Calcium Oxychloride Formation Research Articles

Long-Term Performance of Soybean-Based Concrete Surface Protectant under Laboratory Accelerated Aging Conditions

Soy methyl ester-polystyrene (SME-PS) is an organic material derived from soybeans, which has proven to be an effective protectant for concrete surfaces. This study investigated the long-term performance of cement paste samples treated with SME-PS under laboratory accelerated aging conditions (AAC). The specimens were subjected to cyclic conditions: 8 h of UVA radiation (simulating solar radiation), followed by 6 h of darkness with water condensation and a high temperature of 40°C for 28 days. After the AAC exposure, the samples were immersed in a deicing salt solution, specifically a 29.8 wt. % calcium chloride solution, for 7 days. To evaluate the long-term behavior of SME-PS, a series of experiments, including visual observation, thermogravimetric analysis (TGA), and low-temperature differential scanning calorimetry (LT-DSC) was conducted. Visual observations revealed slight damage in SME-PS-treated samples after AAC exposure, while control samples experienced microcrack formations. SME-PS chemical compositions remained unaffected by AAC, in contrast to the control samples where a decrease in the quantity of calcium hydroxide and an increase in calcium carbonate content were observed as a result of carbonation during AAC exposure. LT-DSC results indicated that SME-PS-treated samples showed a significant reduction in the enthalpy of fusion associated with calcium oxychloride (CAOXY) formation, indicating that the SME-PS remained effective after AAC exposure, while control samples exhibited higher CAOXY enthalpy of fusion.

Mitigating calcium oxychloride formation in cementitious paste using alternative supplementary cementitious materials

Supplementary cementitious materials (SCMs) are known to reduce calcium oxychloride (CAOXY) contents in cementitious pastes. However, when availability or cost precludes the use of traditional SCMs, such as fly ash, mitigation could be provided through alternative materials. Fly ash (FA), rice husk ash (RHA), bottom ash (BA), limestone filler (LS), nepheline syenite filler (NS), sandstone filler (SS), and silica flour (SFL) were evaluated for CAOXY mitigation in cementitious paste using low-temperature differential scanning calorimetry, reactivity testing, thermogravimetric analysis, and compressive strength testing. The order of CAOXY mitigation from least to most effective is SS, LS, SFL, NS, BA, FA, and RHA.

Utilizing Nano Silica to Reduce Calcium Oxychloride Formation in Cementitious Materials

This paper examines the use of two nano silica (NS) materials as an additive that can reduce the susceptibility of concrete to deicing salt damage. The motivation for this research is to evaluate whether NS can be used to improve resistance to calcium oxychloride formation because of deicing salts. Deicing salts, like calcium chloride and magnesium chloride, can react with water and calcium hydroxide in concrete to form an expansive product called calcium oxychloride. This work builds on previous observations that supplementary cementitious materials (SCMs), such as Class F fly ash, slag, and silica fumes, can reduce calcium oxychloride formation through dilution of the cement, which results in a reduction in calcium hydroxide and the pozzolanic reaction, which further reduces calcium hydroxide through chemical reaction. This paper investigates whether NS additions during the mixing process can provide similar results to other SCMs. Both NSs had the same particle size distribution and specific surface area, but NS2 had alumina on the surface while NS1 did not. Toward this end, the calcium hydroxide content and calcium oxychloride were measured using thermal gravimetric analysis and low-temperature differential scanning calorimetry, respectively. The addition of NS to a mixture was found to reduce the calcium oxychloride at lower dosages as compared to Class F fly ash.

The influence of air voids and fluid absorption on salt-induced calcium oxychloride damage

Calcium and magnesium deicing salts may damage concrete due to calcium oxychloride formation (CaOXY). Previous work has shown that replacing a portion of the cement in a mixture with supplementary cementitious materials reduce CaOXY formation. AASHTO PP-84 was developed to help specify damage-resistant mixtures by limiting the CaOXY amount in paste. This limit was established based on empirical observations; however, this did not consider other aspects of the mixture such as paste volume or air content. This paper investigates how fluid absorption, paste volume, and air content are all key parameters in determining damage from CaOXY. Concrete with a higher paste volume has more CaOXY and is more susceptible to damage. Concrete with a higher air content is less susceptible to damage as the voids provide space for fluid absorption and CaOXY formation; however this only occurs for mixtures with a specific range of calcium hydroxide (Ca(OH)2) (between 7 and 12 g Ca(OH)2/100 g paste). This paper incorporates these factors to provide a more comprehensive explanation for CaOXY-induced damage in concrete.

Durability of Mortars Manufactured with Low-Carbon Binders Exposed to Calcium Chloride-Based De-Icing Salts

Calcium chloride is one of the main de-icing salts for removing snow and ice from roads, infrastructures and service areas. It is well known that reinforced concrete structures, if exposed to calcium chloride, can suffer from severe damages due to both corrosion of steel reinforcement and chemical attack of the cement paste. This paper aims at evaluating the resistance to chemical attack of mortars manufactured with different low-carbon binders (alkali activated slag cements, calcium sulphoaluminate cement-based blends, high volume ultrafine fly ashes cements) in presence of CaCl2-based de-icing salts in cold weather (temperature about 4°C). Results indicated that alkali activated slag-based mortars are quasi-immune to calcium chloride attack due to their mineralogical composition. On the contrary, calcium sulphoaluminate-based blends show the total loss of binding capacity, especially when calcium sulphoaluminate cement is used with gypsum and Portland cement. Finally, the partial substitution of Portland cement with ultrafine fly ash strongly reduces the mass change and the strength loss of mortars submerged in 30 wt.% CaCl2 solutions due to the strong reduction of calcium hydroxide responsible for the calcium oxychloride formation in the cement paste.

Investigating concrete deterioration due to calcium oxychloride formation

Calcium oxychloride is a serious deterioration mechanism affecting concrete pavements. In order to mitigate calcium oxychloride deterioration in concrete, fly ash is used as partial cement replacement in conjunction with entrained air. Concrete specimens were stored in a 30% calcium chloride solution at 5 °C for 202 days. Following storage, specimens were evaluated through compressive and flexural strength loss along with mass change, length change, and chloride penetration. Results indicate that a partial cement replacement with 15% fly ash mitigates deterioration in concrete specimens when tested for flexural strength loss; however, 30% or more fly ash is needed for similar mitigation based on compressive strength. Further, results indicate that specimens cast with 5% entrained air outperform those without air entrainment. Class C fly ash generally mitigated strength loss to a greater extent than Class F fly ash.

Synergistic effects of air content and supplementary cementitious materials in reducing damage caused by calcium oxychloride formation in concrete

Pavement damage occurs in cold-region concrete exposed to high concentrations of calcium chloride (CaCl2). The damage is caused by a combination of conventional freeze-thaw damage and the formation of a deleterious phase known as calcium oxychloride from a reaction between CaCl2 and calcium hydroxide in the concrete. Much research has focused on calcium oxychloride mitigation in cement pastes, but not on concrete damage due to calcium oxychloride. In this study, the synergistic roles of air and supplementary cementitious materials (SCMs) in reducing damage in concrete exposed to high concentrations of CaCl2 and freeze-thaw conditions is studied. Concrete mixtures were made with different SCM replacement levels and air contents and immersed in 25% CaCl2 solutions and subject to freeze-thaw cycles (−8 °C–25 °C) for 600 days. Bulk resistivity and visual assessment of damage were excellent descriptors of the damage progression. Damage was reduced as the SCM content and air content were increased. Mixtures which had 20% SCM and 8% air and mixtures which had 35% SCM and more than 4% air showed strong durability against calcium oxychloride damage.

Quantification of Calcium Oxychloride by Differential Scanning Calorimetry: Validation and Optimization of the Testing Procedure

Abstract The American Association of State Highway and Transportation Officials (AASHTO) T 365 standard, Standard Method of Test for Quantifying Calcium Oxychloride Formation Potential of Cementitious Pastes Exposed to Deicing Salts, describes a test methodology that uses low-temperature differential scanning calorimetry (LTDSC) to quantify the formation of calcium oxychloride in cementitious systems exposed to concentrated calcium chloride solutions. AASHTO T 365 is included in AASHTO PP 84, Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures, as a performance indicator for mixtures at risk of calcium oxychloride formation. During the test, the sample temperature is first dropped to −90°C, looped through a brief thermal cycle, then slowly increased to a maximum of 50°C, at a constant heating rate of 0.25°C/minute (min), for a total testing time of approximately 11 hours. The objective of this work is to modify the test to reduce its duration to facilitate wide adoption among practitioners. It is found that by increasing the minimum conditioning temperature from −90°C to −5°C, as well as by increasing the heating rate from 0.25°C/min up to 1°C/min, the test duration can be reduced from approximately 10.7 hours to approximately 1.6 hours without any statistically significant difference in the numerical test results, although an offset of the melting peak and a change in its shape were observed. This change can provide valuable savings in terms of time and energy/gas consumption and make AASHTO T 365 more competitive with other available tests for the estimation of calcium oxychloride formation, such as thermogravimetric analysis (TGA). TGA and LTDSC are compared to each other in terms of mixture classification for susceptibility to calcium oxychloride formation. It is shown that the two tests show good agreement, with 85 % of cases (out of 30 tested) receiving the same classification.

Using compressive strength and mass change to verify the calcium oxychloride threshold in cementitious pastes with fly ash

Calcium oxychloride (CAOXY) formation is a deterioration mechanism known to cause joint damage in concrete pavements. The accepted CAOXY mitigation threshold in paste is 15 g/100 g paste; however, this limit was developed using flexural strength testing of pastes. This investigation seeks to verify this threshold using compressive strength and mass change testing. Cementitious pastes were cast with portland cement and fly ash (up to 50% mass). Specimens were stored in a 30% mass CaCl2 at 5 °C to accelerate deterioration. Visual observations, thermogravimetric analysis, low-temperature differential scanning calorimetry, mass change, and compressive strength results were recorded. Partial replacement of cement with fly ash reduces the Ca(OH)2, CAOXY, and damage levels. Using mass change, a threshold at which no damage occurs is established at 20 g/100 g paste, indicating that the current threshold is conservative. For compressive strength, while increasing the amount of fly ash reduces damage, damage is noted in all specimens tested; however, strength loss noted in this work is similar to the research which established the current threshold. Therefore, the compressive strength results generally validate the CAOXY threshold level of 15 g/100 g paste. Careful correlations between paste and concrete damage are needed in order to further verify the threshold value.

Petrographic analysis of in-service cementitious mortar subject to freeze-thaw cycles and deicers

Chloride-based deicers, especially CaCl2 and MgCl2, can damage cementitious materials due to the formation of mineral phases such as calcium oxychloride and brucite. However, there are only limited direct observations of calcium oxychloride formed in cementitious materials in the field. This paper uses petrographic methods to evaluate damage of an in-service cementitious mortar substrate subject to freeze-thaw cycles and deicers for six years. The amount of calcium hydroxide in the mortar was quantified using thermogravimetric analysis. Changes in hydration products and microstructure were characterized by optical microscopy. Scanning electron microscopy coupled with energy dispersive X-ray spectroscopy was used to examine the morphology and elemental composition of secondary deposits related to the deicer damage. The mortar with less than 3% air exhibits horizontal cracks and microcracks cutting around aggregate particles. The cracks and microcracks are partially filled with calcium oxychloride due to the application of CaCl2. A densified crust of brucite and calcite, likely associated with the usage of MgCl2, covers the top surface of the damaged mortar. The deicer exposure results in leaching of calcium hydroxide mainly due to the formation of calcium oxychloride. Calcium leaching increases the apparent paste porosity in the damaged mortar, which likely weakens the physicomechanical properties of the mortar and accelerates the ingress of external deicer solutions. Moreover, the deicer application results in air-void-filling by calcium oxychloride and secondary ettringite, which may reduce the space available to release the internal stresses associated with ice formation and thus compromises the freeze-thaw durability.

Calcium oxychloride: A critical review of the literature surrounding the formation, deterioration, testing procedures, and recommended mitigation techniques

Deicing salts have long been known to cause deterioration in concrete pavements. Freeze/thaw, surface scaling, and reinforcement corrosion are well documented deterioration mechanisms. However, another mechanism exists causing severe concrete damage that is much less understood. This deterioration is due to the formation of calcium oxychloride, from chemical interactions between the cementitious paste and certain chloride-based deicing salts. The basic chemical structure of calcium oxychloride, with slight variations, has been reported in deteriorated samples. Ideas have been postulated about failure mechanisms associated with the formation of calcium oxychloride. Further, testing techniques such as thermogravimetric analysis, low-temperature differential scanning calorimetry, and volume change measurements have been successfully utilized to better understand/quantify calcium oxychloride. Mitigation techniques to minimize the impact of calcium oxychloride include reducing cement content through the use of supplementary cementitious materials or other means, the use of adequate air entrainment, preferential carbonation, and the use of concrete sealants. This review of the literature highlights the current understanding of calcium oxychloride, provides best practice guidance and identifies new areas of research needed in order to effectively mitigate calcium oxychloride damage in concrete pavements.

The Durability of One-Part Alkali-Activated Slag-Based Mortars in Different Environments

The paper assesses the durability of one-part alkali-activated slag-based mortars (AAS) in different aggressive environments, such as calcium chloride- and magnesium sulphate-rich solutions, in comparison with traditional cementitious mortars at equal water to binder ratio. Moreover, the freezing and thawing resistance was evaluated on mortars manufactured with and without air entraining admixture (AEA). Experimental results indicate that the alkali content is a key parameter for durability of AAS: the higher the alkali content, the higher the resistance in severe conditions. In particular, high-alkali content AAS mortars are characterized by freeze–thaw resistances similar to that of blast furnace cement-based mixtures, but lower than that of Portland cement-mortars while AAS with low activators dosages evidence a very limited resistance in cold environment. The effectiveness of AEA in enhancement of freeze–thaw resistance is confirmed also for AAS mortars. Moreover, AAS mixtures are quasi-immune to expansive calcium oxychloride formation in presence of CaCl2-based deicing salts, but they are very vulnerable to magnesium sulphate attack due to decalcification of C-S-H gel and gypsum formation.

Material characterization to assess effectiveness of surface treatment to prevent joint deterioration from oxychloride formation mechanism

Joints in a rigid pavement can act as local reservoirs trapping deicing salts and moisture. Such a harsh micro-environment can impact the durability of sawn joint surfaces, resulting in premature distress even in cases where the bulk of pavement exhibits sufficient durability against frost action and chemical attack by deicing salts. A comprehensive experimental program was undertaken in this study to elucidate the mechanisms of deterioration of concrete exposed to de-icing salts. Plain cement paste samples cast with water-to-cement ratio of 0.40 were exposed to salt solutions prepared with 4% and 20% concentrations of CaCl2 and MgCl2 at 4 °C. A second series of paste specimens, treated with a wide range of sealers representing various generic types, were also exposed to the aforementioned salt solutions. Mechanisms of deterioration and formation of chemical compositions and phases were monitored at different exposure periods using X-ray diffraction (XRD), and differential scanning calorimetry (DSC). Moreover, concrete specimens were cast and treated with the same sealers to expand the fundamental observations from paste to concrete phase.Data obtained from plain cement paste specimens indicated no sign of calcium or magnesium oxychloride formation when exposed to 4% concentration of salt solutions, while oxychloride formation was detected at 20% concentrations. Potential for calcium oxychloride formation in sealed samples correlated well with paste expansion and visual concrete deterioration rates. Results indicated that an expansion threshold of 0.20 mm corresponded to the recommended threshold of oxychloride formation potential of 15 g per 100 g of paste (gOXY/gPaste).

Microbial damage mitigation strategy in cementitious materials exposed to calcium chloride

Deterioration of concrete pavements in the United States has increased over the past decade. This damage is triggered by two possibilities: classic freeze-thaw behavior, as well as the formation of calcium oxychloride (CAOXY) that originates from calcium chloride (CaCl2) in deicing salt. CAOXY is an expansive phase leading to damage and cracking in the cementitious matrix. This study investigates use of alkaliphilic, spore-forming bacteria to mitigate formation of CAOXY. Cementitious samples were made with ordinary portland cement (OPC); OPC combined with nutrients; and OPC combined with bacteria and nutrients. Low-temperature differential scanning calorimetry, thermogravimetric analysis, sorption analyzer, and acoustic emissions were used to quantify the amount of CAOXY, calcium hydroxide, microstructural change, and damage caused by CaCl2 salt in the cementitious samples, respectively. It was observed that the addition of bacteria changes in the micropore structure of cement pastes and significantly reduces the formation of CAOXY.

Role of Supplementary Cementitious Material Type in the Mitigation of Calcium Oxychloride Formation in Cementitious Pastes

AbstractPremature deterioration has been observed at some joints in concrete pavements. This joint damage has been attributed, in part, to a deleterious chemical reaction between chloride-based dei...

Properties of quicklime(CaO)-activated Class F fly ash with the use of CaCl2

This study reports the significant effect of CaCl2 on strength improvement in CaO-activated Class F fly ash system. In these systems, the presence of CaCl2 promotes (1) a higher degree of fly ash dissolution, (2) increasing C-S-H formation, and (3) an overall reduction of pore size and volume, resulting in increased strength. However, while more C-S-H, which is responsible for strength increase, was produced with higher CaCl2 content, extreme doses of CaCl2 resulted in strength degradation; more importantly, the best quantity of CaCl2 for the greatest strength was dependent on the water-to-binder weight ratio (w/b). This dependency was closely related to the formation of calcium oxychloride, which generally causes severe expansive cracking and depends on w/b.

Damage in cement pastes exposed to MgCl2 solutions

Magnesium chloride (MgCl2) reacts with cement pastes resulting in calcium leaching and the formation of calcium oxychloride, which can cause damage. This paper examines the damage in different cement pastes exposed to MgCl2 solutions. Volume change measurement and low temperature differential scanning calorimetry are used to characterize the formation of calcium oxychloride. Thermogravimetric analysis and X-ray fluorescence are used to quantify calcium leaching from Ca(OH)2 and C-S-H. The ball-on-three-balls test is used to quantify the flexural strength reduction. Calcium oxychloride can form in cement pastes exposed to MgCl2 solutions with a (Ca(OH)2/MgCl2) molar ratio larger than 1. As the MgCl2 concentration increases, two-stages of flexural strength reduction are observed in the plain cement pastes, with the initial reduction primarily due to calcium leaching from Ca(OH)2 and the additional reduction due to the calcium leaching from C-S-H (at MgCl2 concentrations above 17.5 wt%). For the cement pastes containing fly ash, there is a smaller reduction in flexural strength as less Ca(OH)2 is leached, while no additional reduction is observed at high MgCl2 concentrations due to the greater stability of C-S-H with a lower Ca/Si ratio. The addition of fly ash can mitigate damage in the presence of MgCl2 solutions.

Extending Low-Temperature Differential Scanning Calorimetry from Paste to Mortar and Concrete to Quantify the Potential for Calcium Oxychloride Formation

Abstract Calcium chloride–based deicing salts can react with calcium hydroxide in concrete pavements, resulting in the formation of calcium oxychloride. The formation of calcium oxychloride can cause damage in the pavements, especially at the joints. Recently, it has been shown that low-temperature differential scanning calorimetry can be used to measure calcium oxychloride contents in cement pastes exposed to calcium chloride. This article explores the extension of the low-temperature differential scanning calorimetry test method from applications on ground paste to ground mortar and concrete. Specifically, the influence of dilution due to the aggregate volume causes the measured amount of calcium oxychloride to be smaller in mortar and concrete than the pastes. To successfully measure the amount of calcium oxychloride, a higher powder-liquid ratio is used in concretes as compared to pastes. Low-temperature differential scanning calorimetry can successfully be used to measure the amount of calcium oxychloride in ground mortars and concrete; however, there is an increase in the variation of the measurement, and, as such, it is recommended that the average of three tests should be considered as a test specimen.

Flexural strength reduction of cement pastes exposed to CaCl2 solutions

Calcium chloride (CaCl2) can react with calcium hydroxide (Ca(OH)2) to form calcium oxychloride which can reduce flexural strength and damage concrete. This paper aims to characterize the reduction in flexural strength of cement pastes exposed to CaCl2 solutions using the ball-on-three-balls test. The amounts of Ca(OH)2 and calcium oxychloride in the cement paste are measured using thermogravimetric analysis and low-temperature differential scanning calorimetry, respectively. The volume change that occurs as a result of the reactions between the cement paste and CaCl2 is also measured. The reduction in flexural strength increases as the concentration of the CaCl2 solution increases and the exposure temperature decreases. The flexural strength reduction can be mitigated by increasing the amount of supplementary cementitious materials (fly ash) in the cement pastes. Lowering the water-cementitious materials ratio also reduces the flexural strength reduction. The flexural strength reduction is correlated with the amount of calcium oxychloride and the volume change in the cement pastes exposed to the CaCl2 solution. While the flexural strength reduction is believed to be primarily due to the formation of calcium oxychloride, the formation of Friedel's salt and Kuzel's salt also contributes to the flexural strength reduction.

Calcium Oxychloride Formation Potential in Cementitious Pastes Exposed to Blends of Deicing Salt

Calcium Oxychloride Formation Potential in Cementitious Pastes Exposed to Blends of Deicing Salt