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.

Concrete formulation, despite recent progress, remains challenging due to the increasing number of constituents and performance requirements. This study explores a parallel approach to physical and semi-empirical experimental proportioning methods, utilizing machine learning (ML) or deep learning (DL). By harnessing big data from concrete production and high throughput experimentation, ML/DL algorithms can optimize mixes, minimizing waste and maximizing performance. This approach, combined with digital fabrication, addresses environmental and productivity concerns in construction. However, challenges such as diverse non-digital experimental methods, lack of basic data on waste streams, and limited open repositories on cement-based materials hinder the widespread use of data-driven techniques. This paper examines the background and potential of data-driven techniques in the field of concrete technology.

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.

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.

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.

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.

In construction, three-dimensional concrete printing technology is an innovative method that opens new design possibilities, reducing the construction time process. The incremental material deposition allows organic shapes without formwork, a mandatory constraint in preparatory phases of conventional complex concrete structures. Nowadays, in three-dimensional printing for construction industry, concrete is the most used material due to its workability, extrudability, and pumpability properties favorable for the printing conditions. Hence, this composition still has a poor sustainable efficiency due to the high levels of Portland Cement. In this research, a reduction of this material was studied and experimented searching for a mortar composition with better ecological footprint, with the objective of decreasing the CO 2 emissions. A bibliometric analysis was made to study the constituents of a mortar for three-dimensional printing and respective dosage. The knowledge acquired in the analysis of the compositions contributed to the development of mortars with lower Portland Cement content. A mechanical extruder was used to check the extrusion capacity of the developed mortars, and the best compositions are presented.

Ultra-high performance fibre reinforced cementitious composites (UHPFRC) is a family of advanced cementitious materials with optimized matrix packing density, very low water/binder ratio (w/b 90%) with high pozzolanic activity similar to SF. The average particle diameter of the ECat is 91.65 m and they possess a very high internal porosity with high water affinity. Previous results obtained on UHPFRC incorporating ECat showed that this material acts as an internal curing agent reducing the autogenous shrinkage. This research focuses on the microstructural behaviour of a recently developed UHPFRC incorporating ECat. For this purpose, to quantitatively estimate the influence of ECat particles on the amount of hydration products, thermogravimetric analysis (TGA) was performed on specimens at different ages. Similarly, the influence of ECat particles on the pore structure of the newly developed mixture is also assessed by performing mercury intrusion porosimetry (MIP). The relation between the hydration products and the pore structure is analyzed.

The high cost of UHPFRC is a limitation on the practical application in real construction projects. However, a very competitive UHPFRC approach is the hybrid structural elements, where thin layers of UHPFRC are employed to rehabilitate/strengthen damage cover concrete. New layers subjected to harsh conditions (loads and/or environmental) can eventually crack under service conditions, changing the local transport properties and thus, a faster ingress of detrimental substances occur, such as chlorides ions. Most of the studies on chloride penetration in UHPFRC have focused on determining the transport properties of sound, non-cracked specimens. Thus, an experimental campaign was carried out to assess chloride ingress in loaded and/or cracked UHPFRC and the effect of such ions on mechanical performance. Typical service cracks patterns were imposed on UHPFRC specimens and then exposed to wetting-drying cycles in a chloride solution. After 1-year chloride exposure, UHPFRC specimens were in good condition with no significant losses in flexural strength; however, stiffness might be affected. The chloride contents up to 20 mm depth were superior to the European standards critical chloride content. A minimum cover depth of 20 mm of new UHPFRC is recommended to protect a concrete substrate in hybrid structures for exposure classes XS3.

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.

Self-compacting concrete (SCC) is currently among the most technologically advanced concrete types. Its remarkable properties are determining its growing interest. However, as many other human activities, it is facing a challenge regarding sustainability. This chapter presents the current ecological fragility of concrete and opportunities to decrease SCC environmental footprint by, for example, incorporating supplementary cementitious materials in its composition (industrial wastes, calcined clays, vegetable ashes, and fillers), optimizing mix-design approaches (namely leading to low-cement SCC content, while maintaining product performance and cost), and the free-clinker self-compacting alkali-activated concrete. The chapter highlights the enormous potential of SCC to contribute for reducing the current colossal waste stockpiles, as well as for a definitive shift toward the Circular Economy.

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 "GaliciaeNorth 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 selfcompacting 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 m(3). 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. (c) 2020 Elsevier Ltd. All rights reserved.

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.

The main goal of the current paper is to optimize ultra-high performance cementitious material (UHPC) mixes incorporating the spent equilibrium catalyst (ECat) to mitigate autogenous shrinkage. Design of experiments approach was used to optimize mixtures targeting different engineering properties, namely, self-compactibility, low early-age shrinkage and cracking risk, improved durability and high mechanical performance. The statistical models established indicated that ECat exhibits a strong positive effect on the autogenous shrinkage mitigation of UHPC attributed to the water absorbed in the porous of ECat particles. The proposed optimal UHPC mixture represents the best compromise between low autogenous shrinkage - 32% of reduction - and high resistivity at 28 days without impairing self-compatibility and compressive strength. This optimal UHPC combined with 3% high-strength steel fibres (l(f)/d(f) = 65) proved to be comparable to other Ultra High-Performance Fibre Reinforced Composites (UHPFRC), in terms of mechanical behaviour, and more eco-friendly and cost-efficient than UHPCs reported in the literature.

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 UHP-FRC-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.min0.5), 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).

The Philips Pavilion by Le Corbusier and Jannis Xenaquis was a landmark project in thin shell concrete construction, only made possible by an experimental precasting strategy that deeply defined the architectural character of the hyperbolic paraboloid surfaces of the pavilion. Using this historic precedent this research presents a reinterpretation of the design of the Philips Pavilion, specifically tailored for Robotic Hot Wire Cutting technologies and a layered mold system, combining speed and material optimization towards more sustainable concrete construction processes. By documenting the realization of an experimental prototype at a 1:2 scale, this paper demonstrates the feasibility of the proposed strategy and its value in comparison with existing construction scale digital fabrication technologies for concrete.

The Philips Pavilion by Le Corbusier and Jannis Xenaquis was a landmark project in thin shell concrete construction, only made possible by an experimental precasting strategy that deeply defined the architectural character of the hyperbolic paraboloid surfaces of the pavilion. Using this historic precedent this research presents a reinterpretation of the design of the Philips Pavilion, specifically tailored for Robotic Hot Wire Cutting technologies and a layered mold system, combining speed and material optimization towards more sustainable concrete construction processes. By documenting the realization of an experimental prototype at a 1:2 scale, this paper demonstrates the feasibility of the proposed strategy and its value in comparison with existing construction scale digital fabrication technologies for concrete.