scholarly journals PROCESSES OF CARBONIZING SHRINKAGE OF CONSTRUCTION MATERIALS

2019 ◽  
pp. 178-194
Author(s):  
V. K. Kozlova ◽  
V. A. Lotov ◽  
Yu. S. Sarkisov ◽  
V. V. Logvinenko ◽  
I. A. Rakhmanova ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Cement Paste ◽  
Calcium Silicate ◽  
Building Materials ◽  
Solid Phase ◽  
Pore Space ◽  
Construction Materials ◽  
Cement Stone ◽  
Hydration Products ◽  
Wall Structures

Relevance: This paper studies the durability of structures made of various building materials and the effect of carbon dioxide on building materials with a view to reduce its aggressive and destructive effects. Purpose: The aim of the paper is to identify and eliminate the causes of the building material destruction during their carbonization. Materials/Methods: Silicate brick, cement stone and concrete. Research findings: Research is carried out into the destruction of wall structures made of calcium silicate brick and carbon dioxide corrosion of hydration products in calcium silicate brick and cement brick in concrete. It is found that carbonization in hydration products results in their transfer to a denser state which is accompanied by the reduction in the volume of shrinking deformations which cause sometimes the breach and fracture of material. When considering the water/cement system, it is shown that more credible and visible results on shrinkage processes can be obtained through parameters of its volume phase composition which allow controlling the parameters of the structure rearrangement from the initial to final states of the system, i.e. from cement paste to cement brick hardened at different time intervals. It is shown that after 28 days of hardening, the degree of filling the initial pore space with hydration products reaches 67%, while the porosity of cement brick in the final state is 16.5% at the initial composition of the solid phase Fs1 = 0.5; 13.5% at Fs1 = 0.55; 12.8% at Fs1 = 0.6; 11.2% at Fs1 = 0.65 and 0.7-9.0% at Fs1 = 0.7. It follows that shrinkage processes intensify in cement paste with the initial porosity over 40-50 %. It is possible to reduce the negative effect from shrinkage processes via the addition of carbonate-containing mineral additives such as lime rock or dolomite to the cement or lime and sand composition.

scholarly journals INFLUENCE OF MECHANOMAGNETIC ACTIVATION OF SOLUTIONS CaCl2 AND Na2S2O3 ON PHASE STRUCTURE OF CEMENT STONE

2019 ◽  
Vol 62 (12) ◽  
pp. 101-107
Author(s):  
Tatyana E. Slizneva ◽  
Marina V. Akulova ◽  
Pavel B. Razgovorov
Keyword(s):  
Solid Phase ◽  
Tap Water ◽  
Pore Space ◽  
Control Sample ◽  
Hydrodynamic Cavitation ◽  
Cement Stone ◽  
Cement Pastes ◽  
Carbonate Ion ◽  
Joint Influence ◽  
Reactive Oxygen Forms

The mechanism of the joint influence of the magnetic field and hydrodynamic cavitation on the properties of CaCl2 and Na2S2O3 solutions used for mixing cement pastes is considered. Hydrodynamic cavitation leads to the formation of reactive oxygen forms, HCO3– anions, carbon dioxide nanobubbles, and initiates the interaction of new forms with impurity metal cations dissolved in water. After mechanomagnetic treatment of the solutions, particles of a solid phase with sizes of 5...10 and 10...100 nm were found in them. The observed increase in the ξ- potential indicates the stabilization of such dispersed systems with the preservation of nanoscale fractions in them (up to 3 days). At the same time, the progress of reactions under the conditions of tightness that occur after cement paste has been mixed. The effect of activating factors in tap water is more pronounced than in distilled water, which is explained by the process of hydration of the carbonate ion and the formation of fine nucleation centers. Using X-ray phase analysis, it was found that, along with calcite, aragonite crystallizes in the resulting cement stone, which is practically absent in the control sample. In addition, the analysis of diffraction patterns taken on the modified samples reveals the inclusion of a carbonate ion. Obviously, optimization of the pore space in the cement stone is achieved both by clogging the pores with fine calcium carbonate, and by forming small pores during crystallization of ettringite-like phases. It is established that the resulting cement stone is characterized by increased strength (by 9-30%) and frost resistance (up to 55%) compared to that obtained by the traditional method.

Early Stage Development of Cement Paste Microstructure

2017 ◽  
Vol 1144 ◽  
pp. 14-21
Author(s):  
Vladimír Hrbek ◽  
Veronika Petranova ◽  
Jiří Němeček
Keyword(s):  
Electron Microscopy ◽  
Carbon Dioxide ◽  
Cement Paste ◽  
Early Stage ◽  
Cementitious Materials ◽  
Hydration Products ◽  
Crucial Aspect ◽  
Micromechanical Properties ◽  
Stage Development ◽  
Overall Performance

The early stage development of the cement microstructure is a crucial aspect affecting the overall performance of cementitious materials. The formation of hydration products depends on the presence of water and carbon dioxide, as well as on the distribution and re-crystallization of the cement particles. In this paper we evaluate the micromechanical properties evolution of cement phases over first 28 days after casting by the electron microscopy and static areal indentation.

Thermodynamic Interpretation of Carbonation Process of Portland Cement Hydration Products

2013 ◽  
Vol 753-755 ◽  
pp. 543-557
Author(s):  
Yan Jun Liu ◽  
Bo Tian Chen ◽  
Yong Chao Zheng
Keyword(s):  
Carbon Dioxide ◽  
Free Energy ◽  
Gibbs Free Energy ◽  
Cement Paste ◽  
Cement Hydration ◽  
Hardened Cement ◽  
Hydration Products ◽  
Hardened Cement Paste ◽  
Equilibrium Pressure ◽  
Carbonation Process

Cement hydration products carbonation is not only blamed for the carbonation-induced hardened cement paste or concrete cracking, also attributed to the pore water PH-value decrease, which causes the reinforcement corrosion under the existence of water and oxygen due to removal of oxide film passivating rebar surface, in hardened cement paste and concrete. Based on chemical thermodynamics, this paper presents the susceptibility of different cement hydration products to carbonation through calculating their Standard Gibbs Free Energy respectively, Gibbs free energy under temperature variation and the minimum equilibrium pressure of carbon dioxide triggering the carbonation process. The calculated results show that, under standard state (25°C, 100kpa), the minimum equilibrium pressure of carbon dioxide triggering carbonation process is significantly variable for different types of cement hydration products. For example, mono-sulfate sulfoferrite hydrates (3CaOFe2O3CaSO412H2O) is the most susceptible to carbonation, followed by mono-sulfate aluminate hydrates (3CaOAl2O3CaSO412H2O), while multi-sulfate sulfoaluminate hydrates (3CaOAl2O33CaSO432H2O) is the least vulnerable to carbonation, followed by silicate hydrates (5CaO6SiO25.5H2O). The findings in this paper are significant in understanding thermodynamic mechanism of cement hydrates carbonation and seeking the solution to prevent cement hydrates from carbonation-induced deterioration.

The Influence of Salts’ Presence in the Materials on their Moisture and Thermal Conductivity

2020 ◽  
Vol 1011 ◽  
pp. 179-187
Author(s):  
Tatyana Elchishcheva ◽  
Vladimir Erofeev
Keyword(s):  
Thermal Conductivity ◽  
Building Materials ◽  
Solid Phase ◽  
Pore Space ◽  
Chemical Properties ◽  
Salt Solutions ◽  
Liquid Phases ◽  
Salt Crystals ◽  
Crystalline Salt ◽  
Hygroscopic Salts

Energy saving in buildings is largely determined by the energy efficiency of the external building envelopes. The latter, as a rule, are the multilayer and incorporate structural and heat-insulating layers. The presence of individual hygroscopic salts and their mixtures in building materials changes their physical and chemical properties. Due to the increase in the sorption properties of building materials and changes in the inter-pore substance composition, humidity increases and the heat-protective properties decrease. This paper presents the results of the experimental and theoretical studies on the salts’ effect assessment on the change in moisture content and thermal conductivity of building materials due to the salt solutions and crystals’ presence in the pore space. To study the saline building materials’ thermal conductivity, the mathematical modeling methods using the theory of flow and bringing the materials’ structure to a unit cell are used. It is shown that the change in thermal conductivity occurs due to the crystalline salt precipitation from the solutions in the material’s pores, to the changes in their initial chemical properties, to the changes in the properties of the vapor-air mixture above the salt solutions due to diffusion. The results obtained make it possible to establish the hygroscopic salts’ influence significance in solid and liquid phases on the building materials’ thermal conductivity. A scheme for determining the thermal conductivity of building materials is proposed, taking into account salt effects, including the determination of: the components’ volume concentrations; sequentially the thermal conductivity of the material’s shell; salt crystals, a solid phase consisting of the material’s shell and crystalline salt, a binary and multicomponent saline solution, the pore space and the pore substance inside. The general formula for determining the thermal conductivity of a saline building material is given.

Carbon Dioxide Uptake by Concrete Modified With Carbon Nanotube

2013 ◽  
Author(s):  
Mariano Martin Escobar ◽  
Adrián Di Paolo ◽  
Analía Vazquez
Keyword(s):  
Carbon Dioxide ◽  
Carbon Nanotubes ◽  
Calcium Carbonate ◽  
Cement Paste ◽  
Carbon Dioxide Emission ◽  
Cement Industry ◽  
Maximum Temperature ◽  
Hydration Products ◽  
Multi Walled Carbon Nanotubes ◽  
Walled Carbon Nanotubes

CO2 emission from fossil fuel fired power plants contributed 30% of global emissions in 1990. In the same year, the cement industry contributed about 5% of the total. According to Kyoto Protocol, a tremendous effort is required to reduce the carbon dioxide emission. One potential technology in CO2 mitigation responses is the use of concrete products as carbon sink through the early age fast curing. The cement compounds C3S and C2S are instantaneously carbonized into calcium carbonate and silica gel, once cement is mixed with water and exposed to the carbon dioxide gas. The objective of this work is to evaluate the effect of adding carbon nanotubes in cement paste matrix on the capacity as CO2 sink. Adiabatic temperature was determined for different carbon nanotubos content on the cement paste. The microstructure was studied by scanning electronic microscopy. The calcium carbonate and calcium hydroxide content were determined by a thermogravimetric analysis. The storage modulus was measured for the specimens of cement paste before and after the immersion in CO2. Carbon nanotubes act as nuclear agent of the calcium carbonate and increase the maximum temperature and decrease the time of hydration. The incorporation of carbon nanotubes to Portland cement paste could modify the transport properties of the matrix. In fact, it was shown that interfacial interactions between the hydration products and multi-walled carbon nanotubes occur; and it was observed the insertion of multi-walled carbon nanotubes between the hydration products.

scholarly journals ROLE OF GRANULOMETRY OF MIXED BINDERS IN FORMATION OF THEIR MICROSTRUCTURE AND STRENGTH

2021 ◽  
Vol 6 (7) ◽  
pp. 33-43
Author(s):  
L. Zagorodnyuk ◽  
D.S. Mahortov ◽  
V. Ryzhikh ◽  
D. Sumskoy ◽  
M. Dayronas
Keyword(s):  
Portland Cement ◽  
Volcanic Ash ◽  
Pore Space ◽  
Ash Content ◽  
Cement Stone ◽  
Hydration Products ◽  
Mechanical Mixing ◽  
Mineral Fillers ◽  
Active Interaction

A complex system is formed when grinding Portland cement and various mineral fillers. It consists of grains of various sizes with a predominance of a highly dispersed phase. The work investigates the effect of mixed binders prepared on the basis of Portland cement and volcanic ash at various dosages. The analysis of volcanic ash particles is carried out. It is found that the presence of the smallest fractions in the range from 0.3 to 0.07 microns predicts active interaction in the system and the filling of the pore space with hydration products. It has been established that mixed binders obtained by mechanical mixing (without grinding) with a content of 10% volcanic ash have a strength 13% higher than no addition cement. Mixed binders activated by milling in a vibration mill with a volcanic ash content of 10% are characterized by an increase in compressive strength by 22%, which saves Portland cement by up to 10%. Mixed binders with a volcanic ash content of 20% correspond to the strength of cement free. The results obtained indicate the effectiveness and feasibility of using volcanic ash as a mineral component of mixed binders. The microstructure of a cement stone sample from an activated mixed binder is highly homogeneous, dense intergrown plates of a secondary hydrosilicate structure are clearly visible in the sample cleavage, and crystalline products of pozzolanic reactions between ash particles and cement hydration products are formed on the surfaces of secondary hydrosilicate structures. The purpose of this article is to study the role of granulometry of mixed binders in the formation of their microstructure and strength.

scholarly journals Rheological Behaviour of Cementitious Materials Incorporating Solid–Solid Phase Change Materials

Materials ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 20
Author(s):  
Lionel Plancher ◽  
Alexandre Pierre ◽  
Giao T. M. Nguyen ◽  
Ronan L. Hébert ◽  
Béatrice A. Ledésert ◽  
...  
Keyword(s):  
Yield Strength ◽  
Phase Change ◽  
Building Materials ◽  
Phase Change Materials ◽  
Solid Phase ◽  
Construction Materials ◽  
Rheological Behaviour ◽  
Cementitious Materials ◽  
Major Step ◽  
High Latent Heat

Nowadays, thermal regulation of the indoor environment is mandatory to reduce greenhouse gas emissions. The incorporation of Phase Change Materials (PCMs) and especially solid–solid PCMs (s/s PCMs) into building materials can be a major step forward in reducing energy consumption. Such materials are used for their high latent heat to save and release heat during phase change. To integrate these products in the fabrication of cementitious materials, it is essential to predict their influence on the rheological behaviour of construction materials. In this work, rheological measurements were carried out on composite suspensions made of cement or mortar plus s/s PCMs. Results showed that the fitting of the Herschel–Bulkley model with a constant value of flow exponent was reliable. The s/s PCMs influenced the consistency and the yield strength values, with the yield strength value being only slightly affected. The adaptation of an existing viscosity model is proposed to predict the consistency value of suspensions. Finally, an innovative approach to predict the flow behaviour is proposed and we highlight the research needs to mainstream the use of s/s PCMs in construction materials.

Sulfoaluminate Cements Composition and Properties

2017 ◽  
Vol 265 ◽  
pp. 734-737 ◽  
Author(s):  
F.L. Kapustin ◽  
A.A. Ponomarenko ◽  
V.N. Oleinik
Keyword(s):  
Mechanical Properties ◽  
Mineral Composition ◽  
Cement Paste ◽  
Heat Dissipation ◽  
Strength Class ◽  
Cement Content ◽  
Cement Stone ◽  
Hydration Products ◽  
Mineral Compositions ◽  
Kinetics Of

The chemical and mineral composition, physico-mechanical properties of sulfoaluminate cements of various classes of strength manufactured in China which are used in Russia to build and repair buildings and structures have been considered. It is shown that the sample sulfoaluminate cement depending on the strength class differ not only in chemical and mineral compositions, but also in their hydrophysical properties, kinetics of dissipation and hardening of cement, and hydration products. It is established that with the increasing strength class of the cement content it has calcium increases, the adhesion of the cement paste is slowed down, the duration of heat dissipation increases, the temperature dissipation is reduced, the hardening of the cement stone slows down.

scholarly journals Effect of Epoxy Resin Emulsion on the Mechanical Properties of Oil Well Cement-Based Composites

2020 ◽  
Vol 2020 ◽  
pp. 1-9
Author(s):  
Miao He ◽  
Jianjian Song ◽  
Mingbiao Xu ◽  
Lei He ◽  
Peng Xu
Keyword(s):  
Mechanical Properties ◽  
Epoxy Resin ◽  
Cement Paste ◽  
Styrene Butadiene Rubber ◽  
Cement Stone ◽  
Oil Well ◽  
Hydration Products ◽  
Cement Slurry ◽  
Oil Well Cement ◽  
Well Cement

Oil well cement is a brittle material, which can not ensure the long-term sealing integrity of oil and gas wells when used in cementing operations directly. As a kind of polymer emulsion material, epoxy resin emulsion has a bright future for improving the properties of the cement slurry. Epoxy resin emulsion was added to oil well cement and its workability and mechanical properties were studied, the stress-strain behavior of cement samples was evaluated, and the microstructure was observed by scanning electron microscope (SEM) and X-ray diffraction (XRD). The results show the epoxy resin emulsion used in oil well cement will affect the fluidity, but the rheological property of cement slurry with different content of resin meets the construction requirements. The resin reduces the water loss of cement paste and has no adverse effect on the thickening time. The compressive strength of cement stone decreases with the increase in resin content. When the content of resin is 6%, the flexural strength and impact strength of the cement sample are the largest, and 50.7% and 20.2% higher than that of the specimen without resin, respectively, after curing for 28 days. Further comparison shows that epoxy resin emulsion can improve the mechanical properties of oil well cement better than styrene-butadiene rubber latex. Meanwhile, the resin obviously improves the deformability and decreases the elastic modulus of cement stone. Compared with pure cement, resin cement slurry has no extra hydration products, but the formation of hydrated calcium silicate is inhibited. The microstructure shows that the resin forms a polymer film in the cement matrix and interweaves with cement hydration products, thus improving the flexibility of cement paste.

scholarly journals FEATURES OF THE STRUCTURE OF NEW GENERATION CONCRETE WITH THE USAGE OF ARTIFICIALLY-PRODUCED MATERIALS

2018 ◽  
Vol 15 (4) ◽  
pp. 588-595 ◽  
Author(s):  
A. D. Tolstoy ◽  
V. S. Lesovik ◽  
A. S. Milkina
Keyword(s):  
Structure Formation ◽  
Building Materials ◽  
Raw Materials ◽  
Experimental Studies ◽  
Construction Materials ◽  
High Strength ◽  
Standard Test ◽  
Cement Stone ◽  
Organic Additives ◽  
Test Procedures

Introduction. The important national economic task is to provide the modern construction industry with high-strength and effective materials made using new technological approaches and artificiallyproduced materials. These materials differ from the usual one by high content of cement stone, smaller grain size, multicomponent composition, increased specific surface of the filler. Therefore, the research of such problem would be always relevant according to the constant growth of requirements for the building materials and structures quality.Materials and methods. Experimental studies were conducted in the laboratories of the Department of Construction Materials, Products and Structures. The literary sources’ analysis was made in the scientific and technical library of the Belgorod State Technological University named after V. G. Shukhov. At the same time, standard test procedures and the provisions of the operating instructions for individual devices and equipment were used in the research.Discussion and conclusions. As a result, the models of structure formation in high-strength hardening compositions, in which the principle of structure optimization consisting in creation of the high degree ordering of its constituent elements and tumors, as well as in increasing the adhesion of cement stone particles, are implemented. In addition, the usage of artificially-produced materials and organic additives produces the possibility of reducing the consumption of raw materials and consumption of energy and resources. The mechanism and principles of structure formation management are intensively studied and would be explained later on the basis of synergetic concepts.

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