Investigating the Effects of Additives and Protective Coatings on the Mechanical Properties of Concrete Under Sulfate Attack and Salt Crystallization Using Best-Worst Method (BWM) Decision Techniques

Abstract

An investigation of causes and impacts of concrete failure in contact with wastewater tends to be more dependent on the type of concrete made. For this, to decide the strength of all types of concrete against failure factors, the Best Worst Method (BWM), as one of the modern multicriteria decision-making techniques, was used. In this model, 5 criteria and 12 options were used. In the end, according to ranking processes, mixed designs were developed and tested in a laboratory environment. The permeation of soluble salts into concrete structures and their chemical reactions with hydration products, the drying and wetting of these structures over the years, the recrystallization of these salts inside cavities, and internal pressures cause damage to concrete. To reduce maintenance costs and improve concrete durability, it is pivotal to investigate solutions to protect concrete against aggressive environments. One of these solutions is to provide suitable material additives and concrete surface coating. The present study aimed to investigate the effects of additives, including latex polymer and microsilica, and protective coatings such as epoxy and crystallizing coatings on concrete durability under the simultaneous effects of sulfate attack and salt crystallization. In this connection, concrete samples were both submerged in sodium sulfate solution and were subjected to more successive wetting and drying cycles. Then, using compressive strength and indirect tensile strength tests, sample concrete strength decrease against failure factors was determined. Results indicated that the appropriate amount of additives to deal with the simultaneous failure effects of sulfate attack and salt crystallization on compressive strength and indirect tensile strength tests varied, with the [concrete sample] strength experiencing a minimum decrease in compressive strength tests using a 10% of latex and 5% of microsilica, and in indirect tensile strength tests using 20% of latex and 10% of microsilica. Using epoxy coating was found to have a better performance than crystallizing coating in increasing concrete durability. Also, the simultaneous use of additives and coatings had a significant effect on increasing concrete durability.