Materials Science Forum Vol. 1011

Abstract: The alkaline clinker-free binders formulations activation development based on fine powders of aluminosilicate nature will allow to obtain the effective building composites. The paper reveals the issues related to the theoretical foundations of the cement stone structure and strength formation based on the alkaline activator. The research results, in our opinion, are undoubtedly of practical importance for the construction industry, since the proposed recipes for clinker-free cements will replace the expensive and energy-consuming Portland cement, allowing to create strong and durable concrete and reinforced concrete structures. The results presented in this article have been obtained in the framework of research on the implementation of scientific project No. 05. 607.21.0320. “Development of technology for new building composites on clinker-free alkaline binders using substandard natural and secondary raw materials” which received support from the federal target program “Research and Development in Priority Directions for the Development of the Russian Science and Technology Complex for 2014-2020”. The unique identifier for the agreement is RFMTFI60719X0320.

Abstract: Currently, construction volumes around the world are growing rapidly. Because of this fact the anthropogenic load on the natural resource potential of our planet is increasing, so special attention is paid to the development of less resource and energy-consuming technologies for building production, the development of new building composites based on the use of local secondary and substandard raw materials, the receipt of which high-temperature and expensive processing is not required. In this regard, the Grozny Scientific School of Energy and Resource Saving in the production of modern building materials has carried out the comprehensive studies to study the effectiveness of clinker-free alkaline binders as an alternative to traditional cement binders. The results presented in this article were obtained in the framework of the research on the implementation of scientific project No. 05. 607.21.0320. “Development of technology for new building composites on clinkerless alkaline binders using substandard natural and secondary raw materials” that received support from the federal target program “Research and Development in Priority Directions for the Development of the Russian Science and Technology Complex for 2014-2020”. Unique Agreement Identifier RFMTFI60719X0320

Abstract: With the increase in the number of finely dispersed mineral additives in concrete, their water demand increases and the effect of micro-filling weakens. To solve this problem, various methods of dry surface modification are proposed. As a result of the finely dispersed mineral powders’ surface modification, an improvement in their rheological characteristics, a decrease in wettability, a change in granulometry and other properties are achieved. This article discusses the surface modification effect’s laws in a high-voltage electric field on the autogenous properties of mineral dispersed concrete components, structure formation processes, mechanical properties, and cement stone hydration products. According to the results of the study, it was found that the surface modification of bulk materials - concrete components - in a high-voltage electric field changes autohesion properties in comparison with control samples. The data indicate lower values ​​of bulk density and angle of repose. This is due to a change in the balance of forces that arise during the mutual contact of particles after surface modification. With a certain balance of these forces, autohesion will contribute to the dense packing of particles and thereby affect the structure formation processes. The results of changes in the plastic strength of cement pastes confirm that there is an intensification of the structure formation process. Moreover, a more intense increase in plastic strength is observed during bipolar charging of particles in comparison with unipolar charging. This is due to an increase in the number of heterogeneous charges in the system and, as a consequence, an increase in the strength of adhesive contacts, as evidenced by the data of X-ray phase analysis.

Abstract: The aim of the research was to study the activation technology of the materials for concrete by their surface modification in a high-voltage electric field. It is noted that the mineral additives modified in a high-voltage electric field are characterized by a higher activity of the calcium hydroxide absorption. It was established that, despite the presence of a large number of crystalline compounds in metakaolin, its pozzolanic activity in the absorption of calcium hydroxide from a saturated solution is quite high. The same value of the hydration activity coefficient is also determined for the ground slag. The authors found that a characteristic feature of the dispersed mineral additives, surface-modified in a high-voltage electric field in comparison with control samples, are the lower values ​​of bulk density and repose angle. This is due to a change in the forces balance that occurs during the mutual contact of particles. The influence of the mineral additives’ surface modification in a high-voltage electric field on interparticle interactions in the “solid – liquid” system is evaluated. It is established that in the absence of a repulsion barrier, the particles form the aggregates that increase their sedimentation rate. During unipolar or bipolar charging of particles in an electric field, the sedimentation rate slows down or accelerates accordingly. These effects are used to modify the cement surface.

Abstract: Of all the known methods for increasing the cement activity, mechanical grinding is distinguished in the work. For mechanical grinding, technological characteristics of grinding in an electromagnetic field are established (mill - linear induction rotator, LIV). The value of the increment of activity is determined depending on its initial (initial) value. To determine the estimated value of the cement consumption, the methods provided by the state standard of the Russian Federation were used. The experiments, as well as the measurement of the compressive strength (R), were carried out in accordance with the GOST requirements. The cement mechanical grinding effective application field in electromagnetic field is determined by comparing the costs and savings. The costs are calculated as the cost of electricity needed for grinding. The savings are the cost of the established difference between the cement consumption for the initial activity of cement and the actual value, which is able to provide the concrete with a given design strength. The results describing the field of the cement mechanical grinding effective application are presented in tabular form and graphically. When determining the area of ​​ the mechanical grinding effective use, the conclusion that it is necessary to adjust the technological grinding regimes depending on the initial activity of the cement, as well as on the chemical composition of the clinker (manufacturer) was confirmed. The prospects for the research on mechanical grinding technology are associated with obtaining grinding regimes depending on the initial size and composition of the clinker. The area of ​​effective application of mechanical activation should be determined each time depending on the physical and mechanical cement properties.

Abstract: Modern housing practice involves the widespread use of silicate brick. The main disadvantage of this building material is its high average density, accompanied by high thermal conductivity, which is accompanied by large heat losses through the enclosing walls of buildings and structures. This article discusses the possibility of improving the thermal characteristics of silicate materials through the use of ash microspheres in the production of piece silicate products, which will significantly reduce the thermal conductivity of the manufactured material. Ash microspheres, being a component of ash and slag waste from the thermal power plants, have a number of valuable properties: firstly, very low density, secondly, closed micro porosity, thirdly, chemical and mineralogical composition prone to reactions under conditions of elevated temperatures and pressures. We have studied the chemical and mineralogical composition as well as physical and mechanical properties of ash microspheres, developed the compositions and technological parameters for the silicate materials production. It has been established that the replacement of quartz sand with ash microspheres as part of the molding mass makes it possible to obtain a silicate brick of medium density class 1.0 and strength sufficient to erect load-bearing enclosing products and structures. Compositions of molding materials using a silicate binder and aluminosilicate ash microspheres using the generally accepted methods were developed and the properties of the obtained silicate material and were studied in accordance with the current GOST requirements for the similar materials.

Abstract: The complexity and a large number of variable factors of the bacterial carbonate mineralization process in the cement stone system, which is a polylineal and polydisperse system, has led to the question of each component’s role in bio consolidation processes. For carbonate biomineralization occurring in cement concrete during its restoration, it is impossible to fully describe the bio consolidation mechanism without studying the effect on individual components of the cement system (aggregate and binder). In the environment of quartz sand (the most common type of aggregate in cement concrete) there is no direct source of calcium, which is found in cement stone, which excludes the influence of abiotic factors (alkalinity of the medium) on the calcium carbonate production by bacterial cultures. This article presents the results of the study of carbonate biomineralization by urolithic bacterial cultures in a filler medium, in which quartz sand of three fractions (1.25–0.63; 0.63–0.315; 0.315–0.16) was used to assess degree and intensity of induction processes. As a result of the study, the physical and chemical factors of the bacterial carbonate mineralization process intensification in quartz sand samples were established. The time boundaries of the appearance of a consolidated layer were revealed within two fractions (0.63–0.315 and 0.315–0.16), which are directly related to the penetration depth of the solution with precursors and the bacterial inoculum by the percolation method. The analysis of the cemented layers’ microstructure is carried out, the features of neoplasms are considered. The type of bacterial culture that exhibits the most active cementing properties - Bacillus pumilus (VKM B-23).

Abstract: The results of the studies aimed at increasing the water resistance of the pressed building materials based on gypsum and magnesia binders due to their modification with active dispersed fillers from secondary resources are presented. The gypsum binder modification was carried out by the joint introduction of carbonate-containing sludge from it into the chemical treatment of thermal power plants and monoammonium phosphate, and of magnesia cement - silica fume and finely ground burnt mines. Physical and mechanical characteristics of the materials’ control samples were determined according to the standards and generally accepted methods. The increase in water resistance of the pressed modified composites was evaluated by changing the softening coefficient. It is shown that when using gypsum binders, an increase in the water resistance of products based on them can be achieved by changing the structure formation of the pressed material and the formation on the elements’ surface of its fine-crystalline structure of the sparingly soluble calcium phosphates’ screening protective films. The increase in water resistance of pressed products made of modified magnesia binders is explained by the appearance of insoluble hydro silicates, hydro aluminates and hydro aluminosilicates of magnesium, in the structure of the hardened artificial stone as well as the formation of a complex combined structure containing coagulation, condensation and crystallization phases. The technical characteristics of the materials obtained are sufficient for their use, in particular, in the building envelope. The possibility of replacing a significant amount of binders with secondary resources has been identified. This allows not only to increase the water resistance of the pressed products on the basis of the proposed modified binders, but also to reduce their cost, as well as free up the land allocated for dumps.

Abstract: The use of finely dispersed fillers for cement concrete is accompanied not only by the cement binder saving, but also by a change in the technological characteristics of the cement mixtures. Depending on the nature of the additive used, both a positive and a negative water-reducing effect can be observed. The nature of the synthetic calcium silicates additives’ effect obtained by the method of sucrose-modified calcium hydro silicates thermolysis on the technological properties of the cement systems is considered. The independent methods determined the polymodal nature of the calcium silicates dispersions. The effect of the various dimensional scales particles on the technological properties of the cement system is determined. Micron particles affect the powder mixture compaction, the optimal content of calcium silicate additives is 20–40%. Nanometric particles, as well as residual freely extractable sucrose, determine the plasticizing effect of the synthetic calcium silicates additives introduction, the maximum manifestation of which is observed when the additive content is 20%. The visco-plastic properties of the “cement - synthetic calcium silicates” system’s mixtures were evaluated at various additive contents.