Binder Hydration Research Articles

Numerical Analysis of the Hydraulic and Mechanical Behavior of In Situ Cemented Paste Backfill

Although the most explicit approach to acknowledge the behavior of in-stope CPB is to utilize monitoring instruments to collect relevant data, such as pore water pressure, total stress and temperature, the in situ monitoring may lead to production delays and rising costs. An alternative solution is using numerical simulation method to understand the behaviors of field CPBs that are placed in stopes. Hence, a numerical model, which considers the binder hydration process, hydraulic (pore water pressure) and mechanical (total stress, uniaxial compressive stress) properties, is developed to analyze the performances of in-stope CPBs. The proposed model is validated by comparing field monitoring data with corresponding results predicted by model simulation. Satisfactory agreement is detected between the modeling results and monitoring data, validating the capability of the developed model in well describing the hydraulic and mechanical behaviors of CPBs placed in field stopes. Understanding the characteristics of field paste backfill matrix is of great importance in improving its ultimate mix design with respect to cost savings. This study also contributes to a better understanding of the hydro-mechanical performance of field CPB structures.

Hydration and Crystallization Behavior of MgO in Cold-Bonded Pellets Containing Basic Oxygen Furnace Dust

Basic oxygen furnace (BOF) dust is a kind of solid waste in the metallurgical steelmaking process, which contains more than 50 pct total iron and a certain amount of overburned MgO and CaO. Based on the nonhydraulic cementitious property of MgO in BOF dust, MgCl2 is added together as a binder to prepare cold-bonded pellets returning to BOF, which is the most economical route to recycle secondary resources. In this study, we investigated the hydration and crystallization behavior of MgO-based binder prepared by MgO superheated at 1500 °C and MgCl2 in cold-bonded BOF dust pellets, to solve the problem of whether the overburned MgO can be hydrated with MgCl2 to form crystalline phases, and generated nonhydraulic cementitious structure with high strength to consolidate the pellets. The results show that the overburned MgO prepared at 1500 °C and MgCl2 can form adhesive gels to absorb BOF dust particles by hydration reaction. The gels develop to 5Mg(OH)2·MgCl2·8H2O crystalline phase with a reticular structure after solidification, and the crystalline phase produces pellet mechanical strength by wrapping and connecting bridge. The hydration reaction produced by overburned MgO is incomplete, and the hydration reaction degree is 50 to 65 pct.

POLYMINERAL COMPOSITE BINDERS FOR FOAM CONCRETE: FEATURES OF HYDRATION AND HARDENING

Introduction. The paper devotes to the features of hydration and hardening of polymineral composite binders. The authors carry out the complex research of the phase composition, hydration and structure formation processes of hardened composite binders with active mineral additives by X-ray phase analysis, differential scanning calorimetry and electron microscopy. The study using a Tescan MIRA 3 scanning electron microscope reveals differences in the microstructure of hardened binders and the authors confirm the results by microprobe studies. The authors study the hydration of the composite binder prepared on the basis of Portland cement and mineral components. Moreover, the paper demonstrates the dynamics of the system’s heat dissipation from the moment of mixing with water and hardening up to 24 hours and up to 72 hours by the expressed bond of dQ / dt = f (t) using a differential calorimeter.Methods and materials. The authors carried out experimental studies at Belgorod State Technological University named after V.G. Shukhov, at the Department of Building Materials, Products and Structures, at the High Technology Center and “BelGTASM-Certificate” Test Center. Therefore, the authors used the existing basic research methods, including modern physicochemical methods of analysis: X-ray phase, scanning electron microscopy, etc. The paper determined the main characteristics of raw materials, composite binders and foam concrete using standard methods and regulatory requirements.Results. The authors obtained the results that testified the peculiarities of hydration and hardening processes of polymineral composite binders on the basis of Portland cement and mineral additives: opoka marl and fly ash.Conclusion. The research establishes the hydration and hardening processes of polymineral composite binders. As a result, the authors demonstrate that the opoka marl introduced into the cement leads to the increased hydration in the induction and accelerated periods and also increases the hydration completeness of the main clinker minerals due to the manifestation of the pozzolanic reaction and the active binding of blocking Portlandite, as well as to the higher concentration of accumulated neoplasms, second generation calcium hydrosilicates.Financial transparency: the authors have no financial interest in the presented materials or methods. There is no conflict of interest.

Possibilities for Intensifying Construction Work’s Dynamic on Objects of the Annual Production Program by Winter Concreting Technology

The authors make decomposition of construction and installation works during the implementation of large investment and construction projects on the territory of mega-cities from monolithic reinforced concrete. Particular attention is focused on the seasonality of these works, on the features of organizational and technological solutions related to the effect of low temperatures on the binder hydration processes in the concrete mix, as well as on possible ways to minimize the increment of labor intensity and cost of work during these periods. As a result of the study, the authors of the article describe the principal algorithm for taking into account the features of winter concreting technology at the stage of current planning of annual production programs of construction organizations.

Use of calorimetry and thermal analysis to assess the heat of supplementary cementitious materials during the hydration of composite cementitious binders

The present paper focuses on the suitability, variability and versatility of thermal analysis and calorimetry methods in the study of cement hydration as physical and chemical process including pozzolanicity and hydraulicity of supplementary cementitious materials. Isothermal calorimeter TAM AIR and simultaneous TGA/DSC were used. Not only activation energy of system comprising SCMs, but also heat generated through alkali-activated reaction of metakaolin and ground granulated blast furnace slag (BFS) can be successfully determined by using conduction calorimetry. The incremental heat flow and incremental cumulative heat of the alkali-activated reaction of ground granulated BFS and metakaolin (MK) were determined and found dependent on temperature and mass ratio between cement and SCMs. The incremental heat flow presents the same characteristics as parent heat flow with different peaks, denoting the formation of C–S–H, ettringite and C–A–S–H trough alkali-activated reaction. While BFS and MK influenced moderately the formation of C–S–H, their influence on the formation of C–A– $${\bar{\text{S}}}$$ –H (ettringite and monosulphate) and C–A–S–H is significant as evidenced by peak position and intensity. The method of calorimetry coupled with thermal analysis was considered sufficient to assess the pozzolanicity and hydraulicity of SCMs.

Influence of Gypsum Binder Phase Composition on Operational and Mechanical Properties of the Hydration Product

The properties of various thermal modifications and forms of calcium sulfate and the conditions of their mutual transition are studied. It is established that the mode of heat treatment of gypsum raw materials affects significantly the nature of the subsequent hydration of the gypsum binder. It is established that the values of pH and pCa suspensions of gypsum binders depend on the temperature of heat treatment of natural gypsum, vary over time and characterize the processes occurring during hydration and hardening of gypsum binders. The values of pH and pCa suspensions of gypsum binders can serve as design criteria for innovative multiphase gypsum binders.

Study of the influence of properties of dusty ferromagnetic additives on the increase of cement activity

Sustainable development of construction materials is directly related to research on the processes of hydration of binders. Builders need better types of cement, with lower cost and energy consumption in production. The development of spin chemistry methods allows us to consider the processes of hydration and structure formation of binders from the spin state of the elements involved in chemical reactions. Magnetic interactions have a significant effect on the spin dynamics and the control of the spin multiplicity of radical pairs. The practical implementation of magnetic effects on a binder can be carried out in various ways. However, a long-term impact can be achieved only by introducing ferromagnetic substances into the binders. In the paper presented the results of a study of the influence of the characteristics of finely dispersed powdered ferromagnetic additives on the strength characteristics of cement. Ferromagnetic additives regulate the behavior of the reactants during rotation during the hydration of the binders due to magnetic interactions and control the reactivity of the chemical reaction. A comparative analysis revealed that it is most expedient to use as powdery ferromagnetic additives are the waste from mining and processing enterprises of the Krivorozhsky field. The work investigated the magnetic and dispersed characteristics of 12 different dust. The experiments showed that the origin of dust and the method of their capture are determined their magnetic characteristics. Preparation of samples with the dust and determination of the strength characteristics of cement were carried out by standard methods. The results obtained made it possible to reveal the laws of the effect of the dispersed and magnetic properties of various dust on the degree of activation of binders.

ВЛИЯНИЕ НЕОРГАНИЧЕСКИХ ЭЛЕКТРОЛИТОВ НА УСКОРЕНИЕ СХВАТЫВАНИЯ ПОРТЛАНДЦЕМЕНТНЫХ СИСТЕМ

The study showed that in order to accelerate the hydration of inorganic binders it is necessary to use additives of such electrolytes that increase the concentration of calcium ions in the liquid phase of the cement suspension. Electrolytes (soda ash, sodium and potassium hydroxides), precipitating calcium ions in the liquid phase, promote their exit from the "shut-off" layer of hydration products. In this paper, we studied the additives – electrolytes – as regulators of the setting time of fine-grained and porous concrete. To increase the activity of the additive as a concrete mixtures setting time regulator, acidic varieties were used instead of main salts. The studied additives – electrolytes – draw practical interest, as their usage in production of foam concrete and fine-grained concrete lets accelerate hardening of products and speed up reuse of mould.

Study of the Hydration Processes of Modified Binders by Infrared Spectroscopy

Many Russian and foreign scientists have been studying the processes of hydration of cement binders, but the processes of binders hydration with the use of mineral and organic additives have not been studied enough. The question of the superplasticizers influence on binder compositions consisting of cement and various mineral fillers requires a deep and detailed study in each case. In this regard, the aim of this work is to study the processes of portland cement hydration, modified by organomineral additive. Research was carried out on the study of changes occurring during the structure formation of modified binders by infrared spectroscopy (IR).

Investigating a new method to assess the self-healing performance of hardened cement pastes containing supplementary cementitious materials and crystalline admixtures

The autogenous healing of cementitious materials allows for the self-healing of cracks in concrete structures. It is known to be caused by (a) further hydration occurring when water penetrating the crack reacts with the unreacted binder on the crack face and (b) calcite precipitation resulting from the reaction between Ca2+ diffused from the cement paste and CO32− in penetrated water. Herein, isothermal calorimetry was used to analyze the further hydration of unreacted binder in hardened pastes containing ordinary Portland cement (OPC), supplementary cementitious materials, and crystalline admixtures. The amount of heat produced decreased with increasing sample age because of the reduction in the unreacted binder amount. Long-term further hydration in samples containing ground granulated blast-furnace slag and silica fume caused them to show increased heat production compared to OPC. However, no particular difference in comparison to OPC was detected for samples containing fly ash. When calcium sulfoaluminate was used as an expansion agent, heat production increased for a material age of 7 days and decreased after 28 days (compared to the case of OPC). Finally, self-healing products were analyzed by scanning electron microscopy with energy dispersive spectrometry. The results showed that the products contained calcite and an amorphous material regardless of the binder, while ettringite was observed to form in calcium sulfoaluminate and crystalline admixtures containing samples.

Novel drying additives and their evaluation for self-flowing refractory castables

The drying step of dense refractory castables containing hydraulic binders is a critical process, which usually requires using slow heating rates due to the high explosion trend of such materials during their first thermal treatment. Thus, this work investigated the performance of alternative additives to induce faster and safer drying of self-flowing high-alumina refractory castables bonded with calcium aluminate cement (CAC) or hydratable alumina (HA). The following materials were analyzed for this purpose: polymeric fibers, a permeability enhancing compound (RefPac MIPORE 20) and an organic additive (aluminum salt of 2-hydroxypropanoic acid). The drying behavior and explosion resistance of the cured samples were evaluated when subjecting the prepared castables to heating rates of 2, 5 or 20 °C/min and the obtained data were then correlated to the potential of the drying agents to improve the permeability and mechanical strength level of the refractories at different temperatures. The collected results attested that the selected additives were more efficient in optimizing the drying behavior of the CAC-bonded compositions, whereas the HA-containing castables performed better when the aluminum-based salt was blended with a small amount of CAC (0.5 wt%), which changed the binders hydration reaction sequence and optimized the permeability level of the resulting microstructure. Consequently, some of the designed compositions evaluated in this work showed improved drying behavior and no explosion was observed even during the tests carried out under a high heating rate (20 °C/min).

A Coupled Thermo-mechanical Damage Modeling Application of Cemented Coal Gangue-Fly Ash Backfill Under Uniaxial Compression

Cemented coal gangue-fly ash backfill (CGFB), which is a mixture of coal gangue, fly ash, cement and water, is introduced and used for waste disposal and ground control. Once placed underground, the CGFB is required to possess satisfactory strength and stability for the support of overlying roof. Therefore, it is crucial to understand the mechanical behavior and damage evolution of CGFB, which is also affected by thermal factors. This paper develops a coupled thermo-mechanical damage model to describe the mechanical response and damage of CGFB under uniaxial compression. The developed model considers the thermal factors of heat conduction and binder hydration. The validity of the developed model is verified by the comparison of simulation results and data from an experimental study. The developed model is then used for some applications. The modeling results can contribute to a better design and preparation of stable and endurable CGFB structures.

Heat Emission Kinetics and Hydration Behavior of Modified Polymer–Cement Mixtures for 3D Printing Construction

Abstract—The process of heat emission is investigated during the hydration of the binder in polymer–cement mixtures and mixtures modified by phloroglucinol–furfural superplasticizer. The specific binder hydration enthalpy in the presence of a polyvinyl acetate dispersion and redispersible polymer powder is determined. It is established that the specific enthalpy of polyvinyl acetate polymer–cement systems is positive, which indicates the endothermic nature of the overall process. The dependence of the absolute heat emission values in the initial periods of material hardening on the binder hydration time in the presence of organic mixture components (polyvinyl acetate and phloroglucinol–furfural modifier) is studied. It is proved that, when modifying polymer–cement systems, there is a decrease in the heat emission peak, a reduction in the timing of the initial hydration period, and an increase in the duration of the second (induction) period. The heat emission kinetic curves of the modified polyvinyl acetate–cement mixtures are presented, and the hydration behavior of the studied systems is considered. It is established that, in the initial period of hardening, polyvinyl acetate increases and phloroglucinol–furfural superplasticizer reduces the heat emission rate, while when modifying the polymer–cement system with a polymer in the form of a polymer dispersion, this process is partially balanced.

Synthesis of β-C2S-based binder from limestone and calcium silicate wastes

The present paper deals with the preparation of eco-friendly and low-energy cementitious binders using industrial by-products or materials based on waste sludge from mining and washing of limestone. Supplementary raw material containing mainly tobermorite and xonotlite is the waste of calcium silicate materials used as porous filling material of acetylene gas cylinders. Mixtures of raw materials were calcined at temperature 1150 °C for 120 min. Hydration products were characterized by thermogravimetric analysis (TG/DTA) and by X-ray diffraction. The heat of hydration of binder was investigated by means of isothermal calorimeter. Other techniques, such as scanning electron microscopy, were also used to characterize the microstructure. The compressive strength of pastes cured standard conditions was lower than 5 MPa even during 90 days. After pre-curing during 2, 5 and 7 days, samples were submitted to the hydrothermal curing at 170 °C for 24 h. Samples developed much higher compressive strengths (30 MPa). The formation of α-C2SH and γ-C2S was observed in samples after autoclaving. Pre-curing duration and hydrothermal curing conditions significantly influence the performances of cementitious materials.

Possibilities of ammonium ions fixation into mixed binders

The purpose of this study is to analyze the usability of ammonium ions fixation in mixed binders with the addition of high temperature fly ash. The experiment used high-temperature fly ash from operations in which the secondary flue gas denitrification methods have been implemented, specifically by the method of the selective non-catalytic reduction, known as DeNOx. The fixation of ammonium ions was performed by the addition of sodium hexanitrocobaltate(III). The study examines the influence of addition of cobalt(III) complex compound on the release of ammonia into the environment during the mixing the mixed binder. The released ammonia was quantitatively captured into the acid and subsequently titrated. The effect of cobalt(III) complex compound on the rate of hydration and mechanical properties of the mixed binders was also studied. The influence on the environment in terms of leachability was observed.

Effects of Expansive Agents on the Early Hydration Kinetics of Cementitious Binders.

The addition of expansive agents could overcome the main disadvantages of raw concrete including high brittleness and low tensile strength. Few studies have investigated the early hydration kinetics of expansive cementitious binders, though the findings from the early hydration kinetics are helpful for understanding their technical performances. In this study, mixtures of 3CaO•3Al2O3•CaSO4 and CaSO4 (i.e., ZY-type™ expansive agent) with different proportions of mineral admixtures (e.g., fly ash and slag) were added into cement pastes to investigate the early hydration kinetics mechanism of expansive cementitious binders. Early hydration heat evolution rate and cumulative hydration heat were measured by isothermal calorimeter. Kinetic parameters were estimated based on the Krstulovic–Dabic model and Knudsen equations. Mechanical performances of expansive cementitious binders were tested in order to evaluate if they met the basic requirements of shrinkage-compensating materials in technical use. The early hydration heat released from cementitious binders containing ZY-type™ expansive agent was much greater than that released by pure cement, supporting the idea that addition of the expansive agent would improve the reaction of cement. The early hydration kinetic rates were decreased due to the reactions of the mineral admixture (e.g., fly ash or slag) and the ZY-type™ expansive agent in the cement system. The hydration reaction of cementitious binders containing ZY-type™ expansive agent obeyed the Krstulovic–Dabic model well. Three processes are involved in the hydration reaction of cementitious binders containing ZY-type™ expansive agent. These are nucleation and crystal growth (NG), interactions at phase boundaries (I), and diffusion (D). The 14-day expansion rates of cementitious binders containing ZY-type™ expansive agent are in the range of 2.0 × 10−4 to 3.5 × 10−4, which could meet the basic requirements of anti-cracking performances in technical use according to Chinese industry standard JGJ/T 178-2009. This study could provide an insight into understanding the effects of expansive agents on the hydration and mechanical performances of cementitious binders.

ТЕХНОЛОГІЯ ВИГОТОВЛЕННЯ ПОЛЕГШЕНИХ СКЛАДІВ ЦЕМЕНТНИХ СУХИХ БУДІВЕЛЬНИХ СУМІШЕЙ З МІНЕРАЛЬНИМИ ДОБАВКАМИ


 
 
 The article deals with the technological features of manufacturing of lightweight cements of dry building mixtures with mineral additives. The technology of obtaining mortars from dry mixtures should take into account the fact that the processes of hydration of cement binder occur with insufficient water. Therefore, the possibility of obtaining lightweight dry mixtures based on Portland cement and mineral additives with the use of foaming additives is investigated. The use of a complex of technological operations allows you to obtain mixtures for the installation of warm floors, which are characterized by stable technological and physical and mechanical properties, as well as the simplicity and economy of manufacturing technology. Effective mixtures of porous structure have been obtained from for the warm floors on the basis of conventional dense (heavy) fillers and fillers, such as quartz sand, clay, carbonate sand, ash-removal of thermal power plants. The technological scheme of factory production of dry mixtures has been obtained while saving the binder component.
 
 

Effective Fine-Grained Concrete with High-Dispersed Additive Based on the Natural Mineral Wollastonite

Micro-fillers based on natural mineral wollastonite, modifying fine-grained concrete and improving its physical and mechanical characteristics, are developed and studied. The influence of the most common stabilizers on the aggregate stability of wollastonite-based microdispersed systems in the aquatic dispersion environment is considered. The optimal parameters, ensuring the production of micro-fillers in the form of stable suspensions, are developed. The application efficiency of the wollastonite-based filler due to its micro-reinforcing properties is revealed. These properties are specified by the formation of needle-shaped crystals by the ultrasonic dispersion in the aquatic environment, chemically related to cement-containing raw materials and contributing to the active selective adsorption of the binder hydration products. It has a significant influence on the rheological parameters of cement composites, on structure formation, as well as on their strength and deformation properties.

An evolutive bounding surface plasticity model for early-age cemented tailings backfill under cyclic loading

Cemented tailings backfill (CTB), an evolutive man-made soil or porous medium, is extensively utilized in underground mines as a sustainable solution for the disposal of tailings (mine waste) and/or ground control. At the early stages of curing, CTB is commonly saturated and weakly cemented, and thus subjected to the risk of seismically-induced liquefaction caused by mine blasts, rock bursts and earthquakes. The resulting intrusion of liquefied backfill mass into the mine tunnels may give rise to significant casualties and loss of production. In the present study, an evolutive bounding surface plasticity model is developed to capture the hydro-mechanical response of hydrating CTB under cyclic loading. Specifically, the changes of model components (yield and plastic potential functions, etc.) due to evolution of material properties are incorporated into the prototype bounding surface model. Then, the material property changes induced by binder hydration are determined and coupled to a binder hydration model that quantifies the curing process of CTB. Therefore, the developed model can be employed to assess the cyclic response of hydrating CTB at any given time of interest during its early age of curing when seismically induced liquefaction is of primary concern. The simulated results show good agreement with the experimental data for both monotonic and cyclic loadings. The proposed model can therefore provide more insight into the behavior of early-age CTB under seismic loading, and contribute to designing cost-effective CTB structures and assessing the risk of liquefaction.

Influence of modifying composition of gypsum binders on the structure of composite materials

At present, the modern society utilizes composite materials in various branches of the national economy. The properties of such materials depend on their composition and structure, and may considerably differ from the properties of source materials. In turn, texture and structure of crystals, their packing order, size and level of sophistication affect the structure of materials. This is particularly demonstrated by hydration curing materials on the basis of gypsum and magnesia binding materials, as well as portland cement. Structuring control is one of the key problems of composite materials. Gypsum binding materials with various modification composition are suggested as a model system to study the influence of texture and structure of materials on their properties. One of them is the construction gypsum – an anhydrite binder and a multiphase gypsum binder (MGB). Scanning electron microscopy (SEM) was chosen as the main method of study. It is found that gypsum crystals that are formed during hydration and curing of gypsum binders with various modification composition have different texture and structure. It prevents from getting the optimal packing of a material. It is justified and confirmed that the MGB consisting of several modifications of calcium sulfate allow choosing the best material composition due to the combination of crystals having different size and form. Besides, MGB contains significant amounts of insoluble anhydrite that reduces the water-gypsum ratio of a binder and compacts its structure. Considerable attention is paid to microfillers, which significantly affect the texture and structure of materials based on gypsum binders. Iron ore concentrate of the Lebedinsky GOK generally consisting of magnetite, as well as impalpable flour cullet waste of sodium and potassium glass were used as microfillers in the given study. Ultra- and nanodispersed powders at their introduction to gypsum and anhydrite compositions change the size and morphology of crystal newgrowths and ensure the formation of ordered, denser and uniform fine-crystalline structures of composite materials, which leads to the reduction of structure imperfection, porosity and increase in contact areas of crystalline hydrates increasing physical and mechanical performance of gypsum materials. Efficient composite construction materials are obtained on the basis of MGB and microfillers.