This investigation employs a Central Composite Design-based Design of Experiments (DoE) methodology to develop hydraulic lime mortars incorporating equilibrium catalyst (ECat), a by-product generated at the fluid catalytic cracking unit in oil refineries. The derived mathematical models describe the quantitative effects of key mixing variables, specifically ECat content, water-to-binder ratio and water repellent dosage, as well as their cross-interactions, on mortar properties, namely workability, compressive strength, ultrasound propagation velocity and dynamic modulus of elasticity. Numerical optimisation techniques enabled the identification of optimal lime mortar compositions that maximise eco-efficiency while ensuring compliance with both regulatory and technological requirements for diverse masonry applications, including the rehabilitation of ancient buildings. Results confirm the by-product upcyclability of ECat, with feasible incorporation levels up to 56.6 % by mass, yielding mortars with significant potential for reducing the environmental impact of the built environment while advancing the circular economy and fostering technological innovation in the construction sector.

This review provides an in-depth examination of machine learning applications in assessing concrete durability from 2013 to 2024, with a particular focus on critical degradation mechanisms, including carbonation, chloride-induced deterioration, sulfate attack, frost damage, shrinkage, and corrosion. It underscores the field’s heavy reliance on laboratory-based data and notes the limited use of field data and the scarcity of newly generated datasets. The review reveals that most studies utilize existing literature-based datasets, with few contributing novel data and limited open access to these databases, which hampers broader validation and application. The review classifies the features analyzed in studies into categories such as mixture proportions, engineering properties, exposure conditions, test parameters, and chemical compositions, highlighting a growing emphasis on chemical compositions. Modeling approaches are predominantly standalone, though ensemble and hybrid models are increasingly prevalent, with ensemble models showing particularly strong performance in recent years. High accuracy is observed across studies, with ensemble models, neural networks, and hybrid models leading in performance. Furthermore, the review stresses the growing importance of model explainability, noting that model-agnostic methods like SHAP are frequently used and that the focus on explainability has increased. To propel the field forward, the review advocates for the development of diverse new datasets that include both the chemical and physical properties of various mix ingredients and improved data-sharing practices. It recommends adopting a multi-task learning approach to simultaneously address multiple deterioration mechanisms, which can yield deeper insights and support the creation of more durable concrete structures.

The development of the cement industry and technology was a significant driver of progress in construction and artistic applications. Between the late 19th and 20th centuries, cement-based mortars and concrete were widely used in both utilitarian and artistic heritage, serving as structural materials and decorative ornaments. This paper presents a historical overview of the Portuguese cement industry within an international framework. It traces the evolution of modern hydraulic binders from the 18th-century experiments with clay-rich limestone and pozzolan to the 19th-century development of artificial hydraulic lime and major improvements in production processes, kiln design, and chemical analyses, resulting in the standardization of modern artificial Portland cement. These advancements shaped the adaptation and industrialization of cement in Portugal, and marked a gradual transition from natural to artificial cement around the turn of the century. Cement binders imported from England and France continued to dominate the Portuguese market well into the 20th century, even after national production began in the second half of the 19th century. While current research on modern cement heritage often focuses on built structures, this study highlights the cultural significance of cementitious public art. It explores the transition from functional to artistic uses of cement, particularly during the 19th and 20th centuries, through selected case studies that reflect the different techniques and mortar formulations, as well as international influences on Portuguese cementitious heritage. An early example is the Teatro Nacional de São João, where ornaments created with cement-based mortars reinforced with steel bars and metal mesh reflect the influence of French engineering and the pioneering work of Joseph Monier. By contextualizing the Portuguese case within broader technological and artistic trends, this study contributes to a deeper understanding of cementitious heritage and emphasizes the need for further research on Portuguese cement-based artworks from the 20th century. The findings reveal compositional variations and applications that often relied on evolving techniques and experimental mortar formulations. Thus, understanding the material and technical evolution of cement-based mortars, as well as the cross-cultural exchanges that have shaped their use, is essential for the effective preservation and appreciation of this understudied part of modern heritage.

The tensile response of ultra-high performance fibre-reinforced composites (UHPFRC) is decisive in many applications and depends on the steel fibre content and orientation. These vary troughout the structural element and may differ from those in the laboratory specimens used to characterize the material behaviour. This work presents the developments on a non-destructive test method based on the measurement of the magnetic inductance, substantiating its use for the determination of the fibre content and orientation in thin UHPFRC elements and allowing the estimation of the directionally dependent post-cracking tensile strength of the material in the structure. Starting from a probabilistic description of the fibre orientation, an existing physical model of the magnetic circuit composed of a U-shaped inductor and the composite is generalized and is used to derive the relations between the magnetic inductance measurements, the fibre volumetric fraction and the fibre orientation factor. A second-order tensor approximation of the relative magnetic permeability of the composite is proposed to determine the in-plane fibre orientation factor along any direction based on any three non-collinear measurements. Experimental evidence is presented supporting the theoretical developments. The factors that may affect the measurements are experimentally quantified. The paper concludes with an application example.

The current work provides an integrated analysis of autogenous shrinkage, isothermal calorimetry, and modulus of elasticity measurement through ambient response method (EMM-ARM), to characterise the hardening behaviour of a non-proprietary and more eco-friendly ultra-high performance fibre reinforced cementitious composite (UHPFRC). Isothermal calorimetry revealed that induction period ends at 3 h, and the rapid evolution of hydration heat occurs up to 9 h. Then, the hydration reaction still undergoes but at a very slow rate. The autogenous shrinkage exhibited a strong increase, particularly in the first 6 h, after which a dramatic reduction in the slope of the curves occurred, corroborating with the heat of hydration measurements. The modulus of elasticity evolution pattern revealed a typical cementitious material S-shaped curve, with a strong evolution in the first 8 h and reached 37 GPa at 7 days. As the current study perceives, UHPC/UHPFRC-3 % MOE evolution mainly occurs at very early ages. Thus, using EMM-ARM method for evaluating stiffness-related properties since casting age of UHPC/UHPFRC is of utmost importance to take advantage of the remarkable properties of such advanced material with no waste of time and resources. Furthermore, the UHPFRC developed with a lower amount of cement and silica fume decreases the heat of hydration, shrinkage, and reduced costs and ecological footprint without significantly impairing the MOE, compared to other non-proprietary blended UHPC/UHPFRC mixtures.

Strengthening existing reinforced concrete (RC) flat slabs by casting a thin layer of ultra-high performance fibre-reinforced cementitious composite (UHPFRC) over the top surface constitutes an efficient solution for significant durability and flexural capacity enhancements. Previous research has shown that also the punching shear capacity can be substantially increased. However, the existing experimental evidence is still limited and does not allow a systematic evaluation of the influence of the governing parameters. In the present work, eight slabs without transverse reinforcement were tested up to punching shear failure. The following parameters were studied: the contribution of the UHPFRC overlay with and without reinforcement bars, the shape of the column (square or rectangular), the effect of the reinforcement ratio in the existing slab, the eccentricity of the punching force and the material of the strengthening layer (UHPFRC or ordinary RC). The height of the RC substrate and UHPFRC layer thickness were kept constant at 180 mm and 40 mm, respectively. The results confirm the significant contribution of the UHPFRC layer to the punching shear strength. The experimental failure loads are compared to the predictions provided by a composite failure criterion based on the Critical Shear Crack Theory and taking into account the contribution of the UHPFRC layer. Good agreement was obtained with the model being capable of reproducing the effect of all the studied variables.

The suitability of a recently developed ultra-high performance fibre reinforced cementitious composite (UHPFRC) incorporating Spent Equilibrium Catalyst, ECat, for structural applications is investigated through a systematic multi-level investigation across micro, meso and composite levels. Scanning electron microscopy, isothermal calorimetry, thermogravimetric analysis, and mercury intrusion porosimetry tests were performed to evaluate the microstructure of the composite. At the meso-level, the mechanical properties of fibre to matrix ITZ were characterised by single fibre pullout tests on fibres embedded with various fibre orientation angles. At the composite level, specimens with 3% fibre content and different fibre orientation profiles were prepared to determine uniaxial tensile behaviour. The relation between the tensile fracture parameters and fibre structure parameter was assessed. In each level, the results are compared to a conventional ternary UHPFRC mixture and point towards the suitability of the newly developed mixture for structural applications.

The current paper analyses the mechanical and fracture behaviour of a High-Performance Fibre Reinforced Concrete (HPFRC). An HPFRC was developed in a previous stage aiming to simultaneously, maximise aggregates content, achieve a compressive strength of 90–120 MPa and maintaining self-compactability (SF1+VS2). The benefits of fibres hybridisation (using fibres with lengths of 13, 35 and 60 mm) on flexural strength are investigated using the wedge-splitting test, in order to achieve the highest performance while keeping a relatively low fibre content. The final selected mixture was characterised in terms of workability, compressive strength and modulus of elasticity. Six notched prismatic specimens were subjected to three-point bending tests, according to EN 14651, for classification according to the MC2010. Based on the bending tests data, the simplified linear characteristic tensile stress vs. crack opening displacement relationship of the HPFRC was evaluated according to MC2010 and two other analytical approaches available in the literature.

Strengthening existing reinforced concrete (RC) beams and slabs using a thin layer of ultra-high performance fibre reinforced cementitious composites (UHPFRC), plain (U) or reinforced (RU) with ordinary steel bars, has been shown to be a very effective way of increasing the flexural capacity in hogging moment regions. However, as the increase in the flexural strength can be very significant, the shear strength of the composite RC-RU or RC-U elements may govern the capacity of the strengthened element and must be conveniently assessed to provide suitable design recommendations. In this regard, the available experimental evidence concerning the shear strength of beams (or one-way shear strength for slabs) is relatively limited. In this work, the results of an experimental campaign are presented where the influence of important parameters was systematically evaluated, namely the reinforcement ratios in the original RC beam and the new UHPFRC layer, the size effect, the thickness of the UHPFRC layer and the sign of the being moment - hogging or sagging - changing the state of stress in the UHPFRC layer from tensile to compressive. The structural behaviour is discussed, and an analytical approach for calculating the shear strength is evaluated.

This paper provides an overview of the use of the magnetic NDT method for estimating the fibre content, and fibre orientation and efficiency factors in thin UHPFRC elements/layers, along any two orthogonal directions. These parameters are of utmost importance for predicting the post-cracking tensile strength in the directions of interest. After establishing meaningful correlations at the lab-specimen scale, this NDT method can be effectively implemented into quality control protocols at the industrial production scale. The current study critically addresses the influence of key factors associated with using this NDT method in practice and provides recommendations for its efficient implementation.

UHPC is an advanced cementitious material able to meet the current construction industry challenges regarding structural safety and durability. However, new UHPC formulations with limited shrinkage are still being pursued to reduce residual tensile stresses in the UHPFRC layers, for rehabilitation/strengthening applications. This investigation estimates the durability of a non-proprietary UHPC incorporating a by-product originated by the oil refinery industry (ECat), as an internal curing agent. Direct and indirect transport properties measurements as well as the carbonation assessment and evaluation of dimensional resilience to potential deleterious reactions revealed that the new UHPC possesses an excellent durability performance, typical of these materials. These results combined with its self-compacting ability, low autogenous shrinkage and high compressive strength confirm the belief in the role of this new UHPC towards a high-tech construction.

This paper presents and discusses experimental results on the tensile mechanical performance of a newly developed ultra-high performance cementitious material, UHPC, incorporating spent equilibrium catalyst (ECat), a waste generated by the oil refinery industry, as a supplementary cementitious material. The results are compared to a previously developed conventional UHPC. The influence of ECat on the heat of hydration in UHPC is evaluated by isothermal calorimeter under a constant temperature of 20 ℃. To determine the evolution of the tensile behaviour with time, a series of uniaxial tensile tests are performed on the specimens at different ages, i.e. 1, 3, 7, 28 and 91 days after casting. Afterwards, the fibre to matrix interfacial bond properties were characterized by executing a series of single fibre pullout tests at the age of 28 days on the steel fibres embedded in UHPCs with 0°, 30° and 60° orientation angles. The results confirmed the adequate performance of the new developed UHPC for the structural application.

Fibre-reinforced cementitious materials represent one of the most significant developments in the field of concrete technology of the last decades. The improved performance of this new class of materials (in terms of workability, compressive strength, flexural/tensile behaviour and/or durability) allows rethinking several of the existing structural solutions. This paper describes research on high-performance fibre reinforced concrete (HPFRC) to be used at the slab-column connection zones of flat slabs, in order to improve its punching shear resistance. Design of Experiments (DoE) approach was used to design HPFRC paste and aggregate particle phases. As such, a central composite design was carried out to mathematically model the influence of mixture parameters and their coupled effects on deformability, viscosity and compressive strength. After that, a numerical optimization technique was applied to the derived models to select the best mixture, which simultaneously, maximizes aggregates content and allows achieving a compressive strength of 90–120 MPa, while maintaining self-compactability (SF1 + VS2), incorporating 1% steel fibres content.

Given the rising societal pressure towards sustainable waste management and resource efficiency, in a more circular economy, an increased use and diversification of supplementary cementitious materials (SCM) will be necessary to achieve the CO₂ mitigation goals. The current study addresses the development of self-compacting concrete, replacing part of the cement (the primary source of CO₂ emissions) by metakaolin and wastes derived from two industrial sectors operating in the “Galicia–North of Portugal Euroregion”: wood manufacturing and natural stone quarrying. A study was carried out at the mortar level to investigate the effect of the mix design variables on several engineering properties of the self-compacting concrete. Statistically designed experiments reveal that an increase in water/powder volume ratio has a dominant effect on the fresh state properties, whereas the water/cement weight ratio has a dominant effect on the hardened state properties. A like-for-like comparison of the proposed quaternary blends and previously studied binary/ternary blends indicates that these mixtures exhibit improved self-compacting ability, greater compressive strength, and can offer interesting opportunities to reduce the unit cost and environmental impact of self-compacting concrete per m³. Four different mortar mixtures were optimised to achieve excellent self-compacting ability yet with distinct compressive strength levels at 28 days (65, 70, 75, and 80 MPa). A single measure of the material efficiency is proposed herein to reflect the engineering properties improvement (workability, compressive strength, and durability) over its economic (unit cost) and environmental impact.

The tensile behaviour of Ultra-High Performance Fibre Reinforced Cementitious Composites (UHPFRC) is decisive in many structural applications. A non-destructive test method (NDT) based on the magnetic properties of the steel fibres is used to determine suitable fibre content and orientation parameters. These parameters are employed in a constitutive model providing the corresponding directional dependent tensile response, which varies throughout the structure. This information is then provided to the mechanical model of the beams used to simulate the four point bending tests (FPBT). The resulting numerical F-d curves and crack patterns are confronted with those from experimental tests with a good match being generally attained.

UHPFRC has become one of the most promising cement-based materials for the next generation of infrastructures because of its good workability, outstanding mechanical properties, and excellent durability. A promising field of application is the rehabilitation and/or strengthening of existing reinforced concrete structures, in which a new layer of UHPFRC replaces the deteriorated concrete (cracked, carbonated, chloride attack, etc.). The combination of the UHPFRC as protective layer, which can be reinforced, provides a simple and efficient way of increasing the durability (extending the service life), the stiffness and structural resistance capacity while keeping compact cross sections. A study was carried out to test a non-proprietary UHPC mix containing equilibrium catalyst to determine whether this new mix is a viable option for rehabilitation/strengthening applications. Several mechanical properties and durability were assessed, such as early age E-modulus development and autogenous shrinkage, compressive strength evolution in time, uniaxial tensile strength, water absorption by capillarity, chloride ion penetration, alkali-silica reactivity and sulphates attack resistance. Test results show that new UHPC developed present equivalent performance to other UHPCs cured under normal curing conditions.

A simple model is proposed to predict the uniaxial tensile behaviour of ultra-high performance fibre-reinforced cementitious composites (UHPFRC) based on a meso-level description of the involved mechanics. The model relies on quantifiable material properties of the both matrix and fibres, on basic information concerning the fibre structure (such as fibre volumetric fraction, fibre orientation and geometry) and on three model parameters. Pullout tests on short fibres embedded in ultra-high performance cementitious matrix with different orientation angles and embedded lengths were developed for estimating the representative value of the average fibre-to-matrix bond-strength to be adopted, as well as for defining the fibre efficiency function describing the effects of fibre orientation on the pullout force. The model performance is validated against a series of uniaxial tensile tests on UHPFRC specimens covering a wide range of tensile behaviours. It is shown that the tensile response of UHPFRC can be well reproduced both in the hardening and softening stages with a single set of model parameters, and for a significant range of fibre contents and orientation profiles.

The primary goal of the present paper is to investigate the influence of cracking on water transport by capillary suction of UHPFRC. Prismatic specimens were firstly loaded under four-point bending up to specific crack open displacement (COD). Target COD, under loading, was varied between 200 and 400 μm, in steps of 50 μm. After unloading, a COD recovery was observed with residual COD ranging between 116-334 μm and 75-248 μm for UHPFRC-1.5% and UHPFRC-3.0% specimens, respectively. The crack pattern created was characterised (number of cracks and crack width) before capillarity testing. Sorptivity results of cracked UHPFRC-1.5% and UHPFRC-3% specimens remained in the range of 0.024 to 0.044 mg/(mm².min^0.5), which are about 2 to 4 times higher than the sorptivity results of non-cracked UHPFRC specimens. However, the maximum sorptivity observed on cracked UHPFRC is relatively low as compared to typical sorptivity results found in good quality conventional concrete or engineered cementitious composites (ECC).