According to the results of the experiments, the mobility of the concrete mixture is increased by 12%, the fluidity - by 83%. The strength of concrete was increased by 19%, its water resistance - by 22%. In addition, the ultimate deformations of concrete decreased by 14%, and the modulus of elasticity increased by 11%, the quantitative increase in the technological and rheological characteristics of the resulting self-compacting concrete was 83%.
– In modern conditions of rising prices for energy, raw materials, machinery and equipment, taking into account inflation and tightening requirements for the quality of building materials, the requirements for environmental friendliness and efficiency of construction are also growing, – commented Sergey Stelmakh, a member of the scientific group, associate professor of the Department of Engineering Geology, Foundations and Foundations of DSTU. – Today, the development of the most technologically advanced, high-functional concrete mixes of a new generation is particularly relevant, which make it possible to achieve savings on all key points: transportation, laying, compaction, care of hardening concrete, the timing of the construction of buildings and structures.
According to construction technologists, self-sealing concrete mixes allow to bypass such problems of modern construction as high density of reinforcement, the impossibility of manual or machine compaction of concrete mix in hard-to-reach concrete structures.
Fly ash from thermal power plants (so-called fly ash), ground granulated blast furnace slag, metacaolin, and microsilicon were used as nanomodifiers in self-compacting concretes with improved performance characteristics.
– The mineral additive activates the hydration processes of the binder solution and contributes to an increase in the volume and degree of crystallinity of the hydrates formed, which significantly increases the microhardness of hydrate fillers, – said Sergey Stelmakh.
DSTU scientists are confident that the use of fine mineral additives can improve the technological characteristics of self-compacting concrete mixtures and the physical and mechanical properties of concrete. At the same time, the most significant effect in the mentioned improvement can be achieved by using rationally selected combinations and dosages of mineral additives together with a superplasticizer that optimizes the granulometric composition of aggregates, which makes it possible to obtain high-strength concrete as a result.
– The composition of self-compacting concrete mixes includes superplasticizers containing various dispersed materials, such as Portland cement, mineral additives, fillers, fine and very fine sand. The addition of a superplasticizer to the composition of the concrete mixture allows you to preserve the rheological properties of the concrete mixture – its viscosity – for a time sufficient for transporting and molding products and structures from it, – explained the scientific leader of the Student Scientific Society "Promising Technologies of effective Building Materials" of DSTU Diana Elshaeva. – Different types of superplasticizers based on polycarboxylates, lignosulfonic acid, melamine formaldehyde sulfonic acid, naphthalene formaldehyde sulfate acid have different effects on the fluidity and loss of fluidity of concrete mixtures. Moreover, the mechanism of action of the additive, as well as its exact dosage, are individual and need to be adjusted for each specific case.
According to Sergey Stelmakh, the combined inclusion of a superplasticizer and a mineral additive in a self-compacting concrete mixture increases the effect compared to using only one of these types of additives.
Using the example of cement stone, DSTU scientists presented differences in the relative value of the modulus of elasticity when using only a superplasticizer (an increase up to 10%) and when using a superplasticizer with a mineral additive (an increase up to 20%).
Scientists managed to find out that the use of complex additives (chemical and mineral) allows to reduce cement consumption, maintain the workability of concrete mixtures for a long time, increase the density of the structure and, as a result, the strength and durability of concrete during operation.
Experimentally, it was found that the partial replacement of Portland cement with fly ash increases the water demand and plastic viscosity of the cement mass by 40%.
Note that the deformation measurements of concrete samples were carried out by a chain of strain gauges on experimental prisms. In addition, experimental prisms were tested for axial compression and axial tension at a constant strain rate to obtain the strength and deformation characteristics of concrete. The water resistance of the samples was determined by the "wet spot" method – by the maximum water pressure, at which no seepage was observed on four of the six samples.
All manufactured prototypes were tempered under normal conditions at a temperature of 20 ± 2 ° C for 28 days.
The results of the research of DSTU construction technologists can be used by construction organizations and enterprises producing self-compacting concrete.
The study was led by the Vice-Rector for Academic Affairs and International Activities of DSTU, Doctor of Technical Sciences, Professor Alexey Beskopylny and corresponding member of the RAASN, Doctor of Technical Sciences, Professor Levon Mailyan.
The conducted research corresponds to the Priority 2030 strategic academic leadership program in the direction of "New eco-friendly materials for the construction of buildings and structures from plant raw materials and agricultural waste".
The study is published in the scientific article titled Development of High-Tech Self-Compacting Concreate Mixtures Based on Nano-Modifiers of Various Types in the journal Materials, Volume 15, issue 8, April 2022. The full text of the article can be accessed at https://www.mdpi.com/1996-1944/15/8/2739