Alumina Cement Concrete Research Articles

Compressive failure analysis of seawater-mixed aluminate cement concrete based on digital image correlation technique

For coastal and marine construction projects where fresh water is not readily available, the direct use of seawater in concrete production is an alternative option. In this paper, the digital image correlation (DIC) technique was utilized to observe the full-field deformation of seawater-mixed aluminate cement concrete under the curing conditions of freshwater/seawater (CAF/CAS) in the whole process of compression. The displacement and strain fields of the concrete cubes were mathematically obtained by way of correlation registration algorithms and strain window method to clarify the compressive deformation and failure mechanism of seawater-mixed aluminate cement concrete. The test results revealed that the deformation process could be divided into four stages, including the compaction stage, the elastic deformation stage, the crack propagation stage, and the failure stage. Furthermore, the crack propagation in the concrete was quantitatively evaluated by the local strain analysis, which demonstrated that the failure of both CAF and CAS resulted from the combination of shear failure and tensile failure perpendicular to the loading direction. However, cracks in CAF were dispersed and discontinuous whereas those in CAS was concentrated perforation and showed obvious brittle failure characteristics. Subsequently, the statistical analysis of displacement and strain in the concrete revealed the improved internal bond strength and compressive strength in CAS in comparison with CAF.

EFFECT OF DOSE AND TYPES OF THE WATER REDUCING ADMIXTURES AND SUPERPLASTICIZERS ON CONCRETE STRENGTH AND DURABILITY BEHAVIOUR: A REVIEW

As one of the concrete admixtures, water reducing admixtures and superplasticizers are usually used to reduce the mixing water volume and improve the performance of the harden concrete while maintaining better workability of the fresh concrete. However, the concrete strength and durability properties are affected differently by different types and dosages of the water reducing admixtures and superplasticizers. Based on the published literatures, this paper comprehensively reviews and analyzes this problem. Different types of the concretes, including ordinary Portland cement concrete, ordinary Portland cement concrete containing pozzolan, fly ash and ground granulated blast furnace slag, calcium sulfoaluminate cement concrete, ferrite aluminate cement concrete, recycled aggregates concrete, lightweight aggregate concrete, self-compacting concrete and ultra-high performance concrete, are considered to discuss the influence of types and dosages of the water reducing admixtures and superplasticizers on their strengths. Water absorption, frost resistance and permeability resistance of the concrete are mainly reviewed to discuss this influence on the durability properties of the concrete. Then, some suggestions on the application of the water reducing admixtures and superplasticizers in reinforced concrete structures and projects are proposed.

Investigation of the effect of different curing conditions on the mechanical performance of calcium aluminate cement concrete at elevated temperatures

Research on improving the performance of concrete at elevated temperatures has been increasing in recent years. In this context, Calcium Aluminate Cement (CAC) can be used in concrete mixes to increase the performance of concrete at elevated temperatures. However, the use of CAC has not yet become widespread in structural applications due to the unstable nature of CAC, which is highly affected by curing temperature and humidity. Therefore, it is of great importance to investigate the curing conditions that directly affect the unstable nature of CAC. In the present study, different curing methods were applied to calcium aluminate cement concretes (CACC) and their performance at elevated temperatures (300 °C, 600 °C, 900 °C) was investigated. In this framework, compressive strength, modulus of elasticity and flexural strength of the samples were determined, load–displacement relations and microstructural changes were evaluated. As a result of the study, it has been determined that CACC samples have better mechanical performance than normal concrete at elevated temperatures and especially the mechanical performance of CACC samples cured at high temperature (CACCH) is better than CACC samples cured under normal conditions (CACCN).

Effect of curing temperature and water-to-cement ratio on corrosion of steel in calcium aluminate cement concrete

• CAC specimens were made with different w/c, and cured at different temperatures. • The w/c and temperature played a crucial role in the porosity of CAC. • Increasing the curing temperature can improve the corrosion resistance of CAC. This study evaluated the corrosion resistance of pure calcium aluminate cement (CAC) concrete specimens made with water-to-cement ( w/c ) ratios of 0.4, 0.5, and 0.6 and cured at 4, 21, and 90 °C following the ASTM G109 standard. Thermogravimetric analysis results showed increased CAC conversion with increased curing temperature. Compressive strength and bulk electrical resistivity measurements showed that the CAC specimens had lower strength and higher bulk electrical resistivity than ordinary portland cement (OPC) concrete. Macrocell corrosion currents measured after cyclic exposure to chloride solutions showed that the CAC specimens were highly permeable and less resistant to chloride-induced corrosion than OPC concrete. Among the different CAC specimens tested in this study, the specimens made with a w/c of 0.4 and cured at 90 °C showed the highest corrosion resistance.

Rice Husk Ash Incorporation in Calcium Aluminate Cement Concrete: Life Cycle Assessment, Hydration and Strength Development

In this research effect of rice husk ash (RHA), as silicate impurities, on the hydration reaction and mechanical strength of calcium aluminate cement (CAC) concrete, as one of the most important non-Portland cements, was investigated. Furthermore, in order to evaluate the environmental performance of mixtures, a lifecycle assessment was performed using the recipe midpoint and endpoint method. Compressive and tensile strength tests were conducted at the ages of 7, 28, and 90 days on specimens containing different contents of RHA (0, 2.5, 5, 7.5, and 10%) substituting for cement at the water-cement ratio of 0.4. Moreover, in order to calculate the hydration reaction of the specimens, thermogravimetric analysis (TGA) was performed at a rate of 10 °C/min to up to 1000 °C. The results revealed that the use of rice husk ash as a partial replacement at a concentration of 5% could reduce CO2 emission and ozone depletion by 18.75% and 31%, respectively. The findings indicate that, at 90 days, the mechanical strength of the mixes containing RHA were higher than those of the control mix, with the maximum improvement occurring at the substitution percentage of 5%. In accordance with TGA analysis the substitution of 5% RHA in CAC concrete led to a higher hydration level, which in turn improved the mechanical properties relative to the specimen without RHA at 90 days.

A comprehensive evaluation of fracture toughness, fracture energy, flexural strength and microstructure of calcium aluminate cement concrete exposed to high temperatures

In this study, a comprehensive experimental program was developed to determine the microstructural, mechanical, and fracture features of calcium aluminate cement concrete (CACC) after exposure to high temperatures. The residual fracture parameters, including fracture toughness, fracture energy, and characteristic length, were obtained based on RILEM recommendations. In addition, XRD and SEM were used to evaluate microstructural changes after exposure to different temperatures. Mechanical properties such as the residual compressive, tensile, and flexural strengths, as well as the elastic modulus, were also assessed. The SEM images revealed that the voids among the particles increased due to increasing internal vapor pressure, indicating that the number of pores in the concrete structure increased. Furthermore, the results showed that after subjecting the specimens to high temperatures, the concrete became more ductile, which may be due to the increase in the number of pores after water evaporation. The residual fracture energy of CACC was observed to increase with increasing temperature. However, the residual fracture toughness and flexural strength decreased as temperatures increased. In addition, the results demonstrated that, above 400 °C, the weight loss in the concrete is mainly due to the evaporation of chemically bound water and decomposition of cement hydration compounds, which are chemical processes.

Investigation of the Effect of Different Curing Conditions on the Mechanical Performance of Calcium Aluminate Cement Concrete at Elevated Temperatures

Investigation of the Effect of Different Curing Conditions on the Mechanical Performance of Calcium Aluminate Cement Concrete at Elevated Temperatures

Effect of rice husk ash on mechanical properties, fracture energy, brittleness and aging of calcium aluminate cement concrete

The calcium aluminate cement (CAC) is considered as eco-cement due to the reduced carbon emission during its production; it has various applications due to its high early age strength and enhanced durability in harsh environments. However, the initial hydration products of CAC concrete are temperature dependent and meta stable that will gradually convert to more stable phases. Such transition from an initial product that are dense and strong to more stable phases that are weaker and more porous, causes a reduction in strength and durability over time. This article discusses the results of a comprehensive study on incorporating rice husk ash (RHA) in CAC concrete in order to limit the phase transition of CAC hydration product and stabilize its long-term properties. Various concrete mixtures with different contents of RHA (0, 2.5, 5, 7.5, and 10%) as a cement replacement material were examined. In addition to the workability properties of the fresh concrete, the microstructural and mechanical properties of hardened concrete are characterized at the ages of 7, 28 and 90 days. The findings indicate that, at 90 days, the mechanical strengths of the mixes containing RHA were higher than those of the control mix, with the maximum improvement occurring at the substitution percentage of 5%. In accordance with TGA analysis the substitution of 5% RHA in CAC concrete led to a higher hydration level, which in turn improved the mechanical properties relative to the specimen without RHA at 90 days.

Physicochemical, Mineralogical, and Mechanical Properties of Calcium Aluminate Cement Concrete Exposed to Elevated Temperatures

One commonly used cement type for thermal applications is CAC containing 38–40% alumina, although the postheated behavior of this cement subjected to elevated temperature has not been studied yet. Here, through extensive experimentation, the postheated mineralogical and physicochemical features of calcium aluminate cement concrete (CACC) were examined via DTA/TGA, X-ray diffraction (XRD), and scanning electron microscopy (SEM) imaging and the variation in the concrete physical features and the compressive strength deterioration with temperature rise were examined through ultrasonic pulse velocity (UPV) values. In addition, other mechanical features that were addressed were the residual tensile strength and elastic modulus. According to the XRD test results, with the temperature rise, the dehydration of the structure occurred, which, in turn, led to the crystallization of the monocalcium dialuminate () and alumina () structures. The SEM images indicated specific variations in morphology that corresponded to concrete deterioration due to heat.

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.

Silicate impurities incorporation in calcium aluminate cement concrete: mechanical and microstructural assessment

ABSTRACT In this paper, the effect of rice husk ash (RHA), as silicate impurities, on the microstructure and mechanical properties of calcium aluminate cement concrete (CACC) is explored. Various mechanical tests, including tests for obtaining the compressive, splitting tensile, flexural strengths and elastic modulus, were performed on different mixture designs containing different volume percentages of RHA (0, 2.5, 5, 7.5, and 10%) at W/Cs of 0.4 and 0.5. Furthermore, the impact of RHA on the microstructure of this concrete was examined through careful analysis of the scanning electron microscope (SEM) images and energy dispersive X-ray spectroscopy (EDS) results. The results demonstrate that, At W/C of 0.5, the microstructure and mechanical properties were improved, with the greatest improvement for the RHA substitution percentage of 5%. However, at W/C of 0.4, the addition of RHA showed no positive effect, which can be attributed to a higher specific surface area of RHA than cement.

Effects of silicate impurities on fracture behavior and microstructure of calcium aluminate cement concrete

In this paper, to accurately evaluate the effect of the variation of the silica content in Calcium aluminate cement concrete, the fracture parameters of concrete made with this cement were investigated at different substitution levels of rice husk ash (RHA), as a material containing the amorphous silica content of more than 90%. The three-point bending test was conducted on 150 notched beams with water to cement ratios (W/Cs) of 0.4 and 0.5 based on the RILEM code specifications. For all of the mix designs, the fracture parameters were determined via two different methods, i.e., the work of fracture method (WFM) and the size effect method (SEM). At W/C of 0.5, substituting RHA led to improved fracture parameters, with the maximum values seen in the mix with a substitution level of 5%. However, at W/C of 0.4, as the substitution level of RHA increased, the fracture parameters decreased. The pozzolanic property, higher specific surface area, and greater water demand of RHA relative to cement at the W/C of 0.5 (due to more free water relative to W/C of 0.4) improved the integrity, hydration, microstructure, and fracture properties of the concrete. Further, the results demonstrated that there was a significant correlation between GF and Gf (GF/Gf=2.38).

The fracture behavior and microstructure of calcium aluminate cement concrete with various water-cement ratios

The present paper is aimed to examine the fracture behavior of calcium aluminate cement concrete. A total of 90 notched beams with water-cement ratios (W/C) between 0.3 and 0.55 were selected and subjected to the three-point bending tests. Two methods, i.e. the size effect method (SEM) and the work of fracture method (WFM), were adopted to calculate the fracture parameters for all the mix designs. As shown by the obtained results, a decrease in the W/C ratio from 0.55 to 0.3 caused a linear increase in the fracture toughness. In this condition, the brittleness number increased by around 50%. In addition, the results also indicated that the maximum fracture energies, Gf and GF, obtained from the SEM and WFM, respectively, were seen at W/C = 0.4 and also the characteristic length, lCh, in the WFM and the effective length of the fracture process zone, Cf, in the SEM reduced. Furthermore, the concrete fracture surface became somehow smoother due to better cohesion between the cement paste and aggregate. Furthermore, the findings also confirmed the existence of an approximate correlation between the fracture energy obtained by the WFM and the one by the SEM (GF=2.28Gf).

Study on the Property and Mix Ratio of CA and L•SAC Recycled Aggregate Planted Concrete

This paper studies the influence of different water-cement ratio configuration of recycled aggregate planted concrete on performance, the permeable property and drying shrinkage and the influence of different gelled material against compressive strength. At last, the plant growth performance of the planted concrete is analyzed through the whole process of screening, seeding and long-potential recording of the plants. It is found that the compressive strength of CA-R (recycled aggregate aluminate cement concrete) and L•SAC-R (recycled aggregate have low alkalinity) is higher, which is 7.6 MPa and 7.4MPa, respectively. Compared with the natural aggregate, the against compressive strength of the recycled aggregate is much smaller, and the difference of the experiment blocks with different age conditions is not large; It is better to set the porosity of the planted concrete between 22% and 35%: On the one hand, the total porosity of the recycled aggregate planted concrete is always slightly higher than that of the natural aggregate planted concrete, which is basically maintained at 31.7% and slightly higher than the design value; On the other hand, the total porosity of CA-R is larger than that of L•SAC-R and P•O-R (recycled aggregate ordinary Portland cement concrete), and compared with the total porosity, the variation of connected porosity is not obvious. In addition, the water permeation coefficient of 20-40mm single-stage concrete is between 15-19mm/s; And the dry shrinkage of aluminate recycled aggregate planted concrete is larger, there are different degrees of cracks on the surface and aggregate bonding. Among the three plants selected during the experiment, Festuca arundinacea and Alfalfa had good adaptability, but Bermuda grass had low adaptability.

Evaluation of a Procedure for Determining the Converted Strength of Calcium Aluminate Cement Concrete

Abstract There is renewed interest in North America for the use of calcium aluminate cement (CAC) in infrastructure repair because of its ability to gain strength rapidly even at low temperatures, the ability to customize its fresh workability, and its durability in adverse environments. Conversion of the hydration products of concrete where CAC is the only binder is a well-known phenomenon that is typically accompanied by strength loss, the rate and extent of which is dependent on the temperature history of the concrete, the w/cm, the cement content, and the concrete mixture design. An accelerated method of determining the converted strength of CAC concrete that is convenient for use in the field is presented. This test allows the samples to be cast in the field and left at ambient field temperatures for the first 24 hours; then the specimens are moved to the laboratory and placed in a water bath at 50°C to promote conversion. Robustness testing results are presented for the test method. The effects of the water to cement ratio, the initial (first 24 hours) curing temperature, the length of time before placing the specimens in the 50°C water bath, and the aggregate type are examined. The impact of the low replacement rates (up to 10 %) of finely ground limestone (FGLS) for CAC in concrete mixtures on converted concrete strengths was also studied. Results from testing showed that the majority of mixtures converted 48 hours after submersion in the 50°C water bath; however, differences in the initial curing temperature or aggregate type can delay conversion up to 11 days when specimens are cured following this procedure. Results also indicate that FGLS at replacement rates of 5 % and below in CAC systems may help increase the converted strength observed without reducing initial early strength gain.

Influence of aggregate type on conversion and strength in calcium aluminate cement concrete

Calcium aluminate cement (CAC) is gaining popularity in North America as a rapid repair material due to its ability to quickly gain strength, even at low curing temperatures. Use of CAC has been limited due to a lack of understanding of the process of conversion and the role of aggregates in CAC concrete. Conversion, which occurs only in 100% CAC systems, is a chemical process in which metastable hydrates convert into denser, stable hydrates. Presented is an examination of aggregate source impacts on this conversion process and converted CAC concrete strengths. Nine different concrete systems with fifteen varying aggregate sources were examined. Results indicated that carbonate limestone and siliceous limestone aggregate systems had significantly less strength reduction due to conversion compared to siliceous aggregate systems. Microstructural analysis of systems suggested that the carbonate limestone system had less porosity and better-formed aggregate/paste interfacial transition zones compared to the siliceous systems. Chemical analysis of the concrete pore solution indicated that the carbonate limestone system's pH and ionic concentrations of aluminum, sodium, and potassium were significantly higher than that of a siliceous system, indicating more dissolution of unhydrated cement in the carbonate limestone system. These studies are presented along with a proposed theory explaining the cause of the significant converted strength differences in CAC concrete systems made with limestone aggregates compared to siliceous aggregates.

Nanometer-Resolved Spectroscopic Study Reveals the Conversion Mechanism of CaO·Al2O3·10H2O to 2CaO·Al2O3·8H2O and 3CaO·Al2O3·6H2O at an Elevated Temperature

The main binding phases of calcium aluminate cement (CAC) concrete, CaO·Al2O3·10H2O (CAH10) and 2CaO·Al2O3·8H2O (C2AH8), slowly convert to 3CaO·Al2O3·6H2O (C3AH6) and Al(OH)3 (AH3). This reaction significantly speeds up at a temperature higher than ∼30 °C, and over time leads to significant strength loss in CAC concrete. Because of the lack of direct evidence that simultaneously probes morphological and chemical/crystallographic information, intense debate remains whether the conversion is generated by a solid-state or through-solution reaction. The conversion of CAH10 at an elevated temperature is studied herein using synchrotron-radiation-based X-ray spectromicroscopy capable of acquiring near edge X-ray absorption fine structure data and ptychographic images with a resolution of ∼15 nm. We show that, when stored at 60 °C, CAH10 first converts to C2AH8 by solid-state decomposition, followed by the through-solution formation of C3AH6. The C3AH6 crystallizes from both the relics of dissolved C2AH8 and fro...

High temperature material properties of calcium aluminate cement concrete

In this study, material properties of calcium aluminate cement concrete (CACC) were investigated at various temperatures of 23, 200, 400, 600 and 800°C. Material properties namely compressive strength, splitting tensile strength, elastic modulus, stress–strain response, mass loss and compressive toughness were measured using unstressed and residual test methods. High temperature performance of CACC was compared with conventional normal strength concrete (NSC). Data from high temperature tests of CACC revealed that the presence of alumina as a binding agent showed considerable enhancement in the mechanical performance compared to NSC. At elevated temperatures, reduction in the stress–strain response was observed in both CACC and NSC; however, increase in axial strain was more in case of CACC. Compressive toughness was higher in case of CACC as compared to NSC which increases up to 200°C, but decreases beyond this temperature. Scanning electron microscope (SEM) was used to differentiate the microstructural changes in both types of concrete at temperatures up to 600°C. Visual investigations after high temperature exposure revealed that CACC exhibits low cracking with less color changes as compared to NSC. Data generated from material property tests was utilized to develop simplified relations for expressing material properties of CACC as a function of temperature.

Corrosion Resistance of Calcium Aluminate Cement Concrete Exposed to a Chloride Environment.

The present study concerns a development of calcium aluminate cement (CAC) concrete to enhance the durability against an externally chemically aggressive environment, in particular, chloride-induced corrosion. To evaluate the inhibition effect and concrete properties, CAC was partially mixed with ordinary Portland cement (OPC), ranging from 5% to 15%, as a binder. As a result, it was found that an increase in the CAC in binder resulted in a dramatic decrease in the setting time of fresh concrete. However, the compressive strength was lower, ranging about 20 MPa, while OPC indicated about 30–35 MPa at an equivalent age. When it comes to chloride transport, there was only marginal variation in the diffusivity of chloride ions. The corrosion resistance of CAC mixture was significantly enhanced: its chloride threshold level for corrosion initiation exceeded 3.0% by weight of binder, whilst OPC and CAC concrete indicated about 0.5%–1.0%.

A new insight on alkaline hydrolysis of calcium aluminate cement concrete: Part I. Fundamentals

In this work a hypothesis to explain the alkaline hydrolysis degradation process of calcium aluminate cement concrete (CACC) is presented. The hypothesis is based on x-ray diffraction (XRD) data of some samples taken from real Spanish CACC structures. The identification from XRD data of a hydrated alkaline aluminate could serve as a guide to differentiate both processes of normal carbonation and alkaline hydrolysis.