English English

Fediuk R.S.

Candidate of Engineering Sciences (Ph.D.), Associate Professor, Far Eastern Federal University, Russia

Injection mortars based on composite cements for soil fixation

https://doi.org/10.58224/2618-7183-2023-6-4-15-29
, , , ,
 15-29 p.
Abstract
The fixation of subsidence soils is an important practical scientific and technical task, which makes it possible to carry out construction and repair work on weak (subsidence) base soils. Composite cements (CC) have been developed, including aluminosilicates (AS), obtained by enrichment of ash and slag mixture (up to 65 wt.%), Portland cement clinker and gypsum. Based on the developed CC, a wide range of injection solutions with water-binding ratios from 1.0 to 2.0, including screening of crushed granite from 0.7 fineness modules, has been created. The developed injection mortars are capable of effectively fixing the soils of the foundations of underground structures, providing the strength of the soil-concrete mass up to 25.6 MPa with a deformation modulus of 10.1 GPa. According to the sedimentation analysis of solutions, it can be seen that these materials have a percentage of water separation from 22.5% at W/B=1 to 36.5% at W/B=2. At the same time, the viscosity indicators of these materials indicate a high penetrating ability, since the time of the expiration of mortars through a Marsh viscometer for mortars IR5 and IR6 is 39 and 40 seconds at W / B = 1.5 and W/ B = 2, respec-tively. The effect of increasing the density of injection mortars on composite cement at the age of 28 days was maximum at an AS dosage of 45% by weight, then it decreased with an increase in the con-tent of the aluminosilicate component. There are high ratios of the values of strength properties on the second day to similar indicators in the 28-days age: for compressive strength 0.24 (0.20-0.22 for addi-tive-free clinker compositions), for flexural strength 0.16 (0.15 for additive-free clinker compositions; while increasing the AS content above 45%, this ratio decreases to 0.14). High early strength makes it possible to effectively use injection mortars for urgent fixing of soils during the repair of underground structures.
PDF

Reinforcement of construction of underground structures with shotcrete

https://doi.org/10.58224/2618-7183-2022-5-6-5-18
, ,
 5-18 p.
Abstract
An urgent scientific task, which is of great practical importance for increasing the defense capability of the state and preserving the population, is the improvement of constructive methods for the complex repair of underground structures. Reinforced shotcrete concretes have been developed and their research has been carried out to strengthen underground structures. Achieving the uniform workability of shotcrete (slump 19 cm) was carried out by varying the dosage of the superplasticizer, which has a high water-reducing ability (40%). Some reduction in slump flow (47 cm) was observed at a dosage of ACC in the amount of 35 wt. %. An increase in the density of the mixed mixture with an increase in the content of the aluminosilicate component in the polymineral binder was established. The introduction of the alumino-silicate component in small quantities (up to 25 wt.%) slightly increases the 28-day density of the cement paste (0.3-0.4%). With an increase in the dosage of ACC (up to 35 percent by weight), an increase in the density of 28-day-old samples was noted, which linearly raised with an increase in the amount of introduced aluminosilicates. The effect of increasing the compressive strength of shotcrete concretes on a polymineral binder increased with an increase in the dosage of ACC up to 35% by weight, and the maximum effect is noted for early strength values, in particular, at the age of 1 day, an increase in compressive strength by compared with the composition without additives was 56%, and with bending 62%. This is also confirmed by the high ratios of the values of strength properties in the first day to similar indicators in the grade age: for compressive strength 0.27 (0.23 for clinker compositions without additives), for bending strength 0.30 (0.26 for additive-free clinker compositions). Theoretically and practically proved the effectiveness of the use of the developed shotcrete for strengthening the supporting structures of underground structures with an increase in strength of more than 2 times, which is explained both by the high strength of the obtained repair composition and the monolithic contact zone between the old and new layers of concrete. The developed shotcrete is able to provide the necessary degree of strengthening of the supporting structures of underground structures, while the thickness of the repair layer of 6 cm (with proper soil fixation) allows the use of underground structures as dual-use facilities.
PDF

INCREASING IN IMPACT VISCOSITY OF FIBER-ASH-CONCRETE

https://doi.org/10.34031/2618-7183-2020-3-6-5-16
, , , , ,
 5-16 p.
Abstract
The trend in building materials science is to replace the different proportions of Portland cement in the binder. Therefore, the paper proposes the principles of controlling the static and dynamic strength of fiber-reinforced concrete, consisting in the complex effect of the hydro-removed ash and slag mix and basalt fiber on the processes of structure formation of the cement composite. A four-stage purification system for the hydro-removed ash and slag mixture has been developed, including disintegration, flotation and two-stage magnetic separation. It was found that the density of the fresh mix from the dose behaves naturally, and the density of solid samples at low doses slightly decreases. High early strength of the developed composites is noted, in particular, for specimens with ASM, one and a half increase in compressive strength is traced in comparison with non-additive specimens. Combinations of "fiber + ASM" with a quadrupling of strength have a significant effect on bending strength. Successful approximations of the compressive strength and bending strength on the ASM dose for different ages (1, 7, 28 days) are traced with the regular behavior of the coefficients in the power dependences. Revealed a multiple increase in the impact strength of the developed compositions. The use of the results will lead to the possibility of designing high-strength concretes, including for special structures.
PDF

EFFECT OF WOLLASTONITE ON THE MECHANICAL CHARACTERISTICS OF CONCRETE

https://doi.org/10.34031/2618-7183-2020-3-5-34-42
, , , , ,
 34-42 p.
Abstract
Improvement of the physical and mechanical properties of cement composites should be accompanied by the disposal of industrial waste of various generation. Therefore, the paper proposes the principles of con-trolling the strength properties of concrete, which consist in the complex effect of wollastonite obtained from boron production waste on the processes of structure formation of the cement matrix. When this introduced in an amount of 2-8 wt. % wollastonite has a dual function as a mineral filler and a reinforcing fiber. It has been proven that in the presence of wollastonite, the concrete mix becomes lighter without reducing its physical and mechanical properties. It was revealed that the early strength for all the developed compositions with the addition of wollastonite increases due to the acceleration of hydration processes. Calcium silicate, which is wollastonite CaSiO3, has a close chemical composition with cement clinker, especially with Ca2SiO4 belite and Ca3SiO5 alite. This leads to the formation of a chemically homogeneous and, as a result, hardened microstructure. Elongated wollastonite fibers with good adhesion to the cement stone provide effective micro-reinforcement of the concrete composite. Using the results will lead to the possibility of designing high-strength concretes, including for special structures.
PDF

EFFECT OF POROUS STRUCTURE ON SOUND ABSORPTION OF CELLULAR CONCRETE

https://doi.org/10.34031/2618-7183-2020-3-2-5-18
, ,
 5-18 p.
Abstract
The compositions of gas and foam concrete with improved acoustic characteristics were developed. The optimal form of porosity, which contributes to the absorption of sound waves, both in the range of audible frequencies and at infrasonic and ultrasonic frequencies, is revealed. The mathematical model for designing sound-absorbing concrete was improved, taking into account both the porosity of the composite and the influence of the porous aggregate. The laws of synthesis of aerated concrete and foam concrete are established, which consist in optimizing the processes of structure formation due to the use of a polymineral cement-ash binder and blowing agent. The composition of the composite intensifies the process of hydration of the system, which leads to the synthesis of a polymineral heterodisperse matrix with an open porosity of more than 60%. Peculiarities of the influence of the “Portland cement – aluminosilicate – complex of modifiers” system on the rheology of the concrete mixture was identified, which can significantly reduce shear stress and create easily formed cellular concrete mixtures. The increased activity and granulometry of aluminosilicates predetermine an increase in the number of contacts and mechanical adhesion between particles during compaction, strengthening the frame of inter-pore septa. The mechanism of the influence of the composition of the concrete mixture on the microstructure of the composite is estab-lished. The presence of refined aluminosilicates and a complex of additives in the system along with cement contribute to the synthesis of the matrix with open porosity, thereby increasing the sound absorption coefficient.
PDF

USE OF IRAQ CONCRETE SCRAP AS FILLER AND AGGREGATE OF HEAVYWEIGHT AND LIGHTWEIGHT CONCRETE

https://doi.org/10.34031/2618-7183-2020-3-3-28-39
, , , ,
 28-39 p.
Abstract
The relevance of the paper is due to the search for alternative sources of raw materials for the construction industry, associated with the disposal of man-made waste. The novelty of the article is to identify the sci-entific laws of the influence of demolition waste on buildings and structures on the formation of the microstructure of lightweight and heavyweight concrete. Concrete waste was prepared as both fillers of cement materials and fine aggregates, based on which concrete with high mechanical properties was created. The mix design was carried out from the point of view of geomimetics, in particular, taking into account the law of affinity of structures. The strength characteristics of concrete mixtures were investigated in accordance with EN 12390-3. In addition, the microstructural, morphological and thermal properties of the raw materials and concrete were determined during 28-day curing. For the first time, the dense microstructure of the composite was ensured, both with Portland cement products and with hydration, and, in part, with hydration products of previously unreacted clinker, whose minerals are present in concrete waste and are activated when they are crushed. The use of demolition waste of buildings and structures as a filler of cementing material when replacing Portland cement up to 20% allows to obtain better compressive strength of both heavyweight and lightweight concrete.
PDF