No 7 (2024)

A fairly large number of works by both Russian and foreign researchers have been devoted to the development of building materials based on anhydrite binders. An astringent based on insoluble anhydrite refers to slow-hardening. This fact often deters manufacturers of building materials from using this binder. To date, there are many activators for the hardening of insoluble anhydrite. The efficiency of accelerators depends on a number of factors. But there is no unambiguous explanation for the action of additives used to obtain anhydrite materials with optimal properties, and this problem needs a comprehensive study. The use of anhydrite in the production of building products and materials is a promising direction in construction, since anhydrite binder is an interchangeable local material and can be used instead of cement or gypsum binders.

The issue of the limit of technical and economic optimization of dry building mixes compositions does not lose its relevance and remains one of the main and priority issues in the industry. One of the ways to solve this issue is to use the most advanced chemical additives that minimize the cost of mixtures while maintaining the characteristics of the products. This paper discusses the use of rheological additive REOLIN RA 120 to optimize the compositions of plaster mixtures based on gypsum binder. It is shown that the use of REOLIN RA 120 in gypsum compositions reduces the complexity of plastering by increasing the range of permissible water-solid ratio, reducing the consumption of dry mix and improving the surface texture. The algorithm of introducing the additive and its effect on the indicators characterizing the complexity of preparation, application, leveling of the solution and subsequent treatment of the plaster surface is described.

3D concrete printing (3DCP) is one of the most important priorities for the development of the construction industry around the world. Despite optimistic forecasts for the growth of additive construction technology in the long term, there are various risks that can influence the pace of this development, which are associated, first of all, with the need to develop the regulatory framework, train qualified personnel, create and improve equipment and materials for 3DCP – seal. There is a lot of research aimed at creating and developing the scientific basis for the design of concrete for construction 3D printing; compositions of dry mortars for additive manufacturing based on mineral binders, mainly cement, have been proposed; much less attention is paid to composites based on gypsum and mixed – gypsum-cement-pozzolan binders (GCPB). The purpose of this work is to study the structure and properties of fine-grained concrete for 3DCP based on gypsum-cement-pozzolan dry mortars. The molding of samples during experimental studies was carried out using the layer-by-layer extrusion method on a workshop construction 3D printer “AMT S-6044”. The rationality of using concrete with a ratio of GCPB:aggregate = 1:2 in the additive manufacturing technology with a sand fineness modulus of M_k 3 has been substantiated. A composition of gypsum-cement-pozzolanic concrete (GCPC) modified with a multifunctional complex additive has been developed, which allows increasing the compressive strength by 35.3%, water resistance – by 73% (up to 0.85) compared to the control unmodified composition. It has been established that modification of GCPB with the developed multifunctional complex additive leads to a decrease in the volume of open capillary pores by 20.5%, the volume of open non-capillary pores – by 66.7%, an increase in the volume of conditionally closed pores by 28.1%, and the microporosity index – from 0.22 to 0.89. The synergistic interaction of chemical additives in complex additive composition is confirmed by the results of studies performed to determine the electrokinetic potential on the surface of GCPB particles and the kinetics of heat release during its hydration.

One of the directions of development of concrete science is the combination of positive qualities of heavy and lightweight concretes. The problem of optimizing the structural properties of heavy concrete and the thermal properties of lightweight concrete is solved in a large number of scientific papers. In Russia, the most popular structural lightweight concretes are those based on expanded clay aggregate. Recently, there has been experience in reconstructing bridges made of lightweight concrete on hollow microspheres. Over the past 10 years, the possibilities for producing lightweight concrete with increased strength have improved significantly. The paper presents models demonstrating the features of the formation of the structure of lightweight concrete on hollow and porous aggregates. The advantages and limitations are described for each of the aggregates for obtaining lightweight concrete with a given average density and strength. The described models show that it is advisable to use porous filler to obtain high-strength lightweight concrete with an average density of more than 1600 kg/m³, and hollow filler at ρ_lb<1600 kg/m³. The thickness of the filler shell becomes the determining factor in achieving the required specific strength of lightweight concrete.

The influence of highly dispersed tungsten-containing powders (WC, WO₃, a mixture of WC, TiC) obtained as a result of recycling of carbide products on change in the structural and physico-mechanical properties of cement materials at elevated temperatures has been studied. Powders of tungsten carbide WC, tungsten oxide WO₃, mixtures of tungsten and titanium carbides WC, TiC (average particle size 20–150 nm, agglomerates 300 nm – 1.5 microns) were added to the cement mortar, by partial replacement of the binder, in various concentrations (1–5 wt. %). The effect of additives on the thermal stability of cement samples was assessed by weight loss, residual compressive strength, exposed to temperatures at 300, 600 and 800^оC for 2 hours. The microstructural analysis was performed using scanning electron microscopy (SEM) with an integrated energy dispersion analysis system. It was established that in the entire temperature range under consideration (20–800^оC), the modified samples demonstrate a denser microstructure, have less mass loss and have increased residual compressive strength compared with the control composition. The obtained research results are of considerable value for understanding the mechanisms of influence of highly dispersed tungsten-containing particles on the characteristics of cement materials under high-temperature exposure.

Increasing and maintaining the pace of construction and repair work associated with the development of the highway network, as well as improving the quality of communication between subjects and transport hubs, requires a huge amount of resource consumption, and, accordingly, creates a significant burden on the country’s economy. One of the rational solutions in the road construction industry, which allows reducing the cost of raw materials, is the reuse of materials from existing highway structures. The most common options in both domestic and foreign practice is the use of regeneration technologies for the quantitatively predominant asphalt concrete road surfaces. However, when reusing asphalt concrete, in order to establish the recipe and technological features of the designed composites, it is necessary to evaluate the properties of asphalt concrete after wear and the possible mutual influence of the components used in its composition on the formation of the final properties of new composites. In this regard, the presented work is devoted to the analysis of a complex of properties of asphalt granulate samples and the establishment of patterns of their changes depending on the composition and service life. Based on the studies conducted, it was established that the composition of the mineral part of asphalt granulate and the amount of organic binder are within the standardized ranges. Noteworthy is the decrease in the physical and mechanical characteristics of the mineral part with an increase in the service life of asphalt concrete for more than five years, as well as a change in the composition of the organic binder, leading to a decrease in its relaxing ability. Depending on the composition and properties of asphalt granulate, options for its further use are proposed.