Strength Of Cement Stone Research Articles

INFLUENCE OF MECHANICAL ACTIVATION ON THE PROPERTIES OF CEMENT-WATER COMPOSITIONS WITH THE ADDITION OF GROUND LIMESTONE

The paper considers the issue related to determining the effect of mechanical activation of a mineral binder on the properties of both hardening and hardened cement-water compositions. The mechanical activation of cement in combination with the consumption of ground limestone, the amount of which was adjusted in the range from 0 to 40 % of the cement mass, is relevant for this study. The effect of mechanical chemical activation of Portland cement only and Portland cement with the addition of 20 and 40 % ground limestone on changing the water-solid ratio of equiviscous compositions was studied. It was shown that mechanical and chemical activation of a cement-water composition has a positive effect on reducing the W/S ratio of equiviscous compositions from 0.42 (no activation) to 0.38 (activation period 180 sec). The obtained experimental results indicate the presence of an induction period of heating of the cement paste both on Portland cement not subject to mechanical activation (this period is approximately 6 hours from the moment of interaction of cement with water) and on Portland cement subject to mechanical activation. In this case, the induction period was no more than 2 hours. Joint mechanical activation of an aqueous mixture of Portland cement and ground limestone ensures acceleration of the hydration processes of the binder, which is confirmed by the intensification of the exothermic heating of the filled cement-mixing compositions. The positive role of mechanical activation is also reflected in the acceleration of the thickening rate of the compositions, which was recorded by the kinetics of the decrease in the diameter of their spread over time. The positive role of mechanical activation in reducing the effective viscosity of cement-containing compositions is confirmed, which ensures a decrease in their water-solid ratio by an average of ‒ 8 ... 10 %. A positive effect of mechanochemical activation of Portland cement with the addition of ground limestone on the strength of cement stone at the age of 3 days has been revealed. Experimental studies indicate that only due to mechanical activation the strength of samples made of cement stone with the addition of ground limestone can be increased by almost 25...30 %.

Strength characteristics of cement slurry in high geothermal tunnel environment

The early-age strength of grouting material is crucial for tunnel support under high geothermal temperatures. Grouting materials (such as the most commonly used cement slurry) hydrate and solidify under the condition of variable-temperature curing after entering the real stratum. However, the development process of the early strength of cement paste under the condition of variable-temperature curing is still unclear. This aim of this study was to elucidate the environmental effects of high-ground-temperature tunnels on the early strength development of cement stone. Cement slurry was subjected to variable-temperature curing under three different temperatures (T = 40°C, 60°C and 80°C) and two different relative humidities (H = 5% and 95%) through design experiments. Compressive strength tests were conducted, along with microscopic analysis using X-ray diffraction, scanning electron microscopy and nuclear magnetic resonance. The results indicate that the strength of cement stone under variable-temperature curing was lower than that under constant-temperature curing at the same temperature. The influence of variable-temperature curing conditions on the strength variation of samples with a high water/cement ratio at later age was greater for curing at 80°C. The research results are helpful to understand the influence of environmental effects of high-ground-temperature tunnels on the properties of grouting materials.

True-triaxial strength characteristics of cement stone subjected to sulfuric acid corrosion: An experimental and theoretical study

True triaxial tests were conducted to investigate the effect of sulfuric acid corrosion on the true triaxial strength of cement stone under different acid immersion times, including the common loading path and novel loading path with constant Lode angle. The chemical composition and microstructure of cement stone under different acid immersion times (0, 7, 14, and 28 d) were examined via X-ray diffraction and scanning electron microscopy. As the duration of acid immersion increases, the concentrations of portlandite (Ca(OH)2) and calcium silicate hydrate (C-S-H) within the cement stone exhibit a gradual decline, while the presence of calcium sulfate (CaSO4) progressively rises. The microstructure of the cement stone was primarily affected by two factors: the damaging and strengthening effects of sulfuric acid and CaSO4, respectively. The damaging effects of the acid were dominant for days 0–14 of immersion, with continuous increase in microstructure damage. Subsequently, the strengthening effect of CaSO4 became apparent for days 14–28 of immersion, with continuous improvement in microstructure integrity. Consequently, the strength of cement stone exhibited a diminishing trend during the initial immersion period of 0–14 days, followed by an enhancement in strength from 14 to 28 days of immersion. Furthermore, a three-dimensional strength criterion was proposed by combining the Hoek–Brown and Matsuoka–Nakai criteria. The failure envelope first shrank and then expanded with increasing immersion time, accurately describing the variation in strength in the three-dimensional principal stress space.

The Influence of the Aggressive Medium upon the Degradation of Concrete Structures: Numerical Model of Research

This article discusses the impact of the aggressive environment on the pattern of pore distribution, strength, and mass absorption of investigated samples. For this purpose, a physical and numerical research model has been developed based on Fick’s second law and Zhurcov’s theory. Consequently, computer tomography research revealed that pore redistribution was revealed in test samples due to exposure. The degradation model is proposed assuming that in the first stage of interaction between concrete constructions and aggressive medium, the product of interaction is accumulated in the surface of structures and pores. Interaction products in the form of needle-shaped crystals grow in time and create additional stress in the body of the structure, resulting in partial distribution of the surface of the structure due to the growth. In this state, the excretion of dissolved substances (in the form of citrate and calcium acetate), leaching of Ca(OH)2, and decalcination of CSH lead to a decrease in the strength of cement stone. Based on the developed numerical models, the dependences of aggressive environment impact on the on the parameters of the structure of cement composites at different exposure times were obtained. For the samples obtained during the activation of Portland cement in the electromagnetic mill, energy parameters of the destruction process are 1.85–2.2 times heavier than the control compositions. The samples obtained by activating Portland cement in the electromagnetic mill have a higher susceptibility to an aggressive environment (they absorb 1.8 times more energy per unit of time for structure transformation). However, the higher U-energy barrier (1.85 times greater than the control composition) provides both a longer term of exploitation and a lower kinetics of the change in the strength of the material.

Еffect of synthetic calcium hydrosilicate on the hydration of portland cement

The regularities of the synthesis of calcium hydrosilicates of tobermorite composition in the system “amorphous silica – calcium hydroxide – water” were investigated. The effect of calcium hydrosilicates additive on the hydration processes of Portland cement and the nature of changes in the strength of cement stone at different stages of its hardening was studied. The methods of determining the heat of hydration of cement dough during hardening and X-ray phase analysis showed that the addition of calcium hydrosilicates at the initial stages of hardening accelerates the physicochemical processes of hydration of clinker minerals.

СИНТЕЗ И СВОЙСТВА КАЛЬЦИЕВО-АЛЮМОФЕРРИТОВОГО ЦЕМЕНТА С ИСПОЛЬЗОВАНИЕМ ТЕХНОГЕННЫХ МАТЕРИАЛОВ

The article discusses the production of calcium-aluminoferrite clinker (cement) from a three-component mixture (by sin-tering), where 56.2-57.4 wt.% of the mixture consists of aluminum– and iron-containing man-made waste. It was found that the use of man-made waste as a component of the raw material mixture leads to a decrease in the amount of waste generat-ed by 4.9-5.4%, based on the production of 300,000 tons of calcium-alumoferrite cement per year. The results of qualitative and quantitative X–ray phase analysis of the clinkers obtained are presented, which indicate the formation of calcium aluminates (CA,C3A,C12A7), calcium aluminoferrite(Ca2(Al,Fe)2O5) and calcium silicate (α-, β-C2S) as the main clinker phases in all samples. Clinker phases of aluminate and calcium aluminoferrite are formed not in pure form, but with the introduction of impurity elements (Mg2+, Ti4+). Determination of the hydration activity of CAFC showed that the quantitative ratio of clinker phases CA:Ca2(Al,Fe)2O5 = 38.8:33.8 (CAFC I) and CA:Ca2(Al,Fe)2O5 = 27.6:23.9 (CAFC II) leads to an increase in the strength of cement stone in the initial periods of hardening by 48 and 32 MPa, and in later periods (28 days) - to an increase in strength by 28 and 8 MPa, respectively.

МОДИФИЦИРОВАНИЕ СВОЙСТВ ГИДРОТЕХНИЧЕСКИХ БЕТОНОВ ДОБАВКАМИ НА ОСНОВЕ ВЫСОКОМОЛЕКУЛЯРНЫХ СОЕДИНЕНИЙ

Ensuring high water resistance, frost resistance and corrosion resistance of hydraulic structures is achieved by creating concrete with a dense structure that can absorb aggressive influences. This is possible by modifying the structure of concrete with polymer additives of new generation. The introduction of polymer additives has a plasticizing effect and contributes to the preservation of technological properties of the concrete mixture, modifies the pore structure of concrete and influences the formation of cement stone strength. The paper presents the results of research on the effect of polymer additive based on polyvinylpyrrolidone on the basic properties of Portland cement binder. It was found that the compressive strength at the age of 2 days increases by 7% at the content of polymer additive in the amount of 0.8%. Also, in-troduction of polymer additive increases the compressive strength at the age of 28 days at its content of 0.6 and 0.8% by 22 and 27%, respectively. The effect of polymer modifier on the formation of the initial structure, manifested in the increase in the time of the beginning and accel-eration of the end of setting has been established. The kinetics of heat release of cement dough in the presence of polymeric modifier in the amount of 0.6 % has been studied. The data on the phase composition of cement stone in the presence of polymer modifier are given. It is established by means of electron microscopic analysis that the introduction of polymeric admixture promotes modification of cement stone microstructure with formation of more dense homogeneous structure. The given research results are taken into account in the development of concrete compositions with a set of specified properties required for the construction of hydraulic structures.

The effect of modified basalt fiber on mechanical properties of oil well cement slurry

To address the shortcomings of oil well cement stone like high brittleness and susceptibility to cracking, basalt fiber (BF) can be incorporated to increase the toughness. However, the interfacial bonding between BF and the cement matrix is weak, which cannot give full play to the role of BF. Grafting graphite oxide (GO) onto BF surface enhances its hydrophilicity, increases surface roughness, and promotes interfacial interaction with the cement matrix. The role and mechanism of toughening of modified basalt fiber (MBF) were investigated by mechanical property tests and microscopic characterization. The results showed that: (1) MBF has superior hydrophilicity, a rougher surface, and higher interfacial shear strength compared to BF. (2) MBF can enhance the compressive strength of cement stone, when the MBF dosage is 0.4%, after 1, 3, 7 and 14 days of curing, the strength increased by 21.41%, 21.02%, 22.39% and 26.91%, respectively, compared with the blank sample. (3) According to microstructural characterisation, the addition of BF and MBF does not alter the hydration products of cement. The samples exhibited pore diameters predominantly ranging from 10 to 150 nm. The introduction of MBF resulted in a reduction of 11.01% in the porosity of the samples compared to the blank samples. The primary factor behind the improvement of cementite's mechanical characteristics by the fiber was the decrease in porosity.

Combined use of mullite and basalt fiber to inhibit the strength decline of oil well cement stone under alternating conditions of temperature rise and fall

During the development process of heavy oil with steam huff and puff, the wellbore undergoes alternating conditions of temperature rise and fall, leading to a significant decline in the strength of the cement sheath. This work studied the inhibition effect and mechanism of the composite material composed of mullite and basalt fiber on the strength decline of cement stone (the hardened body of cement slurry) under simulated wellbore temperature alternating conditions from 80 °C to 260 °C. The pore structure distribution of cement stone was investigated by mercury intrusion porosimetry (MIP), the microstructure and phase composition of cement stone was characterized by scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), together with quantitative X-ray diffraction (XRD) analysis. After 4 rounds of curing under alternating temperature conditions, the compressive strength of cement stone containing mullite and basalt fiber composite material was 28.6 MPa at 260 °C, which was only 9.2 % lower than that at 80 °C. However, the compressive strength of the blank cement stone without composite materials decreased to 22.5 MPa at 260 °C, which was 20 % lower than that at 80 °C. After 4 rounds of alternating temperature cured, the harmful pores of the cement stone without composite materials increase, and the xonotlite flakes and stacks together. The cement stone added with mullite has a finer pore structure after 4 rounds of alternating temperature cured because mullite reacts with portlandite to form C-A-S-H gel. The xonotlite remains fibrous, and a small amount of new phase hibschite is formed. Furthermore, basalt fiber can react with C-A-S-H gel at high temperatures, and the two phases are closely combined to further improve the high-temperature resistance of cement stone.

Research on surface modification of polypropylene fiber and its application evaluation in oil well cement

In order to improve the compatibility and dispersibility of polypropylene fiber (PPF) in oil well cement and enhance the mechanical properties of cementing cement sheath, the surface modification of PPF was carried out in this study. After surface impurity removal of PPF, reaction of catechol with polyamines, and subsequent treatment with γ- aminopropyltriethoxysilane (KH-550) and Ethyl orthosilicate (TEOS), modified polypropylene fiber (MPF) was obtained. The MPF was characterized and analyzed using FTIR, XPS, SEM, and EDS, showing a transformation in the surface properties of the fibers. The most significant change was that the contact angle between MPF and water decreased from 123.87 ° to 46.32 °, marking the successful transition of the fiber from hydrophobicity to hydrophilicity. Image analysis showed that the dispersion of MPF improved significantly. The dispersion coefficient of MPF in water and cement stone was increased by 86.90% and 14.48% compared with PPF, respectively. The effect of MPF on mechanical properties of oil well cement stone was studied. The comparative analysis results showed that MPF can significantly improve the flexural and compressive strength of the cement matrix. The flexural and compressive strength of cement stone mixed with MPF were increased by 10.25% and 6.43%, respectively, compared to cement stone mixed with PPF. SEM, MIP, and fiber single fiber pull-out experiments showed that the porosity of cement stone added with MPF was lower, the rough surface structure of MPF enhanced the bonding between fibers and cement stone, and the bridging effect of fibers in cement stone ultimately improved the mechanical properties of oil well cement stone.

СТРУКТУРООБРАЗОВАНИЕ ЦЕМЕНТНОЙ МАТРИЦЫ С ВОДОРЕДУЦИРУЮЩЕЙ ДОБАВКОЙ В УСЛОВИЯХ ГИДРОТЕРМАЛЬНОГО СИНТЕЗА

The article presents the results of research related to the possibility of increasing the strength of cement stone based on high-base calcium hydrosilicates synthesized during autoclave processing by reducing the water-cement ratio using superplasticizers. Despite the fact that autoclave stone based on high-base calcium hydrosilicates is inferior in strength to low-base ones, but it allows improving weather resistance. This approach is due to the fact that the effect of diluent additives in silicate mixtures increases with basicity increasing, and concrete samples based on a cement matrix containing C2SN(A) in a compacted state exhibit higher strength. The study shows water-cement ratio reducing in cement dough by 20% with the help of superplasticizers increases the compressive strength of autoclave cement stone samples by 30%. At the same time, the strength growth of similar composition samples hardened for 28 days under normal conditions did not exceed 12%. It is noted that the strength of the matrix is determined not only by the shape and size of the crystals of the highly basic hydrate phases C2SN(A) and C2SN(C), but also by the degree of fusion and the number of contacts between them.

Вплив механохімічної активації композиційного цементу на міцність будівельного розчину

The article discusses issues related to the use of technology for the production of mortar mixtures and mortars based on high-speed mixers, the operation of which causes mechanochemical activation of the binder. The rotary counterflow mill used in the work acts as an activator of the surface zone of both Portland cement grains and quartz sand grains and, thus, contributes to the intensification of the processes of structure formation of cement paste and mortar based on it. Based on the fact that one of the promising ways to reduce the cost of cement activation is to reduce the energy intensity of the dispersion process itself, the use of relatively low-energy rotary mills can be considered as an effective way to increase the activity of the binder. After the joint activation of Portland cement and unground quartz sand (the amount of which was adjusted from 0 to 50 % of the cement mass; activation period - 300 seconds), samples were made from equal-viscosity cement paste. It was experimentally established that the maximum strength of cement stone at 28 days of age was achieved when using composite cement with a 20 % content of activated sand. To determine the influence of the studied factors, such as the consumption of mechanically activated composite binder, the concentration of superplasticizer C-3 (0...1,5 %) and the consumption of microsilica (0...10 %) on the strength of the mortar in 2 and 28-day old, a 3-factor experiment was conducted. It was established that in the studied hardening period, the content of mechanically activated composite cement has the greatest influence on the compressive strength for the studied mortar compositions (from 1:3 to 1:1). The next most important influence on the strength of the mortar is the consumption of superplasticizer C-3. The increase in compressive strength of a mortar from the introduction of microsilica into its composition does not exceed 10-15 %. The combined effect of mechanical activation of the binder and the use of the C-3 additive ensures an increase in the strength of the mortar (mortar composition 1:1) at 28 days of age from 43,5 MPa (non-activated binder; no C-3 additive) to 63 MPa, that is, almost by 45 %. For a mortar of similar age with a lower consumption of composite cement (mortar composition 1:3), mechanical activation of the binder in the presence of 1,5 % C-3 additive ensures an increase in the compressive strength of the mortar from 21 MPa (non-mechanically activated binder; C-3 = 0 %) to 39 MPa.

АКТИВАЦІЯ ЦЕМЕНТУ І ЇЇ ВПЛИВ НА СТРУКТУРОУТВОРЕННЯ ЦЕМЕНТОВМІЩУЮЧИХ КОМПОЗИЦІЙ

The article discusses issues related to the mechanochemical activation of the cement binder in a specially designed rotary counterflow mill. The given brief description of the design of a counterflow mill gives a general idea of the principle of its operation as an activator of the surface zone of a mineral binder. Typically, a positive characteristic of mineral binders is their rapid increase in strength. Therefore, scientific research related to the development of technology aimed at intensifying the processes of structure formation of cement paste and stone based on it is relevant. The use of this technology makes it possible to significantly increase the specific surface area of cement during its activation, reduce the setting time, increase the amount of chemically bound water and intensify the exothermic heating of hardening cement stone. The presented experimental data made it possible to optimize the activation period of the binder, which ranged from 60 to 600 seconds. It has been established that the optimal time from the point of view of the energy intensity of the process is the activation period of the binder for 300 seconds. During this activation period, there is an increase in the specific surface area of cement by an average of 8...10%, acceleration of setting time by 50...60 minutes, an increase in the amount of chemically bound water at 28 days of age from 13 to 16.3%, an increase in the maximum temperature of exothermic heating cement stone from 53.8 to 64.0 °C. A further increase in the activation period (up to 600 seconds) has little effect on the change in the listed properties. The effect of mechanochemical activation is significantly reflected in the compressive strength of cement stone. It has been established that activation of cement for 300 seconds causes an increase in the compressive strength of cement stone from 48 to 57 MPa, that is, by almost 20%. The effect of mechanochemical activation of cement is enhanced by the introduction of quartz sand into its composition. It has been experimentally established that the activation of cement with the addition of 20% quartz sand increases the strength of the filled cement stone by almost 30% relative to the strength of the stone using unadded cement that is not subject to mechanical activation.

Study on the influence mechanism of calcium carbonate particles on mechanical properties of microcrack cement

Restoration of cementitious materials using induced calcium carbonate precipitation is a highly anticipated research domain, offering a promising avenue of study within the realm of environmentally friendly methodologies. In this study, the numerical simulation software PFC is employed to simulate internal microcracks within cement stone subject to calcium carbonate remediation. The simulation outcomes unveil the repair mechanism from a microscopic perspective, providing theoretical guidance for indoor experiments. The research results reveal that microcracks detrimentally impact the compressive strength of cement stone, experiencing a drastic reduction of 79.51% at a 6.56% crack rate, reaching merely 6.65 MPa. Calcium carbonate serves to fill, bond, and support the microcracks, retarding crack development and structural deterioration, thereby enhancing the compressive strength of the cement stone. The compressive strength of the cement stone after repair correlates positively with the bonding strength and filling rate of calcium carbonate, while particle size has little effect. The repair effect on small-size microcracks with size of 0.3 mm × 1 mm is better, and large-size microcracks with size of 0.7 mm × 3 mm will have irreversible effects on cement stone. Calcium carbonate particles will play a better repair effect when the filling rate is in rage of 50%− 80%.

Preparation of epoxy resin elastic particles and their application in oil well cement

AbstractTo solve the problem of high brittleness and easy cracking of cement stone, epoxy resin powder elastic particles (HEEP) were developed to improve the elasticity of cement stone. HEEP was prepared from epoxy resin and trimeric anhydride by solution polymerization. The surface wettability and particle size of HEEP were analyzed by contact angle test and laser particle size analysis respectively. Mechanical performance tests, scanning electron microscope (SEM) analysis and x‐ray diffraction analysis were conducted on the cement stone containing HEEP. The results showed that HEEP was the target product, with a hydrophilic surface and a water contact angle of 75.2° on the HEEP surface. The particle size distribution of HEEP was uniform, and the median particle size was 36.5 μm. The initial decomposition temperature of HEEP was 300°C, indicating a good thermal stability. The stress–strain curve showed that when the HEEP dosage was 3%, 6%, and 9%, the elastic modulus of the cement stone was 6.382, 4.017, and 3.148 GPa, respectively. Compared with the blank cement without HEEP, the elastic modulus was reduced by 28.3%, 54.9%, and 64.6%, respectively. This showed that HEEP could effectively improve the elasticity of cement stone. In addition, the compressive strength and flexural strength of cement stone containing HEEP can meet the requirements of on‐site applications. SEM analysis of cement stone showed that HEEP was well filled in cement stone. When the cement stone was subjected to complex stress, HEEP could effectively buffer and disperse the stress, thereby enhancing the resistance of cement stone to external force impact.

Research on graphene oxide modified polymer as multifunctional filtration reducer for oil-well cementing

Conventional filtration reducers have limited utility in cementing at deep oil and gas fields because of their poor temperature resistance and single function. As a novel multifunctional filtration reducer, graphene oxide-modified polymer GO-PADI was developed by radically copolymerizing 2-acrylamido-2-methylpropane sulfonic acid (AMPS), N, N-dimethyl acrylamide (DMAM) and itaconic acid (IA) between graphene oxide sheets. The microstructure of GO-PADI was confirmed through the utilization of different methods such as fourier transform infrared spectroscopy (FT-IR). The performance evaluation results showed that GO-PADI had the high thermal stability, and could control filtration of cement slurry as conducted by the American Petroleum Institute (API) less than 50 mL, which is 17 % lower than that of the traditional filtration reducer PADI. GO-PADI could increase compressive strength of cement stone by 30.3 %, and decrease elastic modulus by 10.9 % in three-day curing period. GO-PADI has the multifunctional functions of reducing fluid loss, strengthening and toughening, and can effectively improve the engineering performances for high-temperature cement slurry.

Identifying the influence of basalt fiber reinforcement on the deformation and strength characteristics of cement stone

The object of the research is the quality of cementing oil and gas wells with increasing the strength and deformation capacity of cement stone using basalt fibers. Cement slurry used in cementing oil and gas wells faces the problem of failure under the influence of hydraulic fracturing and perforation procedures. This failure leads to the formation of cracks and may require remedial cementing, which increases operating costs and complicates the process of oil and gas production. Moreover, this problem can lead to premature well water breakthrough and cause serious damage such as oil and gas shows and blowouts, which poses a threat to the environment and safety. To solve the problem of the destruction of cement stone under external influences, the study proposed the approach of reinforcing with basalt fiber. During the study, a cementing material based on Portland cement, reinforced with various concentrations of basalt fibers (0.1 %, 0.5 %, 1 % and 2 %), was developed and tested. Cement strength tests at 2, 7, and 14 days, along with deformation monitoring under load, were performed. The addition of basalt fibers to cement stone significantly improved its strength characteristics. The most successful results were achieved with the addition of 0.5 % basalt fibers, resulting in an 11 % increase in compressive and flexural strength. Basalt fibers complement the structure of cement stone, increasing its ability to deform. One of the key features of the obtained results is the possibility of improving the strength of the cement stone without losing its fluidity as a cement slurry. The results obtained are applicable in the development and production of cement materials based on basalt fibers. This will improve the quality of well cementing and reduce the risks of complications

SECONDARY RESOURCES IN PRODUCTION OF COMPOSITE BUILDING MATERIALS BASED ON CEMENT

Link for citation: Kopanitsa N.O., Demyanenko O.V., Kulikova A.A., Tkach E.V., Shestakov N.I., Stepina I.V. Secondary resources in production of composite building materials based on cement. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 10, рр. 49-60. In Rus. The relevance of the research is caused by the importance of the problem of rational use of natural resources in production of composite building materials. The possibility of partial replacement of natural non-renewable raw materials used in the production of multi-ton concrete and mortar mixtures based on cement with secondary products from the production of various industries will solve the problems of: resource saving, energy consumption and ecology. The construction industry is the largest consumer of by-products of mining enterprises: overburden and waste from mining and processing enterprises, which is hundreds of millions of tons per year. The most studied are the issues related to their use as fine and coarse aggregates in concrete and mortar mixtures for various purposes. The expansion of the possibility of using secondary products of mining enterprises in the production of composite building materials is associated with the production of active mineral additives, fillers in concrete and mortar mixtures, as well as energetically active nanomodifiers. The use of by-products of different chemical composition and dispersion makes it possible to control the processes of structure formation and hardening of composite materials based on cement and to obtain composite materials with the required performance properties. The main goal of the research is to scientifically substantiate and investigate the possibility of using waste from mining enterprises as components in concrete and mortar mixtures based on cement. Objects: modifying additives based on secondary products; composite materials with enhanced performance properties. Methods: determination of the mobility of mixtures, normal density, hardening time, flexural and compressive strength according to SS; thermal analysis; electron microscopy, x-ray phase analysis, colorimetry. Results. The paper introduces the results of studies necessary for the scientific substantiation, development and implementation in the construction industry of the technology for production of building mortar mixtures obtained using secondary products of mining enterprises as well as the comparative results of studies on the effect of a complex additive of microcalcite and nano-SiO2 on the properties of cement systems. It is shown that the introduction of a complex additive increases the compressive strength of cement stone, reduces the consumption of cement without reducing its standard characteristics and improves the performance properties of concrete.

SUGGESTIONS FOR CALCULATION OF RELATIVE STRAIN OF THE TOTAL SHRINKAGE OF EXPANDED CLAY CONCRETE

The article provides an analytical review of studies on the shrinkage strain development of expanded clay concrete, based on which it was established that a significant factor is the local raw material base. It means that for each region it is important to accumulate experimental data and correct design models for the analytical determination of the total shrinkage strain. In this regard, the task of the study was to develop suggestions for calculating the relative strain of the total shrinkage of expanded clay concrete, made on the basis of the local raw material base. Predicated on the results of the study and according to the provisions of SP 5.03.01 and Eurocode 2, the improved model for the analytical determination of the values of relative strain of the total shrinkage of structural expanded clay concrete was developed. The proposed model takes into account the value of cement activity as a determining factor of the cement stone strength, and it takes into account the water-cement ratio and the coarse aggregate volume. The proposed design model makes it possible to determine with sufficient accuracy the value of the relative strain of the total shrinkage of expanded clay concrete at the age of 28 to 120 days.

Measurement of tensile strength of well cement sheath in underground gas storage based on tensile failure method

AbstractDuring gas injection in gas storage, the inner pressure increase, potentially leading to tensile failure of the cement sheath. At present, the fracture strength of cement stone is measured using the Brazilian splitting method (BSM), which is prone to errors due to stress concentration at the loading point. To overcome this drawback, a novel test device and measurement method were developed to assess the tensile. This device utilizes the tensile failure method (TFM) to evaluate the sealing integrity of the cement sheath. The tensile strength tested by the BSM was found to be 40% higher than that tested by the TFM. Furthermore, based on the optimization of the cement slurry for underground gas storage (UGS) in the Jidong oilfield using both the TFM and the BSM. We found that using the BSM cannot optimize the cement slurry that meets the requirements for gas storage well cementing. The latex cement slurry was selected by the TMF for UGS well.