Influence of Variatropy on the Evaluation of Strength Properties and Structure Formation of Concrete under Freeze-Thaw Cycles

Abstract

The resistance of concrete structures to the impact of cyclic freezing and thawing is one of the key long-term characteristics, which further determines the operation and its service life. To date, the resistance to alternating freeze-thawing cycles under various operating conditions of concrete structures has been little studied related to several manufacturing processes: simple vibrated, variotropic centrifuged, and improved variotropic vibrocentrifuged. The purpose of this study is to investigate the effect of heavy concrete manufacturing technology on the resistance of concrete to alternate freezing and thawing in an aggressive environment of 5% sodium chloride solution, as well as to study the trend in strength characteristics and weight loss of vibrated, centrifuged and vibrocentrifuged concretes after a series of freezing and thawing cycles. Standardized techniques for assessing the characteristics of concrete and scanning electron microscopy were used. Vibrated, centrifuged, and vibrocentrifuged concretes made from the same raw materials have differences in weight loss of 4.5%, 3%, and 2%, respectively, and in strength of 15.0%, 13.5%, and 10%, respectively, when tested for frost resistance in similar environments after 15 cycles by the accelerated method. Centrifuged and especially vibrocentrifuged variotropic concrete have greater resistance and endurance to cycles of alternate freezing and thawing compared to vibrated.

Prediction of the Compressive Strength of Vibrocentrifuged Concrete Using Machine Learning Methods

“…After molding, the samples were kept for 24 h, and then were taken from the molds and kept for 28 days in appropriate conditions. Then, they were subjected to various types of aggressive influences, such as freeze-thaw cycles; chloride attack, sulfate attack, and wet-dry cycles [5,[8][9][10]42]. The compressive strength of vibrocentrifuged concrete was 58.2 MPa.…”

“…Particular attention should also be paid to predicting the strength characteristics of vibrocentrifuged concrete. Structures made from vibrocentrifuged concrete must withstand extreme operating conditions, and accurate prediction of their properties is important, first of all, to ensure the required level of safety [6][7][8][9][10]. Along with traditional methods for calculating strength, which involve the formation of a sample and its subsequent testing in laboratory conditions, modern, fast and equally predictive methods of machine learning are used today [11][12][13][14].…”

“…The review made it possible to select the most suitable methods for accurately predicting the strength of concrete with a non-uniform cross-section of elements in terms of thickness. In this regard, there is a scientific deficit, which comprises providing methods for predicting the characteristics of concrete characterized by different cross-sectional properties (the so-called variatropy) [5,[8][9][10]42,43]. Hence, the uniqueness of this work can be discerned in three dimensions: theoretical, applied, and recommendatory.…”

Prediction of the Properties of Vibro-Centrifuged Variatropic Concrete in Aggressive Environments Using Machine Learning Methods

“…After molding, the samples were kept in the molds for 24 h, then removed from the molds and hardened under natural conditions until they reached 28 days of age. The manufactured ring-section elements were sawed on a stone-cutting machine into samples of standard sizes and shapes and were exposed to cycles of freezing and thawing, wetting and drying, and chloride and sulfate attacks [44][45][46][47].…”

“…As a result of laboratory tests to determine the compressive strength of vibro-centrifuged variatropic concrete, a dataset was generated that describes the impact of aggressive environmental factors on the final characteristics [44][45][46][47].…”