Ключевые слова: variatropic concrete

Variatropic concrete compressive strength prediction under freeze-thaw conditions using machine learning methods

https://doi.org/10.58224/2618-7183-2025-8-6-10
Аннотация
The introduction of intelligent models, in particular using machine learning methods, opens up prospects for the development of the construction industry. The construction of regression models for predicting the physical and mechanical properties of various types of building materials is a promising and relevant area. The use of such models makes it possible to take into account complex and multifactorial dependencies, while minimizing the influence of the human factor. In the present study, variatropic concrete B30, obtained by centrifugation, acts as the test material. The dataset (351 objects) was assembled during laboratory studies to study the effect of freeze-thaw cycles on the strength characteristics of the material. Using the computer vision method based on the convolutional neural network U-Net, the damage on each of the concrete layers was assessed on different cycles. 4 machine learning models for predicting compressive strength were trained and tested on the collected dataset: Ridge Regression (RR), Random Forest (RF), CatBoost (CB) and Multi-layer Perceptron (MLP). The hyperparameters of the models were optimized using Grid Search + 3-fold cross-validation. As a result of testing the algorithms on a test sample, the best quality metrics were demonstrated by tree architectures: MAE for RF and CB 0.09 and 0.17 MPa, respectively, R2 = 0.99. The results are supplemented by SHAP analysis. The results obtained are a useful tool for optimizing the composition of variatropic concretes used under aggressive conditions.
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Study of thermophysical characteristics of variatropic concretes

https://doi.org/10.58224/2618-7183-2024-7-4-2
Аннотация
An important task in the development of the construction industry is to find rational technologies, materials and solutions that ensure energy efficiency in construction and create conditions for obtaining energy-saving products and structures for various construction projects. At the same time, the issue of structures made of the same material, but having a difference in their properties and characteristics in thickness, the so-called variatropic building material, which, due to differences in structure and properties, ensures variatropic properties of the building structure itself, has been poorly studied. The goal of this study was to eliminate a significant scientific deficit, consisting in the absence of a systematized knowledge base on the structure and thermophysical properties of variatropic products and structures made of concrete or reinforced concrete. The modeling was performed in the ANSYS environment (Ansys version 2024 R1). An element selected for modeling was a ring-section heavy concrete pillar with an outer diameter of 450 mm and an inner diameter of 150 mm. Variatropy was specified by conventionally dividing the element’s cross-section into several layers with different physical and mechanical properties: three for centrifuged concrete and four for vibrocentrifuged concrete. In the course of modeling, the authors determined the main initial data for the calculations, and based on the results of the calculations, dependencies were established confirming the improvement of the concrete’s heat-insulating properties due to the use of centrifugal compaction technology. The phenomenon of variatropy leads to an increase in heat-transfer resistance – from 13% for centrifuged concrete to 23% for vibrocentrifuged concrete in comparison with vibrated concrete. At the same time, vibrocentrifuged concrete turned out to be 8% more efficient than centrifuged concrete in terms of “heat-transfer resistance”. The conducted modeling shows that variatropic concrete is promising for further research and practical application in terms of its thermophysical characteristics.
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Structure and Properties of Variatropic Concrete Combined Modified with Nano- and Micro-silica

https://doi.org/10.58224/2618-7183-2024-7-2-3
Аннотация
The lack of systematic information on the influence of the combined modification of variatropic concrete on their characteristics was revealed. The purpose of this work was to study the influence of the type of modifying additive, namely micro-silica, nano silica and their combination on the properties of concrete made using three different technologies - vibration (VC), centrifugation (CC) and vibration centrifugation (VCC). Concrete elements made using centrifugal compaction technology were subjected to additional sawing. Three types of modifiers were studied: micro-silica (MS), nano silica (NS) and their combinations. To determine the degree of effectiveness of each recipe solution, the following main characteristics were monitored: workability of concrete mixtures; density of hardened composites; compressive strength (CS) and water absorption (WA). When modifying MS, the greatest effect for VC, CC and VCC was observed with its amount of 8% instead of part of the cement. CS gains were up to 17% for VCC, and WA decreased to 25% for VCC. The NS modification showed the greatest effectiveness at a dosage of 4%. CS gains were up to 19% and WA decreased to 28% for VCC. A combined modifier of 75% MS and 25% NS showed the greatest effectiveness. CS increased up to 17% compared to effective dosages of single-component modifiers. The effectiveness of VCC, characterized by the percentage increase in CS, was up to 55% higher in comparison with VC and up to 25% higher in comparison with CC. WA of concrete decreased to 14% in comparison with effective dosages of one-component modifiers. The effectiveness of VCC, characterized by the percentage reduction in WA, was up to 30% higher compared to VC and up to 12% higher compared to CC. The greatest efficiency of all types of modifiers was observed in combination with the synthesized vibration centrifugation technology.
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