Effect of the addition of nanoparticles of CaCO3 and different water-to-powder ratios on the physicochemical properties of white Portland cement

The addition of calcium carbonate nanoparticles (nano-CaCO₃ ) accelerates the hydration of Portland cement improving its mechanical properties. Conversely, nano-CaCO₃ addition leads to reduction in the water required during initial PC hydration. Therefore, the use of a correct water-to-powder ratio is fundamental for manipulating this hydraulic cement. This study evaluated the effect of nano-CaCO₃ addition and different water-to-powder ratios on the physicochemical properties of white Portland cement (WPC). WPC was associated to different concentrations of nano-CaCO₃ , and the following experimental groups were created: G1a (no nano-CaCO₃ ); G2a (0.5% nano-CaCO₃ ), G3a (1% nano-CaCO₃ ), G4a (2% nano-CaCO₃ ), and G5a (5% nano-CaCO₃ ). The setting-time (ST), compressive strength (CS), dimensional change (DC), solubility (S), and pH were assessed (24 hr and 30 days). Next, WPC + 5% nano-CaCO₃ was manipulated varying the water-to-powder ratio: G1b (WPC/0.33 ml); G2b (WPC/nano-CaCO₃ /0.33 ml); G3b (WPC/0.29 ml); G4b (WPC/nano-CaCO₃ /0.29 ml); G5b (WPC/0.26 ml); and G6b (WPC/nano-CaCO₃ /0.26 ml). The tests were repeated. The data analysis (2-way ANOVA and Tukey test, α = 5%) demonstrated that ST was shorter for samples containing nano-CaCO₃ (p < .05). Reduction in CS was observed for all groups at 30 days, except G5a, G2b, and G6b (p < .05). DC and S had no statistical difference among groups (p > .05) independently of nano-CaCO₃ water-to-powder ratio. After 30 days, there was significant reduction in pH for G3a and G6b (p < .05). The different concentrations of nano-CaCO₃ and water-to-powder ratios affected the physicochemical properties of WPC, especially the setting-time and compressive strength.

Effects of Portland Cement and Polymer Powder on the Properties of Cement-Bound Road Base Mixtures

This article presents the test results for the physical and mechanical properties and fracture toughness of polymer-modified hydraulically-bound mixtures (HBM) produced with Portland cement for road base layers. The modifier used was a redispersible polymer powder (RPP) based on a vinyl ethylene acetate (EVA) copolymer obtained by spray drying. A three-level full factorial design with two factors was applied to determine the contents of Portland cement and polymer powder in the cement-bound mixture (CBM). Both Portland cement and polymer powder were added at three levels: 0%, 2%, and 4%. The assessment included basic physical properties (water absorption, density, and bulk density) and mechanical properties (stiffness modulus, axial compressive strength, and indirect tensile strength) of the CBM. Particular attention was paid to the assessment of fracture toughness in the semi-circular bending test. The results of the research show that polymer powder positively influenced the mechanical properties of CBM by improving its cohesion while maintaining its stiffness. Another benefit coming from the use of polymer powder was the CBM’s increased resistance to cracking, which is the desired characteristic from the perspective of pavement durability.

Self-Healing Properties of Bioinspired Amorphous CaCO3/Polyphosphate-Supplemented Cement

There is a strong interest in cement additives that are able to prevent or mitigate the adverse effects of cracks in concrete that cause corrosion of the reinforcement. Inorganic polyphosphate (polyP), a natural polymer that is synthesized by bacteria, even those on cement/concrete, can increase the resistance of concrete to progressive damage from micro-cracking. Here we use a novel bioinspired strategy based on polyP-stabilized amorphous calcium carbonate (ACC) to give this material self-healing properties. Portland cement was supplemented with ACC nanoparticles which were stabilized with 10% (w/w) Na-polyP. Embedding these particles in the hydrated cement resulted in the formation of calcite crystals after a hardening time of 10 days, which were not seen in controls, indicating that the particles dissolve and then transform into calcite. While there was no significant repair in the controls without ACC, almost complete closure of the cracks was observed after a 10 days healing period in the ACC-supplemented samples. Nanoindentation measurements on the self-healed crack surfaces showed a similar or slightly higher elasticity at a lower hardness compared to non-cracked surfaces. Our results demonstrate that bioinspired approaches, like the use of polyP-stabilized ACC shown here, can significantly improve the repair capacity of Portland cement.

Mechanisms Accompanying Chromium Release from Concrete

The use of mineral additives from the power and metallurgy industries in the production of building materials still raises questions about the ecological safety of such materials. These questions are particularly associated with the release of heavy metals. The article presents research related to the leaching of chromium from concretes made of Portland cement CEM I and slag cement CEM III/B (containing 75% of granulated blast furnace slag). Concrete was evaluated for leaching mechanisms that may appear during tank test over the long term (64 days). It has been presented that the dominating process associated with the leaching of chromium from both types of concrete is surface wash-off. Between the 9th and 64th day of the test, leaching of Portland cement concrete can be diffusion controlled. It has been proven that the participation of slag in the composition of concrete does not affect the level of leaching of chromium into the environment from concrete.

Chloride Resistance of Portland Cement-Based Mortar Incorporating High Aluminate Cement and Calcium Carbonate

Whether chloride resistance is highly influenced by chloride binding capacity remains unknown. In this study, the chloride resistance of Portland cement-based mortar incorporating aluminate cement and calcium carbonate was investigated considering the chloride binding capacity, pore structures and chloride diffusion coefficient from non-steady state chloride migration and natural chloride diffusion. The cement hydrates were investigated using X-ray diffraction and thermogravimetric analysis. The chloride binding capacity was evaluated based on the chloride adsorption from the solutions using the adsorption isotherm. The aluminate cement, as an available alumina source, can stimulate the formulation of layered double hydroxides, which in turn can increase the chloride binding capacity. The results of mercury intrusion porosimetry show that non-substituted (control) and substituted (only aluminate cement) specimens have capillary pore volume 8.9 vol % and 8.2 vol %, respectively. However, the specimen substituted with aluminate cement and calcium carbonate shows a higher capillary volume (12.9 vol %), which correlates with the chloride diffusion coefficient. Although the specimen substituted with calcium carbonate has a higher chloride binding capacity than the control, it does not necessarily affect the decrease in the chloride diffusion coefficient. The capillary pore volume can affect not only the chloride diffusion but also the chloride adsorption.

Recycling hazardous textile effluent sludge in cement-based construction materials: Physicochemical interactions between sludge and cement

The textile industry produces a large amount of textile effluent sludge (TES). Many studies have explored the potential use of TES in cement-based materials. However, the physicochemical interactions between the TES and ordinary Portland cement (OPC) have rarely been studied. In this study, the effects of increasing dosage (0-20% by OPC) of TES on the performance of OPC-TES blends were investigated in terms of hydration progress, mechanical strength, microstructure evolution and metal leachability. The results showed that TES markedly delayed the OPC hydration at the early age, and increasing dosages of TES decreased the portlandite content at 7 and 28 days' age. Compared to the reference, the OPC-TES mortar exhibited seriously degraded mechanical strength; when using 20% TES, the decrease in compressive and flexural strength reached up to 71% and 42% respectively at the age of 28 days. Scanning electron microcopy and mercury intrusion porosimetry found the inclusion of TES introduced more weak interfaces in the cement mortar, thus increased the total porosity especially the macropores. But leachability tests revealed all the toxic metals in the TES were stabilized after the incorporation of OPC and exhibited very low metal mobility in the OPC-TES mortar, which posed no environmental risk.

Characterization data of reference cement CEM I 42.5 R used for priority program DFG SPP 2005 "Opus Fluidum Futurum - Rheology of reactive, multiscale, multiphase construction materials"

A thorough characterization of starting materials is the precondition for further research, especially for cement, which contains various phases and presents quite a complex material for fundamental scientific investigation. In the paper at hand, the characterization data of the reference cement CEM I 42.5 R used within the priority program 2005 of the German Research Foundation (DFG SPP 2005) are presented from the aspects of chemical and mineralogical compositions as well as physical and chemical properties. The data were collected based on tests conducted by nine research groups involved in this cooperative program. For all data received, the mean values and the corresponding errors were calculated. The results shall be used for the ongoing research within the priority program.

Humidity Driven Transition from Insulator to Ionic Conductor in Portland Cement

This work aims to assess ionic conduction in anhydrous cement particles and hydrated cement pastes with aging periods of 5–25 days. When a cement sample was humidified (relative humidity = 100%) over the range of 50–100 °C, it exhibited bulk conductivities of 10⁻³–10⁻² S cm⁻¹, regardless of the hydration level, whereas the interfacial conductivities varied in the range of 10⁻⁷–10⁻³ S cm⁻¹, depending on the structural defects or conduction pathways of the sample. Both the bulk and interfacial conductivities were increased to 0.01 S cm⁻¹ or higher at 100 °C, although the sample required previous moistening with water mist. The major charge carrier in the sample was determined to be hydroxide ions, and the total ion transport number was approximately 1. Exposing the sample to a mixture of carbon dioxide and water vapor caused a decrease in the bulk and interfacial conductivities; however, the bulk conductivity was returned to the initial value by treatment with an acid.

Influences of coal fly ash containing ammonium salts on properties of cement paste

This paper aims to investigate the influence of coal fly ash containing ammonium salts on properties of cement paste. Fly ash was incorporated at percentage of 20% by weight of the total binder to replace Portland cement. Ammonium hydrogen sulfate (NH₃HSO₄) or ammonium sulfate ((NH₃)₂SO₄) were introduced at percentages of 3.0%-6.0% or 1.5%-3.0% by fly ash weight. Compressive strength, setting time and hydration heat were evaluated on variable blend mixtures. Adsorption behaviors of polycarboxylate-based superplasticizer and air entraining agent on fly ash particles were also evaluated using total organic carbon (TOC) method. Semi-adiabatic calorimetry, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry-differential thermal analysis, mercury intrusion porosity and scanning electron microscope measurements were carried out on typical samples. Experimental results showed that the chemical admixtures adsorbed by coal fly ash were increased by the introduction of NH₃HSO₄ or (NH₃)₂SO₄. The addition of 3.0%-6.0% NH₃HSO₄ and 1.5%-3.0% (NH₃)₂SO₄ decreased the 28d compressive strength of fly ash-cement pastes by 4.3%-10.4% and 6.3%-8.9%, respectively. The initial and final setting times were delayed and the early age hydration of Portland cement was also retarded. Moreover, the pore structure was coarsened and porosity was increased for the hardened cement specimens due to the release of ammonia and lower hydration degree. Therefore, more attention should be paid to the application of denitration fly ash to the cement and concrete industry.

Strength Development and Strain Localization Behavior of Cemented Paste Backfills Using Portland Cement and Fly Ash

This study examines the combined performance of Portland cement (PC), the binder, and fly ash (FA), the additive, towards improving the mechanical performance of the South Australian copper-gold underground mine cemented paste backfill (CPB) system. A series of unconfined compressive strength (UCS) tests were carried out on various mix designs to evaluate the effects of binder and/or additive contents, as well as curing time, on the CPB's strength, stiffness and toughness. Moreover, the failure patterns of the tested samples were investigated by means of the three-dimensional digital image correlation (DIC) technique. Making use of several virtual extensometers, the state of axial and lateral strain localization was also investigated in the pre- and post-peak regimes. The greater the PC content and/or the longer the curing period, the higher the developed strength, stiffness and toughness. The use of FA alongside PC led to further strength and stiffness improvements by way of inducing secondary pozzolanic reactions. Common strength criteria for CPBs were considered to assess the applicability of the tested mix designs; with regards to stope stability, 4% PC + 3% FA was found to satisfy the minimum 700 kPa threshold, and thus was deemed as the optimum choice. As opposed to external measurement devices, the DIC technique was found to provide strain measurements free from bedding errors. The developed field of axial and lateral strains indicated that strain localization initiates in the pre-peak regime at around 80% of the UCS. The greater the PC (or PC + FA) content, and more importantly the longer the curing period, the closer the axial stress level required to initiate localization to the UCS, thus emulating the failure mechanism of quasi-brittle materials such as rock and concrete. Finally, with an increase in curing time, the difference between strain values at the localized and non-localized zones became less significant in the pre-peak regime and more pronounced in the post-peak regime.

Geopolymer, Calcium Aluminate, and Portland Cement-Based Mortars: Comparing Degradation Using Acetic Acid

In this paper, we comparitvley studied acetic acid attacks on geopolymer (GP-M), calcium aluminate (CAC-M), and Portland cement (PC-M)-based mortars. Consequent formations of deteriorated or transition layers surrounding the unaltered core material was classified in these three mortars, according to different degradation levels depending on what binder type was involved. Apart from mass loss, hardness, and deterioration depth, their microstructural alterations were analyzed using test methods such as scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), mercury intrusion porosimetry (MIP), powder X-ray diffraction (XRD), and thermogravimetric analysis-differential scanning calorimeter (TGA-DSC), which showed the different mechanisms for each binder type. Elemental maps revealed the decalcification (PC-M and CAC-M) and depolymerization (GP-M) that occurred across the mortar sections. The mass loss, hardness, and porosity were the least affected for GP-M, followed by CAC-M. These results points out that geopolymer-based mortars have improved acid resistance, which can be used as a potential alternative to conventional cement concretes that have been exposed to agro-industrial environments.

Application of Isothermal and Isoperibolic Calorimetry to Assess the Effect of Zinc on Hydration of Cement Blended with Slag

This work deals with the influence of zinc on cement hydration. The amount of zinc in cement has increased over recent years. This is mainly due to the utilization of solid waste and tires, which are widely used as a fuel in a rotary kiln. Zinc can also be introduced to cement through such secondary raw materials as slag, due to increased recycling of galvanized materials. The aim of this work was to determine the effect of zinc on the hydration of Portland cement, blended with ground blast furnace slag (GBFS). This effect was studied by isothermal and isoperibolic calorimetry. Both calorimetry methods are suitable for measurements during the first days of hydration. Isoperibolic calorimetry monitors the hydration process in real-life conditions, while isothermal calorimetry does so at a defined chosen temperature. Zinc was added to the cement in the form of two soluble salts, namely Zn(NO₃)₂, ZnCl₂, and a poorly soluble compound, ZnO. The concentration of added zinc was chosen to be 0.05, 0.1, 0.5, and 1mass percent. The amount of GBFS replacement was 15% of cement dosage. The newly formed hydration products were identified by X-ray diffraction method (XRD).

The possibility of fly ash and blast furnace slag disposal by using these environmental wastes as substitutes in portland cement

The possibility of disposing of fly ash (FA) and blast furnace slag (BFS), which are environmental wastes, by using them as substitutes in portland cement was examined in this study. Portland cement (CEM I), FA, BFS, CEN standard sand, and water were used in the production of mortars. Blended cements were obtained by substituting FA, BFS, and a mixture of FA and BFS (FABFS) at 5.0%, 10.0%, 15.0%, and 20.0% ratios in portland cement. Physical (Blaine area, density, initial and final setting time, and fineness), mechanical (flexural strength and compressive strength), radiation permeability (determination of linear absorption coefficient) and high-temperature experiments were performed on the FA, BFS, and FABFS samples. Mortar prism samples with a size of 40 × 40 × 160 mm were obtained using these cements. The samples were exposed to five temperatures: 20, 150, 300, 700, and 900 °C. Mortar samples kept at 20 °C were used as references. A total of 390 samples were studied under air cooling (spontaneous cooling at 20 ± 2 °C in laboratory environment). After the mortar samples reached at room temperature, flexural strength and compressive strength tests were carried out on the 28th and 90th days. The test results showed that FA, BFS, and FABFS can be used as pozzolanic additives in cement mortars both alone and together and can be applied in buildings with a high risk of fire up to certain temperature values. The sample with the highest linear absorption coefficient was the FABFS sample, and as the sample with the lowest radiation permeability, it was determined to be appropriate for use in buildings that are exposed to radiation effects.

Effect of different water-to-powder ratios on the dimensional stability and compressive strength of mineral aggregate-based cements

Purpose:

The aim of this study was to evaluate the effect of different water-to-powder ratios on the dimensional stability and compressive strength of Portland cement and Mineral Trioxide Aggregate (MTA).

Materials and methods:

Five different volumes of distilled water (0.26; 0.28; 0.30; 0.33 and 0.35 mL) were used for every 1 g of the cements. Twelve samples (12 mm long x 6 mm in diameter) were prepared in Teflon molds. After measuring the initial length, the specimens were stored in distilled water for 24 hours or 30 days. At the end of these time intervals, the specimens were measured again, and the dimensional change was calculated. The same samples used in the previous test were submitted to compression in a universal test machine (1 mm/min-1).

Results:

Analysis of the dimensional stability results showed no statistical difference between the cements, proportions and time intervals tested, or between their interactions. After 24 hours, MTA was more resistant than Portland cement (p<0.05). At 30 day-period, both cements had similar, and significantly higher resistance than they did at 24 hours (p<0.05).

Conclusion:

The powder/water ratio had no influence on the dimensional stability of cements. Compressive strength of Portland cement was affected at the proportions of 0.30 and 0.35 mL/g.

Transformation of Construction Cement to a Self-Healing Hybrid Binder

A new biomimetic strategy to im prove the self-healing properties of Portland cement is presented that is based on the application of the biogenic inorganic polymer polyphosphate (polyP), which is used as a cement admixture. The data show that synthetic linear polyp, with an average chain length of 40, as well as natural long-chain polyP isolated from soil bacteria, has the ability to support self-healing of this construction material. Furthermore, polyP, used as a water-soluble Na-salt, is subject to Na+/Ca2+ exchange by the Ca2+ from the cement, resulting in the formation of a water-rich coacervate when added to the cement surface, especially to the surface of bacteria-containing cement/concrete samples. The addition of polyP in low concentrations (<1% on weight basis for the solids) not only accelerated the hardening of cement/concrete but also the healing of microcracks present in the material. The results suggest that long-chain polyP is a promising additive that increases the self-healing capacity of cement by mimicking a bacteria-mediated natural mechanism.

High-Performance Graphene-Based Cementitious Composites

This study reports on the development of a cementitious composite incorporating electrochemically exfoliated graphene (EEG). This hybrid functional material features significantly enhanced microstructure and mechanical properties, as well as unaffected workability; thus, it outperforms previously reported cementitious composites containing graphene derivatives. The manufacturing of the composite relies on a simple and efficient method that enables the uniform dispersion of EEG within cement matrix in the absence of surfactants. Different from graphene oxide, EEG is found to not agglomerate in cement alkaline environment, thereby not affecting the fluidity of cementitious composites. The addition of 0.05 wt% graphene content to ordinary Portland cement results in an increase up to 79%, 8%, and 9% for the tensile strength, compressive strength, and Young's modulus, respectively. Remarkably, it is found that the addition of EEG promotes the hydration reaction of both alite and belite, thus leading to the formation of a large fraction of 3CaO·2SiO2·3H2O (C-S-H) phase. These findings represent a major step forward toward the practical application of nanomaterials in civil engineering.

Quantitative disentanglement of nanocrystalline phases in cement pastes by synchrotron ptychographic X-ray tomography

Mortars and concretes are ubiquitous materials with very complex hierarchical microstructures. To fully understand their main properties and to decrease their CO₂ footprint, a sound description of their spatially resolved mineralogy is necessary. Developing this knowledge is very challenging as about half of the volume of hydrated cement is a nanocrystalline component, calcium silicate hydrate (C-S-H) gel. Furthermore, other poorly crystalline phases (e.g. iron siliceous hydrogarnet or silica oxide) may coexist, which are even more difficult to characterize. Traditional spatially resolved techniques such as electron microscopy involve complex sample preparation steps that often lead to artefacts (e.g. dehydration and microstructural changes). Here, synchrotron ptychographic tomography has been used to obtain spatially resolved information on three unaltered representative samples: neat Portland paste, Portland-calcite and Portland-fly-ash blend pastes with a spatial resolution below 100 nm in samples with a volume of up to 5 × 10⁴ µm³. For the neat Portland paste, the ptychotomographic study gave densities of 2.11 and 2.52 g cm^-3 and a content of 41.1 and 6.4 vol% for nanocrystalline C-S-H gel and poorly crystalline iron siliceous hydrogarnet, respectively. Furthermore, the spatially resolved volumetric mass-density information has allowed characterization of inner-product and outer-product C-S-H gels. The average density of the inner-product C-S-H is smaller than that of the outer product and its variability is larger. Full characterization of the pastes, including segmentation of the different components, is reported and the contents are compared with the results obtained by thermodynamic modelling.

Recycling of waste autoclaved aerated concrete powder in Portland cement by accelerated carbonation

To recycle waste autoclaved aerated concrete (WAAC) and minimize environmental pollution induced by Portland cement (PC), carbonation curing was performed on cement pastes containing variable replacement levels (0-50%) of waste autoclaved aerated concrete powder. Compressive strength and chloride ion permeability of PC-WAAC specimens were measured and related mechanisms were demonstrated by X-ray diffraction (XRD), ²⁹Si solid-state Nuclear Magnetic Resonance (NMR), thermogravimetry-differential thermal analysis (TG-DTA), mercury intrusion porosimeter (MIP), scanning electron microscope (SEM) and back scattered electron images (BSE) measurements. Results showed that the PC-WAAC specimens presents a higher compressive strength increase than the pure PC specimen after carbonation curing and the optimal dosage of WAAC is 20%. This effect compensates the decreasing strength induced by the incorporation of WAAC. Chloride ion penetration resistance of cement pastes were also improved by carbonation curing due to the refinement of pore structure. Up to 20% of WAAC can be successfully recycled to replace PC without compromising strength and chloride ion permeability. Moreover, around 11.23-19.02% of CO₂ by the total binder weight can be captured. Therefore, this technology has a great environmental potential to both recycling of construction waste and capture of greenhouse gas.

The role of secondary minerals in remediation of acid mine drainage by Portland cement

To test the effects of secondary mineral formation on cement neutralisation of acid mine drainage (AMD), cement samples were leached with AMD and dilute sulfuric acid of approximately equal acidity. In both cases the neutralising efficiency of the cements, due to dissolution of portlandite as well as the hydrated calcium silicate and aluminate phases, decreased as secondary minerals accumulated on the cement surfaces. The AMD-leached cement became coated with Fe hydroxides, whereas the H₂SO₄-leached cement was covered primarily with gypsum. Ettringite and thaumasite also formed within the cement in both cases, however in much greater amounts in cement leached with AMD. The AMD penetrated deeper into the cement than H₂SO₄ because the higher amounts of ettringite and thaumasite in AMD-leached cement caused expansion and cracking. The cracking, which resulted in a substantial loss of strength of the cement, was enhanced when the cement samples were allowed to dry out. This indicates that cement used for passive treatment of AMD will likely provide better long-term neutralisation in at least partially unsaturated conditions where the cement dries out periodically, facilitating cracking to allow deeper penetration of AMD.

Study on the Effect of Graphene Oxide with Low Oxygen Content on Portland Cement Based Composites

The current study presents research into the effect of graphene oxide (GO) with a carbon to oxygen ratio of 4:1 on the fluidity, hydration, microstructure, mechanical and physical properties of Portland cement pastes and mortars. The amounts of GO investigated were 0.02%, 0.04%, and 0.06% by weight of cement, while for mortars, an extra composition with 0.1% was also prepared. According to the results, the fluidity of cement paste and mortar increased and the hydration process was slightly retarded with the addition of GO. Despite this, improvements in compressive and flexural strength were established in the mortars containing GO. The maximum effects (~22% and ~6%, respectively) were obtained with the addition of 0.06% GO. The calculation of estimated strength proportional to samples of equal density showed that for mortars cured for 7 days the gain in strength was directly related to the gain in density. For mortar samples cured for 28 days, the estimated strength was found to be significantly higher than that of the reference sample, indicating that besides density there are other factors determining the improvement in strength of mortars modified with GO. The possible structure strengthening mechanisms are discussed.

Sealing Ability of MTA vs Portland Cement in the Repair of Furcal Perforations of Primary Molars: A Dye Extraction Leakage Model-An In Vitro Study

AIM

The purpose of this present study is to compare the ability of MTA and Portland cement to seal furcal perforations in extracted primary molars using the dye extraction leakage model.

MATERIALS AND METHODS

Sixty primary molars were selected and randomly divided into four groups after access openings and furcal perforations were created in the pulp chamber floor. Group I (n = 20) in which perforations were repaired with MTA (ProRoot MTA, MTA-Angelus), group II (n = 20) in which perforations were repaired with the Portland cement, group III (n = 10) in which perforations were left unsealed (positive control), and group IV (n = 10) without perforations (negative control). All samples were subjected to 1% of basic fuchsin dye challenge followed by dye extraction with 65 wt% of nitric acid. Samples were analyzed using the automatic microplate spectrophotometer 545 nm and the readings were statistically analyzed.

RESULTS

There was no statistically significant difference in the microleakage between MTA and Portland cement repair groups.

CONCLUSION

Portland cement provides an effective seal for primary teeth furcal perforations and can be considered a more economic substitute for MTA as a repair material enhancing the prognosis of perforated primary teeth that would otherwise be extracted.

HOW TO CITE THIS ARTICLE

Reddy NV, Srujana P, et al. Sealing Ability of MTA vs Portland Cement in the Repair of Furcal Perforations of Primary Molars: A Dye Extraction Leakage Model-An In Vitro Study. Int J Clin Pediatr Dent 2019;12(2):83-87.

Prevalence of chronic obstructive pulmonary disease (COPD) among Congolese cement workers exposed to cement dust, in Kongo Central Province

Chronic exposure to cement dust may induce adverse health effects, including a significant decrease in lung function. The study investigated whether the prevalence of COPD and respiratory symptoms was associated with working at different tasks exposed to varying levels of cement dust. The cross-sectional study was carried out among 223 exposed and 156 less exposed workers from two cement factories from November 20 to December 15, 2016 in DRC. Workers completed a questionnaire and spirometry was performed. Multivariate analysis was performed to evaluate the association between occupation exposed to cement dust, COPD, and respiratory symptoms, after adjustment for confounders. Morning cough and cough on most days for as much as 3 months each year were significantly higher in the exposed group (p < 0.05) (p = 0.001) than in the less exposed group. As compared to the less exposed group, the prevalence of COPD was higher among the exposed group, 28.2 and 9.6% respectively (p < 0.001). A significant association with COPD, aOR 14.49 (5.33; 39.40), aOR 3.37 (1.44; 7.89), and aOR 3.09 (1.58; 6.05) was found among cleaning, transportation, and production workers, respectively. Working at certain tasks exposed to cement dust is associated with the higher prevalence of COPD and respiratory symptoms. A greater risk is being among cleaning, transportation, and production workers. This suggests the necessity to prioritize the quality of preventive measures in each work area.

CO₂ Uptake of Carbonation-Cured Cement Blended with Ground Volcanic Ash

Accelerated carbonation curing (ACC) as well as partial replacement of cement with natural minerals are examples of many previous approaches, which aimed to produce cementitious products with better properties and environmental amicabilities. In this regard, the present study investigates CO₂ uptake of carbonation-cured cement blended with ground Saudi Arabian volcanic ash (VA). Paste samples with cement replacement of 20%, 30%, 40%, and 50% by mass were prepared and carbonation-cured after initial curing of 24 h. A compressive strength test, X-ray diffractometry (XRD), and thermogravimetry were performed. Although pozzolanic reaction of VA hardly occurred, unlike other pozzolana in blended cement, the results revealed that incorporation of VA as a supplementary cementitious material significantly enhanced the compressive strength and diffusion of CO₂ in the matrix. This increased the CO₂ uptake capacity of cement, reducing the net CO₂ emission upon carbonation curing.

Binders alternative to Portland cement and waste management for sustainable construction-part 1

This review presents "a state of the art" report on sustainability in construction materials. The authors propose different solutions to make the concrete industry more environmentally friendly in order to reduce greenhouse gases emissions and consumption of non-renewable resources. Part 1-the present paper-focuses on the use of binders alternative to Portland cement, including sulfoaluminate cements, alkali-activated materials, and geopolymers. Part 2 will be dedicated to traditional Portland-free binders and waste management and recycling in mortar and concrete production.

Recovery of ilmenite mud as an additive in commercial Portland cements

This work is focused on the manufacture of commercial cement using as additive ilmenite mud, a waste generated during TiO₂ pigment production. The cements were produced by adding different proportions of mud (2.5, 5 and 10 wt%) to ordinary Portland cement (OPC). The ilmenite mud and the ilmenite mud cements (IMCs) were characterised physico-chemically by X-ray fluorescence (XRF), inductively coupled plasma mass spectrometry (ICP-MS) and X-ray diffraction (XRD). Moreover, the technological properties of the IMCs were evaluated and compared with a reference material (OPC). Since waste from the TiO₂ industry is classified as a NORM (naturally occurring radioactive material), the concentrations of radionuclides were measured by high-resolution low-background gamma and alpha spectrometry techniques. Finally, the TCLP leaching test (Toxicity Characteristic Leaching Procedure, USEPA), the radiological index ("I") and the Ra equivalent concentration were also calculated to evaluate the environmental risks. As a final conclusion, it can be pointed out that the addition of ilmenite mud to OPC plays a beneficial role since it reduces the heat of hydration, the final setting time, the expansion and the linear retraction compared to standard OPC. The compression strength improves with the addition of up to 5 wt% mud. Moreover, the environmental impact of IMC2.5 and IMC5 can be considered negligible.