Portland Cement (portland + cement)

Distribution by Scientific Domains


Selected Abstracts


Residual compressive behavior of alkali-activated concrete exposed to elevated temperatures

FIRE AND MATERIALS, Issue 1 2009
Maurice Guerrieri
Abstract This paper reports the effect of elevated temperature exposures, up to 1200°C , on the residual compressive strengths of alkali-activated slag concrete (AASC) activated by sodium silicate and hydrated lime; such temperatures can occur in a fire. The strength performance of AASC in the temperature range of 400,800°C was similar to ordinary Portland cement concrete and blended slag cement concrete, despite the finding that the AASC did not contain Ca(OH)2 , which contributes to the strength deterioration at elevated temperatures for Ordinary Portland Cement and blended slag cement concretes. Dilatometry studies showed that the alkali-activated slag (AAS) paste had significantly higher thermal shrinkage than the other pastes while the basalt aggregate gradually expanded. This led to a higher thermal incompatibility between the AAS paste and aggregate compared with the other concretes. This is likely to be the governing factor behind the strength loss of AASC at elevated temperatures. Copyright © 2008 John Wiley & Sons, Ltd. [source]


Effects of Saccharide Set Retarders on the Hydration of Ordinary Portland Cement and Pure Tricalcium Silicate

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2010
Linghong Zhang
The effects of aliphatic sugar alcohols (e.g., threitol, xylitol, sorbitol) on the hydration of tricalcium silicate (C3S) and ordinary portland cement (OPC) were investigated and compared with those of sucrose, a well-established cement set retarder. Only sugar alcohols which contain threo diol functionality retarded the setting of C3S and OPC, their efficacy increasing with the number of threo hydroxy pairs and, to a smaller extent, with the overall population of hydroxy groups. None, however, were as effective as sucrose. The initial and final setting times increased exponentially with the concentration of saccharide, although the hydration of OPC was less inhibited than that of C3S. Saccharides function as "delayed accelerators," that is, cement hydration is first inhibited and then proceeds faster than in saccharide-free cement. This behavior is consistent with the theory that the induction period is controlled by slow formation and/or poisoning of the stable calcium silicate hydrate (CSH) nuclei. The early inhibiting influence of saccharides on CSH precipitation is apparently stronger than on the growth of crystalline calcium hydroxide. Saccharides did not negatively affect the degree of hydration and compressive strength of fully set OPC paste; on the contrary, sorbitol yielded modest increases. [source]


Chemical Speciation of Trace Zinc in Ordinary Portland Cement Using X-ray Absorption Fine Structure Analysis

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2004
Isao Tsuyumoto
Chemical change of trace zinc in ordinary portland cement (205.1 ppm) was investigated in hydration process using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). Intensities of the peaks appearing at the same energy of ZnO in XANES spectra were decreased with cement hydration. The interatomic distances and the coordination numbers of the first and the second shells calculated from EXAFS spectra indicated that ZnO hydrolyzed to zincate ion [Zn(OH)4]2, with cement hydration keeping their fundamental structure of ZnO4 tetrahedra. [source]


Cytotoxicity of MTA and Portland cement on human ECV 304 endothelial cells

INTERNATIONAL ENDODONTIC JOURNAL, Issue 9 2005
G. De Deus
Abstract Aim, To evaluate the cytotoxic effects of two brands of mineral trioxide aggregate (MTA) (Pro-Root MTA® and MTA Angelus®) and Portland cement (PC) on the human ECV 304 endothelial cell line. Methodology, Endothelial ECV 304 cells were incubated at 37 °C in an atmosphere of 95% air, 5% carbon dioxide and 100% humidity for 7 days and grown in F12 medium supplemented with 10% fetal bovine serum with 50 ,g mL,1 of gentamicin sulphate. Effects of the materials on mitochondrial functions were measured by a colorimetric assay. At each experimental time interval (24, 48 and 72 h), a dimethyl-thiazol-diphenyl tetrazolium bromid assay was conducted to measure cell viability. All assays were repeated three times to ensure reproducibility. Results were expressed as average absorbance (A570\,nm) ± SD and the data were analysed statistically by one-way analysis of variance and the Bonferroni post-test. A P -value <0.05 was considered statistically significant. Results, No statistically significant difference was shown between any of the experimental materials (P > 0.05). Conclusions, The two brands of MTA analysed, as well as the PC, initially showed a similar elevated cytotoxic effect that decreased gradually with time allowing the cell culture to become reestablished. [source]


Rietveld quantitative amorphous content analysis

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2001
A. G. De La Torre
A procedure for Rietveld quantitative amorphous content analysis (RQACA) is outlined, in which the effects of systematic errors in the powder patterns are studied. The method derives the amorphous content from the small overestimation of an internal crystalline standard in a Rietveld refinement of an appropriate mixture. Of several standards studied, Al2O3 gave the best results. The statistical analysis of standard mixtures with a known amount of amorphous content indicated that this is a precise and accurate tool. It enables the measurement of the amorphous content with an accuracy close to 1%. Sample preparation and Rietveld analysis need to be optimized in order to minimize the systematic errors. The analysis of samples with phases displaying strong preferred orientation effects gives very high errors in the amorphous content. Samples with different absorption coefficients have also been studied in order to evaluate the importance of microabsorption. This plays an important role but it can be adequately corrected if the absorption coefficients of the standard and the sample are not very different. RQACA has been applied to tricalcium silicate, C3S, which is the main component of Portland cement. The average amorphous content of C3S, after microabsorption correction using two standards of higher and lower absorption coefficients, was found to be 19%. [source]


Use of recycled copper slag for blended cements

JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 3 2008
M Isabel Sánchez de Rojas
Abstract Copper slag is a by-product generated during smelting to extract copper metal from the ore. The copper slag obtained may exhibit pozzolanic activity and may therefore be used in the manufacture of addition-containing cements. In this paper the effect of the incorporation of the copper slag in cement is measured. Blends of copper slag with Portland cement generally possess properties equivalent to Portland cement containing fly ash, but very different to the silica fume incorporation. Copper slag and fly ash reduce the heat of hydration more effectively than silica fume in mortars. The replacement of 30% cement by copper slag reduces the flexural and compressive strength in a similar way to fly ash; however, after 28 days, the reduction is less than the percentage of substitution. Hydrated calcium aluminate phases were analysed using scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The pozzolanic activity of copper slag is similar to that of fly ash and higher than silica fume. In the presence of low water/cement ratios, certain pozzolanic materials produce a very compact cement paste that limits the space available for hydration products, a determining factor in the formation of hydrated calcium aluminates. SEM was found to be a useful analytical technique when aluminates are formed and can be clearly detected by XRD. Copyright © 2008 Society of Chemical Industry [source]


Cement Manufacture and the Environment: Part I: Chemistry and Technology

JOURNAL OF INDUSTRIAL ECOLOGY, Issue 1 2002
Hendrik G. van Oss
Summary Hydraulic (chiefly portland) cement is the binding agent in concrete and mortar and thus a key component of a country's construction sector. Concrete is arguably the most abundant of all manufactured solid materials. Portland cement is made primarily from finely ground clinker, which itself is composed dominantly of hydraulically active calcium silicate minerals formed through high-temperature burning of limestone and other materials in a kiln. This process requires approximately 1.7 tons of raw materials per ton of clinker produced and yields about 1 ton of carbon dioxide (CO2) emissions, of which cal-cination of limestone and the combustion of fuels each con-tribute about half. The overall level of CO2 output makes the cement industry one of the top two manufacturing industry sources of greenhouse gases; however, in many countries, the cement industry's contribution is a small fraction of that from fossil fuel combustion by power plants and motor vehicles. The nature of clinker and the enormous heat requirements of its manufacture allow the cement industry to consume a wide variety of waste raw materials and fuels, thus providing the opportunity to apply key concepts of industrial ecology, most notably the closing of loops through the use of by-products of other industries (industrial symbiosis). In this article, the chemistry and technology of cement manufacture are summarized. In a forthcoming companion ar-ticle (part II), some of the environmental challenges and op-portunities facing the cement industry are described. Because of the size and scope of the U.S. cement industry, the analysis relies primarily on data and practices from the United States. [source]


Growth of Cement Hydration Products on Single-Walled Carbon Nanotubes

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2009
Jonathan M. Makar
Single-walled carbon nanotubes (SWCNT) were distributed on the surface of ordinary Portland cement (OPC) grains. The OPC/SWCNT composite was then hydrated at a 0.5 w/c ratio. The effects of the SWCNT on the early hydration process were studied using isothermal conduction calorimetry, high-resolution scanning electron microscopy and thermogravimetric analysis. The observed behavior of the composite samples was compared with both OPC sonicated without SWCNT and previously published data on as-delivered OPC. The SWCNT were found to accelerate the hydration reaction of the C3S in the OPC. The morphology of both the initial C3A and the C3S hydration products were found to be affected by the presence of the SWCNT. In particular, the nanotubes appeared to act as nucleating sites for the C3S hydration products, with the nanotubes becoming rapidly coated with C,S,H. The resulting structures remained on the surface of the cement grains while those in the sonicated and as-delivered OPC samples grew out from the grain surfaces to form typical C,S,H clusters. Classical evidence of reinforcing behavior, in the form of fiber pullout of the SWCNT bundles, was observed by 24 h of hydration. [source]


Structural, Mechanical, and Reactivity Properties of Tricalcium Aluminate Using First-Principles Calculations

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2009
Hegoi Manzano
Although tricalcium aluminate (C3A) is one of the most important components of Portland cement, neither its reactivity nor its elastic moduli tensor have been fully determined yet. This work aims to shed some insights on these questions by means of ab-initio simulations. First our simulations have reproduced the details of its crystalline structure. Second, we have computed the full elastic moduli tensor of C3A, where we found that our value for the Young modulus (E=138.7 GPa) is in agreement with the values obtained by nanoindentation measurements. Finally, we have identified which atoms and sites are more suitable to suffer chemical attacks. [source]


High-Pressure Device for Fluid Extraction from Porous Materials: Application to Cement-Based Materials

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2008
Martin Cyr
A high-pressure device, reaching an axial pressure of 1000 MPa, intended to the extraction of the pore solution of rigid and slightly porous materials, has been developed to improve the efficiency of extraction. This paper gives an application of fluid extraction from mortars made with Portland cement. It includes an experimental study of the performance of the apparatus, and an analysis of the results in terms of efficiency of extraction, repeatability of measurement, and effect of the squeezing pressure on the pore solution composition. Results shows that: (1) the squeezing efficiency using our apparatus is higher than those found in the literature; (2) the measurement uncertainty ranges between 1.5% and 14%; (3) no significant effect of pressure (up to 1000 MPa) is observed for concentrations of Ca, Na, K, and Si. This paper suggests conducting extraction at 1000 MPa, especially on old concrete or concrete made with low W/C ratios. [source]


Comparative SEM study of the marginal adaptation of white and grey MTA and Portland cement

AUSTRALIAN ENDODONTIC JOURNAL, Issue 1 2007
Maryam Bidar dds
Abstract The use of a suitable substance that prevents egress of potential contaminants into the periapical tissues is important in endodontic surgery. The aim of the present study was to compare the marginal adaptation of three root-end filling materials (white mineral trioxide aggregate (MTA), grey MTA and Portland cement), using scanning electron microscopy. Seventy-five single-rooted extracted human teeth were used. The canals were instrumented and filled with gutta-percha. Following root-end resection and cavity preparation, root-end cavities were filled with white MTA, grey MTA or Portland cement. Using a diamond saw, roots were longitudinally sectioned into two halves. Under scanning electron microscopy, the gaps between the material and dentinal wall were measured. The data were analysed using Kruskal,Wallis test. The mean of the gap in grey MTA, white MTA and Portland cement was 211.6, 349 and 326.3 µm, respectively. The results indicate that the gap between grey MTA and the dentinal wall is less than other materials, but there was no significant difference between the materials tested in this study (P > 0.05). [source]


The biocompatibility of modified experimental Portland cements with potential for use in dentistry

INTERNATIONAL ENDODONTIC JOURNAL, Issue 12 2008
J. Camilleri
Abstract Aim, To evaluate the biocompatibility of a group of new potential dental materials and their eluants by assessing cell viability. Methodology, Calcium sulpho-aluminate cement (CSA), calcium fluoro-aluminate cement (CFA) and glass,ionomer cement (GIC; Ketac Molar), used as the control, were tested for biocompatibility. Using a direct test method cell viability was measured quantitatively using alamarBlueÔ dye, and an indirect test method where cells were grown on material elutions and cell viability was assessed using methyltetrazolium (MTT) assay as recommended by ISO 10 993-Part 5 for in vitro testing. Statistical analysis was performed by analysis of variance and Tukey multi-comparison test method. Results, Elution collected from the prototype cements and the GIC cured for 1 and 7 days allowed high cell activity after 24 h cell exposure, which reduced after 48 h when compared to the nontoxic glass,ionomer control, but increased significantly after 72 h cell contact. Elutions collected after 28 days revealed reduced cell activity at all cell exposure times. Cells placed in direct contact with the prototype materials showed reduced cell activity when compared with the control. Conclusions, Cell growth was poor when seeded in direct contact with the prototype cements. GIC encouraged cell growth after 1 day of contact. The eluted species for all the cements tested exhibited adequate cell viability in the early ages with reduced cell activity at 28 days. Changes in the production of calcium hydroxide as a by-product of cement hydration affect the material biocompatibility adversely. [source]


Characterization of Portland cements by X-ray spectrometry allied to chemometrics

JOURNAL OF CHEMOMETRICS, Issue 11-12 2006
Karen Goraieb
Abstract This work reports the use of X-ray spectrometry (XRS) allied to chemometric techniques to easily distinguish types of Portland cements, as well as to quantify some of their constituent elements. The samples were irradiated as powders for 200,s using two distinct irradiation conditions, one more adequate for heavier elements (condition 1) and the other (condition 2) for lighter elements, using a conventional bench top energy dispersive X-ray fluorescence (EDXRF) equipment. The spectra were processed via the software The Unscrambler, version 9.2. The PLS 1 LV1,×,LV2 scores graph shows a classification into five groups, in accordance with the calcium concentration, using condition 2. The classification of the cements by producer was feasible using the PLS1 LV1,×,LV3 scores graph, with condition 1. The elements Ca, Si, Al and Mg were successfully quantified using multivariate calibration of the whole spectra. However, for Fe, S and K, better results were obtained by correlating their corresponding K, peaks with concentrations in a univariate procedure, using irradiation condition 2. Chemometric tools allied to XRS are powerful techniques to classify Portland cements, regarding to their origins and their calcium concentration, which is related to the cement type. The PLS chemometric tool was very useful to easily quantify light elements, such as Al, Si and Mg, a challenge in most X-ray analytical methods, since their K, emission peaks are very close to each other. Copyright © 2007 John Wiley & Sons, Ltd. [source]


Effects of Saccharide Set Retarders on the Hydration of Ordinary Portland Cement and Pure Tricalcium Silicate

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2010
Linghong Zhang
The effects of aliphatic sugar alcohols (e.g., threitol, xylitol, sorbitol) on the hydration of tricalcium silicate (C3S) and ordinary portland cement (OPC) were investigated and compared with those of sucrose, a well-established cement set retarder. Only sugar alcohols which contain threo diol functionality retarded the setting of C3S and OPC, their efficacy increasing with the number of threo hydroxy pairs and, to a smaller extent, with the overall population of hydroxy groups. None, however, were as effective as sucrose. The initial and final setting times increased exponentially with the concentration of saccharide, although the hydration of OPC was less inhibited than that of C3S. Saccharides function as "delayed accelerators," that is, cement hydration is first inhibited and then proceeds faster than in saccharide-free cement. This behavior is consistent with the theory that the induction period is controlled by slow formation and/or poisoning of the stable calcium silicate hydrate (CSH) nuclei. The early inhibiting influence of saccharides on CSH precipitation is apparently stronger than on the growth of crystalline calcium hydroxide. Saccharides did not negatively affect the degree of hydration and compressive strength of fully set OPC paste; on the contrary, sorbitol yielded modest increases. [source]


FIB-Nanotomography of Particulate Systems,Part II: Particle Recognition and Effect of Boundary Truncation

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2006
Beat Münch
The focused ion beam-nanotomography (FIB-nt) technique presented in Part I of this article is a novel high-resolution three-dimensional (3D) microscopy method that opens new possibilities for the microstructural investigation of fine-grained granular materials. Specifically, FIB-nt data volumes allow particle size distributions (PSD) to be determined, and the current paper discusses all the processing steps required to obtain the PSD from 3D data. This includes particle recognition and the subsequent PSD estimation. A refined watershed approach for 3D particle recognition that tolerates concavities on the particle surfaces is presented. Particles at the edge of the 3D data volume are invariably clipped, and because the data volume is of a very limited size, this effect of boundary truncation seriously affects the PSD and needs to be corrected. Therefore, two basic approaches for the stereological correction of the truncation effects are proposed and validated on artificially modeled particle data. Finally, the suggested techniques are applied to real 3D-particle data from ordinary portland cement and the resulting PSDs compared with data from laser granulometry. [source]


Chemical Speciation of Trace Zinc in Ordinary Portland Cement Using X-ray Absorption Fine Structure Analysis

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2004
Isao Tsuyumoto
Chemical change of trace zinc in ordinary portland cement (205.1 ppm) was investigated in hydration process using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). Intensities of the peaks appearing at the same energy of ZnO in XANES spectra were decreased with cement hydration. The interatomic distances and the coordination numbers of the first and the second shells calculated from EXAFS spectra indicated that ZnO hydrolyzed to zincate ion [Zn(OH)4]2, with cement hydration keeping their fundamental structure of ZnO4 tetrahedra. [source]


Properties of Portland Cement Pastes Incorporating Nanometer-Sized Franklinite Particles Obtained from Electric-Arc-Furnace Dust

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2001
Antonio Balderas
The present work presents preliminary results concerning ordinary portland cement (OPC) blended with electric-arc-furnace dust (EAFD) obtained from steel-smelting plants. The powder obtained after acid treatment of the EAFD consisted basically of nanometer-sized particles of ZnFe2O4. Incorporation of the EAFD in the OPC produced retardation of the setting process. Nevertheless, after 7 d, the compressive strength of the OPC/EAFD pastes was superior to undoped OPC, and, after 28 d, the extent of hydration of the OPC/EAFD pastes was equivalent to undoped OPC. A compressive strength of 72 MPa was attained after 42 d for OPC doped with 10 wt% EAFD. [source]