Segregación en hormigones ligeros

Resumo

Lightweight aggregate concrete (LWAC) is a material essentially composed of a mixture of Portland cement, water and lightweight aggregates, such as expanded clay, perlite, and vermiculite, among others. This mixture is used in construction for various purposes, both structural and filler, such as precast slabs and panels, structural elements of different geometries, filling concrete, slope formation, among others. The use of LWAC dates back to ancient civilizations, such as the Romans, who already used a mixture of lime, natural pozzolans, and volcanic rocks to make the first concretes. Among the main advantages of LWAC are the reduction of the structure's weight, greater thermal and acoustic efficiency, easier transport and handling, and, because of its low density, a consequent reduction in material consumption and construction costs. Above all, because of the large difference in densities between the materials used in producing LWAC, this type of concrete is subject to a pathology known as segregation. Segregation occurs when lighter aggregates separate from the mortar matrix and move to the higher parts of the concrete, while heavier aggregates move to the lower regions. This phenomenon can prejudice the quality and durability of lightweight concrete, reducing its strength and leading to structural failure. It is therefore essential to study the factors that influence its occurrence and to seek solutions to minimize it during concrete production, transport, and placement. Among the objectives of this research are the quantification of segregation in LWAC, the evaluation of its impact on the mechanical properties and durability of these concretes as well as the proposal of measures to reduce the occurrence and intensity of the phenomenon. To achieve these objectives, this study is based on three main questions: how to quantify the segregation phenomenon; what is its impact on the mechanical properties and durability of these concretes; and how to establish measures to reduce its occurrence and intensity. Over the years, several experimental studies have been carried out to try to establish methods to quantify segregation, but there is still no universally accepted method for its determination. Currently, there are some techniques based on density measurement; image analysis as well as ultrasonic pulse velocity measurement (UPV) that are being developed to quantify segregation in a more accurate and non-destructive way. The application of these techniques can help establish a reliable segregation index for lightweight concrete, allowing the impact of segregation on material performance to be accurately assessed. In this sense, this research performs an analysis of several existing segregation quantification methods; delves into the feasibility analysis of applying non- destructive techniques to estimate the pathology; presents a new method based on image analysis capable of providing, as a result, a segregation index and, finally, evaluates the impact of segregation on the mechanical strength, structural efficiency and durability of HAL. Moreover, the research presents different results related to the concrete dosage parameters and the use of different supplementary cementitious materials that can affect the segregation of the material.