the amalgamator and ultrasonic techniques significantly decreased the setting time (P<0.05).ConclusionsThe mixing technique exerted no significant effect on the flow, film thickness and compressive strength of Portland cement samples. Key words:Physical properties, Portland cement, mixing methods.

Feasibility of halogen determination in noncombustible inorganic matrices by ion chromatography after a novel volatilization method using microwave-induced combustion

A microwave-induced combustion (MIC) system based on the volatilization process was applied for subsequent halogen determination from noncombustible inorganic matrices. Portland cement samples were selected to demonstrate the feasibility of the proposed method, allowing the subsequent determination of Cl and F by ion chromatography (IC). Samples were mixed with high-purity microcrystalline cellulose, wrapped with a polyethylene film and combusted in quartz closed vessels pressurized with oxygen (20bar). Water and NH4OH (10, 25 or 50mmolL−1) were evaluated for Cl and F absorption, but water was selected, using 5min of reflux after volatilization. Final solutions were also suitable for analysis by pontentiometry with ion-selective electrode (ISE) for both analytes, and no difference was found when comparing the results with IC. The accuracy of the proposed method for Cl was evaluated by analysis of certified reference materials (CRMs), and agreement with certified values ranged from 98% to 103%. Results were also compared to those using the procedure recommended by the American Society of Testing and Materials (ASTM) for the determination of total chlorides (C114-13), and no difference was found. Volatilization by MIC using a mixture of cement, cellulose and a biological CRM was carried out in order to evaluate the accuracy for F, and recovery was about 96%. The proposed method allowed suitable limits of detection for Cl and F by IC (99 and 18mgkg−1, respectively) for routine analysis of cement. Using the proposed method, a relatively low standard deviation (<7%), high throughput (up to eight samples can be processed in less than 30min) and lower generation of laboratory effluents, when compared to the ASTM method, were obtained. Therefore, the method for volatilization of Cl and F by MIC and subsequent determination by IC can be proposed as a suitable alternative for cement analysis.

Strength, fragmentation and fractal properties of mixed flaws

Experiments on Portland cement samples containing mixed flaws are conducted to investigate the strength, fragmentation and fractal properties. Flaw geometry is a new combination of two edge-notched flaws and an imbedded flaw, which is different from those in the previous studies, where parallel or coplanar flaws are used. The physical implications of the shear-box test applied to result to rock slopes are studied. The physical and analytical fragmentation characteristics of preflawed samples are analyzed through the sieve test and fractal theory, respectively. Three different patterns of tensile cracks and shear cracks are observed. A sliding crack model is presented to elucidate the brittle failure flaws. In all of the cases of the shear-box tests, the coalescence is produced by the linkage of shear cracks, and two types of coalescence (Type C1 and Type C2) have been classified, which tend to confirm the observations from the numerical model and field of jointed rock slopes. The shear strength is a function of the flaw geometry and the shear–normal stress ratio. The result of sieve tests indicates that the fragment size distribution of fragments has the fractal property, providing a physical understanding of the fragmentation mechanism. The fragments under the shear-box test have fractal dimensions between 2.2 and 2.6, which are larger than those under the compression test but similar to those in the fault cores. The fragmentation in the case of Type C2 has a smaller fractal dimension, corresponding to a larger shear strength.

Quantification of Cement Hydration through Neutron Radiography with Scatter Rejection

The unique capabilities of neutrons to penetrate materials opaque to X-rays and at the same time to interact with hydrogen make neutron radiography a technique of choice for the nondestructive quantification of hydrogen-containing substances. However, scattering rather than absorption of neutrons by hydrogen atoms can substantially decrease the accuracy of this quantification. Various post-experiment data processing techniques were developed to correct and mitigate the effects of scattering. A complementary “hardware” solution is to simply eliminate the detrimental scattering component from the detected signal through the use of neutron collimators. Compact polycapillary collimators, merely a few millimeters thick, enable accurate, high spatial resolution quantification for a wide range of neutron scattering materials. This paper demonstrates the improved quantification of water absorption with sub- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\hbox{100}}~\mu\hbox{m}$</tex></formula> spatial resolution in <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$1 \times 1\times \hbox{2~cm}^{3}$</tex></formula> Portland cement samples. A compact polycapillary neutron collimator (2 mm thick) was used for scatter rejection in our experiments. The results of these measurements indicate that such devices can be attractive for studies where samples must be placed in quite close proximity (e.g., only a few centimeters or closer) from the neutron detector active surface.

A gas adsorption porosimetry analysis of Portland cement prepared by compaction vs. compaction with indirect ultrasonic agitation

Background: Mineral trioxide aggregate (MTA), is commonly used in endodontic and restorative procedures. Objective: Our objective was to introduce gas adsorption porosimetry as a viable method for evaluation of general porosity and specific pore characteristics of set Portland cement used in substitute for MTA, to investigate the effect of two different obturation methods (compaction and compaction in conjunction with indirect ultrasonic agitation of the cement paste), and to evaluate the correlation between the specific pore characteristics to compressive strength in general. Material and Methods: Portland cement samples were prepared and divided into two groups based on compaction techniques. An initial stereomicroscopic evaluation was done to assess any differences in appearance of pores randomly selected from either of the two experimental groups. Specific pore characteristics and compressive strength were quantified by a gas adsorption porosimeter and an Instron universal testing machine. A two tailed student t-test was used for statistical comparison of data, and a regression analysis was done to evaluate the correlation between each specific pore characteristic and compressive strength in general. Results: The gas porosimetry method provided measurable values relating to specific pore characteristics of Portland cement. The stereomicroscopy evaluation revealed marked differences between samples from the two groups, namely visibly larger pores both on the outside surface and in cross-sections of specimens prepared by the indirect ultrasonic activation method. Conclusions: Gas adsorption porosimetry is a feasible method for evaluation of specific pore characteristics of Portland cement and potentially other dental materials as well.

Comparison of Portland Cement (KS and API Class G) on Cement Carbonation for Carbon Storage

AbstractPortland cement is a common sealing material used in wellbores for geological carbon sequestration. Two types of portland cement were reacted with carbon dioxide (CO2) in supercritical, gaseous, and aqueous phases, under various pressure and temperature conditions, to simulate a cement-CO2 reaction along the wellbore from the carbon injection depth to the near surface. In this study, two types of cement were used: Korean Standard (KS) portland cement (Type I) and American Petroleum Institute (API) class G portland cement. The top halves of hydrated portland cement sample columns (14-mm diameter×90-mm long;water-to-cement ratio=0.5), including additives such as fly ash, were reacted with CO2 in an unsaturated (dry, no contact with water) condition. The bottom halves of the columns were reacted with CO2 in a saturated (wet, in contact with water) condition. These conditions were maintained under high pressure (8 MPa) and temperature (40°C) for 10 and 100 days to determine the potential of this pr...

Interferometric microscopy study of the surface roughness of Portland cement under the action of different irrigants

Objectives: Some investigations suggested common Portland cement (PC) as a substitute material for MTA for endodontic use; both MTA and PC have a similar composition. The aim of this study was to determine the surface roughness of common PC before and after the exposition to different endodontic irrigating solutions: 10% and 20% citric acid, 17% ethylenediaminetetraacetic (EDTA) and 5% sodium hypochlorite. Study Design: Fifty PC samples in the form of cubes were prepared. PC was mixed with distilled water (powder/liquid ratio 3:1 by weight). The samples were immersed for one minute in 10% and 20% citric acid, 17% EDTA and 5% sodium hypochlorite. After gold coating, PC samples were examined using the New View 100 Zygo interferometric microscope. It was used to examine and register the surface roughness and the profile of two different areas of each sample. Analysis of variance (ANOVA) was carried out, and as the requirements were not met, use was made of the Kruskal-Wallis test for analysis of the results obtained, followed by contrasts using Tukey’s contrast tests. Results: Sodium hypochlorite at a concentration of 5% significantly reduced the surface roughness of PC, while 20% citric acid significantly increased surface roughness. The other evaluated citric acid concentration (10%) slightly increased the surface roughness of PC, though statistical significance was not reached. EDTA at a concentration of 17% failed to modify PC surface roughness. Irrigation with 5% sodium hypochlorite and 20% citric acid lowered and raised the roughness values, respectively. Conclusions: The surface texture of PC is modified as the result of treatment with different irrigating solutions commonly used in endodontics, depending on their chemical composition and concentration. Key words:MTA, Portland cement, citric acid, ethylenediaminetetraacetic acid, sodium hypochlorite, surface roughness.

Spectrophotometric Determination of Water-Soluble Hexavalent Chromium and Determination of Total Hexavalent Chromium Content of Portland Cement in the Presence of Iron (III) and Titanium (IV) Using Derivative Ratio Spectrophotometry

A rapid, reliable and accurate method for the determination of hexavalent chromium in Portland cement is developed. The proposed method includes direct spectrophotometric determination of Cr (VI) in Portland cement with 1, 2, 5, 8 Tetrahydroxyanthraquinone, (Quinalizarin, QINZ) at pH 1.5. The European Directive (2003/53/EC) limits the use of cements so that it contains no more than 2 mg.Kg-1 of water-soluble Cr (VI). The absorbance at 565 nm due to Cr (VI)-QINZ complex is recommended for the determination of water-soluble Cr (VI) in Portland cement. The quantification of Cr (VI) released from cement when mixed with water is performed according to TRGS 613 (Technical Rules of Hazardous Substances). The validity of the method is thoroughly examined and the proposed method gives satisfactory results. A derivative spectrophotometric method has been developed for the determination of total Cr (VI) in Portland cement in the presence of Fe (III) and Ti (IV). The hexavalent chromium complex formed at pH 1.5 allows precise and accurate determination of chromium (VI) over the concentration range 0.05 to 3.0 mg.L-1of chromium (VI). The validity of the method was examined by analyzing several Standard Reference Material (SRM) Portland cement samples. The MDL (at 95% confidence level) was found to be 25 ng/mL for chromium (VI) in National Institute of Standards and Technology (NIST) cement samples using the proposed method.

Influence of carbonated additives on Portland cement hydration in chloride environment

This study investigated the influence of natural pozzolana (opoka) and limestone additives on the hydration of Portland cement and the effects of chloride ions on the formed hydrates. In the samples, 25% (by weight) of the Portland cement was replaced with additive. The specimens were then hardened for 28 days in water and then soaked in saturated sodium chloride (NaCl) solution for 3 months at 20°C. It is estimated that, under normal conditions, pozzolana and limestone additives accelerate the hydration of calcium silicates and initiate the formation of monocarboaluminate (CO32––AFm). Monocarboaluminate affected by NaCl becomes unstable and takes part in reactions producing Friedel's salt. More Cl−-containing compounds were formed in the samples with limestone than in the Portland cement samples after treatment in saturated NaCl solution. Meanwhile, pozzolana additive reduced the penetration of Cl– ions into the structure of Portland cement hydrates and impeded the formation of aluminium chloride hydrates.

The Influence of Micro Algae on Corrosion of Steel in Fly Ash Geopolymer Concrete: A Preliminary Study

Chloride is not the only main cause of corrosion of reinforced concrete structures in seawater environment. Microorganisms, such as bacteria and microalgae, in the seawater can induce microbiologically influenced corrosion (MIC) that leads to degradation of the concrete structures by formation of biofilm on the metallic surface. In this preliminary study, the impact of microalgae on the corrosion of steel reinforced bars in fly ash geopolymer concrete was studied. Corrosion potential, algae cells number, and pH measurement were carried out for fly ash geopolymer concrete and a control mix (Ordinary Portland Cement) samples. The results indicate that the corrosion potential of fly ash geopolymer concrete was influenced by the cathodic reaction during photosynthesis activities. The geopolymer concrete in algae-inoculated medium was found to be more tolerant to algal growth than the control mix (OPC concrete). There was a positive correlation between algae cell densities and the potential reading of the geopolymer.

Stabilization of chromium salt in ordinary portland cement

Ordinary Portland cement (OPC) samples containing the chromium salt have been investigated using differential microcalorimetry, conductometry and Fourier transform infrared spectroscopic analysis. The effect of chromium on OPC hydration was evaluated by continuous observing of early hydration. The microcalorimetrical results show that with increasing the share of chromium salt, heat maximums assume lower values and the occurrence of the maximum registered in the earlier hydration times. Conductometrical measurements show that with increasing addition of chromium salt, curve did not show any specific shape, immediate drop in specific conductivity is noticed and the maximum is reached earlier. This coincides with microcalorimetrical results. It can be concluded that the addition of chromium does not affect the mechanism of the hydration process, but it does affect the kinetic parameters and dynamics of the cement hydration process. It was found that chromium salt addition to the cement–water system is acceptable up to 2 wt.%. According to standard EN 196-3 for OPC, the beginning of binding time should occur after 60 minutes. Increased amount of chromium over 2 wt.% significantly accelerate the beginning of binding time and for the system it is not acceptable.

Calorimetric determination of the effect of additives on cement hydration process

AbstractPossibilities of a multicell isoperibolic-semiadiabatic calorimeter application for the measurement of hydration heat and maximum temperature reached in mixtures of various compositions during their setting and early stages of hardening are presented. Measurements were aimed to determine the impact of selected components’ content on the course of ordinary Portland cement (OPC) hydration. The following components were selected for the determination of the hydration behaviour in mixtures: very finely ground granulated blast furnace slag (GBFS), silica fume (microsilica, SF), finely ground quartz sand (FGQ), and calcined bauxite (CB). A commercial polycarboxylate type superplasticizer was also added to the selected mixtures. All maximum temperatures measured for selected mineral components were lower than that reached for cement. The maximum temperature increased with the decreasing amount of components in the mixture for all components except for silica fume. For all components, except for CB, the values of total released heat were higher than those for pure Portland cement samples.

Multifractal Analysis of Calcium Silicate Hydrate (C–S–H) Mapped by X‐ray Diffraction Microtomography

An investigation of Calcium Silicate Hydrate (C–S–H) topological distribution and modes of precipitation is performed by combining X‐ray powder diffraction tomography, performed on an ordinary Portland cement sample, with a numerical scheme that simulates C–S–H precipitation. C–S–H distribution maps obtained both experimentally and numerically are analyzed by means of a quantitative method based on the principles of multifractal systems. The combination of these methods allows C–S–H spatial distribution and modes of precipitation and aggregation to be assessed quantitatively. In particular, the multifractal spectra obtained from the digital images of the cement paste microstructure, act as a structural probe, which is able to quantify the tendency of C–S–H to form clusters. The results of this combined approach suggest that a multifractal network forms by aggregation of C–S–H clusters heterogeneously nucleated on clinker grains and preexisting clusters that are partly homogeneously nucleated in the porous space.