The discovery of a two-dimensional carbon form – graphene, consisting of a single layer of atoms connected by a structure of chemical bonds, gave impetus to developing a new wide field of its application in construction. An urgent task is to improve the performance of heavy cement concretes on dense boulders. One of the most effective ways is the use of a new generation of carbon-containing modifiers. The physical and mechanical properties of cement concrete should be regulated at the micro-level by optimizing the process of forming a cement matrix structure. A promising direction is the use of graphene as a carbon-containing modifier. Data from research studies devoted to oxidized thermally expanding graphite are presented. The results of microscopic and laser diffraction granulometric investigations are discussed. The conducted studies allowed the properties of the heavy concrete under study to be assessed. The granulometric composition was analysed using a Fritsch NanoTeс laser particle size measurement device equipped with a dispersion unit in a liquid medium with a total measurement range from 0.01 to 2100 µm. This analysis showed a reduction in size from 574 µm to 22.2 µm. Microscopic examination was performed using a scanning electron microscope TESCAN Mira 3 with a magnification range of x1–x1,000,000. The conducted experimental studies proved the effectiveness of using a carbon-containing additive as a modifier of heavy cement concretes on dense boulders. The use of oxidized thermo expandable graphite allows for a denser packing of the structure and provides an opportunity to create additional cites for new formations. This allows the physical, mechanical and operational characteristics of the final material to be improved.
This article considers the problems of obtaining construction products in winter, along with complex technological processes, in the light of scientific achievements and analysis of influencing factors when solving thermophysical problems, as well as evaluating the results on production indicators, especially those related to economics. The accumulated domestic and foreign experience reflects years of intensive work carried out by scientists and engineers, which continues to this day. In Eastern Siberia and neighbouring regions characterised by a prolonged winter period, construction works are carried out all year round. Special attention should be paid to planning construction activities in winter and developing working documentation in view of the seasonality of work. The material and technical resources of the construction contractor should be taken into account, mainly the feasibility of the operational plans for construction and installation activities and the financing schedule. The paper includes examples of winter construction demonstrating the existing limitations, in particular the increased energy consumption. Some recommendations are given aimed at improving the quality of project documentation.
The negative impact of a dry hot climate on the strength characteristics of heavy concrete is considered. At elevated air temperatures, significant evaporation of moisture from the solidified concrete mix may subse-quently lead to the formation of cracks and other deformations in the concrete body. The abovementioned problems can be prevented by introducing plasticising additives into the concrete mix. The compressive strengths of concrete made of concrete mixtures with different percentages of plasticising agents and ex-posed to elevated temperatures are determined in the study. The compressive strength of the studied sam-ples was determined in accordance with GOST 10180-2012 “Concretes. Methods for determining the strength of the control samples." The optimum amount of the additive CentramentAir 202 in concrete is 0.25% by weight of cement, while the increase in compressive strength of concrete is 11.5% at the age of 14 days and 1.7% at the age of 28 days, in relation to the compressive strength of the control composition. The in-troduction of the hyperplasticiser MC-PowerFlow 2695 in the amount of 0.4 to 0.6% by weight of cement reduces the compressive strength of concrete samples by an average of 29% at the age of 14 days and by 39.4% at the age of 28 days. Superplasticiser CentramentN 101 in an amount of from 0.6 to 1% by weight of cement reduces the compressive strength of concrete samples by 11.5% ÷ 35% at the age of 14 days and by 19–37.4% at the age of 28 days. The optimal amount of MC-Techniflow 70 additive in concrete is 1.2% by weight of cement, while the compressive strength of concrete is increased by 2.1% at the age of 14 days and by 0.6% at the age of 28 days. According to the results of the experiments, a highly plasticis-ing additive MC-Techniflow 70 with an optimal dosage in the amount of 1.2% by weight of cement was acknowledged as effective, allowing to obtain high strength characteristics both at 14 days of age (29.2 MPa) and at 28 days of normal hardening (35.0 MPa).
Reducing the consumption of cement in the production of concrete mixtures has been a topical issue in the construction industry. The study aims to optimise the structure of concrete stone by selecting the particle size distribution of the components to nanoscale values. Such microfillers include silica fume, metakaolin, ashes, nanographite/graphene, etc. Thus, producing additives of complex action having a plasticising ability, as well as containing finely dispersed fillers forming binding material, is promising. Expandable graphite was dispersed in an aqueous medium and subjected to ultrasonic treatment using an ultrasonic bath with an 80 W generator. The particle size distribution in the graph-ite-containing suspension was studied using a laser diffraction particle analyser FritschNanoTeс with a wet dispersion system (measuring range of 0.01 to 2100 μm). Microscopic examination was carried out using a scanning electron microscope TESCAN Mira 3 with a magnification range of up to 1,000,000 times. In the present work, the physical-mechanical properties of heavyweight concrete containing modified oxidised expandable graphite were investigated. The results of microscopy and particle size distribution analysis of the graphite-containing suspension are presented. The research indicates the efficiency of ultrasonic treatment of a graphite-containing suspension and its effect on the strength characteristics of concrete. The presented results demonstrate the potential of ultrasonic treatment for additional disintegration of graphite particles in a graphite-containing suspension improving the physi-cal and mechanical characteristics of a concrete stone by adding this suspension to its composition.
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