Calcium Aluminate Cement Mortars Research Articles

Durability of calcium aluminate and sulphate resistant Portland cement based mortars in aggressive sewer environment and sulphuric acid

This study aims to compare the performance of sulphate resisting (SR) Portland cement mortar (SRm) and calcium aluminate cement mortars (CACm) in both natural sewer environment and sulphuric acid. Specimens were extracted after 12 and 24 months from field exposure, and were also removed from 1.5% sulphuric acid (H2SO4) after 6 months to investigate the deterioration caused by chemically induced corrosion. Visual, physical and extensive microstructural analyses were performed to evaluate the degradation of CACm and SRm matrix using techniques such as Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDX), X-Ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) Spectroscopy. Surface pH was estimated after 12 and 24 months of field exposure to identify the initiation of biotic film development due to microbial induced corrosion (MIC). Material properties such as mass loss, compressive strength, linear expansion, and pH profile with respect to neutralization depth were also measured. The difference in mechanism of deterioration was also highlighted based on microstructural investigations between in field experimentation and acid exposure. The results showed that overall CACm performed significantly better than SRm in onsite sewer environment and sulphuric acid solution in terms of visual observations, loss in mass, compressive strength reduction, depth of neutralization, reduction in pH and penetration of sulphur. Crystallization of gypsum within the matrix of both mixes was the main factor behind the deterioration observed using XRD and FTIR from both in field and acid attack exposure, with higher deterioration within the matrix of SRm as compared to CACm. Moreover, sulphuric acid testing is suitable for screening the mixes rapidly against acidic environment, but due to the major differences observed in deterioration processes with natural field conditions this method is unsuitable for service life design of sewage structures.

Development of Strength for Calcium Aluminate Cement Mortars Blended with GGBS

In the present study, the development of strength in different calcium aluminate cement (CAC) mixture mortars with granulated ground blast-furnace slag (GGBS) was investigated. The substitution of GGBS levels was 0, 20, 40, and 60% weight of binder, of which the CAC used in this study naturally contained C2AS clinker as a secondary phase. To activate a hydraulic nature of the phase, in addition to the mineral additive, all specimens were cured at 35 ± 2°C for the first 24 hours and then stored in a 95% humidity chamber at 25 ± 2°C. The penetration resistance of fresh mortar was measured immediately after pouring, and the mortar compressive strength was monitored for 365 days. Simultaneously, to evaluate the hydration kinetics at early ages, in terms of heat evolution, the calorimetric analysis was performed at the isothermal condition (35°C) for 24 hours. The hydration behavior in the long term was characterized by X-ray diffraction, which was supported by microscopic observation using scanning electron microscopy with energy dispersive spectroscopy. Furthermore, an examination of the pore structure was accompanied to quantify the porosity. As a result, it was found that an increase in the GGBS content in the mixture resulted in an increased setting time, as well as total heat evolved for 24 hours in normalized calorimetry curves. In addition, the strength development of mortar showed a continuous increased value up to 365 days, accounting 43.8–57.5 MPa for the mixtures, due to a formation of stratlingite, which was identified at the pastes cured for 365 days using chemical and microscopic analysis. However, GGBS replacement did not affect on the pore size distribution in the cement matrix, except for total intrusion volume.

The influence of lithium compounds on alkali – silica reaction in calcium aluminate cement mortars subjected to the deicing salts attack

Paper presents the results of research on the effect of the lithium nitrate and carbonate addition on the alkali – silica reaction in calcium aluminate cement mortars, subjected to the a deicing salts attack. Mortars with the addition of quartz glass as the reactive aggregate were immersed in 4.5 molar sodium acetate, chloride and hydroxide solutions according to the modified ASTM C1260 method. In all cases, the mortars exhibited expansion, the highest for samples immersed in the acetate solution, and the lowest in the hydroxide solution. The addition of 1% of lithium carbonate in respect to the cement mass slightly reduces the expansion of mortars immersed in sodium acetate and hydroxide solutions. The addition of 1.86% and 3.73% of lithium nitrate increases the expansion of mortars immersed in both solutions. The addition of 1.86% lithium nitrate reduces the expansion of the mortar stored in sodium hydroxide solution, while 3.73% of this addition increases the expansion of this mortar. Changes in the microstructure were also presented.

Biodeterioration of mortars exposed to sewers in relation to microbial diversity of biofilms formed on the mortars surface

Strong deterioration of concrete in sewer systems is mainly due to microorganisms and especially to sulfur-oxidizing bacteria. Mortars made either with ordinary Portland cement (OPC) or calcium aluminate cement (CAC) were exposed in a waste water collector for five years. Mortar microstructure observed by microscopy reported a larger thickness of the degraded zone for OPC mortar. Taxonomic identification of bacterial communities performed on biofilms collected at the mortar surface reported similar bacterial diversities, but strong differences of relative abundance. A greater neutrophilic sulfur-oxidizing bacterial (NSOB) activity was observed for OPC mortar certainly in conjunction with its larger acid neutralization capacity. Thus, CAC mortar was less biodeteriorated than OPC mortar as less NSOB were able to settle on its surface in relation with its specific microstructure. The results of the reported field experiments have been compared with bioleaching laboratory experiments performed on identical mortars in the presence of Halothiobacillus neapolitanus as NSOB. As the deterioration mechanisms involved were similar, an acceleration factor with respect to the rate of in situ biodeterioration was determined for laboratory experiment.

Modeling of Corrosion Rate and Resistivity of Steel Reinforcement of Calcium Aluminate Cement Mortar

Calcium aluminate cement (CAC) is a binder whose hydrated compounds change over time from cubic phases to hexagonal phases, producing an increase of porosity in reinforced concretes. Thereby, chloride ions, among other steel corrosion promoters, can enter the concrete more easily leading to an increase of the reinforcement corrosion process. When such a transformation of phases is completed, a characteristic value regarding both corrosion intensity (Icorr) and resistivity (related to the ohmic drop of the cementitious material) is reached, which depends mainly on the mix proportions of the material and the curing procedure. This paper presents the characteristic corrosion intensity values of steel embedded in mortars made of CAC after five years of exposure to either a 0.5 mol/l or 1.5 mol/l NaCl solution in order to be applied to estimate the service life of reinforced concrete made of calcium aluminate cement (CAC) which is used in real construction structures. Ohmic drop measurements are also presented to support the values obtained. The aim of this paper is to model the corrosion rate and resistivity of the steel reinforcement of calcium aluminate cement mortar with regard to environmental factors (temperature and chloride content) and mortar quality (water/cement ratio).

The Effect of TiO₂ Doped Photocatalytic Nano-Additives on the Hydration and Microstructure of Portland and High Alumina Cements.

Mortars with two different binders (Portland cement (PC) and high alumina cement (HAC)) were modified upon the bulk incorporation of nano-structured photocatalytic additives (bare TiO2, and TiO2 doped with either iron (Fe-TiO2) or vanadium (V-TiO2)). Plastic and hardened state properties of these mortars were assessed in order to study the influence of these nano-additives. Water demand was increased, slightly by bare TiO2 and Fe-TiO2, and strongly by V-TiO2, in agreement with the reduction of the particle size and the tendency to agglomerate. Isothermal calorimetry showed that hydration of the cementitious matrices was accelerated due to additional nucleation sites offered by the nano-additives. TiO2 and doped TiO2 did not show pozzolanic reactivity in the binding systems. Changes in the pore size distribution, mainly the filler effect of the nano-additives, accounted for the increase in compressive strengths measured for HAC mortars. A complex microstructure was seen in calcium aluminate cement mortars, strongly dependent on the curing conditions. Fe-TiO2 was found to be homogeneously distributed whereas the tendency of V-TiO2 to agglomerate was evidenced by elemental distribution maps. Water absorption capacity was not affected by the nano-additive incorporation in HAC mortars, which is a favourable feature for the application of these mortars.

Effects of the addition of inertized MSW fly ash on calcium aluminate cement mortars

The large urban development carried out in the cities has promoted the increase of municipal solid wastes (MSW). While the incineration process is considered as the best possible method to manage this waste, however, among all the incineration products, MSW fly ashes produce the greatest environmental problems. The inerting of this hazardous toxic waste, as well as its valorization as a by-product is achieved due to its stabilization in the form of insoluble carbonates. In this way, a new “raw material” is produced and available at low cost, and the toxic and hazardous waste is eliminated by its subsequent encapsulation in mortar matrixes. Consequently, conservation of alternative natural resources is strengthened. In this research, calcium aluminate cement (CAC) mortars have been developed incorporating treated fly ash as filler, assimilating 10% in weight of the aggregate and adding it into the mortar dosage as a new formulation. The amount of 10% was chosen taking into account the positive outcomes in the bibliography. Likewise, samples tested covered different cement proportions, both using aggregates with different diameters (0/2 mm and 0/4 mm), and using different cement/aggregate ratios (1/1 and 1/3) of the stated CAC. After having analyzed the physical/mechanical properties of these mortars, the conclusions drawn are that the tested mortars are technically acceptable, with a much shorter workability period than the reference mortars. They also present better dimensional stability and an increase in bulk density. Mercury intrusion porosimetry displays a porosity decrease. In addition, the contribution of CaCO3 develops calcium monocarboaluminate hydrate (C3A·CaCO3·11H2O) which increase the resulting mixtures-those made with CAC·0/4·1/1-compressive strengths up to 48.62% more than the reference mortars.

Interactions between Halothiobacillus neapolitanus and mortars: Comparison of the biodeterioration between Portland cement and calcium aluminate cement

Biodeterioration of mortars made either with ordinary Portland cement or calcium aluminate cement by Halothiobacillus neapolitanus was investigated by bioleaching experiments. Mortar deterioration, determined by a leaching coefficient calculated with the amounts of chemical elements leached from the mortar to the bacterial suspension, was greater for ordinary Portland cement. The amount of biogenerated sulfuric acid, estimated by the consumption of sulfur-containing components, varied markedly due to the interactions between H. neapolitanus and the mortar that depended on two main mechanisms. First, the different mineralogy of both cement pastes led to a weaker acid-neutralizing capacity of calcium aluminate cement in the pH range 6.5 to 3. Second, a restricted oxidation of tetrathionate by H. neapolitanus, that limited the biogeneration of sulfuric acid, was observed when pH approached 3 more rapidly. Consequently, the weaker acid-neutralizing capacity of calcium aluminate cement induced a quicker drop of the pH of the bacterial suspension from 6.5 to 3, leading to a decrease of the amount of biogenerated sulfuric acid. Thus, calcium aluminate cement mortar in the presence of H. neapolitanus bacterial suspension was less deteriorated than ordinary Portland cement mortar in the pH range considered.

Carbonation of calcium sulfoaluminate mortars

This study investigated potential physical and chemical parameters that could govern the carbonation rate of calcium sulfoaluminate (CSA) mortars and endeavored to elucidate the microstructural and chemical factors that govern CSA cement's carbonation rate. Experiments included: water absorption, oxygen diffusion, mercury intrusion porosimetry, quantitative X-ray diffraction, thermogravimetric analysis, accelerated carbonation, compression and flexure tests. Additionally, the carbonation process was investigated using thermodynamic modeling. The results show that CSA mortars carbonate much faster than Portland cement mortars and at approximately the same rate as calcium aluminate cement mortars. Additionally, CSA mortars carbonate slower with decreasing w/c, and the anhydrite content of the CSA mortars strongly affects the ye'elimite reaction kinetics which plays an important role in imparting carbonation resistance in CSA mortars. Finally, calcium sulfate additions to CSA clinker to produce CSA cement dilutes the clinker content and reduces the amount of CO2 that the CSA cement can ultimately bind.

Influence of the binder on the behaviour of mortars exposed to H2S in sewer networks: a long-term durability study

The present study deals with the exposure of four different mortar formulations in the headspace of two distinct sewer networks prone to biodeterioration phenomenon due to the presence of hydrogen sulphide. Cylindrical specimens composed of two cements, ordinary Portland cement (OPC) and calcium aluminate cement (CAC), with or without a substitution of 75 % of cement by blast furnace slag (BFS) were prepared and exposed. During the exposure, the evolution of cement materials was monitored. After 4 years exposure, OPC materials without BFS are deeply deteriorated at high speed. Best performances have been observed with CAC mortars correlated to their higher content in aluminium ion (Al3+). The rank of durability observed on site is OPC < OPC+BFS < CAC+BFS < CAC. Molecular biology analysis revealed that microbial diversity is varying according to binder type as well as during the exposure duration.

칼슘알루미네이트 시멘트 모르타르의 성능 평가

In this study, several properties of mortars made with calcium aluminate cement (CAC) such as hydrated products, strength characteristics, absorption, surface electric resistivity and chloride ions penetration resistance were experimentally investigated. The properties of CAC mortars were compared to those of ordinary portland cement (OPC) mortars. From the test results, it was found that the main hydrated products for CAC mortars were of and , while CH, ettringite and calcite for OPC mortars. The surface electric resistivity and chloride ions penetration resistance of CAC mortars were significantly beneficial compared to those of OPC mortars. However, it should be noted that the absorption properties of CAC mortars were negatively examined. Thus, it needs to have more study for the improvement of surface absorption of CAC matrices. In addition, the combined mixture of CAC and OPC were ineffective to improve some performances of mortars.

Effect of polycarboxylate superplasticiser on properties of calcium aluminate cement mortar

The effect of polycarboxylate ether (PCE)-based superplasticiser on the fresh and hardened properties of calcium aluminate cement (CAC)-based materials was investigated. Cohesion of the fresh mortar was improved by addition of methyl cellulose, thus avoiding segregation induced by the superplasticiser action. As PCE significantly retarded the setting time, lithium carbonate (Li2CO3) was investigated as an accelerator by calorimetric measurements. Compressive and flexural strengths, porosity and dynamic modulus were tested after 1 d and 9 d cured at 23°C and after transformation of metastable hydration products to stable ones at 60°C. The combined usage of PCE with methyl cellulose and lithium carbonate showed promising superplasticising properties for CAC that improved properties of the material.

A novel use of calcium aluminate cements for recycling waste foundry sand (WFS)

The recycling of WFS in calcium aluminate cement mortars at high level of replacement (50%) was studied. Consistency and setting time were measured in fresh mortars. Two different curing conditions were used, the second one with the aim of enhancing the formation of stable cubic calcium aluminate hydrates. Compressive strength, pore size distribution and SEM examination were carried out to assess the effectiveness of CAC matrix in the recycling of WFS. The effect of the incorporation of a polymeric admixture – a chitosan derivative – was also explored. Leaching studies on hardened mortars of three target pollutants of the WFS (toxic metals Pb, Cr and Zn) were also done to evaluate their immobilization. By comparison with OPC mortars, the use of CAC showed several advantages, improving the compressive strength and the toxic metal retention.

Solidification/stabilization of toxic metals in calcium aluminate cement matrices

The ability of calcium aluminate cement (CAC) to encapsulate toxic metals (Pb, Zn and Cu) was assessed under two curing conditions. Changes in the consistency and in the setting time were found upon the addition of the nitrates of the target metals. Both Pb and Cu caused a delay in CAC hydration, while Zn accelerated the stiffening of the mortar. Compressive strengths of the metal-doped mortars, when initially cured at 60°C/100% RH, were comparable with that of the free-metal mortar. Three different pore size distribution patterns were identified and related to the compounds identified by XRD and SEM. Sorbent capacities of CAC for the toxic metals were excellent: a total uptake was achieved for up to 3wt.% loading of the three metals. In this way, CAC mortars were perfectly able to encapsulate the toxic metals, allowing the use of CAC for waste management as proved by the leaching tests.

Mechanical properties and corrosion of CAC mortars with carbon fibers

The changes in mechanical properties of Calcium Aluminate Cement (CAC) mortars due to the addition of carbon fibers (CFs) to the mix have been studied. Compressive and flexural strengths have been determined in relation to the amount of CF added to the mix, water/cement ratio (w/c), curing time and porosity. The relationship between the values of ultrasonic pulse velocity (UPV) and compressive strengths for CAC mortars have also been obtained. Additionally the corrosion level of reinforcing steel bars embedded in CAC mortars containing CF and silica fume (SF) has also been investigated. The proportion of CF and SF in the mix, the w/(c+SF) ratio and the type of aggressive media have been chosen as test parameters. The study demonstrates that the addition of small amounts of CF to the mix increases significantly the mortar strength, but at the same time reduces its resistivity and the steel protection capacity, increasing porosity.

Evaluation of coatings, mortars and mix design for protection of concrete against sulphur oxidising bacteria

Deterioration of concrete in cooling tower basins by microbiologically influenced corrosion (MIC) is a concern in geothermal power plants. The effect of supplementary cementitious materials, epoxy coatings, latex-modified mortars and calcium aluminate cement mortar for protecting concrete from MIC was investigated. Laboratory exposure tests to a particular type of sulphur and iron oxidising bacteria, Thiobacillus ferrooxidans, were performed to rank candidate materials and these were followed by field exposure tests of the best materials in a cooling tower basin. It was determined that partial replacement of cement with 40% blast furnace slag or 5% to 10% silica fume improved resistance to MIC. A replacement level of 60% slag resulted in similar performance to concrete made with ordinary Portland or sulphate resistant cement. Epoxy- and styrene butadiene latex-modified mortars offered protection to concrete but still underwent a degree of attack. Epoxy coatings were found to be effective in protecting concrete. Calcium aluminate cement mortar showed excellent durability in laboratory and field tests.

Synthesis and crystal structure determination of hydrated potassium dawsonite from powder diffraction data

During the optimisation of the synthesis conditions of non-hydrated potassium dawsonite, a compound which has been recently shown to be involved in the alkaline hydrolysis of calcium aluminate cement (CAC), a new closely related hydrated phase appearing below T = 25°C was detected by powder X-ray diffraction. To gain a more complete understanding of the crystal chemistry of CAC, this new phase was synthesised in pure form and its crystal structure solved from powder X-ray diffraction data. The crystal data are a = 8.3312(4), b = 11.2670(5), c = 5.661(2)A, Pna 2 1 (No. 33) and the resulting chemical formula is KAl(CO 3 )(OH) 2 .H 2 O with Z = 4. From the refined positions of the non-hydrogen atoms and from the balance of bond valences, the chemical nature of the O atoms could be univocally established [R wp = 0.132, R B = 0.056, Chi 2 = 1.15]. The unit cell of this hydrated compound contains two carboaluminate chains formed by the basic unit [Al 2 (OH) 4 (CO 3 ) 2 ] 2− propagating along the c axis and being stabilised by a complex H-bond network. The arrangement of these chains is similar to that found in dawsonite, so that the atomic positions of K + and Na + in both structures are also similar. As confirmed by the X-ray diffraction study of a one-year-old sample, hydrated potassium dawsonite slowly transforms into the non-hydrated form at room temperature. Due to the more favourable formation conditions, i.e. lower temperature and higher humidity, this hydrated phase could be eventually found in CAC pastes or mortars.

Metallic corrosion of steels embedded in calcium aluminate cement mortars

In the present paper, the corrosion levels of reinforcing steels embedded in Calcium Aluminate Cement (CAC) mortars have been studied. Experiments were designed to investigate the influence of the following factors in steel corrosion: cover thickness, type of steel (carbon steel (CS) and stainless steel (SS)), temperature at mixing and curing, influence of chloride concentration, nitrite ion as corrosion inhibitor and carbonation of mortar. The reinforcing steel bars do not become more corroded because of the carbonation of the CAC mortar cover; in some cases, this carbonation seems to have an inhibitor effect in the steel corrosion. The higher the process of carbonation in CAC, the higher the intensity of the X-ray reflections of Friedel's salt and the smaller the values of corrosion rates.

General study of alkaline hydrolysis in calcium aluminate cement mortars under a broad range of experimental conditions

In the present paper the phenomenon of alkaline hydrolysis of calcium aluminate cement (CAC) mortars has been studied. It has been reproduced from different conditions, in specimens manufactured at temperatures of 5°C and 60°C. Phase evolution was studied from X-ray diffraction (XRD) spectra. An evaluation of the compressive and flexural strengths obtained from different curing conditions is also described. The carbonation process in the absence of alkalis can be considered beneficial when it takes place on totally converted CAC mortars. The degradation process through alkaline hydrolysis, and hence the loss of resistance characteristics, takes place only when CAC conglomerates contain hydrated CAC.

Overview on electrochemical parameters to assess the corrosion state of steel reinforcement in CAC mortar and concrete

Calcium Aluminate Cement (CAC) can be used successfully in mortars and concretes for special applications such as refractory and sulphate-resistant materials. However, some failures have been reported when used in reinforced concretes exposed to wet environments in presence of chloride ions. Chloroaluminates formation in either reinforced CAC mortar or concrete could be a way to reduce chloride ions in the pore solution of this material, thereby, decreasing the risk of corrosion. This paper presents the characteristic values of corrosion rate, corrosion potential and resistivity and the relationship between them. Assuming a significant corrosion state at corrosion rate values over 0.1 μA/cm2, we can establish a threshold level for corrosion initiation in reinforced mortar or concrete of −250 mV and 104 Ω·cm. Therefore, lesser values constitue important corrosion rates.