Hydration of Cement in the Presence of Biocidal Modifiers Based on Metal Hydrosilicates

This article presents the results of a study of the characteristics of hydration and properties of a composite biocidal cement binder containing hydrosilicates of barium, copper or zinc. It was found that copper hydrosilicates block hydration processes, and when zinc hydrosilicates are used, the rate of hydration is determined by the content of silicic acid. The limiting concentrations of biocidal modifiers have been established: zinc hydrosilicates—no more than 4% and copper hydrosilicates—no more than 0.5%, which are advisable to use for the manufacture of a biocidal composite binder. It is shown that modifying additives slow down the setting time, the amount of tricalcium silicate in cement stones increases, and their strength for some compositions decreases. Active binding of portlandite with the formation of calcium hydrosilicates occurs when the content of zinc hydrosilicates is 2%, which leads to an increase in the strength of the materials.

X-ray diffraction of concrete composites of high structural strength and density

Аn analysis of the structure formation of concrete composites, compressive strength of which exceeds 120 MPa and a quantitative analysis of their qualitative composition and hydration products by X-ray diffraction, x-ray spectral analysis. The main factors affecting the physicomechanical parameters of the complex of various nanofillers and the formation of a denser cement stone structure, which mainly includes calcium hydrosilicates, calcium silicate hydroaluminates and hydroaluminates of various basicity, are studied.

Processes of structure and phase formation of aerated concrete of non-autoclave hardening containing ferrosilicon as a gasifier

The paper deals with the structure and phase composition of non-autoclave aerated concrete with a density of 600–800 kg m–3 using ferrosilicon as a gasifier. The conditions of formation of porous structure of aerated concrete and preparation of calcium hydrosilicates were considered. Phase composition of the samples was investigated by means of X-ray phase analysis and differential thermal analysis. Analysis of X-ray patterns showed that the test samples contained tobermorite 11.3 Å (5CaO6SiO25.5H2O), xonotlite (6CaO6SiO2H2O) and -dicalcium silicate hydrate (2CaOSiO2H2O) as a binder. It was established that there is an increase in the content of hydrosilicate phases with an increase in the content of gasifier in the vast majority of cases. The obtained data were confirmed by the results of differential thermal analysis.

Effect of electrolytes with multicharged cations on the strength of stone made of a modified mixed air binder

The possibility of obtaining mixed air binder of high strength and water resistance by using active mineral additives has been considered. In this work, the gypsum binder has been replaced by a combination of hydrated lime with active additives - metakaolin and granulated slag. The ratio effect of the silica component to the binder on the compressive strength of the stone was studied. According to the results of X-ray phase analysis, the presence of tobermorite-like calcium hydrosilicates and the absence of hydrate lime phase were diagnosed in the stone. The influence of electrolyte additives - salts with three-charged cations - on stone hardening kinetics is shown. Increase in the compressive strength of 28-day-old stone from the modified mixed air binder by 5% with the introduction of 1% of the binder mass aluminum sulfate in the mixing water was established. The use of FeCl3 solution for mixing the modified mixed air binder leads to a decrease in the compressive strength of the 28-day-old stone. The mixing of the modified mixed air binder with Al2(SO4)3 solution reduces the time of setting.

Gypsum Compositions Modified with Metallurgical Wastes

The main results of the study of the influence of man-made products of the metallurgical industry on the properties and structure of gypsum binder are presented. It has been proved that the introduction of man-made modifiers, metallurgical dust, and slag leads to an increase in the strength properties and electric conductivity of the material, but, over time, the waste efficiency decreases. The use of Portland cement as an activator leads to the formation of amorphous hydration products based on calcium hydrosilicates, which bind calcium sulfate crystals and provide an increase in the physicomechanical characteristics and electric behavior of the gypsum composite.

CHANGES IN THE STRUCTURAL AND PHASE COMPOSITION OF CEMENT CONCRETE DURING MICROBIOLOGICAL CORROSION

The article considers the change in the structural and phase composition of cement stone made of Portland cement of the CEM I 42.5 N brand in the process of bacterial and fungal corrosion during 6 months when humidified. The X-ray images of cement stone show peaks that characterize the non-hydrated components of Portland cement alite, belite, tricalcium aluminate, four-calcium aluminoferrite and gypsum. By the method of X-ray phase analysis, it is found that during microbiological corrosion, the content of all phases of cement stone decreases. The aspergillus niger van Tieghem fungi have a stronger effect on the structural and phase composition of cement stone. Fungal microorganisms destroy the crystalline phases and absorb amorphous phases – calcium hydrosilicates C-S-H (I) and C-S-H (II) and tobermorite. When bacteria Bacillus subtilis affects the cement stone, the content of the calcite phase increases, which is a product of corrosion, while the action of black mold reduces the intensity of CaCO3 peaks. A decrease in the content of low-base calcium hydrosilicates and ettringite, as well as other crystalline phases, leads to a decrease in the compressive strength of the cement stone. During 6 months of microbiological corrosion of cement concrete under conditions of constant wetting, the compressive strength decreases by about 35 %.

Investigation of the Synthesized Calcium Hydrosilicates Effect on the Properties of Energy-Saving Wall Silicate Blocks Obtained on the Basis of Technogenic Raw Materials

Currently, building blocks are widely used in the construction industry, the use of which contributes to an increase in the speed of construction several times, and also reduces labor costs. To obtain wall blocks, various binders are currently used, but the use of composite binders obtained on the basis of new types of raw materials, is relevant. Among the currently non-used natural raw materials, it is possible to single out aluminosilicate rocks, unconventional for the construction industry, characterized by the presence of clay rocks of mineral formation unfinished stage (aggregates) in their composition. Based on the results of the studies carried out, the effect of the synthesized calcium hydrosilicates addition was established as СSH (I) and С2SH(A) on the properties of energy-saving wall silicate blocks obtained on the basis of technogenic aluminosilicate raw materials. The rational content of the СSH (I) additive is 1.5 wt. %, which contributes to an increase in the products’ strength by 30-50%. The optimum lime content in the raw mix is 12 wt. %. The nature of the influence С2SH(A) on the properties of non-autoclave silicate materials obtained by the method of injection technology, in general, coincides with the addition of CSH (I). The resulting material can be used as a structural material (non-supporting structures) inside low-rise buildings and structures. Low average density of this material (1300–1450 kg/m3) indicates the best thermal properties (the thermal conductivity coefficient of the samples is 0.17 W/m·K).

FEATURES OF THE FORMATION OF THE MICROSTRUCTURE OF GRANULAR AGGREGATES ON DIFFERENT BINDING COMPOSITIONS

This work includes a study of the microstructure of granular aggregates prepared on various binding compositions. The presented work includes three parts devoted to the analysis of the microstructures of granular aggregates taking into account the change in the percentage of the mineral filler in binding compositions. The article deals with the main aspects of the formation of the structure of granular aggregates during the hydration of Portland cement (PC 500-D0-N) and a binder composition (PC 500-D0-N + 10 % quartz sand) prepared in a vortex jet mill. The main regularities of the influence and dispersion of quartz mineral filler (fractions ≤0.16; ≤0.315; ≤0.63 mm) on structure formation during the hydration of binding components differing in the composition and particle dispersion are revealed. The paper analyzes physical and mechanical tests of the most promising samples with a study of their microstructure features. The study of the sample microstructures reveals the general regularities of the growth of crystalline phases of different densities. It is established that the introduction of 1 0% mineral fine-dispersed filler, in the form of quartz sand, contributes to the formation of sub-microcrystalline hydrate phases, which are centers of hydration, additionally binding individual grains of granular aggregates and compacting the structure of the overall system. In all samples, the formation of a block-rhythmic structure is observed, with the presence of individual block-aggregates. There is an overgrowth of microscopic pores with small crystalline neoplasms of calcium hydrosilicates. It is revealed that the structure of granular aggregates prepared on the basis of binder composition No. 1 (BK-1) has higher density than on Portland cement PC 500-D0-N.

Properties of Concretes Incorporating Recycling Waste and Corrosion Susceptibility of Reinforcing Steel Bars

In this paper, properties of concretes incorporating recycling waste and corrosion susceptibility of reinforcing steel bars were studied. It was established that fineness of ground granulated blast furnace slag (GGBFS) and fly ash (FA) and their simultaneous combination have an influence on the kinetics of strength development of Portland cements and concretes. The compressive strength of concrete containing 10% by mass of GGBFS and 10% by mass of FA even exceeds the compressive strength of control concrete by 6.5% and concrete containing 20% by mass of GGBFS by 8.8% after 56 days of hardening. The formation of the extra amount of ettringite, calcium hydrosilicates as well as hydroaluminosilicates causes tightening of a cement matrix of concrete, reducing its water absorption, and improving its resistance to freezing and thawing damage.