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See detailOptimisation of the mechanical properties of Miscanthus lightweight concrete (Top 10 Journal)
Pereira Dias, Patrick UL; Waldmann, Danièle UL

in Construction and Building Materials (2020)

In this paper, Miscanthus fibres are used to develop lightweight concrete. The amount of Miscanthus and cement, as well as the water/cement ratio, are varied to analyse the behaviour of the mixture ... [more ▼]

In this paper, Miscanthus fibres are used to develop lightweight concrete. The amount of Miscanthus and cement, as well as the water/cement ratio, are varied to analyse the behaviour of the mixture concerning the physical and mechanical properties. The Miscanthus was pre-treated with a silicate sealant or a cement-based fluid. The current paper analyses the impact of the pre-treatment of the Miscanthus fibres on the compressive strength as well as on the long-term deformations. The specimens with a pre-treatment based on a silicate sealant reached a compressive strength of 19.3 MPa, which is higher than the compressive strength of a conventional LC 16/18, a Young's Modulus above 9.9 GPa and a shrinkage deformation of 2244 μm/m. Nevertheless, considering the density the pre-treatment showed not to be beneficial. [less ▲]

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See detailOvercome of bed-joint imperfections and improvement of actual contact in dry-stacked masonry
Chewe Ngapeya, Gelen Gael UL; Waldmann, Danièle UL

in Construction and Building Materials (2020)

Several researchers studied dry-stacked masonry walls (DSM) and inferred that the actual contact surface between the different block rows and the compressive strength in such walls are reduced by bed ... [more ▼]

Several researchers studied dry-stacked masonry walls (DSM) and inferred that the actual contact surface between the different block rows and the compressive strength in such walls are reduced by bed-joint imperfections as well as by height differences between different masonry blocks leading both to high stress concentration. This paper concentrates on the first type on imperfections. Through experimental tests, it analyses the influence of bed-joint roughness on the load bearing capacity and investigates a strategy to improve the load-bearing capacity of DSM by placing an additional horizontal layer on the top face of raw masonry blocks. First, different contact layers using conventional and auxetic materials were applied. Then 20 dry-stacked masonry prisms built with raw and improved masonry blocks were tested under axial compressive load until failure. Prescale Fujifilm strips were used to measure the actual contact in the bed-joints. Experimental tests show that the use of a contact layer with well-defined material properties enables firstly to increase the actual contact area in the bed-joints from 23% to 98% of the nominal contact area and secondly to increase the load-bearing capacity by 14 to 97%. In addition, the contact layer with an auxetic material shows a significant capacity in altering the lateral expansion in the block units. The outcomes show that although the bed joint roughness influences the stress distribution in a dry-stacked masonry block, a contact layer with well-defined material properties enables to overcome the roughness induced by the bed-joint imperfections. [less ▲]

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See detailExperimental and numerical analysis of early age behavior in non-reinforced concrete
Nguyen, Thanh Tung UL; Weiler, Michael UL; Waldmann, Danièle UL

in Construction and Building Materials (2019), 210

An approach combining numerical simulations and experimental techniques is proposed to investigate the early-age properties of non-reinforced concrete. Both thermo-mechanical and fracture behaviors are ... [more ▼]

An approach combining numerical simulations and experimental techniques is proposed to investigate the early-age properties of non-reinforced concrete. Both thermo-mechanical and fracture behaviors are studied, providing a deep insight into the hydration process. This work makes an important step in understanding the effects of hydration on the performance of cement-based materials. More specifically, in the first part, the shrinkage and fracture properties of a non-reinforced concrete have been experimentally considered, along with the characterization of several material parameters. The experimental results exhibit a high risk of early-age cracking for this kind of concrete. Especially, the fracture phenomena are complex, including multi-evolution-stages, initiation, propagation, stop-growing, and re-growing. In the second part, the computational modeling based on the phase field method of failure mechanism is applied to simulate the thermal, mechanical and fracture behavior due to early-age hydration. A detailed discussion on the identification of model/material parameters and the construction of numerical model including the boundary conditions is given. We provide the following comparison between predictions of the numerical simulation with the experimental observations. An excellent predictive capability of the computational model is noted. More importantly, this work demonstrates the performance of the proposed approach, which requires only a few tests to identify the model inputs. Most of the chemo-thermal parameters can be theoretically determined based on the concrete mix and the chemical/mineral compositions of the cement. [less ▲]

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See detailStrain monitoring of concrete components using embedded carbon nanofibers/epoxy sensors
Wang, Y.L.; Wang, Y.S.; Han, B.G. et al

in Construction and Building Materials (2018)

In this study, embedded strain sensors based on the principle of piezoresistivity were fabricated by epoxy-based composites filled with different contents of carbon nanofibers (CNFs). The piezoresistive ... [more ▼]

In this study, embedded strain sensors based on the principle of piezoresistivity were fabricated by epoxy-based composites filled with different contents of carbon nanofibers (CNFs). The piezoresistive performances and relevant parameters including gauge factor, linearity, repeatability and hysteresis of these sensors were investigated. A compensation circuit was proposed to eliminate the influence of temperature on sensing signals of the sensors. The CNFs/epoxy sensors were embedded into concrete cylinders to monitor their compressive strains under monotonic and cyclic loadings, thereby assessing practical applications of the CNFs/epoxy sensors as strain sensors for monitoring concrete structures. The results indicate that the sensors containing 0.58 vol% of CNFs, which have a gauge factor of 37.1, a linearity of 5.5%, a repeatability of 3.8% and a hysteresis of 6.3%, exhibited better piezoresistive performance compared to those containing 0.29 vol% of CNFs. The calibration and monitoring curves exhibited a consistent variation trend when the cylinders embedded with sensors were subjected to monotonic and cyclic loadings. This demonstrates that the CNFs/epoxy sensors have considerable potential to be used as embedded strain sensors for structural health monitoring of concrete structures. [less ▲]

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See detailBasic mechanical behaviours and deterioration mechanism of RC beams under chloride-sulphate environment
Wang, J.H; Cai, Gaochuang UL; Wu, Q.

in Construction and Building Materials (2018)

This paper investigates the basic mechanical behaviour of reinforced concrete (RC) beams using chloride corrosion-damaged steel reinforcements and subjected to sulphate ions environment. To this end, ten ... [more ▼]

This paper investigates the basic mechanical behaviour of reinforced concrete (RC) beams using chloride corrosion-damaged steel reinforcements and subjected to sulphate ions environment. To this end, ten RC beams were studied which contained 5% sodium chloride and implemented by a series of drying-immersion cycling (15% sodium sulphate immersion solution). Test results indicated that the flexural capacity, ductility, and stiffness of the beams were improved at early stage of the corrosion. This was attributed to the fact that concrete strength and steel-concrete interfacial bond were enhanced. The former is for the filling effects of micro-expansive Ettringite and gypsum sulphate, while the latter is due to the slight surface corrosion pits of steel bars at the stage. However, the mechanical properties of the beams decreased subsequently for the deteriorations in the concrete strength due to excessive expansion of Ettringite and gypsum sulphate, and the degradation of self-property of reinforcement and its interface bond with the concrete. Based on the study, the deterioration mechanism of RC beams under chloride-sulphate environment was discussed and its main determining factors at different stages were analysed. [less ▲]

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See detailA new thickness-based accelerated aging test methodology for resin materials: theory and preliminary experimental study
Wang, Yanlei; Zhang, Xue; Gaochuang, Cai et al

in Construction and Building Materials (2018)

Detailed reference viewed: 198 (23 UL)
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See detail3D meso-scale modelling of foamed concrete based on X-ray Computed Tomography
Nguyen, Tuan; Ghazlan, Abdallah; Kashani, Alireza et al

in Construction and Building Materials (2018), 188

Foamed concrete has been widely used in infrastructure construction and poses new challenges to design and modelling. This paper investigates the behaviour of foamed concrete with the help of X-ray ... [more ▼]

Foamed concrete has been widely used in infrastructure construction and poses new challenges to design and modelling. This paper investigates the behaviour of foamed concrete with the help of X-ray Computed Tomography (XCT), which is capable of characterising the microstructure of foamed concrete. An in situ compressive test-XCT scan is carried out to observe the failure mechanism of foamed concrete by XCT when subjected to compression load. A meso-scale simulation based on XCT images is conducted to simulate the behaviour of foamed concrete. An algorithm that directly reconstructs the meso-scale model from XCT images is developed. The experimental and numerical results show that foamed concrete exhibits a significant change in mechanical behaviour; it is less brittle compared to the response of dense samples. However, the reduction in the level of brittleness is accompanied by a significant decrease in compressive strength. Failure development inside samples is successfully captured by the XCT scan and the meso-scale modelling. The topology of foamed structures, in particular the chain of interconnected pores, influences the failure mechanism of foamed concrete. The combination of XCT scan and meso-scale modelling provides a comprehensive framework to understand the mechanical behaviour of foamed concrete. [less ▲]

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See detailSteel fibres as only reinforcement for flat slab construction
Julien, Michels; Waldmann, Danièle UL; Maas, Stefan et al

in Construction and Building Materials (2011)

Detailed reference viewed: 26 (4 UL)