Air Shrinkage Research Articles

Estimation of Chemical and Mineral Composition, Structural Features, and Pre-Firing Technological Properties of Waste Coal Heaps for Ceramic Production

The relevance of the investigation and creation of a new non-traditional raw material base for wall ceramics for the south of Russia is shown in connection with the decreasing availability of traditional raw materials—loams. Characterizations of the mineral and chemical constituent rock formations of the rocks composing the dumps of coal waste heaps and enrichment plants are given. A serious constraint for the industrial development of coal wastes is the requirement for a great variety of mineral constituents. The chemical and mineralogical compositions and the pre-firing ceramic properties of the waste coal heaps are studied and presented in detail. It is mentioned that fine and thin materials contain coal in an increased amount; due to this, they cannot be considered as the main raw material for the production of wall ceramics. The materials of the medium-sized grain group (2.0–5.0 mm, sifting) can contain up to 2–3% of coal and are most often represented by a mixture of mudstones, siltstones, and sandstones, with the predominance of one or another type of rock. The granulometric composition and the content of large-grained inclusions, molding moisture, plasticity, cohesiveness, desiccation properties, and air shrinkage were studied and determined. It is concluded that the middle group of waste coal heaps in particular are of the greatest interest as a basic raw material for the production of wall ceramic products.

Assessment and Characteristics of Molding Masses Based on Loam during Production Soft Molded Ceramic Brick

опThe article discusses the issues of assessing the properties of loams and selecting the composition of molding compounds based on them for the production of ceramic bricks using the soft molding method. It is noted that for soft molding technology, to date, no recommendations have been developed for the evaluation of raw materials with the establishment of relationships between the composition, technological properties, molding features and aesthetic features of the front edges of products. According to technological features, the method of soft molding of ceramic bricks is conventionally divided into 4 methods: manual molding, accelerated molding, pressing method and vibration molding method. The results of our work made it possible to identify the main indicators when assessing clay raw materials and to develop the basic principles for selecting the composition of molding masses. Thus, the critical compression stress and the degree of deformation of the workpieces should be on average 0.2–0.8 kg/cm2 and 3–5 units, respectively. In this case, the molding masses should have the minimum possible water content and stickiness, have minimal air shrinkage (less than 6–7%), and be slightly or moderately sensitive to drying. An algorithm has been developed for selecting molding compounds, including determination, in addition to generally accepted indicators, such as the degree of deformation and critical compressive stress at different water contents, specific penetration resistance, determination of the optimal electrolyte content, and stickiness. For typical loams, the dependences of the degree of deformation of the samples and the critical compressive stress on the water content of the molding masses are shown, as well as the influence of electrolytes on the water content. It has been shown that the introduction of electrolytes can significantly reduce the water content of molding masses. It is noted that the genesis of loams, their variable composition and the frequent presence of undesirable harmful impurities predetermined the situation that high-quality loams that meet the necessary requirements are quite rare and the only alternative can be the selection of compositions of molding compounds based on correct scientific and methodological

Technology and Peculiarities of Production of Large-format Ceramic Stones Based on Opoka-like Rocks

Introduction. One of the urgent tasks of the wall ceramics industry at present is the production of large-format ceramic stones with compressive strength of 10–15 MPa and thermal conductivity less than 0.12 W/(m·оС), while the market cost per 1 m3 should be competitive with gas-concrete blocks and be in the range of 5–6 thousand rubles per 1 m3. This problem can be solved by developing modern energy-efficient production technology and using opoko-like rocks and coal processing wastes as the main raw material as fuel and burnout additive.Materials and Methods. The opoka-like rocks — opokas from the deposits of southern Russia — Nagolnovskoye, Bakanskoye, Shakhtinskoye, Avilo-Fyodorovskoye, and coal cake produced by Pyramida LLC were used for research. The study of chemical and mineral composition was carried out by standard methods on prepared samples. The study of ceramic and technological properties (plasticity, molding moisture, degree of crushing, air and fire shrinkage, compressive strength, water absorption) of raw materials was carried out according to generally accepted methods on samples precrushed to a certain grain composition, since opokas, depending on the type, do not soak or slowly soak in water.Results. Pre-firing technological properties of opokas and their differences from traditional clay raw materials soaked in water were confirmed: increased molding moisture, small air shrinkage, low sensitivity to drying. The dependence of density and strength of samples on the degree of pulverization of opoka, firing temperature and the amount of carbon cake in the raw material mixture has been established. The influence of coal preparation wastes and their optimal amount on physical and mechanical properties of fired samples has been determined. The introduction of carbon cake allows to exclude the use of gas for firing or minimize its introduction. On the basis of the obtained results a simplified technological scheme for the production of large-format stones with minimum production cost has been developed.Discussion and Conclusion. The proposed technological scheme consists of two units of the main mass preparation equipment, molding of products is carried out by semi-rigid extrusion, drying of products is carried out directly on kiln cars, and for firing coal cake is used, which is introduced into the raw mix. These factors and technological methods allow to obtain products with low thermal conductivity, but with strength 3–5 times higher than that of aerated concrete blocks of similar density. The prime cost of ceramic stones will amount to 3–3.5 thousand rubles per 1 m3 of products. Rostov region, possessing opoka-like rocks and unclaimed reserves of technogenic coal raw materials, can become a center of production of large-format ceramic stones with low cost and provide the south and central part of the country with highquality wall materials.

Deformation characteristics of dense and foamed mortars based on cement and gypsum-to-cement binders for 3D printing

Construction 3D printing is one of the revolutionary construction technologies, which involves the use of highly fluid cement and gypsum-to-cement mixes. However, this requires an additional study of the deformation characteristics of multicomponent materials. The article is devoted to the study of the own deformation characteristics of mortars based on cement and gypsum-to-cement binders, as well as fine-grained concrete for printing the contours of wall structures and foamed mortar for filling, monolithic and thermal insulation of their internal space. A wide range of cement and gypsum-to-cement materials has been studied, incl. foamed mortar. For these materials, comprehensive studies of deformation characteristics have been carried out, confirming the results obtained by X-ray diffraction analysis, SEM, heat of hydration, fresh and physical and mechanical properties. It has been established that in gypsum-to-cement materials, the revealed deformations of the expansion of gypsum overlap the negative deformations of air shrinkage. The resulting materials have a slump flow up to 226 cm, which allows the use of these materials for 3D printing of building structures. The high strength of the developed cement and gypsum-to-cement materials in all periods of hardening (above 50 MPa), as well as excellent thermal conductivity (0.10–0.13 W/(m·°C)), shows the promise of fine-grained mortars and foamed ones.

ПІДВИЩЕННЯ МОРОЗОСТІЙКОСТІ ДОРОЖНІХ БЕТОНІВ ЗА РАХУНОК ВИКОРИСТАННЯ ВТОРИННОГО ЗАХИСТУ

The production of road cement-concrete mixtures, their transportation, laying and compaction usually occurs during periods of high positive temperatures and the presence of wind. When cement concretes harden under such conditions, moisture evaporates from them. This can lead to air shrinkage, which causes to the cracking and collapse of concrete. Therefore, to protect the hardening cement concrete from shrinkage and cracking, film-forming materials are applied to its surface. However, the practice of using road surfaces shows that such protection is not sufficient to ensure the durability of cement concretes. Therefore, to increase the resistance of concrete to aggressive environments, it is proposed to use secondary protection. Secondary protection of concrete consists in applying impregnating compounds to the surface of the pavement. The article presents the results of studies of the effect of impregnating compositions on water absorption and frost resistance of concrete of strength class B30 (C32/40). It is shown that the use of impregnating compositions improves the water resistance of concrete. However, such surface treatment does not lead to an increase the frost resistance of road concretes. It was found that some formulations increase the hardness of the concrete surface and do not reduce the resistance of concrete under the simultaneous action of negative temperatures and chloride salts. The article presents the results of studies of the effect of impregnating compositions on water absorption and frost resistance of concrete of strength class B30 (C32/40). It is shown that the use of impregnating compositions improves the water resistance of concrete. However, such surface treatment does not lead to an increase in frost resistance of road concretes. It has been found that some impregnating compositions increase the surface hardness of concrete. At the same time, they do not reduce the resistance of concrete under the simultaneous action of negative temperatures and chloride salts. At the same time, there are compositions, the use of which leads to peeling of the concrete surface when tested for frost resistance. Such peeling leads to destruction of the protective layer of concrete and can reduce the frost resistance of concrete. The reasons for the low efficiency of secondary protection of road concrete when using impregnating compositions are given. It is shown that such compositions should be used selectively for the protection of road concrete. It is indicated for which strength classes the impregnation is an effective means of protection. The use of impregnation for concretes of other strength classes leads to a decrease the resistance of aggressive environments. Keywords: frost resistance, secondary protection, impregnating compounds, concrete protective layer, water absorption.

Entirely environment-friendly polylactide composites with outstanding heat resistance and superior mechanical performance fabricated by spunbond technology: Exploring the role of nanofibrillated stereocomplex polylactide crystals

This study aims at investigating the manufacturing and characterization of all-polylactide composites prepared by melt spunbond spinning technology. To do so, a series of asymmetric stereocomplex polylactide (SC-PLA) blends (PLLA 95 wt%/PDLA 5 wt%) was melt spun. To examine the impact of molecular structure of PDLA, the blends of linear PLLA, and low and high molecular weight as well as branched PDLAs, were subjected to a single step spunbond process. DSC thermograms of the samples showed two melting temperatures at around 170 °C and 210 °C, which were attributed to the melting of homo and stereocomplex crystals, respectively. The samples were spun at 190 °C, between the homo and stereocomplex crystals' melting temperatures, and at 230 °C, above the stereocomplex crystals' melting temperature. Morphology images showed the formation of fibers in the range of 40–50 μm. Shear rheological measurements revealed that the spun SC-PLA samples had a substantially higher viscosity and storage modulus in the low frequency region, and higher shear thinning behavior, compared to the non-spun samples. Extensional rheology measurements also showed that the spun samples demonstrated strain hardening behavior. Substantial enhancement of rheological properties was noted for the samples containing the branched and high molecular weight PDLA spun at 230 °C. After etching, the spun samples at 190 °C exhibited small spherical crystals with diameters in the range of 80–90 nm, whereas comparatively thin fibers in the size range of 60–70 nm were observed for the samples spun at 230 °C. Remarkable enhancements up to 100% and 60% was noted for the tensile modulus and strength, respectively, of the spun SC-PLA samples. The spun fibers also demonstrated a considerable reduction in boiling water and hot air shrinkage. The distinctive role of nanofibrillated stereocomplex crystals as a rheology modifier and a crystallization nucleating agent makes PLA more sustainable and paves the way for the fabricated all-PLA composites in applications requiring high heat resistance and superior mechanical performance. The present study unequivocally indicates a huge potential for the sustainable entirely all-PLA products manufactured by fiber in fiber and, indeed, unfolds unknown opportunities for PLA-based merchandises in future.

Design of drain tube with movable shutter in household refrigerators

• Infiltration of warm and humid air to the freezer results in frost accumulation. • For reduction of inflow, drain tube with a high hydraulic resistance is proposed. • Negative pressure is formed by air shrinkage after door opening and closing. • To release the negative pressure, the proposed drain tube has a movable shutter. • Movable shutter can control air vents depending on the pressure condition. The infiltration of warm and humid air from the outside into a freezer results in frost accumulation around the evaporator in household refrigerators. This can significantly reduce the cooling capacity of refrigerators. In this study, the pressure, temperature, and frost around a proposed drain tube were monitored through in-situ measurements until the first defrost process (about 54 h). The proposed drain tube has 220 times higher hydraulic resistance and shows 55 times lower inflow in computational fluid dynamics (CFD) analysis. Once the door of the freezer compartment is opened and closed, external warm air replaces the cold air in the freezer. Negative pressure is produced by the shrinkage of this external air under low-temperature conditions. The other role of the drain tube is to vent air between the outside and inside of the refrigerator under negative pressure. To release the negative pressure, the proposed drain tube has a movable shutter. In the CFD results, the secondary inlet increases the inflow by 3.2 times compared to the inflow in an I-type tube. To determine the design, the weight and inner diameter of the drain tube were changed. The performance of the proposed tube was validated by the lack of blockage of discharge until the first defrost process. The movable shutter did not allow the negative pressure to exceed -100 Pa by facilitating air venting after opening the door for 10 seconds and then closing it.

Application of oil-containing gabbro-diabase waste sludge for ceramic products manufacturing

The paper presents research findings of the possibility of recycling and using the oil-containing sludge, generated at water-oil emulsions purification with gabbro-diabase powder, in ceramic constructional products manufacture. It is suggested to add the sludge to clay mass as a mineral and pore-forming admixture. The influence of the added sludge weight on such physical and mechanical parameters of ceramic samples as strength, compressive strength, water absorption, air shrinkage and firing shrinkage values and density was studied. The ceramic samples were prepared using natural clays from the Bessonovka (Belgorod region) and Podgornoye (Voronezh region) deposits. It has been demonstrated that adding the sludge to clay mass in amount of 2% wt. increases the compressive strength of samples by 90%, the air shrinkage by 1%, and water absorption by 1-2%. The firing shrinkage stays the same. At increasing the amount of the added sludge up to 7% all the parameters are slightly changed – water absorption and air shrinkage are increased, compressive strength, firing shrinkage and density are reduced. But further, at 7% sludge content in the clay mix the ceramic samples’ strength meets the grade not lower than 150 by GOST 530-2012.

Влияние минеральных добавок на усадочные деформации камня из известкового раствора

The analysis of research works devoted to the study of different mineral admixtures influence on development of shrinkage deformation of cement stone is presented.There were studued strength properties and shrinkage deformation of stone from lime building solution based on binder agent with active mineral admixture. The authors give the data on the influence of active type admixture on the change of air shrinkage of stone aged up to 28 days, and the comparison of these date with plain solution content without admixtures has been carried out. It has been established that shrinkage for stone aged 28 days from mixture with metakaolin is 10 percent lower than that of stone of the same age from mixture with microsilica suspension.

Mass Compositions Calculation on the Basis of Argillites at Ceramic Tiles Production

The results of selection and principles of calculating the ceramic masses composition for the clinker tiles’ production from argillites taking into account the raw materials’ characteristics are presented. The positive properties of argillites, as well as the properties that do not allow the tiles’ production of by stamping, which is traditional for these products’ manufacturing, are noted. Having low sensitivity to drying, low air shrinkage, high strength of the calcined shard, while being fusible sintering raw materials, argillites are low plastic and have insufficient bonding during molding, which indicates the need for corrective additives. In this work, the task to select the composition of ceramic masses to increase the plasticity of argillites while maintaining the positive properties of the main raw material was set. The authors proposed the use of siliceous clays as a corrective additive. An integrated approach was applied in calculating ceramic masses by grain composition and chemical and mineralogical indicators. Based on the research of A.I. Avgustinik, the oxide content Ca, Mg, Fe, Na, K and attitude Al2O3/SiO2 was taken into account. In order to obtain the densest packing, when calculating the grain composition, the natural dispersion of siliceous clays and the grain composition of previously prepared argillites were taken into account. The obtained theoretical calculations were tested in practice. Practical results showed that the 15% introduction of siliceous clay with the ceramic mass composition made it possible to obtain clinker tiles with improved physical and mechanical properties.

The Use of Water Treatment Petroleum Sludge in the Manufacture of Ceramic Products

The paper presents the results of studies of the possibility of utilization of petroleum sludge, obtained during the purification of oil-water emulsions, using gabbro-diabase powder in the production of ceramic building products. The sludge is proposed to add to the clay mass as an entrained additive. The influence of the sludge additive mass on such physical and mechanical indicators of ceramic samples, as density, compressive strength, water absorption, air shrinkage and fire shrinkage, and density, is studied. Ceramic samples were prepared using natural clays, deposits Bessonovka (Belgorod region) and Podgornoye (Voronezh region). It is shown that the addition of 2% mass to the clay mass of the sludge leads to an increase in the compressive strength of the samples up to 90%, an air shrinkage of 1%, an increase in water absorption 1-2%. The value of the fire shrinkage remains unchanged. With an increase in the proportion of sludge additive to 7%, all indicators slightly change. Water absorption and air shrinkage increase, compressive strength, fire shrinkage and density decrease. However, further, when there is 7% of sludge in the clay mixture, the strength of ceramic samples corresponds to a grade not lower than 150, according to GOST 530-2012.

Comparison of Domestic and Overseas Graphite/Antimony Composites and Exploration into Their Antimony-Infiltrating Technology

The technique of pressure-infiltrated antimony in porous graphite can produce sophisticated graphite seal materials. A single batch of samples of graphite/antimony matrix exhibits the differences and disparity in impregnation technology among products manufactured in the US, Japan, and China. In this study, a comprehensive analysis is conducted on the appearance, metallographic microstructure, and physical properties of these graphite/antimony composites. The results indicate that the technology of vacuum pumping before exerting high pressure has been adopted in Japan; this technique is key to removing the isopiestic layer caused by the sheer exertion of high pressure. A method has been proposed by American research where alloying is performed to raise the impregnation rate of large-scale, porous matrix by enhancing the fluidity of molten metal. However, this method cannot eliminate the air's shrinkage cavity and back-pressure and is therefore unable to achieve adequate, comprehensive performance. In China, a technological bottleneck should be investigated to improve the impregnation technology of vacuum pumping before exerting high pressure.

Study on microstructures and macro-properties in cement-based materials adding phosphorous slag

Microstructures and macroproperties of cement-based materials adding phosphorous slag were studied in this paper. As the results show that the hydration heat decreased with the increase of the mix amount of phosphorus slag, and the reducing rate of hydration heat was lower than that of volume percentage. Set cement hydration products include more tabularly cumulated Ca(OH)2 crystals. The hydration products start to form compact tabular structures and the number of holes reduces visibly at the age of 28 days. Meanwhile, phosphorous slag concrete has good frost resistance and anti-permeability. Mixing fly ash and phosphorus slag can improve the wear-resisting strength of the concrete. The self-grown volume of phosphorus slag concrete shrinks slightly in the early age the expansion rate tending to be stable. Air shrinkage of the phosphorus slag concrete is slightly lower in the early period, and it is fairly the same as that of the fly ash concrete in late period.

Patterns and possible mechanisms of soil CO2 uptake in sandy soil

It has been reported that soils in drylands can absorb CO2, although the patterns and mechanisms of such a process remain under debate. To address this, we investigated the relationships between soil CO2 flux and meteorological factors and soil properties in Northwest China to reveal the reasons for “anomalous” soil CO2 flux in a desert ecosystem. Soil CO2 flux increased significantly and exponentially with surficial turbulence at the diel scale under dry conditions (P<0.05), whereas the relationship under wet conditions was insignificant. Furthermore, soil CO2 flux demonstrated remarkable negative correlation with soil air pressure (P<0.05) in both dry and wet conditions. Analysis considering Henry's Law indicated that soil water content was insufficient to dissolve the absorbed CO2 in dry conditions, but was sufficient in wet conditions. The concentration of soil HCO3− in the morning was higher than in the evening in dry conditions, but this pattern was reversed in wet conditions. These results imply that CO2 outgassing induced by turbulence, expansion of soil air, CO2 effusion from soil water, and carbonate precipitation during daytime can explain the abiotic diurnal CO2 release. Moreover, CO2 pumping from the atmosphere into the soil, caused mainly by carbonate dissolution, can account for nocturnal CO2 absorption in dry conditions. The abiotic soil CO2 flux pattern (CO2 absorption throughout the diel cycle) in wet conditions can be attributed to downward mass flow of soil CO2 and intensified soil air shrinkage, CO2 dissolving in soil water, and carbonate dissolution. These results provide a basis for determining the location of abiotic fixed carbon within soils in desert ecosystems.

New and emerging applications of carboxylated styrene butadiene rubber latex in polymer composites and blends: review from structure to future prospective

The present review focuses on the properties and developing applications of carboxylated styrene butadiene rubber (XSBR) as a modified grade of styrene butadiene rubber (SBR). Carboxylated polymers, and particularly carboxylated rubbers, are regarded as a new class of polymers with superior physical and mechanical properties over non-carboxylated counterparts. Upon introducing carboxyl groups, the properties such as elasticity range, strength, compatibility towards functional fillers and polymers, resistance to hydrocarbon solvents enhance and cross-linking by non-sulfur reagents becomes possible. The XSBR latex benefits from excellent mechanical and chemical stability, excellent liquidity, high bond and conjunction strength, high toughness and the strength after molding, low water absorption and air shrinkage, excellent durability, abrasion, oil and corrosion resistance of cement products. Due to the polarity offered by carboxyl groups, fiber, and particulate composites of XSBR exhibit improved physical and mechanical properties. The stable interface created between carboxyl group and the second polymer phase generally results in an enhancement for the host polymer.

Research on HEC’s Hardening Effects on Topsoil in China’s Xinjiang Uygur Autonomous Region

In order to solve the problems concerning water loss and soil erosion as well as affected soil stability caused by the construction of towering footing of electric transmission line in Chinas Xinjiang Uygur Autonomous Region, HEC, a new curing agent which is strong and highly water-resistant, is used in the process. In construction, samples acquired are used in some indoor experiments on intensity, air shrinkage, swelling, frost heaving and sluicing. Effects of the consolidated soil on site are observed during a hydrological year and the results show that the material is good enough for wide-spread promotion and application in areas with same conditions.

Study on Causes and Solutions of Cracks on Concrete Hollow Block Wall

Concrete hollow block after being shaped up is possessed of features like strong shrinkage, poor thermal conductivity and repeated contraction after dampness, which leads to many problems in the use of concrete hollow block wall material. This article elaborates the causes of cracks on concrete hollow block wall from multiple perspectives, such as temperature expansion, air shrinkage, construction quality and design structure, and put forward solutions according to the causes from aspects of production, design, construction and technique improvement.

Study and Engineering Practice on Cracks Control Measures for Concrete Face Slab of High CFRD

Being the face slabs of high concrete faced rockfill dams (CFRD) are under complex stress state, the slabs are relative vulnerable. And crack is easy to form on slab, which can influence durability and integrity, then weaken impermeable ability and safety of dam. The factors that contribute to the structural cracks, non-structural cracks and extruding cracks of concrete face-slab are analyzed in detail. The result shows that the structural crack is mainly due to differential settlement, the extruding crack in riverbed position is mainly caused by rockfill body over-settlement of dam beyond 150m high and the non-structural crack is mainly caused by temperature shrinkage and air shrinkage. Therefore, crack control of CFRD face slab should be regulated by the three means coming from structural design, construction control and concrete material. It is proved by the practices in Shuibuya CFRD that face slab cracks on CFRD beyond 200m high can be reduced effectually by the present technique means.

Study and Engineering Practice on Cracks Control Measures for Concrete Face Slab of High CFRD

Being the face slabs of high concrete faced rockfill dams (CFRD) are under complex stress state, the slabs are relative vulnerable. And crack is easy to form on slab, which can influence durability and integrity, then weaken impermeable ability and safety of dam. The factors that contribute to the structural cracks, non-structural cracks and extruding cracks of concrete face-slab are analyzed in detail. The result shows that the structural crack is mainly due to differential settlement, the extruding crack in riverbed position is mainly caused by rockfill body over-settlement of dam beyond 150m high and the non-structural crack is mainly caused by temperature shrinkage and air shrinkage. Therefore, crack control of CFRD face slab should be regulated by the three means coming from structural design, construction control and concrete material. It is proved by the practices in Shuibuya CFRD that face slab cracks on CFRD beyond 200m high can be reduced effectually by the present technique means.

Study on the Performances of Phosphate Repair Material Modified by Fly Ash

Aiming at the characteristics of phosphate repair material, by mixing fly ash in it, its properties can be improved effectively. The experiment has studied the effects of fly ash on the setting time, strength and air shrinkage property of phosphate repair material.the result shows that mixing appropriate fly ash can prolong the setting time, and on the condition of maintain constant fluidity, the strength of phosphate repair material can be enhanced, but with the increase of fly ash admixture, its strength will be reduced, the fly ash admixture within 10% can reduce the air shrinkage of repair material.