Saturated Calcium Hydroxide Solution Research Articles

Consolidation of weak lime mortars by means of saturated solution of calcium hydroxide or barium hydroxide

Abstract This paper presents research results on the effects of repeated treatments with saturated solutions of calcium hydroxide (lime water) or barium hydroxide (barium water) on consolidating a friable lime mortar. The influence of lime or barium water treatment on various mainly mechanical characteristics of consolidated lime mortar was studied in detail by means of tests on non-standard specimens fabricated from a poor mortar of 1:9 vol. lime-to-sand ratio. The traditional lime water technology and barium hydroxide treatment were further compared with distilled water and lime water with added metakaolin. Lime water treatment of a specific lime mortar was shown to be effective after a sufficiently large number of applications (160 saturations) into a weak lime mortar. No consolidating effect of distilled water on the compressive strength of the tested mortar with a low lime content (1:9) was observed. The mechanical characteristics of the tested mortar were not improved by treatment with lime water with added metakaolin. Barium water treatment significantly increased mainly the tensile strength of the tested lime mortar.

Electrochemical Study of the Corrosion of Steel Embedded in Concrete Added with Composite Substituting Cement

In this work, an electrochemical study of the corrosion of steel embedded in concrete was conducted. This five test samples with cement, sand, water are produced; adding composite of hydrophobic cellulose and sugar cane bagasse ash (SCBA) previously treated, both substances are agroindustrial wastes from: Bioppapel and the sugar mill in this city of San Juan Bautista Tuxtepec. After 24 hours of drying, the samples are subjected to curing in saturated solution of calcium hydroxide and electrochemical measurements were started and continued for a period of 28 days. Then a solution of sodium chloride 3% was added according to electrochemical measurements. This study was conducted in order to observe the potential for inhibiting the steel corrosion by adding this new composite to traditional concrete . The electrochemical techniques applyed are: Electrochemical Impedance Spectroscopy and linear polarization resistance using a potentiostat/galvanostat ACM Instruments serial 914 with a calomel reference electrode. The results of these tests will be explained in the poster presentation.

Electrochemical investigations of carbon‐based conductive coatings for application as anodes in ICCP systems of reinforced concrete structures

Carbon‐based conductive coatings are complex composites, consisting of an organic or inorganic binder and conductive carbon components, for application as anodes in impressed current cathodic protection systems of reinforced concrete structures. The electrochemical properties of three coatings at different humidity and in saturated calcium hydroxide solution were studied by electrochemical methods, such as electrochemical impedance measurement, measuring of open circuit potential over time and galvanostatic polarization. The dissolved organic and inorganic carbons in electrolyte solution were quantified by using a photometric method. The structures of the coatings were investigated before and after the electrochemical tests by microscopy and scanning electron microscope/EDX analysis. The results of the electrochemical impedance measurements show that the tested coatings all have a relatively low resistance, which is between 100 and 200 Ω. The binder and the surface porosity influence the degradation behavior of those coatings. Especially the organic binder reacts with the strong alkaline medium under dissolving of organic carbon.

Composite Fiber Based on Sisal Fiber and Calcium Carbonate

The impregnation of a raw sisal fiber in a saturated solution of calcium hydroxide generated a fiber coated by a remarkable quantity of calcium carbonate and calcium oxide. However, some detachments of the inorganic coating were observed at microscopic level, and interstices in the external walls, filled by the precipitated material, were less visible than in raw fiber. Additionally, some fiber components have been removed by the preliminary sodium silicate washing. The final composite exhibited more amorphous characteristics than the original raw fiber, as well as its mechanical behavior was very similar to an elastomeric material with more homogeneous mechanical properties than the original raw fiber.

The passive behaviour of 304 stainless steels in saturated calcium hydroxide solution under different deformation

The passive behaviour of deformed 304 stainless steel samples in saturated calcium hydroxide solution has been studied by electrochemical technologies and X-ray photoelectron spectroscopy (XPS). The passive films on seriously deformed stainless steel become heavily doped. The donor and acceptor densities increase with increasing degree of deformation. The space-charge layer is thinned as the substrate is progressively deformed. The degree of deformation has an obvious influence on the composition of FeII/FeIII cations, but do not have a significant influence on the content of Cr cations. Compared with an elastically deformed sample, the passivity of a plastically deformed stainless steel is more significantly affected.

Ion Association versus Ion Interaction Models in Examining Electrolyte Solutions: Application to Calcium Hydroxide Solubility Equilibrium

The heterogeneous equilibrium of the solubility of calcium hydroxide in water is used to predict both its solubility product from solubility and solubility values from solubility product when inert salts, in any concentration, are present. Accepting the necessity of including activity coefficients to treat the saturated solution of calcium hydroxide (and by extension, all electrolyte solutions) and the inadequacy of any general or nonspecific equation (such as the Debye–Huckel limiting law or Davies equations) to calculate activity coefficients of 1:2 electrolytes, our results uncover (i) how the inclusion of ion pairs in the last mentioned equations makes them adequate for low ionic strength solutions and (ii) the need of sophisticated models, such as the ion-interaction Pitzer equations, for calculating the activity coefficients when ionic strength is high. In addition, we have developed a set of MATLAB scripts and propose the use of the free code PHREEQC version 3 to perform all the calculations descri...

Antibacterial Efficacy of a Human β-Defensin-3 Peptide on Multispecies Biofilms

IntroductionThe aggregation of mixed bacterial flora into sessile biofilms on root canal surfaces can be one of the causes of persistent apical periodontitis. The aim of this study was to evaluate the antibacterial efficacy of human β-defensin-3 (HBD3) peptide on multispecies biofilms by using confocal laser scanning microscopy. MethodsActinomyces naeslundii, Lactobacillus salivarius, Streptococcus mutans, and Enterococcus faecalis were cultured in a peptone-yeast-glucose broth, and their culture suspensions were combined in equal proportions. The mixed bacteria were inoculated on sterile coverslips placed into the wells of tissue culture plates to permit the formation of mixed species biofilm. After incubation for 3 weeks, the samples were treated for 24 hours with saline (control), saturated calcium hydroxide solution (CH), 2% chlorhexidine solution (CHX), and 50 μg/mL HBD3 solution. A commercial biofilm/viability assay kit was used to assess cell viability and analyze the 3-dimensional architecture of biofilms. The percentage of dead cells was determined from the ratio of biovolumes for the red subpopulation and the total biofilm. ResultsThree medication groups showed a significant reduction of biovolume within the biofilms compared with the control group (P < .001). The HBD3-treated biofilms had a higher percentage of dead cells than the other medication groups (P < .05). The CH and CHX groups showed higher levels of bactericidal activity than saline (P < .05), and there was no significant difference between the 2 groups (P > .05). ConclusionsHBD3 peptide exhibited more antibacterial activity against mature multispecies biofilms in vitro than either CH or CHX.

Early age hydration of calcium sulfoaluminate (synthetic ye'elimite, [formula omitted]) in the presence of gypsum and varying amounts of calcium hydroxide

Suspensions of synthetic ye'elimite (C4A3S¯) in a saturated gypsum (CS¯H2) and calcium hydroxide (CH) solution were examined in-situ in a wet cell by soft X-ray transmission microscopy and ex-situ by scanning electron microscopy. The most voluminous hydration product observed was ettringite. Ettringite commonly displayed acicular, filiform, reticulated, and stellate crystal habits. Additionally, pastes with C4A3S¯, 15% CS¯H2, and varying amounts of CH were prepared and examined with X-ray diffraction (XRD) and isothermal calorimetry. The XRD experiments showed that increasing CH content caused more solid solution (SO42−/OH−) AFm phases to form at early ages (<1d) and more monosulfate to form at later ages (>1d). Calorimetry indicated that the increased production of solid solution AFm was accompanied with an increase in the initial (<30min) rate of heat evolution, and increasing CH generally reduced the time till the second maximum rate of heat evolution due to the formation of ettringite and monosulfate.

Biomimetic mineralization on a macroporous cellulose-based matrix for bone regeneration.

The aim of this study is to investigate the biomimetic mineralization on a cellulose-based porous matrix with an improved biological profile. The cellulose matrix was precalcified using three methods: (i) cellulose samples were treated with a solution of calcium chloride and diammonium hydrogen phosphate; (ii) the carboxymethylated cellulose matrix was stored in a saturated calcium hydroxide solution; (iii) the cellulose matrix was mixed with a calcium silicate solution in order to introduce silanol groups and to combine them with calcium ions. All the methods resulted in a mineralization of the cellulose surfaces after immersion in a simulated body fluid solution. Over a period of 14 days, the matrix was completely covered with hydroxyapatite crystals. Hydroxyapatite formation depended on functional groups on the matrix surface as well as on the precalcification method. The largest hydroxyapatite crystals were obtained on the carboxymethylated cellulose matrix treated with calcium hydroxide solution. The porous cellulose matrix was not cytotoxic, allowing the adhesion and proliferation of human osteoblastic cells. Comparatively, improved cell adhesion and growth rate were achieved on the mineralized cellulose matrices.

Effect of calcium lignosulfonate on the hydration of the tricalcium aluminate–anhydrite system

As a plasticizer and retarder, calcium lignosulfonate (CL) frequently leads to quick set of Portland cement containing anhydrite. For exploring the cause of this problem, the hydration characteristics of the tricalcium aluminate–anhydrite system in the saturated calcium hydroxide solution with and without CL were researched from two aspects: the compositions of liquid phases and the formations of hydration products. Results show that the CL can promote the formation of ettringite, which induces a significant decrease in sulfate ion concentration at the initial time of hydration. The size of ettringite crystals becomes large in the presence of CL, which seems to be related to a decrease in calcium sulfate saturation ratio. It can be deduced that the quick set in the presence of CL is mainly caused by the accelerated reaction between the tricalcium aluminate and the anhydrite at the initial time of hydration.

Flexural properties loss of unidirectional epoxy/fique composites immersed in water and alkaline medium for construction application

Epoxy fique composites were evaluated for construction applications and compared with conventional wood used in construction. The composites studied were made with fique fibers treated using Na(OH) solution at 18w/v%, untreated fique fibers were also used. The matrices were epoxy and epoxy with 5wt.% of chemically modified C30B montmorillonite. Unidirectional composites of 90mm×20mm×4mm were elaborated by pultrusion processing technique. The flexural properties loss occurred over 20days of composites submitted to three types of environments: (i) water, (ii) saturated calcium hydroxide solution and (iii) mortar with w/c ratio of 0.45 and 540kg/m3 of cement, cured in a saturated solution of lime stone at 50°C. Results showed that fiber treatment and montmorillonite addition improved the flexural modulus and strength of composites in 40% and 34% respectively. Moreover the flexural properties of composites before and after ageing resulted comparable or even better than conventional wood used in construction.

In vitro susceptibility of oral Candida albicans strains to different pH levels and calcium hydroxide saturated aqueous solution

Candida albicans is present in the oral cavity and in the whole digestive tract of humans and other animals, being frequently related to endodontic treatment failure. The present study determined the incidence of C. albicans in the oral cavity and the susceptibility of isolates to different pH values and saturated calcium hydroxide aqueous solution at pH 12.5. Sixty-five patients attending the Endodontic Clinic at the Sagrado Coração University participated in the study. The collected samples were cultivated in selective media for C. albicans and the isolates were tested in terms of resistance to both alkaline pH and saturated aqueous solution of calcium hydroxide. In relation to time variables, yeast viability was assessed by the Sabouraud's agar culture and fluorescein diacetate and ethidium bromide fluorescent staining method. Results from the different pHs and experimental times, including those from different techniques measuring fungal viability, were compared using the chi-square and Fisher's exact tests (α=0.05). The yeasts became completely inviable after 48 h of contact with the calcium hydroxide solution. On the other hand, when exposed to the alkaline culture broth, the yeasts were found to be viable at pHs 9.5 and 10.5 for up to 7 days. In conclusion, C. albicans can only be completely inhibited by direct contact with saturated calcium hydroxide aqueous solution after 48 h of exposure.

Corrosion in Reinforced Concrete

Corrosion of reinforcing steel produces important damage to concrete structures in coastal, urban, and industrial zones. This damage has increased in recent years in all countries when concrete is a regular construction material, no matter if it is a technologically advanced country or it is in the process of being one. Reinforcing steel is initially protected by concrete alkaline reserve which helps to maintain the reinforcing steel passive layer. However, chlorides from salty water (i.e., marine water and/or deicing salts) or CO2/SO2 present in urban/industrial environment accumulate on the concrete surface and then move towards the rebar by known transport mechanisms like diffusion. When the chloride or CO2 threshold is exceeded, depassivation occurs and a corrosion products layer is formed in the rebar perimeter. The volume of this layer is bigger than the original steel consumed; thus, tensile stresses develop and produce concrete cover cracking and spalling. Besides being aesthetics, cracking decreases steel/concrete adherence and, potentially, the structural capacity of the affected structural element. Then, corrosion of reinforcing steel can produce significant damage affecting the whole structural behavior. Several research groups in the world has been working in the past five decades to determine possible actions to increase the service life of concrete structures, especially the initiation period (time when the aggressive elements such as chlorides and/or CO2 penetrates into the concrete cover until reaching the reinforcing steel and depassivation occurs). This special issue on corrosion of reinforcing steel includes six different papers on this topic: corrosion initiation stage. Three of the papers deal with the effect of acidic environment on the performance of different concretemixture types. One of them also includes some interesting nondestructive ultrasonic method to determine the penetration extent of the concrete degradation by the exposure of such acid solutions. Another paper deals with a multiscale method to obtain a relation between porosity characteristics inside the concrete with the damage process of concrete exposed to this acid environment. The third paper deals with the effect of acid exposure to the tensile strength of concrete specimens. The second topic is directed to a study of an alternative reinforcing steel bar with low alloying nickel content. Results obtained for this low-nickel stainless steel bar in alkaline saturated calcium hydroxide solution showed high corrosion resistance even though chlorides were added to the simulated pore solution or mortar tested as two different electrolytes. The third topic in this special issue includes the use of natural fibers (sugar bagasse cane and cactus) as potential additions to cement-based materials: sugar bagasse cane was used as a mineral addition to decrease the material porosity, and cactus, as corrosion inhibitor. Hope this special publication will help the readers to understand particular ways to increase the corrosion initiation stage of reinforced concrete-like materials, and also encourage the possibility to continue research on this field of expertise for the future generations to come.

Corrosion behaviour of a new low-nickel stainless steel in saturated calcium hydroxide solution

Corrosion behaviour of low-nickel stainless steel (SS), AISI 304 SS and carbon steel was studied using cyclic anodic polarization curves and electrochemical impedance spectroscopy (EIS). Saturated calcium hydroxide (Ca(OH) 2) solution was used to simulate a concrete pore solution at room temperature. The effect of up to 5.0% sodium chloride (NaCl) concentration in the test solution on the passivity of the alloys was studied. Experimental results showed that low-nickel SS exhibits similar behaviour to conventional AISI 304 SS, with E corr and R ct values of the same order and higher corrosion resistance than traditional carbon steel.

Preparation of Nano-ZnO Dispersive Liquid and its Characteristics Analysis by Ion Exchange Controlled Release Method

The 001×7 type cation exchange resins modified by zinc ion which acted as controlled release suppliers of ions composing crystal reacted with sodium hydroxide, saturated calcium hydroxide and ammonia solution respectively, and nano-ZnO dispersive liquid was preparaed. The result of ultraviolet analyse about the dispersive liquid showed that nano-ZnO dispersive liquid prepared by using saturated calcium hydroxide has higher nano-crystallization degree and better dispersity. The exploring results of temperature and reactive time showed that under 60°C and 16 hours conditions nano-ZnO dispersive liquid has better dispersity and can’t agglomeration and sedimentation.

Microbial Participation in the Formation of Calcium Silicate Hydrated (CSH) from Bacillus subtilis

Primary hydration of cement induces the formation of calcium silicate hydrated (C-S-H) gel and the latter contributes towards the strength development of concrete. The secondary hydration derived from pozzolanic materials such as silica fume is dependent upon the formation of C-S-H gel of the primary cement hydration reaction. The additional formation of C-S-H gel as a result of second hydration process, densities the cement microstructures producing low permeability concrete. However, the silica fume is considered expensive material and its availability is limited. Therefore, it is essential to utilise living elements as an alternative agent to form the C-S-H gel. In the present study, the untreated Bacillus Subtilisand chemically modified Bacillus subtilis(CMBS) were prepared. CMBS was prepared by reacting with ethylenediamine to modify its cell wall to become electropositive facilitating the binding of the silicate during the incubation process. The cell was then incubated in the Si solution (Na2SiO3.5H2O) for 10 days which enables the SiO32- (silica ion) from the solution to be bonded with the cell wall. The C-S-H gel is expected to be formed from the bonded silica of the cell wall when mixed with saturated calcium hydroxide solution which the latter simulates the concrete environment. The presence of C-S-H gel was then substantiated using X-Ray Diffraction (XRD) analysis. In another series of study, the difference concentration of Bacillus subtiliswere incorporated into the grade 30 concrete specimens and the compressive strength up to 60 days of age were tested. The results showed that the silicate was adsorbed by Bacillus subtilisand there is no difference in the amount of Si adsorbed between untreated Bacillus subtilisand CMBS. The incorporation of Bacillus subtilisinto the concrete enhanced the compressive strength and the concentration of 106 cell/ml was found tSo be the optimum concentration.

XPS depth profiling study on the passive oxide film of carbon steel in saturated calcium hydroxide solution and the effect of chloride on the film properties

X-ray photoelectron spectroscopy (XPS) was used to study the properties of passive oxide film that form on carbon steel in saturated calcium hydroxide solution and the effect of chloride on the film properties. The thickness of the oxide films was determined to be approximately 4nm and was not affected by the exposure time. Near the film/substrate interface the concentration of the Fe2+ oxides was higher than the concentration of the Fe3+ oxides; the layers near the free surface of the film mostly contained Fe3+ oxides. Chloride exposure decreased the thickness of the oxide films and changed their stoichiometry such that near the film/substrate interface Fe3+/Fe2+ ratio increased.

Bond between galvanized steel and concrete prepared with limestone aggregates

PurposeThe purpose of this paper is to elucidate if there is a loss in bond strength between galvanized steel used as reinforcement, and concrete of water‐to‐cement (w/c) ratio of 0.4 and 0.5, after both types of sample were cured for seven, 21 and 28 days in saturated calcium hydroxide solution, and without curing. The air permeability of the concrete was investigated at the interfacial zone.Design/methodology/approachStructural low‐carbon steel and galvanized steel were embedded in concrete samples, prepared with Portland cement type I and limestone (calcite 94‐97 percent) aggregates. The bond strength between the concrete and the reinforcing bars was measured by means of pull‐out tests.FindingsIn concrete of w/c=0.4 the bond for galvanized steel was 5.4±0.5 MPa, while the bond for black steel was 5.8±0.5 MPa, which is 7 percent higher than bond strength measured for samples with galvanized steel rebars. The bond strength for galvanized steel in concrete with a w/c ratio 0.5 was 5.5±0.6 MPa, which was 9 percent higher than the values obtained for black steel, which was 5.0±1 MPa. The total average bond strength of galvanized steel in concrete of w/c ratio 0.4 (5.4±0.5 MPa) and w/c ratio 0.5 (5.5±0.6 MPa) was very similar. They differed by only 2 percent. No decrease in the air permeability at the interfacial zone concrete/galvanized steel was found due to curing.Originality/valueThis research gives quantitative data on the behavior of galvanized steel used as reinforcing bars in concrete, prepared with limestone aggregates. The results might help to increase the reliability of galvanized reinforcing steel used in infrastructure exposed to very aggressive tropical humid marine environments.

Evaluation of the corrosion inhibition of salts of organic acids in alkaline solutions and chloride contaminated concrete

AbstractThis paper summarizes the results of testing on salts of organic acids for evaluating their use as inhibitors of rebar corrosion in chloride‐contaminated concrete. Initially a screening based on electrochemical tests in alkalinized calcium hydroxide solutions was performed on a number of carboxylic acid salts with different number of carbon atoms in the chain and carboxylic groups, also covering substances with hydroxyl and amine group substituents. The screening was completed by testing on carbon steel rebars in concretes with chlorides and substances added at 1:1 molar ratio, focused on sodium lactate, sodium oxalate and sodium borate for comparison. The monitoring of free corrosion potential and linear polarization resistance of steel bars have confirmed significant inhibition only for lactate. Corrosion was only restricted to occluded zones where the access of substance was limited by disadvantageous geometry, producing shallow attacks.Results of further tests in saturated calcium hydroxide solution are reported in order to assess the inhibition ability of lactate as a function of its content, chloride content and pH.

Characterization of concrete cracking due to corrosion of reinforcements in different environments

This paper shows the results of a laboratory experimental study, characterizing cracking on concrete beams produced by corrosion of steel reinforcement exposed to different atmospheres. These environmental conditions were obtained by means of two electrolytic media: one alkaline, simulating the situation that occurs in an industrial environment, with beams exposed to a saturated solution of Calcium Hydroxide; and another with beams exposed to a Sodium Chloride solution, simulating de-icing or a marine environment. Test samples in reduced lab scale were tested too, in order to identify the different corrosion products generated in each case (and their influence on concrete cracking). Observation showed that the consistency of these products and the variation of the concrete consistency with regard to the environment employed, govern the cracking process.