Effect of a Nitrite/Nitrate-Based Accelerator on the Strength Development and Hydrate Formation in Cold-Weather Cementitious Materials

Recently, there has been increased use of calcium-nitrite and calcium-nitrate as the main components of chloride- and alkali-free anti-freezing agents to promote concrete hydration in cold weather concreting. As the amount of nitrite/nitrate-based accelerators increases, the hydration of tricalcium aluminate (C3A phase) and tricalcium silicate (C3S phase) in cement is accelerated, thereby improving the early strength of cement and effectively preventing initial frost damage. Nitrite/nitrate-based accelerators are used in larger amounts than usual in low temperature areas below −10 °C. However, the correlation between the hydration process and strength development in concrete containing considerable nitrite/nitrate-based accelerators remains to be clearly identified. In this study, the hydrate composition (via X-ray diffraction and nuclear magnetic resonance), pore structures (via mercury intrusion porosimetry), and crystal form (via scanning electron microscopy) were determined, and investigations were performed to elucidate the effect of nitrite/nitrate-based accelerators on the initial strength development and hydrate formation of cement. Nitrite/nitrate-AFm (aluminate-ferret-monosulfate; AFm) was produced in addition to ettringite at the initial stage of hydration of cement by adding a nitrite/nitrate-based accelerator. The amount of the hydrates was attributed to an increase in the absolute amounts of NO2− and NO3− ions reacting with Al2O3 in the tricalcium aluminate (C3A phase). Further, by effectively filling the pores, it greatly contributed to the enhancement of the strength of the hardened cement product, and the degree of the contribution tended to increase with the amount of addition. On the other hand, in addition to the occurrence of cracks due to the release of a large amount of heat of hydration, the amount of expansion and contraction may increase, and it is considered necessary to adjust the amount used for each concrete work.

Download Full-text

Physicochemical Study on the Strength Development Characteristics of Cold Weather Concrete Using a Nitrite–Nitrate Based Accelerator

Materials ◽

10.3390/ma12172706 ◽

2019 ◽

Vol 12 (17) ◽

pp. 2706 ◽

Cited By ~ 3

Author(s):

Heesup Choi ◽

Masumi Inoue ◽

Hyeonggil Choi ◽

Jihoon Kim ◽

Yuhji Sudoh ◽

...

Keyword(s):

Calcium Nitrate ◽

Hydrate Formation ◽

Cold Weather ◽

Strength Development ◽

Early Age ◽

Hydration Reaction ◽

Wide Range ◽

Formation Behavior ◽

Early Strength ◽

Nitrite Nitrate

There has recently been an increased use of anti-freezing agents that are primarily composed of salt- and alkali-free calcium nitrite (Ca(NO2)2) and calcium nitrate (Ca(NO3)2) to promote the hydration reaction of concrete in cold weather concreting. Nitrite–nitrate based accelerators accelerate the hydration of C3A and C3S in cement more quickly when their quantities are increased, thereby boosting the concrete’s early strength and effectively preventing early frost damage. However, the connection between the hydrate formation behavior and the strength development characteristic over time has yet to be clearly identified. Therefore, in this study, a wide range of physicochemical reviews were carried out to clarify the relationship between the hydrate formation behavior and the strength development characteristics, both at an early age and at later ages, which results from the addition of nitrite–nitrate based accelerators to concrete in varying amounts. These accelerators also act as anti-freezing agents. The results show that an increased quantity of nitrite–nitrate based accelerators caused an increase in the early strength of the concrete. This was due to the formation of nitrite and nitrate hydrates in large amounts, in addition to ettringite containing SO42, which is generated during the hydration reaction of normal Portland cement at an early age. On the other hand, at later ages, there was a rise in nitrite and nitrate hydrates with needle crystal structures exhibiting brittle fracture behavior. A decrease in C–S–H gel and Ca(OH)2 hydrates, deemed to have caused a decline in strength on Day 3 and thereafter, was also observed.

Download Full-text

Evaluation of Mechanical and Shrinkage Behavior of Lowered Temperatures Cementitious Mortars Mixed with Nitrite–Nitrate Based Accelerator

Materials ◽

10.3390/ma13173686 ◽

2020 ◽

Vol 13 (17) ◽

pp. 3686

Author(s):

Yusuke Tomita ◽

Akira Yoneyama ◽

Heesup Choi ◽

Masumi Inoue ◽

Jihoon Kim ◽

...

Keyword(s):

Calcium Nitrate ◽

Frost Damage ◽

Cold Weather ◽

Early Age ◽

Calcium Nitrite ◽

Concrete Hydration ◽

Early Strength ◽

Main Components ◽

Nitrite Nitrate ◽

Shrinkage Behavior

Recently, calcium nitrite (Ca(NO2)2) and calcium nitrate (Ca(NO3)2) have been increasingly used as the main components of salt- and alkali-free anti-freezing agents, for promoting concrete hydration in cold-weather concreting. With an increase in the amount of nitrite-based accelerator, the hydration of C3A, C3S, and βC2S in the cement is accelerated, thereby improving its early strength and effectively preventing the initial frost damage. Meanwhile, with an increase in the amount of nitrite-based accelerator, the expansion and shrinkage of the concrete—and, therefore, the crack occurrence—are expected to increase. In this study, various experiments were conducted on shrinkage, crack initiation, and the development of mortar containing a considerable amount of a nitrite-based accelerator. The result confirmed that, as the amount of nitrite-based accelerator was increased, the shrinkage was increased, and cracking in early age was more likely to occur, compared to the cases without the addition of this accelerator.

Download Full-text

Effect of Curing Temperature on Hardened Concrete Properties

Transportation Research Record Journal of the Transportation Research Board ◽

10.1177/0361198105191400112 ◽

2005 ◽

Vol 1914 (1) ◽

pp. 97-104 ◽

Cited By ~ 1

Author(s):

W. Micah Hale ◽

Thomas D. Bush ◽

Bruce W. Russell ◽

Seamus F. Freyne

Keyword(s):

Fly Ash ◽

Cementitious Materials ◽

Curing Temperature ◽

Supplementary Cementitious Materials ◽

Cold Weather ◽

Strength Development ◽

Hardened Concrete ◽

Hardened Properties ◽

Hot Weather ◽

Materials Used

Often, concrete is not mixed or placed under ideal conditions. Particularly in the winter or the summer months, the temperature of fresh concrete is quite different from that of concrete mixed under laboratory conditions. This paper examines the influence of supplementary cementitious materials on the strength development (and other hardened properties) of concrete subjected to different curing regimens. The supplementary cementitious materials used in the research program were ground granulated blast furnace slag (GGBFS), fly ash, and a combination of both materials. The three curing regimens used were hot weather curing, standard curing, and cold weather curing. Under the conditions tested, the results show that the addition of GGBFS at a relatively low replacement rate can improve the hardened properties for each curing regimen. This improvement was noticeable not only at later ages but also at early ages. Mixtures that contained both materials (GGBFS and fly ash) performed as well as and, in most cases, better than mixtures that contained only portland cement in all curing regimens.

Download Full-text

Investigation of the Relationship between Compressive Strength and Hydrate Formation Behavior of Low-Temperature Cured Cement upon Addition of a Nitrite-Based Accelerator

Materials ◽

10.3390/ma12233936 ◽

2019 ◽

Vol 12 (23) ◽

pp. 3936 ◽

Cited By ~ 1

Author(s):

Jihoon Kim ◽

Daiki Honda ◽

Heesup Choi ◽

Yukio Hama

Keyword(s):

Compressive Strength ◽

Calcium Nitrate ◽

Hydrate Formation ◽

Strength Development ◽

Early Age ◽

Enhancement Effect ◽

Freezing Damage ◽

Formation Behavior ◽

Relative Production ◽

The Relationship

When concrete is used for construction in cold-temperature regions, cold-resistant accelerators based on calcium nitrite (Ca(NO2)2) and calcium nitrate (Ca(NO3)2) are added to prevent early freezing damage. Although cold-resistant accelerators increase the early compressive strength and prevent early freezing damage by promoting cement hydration, the strength enhancement effect owing to the formation of such hydrates has not been evaluated quantitatively thus far. This study covers various types of analysis to understand the relationship between cement hydrate formation behavior and strength development upon the addition of varying amounts of nitrite-based accelerator. We find that the early compressive strength is enhanced by the addition of nitrite-based accelerator via the promotion of the relative production of monosulfate and C-S-H in the early age. However, the development of compressive strength decreases with an increase in the curing age. Furthermore, we find that the promotion of hydration reactions at an early age with the addition of nitrite-based accelerator can affect the formation ratio of each hydrate at a late age. We believe our findings can significantly contribute to developments in concrete application and allied fields.

Download Full-text

Vulnerability of sweet cherry cultivars to continuous periods of spring frosts in Plovdiv, Bulgaria

Agricultural Science and Technology ◽

10.15547/ast.2020.04.055 ◽

2020 ◽

Vol 12 (4) ◽

pp. 348-352

Author(s):

S. Malchev ◽

S. Savchovska

Keyword(s):

Sweet Cherry ◽

Weather Conditions ◽

Frost Damage ◽

Cold Weather ◽

Bud Burst ◽

Intermediate Group ◽

Air Temperatures ◽

Wide Range ◽

Group Form ◽

Sweet Cherry Cultivars

Abstract. The periods with continuous freezing air temperatures reported during the spring of 2020 (13 incidents) affected a wide range of local and introduced sweet cherry cultivars in the region of Plovdiv. They vary from -0.6°C on March 02 to -4.9°C on March 16-17. The duration of influence of the lowest temperatures is 6 and 12 hours between March 16 and 17. The inspection of fruit buds and flowers was conducted twice (on March 26 and April 08) at different phenological stages after continuous waves of cold weather conditions alternated with high temperatures. During the phenological phase ‘bud burst’ (tight cluster or BBCH 55) some of the flowers in the buds did not develop further making the damage hardly detectable. The most damaged are hybrid El.28-21 (95.00%), ‘Van’ (91.89%) and ‘Bing’ (89.41%) and from the next group ‘Lapins’ (85.98%) and ‘Rosita’ (83.33%). A larger intermediate group form ‘Kossara’ (81.67%), ‘Rozalina’ (76.00%), ‘Sunburst’ (75.00%), ‘Bigarreau Burlat’ (69.11%) and ‘Kuklenska belitza’ (66.67%). Candidate-cultivar El.17-90 ‘Asparuh’ has the lowest frost damage values of 55.00% and El.17-37 ‘Tzvetina’ with damage of 50.60%.

Download Full-text

Use of Treated Non-Ferrous Metallurgical Slags as Supplementary Cementitious Materials in Cementitious Mixtures

Applied Sciences ◽

10.3390/app11094028 ◽

2021 ◽

Vol 11 (9) ◽

pp. 4028

Author(s):

Asghar Gholizadeh Vayghan ◽

Liesbeth Horckmans ◽

Ruben Snellings ◽

Arne Peys ◽

Priscilla Teck ◽

...

Keyword(s):

Mechanical Performance ◽

Cementitious Materials ◽

Supplementary Cementitious Materials ◽

Partial Replacement ◽

Strength Development ◽

Supplementary Cementitious Material ◽

Performance Requirements ◽

Metallurgical Slags ◽

Leaching Behaviour ◽

Kinetics Of

This research investigated the possibility of using metallurgical slags from the copper and lead industries as partial replacement for cement. The studied slags were fayalitic, having a mainly ferro-silicate composition with minor contents of Al2O3 and CaO. The slags were treated at 1200–1300 °C (to reduce the heavy metal content) and then granulated in water to promote the formation of reactive phases. A full hydration study was carried out to assess the kinetics of reactions, the phases formed during hydration, the reactivity of the slags and their strength activity as supplementary cementitious material (SCM). The batch-leaching behaviour of cementitious mixtures incorporating treated slags was also investigated. The results showed that all three slags have satisfactory leaching behaviour and similar performance in terms of reactivity and contribution to the strength development. All slags were found to have mediocre reactivity and contribution to strength, especially at early ages. Nonetheless, they passed the minimum mechanical performance requirements and were found to qualify for use in cement.

Download Full-text

Coupled Preparation of Ferronickel and Cementitious Material from Laterite Nickel Ores

Materials ◽

10.3390/ma13214992 ◽

2020 ◽

Vol 13 (21) ◽

pp. 4992

Author(s):

Ruimeng Shi ◽

Xiaoming Li ◽

Yaru Cui ◽

Junxue Zhao ◽

Chong Zou ◽

...

Keyword(s):

Direct Reduction ◽

Cementitious Materials ◽

Tricalcium Silicate ◽

Cementitious Material ◽

Raw Material ◽

Tricalcium Aluminate ◽

Thermodynamic Conditions ◽

Nickel Ores ◽

Main Components ◽

Factsage Software

Nickel slags can be produced through ferronickel preparation by the pyrometallurgical processing of laterite nickel ores; however, such techniques are underutilized at present, and serious environmental problems arise from the stockpiling of such nickel ores. In this study, a modification to the process of ferronickel preparation by the direct reduction of carbon bases in laterite nickel ores is proposed. The gangue from the ore is used as a raw material to prepare a cementitious material, with the main components of tricalcium silicate and tricalcium aluminate. By using FactSage software, thermodynamic calculations are performed to analyze the reduction of nickel and iron and the effect of reduction on the formation of tricalcium silicate and tricalcium aluminate. The feasibility of a coupled process to prepare ferronickel and cementitious materials by the direct reduction of laterite nickel ore and gangue calcination, respectively, is discussed under varying thermodynamic conditions. Different warming strategies are applied to experimentally verify the coupled reactions. The coupled preparation of ferronickel and cementitious materials with calcium silicate and calcium aluminate as the main phases in the same experimental process is realized.

Download Full-text

New Approach for the Determination of Radiological Parameters on Hardened Cement Pastes with Coal Fly Ash

Materials ◽

10.3390/ma14030475 ◽

2021 ◽

Vol 14 (3) ◽

pp. 475

Author(s):

Ana María Moreno de los Reyes ◽

José Antonio Suárez-Navarro ◽

Maria del Mar Alonso ◽

Catalina Gascó ◽

Isabel Sobrados ◽

...

Keyword(s):

Fly Ash ◽

Activity Concentration ◽

Gamma Ray ◽

Coal Fly Ash ◽

Cementitious Materials ◽

New Method ◽

Supplementary Cementitious Materials ◽

Hardened Cement ◽

Cement Pastes ◽

Activity Concentrations

Supplementary cementitious materials (SCMs) in industrial waste and by-products are routinely used to mitigate the adverse environmental effects of, and lower the energy consumption associated with, ordinary Portland cement (OPC) manufacture. Many such SCMs, such as type F coal fly ash (FA), are naturally occurring radioactive materials (NORMs). 226Ra, 232Th and 40K radionuclide activity concentration, information needed to determine what is known as the gamma-ray activity concentration index (ACI), is normally collected from ground cement samples. The present study aims to validate a new method for calculating the ACI from measurements made on unground 5 cm cubic specimens. Mechanical, mineralogical and radiological characterisation of 28-day OPC + FA pastes (bearing up to 30 wt % FA) were characterised to determine their mechanical, mineralogical and radiological properties. The activity concentrations found for 226Ra, 212Pb, 232Th and 40K in hardened, intact 5 cm cubic specimens were also statistically equal to the theoretically calculated values and to the same materials when ground to a powder. These findings consequently validated the new method. The possibility of determining the activity concentrations needed to establish the ACI for cement-based materials on unground samples introduces a new field of radiological research on actual cement, mortar and concrete materials.

Download Full-text

Sorption Mechanism of Carbon-14 by Hardened Cement Paste

MRS Proceedings ◽

10.1557/proc-412-435 ◽

1995 ◽

Vol 412 ◽

Cited By ~ 5

Author(s):

K. Noshita ◽

T. Nishi ◽

M. Matsuda ◽

T. Izumida

Keyword(s):

Electrostatic Force ◽

Cementitious Materials ◽

Hardened Cement ◽

Sorption Mechanism ◽

Carbon 14 ◽

Adsorption Sites ◽

Radioactive Waste Repositories ◽

Waste Repositories ◽

Positively Charged

AbstractCarbon-14 sorption by cementitious materials should be enhanced to ensure the long term safety of radioactive waste repositories. The sorption mechanism of inorganic C- 14 (CO32- was investigated using batch sorption experiments and zeta potential measurements. The results suggested that C-14 was adsorbed onto the cement surface by an electrostatic force, due to the reaction between SiO2 and CaO contained in the cementitious composition. That is, SiO2 was originally negatively charged (SiO-) in cement, but became positively charged through the interaction of Ca2+. These positive sites on the SiO2 surface adsorbed inorganic C-14. Ordinary Portland cement (OPC) did not contain enough SiO2 compared with its CaO content to produce sufficient numbers of C-14 adsorption sites. The C-14 distribution coefficient (Kd) was increased from 2,000 to 7,000 mL/g by adding SiO2 to OPC.

Download Full-text