The impregnation of the exterior surface of a masonry wall with a water repellent is a common intervention in (historic) building renovation and maintenance. Such treatments, whilst degrading at the surface with time under influence of ultra violet light, remain effective below the surface several decades after their application. During renovation works of masonry previously treated with a water repellent, the question arises whether it is necessary to repeat the hydrophobic treatment of the entire masonry after repointing. Opposing opinions exist with this regard, but no research clearly supporting one or the other. This research investigates for the first time the effect of hydrophobic treatment when applied on previously treated and repointed masonry walls. Small masonry walls were subjected to rain periods in the laboratory and their water uptake and drying behaviour were studied. Moreover, this laboratory research was followed by 30 months of outdoor exposition of the masonry specimens. The following cases were considered: (1) wall treated with water repellent, (2) wall treated with water repellent, followed by repointing but without new water repellent treatment, (3) wall treated with water repellent, followed by repointing and retreatment. This was done for three different types of pointing mortar: ordinary Portland cement and natural hydraulic lime with standard sand, and natural hydraulic lime with sand with one grain size. The results show that, after prolonged rain periods, the water uptake by repointed but not retreated masonry is comparable to that of untreated, non-hydrophobic masonry, whereas drying is considerably slower. This leads to a high saturation degree in repointed but not retreated masonry, which, in turn, increases the risk of damage to the masonry by e.g. frost. Therefore, retreating repointed hydrophobic masonry should definitively be considered.

In circular concrete design, beside cement replacement with more environmentally friendly cement types, there is also an urgent need for sand replacement with fine recycled concrete aggregates (fRCA). The variations in physical and chemical properties of fRCA and lack of standards for their quality evaluation are the main reasons for not yet using fRCA in new concrete. In this study, an in-depth characterization of different Dutch fRCA is performed in order to examine suitability of fRCA as an alternative material for river sand and define indicators for fRCA quality. These indicators eventually can be related to concrete mix design and performance, so that fRCA can be classified as a material that can be used in structural concrete elements. This is achieved with physical, chemical and mineralogical characterization of individual and total fractions (0–0.250 mm, 0.250–4 mm and 0–4 mm). The physical properties such as grading, density, surface area, water absorption and cement paste content of fRCA were tested. The chemical analyses include quantification of element composition with X-ray fluorescence spectrometry (XRF) and carbonate content with thermogravimetry and mass spectrometry (TG-MS). Potential contamination (chlorides and sulfates) and reactivity of selected fractions were evaluated. In addition, qualitative and quantitative phase analyses with X-ray diffraction (XRD) combined with Rietveld refinement method were performed and supported by optical polarizing-and-fluorescence microscopic (PFM) study. Based on combined experimental approaches, characteristic quality indicators were defined for fRCA. These indicators showed that fRCA were uncontaminated and nonreactive. Despite fRCA were from different origins, they had similar chemical and mineralogical composition and contained comparative chloride content. In contrast, the content and surface area of fine fraction (0–0.250 mm) and particle size distribution of fRCA varied with the source. With this it can be assumed that fRCA will have different effect on the properties of the new concrete.

The elastic modulus of corrosion product (E_cp) has been reported with significant variations in the literature. This study aims to investigate the E_cp of naturally-generated chloride-induced corrosion products formed in different concrete mixes. Microstructural characterization was conducted through nano-indentation, electron microscopy and Raman spectroscopy. The corrosion products were mainly composed of a goethite matrix with portions of maghemite, independently of the concrete composition. Microscopic analysis suggest that layers of corrosion products grow at different times and under different physico-chemical conditions. Our measurements showed that E_cp varied between 80−100 GPa, which can be suggested for numerical models of corrosion induced cracking.

Compatibility of repair materials in conservation is a widely desired goal, but difficult to achieve. In this research, the compatibility of four commercial stone repair mortars, commonly used in conservation practice in the Netherlands and neighbouring countries, is discussed. In order to do so, they have been characterized in laboratory. The composition of the repair mortars, their content of soluble salts, porosity and pore size distribution, hygric dilation and flexural and compressive strength were measured. The effect of curing was assessed by comparing specimens cured in laboratory and under outdoor conditions. The effect of 3 years outdoor exposure on the curing and weathering of the mortars was evaluated. The results show that the composition of the selected mortars varies significantly, even though, based on their technical information sheets, they appeared to be similar. Consequently, their moisture transport properties differ significantly. As expected, both the type of binder and the porosity were shown to affect the mechanical properties of the mortar: the mortar based on an inorganic polymer binder showed the highest mechanical strength; the most porous, lime- or lime-cement-based mortars, showed the lowest mechanical strength. Based on compatibility criteria defined in literature and the results obtained in this research, an attempt was made to assess the technical compatibility of the selected mortars with building stones commonly used in the Netherlands. It was found that some requirements are hard to be fulfilled and not all requirements can be fulfilled at the same time. Besides, technical sheets of commercial mortars are often incomplete; therefore repair mortars can hardly be selected based only on the properties reported by the producers.

The Service life evaluation of reinforced concrete structures is usually limited to initiation of corrosion, whilst in practice corrosion in many structures has already reached the propagation stage. To better understand the processes that lead to the cracking and detachment of concrete cover during this phase, knowledge of corrosion products’ development over time is required. This paper investigates corrosion products found in blast furnace slag cement concrete, in which natural carbonation acted upon original chloride-induced corrosion. The sample was cast in 1998, after curing subjected to wet-dry cycles to enhance chloride penetration, and later was exposed to unsheltered outdoor conditions. Corrosion products and textures at the concrete-steel interface and late carbonate veinlets within them have been characterized by a combination of optical microscopy, SEM, Raman spectroscopy and CT scanning.

Although reinforcement corrosion is a well-known issue, which are the locations of the steel/concrete interface most sensitive to pitting corrosion is still an unclear issue. In this study, X-ray computed tomography is used to characterize eight 20-years-old reinforced concrete cores naturally deteriorated due to chloride-induced corrosion. The deepest and most frequent corrosion pits were observed at the portion of the reinforcement oriented to the outdoor environment and in proximity to interfacial air voids. Therefore, the presence of interfacial air voids should be considered as a relevant factor when assessing the risk of corrosion of reinforced concrete structures.

Although corrosion of reinforcement is a well-known issue for the construction industry, there are still open questions about some fundamentals of corrosion in reinforced concrete. These points include, among others, which are the most sensitive locations of the steel/concrete interface for pitting corrosion to initiate and to propagate. In this study, X-ray computed tomography (CT-scan) is used to characterize eight 20-years-old reinforced concrete cores naturally deteriorated due to chloride-induced corrosion. The volume loss due to corrosion of the reinforcement was quantified through image analysis of CT-scans. The volume loss of the steel was found to be higher for steel rebars embedded in Portland cement specimens rather than in blended cement specimens. Furthermore, CT-scans revealed that the deepest and most frequent corrosion pits, as well as the consequent highest volume loss of steel, were present at the portion of the reinforcement closer to the outdoor environment and in proximity to air voids at the steel/concrete interface. As a consequence, the highest decrease of structural performance of the rebars would be likely localized at those locations. Therefore, the presence of interfacial air voids should be considered as relevant factor when assessing the risk of corrosion of reinforced concrete structures.

Tuffstone elements with a large length/width ratio often suffer damage in the form of cracks parallel to the surface and spalling of the outer layer. This study aimed at verifying if this damage may be the result of a differential dilation between parts with different moisture content. The research, carried out on Ettringen and Weibern tuff, comprised a weathering test and measurements of porosity, moisture transport and hygric behaviour of the stones, supplemented by environmental X-ray diffraction analyses. Results support the hypothesis that moisture gradients in tuff elements may enhance decay in this stone.