Post-fire prediction of residual compressive strength of mortars using ultrasonic testing

The most used binders for coating and laying mortars are Portland cement and hydrated lime. The hydrated lime has been used for centuries due to its properties. However, the construction field has been modernizing and seeking improvements, which led to the use of industrialized mortars. Those mortars are made from a controlled manufacturing and dosing process and typically do not contain lime. Instead, it contains chemical additives that provide the same properties of lime(workability and water retention), without interfering with the compressive strength. Nevertheless, there are still gaps regarding the performance of these mortars, mainly related to the safety of buildings in fire situations. To evaluate these materials regarding a fire situation, the residual compressive strength was identified as one of the most important parameters. In addition, nondestructive tests, such as the ultrasonic test, has been proved to be a great tool to help in this evaluation. In this context, this work aims to investigate the relationship between the residual compressive strength and the UPV of industrialized mortars and mortars with lime, for usual strength classes (laying and coating mortars) subjected to high temperatures. From the results, lime mortars showed lower values for residual UPV. Moreover, the addition of lime was found to be a relevant parameter in evaluating the residual UPV of mortars, while the strength class, for a range of 5-20 MPa, did not show high relevance, indicating that mortars with and without lime should be studied individually. In addition, unlike many studies that propose a correlation without any standard methodology, this work proposes a correlation following a standard methodology and proves, through a validation with data from literature, that residual UPV and residual compressive strength are correlated through a logarithmic regression. Therefore, this work makes a great contribution by providing an estimation of compressive strength through an NDT testing, helping practitioners to adopt a thumb rule in the lab and in the field, especially in post-fire evaluation.