Leaching Of Calcium Ions Research Articles

Mechanism of organic additives-induced carbonation activators on affecting cement mortars

In this study, we investigated the impact of introducing an in-situ activator, produced by carbonating cement particles in an aqueous solution, on the properties of cement mortars through secondary mixing. Two organic additives, ethylenediaminetetraacetic acid (EDTA) and glutamic acid (GLTA), were employed to enhance the leaching of calcium ions during carbonation, thereby improving the carbonation efficiency. A suite of characterization techniques revealed that the presence of organic additives could refine the carbonated particles and influence the morphology. The carbonated activators generated by this process were rich in silica gel and various polymorphic forms of calcium carbonate. These components, serving as fillers and nucleation for cement hydration, significantly accelerated the hydration process of cement mortar and promoted the formation of carboaluminate in the secondary mixing process. This approach effectively decreased the porosity of the cement mortar, refined the pore structure, and enhanced the mechanical strength.

A microcrack-based anisotropic damage model for concrete under mechanical loading and calcium leaching

In underground construction, concrete is always subjected to triaxial stress and calcium ion leaching, which results in anisotropic damage to concrete and reduce the durability of the structure. To capture the anisotropic damage properties of concrete subjected to mechanical-chemical coupling effects and predict the durability of underground concrete structure accurately, a microcrack-based anisotropic damage model is proposed. The mechanical damage, reflecting the density and direction of the microcracks caused by mechanical loading, is defined by a second-order tensor. The degree of chemical damage is defined by the amount of solid calcium phase lost in the concrete. Considering oriented microcrack and the influence of chemical damage on fracture toughness, the anisotropic mechanical damage evolution law of microcrack was established by linear fracture mechanics. A phenomenological chemical model governed by a diffusion law considering the variation of diffusion coefficient with stress induced microcracks is defined to describe the calcium dissolution process. The simulation results are in good agreement with the experimental results. Compared with the traditional elastoplastic damage model, the maximum creep error is only 0.114 ‰.

Heavy metals removal in a graphene engineered concrete-based filter column

In this study, crushed aggregate surfaces were coated with reduced graphene oxide (RGO) using a chitosan-derived solution and included in porous concrete-based filter column samples to improve heavy metal removal. The RGO coating strengthened the aggregate and cement interfaces, thus improving the compressive strength of these samples by up to 18 %. The removal of lead and copper in samples containing RGO coated aggregate (GCA) operated with a minimum hydraulic load was found to be 97 % and 92 %. Increasing the hydraulic load reduced this heavy metal removal, but the presence of GCA increased the active sites for heavy metal ions to immobilize, leading to improved copper removal under such operating conditions. Calcium ions from the cement hydrates were found to leach from the concrete matrices during such a wastewater passage. This leaching of calcium ions was determined to be relatively lesser in RGO decorated concrete samples, pointing out the positive effects of GCA on the resistance of the concrete matrices to aggressive chemicals. Clay particles containing highly turbid water were also passed through these concrete samples to examine the effects on the infiltration rate. Clay particles were found to clog pores, marginally reducing the infiltration rate. Concrete-based water filters are easy to operate and have low maintenance requirements, and industries responsible for heavy metal pollution in aquatic environments can widely adopt them instead of complex treatment methods.

Durability of cementitious mortar: Incorporation of highly dispersed superplasticizer modified graphene oxide in fly ash blended mortar

The present study focuses on the utilization of superplasticizer stabilized graphene oxide (GO) as a reinforcing agent in the fly ash blended cement mortar (30–70 ratio of FA/OPC). GO is moderately stable in water solvent medium while, it agglomerates in the alkaline cement pore solution owing to the interference caused by Mg2+, Na+, Ca2+, and OH− etc. So, here an effort has been made to stabilize the GO via superplasticizer's (PCE-SP) steric effect and has further been used as a reinforcing phase in the cement-fly ash-based mortars. The UV–visible (Agilent Pro) spectrometry was used to measure the degree of stabilization via absorbance values. The increased dispersion of GO due to PCE-SP steric stabilization as compared to without PCE-SP has been monitored by UV–Visible spectroscopy. The results have shown that incorporation of 0.08 % PCE-GO (by weight percentage of blend) amended compressive and split-tensile strength of the mortars by 39.85 % and 48.90 % as compared to control-FA specimen at the curing age of 90 days, respectively. Furthermore, the results achieved were equal or even superior than 100 % cement-based mortar (control-OPC). Micro-structural results showed the acceleration of pozzolanic reactions on the nucleation sites supplied by the PCE-GO's functionalities. Mercury Intrusion Porosimeter studies shows that porosity of fly ash-cement mortar was reduced in comparison to control-FA mortar by 51.5 % after 0.08 % PCE-GO incorporation. The cumulative pore volume also contracted from 0.057 to 0.025 cc/g, depicting densification of C–S–H gel network owing to the synergism acting between FA and PCE-GO in cement-FA matrix. Porosity results are also complying with the enhanced electrical resistivity and reduced water absorption values of mortars. In terms of weight loss and compressive strength gain over various exposure periods, mortars incorporating PCE-GO performed better than control samples in all durability-related aspects. PCE-GO incorporation also resulted in improved acid and sulfate attack resistance, owing to the reduced leaching of calcium ions from hydrated cement-FA matrix. This led to lesser deterioration of PCE-GO incorporated mortars owing to reduced ettringite and gypsum formation, as confirmed by XRD and SEM mapping studies. Overall, the incorporation of PCE-GO in mortars has demonstrated significant enhancements in properties. This development holds great promise for the advancement of the construction and infrastructure sectors. The utilization of high-performance mortars has the potential to enhance the strength, durability, and sustainability of structures, thereby making a valuable contribution to the development of safer and more resilient built environments. Furthermore, the utilization of PCE-GO in an innovative manner has the potential to revolutionize construction methodologies and materials in forthcoming times.

Polycarboxylate superplasticizer as strengthening additive in carbonated artificial steel slag aggregate

This article presents an investigation on the application of polycarboxylate superplasticizer (PCE) to improve the mechanical properties of carbonated artificial steel slag aggregate (CSSA). It is observed that dispersion effect of PCE on steel slag particles significantly improves the degree of compaction of CSSA before carbonation and the PCE molecules slows down the evaporation of water leading to the higher residue water–solid ratio (w/s) of CSSA after carbonation, which are beneficial for the improvement of CO2 uptake and mechanical properties of CSSA. Moreover, the cross-linked PCE molecules by calcium ions from steel slag hinders the early carbonation reaction of steel slag which is conducive to the CO2 diffusion from outside to inside of CSSA thus results in a more homogenous structure of CSSA. Additionally, reconstituted PCE molecules promotes the leaching of calcium ions leading to an increase of CO2 uptake of CSSA at the long-term (24 h) duration of carbonation. At optimum of 1% PCE, the compressive strength of CSSA reaches a maximum value of 164 MPa, which is 141% higher than that of CSSA without PCE.

Effect of curing temperatures and additional activators on chloride ingress and its induced mineralogical alteration of ground granulated blast furnace slag activated by Ca(OH)2

The impact of additional activators (sodium sulfate, sodium nitrite, and calcium nitrite) and curing temperature (20 and 35 °C) on chloride binding and ingress resistance of ground granulated blast furnace slag activated by Ca(OH)2 was studied using X-ray diffraction, scanning electron microscopy, thermogravimetric and thermodynamic modeling. The outcomes of the study indicated that the difference in the chloride binding capacity at low chloride concentrations was primarily affected by the types of the AFm phase. The solid solution formed between Friedel's salt and various types of AFm phases resulted in a decrease in the chloride binding capacity. At a curing temperature of 35 °C, the chloride binding capacity reduced due to the leaching of calcium ions and carbonation induced by the coarse pore structure. It was found that the chloride ingress resistance was significantly related to the leaching of calcium and carbonation, and the denser calcite layer formed at the exposure layer had a positive impact on the chloride ingress resistance.

Evaluation of transport properties of deteriorated concrete due to calcium leaching with coupled CT image analysis and random walk simulation

Concrete may deteriorate when chronically in contact with water due to the leaching of calcium ions. This study conducted a natural diffusion test for calcium ions with a minute cylindrical specimen of 3 mm in diameter and 6 mm in height to determine leaching at 20 and 80 °C in 33 days. One piece of limestone as aggregate was inserted inside each specimen to investigate the effect of the interfacial transition zone (ITZ). Changes in mass transfer in the leaching and non-leaching regions in bulk cement paste were evaluated using synchrotron X-ray computed tomography (CT) in a micrometer order. A deeper dissolution front of Ca(OH)2 inside the specimen was observed for a higher temperature leaching test. Random walk simulation was performed to obtain diffusion parameters. Results showed that the calcium diffusion coefficient of non-deteriorated ITZ is about ten times as high as that of the non-leaching region. For the leaching region, the diffusion coefficient is about 50 times and 100 times as high as that of the non-leaching region at 20 °C and 80 °C, respectively. In addition, the Ca(OH)2 dissolution front appeared deeper inside the specimen in the direction where aggregate is close or exposed to the dissolution front because of ITZ.

Comparison of obturation quality in natural and replica teeth root-filled using different sealers and techniques

ObjectivesThis study aims to assess the obturation efficacy of sealers placed with different techniques using microcomputed tomography (µCT) and assess the influence of µCT testing parameters on the obturation data obtained.Materials and methodsIncisors and mesial roots of lower molars with standardized root length were scanned using µCT, and one tooth of each type was 3D printed in acrylic. Two obturation techniques (warm vertical and single cone) and 4 sealer types (AH Plus, BioRoot RCS, Totalfill BC, and Bio-C Sealers) were assessed following storage in Hank’s balanced salt solution for 3 and 6 months by assessing gap and void volume percentages on both natural and replica incisor and molar roots. The storage solution was analysed to assess calcium ion leaching. The influence of temperature, tooth positioning, and moisture content of the teeth while µCT scanning was also investigated.ResultsThe obturation quality in the incisor group was the same using both natural teeth and replicas (p > 0.05). No changes in void volume were identified when comparing the same sealer using different obturation techniques. The premixed sealers used in single-cone obturation exhibited high void volume in the 3D printed replicas in the long term. The temperature, positioning, and moisture content of the teeth did not affect the outcome of µCT testing.ConclusionsBioRoot RCS, Totalfill BC, and Bio-C Sealers are suitable for obturation of both complex and simple root canal systems using different obturation techniques with BioRoot RCS exhibiting the highest calcium ion release. 3D printed acrylic teeth can be used to assess the obturation quality in uncomplicated root canal systems. µCT parameters had no significant effect on the µCT measurement.Clinical relevanceThe single-cone obturation technique with hydraulic sealer is a simple technique that can be used for obturation of all root canal systems.

Affirmative nanosilica mediated approach against fungal biodeterioration of concrete materials

Microbial biodeterioration has been an important concern for concrete buildings’ durability over time. This study primarily emphasizes on the fungal biodeterioration of concrete and the effectiveness of silicon dioxide nanocoating on concrete in inhibiting fungal growth. A nanosilica coating was optimised and applied on concrete cube surface that was in turn infected with Aspergillus tamarii and monitored physical, mechanical, chemical as well as visual changes for a period of six months. The visual analysis included colour changes, Stereo Microscopy and Scanning Electron Microscopy (SEM) which showed a considerable change on the surface deterioration. Weight loss showed positive in all the concrete specimens (2.08% for biodeteriorated cubes and 2.13% for nanocoated cubes) whereas compressive strength that increased, 35.01% in nanocoated concrete cubes and 24.72% in biodeteriorated cubes. The chemical analysis included pH change in media, Fourier Transform Infrared Spectroscopy (FTIR) and Energy Dispersive X-Ray Fluorescence Spectroscopy (EDXRF) which showed that leaching of calcium ions from the concrete in biodeteriorated cubes was higher than that of nanocoated cubes. Altogether the efficacy of silicon oxide nanocoating against biodeterioration of concrete by Aspergillus tamarii was concluded to be positive.

Effect of Fly Ash on Leaching Characteristics of Cement-Stabilized Macadam Base.

To study the leaching characteristics of a cement-stabilized macadam base with fly ash, a calcium leaching test, using varying cement and fly ash dosages in an ammonium chloride solution, was designed to obtain the rate of calcium ion leaching, porosity, and permeability coefficient of cement-stabilized macadam with leaching time. The results showed that the number of leached calcium ions increased with the cement dosage in the leaching of cement-stabilized macadam. With an increase in the cement dosage, the leaching rate of calcium ions decreased, and the leaching process of the material was delayed. The incorporation of fly ash could effectively slow down the degree of calcium ion leaching. The permeability coefficient increased gradually with the extension of leaching time, and the increase in fly ash content had a more significant effect on the improvement of the permeability coefficient than the increase in cement dosage did.

Migration and formation of an iron rich layer during acidic corrosion of concrete with no steel reinforcement

The present study aimed to study the formation, enrichment, and relocation of iron-rich regions in the corroded area of concrete blocks, made without rebar, subjected to severely corrosive highly acidic conditions. In this work, three different concrete mix designs (a proprietary ready-mixed concrete, and laboratory made mortar and concrete) were corroded under induced accelerated conditions in sulfuric acid solutions at pH 1 for a duration of one to six months, in the absence of reinforcement (i.e. rebar) or iron-oxidizing bacteria. A variety of physicochemical and mechanical techniques were applied to monitor and assess the corrosion progress, and physical and chemical changes in the corroded samples. Results indicated a pronounced presence of iron rich layer (iron oxide/hydroxide) at the border of the corrosion front and the transition zone in all mix designs in the form of a ring. While existing papers in the literature describe the iron coming from the rebar, the only source of mobile iron in this experiment was from the iron oxide (Fe2O3) already in the cement. This zone (in a form of a ring) had an average iron content of 2.0 wt% and moved away from the surface to the center of the samples submerged in a sulfuric acid bath with the increase of immersion time, and it was accompanied by hairline cracks. The movement of this zone was in the same direction as sulfate (from acidic media) ingress and the opposite direction of calcium ion leaching, (Ca leaching). The rate of corrosion, the hardness and the compressive strength of concrete are mostly affected by the concrete mix design, the iron-ring enrichment and relocation had no significant impact on them. Detection of the iron-rich zone is an indication of the depth of corrosion at advanced stages in concrete products.

Effects of soft water attack on Portland and natural zeolite blended cements

The durability of concrete infrastructure is related to the properties of the applied concrete and the effects of the aggressive external environment on it. When concrete is directly exposed to soft water, the leaching of calcium ions from hardened cement or cement-based pastes occurs, causing reduction in strength and further deterioration of the concrete structure. This paper presents the experimental results of soft water attack effects on phase composition and compressive strength of blended cement pastes, when cement is replaced with 0, 10, 20 and 30% of natural zeolite. In order to simulate soft water attack in laboratory conditions, paste specimens were exposed to leaching in deionised water up to 180 days. The evaluation of the changes in phase composition (ettringite, portlandite, calcium silicate hydrate gel) due to calcium ion leaching was made based on X-ray diffraction analysis, Fourier-transform infrared spectroscopy and paste compressive strength tests. The presence of portlandite and ettringite after 180 days of exposure to deionised water indicates that leaching did not influence the stability of the hydration products in blended cement pastes. Moreover, blended cement paste with 10% of natural zeolite had a higher compressive strength than the reference one.

Long-term durability and environmental safety of slurry type of coal ash mixed material

The combustion processes in coal-fired power plants generate a huge amount of coal fly ash (FA) as by-products. In Japan, there has been a continuous annual increase in the emission of FA due to the increased operation of thermal power stations after the Great East Japan Earthquake, which occurred in 2011. However, effectively harnessing these produced ashes has been a challenge. Coal ash mixed materials (CAMMs) (FA, cement and water composite) are being exploited mainly for the construction of port infrastructures in Japan, but their usage has been so far limited. One of the reasons for the lack of effective utilisation is that there are limited research opportunities and knowledge on the long-term durability of CAMM. Hence, this study evaluated the durability of CAMM under different exposure environments (atmospheric curing, water immersion and seawater immersion) in order to provide more understanding of the long-term application of CAMM. Results from this study indicated that the strength of CAMM increases with an increase in cement addition and curing days. However, under seawater exposure conditions, it is probable that the strength decreases after 1 year due to leaching of calcium ions from the CAMM. The deterioration of CAMM starts from the surface. Therefore, in conditions where direct contact with seawater is conceivable, attention should be paid to long-term durability.

Study on leaching damage mechanism of calcium ions of reactive powder concrete (RPC) under ion corrosion

The damage of dissolution and leaching of calcium ions caused by ion corrosion to the macroscopic mechanical properties of RPC is investigated, and the microscopic mechanism of ion corrosion is revealed. Through the unconfined compression test, the effects of different ion corrosion types on the unconfined compression strength (UCS) and failure morphology of RPC, and standard cement mortar (SCM) were studied. The effect of ion corrosion on the micro-structure and element ratio of hydration products was analyzed by SEM/EDS. In addition, through the calcium leaching model test, the effect of NaCl and MgSO4 corrosion on calcium dissolution and destruction of RPC slabs was studied, and the composition of the precipitate was determined by XRD analysis method. A damage constitutive model of RPC with ion corrosion and loading coupling was established, providing a theoretical basis for calculating the ion corrosion depth. The results show that RPC has better resistance to the damage of calcium leaching caused by ion corrosion than SCM. After 90 days of chloride ion and sulfate ion corrosion, calcium precipitation and recrystallization appeared on the surface of RPC, where an insoluble substance formed, and the ion corrosion depth was 13.32 mm and 11.30 mm, respectively.

Exchange Reactions at Mineral Interfaces.

Exchange reactions are a family of chemical reactions that appear when mineral surfaces come into contact with protic solvents. Exchange reactions can also be understood as a unique interaction at mineral interfaces. Particularly significant interactions occurring at mineral surfaces are those with water and CO2. The rather complex process occurring when minerals such as calcium silicate hydrate (C-S-H) phases come into contact with aqueous environments is referred to as a metal-proton exchange reaction (MPER). This process leads to the leaching of calcium ions from the near-surface region, the first step in the corrosion of cement-bound materials. Among the various corrosion reactions of C-S-H phases, the MPER appears to be the most important one. A promising approach to bridging certain problems caused by MPER and carbonation is the passivation of C-S-H surfaces. Today, such passivation is reached, for instance, by the functionalization of C-S-H surfaces with water-repelling organic films. Unfortunately, these organic films are weak against temperature and especially weak against abrasion. Exchange reactions at mineral interfaces allow the preparation of intrinsic, hydrophobic surfaces of C-S-H phases just at room temperature via a metal-metal exchange reaction.

Durability of cement pastes exposed to external sulfate attack and leaching: Physical and chemical aspects

Sulfate ions in seawater or underground can attack the cement paste leading to expansion and strength loss. This expansion is usually related to ettringite and gypsum precipitation. This study aims to characterize the possible altered zone and to identify the mechanisms of degradation under such conditions. For this study, cement pastes manufactured using CEM I with two w/c ratios (0.45 and 0.60) were exposed to sodium sulfate solutions (semi-immersion at a controlled pH = 8.0 ± 0.1) after one year of curing in water. The analysis of the physical aspect of this phenomenon shows that two modes of transfer occur: transfer of sulfate ions to the cement matrix and leaching of calcium ions to the external solution. The analysis of the chemical composition of the affected material highlights the progressive consumption of portlandite at the surface, the decalcification of C-S-H and the formation of AFt from both Afm and aluminium incorporated in C-S-H.

Chloride ingress and binding of coral waste filler-coral waste sand marine mortar incorporating metakaolin

The present study investigates the chloride ingress and binding behaviors of coral waste filler-coral waste sand marine mortar and the influence imposed by metakaolin (MK) addition. The mortars were cured for 4 months and followed by exposing to 0.5 M sodium chloride solution for 45 days. Thereafter, the chloride profiles of mortars were determined by titration method and the phase assemblies of mortars at different depths were determined by X-ray diffraction and thermogravimetry. The results show that coral waste mortars demonstrate dramatically lower ability to resist chloride ingress than normal mortar due to the loose structure of coral waste mortar. Due to the combination of pozzolanic reaction, formation of additional carboaluminate and improved chloride binding capacity by MK addition, chloride penetration is significantly restrained. Carboaluminate can decompose to possible solid solution between hemicarboaluminate (C4Ac0.5H12) and Friedel’s salt (C4ACl2H10) in a low chloride concentration, while it directly converts to Friedel’s salt in a high chloride concentration. Since the large amount of coral waste in system restrains the formation of monosulfoaluminate (C4AsH12), the Kuzel’s salt (C4As0.5ClH12), as an intermediate phase from monosulfoaluminate to Friedel’s salt, is not formed even in low chloride concentration. Owing to the synergistic effects of carbonation and the leaching of calcium ions, the outmost layers of the mortars bind less chloride compared to their neighboring layers.

Effect of reduced graphene oxide, alumina and silica nanoparticles on the deterioration characteristics of Portland cement paste exposed to acidic environment

Acid attack on cement concrete results in the development of a degraded layer surrounding the unaffected material, which causes a deterioration of mechanical properties. The effect of reduced graphene oxide, alumina and silica nanoparticles on the deterioration characteristics of 28-day cured cementitious pastes after storage in 0.5 moL/L HNO3 solution for a period of 56 days is reported in this paper. Samples were collected from the degraded pastes at different time periods and then characterised using various techniques like scanning electron microscopy with energy dispersive spectroscopy, optical microscopy, thermogravimetric analysis, mercury intrusion porosimetry, X-ray computed tomography and nanoindentation. While the porosimetry results showed that the presence of reduced graphene oxide and nano alumina decreased the amount of capillary pores (10 nm–10 μm) by up to 46% and 51% than the control paste after storage in acidic solution for 28 days, the details of the relative zones formed in the paste along with their characteristics were revealed by the microscopy and nanoindentation techniques. Overall, the results suggest that the presence of these nanomaterials refined the pore structure of the cementitious matrix and thereby increased the resistance to leaching of calcium ions from the binder phases exposed to aggressive aqueous media.

Calcium Extraction from Blast-Furnace-Slag-Based Mortars in Sulphate Bacterial Medium

Wastewater structures, such as treatment plants or sewers can be easily affected by bio-corrosion influenced by microorganisms living in waste water. The activity of these microbes results in deterioration and can cause the reduction in structural performance of such structures. In order to improve the durability of mortar and concrete, different admixtures are being used and the best impact is observed in cement based materials combined with blast furnace slag. In this study, mortar samples with blast furnace slag were exposed to bacterial sulphate attack for 90 and 180 days. The leaching of calcium ions from the cement matrix and equivalent damaged depths of studied mortar samples were evaluated. The results showed more significant leaching of samples placed in bacterial environment, compared to the samples placed in non-bacterial environment. Similarly, the equivalent damaged depths of mortars were much higher for the bacteria-influenced samples. The slag-based cement mortars did not clearly show improved resistance in bacterial medium in terms of calcium leaching.

Durability and mechanical properties of C–S–H/nitrobenzoic acid composite systems

The influence of nitrobenzoic acid on the nanostructure of calcium-silicate-hydrate (C–S–H) systems has been recently investigated by the authors. This study focuses on the assessment of durability and mechanical performance of the C–S–H/nitrobenzoic acid composite systems. In this context different nitrobenzoic acid isomers in various concentrations were studied. The C–S–H-based preparations were compacted into porous bodies. Their dimensional stability and the leaching of calcium ions in aqueous salt solutions containing Mg2+, Li+, Cl− or SO42− ions were evaluated. The resistance of the compacted samples to the diffusion of isopropyl alcohol was also obtained by the mass-change measurements. The microindentation technique was used to measure the creep modulus and the hardness of the samples. Evidence was obtained that nitrobenzoic acid has the potential to significantly improve the durability and mechanical properties of the C–S–H systems. This improvement, however, only occurred in the systems with the lower concentration of nitrobenzoic acid. The systems with higher concentration of nitrobenzoic acid had reduced durability and mechanical performance due to the limited interaction of the organic and inorganic phases in these systems.