Abstract
Aggregate segregation in concretes, especially in lightweight aggregate concretes (LWAC), is a pathology that can seriously impact on different material properties, both in terms of mechanical strength and durability. Some studies have already analysed the impact of this phenomenon in the compressive strength of LWAC , almost always adopting segregation quantification methods based on the comparison of variables such as weight or density measured in sections extracted from cylindrical samples. Although the methods used so far are simple and easy to apply, in certain circumstances they may not offer sufficient accuracy to measure the phenomenon. Moreover, the analysis of segregation in LWAC, which due to the lower density of aggregates in relation to the mortar matrix occurs in the opposite direction to the segregation of conventional concretes (from bottom to top), has not been widely studied so far. The analysis of the cross sections of cylindrical concrete samples through image analysis techniques has been increasingly used to estimate parameters related to the distribution of materials inside them. This study aims to measure the impact of segregation on the compressive strength of LWAC cylindrical specimens, employing an image analysis technique capable of quantifying the phenomenon with a more accurate segregation index. During the experimental campaign 22 scenarios were defined, combining different types of aggregate, vibration methods and vibration times, to achieve different levels of segregation. Among the main results it can be noted that the impact of the type of moulding (one layer vs. two layers) considerably affected the mechanical properties of concrete, with concretes vibrated in two layers showing a maximum reduction in compressive strength due to segregation of 9%, while concretes vibrated in only one layer showed reductions ranging from 63% to 118%. Analyzing the type of rupture of the samples, the study identifies the appearance of well-defined compression cones in samples where segregation is excessive, with 90% of the cases presenting this type of rupture and that the size of the compression cone increases as the effect of segregation is accentuated.
Highlights
Because of its advantageous properties, including low density, good thermal insulation and fire resistance, lightweight aggregate concrete (LWAC) has been extensively studied as both structural and nonstructural construction material [1]
For each combination ten results were obtained, eight of them coming from the image analysis performed on the cross sections of four samples and another two coming from the compression strength tests performed on two samples
In order to analyse the influence of segregation on the compressive strength of LWAC, it was first necessary to make sure that different degrees of segregation were caused in the samples, only to be able to study the effect of this phenomenon on the reduction of resistance
Summary
Because of its advantageous properties, including low density, good thermal insulation and fire resistance, lightweight aggregate concrete (LWAC) has been extensively studied as both structural and nonstructural construction material [1]. Sometimes lightweight aggregate concrete may be the most suitable solution for certain types of civil engineering constructions, as thanks to their reduced density (usually from 1500 to 2000 kg/cm3 [2]), they may present better properties than conventional concrete and may be interesting in applications like long span bridges, high rise buildings, and special structures such as floating and offshore platforms [3]. Good compaction of LWAC is crucial to eliminate the trapped air in the mixture and to ensure that the material will fill all the voids in the formworks, the compaction is one of the biggest problems in fresh LWAC because the excessive time of vibration can produce the phenomenon of segregation. Different studies show that LWACs are susceptible to present segregation of aggregates and different factors
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