Rui Neves

This research investigates the historic mortars (Aggregate/Binder (A/B) ratio) of a historical patrimony building, dating from the 15th century, in Algeria, for restoration purposes. It is well known that thorough characterization is essential for successful restoration. To this end, several techniques, including Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and X-ray Fluorescence (XRF), optical microscope were used to characterize the historic mortars. A mechanical test was used to characterize the compressive strength of a historic mortar. For a comprehensive characterization, A/B ratios were estimated using both Digital Image Analyses (DIA) and chemical analyses. The results obtained provided clear information on the fractions of aggregate and binder. The A/B ratios found of the historic mortars were in line with those found in the literature in historical building. It should be noted that chemical analyses were applied to all mortars, whereas the DIA method was limited to a few mortars (not applicable to earth-based mortars). The results of the A/B ratio for both methods are compared. Nevertheless, the estimation of the A/B ratios of historic mortars using the DIA method alone is insufficient and needs to be strengthened with robust methods such as the chemical one for more accurate and reliable estimation.

Fiber corrosion impacts on the mechanical performance of steel fiber reinforced concrete (SFRC) have been considered minor. However, this may be true only for ordinary corrosion conditions. For severe corrosion conditions, such as stray currents, the impacts must be investigated. This study addresses the influence of corrosion at different levels, including severe corrosion, on the flexural performance of SFRC. An experimental study focused on a three-point bending test, considering as variables the corrosion level, the fiber content, and the fiber aspect ratio. It was confirmed that corrosion can shift fiber failure from pullout to rupture, and it was found that corrosion can shorten flexural performance by as much as 80%. Therefore, corrosion impacts, in certain conditions, cannot be considered minor; rather, they have to be considered significant.

Carbonation is one of the critical durability issues in reinforced concrete structures in terms of their structural integrity and safety and may cause the fatal deterioration and corrosion of steel reinforcement if ignored. Many researchers have performed a considerable number of studies to predict the carbonation of concrete structures. However, it is still challenging to predict the carbonation depth or carbonation coefficient, as they depend on various factors. Therefore, creating a model that can learn from available data using Data Driven Techniques (DDT) is a step forward in this research field. This study provides new approaches to predict the carbonation coefficient of concrete through Model Tree (MT), Random Forest (RF) and Multi-Gene Genetic Programming (MGGP) approaches. With 827 case studies, the predicted models can be seen as a function of a set of conditioning factors, which are statistically significant in explaining the carbonation mechanism. The results obtained through MT, RF and MGGP were compared with those obtained through Multiple Linear Regression (MLR), Artificial Neural Networks (ANNs) and Genetic Programming (which were previously developed). The results reveal that the MT, RF and MGGP perform better than the previous models. Moreover, the MT technique displays its output in terms of series of equations, RF as multiple trees and MGGP in form of a single equation, which are more user-friendly and applicable in practice.

The paper describes the main mechanisms of carbonation and chloride penetration into concrete and how the rate of penetration can be measured with laboratory tests. It is also discussed why nondestructive test (NDT) methods for measuring directly the resistance of aged field concrete to carbonation or chloride penetration are not available. Only destructive tests are applicable which, given the very high‐spatial variability encountered, become prohibitive in terms of costs and damage. The only way to assess the resistance of aged field concrete to carbonation or chloride penetration is through surrogate tests measuring variables that are linked to it. There are two standardized test methods with potential as surrogate tests, as they are fast and entirely nondestructive: the coefficient of air permeability kT (“Torrent” method) and the electrical resistivity ρ (“Wenner” method). Data obtained on‐site with both methods are presented, confirming their potential to assess the resistance of aged field concrete to carbonation or chloride penetration.

Textile reinforced concrete (TRC) is an emerging construction material with interesting potential concerning sustainability, providing corrosion-free and lightweight solutions. Ordinarily, fiber bundles, impregnated with resin, are used. In this research the performance of reinforcement with unresin fibers is investigated. Control of cracking is considered the key performance factor and is assessed through tensile testing. However, economic and environmental aspects are addressed as well. Then, four different mixes/matrices were considered, without the addition of special/expensive admixtures. TRC ties were subject to direct tension tests, with load and deformation monitoring to assess the influence of mechanical reinforcement ratio on the cracking, failure and toughness of these composites, as well as of the matrix properties on the maximum load. It was observed that at a macro-level TRC behaves like conventional reinforced concrete, concerning crack control. Based on the maximum loads attained at the different composites, it was found that this particular TRC is economically viable. It is suggested that matrix workability may influence the maximum load.

The derivation of a formula to compute the permeability coefficient in the commented paper assumes that the mass flow is homogeneous in a homogeneous layer of a specimen. This assumption is not correct when there is also, at least, one heterogeneous layer. Moreover, a mathematical lapse was found on one equation, that would prevent the right computation of the permeability coefficient, even if the assumption was correct. Although this does not invalidate the major conclusions of the study and has not an outstanding effect on the presented results, for the sake of rigor and sound background for future studies in this field, corrections to the published formulas and model are proposed.

This research addresses the replacement of cement by an untreated waste from the petrochemical industry. The effects of partial replacement of cement by spent fluid cracking catalyst (SFCC) on properties of mortar were determined. In this study, a series of mortar mixes was prepared with replacement ratios of 0%, 3%, 6%, and 12%. Furthermore, performance enhancing factors such as SFCC treatment or use of plasticizers were avoided. Workability, compressive strength, and durability related properties were assessed. An improvement regarding resistance to chloride penetration was observed, as well as that, when curing in salt water, the use of SFCC may be advantageous regarding compressive strength.