Pure Portland Cement Research Articles

PH and Antimicrobial Activity of Portland Cement Associated with Different Radiopacifying Agents

Objective. The aim of this study was to evaluate the antimicrobial activity and pH changes induced by Portland cement (PC) alone and in association with radiopacifiers. Methods. The materials tested were pure PC, PC + bismuth oxide, PC + zirconium oxide, PC + calcium tungstate, and zinc oxide and eugenol cement (ZOE). Antimicrobial activity was evaluated by agar diffusion test using the following strains: Micrococcus luteus, Streptococcus mutans, Enterococcus faecalis, Pseudomonas aeruginosa, and Candida albicans. After 24 hours of incubation at 37°C, inhibition of bacterial growth was observed and measured. For pH analysis, material samples (n = 10) were placed in polyethylene tubes and immersed in 10 mL of distilled water. After 12, 24, 48, and 72 hours, the pH of the solutions was determined using a pH meter. Results. All microbial species were inhibited by the cements evaluated. All materials composed of PC with radiopacifying agents promoted pH increase similar to pure Portland cement. ZOE had the lowest pH values throughout all experimental periods. Conclusions. All Portland cement-based materials with the addition of different radiopacifiers (bismuth oxide, calcium tungstate, and zirconium oxide) presented antimicrobial activity and pH similar to pure Portland cement.

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.

Estimation of C–S-H and calcium hydroxide for cement pastes containing slag and silica fume

The estimation of Calcium–Silicate–Hydrate (C–S–H) in pure Portland cement paste is difficult due to the uncertainty in obtaining the reasonably accurate Ca/Si ratio. The replacement of pure Portland cement with mineral admixtures further complicates the estimation process due to the formation of a secondary C–S–H with different Ca/Si ratios. This study considered a novel approach of using combined microanalysis by Energy Dispersive X-ray Spectroscopy (EDS) and nonlinear optimization to accurately define the Ca/Si ratio for Portland cement pastes containing slag and silica fume at four different ages. Based on the Ca/Si ratios, the volumes of primary and secondary C–S–H, and calcium hydroxide were estimated. The volume fractions of the primary C–S–H predicted by the optimization method were found to be in close agreement with the experimentally obtained values from EDS. The estimated mass fractions of calcium hydroxide from EDS and those obtained by thermo gravimetric analysis (TGA) also agreed well with R2 of 0.97.

Evolution of CTE–temperature curves of HCP with hydration time

Hydrating cement paste (HCP) may be considered as a kind of porous material. The changes of its pore system and internal moisture state with cement hydration certainly influence its thermal expansion response. This study investigated the influence of hydration time on the coefficient of thermal expansion (CTE) of HCP. Specimens (inner diameter 8 mm × 50 ± 0·5 mm long) were prepared using two water/cement ratios of 0·32 and 0·42. The linear thermal expansion of HCP was measured by a fused silica dilatometer after the HCP had been cured for different periods. The CTE–temperature curves of HCP were plotted from 30 to 60°C at intervals of 5°C. The results demonstrated that the CTE–temperature curve showed an approximately linear decrease, and its linear slope can be regarded as a strong logarithmic function of hydration time. Moreover, its linear slope showed a linear relationship with the degree of hydration. This evidence may potentially be used to show that the hydration development of pure ordinary Portland cement paste can be estimated on the basis of its thermal expansion characteristics over different hydration periods.

Microanalysis and optimization-based estimation of C–S–H contents of cementitious systems containing fly ash and silica fume

In this study, a new approach to characterize hardened pastes of pure portland cement as well as those containing cement with supplementary cementitious materials (SCM) was adopted using scanning electron microscopy (SEM) and energy dispersive X-ray spectra (EDS) microanalyses . The volume stoichiometry of the hydration reactions was used to estimate the quantities of the primary and secondary calcium silicate hydrate (C–S–H) and the calcium hydroxide produced by these reactions. The 3D plots of Si/Ca, Al/Ca and S/Ca atom ratios given by the microanalyses were compared with the estimated quantities of C–S–H to successfully determine the Ca/Si ratio of eleven different cementitious systems at four different ages using a constrained nonlinear least squares optimization formulation by General Algebraic Modeling System (GAMS). The estimated mass fraction of calcium hydroxide from the above method agreed well with the calcium hydroxide content determined from the thermogravimetric analyses (TGA).

Hydration process in Portland cement blended with activated coal gangue

This paper deals with the hydration of a blend of Portland cement and activated coal gangue in order to determine the relationship between the degree of hydration and compressive strength development. The hydration process was investigated by various means: isothermal calorimetry, thermal analysis, non-evaporable water measurement, and X-ray diffraction analysis. The results show that the activated coal gangue is a pozzolanic material that contributes to the hydration of the cement blend. The pozzolanic reaction occurs over a period of between 7 and 90 d, consuming portlandite and forming both crystal hydrates and ill-crystallized calcium silicate hydrates. These hydrates are similar to those found in pure Portland cement. The results show that if activated coal gangue is substituted for cement at up to 30% (w/w), it does not significantly affect the final compressive strength of the blend. A long-term compressive strength improvement can in fact be achieved by using activated coal gangue as a supplementary cementing material. The relationship between compressive strength and degree of hydration for both pure Portland cement and blended cement can be described with the same equation. However, the parameters are different since blended cement produces fewer calcium silicate hydrates than pure Portland cement at the same degree of hydration.

Effect of cement type on the resistance of concrete against chloride penetration

In chloride containing environment, chloride permeability of concrete is an important parameter affecting the service life of concrete structures. The primary objective of this experimental study was to study the effect of cement types on the resistance of concrete against chloride penetration for given compressive strength classes. These cements included two different types of granulated blast-furnace slag cement (CEM III/A 32.5N and CEM III/A 42.5N), a sulfate resisting cement (SRC 32.5), and a Portland cement blended with fly ash; all of which compared to an ordinary Portland cement (CEM I 42.5R). For each binder type, four concretes at different strength classes were produced and as a result 20 mixtures were obtained. Rapid chloride ion penetration tests according to ASTM C 1202 were conducted. In addition, electrical resistivity and capillary water absorption tests were carried out. In order to characterize the concrete quality, compressive strength of the specimens were also obtained. The test results clearly demonstrated that the blast-furnace slag cements have the highest resistance against chloride penetration, while the pure Portland cement and sulfate resisting cement have the lowest resistance. Concretes produced with the sulfate resisting cement had substantially higher capillary sorption compared to other mixtures. Test results confirmed the strong relationship between the chloride permeability and electrical resistivity.

Effect of radiopaque Portland cement on mineralization in human dental pulp cells

The aim of this study was to investigate whether radiopaque Portland cement (RPC) facilitates the mineralization process in human dental pulp cells (HDPCs) compared with pure Portland cement (PC). Under a scanning electron microscope (SEM), cellular morphology was evaluated. Alkaline phosphatase (ALP) activity was analyzed, and nodule formation was assessed by performing Alizarin Red S staining. In addition, the mRNA expressions of mineralization-related proteins were evaluated by performing a real-time polymerase chain reaction. On SEM evaluation, healthy HDPCs were found adhering to the surfaces of PC and RPC. The ALP activity increased in the PC and RPC groups compared with the control group at 1 day. Alizarin Red stain increased in the PC and RPC groups compared with the control group at 2 and 3 weeks. The mRNA expression of dentin sialophosphoprotein increased at 14 days in the PC and RPC groups. These results show that PC and RPC have similar effects in terms of mineralization and suggest that RPC also has the potential to be used as a clinically suitable pulp-capping material.

Radiographic effect of different radiopacifiers on a potential retrograde filling material

The objective of this study was to evaluate the radiopacity of white Portland cement (PC) associated with bismuth oxide (Bi(2)O(3)), barium sulfate (BaSO(4)), iodoform (CHI(3)), and zirconium oxide (ZrO(2)). White mineral trioxide aggregate (WMTA) and PC without radiopacifier were used as positive and negative controls, respectively. Following International Organization for Standardization (ISO) 6876/2001, 5 circular specimens (10 x 1 mm) were made from each material. After the materials set, radiographs were taken using occlusal film and a graduated aluminum step-wedge varying in thickness from 2 to 16 mm. The dental X-ray unit (GE1000) was set at 50 Kvp, 10 mA, 18 pulses/s, and distance of 33.5 cm. The radiographs were digitized, and radiopacity was compared with the aluminum step-wedge, using Wixwin-2000 software (Gendex). Data (mm Al) were analyzed using analysis of variance and Tukey tests. The PC + Bi(2)O(3) and WMTA samples presented greater radiopacity (5.88 and 5.72 mm Al, respectively), followed by PC + ZrO(2) (3.87 mm Al) and PC + CHI(3) (3.50 mm Al). The PC + BaSO(4) and PC samples presented the lowest radiopacity values (2.35 and 1.69 mm Al, respectively), which were below the minimum value recommended by the ISO. Analysis of the present results led to the conclusion that all of the materials tested presented acceptable radiopacity, except PC + BaSO(4) and pure PC.

Synthesis of pure Portland cement phases

Pure clinker phases are often used to test cement hydration behavior in simplified experimental conditions. These phases are in general structurally identical to, but chemically much simpler than their heavily substituted counterparts found in technical clinkers. The synthesis of the pure phases is covered in this paper, starting with a description of phase relations and possible polymorphs of the four main phases in Portland cement, i.e. tricalcium silicate, dicalcium silicate, tricalcium aluminate and tetracalcium alumino ferrite. Details of the process of solid state synthesis are described including practical advice on equipment and techniques. In addition, mix compositions that have been successfully used are given.

C4AF ettringite and calorific synergic effect contribution

The need for cements or other cementitious materials that afford high early age mechanical strength has led to the use of extremely reactive pozzolanic additions such as silica fume, nanosilica, metakaolin and similar. The inclusion of the right proportion of such pozzolanic additions stimulates portland cement hydration, i.e., directly, as they are initially moistened by the mixing water, non-directly when they act as “seed crystals”, and indirectly, because of the pozzolanic reaction between the addition particles and the portlandite forming from the portland cement components hydration; since this reaction is characterized by its intensity and speed, when its occurs it prevails over the other two. Indirect stimulation also causes the fraction of portland cement in the blend to release more heat of hydration than pure portland cement, and its does so on a scale consistent with the existence of a calorific synergic effect. Such greater heat is released in the early stages of hydration primarily by C3A and C3S that react with the mixing water to respectively generate ettringite and hydrated calcium silicates. When portland cements have a low to nil C3A content, less heat of hydration is released due to the absence of an AFt phase that could be transformed into AFm. However, when extremely active pozzolanic additions, such as silica fume, are used, ettringite forms from C4AF, further contributing to origin amounts of hydration heat released comparable to the above calorific synergic effect.

Radiopacity of Portland Cement Associated With Different Radiopacifying Agents

This study evaluated the radiopacity of Portland cement associated with the following radiopacifying agents: bismuth oxide, zinc oxide, lead oxide, bismuth subnitrate, bismuth carbonate, barium sulfate, iodoform, calcium tungstate, and zirconium oxide. A ratio of 20% radiopacifier and 80% white Portland cement by weight was used for analysis. Pure Portland cement and dentin served as controls. Cement/radiopacifier and dentin disc-shaped specimens were fabricated, and radiopacity testing was performed according to the ISO 6876/2001 standard for dental root sealing materials. Using Insight occlusal films, the specimens were radiographed near to a graduated aluminum stepwedge varying from 2 to 16 mm in thickness. The radiographs were digitized and radiopacity compared with the aluminum stepwedge using Digora software (Orion Corporation Soredex, Helsinki, Finland). The radiographic density data were converted into mmAl and analyzed statistically by analysis of variance and Tukey-Kramer test (α = 0.05). The radiopacity of pure Portland cement was significantly lower (p < 0.05) than that of dentin, whereas all cement/radiopacifier mixtures were significantly more radiopaque than dentin and Portland cement alone (p < 0.05). Portland cement/bismuth oxide and Portland cement/lead oxide presented the highest radiopacity values and differed significantly from the other materials (p < 0.05), whereas Portland cement/zinc oxide presented the lowest radiopacity values of all mixtures (p < 0.05). All tested substances presented higher radiopacity than that of dentin and may potentially be added to the Portland cement as radiopacifying agents. However, the possible interference of the radiopacifiers with the setting chemistry, biocompatibility, and physical properties of the Portland cement should be further investigated before any clinical recommendation can be done.

Numerical Simulation of Heat Evolution of Eco-Friendly Blended Portland Cements Using a Multi-Component Hydration Model

With the development of concrete industry, the necessity for utilizing waste materials and decreasing overall energy consumption is becoming increasingly obvious. Fly ash and granulated blast-furnace slag, which are used as blends of Portland cement, are waste materials produced in electric and energy industry, and concretes made with them can have properties similar to ones made with pure Portland cement at lower cost per unit volume. By using blended Portland cement, both ecology benefit and economic benefit can be achieved. Due to the pozzolanic reaction between calcium hydroxide and blended components, compared with ordinary Portland cement, hydration process of blended Portland cement is more complex. In this paper, based on a multi-component hydration model, a numerical model which can simulate heat evolution process of blended Portland cements is built. The influence of water to cement ratio, curing temperature, particle size distribution of cement paste and blended Portland material, and cement mineral components on heat evolution process is considered. The prediction result agrees well with experiment result.

Carbonation rates of concretes containing high volume of pozzolanic materials

The project studies the influence of fly ash and slag replacement on the carbonation rate of the concrete. The experimental work includes samples of pure Portland cement concrete (CEM I 42,5 R), blast-furnace slag concrete (CEM III-B), and fly ash blended concrete. To reveal the effect of curing on carbonation rate, the concretes were exposed to various submerged curing periods during their early ages. After that, the samples were subsequently exposed in the climate room controlling 20 °C and 50% RH until the testing date when the samples had an age of 5 months. Then, the accelerated carbonation test controlling the carbon dioxide concentration of 3% by volume, with 65% relative humidity were started to perform. The depth of carbonation can be observed by spraying a phenolphthalein solution on the fresh broken concrete surface. Finally, according to Fick's law of diffusion theoretical equations are proposed as a guild for estimating the carbonation rate of fly ash and blast-furnace slag concretes exposed under natural conditions from the results from accelerated carbonation tests.

The effect of particle size distribution on the properties of blended cements incorporating GGBFS and natural pozzolan (NP)

This paper investigates the effect of particle size distribution on the properties of blended cements incorporating ground granulated blast-furnace slag (GGBFS) and natural pozzolan (NP). Pure Portland cement (PPC), NP and GGBFS were used to obtain blended cements that contain 10, 20, 30% additives. The cements were produced by intergrinding and separate grinding and then blending. Each group had two different Blaine fineness of 280 m 2/g and 480 m 2/g. According to the particle size distribution (PSD) curves, 46% of the coarser specimens and 69% of the finer specimens passed through the 20 μm sieve. It was observed that the separately ground specimens were relatively finer than the interground ones and had higher compressive strength and sulfate resistance. The separately ground coarser specimens had the lowest heat of hydration. The separately ground finer specimens, which had the highest compressive strength and sulfate resistance, had the highest percent passing for each sieve size. For these specimens 34, 69, 81 and 99% passed through 5, 20, 30 and 55 μm sieves, respectively. For the interground specimens, which had the same fineness, the respective values for the same sieves were 32, 68, 75 and 94%.

Hydration study of mechanically activated mixtures of Portland cement and fly ash

Fly ash (FA) can be used in cement mixtures with certain limitations. The problem of the mentioned mixtures lies in the insufficient activity of the particles of FA in the reactions which are important for the establishment of the mechanical characteristics of cement. This is particularly true for the hydration reactions. As a result of this, cement pastes formed by mixing ash and clinker have worse characteristics compared to those of pure Portland cement (PC), especially in the early period of setting. As is well known, FA can be a good solution for the neutralization of the negative effects generated due to the creation of free Ca(OH)2 during the hydration of PC, provided that the problems with the low activity of FAare overcome. For the experiments in this study, a mixture of Portland cement and fly ash was used, the content of ash in the mixture being 30 % and 50 %. Mechanical activation was performed in a vibrating ring mill. The goal of this study was to demonstrate, through experimental results, that during the mechanical activation of a PC and FA mixture, the components in the mixture which mostly affect the direction, rate and range of hydration reactions occurring in the mixture had been activated. The values of the compressive strength of the activated and non-activated mixtures and the changes of their specific surface area proved that during the grinding process, the mixture PC+FA had been mechanically activated. The highest increase of compressive strength was achieved in the early period of setting, which indicates an improvement in the early hydration of the mixture. XRD, DTA and TG analyses showed that the alite (C3S) and belite (C2S) from the PC and a part of the fly ash were activated. .

In situ imaging of ground granulated blast furnace slag hydration

Ground granulated blast furnace slag (GGBFS) reacts with water in the presence of calcium sulfates and alkalis and is frequently used as a partial replacement for portland cement in concrete. The hydration products are known to be slightly different compositionally and morphologically than those of pure portland cement hydration. In this study, a new technique, soft X-ray transmission microscopy, was used to image the hydration of slag in a variety of solutions to investigate the effects of alkali sulfate and hydroxide activators on the morphology of the resulting hydration products. This microscopy method is unique in that it enables high resolution in situ observation and documentation of the formation of hydration products over time in wet samples at atmospheric pressure.

Influence of initial casting temperature and dosage of fly ash on hydration heat evolution of concrete under adiabatic condition

The calorimetric data of binders containing pure Portland cement, 20% fly ash, 20% slag and 10% silica fume respectively are determined at different initial casting temperatures using an adiabatic calorimeter to measure the adiabatic temperature rising of concrete. The calorimetric data of binders with different dosages of fly ash at two water binder ratios (w/b) are determined, too. Elevation of initial casting temperature decreases the heat evolution of binder, enhances the heat evolution rate of binder and increases the heat evolution rate of binder at early age. The dosage of fly ash in concrete has different effects on the heat evolution of binder with different w/b. At high w/b ratio the heat evolution of binder decreases when dosage of fly ash increases. At low w/b ratio the heat evolution of binders increases when dosage of fly ash increases from 0 to 40% of total binder quantity. The heat evolution of binder decreases after the dosage of fly ash over 40%. An appropriate dosage of fly ash in binder benefits the performance of concrete at low w/b ratio.

Comparison of performance of concrete barriers in a clayey geological medium

Cement based materials play an important role in the design and performance of future deep radioactive waste disposals. The type of materials selected for engineered barrier systems (EBS) is an important issue: protection of waste packages against corrosion and chemical degradation may be greatly enhanced by a proper choice and dimensioning. The long-term geochemical performance of two concrete types, CEM-I (pure Portland cement) and CEM-V (blended Portland, fly ash, blast furnace slag cement) was evaluated using reactive transport simulations of the interactions between the Callovo-Oxfordian mudrock (argillite) and concrete EBS over periods up to 10 6 years at 25 °C. Simulations have been run with cylindrical geometry using the modeling tool Hytec 3.5 (ENSMP/CIG). Diffusion of solutes in the porewater of the solid media was considered to be the dominant transport process. Different scenarios were studied, including the case of sulfate attack. Various assumptions on the transport properties of the EBS and the argillite medium have been considered and compared. The interactions between concrete, CEM-I or CEM-V, and mudrock are in both cases predicted to lead to a significant clogging in the mudrock, in the vicinity of the interface with the concrete EBS. However, the nature and extent of the EBS/mudrock interface transformations greatly differ for the two materials considered. CEM-V, due to lower diffusion coefficients, keeps longer internal high pH conditions which are favorable to the waste packages from a chemical point of view. In addition, simulations predict that CEM-V material should have a better resistance to sulfate attack than CEM-I based barriers. In the case of CEM-I, the altered clay zone has a greater extent (up to 1.3 m in 400,000 y) and the drop of porosity is mainly due to zeolites and reprecipitated illite, quartz and calcite. For CEM-V, the altered clay zone is much smaller (less than 0.2 m in 400,000 y) and secondary smectite and calcite precipitation are predicted to cause porosity reduction.

Mechanical activation of various cements

The mechanical activation in vibromills with rings of Portland cement and Portland cement with various additions (blast furnace slag, ash, and tuff) with the initial specific surface of 300 m 2/kg was studied. To reach a specific surface of 500 m 2/kg, the Portland cement with addition of 20% fly ash needs the shortest time of activation—3 min. Comparing testings of physico-chemical and mechanical properties of the pure Portland cement and Portland cement with various additions, it was found that the mechanical activation improved properties in all samples. Effects of mechanical activation were larger when the mix of Portland cement with addition was activated; then only additions were activated. The highest effects of mechanical activation were with the mix of Portland cement with the addition of 20% fly ash: compressive strength after 28 days of hardening was increased to 57.9%, which is 3.3% more than the compressive strength of the pure Portland cement. Due to mechanical activation of cement, changes in the surface microstructure of clinker minerals present in cement take place, which occurs during investigation of diffraction maxima intensities—characteristic of the basic clinker minerals. It is also noticed that there is an interchange of clinker minerals from larger to smaller particle sizes. Thus, the reactivity of the present mineral phases increases with the hydration reaction rates, which occurs in the process of hardening of Portland cement and Portland cement with mineral additions. A somewhat greater presence of clinker minerals in smaller grain size classes (i.e., in the class of −20+0 μm) enables more complete hydration of their grains, which ensures the improvement of mechanical properties of tested cements.