Calcium Aluminate Cement Mortars Research Articles

Interactions between alkali-activated and cement-based mortars and biofilm and their influence on microbial induced mortar deterioration

Alkali-activated fly ash (AAF) and alkali-activated slag (AAS) mortars were exposed to the sewage environment with acidophilic sulfur oxidizing bacteria and high concentration H2S to study their interaction. It was found that when they suffered the biogenic sulfuric acid attack, both the AAF and calcium aluminate cement (CAC) mortars had a strong inhibition effect on the growth and activity of microorganisms. There are more aluminum ions dissolved from AAF mortar into sewage, and its structure was characterized by the increase in 100-1000 nm pores. Still, a hard high silicon skeleton was formed to keep the apparent intact. However, CAC mortar had a higher killing rate for the bacteria in the attached biofilm. For AAS mortar, the formation of excessive gypsum increased the macropores content and was more conducive to the growth of biofilm, thereby accelerating the penetration of corrosive medium and the deterioration of mortar.

Inhibiting effect of styrene-butadiene copolymer on the whitening of calcium aluminate cement mortar

This paper was based on the results of the research group's previous research on early whitening of mortars. The inhibition of whitening and changes of white deposit on the surface of calcium aluminate cement (CAC) mortar with styrene-butadiene copolymer (SB) were studied using a long-term accelerated whitening method under conditions of (20 ± 2) ℃ and (60 ± 5)% RH. The whitening phenomenon and white deposits of CAC mortars were studied using digital processing of images, optical microscopy (OM) and scanning electron microscopy (SEM). The results indicate that the white deposit on the surface of CAC mortar primarily consists of newly formed carbonation products, calcium carboaluminate hydrate (C4AC¯H11) and calcium carbonate (CaCO3), and with the extension of this exposure time, C4AC¯H11 will be carbonized to generate CaCO3 and Al(OH)3 (AH3). It is interesting to note that SB reduces the production of C4AC¯H11 and CaCO3 and that at SB dosing levels above 12% the C4AC¯H11 disappears and there is hardly whitening of mortar at this time. The inhibition mechanism of SB on the whitening of CAC mortar was investigated using X-ray diffraction (XRD), capillary water absorption and water contact angle tests. The analysis reveals that hydration product of CAC is mainly CAH10 after curing at 20 ℃ for 1 d, and the addition of SB did not change the type of CAC hydration products. Furthermore, incorporating SB enhances the hydrophobicity and reduces the capillary water absorption in CAC mortar, and forms a polymer film in CAC mortar. They prevent the transfer of ions from the interior of CAC mortar to the exterior and the contact of CO2 from the air with the cement hydrate on the surface of CAC mortar, thus reduces the production of white deposit on the mortar surface and inhibits the whitening of CAC mortar.

Potential of sodium chloride solution as mixing water in calcium aluminate cement modified with siliceous minerals

Calcium aluminate cement (CAC) is advantageous in marine engineering, and using materials directly from the sea when mixing CAC can reduce both construction costs and ecological pollution to the sea. However, using seawater as the mixing water in CAC is difficult due to the strength reduction. In this work, CACs were prepared with siliceous minerals (SMs) (diatomite and silica fume (SF)) and sodium chloride solution (SCS) as the mixing water. For comparison, other samples were immersed in SCS rather than mixed with SCS. The strength, mass and length changes of CAC mortars cured at 20°C and 40°C were determined. The phase assemblages and morphology were assessed using X-ray diffraction, thermogravimetric-differential scanning calorimetry and scanning electron microscopy. Using SCS as the mixing water was beneficial to the later strength development of CAC. It promoted the formation of C2ASH8 in CAC pastes and showed no strength loss even when cured at 40°C. The strengths of the SM-modified CAC mortars mixed with SCS were higher than those immersed in SCS. The combination of diatomite and SCS significantly increased the CAC strength, especially at 20°C, while SF contributed to better stability in mass and length.

Chloride Corrosion of Reinforced Calcium Aluminate Cement Mortar

Chloride Corrosion of Reinforced Calcium Aluminate Cement Mortar

Hydration of blended ladle slag and calcium aluminate cement

Partial replacement and co-hydration of calcium aluminate cement (CAC) with ladle slag was investigated in this study as a pathway in valorizing the slag and reducing the economic cost of CAC. The impact of this replacement on the physical and microstructural properties were analysed using different techniques such as mechanical strength test, freeze-thaw, sulfate attack, XRD, SEM etc. Thermodynamic modelling was used to predict the phase assemblages of the blended cement using the hydration kinetics of the system. Experimental results showed the reference CAC mortar and the substituted mortar exhibited comparable strength gain at 7 and 28 days, and durability as measured by sulfate attack, abrasion, and freeze-thaw resistance. A low water-to-binder ratio (0.35) lessened the effect of conversion on the hydrates, as XRD showed metastable CAH10 and C2AH7.5 as the hydrates at 7, 28 and 60 days. This however can convert later to the thermodynamically stable phase C3AH6. Thermodynamic modelling suggests these two metastable phases as major binding phases, while Si-hydrogarnet and FeOOH appeared a minor trace in the binder.*Cement chemistry notation used, where C = CaO, A = Al2O3 and H = H2O

The hydration behavior of polymer-incorporated calcium aluminate cement mortars at different curing temperatures

The hydration behavior of polymer-incorporated calcium aluminate cement mortars at different curing temperatures

The role of Pre-Heating and mineral additive modification on Long-Term strength development of calcium aluminate cement mortars

Strength development of Calcium Aluminate Cement (CAC) under various environmental conditions is an interesting subject of topic that pay attention of researchers for a long time. This special cement usually preferred in applications where quick setting ability, high early strength and resistance to chemical attack is required. However, uncertainty in the hydration process and long-term strength problems, due to conversion reactions in combination with high initial material cost, limit the application of this cement.In order to propose a solution to the above-mentioned problems, blended mortar mixtures were prepared by replacing CAC with variable amounts of microsilica, anhydrite CaSO4 and Portland cement within the scope of this study. The compressive strength development of mortar specimens up to 400 days were investigated under semi-dry curing conditions at 20 ± 5 °C and 60 ± 20% RH. During the initial stages of hydration, a distinct pre-heating based curing procedure was applied to the conjugate specimens. Preliminary stabilization of the unstable hydration products is targeted by this pre-heating method. Accordingly, the crystal structure of the hydration products of specimens was analyzed with the support of microstructural studies (XRD, DTA-TGA, SEM-EDS). The pore size distribution and sub-capillary porosity of specimens were also determined by mercury intrusion porosimetry. The effectiveness of the mineral modification and pre-heating based curing method (exposure to 50 ± 1 °C heating for 21 days) on the long-term strength development of CAC is discussed with the aid of microstructural analysis results. The results showed that it is possible to stabilize the hydration process of CAC and its strength becomes predictable in the long term, if appropriate mineral additives in proper replacement ratios are employed in the mixture design.

Performance of cementitious and alkali-activated mortars exposed to laboratory simulated microbially induced corrosion test

This research presents a laboratory simulated microbially induced corrosion (MIC) test method allowing to assess the performance of low calcium fly ash based geopolymer mortar (FA-GPm), alkali-activated slag-based mortar (AASm), sulphate resistant Portland cement mortar (SRPCm) and calcium aluminate cement mortar (CACm). This experiment runs for a period of six months in which sulphur oxidizing microbes (SOMs) (A. thiooxidans and T. intermedius) were grown in liquid media containing the thiosulphate ion. This test methodology aims to investigate the bacterial attachment phase (stage 2) followed by the initiation of acid attack (stage 3) of MIC. Lowering of the pH of liquid medium and the growth of microorganism was measured to evaluate the aggressiveness of this microbial environment. Visual, physical, chemical and microstructural investigations of mortars were performed over time to estimate the deteriorations. Ions leaching from the matrix and formation of sulphate (SO42−) was monitored using inductively coupled plasma mass spectroscopy (ICP-MS) and ion chromatography (IC), respectively. The results showed that the neutralization of CACm after exposure to biotic reactor was lesser compared to the other mortars, indicating its resistance towards biocorrosion. Moreover, formation of sulphuric acid (H2SO4) and the growth of SOMs showed its dependence on the type of mortar. Scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) spectroscopy was used to predict the depth of degradation and morphological variations at microstructural level. Patterns of deterioration and nucleation of minerals identified were similar to infield exposure, indicating the suitability of this testing method to simulate sewer biocorrosion.

Effect of basalt and polypropylene fibers on crumb rubber mortar with Portland cement and calcium aluminate cement binders: Strength and artificial neural network prediction model

This paper aims to study the influence of basalt fiber (BF) and polypropylene fiber (PPF) in crumb rubber (CR) mortar made of two different types of cement, including ordinary Portland cement (OPC) and calcium aluminate cement (CAC). CR was used to partially (5%, 10%, 15%, and 20% by volume) replace the fine aggregate in OPC and CAC mortars. BF and PPF were added (0.1%, 0.3%, and 0.5% by total volume) in the CR mortars. The consistency, density, compressive, and flexural strength of cement mortars were investigated. The use of CAC cement slightly increased the consistency; however, the results showed that the CR replacement and the addition of both fiber types tend to reduce the consistency in OPC and CAC mortars. Significant reduction in the density of fiber-added CR mortar was found with increasing CR content, whereas the influence of both PPF and BF was minimal. The fiber-added CR mortar made of both binder and fiber types in general exhibited a reducing trend in the 28 days compressive strength when increasing CR and fiber contents. Nevertheless, an enhancement in the compressive strength of CAC mortar with 20% CR was found with the addition of 0.1% of both fibers. The use of CR and addition of the fibers generally decreased the flexural strength of mortar made of both binder types; however, the addition of 0.3% BF in mortars containing 15–20% CR positively affected the flexural performance. Finally, the artificial neural network (ANN) approach demonstrated the ability to predict the compressive strength of fiber-added CR mortars. The model showed a considerably insignificant mean square error (MSE) of 1.4–1.5 and high plot regression (R) results of 0.97–0.98.

The effects of cement type and expanded vermiculite powder on the thermo- mechanical characteristics and durability of lightweight mortars at high temperature and RSM modelling

The results of the impact of cement type and expanded vermiculite powder (EVP) on the thermal, mechanical characteristics and durability of lightweight mortars at high temperature and RSM modelling are presented in the paper. The lightweight mortars were fabricated by replacing fine aggregate with EVP in certain proportions. In the production of the mixtures, two different cement types namely, Portland cement (PC) and calcium aluminate cement (CAC) were used as binders and fine aggregates were replaced with EVP at the rates of 0%, 15%, 30% and 45%. The microstructure, thermal, mechanical properties and durability of PC and CAC mortars produced in this way were determined after standard curing for 28 days at temperatures ranging from 20 °C to 900 °C. Mechanical performance of mortar mixtures was evaluated based on compressive, flexural strength and ultrasonic pulse velocity (UPV). The durability of the specimens was also determined using porosity, water absorption and dry unit weight. Thermal conductivity and Scanning electron microscope (SEM) observations of 28-day mortar specimens were also evaluated. The response surface methodology (RSM) was adopted to develop the relation between parameters and response for thermal conductivity. The test results reported that lightweight refractory and insulating mortar can be manufactured by combined use of CAC and EVP when considered strength and durability and thermal performance after high-temperature exposure. Test results also pointed out that the combined use of CAC and EVP gained significant high-temperature resistance performance in terms of compressive strength as compared to PC blended mortar specimens.

Steel Corrosion Behavior of Reinforced Calcium Aluminate Cement-Mineral Additions Modified Mortar.

Mineral additions can eliminate the conversion in calcium aluminate hydrates and thus inhibit the future strength retraction of calcium aluminate cement (CAC). However, the impacts of these additions on the protection capacity of CAC concrete in relation to the corrosion of embedded steel reinforcement remains unclear. This paper focused on the corrosion behavior of steel reinforcement in slag, limestone powder, or calcium nitrate-modified CAC mortars via XRD and electrochemical methods (corrosion potential, electrochemical impedance, and linear polarization evaluation). The results indicate that strätlingite (C2ASH8), which is formed in slag-modified CAC, has poor chloride-binding ability, leading to decline in corrosion resistance of the steel reinforcement. The electrochemical parameters of specimens immersed in NaCl solution suddenly drop at 14 days, which is 28 days earlier than that of the references. In contrast, the Ca2[Al(OH)6]20.5CO3OH·H2O (CaAl·CO32−-LDH) and 3CaO·Al2O3·Ca(NO3)2·12H2O (NO3-AFm) in limestone powder and calcium nitrate-modified CAC mortar show great chloride-binding ability, thereby improving the corrosion resistance of the steel reinforcement. The electrochemical parameters of specimens modified with calcium nitrate maintain a slow decreasing trend within 90 days.

Alkali-silica reaction in calcium aluminate cement mortars induced by deicing salts solutions

Calcium aluminate cement (CAC) mortars and concrete may be used as high-performance repairing materials for pavement restoration in airfields and roads. During recent years alkali-silica reaction (ASR) was reported in Portland cement concrete subjected to the action of organic deicers. Present paper reports the results of the investigation on the influence of organic and inorganic alkali deicers on ASR potential in CAC mortars containing fused silica as model reactive aggregate. It was shown for the first time, that concentrated solutions of sodium and potassium acetates, as well as sodium chloride, can cause ASR in CAC mortars. Sodium and potassium acetate resulted in much larger expansions comparing to sodium chloride and sodium hydroxide solutions used as a reference. Differences in alkali-silica gel were found depending on the solution which samples were soaked in. It was shown that ASR could proceed in a system without calcium hydroxide and an external source of hydroxyl ions.

Hydration behavior of calcium aluminate cement mortars with mineral admixtures at different curing temperatures

Cement-based materials that are produced with calcium aluminate cement (CAC) exhibit severe strength losses with time and temperature due to the conversion of metastable hydrates (CAH10 and C2AH8) into the stable hydrates (C3AH6 and AH3). On the other hand, using mineral admixtures at different ratios during the production of cement-based materials change the hydration behavior and, thus, mechanical properties of these materials. Therefore, this research focuses on the effects of mineral admixtures on the properties of CAC mortars at two different curing temperatures (20 °C and 38 °C). Mortars were prepared by using constant CAC content, and the sand was replaced by class F fly ash (FA) as 10%, 30%, 60%, granulated ground blast furnace slag (GGBFS) as 10%, 30%, 60% and silica fume (SF) as 5%, 10%, 15%. In addition to fresh mortar tests, other tests, including isothermal calorimetry tests up to 72 h, the flexural and compressive strength tests at 3, 7, 28, and 90 days and the capillary absorption tests, were also conducted. The mineral admixtures, when used as sand replacement materials, accelerated the hydration reactions of CAC mortars. 10% replacement of sand by FA and especially GGBFS resulted in better mechanical strengths at 20 °C (7% and 16% increases in compressive strengths for 10% FA and 10% GGBFS replacements at 90 days). In addition, they were least affected with the increase in temperature to 38 °C as compared to other GGBFS and FA used mixes. On the other hand, silica fume used mixtures had relatively lower strengths, but they showed some improvements with the increase in temperature at later ages (10% and 25% increases at 90 days for 5% and 15% SF, respectively). GGBFS and FA additions in different amounts decreased the heat of hydration values at 38 °C as compared to 20 °C (except 10% GGBFS addition) while silica fume increased the values.

Steel Corrosion in Calcium Aluminate Cement Mortar against Chloride

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Steel Corrosion in Calcium Aluminate Cement Mortar against Chloride

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Influence of ground perlite on the hydration and strength development of calcium aluminate cement mortars

Calcium aluminate cement (CAC) concretes are desirable owing to their rapid strength development and resistance to high temperatures, sulfates and acids. They suffer two drawbacks, however, high cost and strength loss due to conversion of water-rich hydration products to more stable structures, resulting in a drop in strength. Although its rate is dependent on temperature and moisture, the conversion process is thermodynamically inevitable but can be prevented by adding sufficient quantities of supplementary cementing materials (SCMs) to form an alternate, stable hydrate, Stratlingite (C2ASH8). Based on this premise, natural pozzolans could mitigate conversion, also reducing cost. This study investigated the influence, on hydration, of replacing 25–75% of CAC with ground perlite (GP), an inexpensive and abundant natural pozzolan. Paste and mortar mixtures with water-to-binder ratios of 0.40 and 0.60 were cured in air at 23 °C or in water at 40 °C. The influence of adding Na2SO4 to promote Stratlingite formation was also investigated. A multi-method approach comprising X-ray diffraction (XRD), isothermal calorimetry, thermal analysis, and compressive strength development was used. Stratlingite formation was confirmed in many mixtures containing GP. Wet-cured mortars with ≥50% GP and 1% Na2SO4 contained Stratlingite and showed continuous strength increases up to 90 d. Rapid-, or slow-progressing drops in strength were observed in air-cured mixtures or wet-cured mixtures containing < 50% GP. Mortars with 75% GP did not experience conversion but their ultimate strengths were much lower than even the converted strength of the pure CAC mortar. Heats of hydration of pastes decreased linearly with GP replacement of CAC despite their setting times being shortened.

Strain hardening behaviour of PE fibre reinforced calcium aluminate cement (CAC) – Ground granulated blast furnace (GGBFS) blended mortar

Calcium aluminate cement (CAC) is regarded as an effective protective coating material for concrete sewerage pipes to prevent bacterial induced acid corrosion. However, the conversion process occurred in pure CAC mortar limited its application for structural purpose. Ground granulated blast furnace slag (GGBFS) blended with CAC can change the hydration mechanism and stop the conversion process. To better utilise CAC-GGBFS blended mortar for retrofitting concrete sewerage pipes, the inherent brittleness needs to be addressed. Introduction of polyethylene (PE) fibres into CAC-GGBFS blended mortar can help to form multiple tiny cracks under tensile loading for better crack control, give it high potential for the use in concrete structure retrofitting. In this paper, the authors took a first attempt on developing a new type of PE fibre reinforced CAC-GGBFS mortar with strain hardening behaviour. The new composite reached a compressive and flexural strength of 59.76 MPa and 22.12 MPa, respectively. The tensile strength was 5.46 MPa with the corresponding strain of 4.78%. Multiple cracks behaviour was observed under tensile and flexural loads. Classic pseudo strain hardening (PSH) criterion was validated on the new composite.

Effects of hydroxyethyl methyl cellulose ether on the hydration and compressive strength of calcium aluminate cement

Aluminate containing phases such as tricalcium aluminate (C3A) and dodecacalcium heptaaluminate (C12A7) play a key role in the reaction between Portland cement and cellulose ether. In order to simplify such impact from calcium aluminate, calcium aluminate cement (CAC) was applied as a carrier. Effects of hydroxyethyl methyl cellulose ether (HEMC) on the hydration of CAC were characterized by means of isothermal calorimetry, X-ray diffraction analysis, thermal analysis and scanning electron microscopy, respectively. Meanwhile, the setting times, water retention, air content and compressive strengths of HEMC modified CAC pastes or mortars were also determined. Results indicate that HEMC prominently delays the hydration of CAC within 1 day, and the higher dosage of HEMC, the longer setting times. HEMC exerts no obvious impact on the formation amount of CAH10, only leads to a smaller crystal size. From aspect of physical and mechanical properties, the addition of HEMC improves the water retention of fresh CAC mortars, and only with addition of 0.1% HEMC, the water retention of fresh CAC mortars almost approaches 100%. Additionally, the addition of HEMC also significantly promotes the air content of fresh CAC mortars, leading to an obvious decrease in the compressive strengths.

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.