Search Results (118)

The dramatic increase in urban construction waste poses severe environmental challenges. Utilizing waste concrete to produce recycled aggregates (RA) for manufacturing recycled concrete (RC) represents an effective strategy for resource utilization. However, inherent defects in RA, such as high porosity, microcracks, and adherent old mortar layers, lead to significant performance degradation of the resulting RC, limiting its widespread application. Traditional methods for enhancing RA often suffer from limitations, including high energy consumption, increased costs, or the introduction of new pollutants. MICP offers an innovative approach for enhancing RC performance. This technique employs the metabolic activity of specific microorganisms to induce the formation of a three-dimensionally interwoven calcium carbonate gel network within the pores and on the surface of RA. This gel network can improve the inherent defects of RA, thereby enhancing the performance of RC. Compared to conventional techniques, this approach demonstrates significant environmental benefits and enhances concrete compressive strength by 5–30%. Furthermore, embedding mineralizing microbial spores within the pores of RA enables the production of self-healing RC. This review systematically explores recent research advances in microbial mineral gel network for improving RC performance. It begins by delineating the fundamental mechanisms underlying microbial mineralization, detailing the key biochemical reactions driving the formation of calcium carbonate (CaCO₃) gel, and introducing the common types of microorganisms involved. Subsequently, it critically discusses the key environmental factors influencing the effectiveness of MICP treatment on RA and strategies for their optimization. The analysis focuses on the enhancement of critical mechanical properties of RC achieved through MICP treatment, elucidating the underlying strengthening mechanisms at the microscale. Furthermore, the review synthesizes findings on the self-healing efficiency of MICP-based RC, including such metrics as crack width healing ratio, permeability recovery, and restoration of mechanical properties. Key factors influencing self-healing effectiveness are also discussed. Finally, building upon the current research landscape, the review provides perspectives on future research directions for advancing microbial mineralization gel techniques to enhance RC performance, offering a theoretical reference for translating this technology into practical engineering applications. Full article

The development of sustainable cementitious materials is crucial to reduce the environmental footprint of the construction industry. Alkali-activated materials (AAMs) have emerged as promising environmentally friendly alternatives; however, their compatibility with natural stone in heritage structures remains poorly understood, especially regarding salt migration and related damage to stones. This study presents a novel methodology for assessing salt movement in solid materials between two types of stones—Boñar and Silos—and two types of binders: blended Portland cement (BPC) and an AAM. The samples underwent capillarity and immersion tests to evaluate water absorption, salt transport, and efflorescence behavior. The capillarity of the Silos stone was 0.148 kg·m⁻²·t^−0.5, whereas this was 0.0166 kg·m⁻²·t^−0.5 for the Boñar stone, a ninefold difference. Conductivity mapping and XRD analysis revealed that AAM-based mortars exhibit a significantly higher release of salts, primarily sodium sulfate, which may pose a risk to adjacent porous stones. In contrast, BPC showed lower salt mobility and different salt compositions. These findings highlight the importance of evaluating the compatibility between alternative binders and heritage stones. The use of AAMs may pose significant risks due to their tendency to release soluble salts. Although, in the current experiments, no pore damage or mechanical degradation was observed, additional studies are required to confirm this. A thorough understanding of salt transport mechanisms is therefore essential to ensure that sustainable restoration materials do not inadvertently accelerate the deterioration of structures, a process more problematic when the deterioration affects heritage monuments. Full article

Aminotris(methylene phosphonic acid) (ATMP) and poly(acrylic acid) sodium salt (PAA) have shown favorable results in the treatment of porous building materials against weathering damage, showing promising potential as mixed-in additives during the production of lime-based mortars. This study investigates the impact of these additives on microstructure and mechanical properties. Additives were introduced in various concentrations to assess their influence on CaCO₃ crystallization, porosity, strength, and carbonation behavior. Results revealed significant modifications in the morphology of CaCO₃ precipitates, showing evidence of nanostructured CaCO₃ aggregates and vaterite stabilization, thus indicating a non-classical crystallization pathway through the formation of amorphous CaCO₃ phase(s), facilitated by organic occlusions. These nanostructural changes, resembling biomimetic calcitic precipitates enhanced mechanical performance by enabling plastic deformation and intergranular bridging. Increased porosity and pore connectivity facilitated CO₂ diffusion towards the mortar matrix, contributing to strength development over time. However, high additive concentrations resulted in poor mechanical performance due to the excessive air entrainment capabilities of short-length polymers. Overall, this study demonstrates that the optimized dosages of ATMP and PAA can significantly enhance the durability and mechanical performance of lime-based mortars and suggests a promising alternative for the tailored manufacturing of highly compatible and durable materials for both the restoration of cultural heritage and modern sustainable construction. Full article

Historical masonry structures deteriorate over time, requiring restoration and strengthening. Hydraulic lime-based mortars (HLMs), due to their compatibility with historical materials, are commonly used for this purpose. This study examines the fire resistance of masonry walls constructed with HLMs. Masonry prisms with clay bricks were prepared using HLMs in accordance with material testing standards. Specimens were subjected to high temperatures ranging from 200 °C to 800 °C, followed by flexural–compression tests for mortar and compression tests for masonry prisms. A total of 20 masonry prism specimens, 15 brick specimens, and 15 mortar specimens were tested, including reference specimens at room temperature. Experimental results indicate that masonry prisms, clay bricks, and HLMs progressively lose their mechanical properties as temperature increases. The elastic modulus of masonry prisms was evaluated according to relevant standards, and Finite Element Analysis (FEA) was conducted to validate temperature-dependent material properties. The stress–strain response of M15 HLM masonry prisms was determined, addressing the absence of such data in EN 1996-1-2. Additionally, compression test results were compared with digital image correlation (DIC) analyses to enhance measurement accuracy. This study provides critical insights into the thermal performance of masonry walls with HLMs, contributing to the development of fire-resistant restoration materials. Full article

Traditional fiber-reinforced polymer (FRP) retrofit methods can restore the strength of reinforced concrete columns well, but stiffness is also partly restored. To increase the initial stiffness of retrofitted columns, this study investigated the seismic behavior of retrofitted resilient reinforced concrete (RRC) columns that were retrofitted by different methods, including high-strength mortar retrofit, carbon fiber-reinforced polymer (CFRP) retrofit, and CFRP and steel plate retrofit. In addition, the effect of the axial load was also considered. Quasi-static tests were conducted twice on five specimens, i.e., before and after repairing. The first test was used to create earthquake damage, and the second test was used to compare the seismic behavior of the retrofitted columns. The experimental results indicated that the CFRP retrofit method, whether with a steel plate or not, can restore the lateral resistance capacity well; furthermore, the drift-hardening behavior and self-centering performance were well maintained. The residual drift ratio of the CFRP-retrofitted column was less than 0.5%, even at a drift ratio of 3.5%, and less than 1% at the 6% drift ratio. However, the initial stiffness was only partly restored using the CFRP sheet. The introduction of steel plates was beneficial in restoring the initial stiffness, and the stiffness recovery rate remained above 90% when CFRP sheets and steel plates were used simultaneously. The strain distribution of the CFRP sheet showed that the steel plate did work at the initial loading stage, but the effect was limited. By using the steel plate, the CFRP hoop strain on the south side was reduced by 68% at the 6% drift ratio in the push direction and 38% in the pull direction. The axial strain of CFRP cannot be ignored due to the larger value than the hoop strain, which means that the biaxial stress condition should be considered when using an FRP sheet to retrofit RC columns. Full article

The use of binders in construction dates back to antiquity, with lime-based materials historically playing a significant role. However, the 20th century brought the widespread replacement of lime with Portland cement (PC), for its superior mechanical strength, durability, and faster setting time. Despite these advantages, the restoration of historic masonry structures has revealed the incompatibility of PC with traditional materials, leading to damage due to increased brittleness, stiffness, and reduced permeability. Consequently, lime mortars remain the preferred choice for heritage conservation. To enhance their durability while maintaining compatibility with historic materials, the incorporation of carbon-based nanoparticles has gained attention. This study investigated the impact of the carbon nanotubes (CNTs) additive on two types of lime-based mortars, calcium lime (CL) and hydraulic lime (HL), evaluating structural and mechanical properties, heat transport characteristics, and hygric properties after modification by CNTs with dosages of 0.1%, 0.3%, and 0.5% binder weight. Incorporation of CNTs into CL mortar resulted in an increase in mechanical strength and slight reduction in heat transport and water absorption due to changes in porosity. The addition of CNTs into HL mortars reduced porosity, pore size distribution, and other depending characteristics. The utilisation of CNTs as an additive in the investigated lime-based composites has been identified as a potentially effective approach for the reinforcement and functionalisation of these composite materials, as they exhibited enhanced mechanical resistance while preserving their other engineering properties, making them well suited for use as compatible mortars in building heritage repairs. Full article

This paper presents the results of an archaeometric investigation of the preparatory mortars of the pebble pavements of the Basilica of St. Leucio in Canosa di Puglia (Bari, Southern Italy). The main aim of the presented study is to contribute to the dating of some portions of the pebble pavements by analyzing the preparatory layers and determining whether they pertain to the basilica (6^th century CE) or to the pre-existing temple (2^nd century BCE–4^th century CE). Further purposes are to provide information about the production technologies of the mortars and to identify the nature of the pigments found on some pebbles. In order to contribute to the dating studies of the floors, complicated by previous reuse and restoration, 12 samples of mortars, sometimes including pebbles, were collected in different areas of the site. They were analyzed by polarized light microscopy (PLM), X-ray diffractometry (XRPD), X-ray fluorescence spectroscopy (XRF), and scanning electron microscopy coupled with an energy-dispersive spectrometer (SEM-EDS). The results allowed us to advance chronological data on different pavement areas, to deepen our knowledge on mortar production, in terms of both raw materials and technology, and to identify red ochre as the pigment with which the pavement surface was painted. Full article

This study explored the effect of compounding artificial hydraulic lime and silica fume for use as a sandstone grotto patching material. Different proportions of silica fume were added to hydraulic lime in lab tests, and their effects on the mortar’s physical and mechanical properties were studied. The results show that adding silica fume significantly increased the flexural and compressive strengths of the mortar and the shrinkage rate. A comparative analysis revealed that the comprehensive performance of the mortar reached the optimal state when the silica fume content was 10%. This met the strength requirements of repair materials for sandstone grottoes, as well as the control requirements regarding the shrinkage rate. Additionally, it demonstrated excellent weather resistance. This study’s results provide a scientific basis for the restoration of sandstone grottoes and the screening of an appropriate ratio of repair materials, which holds significant practical application value for the protection and reinforcement of stone relics. Full article

Concrete is popular in construction due to its strong performance and low maintenance. However, some structures become unsafe over time due to poor maintenance and design flaws. As demand for maintenance grows, restoring older structures is a cost-effective option. Advanced repair techniques aim to extend service life and improve concrete properties, with a focus on eco-friendly solutions. Recent trends have highlighted the potential of incorporating polymers into repair methods, but the use of glycoluril–formaldehyde, a polymeric material known for its hydrogen bonding capacity, remains unexplored in repairing existing structures. This research investigates the effects of glycoluril–formaldehyde in simple matrices like cement paste and mortar to understand its impact. By examining the chemical reactions between glycoluril–formaldehyde with cement paste, this study delves into the fresh, mechanical, and microstructural characteristics. To evaluate the influence of glycoluril–formaldehyde, cement paste specimens were subjected to various tests, including consistency, initial and final setting time, and miniature slump flow tests. Cement mortar specimens were then subjected to compression strength tests conducted at various ages. The results demonstrate that a 3% addition of glycoluril–formaldehyde in concrete offers optimum performance, ensuring improved mechanical strength and microstructure. The microstructural investigation using optical microscopy, an X-ray diffraction, and SEM analysis confirms the polymerization of glycoluril–formaldehyde and the formation of a denser microstructure. The thermogravimetric (TG) and differential thermogravimetric (DTG) analysis provides crucial insights into the thermal stability of the cementitious system, aiding its characterization for high-temperature applications. Full article

This study investigates structural integrity and proposes retrofitting solutions for the historical two-storey school building in Thrapsano, Crete, severely impacted by the September 2021 earthquake. An extensive methodology was adopted, incorporating field surveys, material characterization, finite element modeling, and experimental analysis. The assessment is focused on identifying structural damage, such as cracking and delamination in masonry walls, and evaluating the dynamic and static performance of the load-bearing system under seismic loads. Key interventions include grouting for masonry reinforcement, replacement of mortar with compatible materials, stitching of cracks, and the addition of reinforced concrete and metallic tie elements to enhance diaphragm action. Advanced numerical simulations, validated through experimental data, were employed to model the pre- and post-retrofit behavior of the structure. The proposed retrofitting measures align with Eurocodes 6 and 8, and the Greek code for masonry structures (KADET), aiming to restore the structural stability and improve seismic resilience while respecting the building’s historical significance. The results from the finite element analysis confirm the effectiveness of the interventions in reducing tensile stresses and improving load redistribution, ensuring compliance with modern safety standards. This case study offers a framework for the seismic retrofitting of heritage structures in a similar context. Full article

The stone Ensemble from Corbii de Piatrǎ Romania arouses a continuous scientific interest, with the final goal being to obtain an exhaustive and multidisciplinary package of results that will become the support of an extensive restoration project. The cave painting stands out as the most important and most affected by the advanced degradation among the historical monuments in Romania. This article provides for the first time a radiocarbon dating of the first forms of painting by establishing the age of the mortar/plaster used as a pictorial support. Being a very complex context from the point of view of the type of datable material and the disappearance over time through degradation of other elements that would ensure a simpler and more reliable radiocarbon dating (such as the straws used to form the material), it was necessary to use a multidisciplinary approach for the selection of samples and for supporting the radiocarbon results. The set of analyses consisted of visualization techniques through microscopy and compositional analysis, providing information on the similarities/differences between the samples, the degradation mechanisms/impurities and the quality of the calcium carbonate dated by the Accelerator Mass Spectrometry (AMS) technique. The results supported each other, ensured the selection of reliable radiocarbon data and established the most probable moment of the early interventions, namely the two phases corresponding to the 14th century. Full article

Lime-based mortars, frequently used in historic structures, are classified as hydraulic and non-hydraulic according to how they gain strength. In the past, various methods were used to improve the strength and durability properties of lime-based hydraulic mortars such as Khorasan mortar. Today, in studies carried out to increase the strength of lime-based mortars, the effects of binders, aggregates, and additives, which are the basic components of the mortar, are examined. In this study, the mechanical properties of Khorasan mortar mixtures, which are frequently used in the restoration of historical structures, were examined under the influence of different parameters. In particular, the effects of variables such as aggregate type and ratio (river sand and crushed brick), binder type and ratio (natural hydraulic lime, metakaolin, and blast furnace slag), and water/total dry material ratio on the strength of mortars were investigated experimentally. In the experimental study, two different aggregate types (river sand and crushed brick) were used in 1/3 and 1/2 ratios, and three different binders (natural hydraulic lime, metakaolin, and blast furnace slag) were used in different ratios. The water-to-total-dry-material ratios were set at 0.2 and 0.25. Standard test samples were then created from the prepared mortar mixtures, and their flexural and compressive strengths were assessed at 28 and 56 days. A statistical analysis of the experimental data was conducted using the Taguchi method, allowing for a detailed examination of how the different parameters influenced the strength of the mortars. Through this analysis, the optimal mixture ratios that maximized mortar strength were successfully identified. Full article

The high seismic vulnerability of unreinforced masonry buildings urgently calls for researchers to develop sustainable reinforcing methods and materials. This paper presents an innovative lime-based mortar reinforced with randomly oriented basalt fibers for the reinforcement of masonry heritage. The main aim of this study is to understand the effect of the content and the length of basalt fibers on the mortar’s mechanical behavior. As a cementitious material made mostly out of lime, the mortar is chemically compatible with the historical substrate and therefore suitable in cases of restoration works on architectural heritage. Moreover, the chopped basalt fibers are randomly oriented, and this characteristic makes the overall layer effective in all directions, as the state of stress induced by seismic action is directionally undetermined. The newly proposed reinforcement system is characterized by a twofold aspect related to sustainability: 30% of the aggregates composing the mortar mix design is a recycled result of the ruins of the 2009 L’Aquila earthquake, and the chopped fibers are made out of basalt, widely known for its environmentally supportable peculiarity. The study consists of testing samples characterized by two fiber lengths and six fiber contents, along with one set of plain mortar samples. Specimens measuring 160 mm × 40 mm × 40 mm are first tested in a three-point bending (TPB) configuration, aiming to determine the flexural strength and the post-peak capacity through the calculation of the fracture energy. Then, the two broken pieces resulting from the TPB tests, each measuring 80 mm × 40 mm × 40 mm, are tested in splitting and compression, respectively, aiming to compute the tensile and compressive strengths. Finally, to provide a trend for the mortar’s mechanical properties, a regression analysis is performed by fitting the experimental data with simple linear, polynomial, and exponential regression models. Results show that: (i) both fiber content and fiber length are responsible for a linear increase of the flexural strength and the fracture energy; (ii) for both short- and long-fiber mortar samples, the tensile strength and the compressive strength parabolically increase with the fiber content; (iii) the increase in fiber content and fiber length always generates a reduction in the conglomerate workability. The fiber content (FC) optimization with respect to the mechanical properties leads to a basalt FC equal to 1.2% for long-fiber samples and an FC equal to 1.9% for short-fiber ones. Full article

The Ateneo Sueco del Socorro, built in 1927 in Sueca, Spain, is a prime example of the 20th-century architectural transformation, using reinforced concrete. Designed by architect Juan Guardiola, it reflects the Art Deco style, incorporating ornamental elements from Eastern civilizations. The building’s structure includes masonry walls, concrete columns, and vaulted ceilings. The building displayed a high level of damage due to the oxidation and corrosion of the reinforcements that compose the façade, which led to the definition of the most appropriate study and intervention methodology, applying contemporary tests for reinforced concrete. The original project’s structural design reflects the construction methods of its time, with sculptural elements using Fallas modeling techniques, resulting in various concrete and mortar types. After the façade presented a pathological condition in the early 21st century that made its restoration urgent, a study methodology was followed with current tests to accurately determine the lesions, their degree of damage, and compatible materials for restoration. Corrosion on the façade is mainly triggered by carbonation and the depassivation of reinforcements, exacerbated by environmental issues like moisture retention and oxygen permeability. Repairs should use compatible pre-mixed mortars, with surface inhibitors recommended to extend the lifespan of reinforcements. Full article

In order to revitalize and preserve the Paimogo Fort, a Portuguese coastline military fortification built in 1674 and classified as of public interest since 1957, several lime-based repair rendering mortars were developed, considering the compatibility requirements with the original ones. In this investigation, the different lime-based mortar compositions proposed are briefly described and their main physical and mechanical characteristics are analyzed at successive ages (28, 90 and 180 days). Furthermore, some applications of the same mortars’ compositions on different porous substrates were carried out and their performances in laboratory and in situ conditions were compared. Finally, the possible degradation mechanisms and the impact of the composition, interaction with the substrate and climatic and environmental conditions on the durability of the mortars are discussed. The main outcomes show that mortars with some content of quicklime result in a balanced solution for the restoration work of the fort; they show an increase of more than 50% of strength compared to slaked air lime mortars, namely when applied on a medium-absorbent substrate. When applied on very absorbent substrates, although improving the compressive strength and porosity, all lime-based mortar compositions suffer a decrease in their modulus of elasticity and adhesion to the substrate. Air lime mortar compositions applied on a very absorbent and porous substrate generally show an increase in their mechanical strength when subjected to the severe marine environment of the fort. Full article