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.

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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.

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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.@en

The subject of this paper is the extent to which, during wetting–drying cycles, chloride ions can penetrate Ultra-high-Performance Fibre Reinforced Cementitious Composites (UHPFRC) specimens subjected to combined mechanical and environmental load. Pre-cracking was obtained by subjecting prismatic specimens (40 × 40 × 60mm³) to four-point bending until a predefined crack opening displacement (COD) is reached, using a dedicated test setup. Three target CODs were studied: 300, 350 and 400 µm. Exposure to a concentrated chloride solution (3.5% NaCl) was used as an environmental load. Specimens we subjected to wetting–drying cycles for one year. After this exposure period, the chloride penetration was characterised both qualitatively (by colourimetric analysis with silver nitrate) and quantitatively (by determining the chloride profile). The effect of damage level on chloride penetration and its impact on structures durability is discussed in the current paper.

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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.

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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).

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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.

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