Experimental and numerical analysis of early age behavior in non-reinforced concrete

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 ▲]

Phase field modeling of interfacial damage in heterogeneous media with stiff and soft interphases

in Engineering Fracture Mechanics (2019), 218

Behaviour of Circular Fiber-Reinforced Polymer-Steel-Confined Concrete Columns Subjected to Reversed Cyclic Loads: Experimental Studies and FE Analysis

in Journal of Structural Engineering (2019)

This paper studies experimentally the behaviour of circular FRP-steel-confined columns subjected to reversed cyclic loads. The influence of main structural factors on the cyclic behaviour of the columns ... [more ▼]

This paper studies experimentally the behaviour of circular FRP-steel-confined columns subjected to reversed cyclic loads. The influence of main structural factors on the cyclic behaviour of the columns is discussed. Test results show the outstanding seismic performance of FRP-steel confined reinforced concrete (RC) and steel-reinforced concrete (SRC) column. The lateral confinement effectiveness of FRP materials is verified in the steel tube confined RC columns. A simplified finite element method (FEM) model supported by OpenSees is developed to simulate the experimental results of the test columns. Based on the proposed FEM model, a parametric analysis is conducted for investigating the effects of several main factors on the reversed cyclic behaviour of GFRP-steel confined RC columns. Based on the test and numerical analyses, the study discusses the influence of variables such as the lateral confinement on the plastic hinge region and peak drift ratio of the studied concrete columns under reversed cyclic loads. Results indicate that the lateral confinement significantly affects the height of plastic hinge region of circular confined columns without H-steel. Based on the analysies of test data from the study and literature, the paper suggests a simple model to predict the peak drift ratio of the confined RC columns. [less ▲]

Assessment of the suitability of gravel wash mud as raw material for the synthesis of an alkali-activated binder

in Applied Clay Science (TOP10 Journal in Mineralogy) (2018), 161(C), 110-118

Gravel wash mud (GWM), a waste product from gravel mining was dried and processed into a fine powder to be activated by different concentrations of sodium hydroxide (NaOH) solutions for the synthesis of ... [more ▼]

Gravel wash mud (GWM), a waste product from gravel mining was dried and processed into a fine powder to be activated by different concentrations of sodium hydroxide (NaOH) solutions for the synthesis of an alkali-activated binder. The GWM powders were thermally treated at five different calcination temperatures 550, 650, 750, 850 and 950°C. The characterisation of the raw material comprises the particle size distribution (PSD) by laser granulometry, the chemical and mineralogical composition by X-ray fluorescence and X-ray diffraction analysis respectively, and simultaneous thermal analysis. The performance of the alkali-activated binders was examined using compression strength tests and the microstructure was observed using scanning electron microscopy (SEM). The GWM was classified as an aluminosilicate raw material with kaolinite and illite as main clay minerals. Furthermore, a mean particle size around 6.50μm was determined for the uncalcined and calcined GWM powders. The SEM images of the developed binders showed the formation of a compact microstructure, however, relatively low strengths were achieved. This preliminary study highlights an example of an aluminosilicate prime material, which shows very promising chemical and mineralogical characteristics, but its suitability for alkaline activation without further additives was not confirmed as far as performance-based criteria are considered. [less ▲]

Impact of the height imperfections of masonry blocks on the load bearing capacity of dry-stack masonry walls

in Journal of Construction and Building Materials (2018), 165

Dry-stacked masonry walls gives rise to geometric imperfections: the height variation of different masonry blocks ΔH and the roughness of the support area Δh. This paper studies the effect of ΔH on the ... [more ▼]

Dry-stacked masonry walls gives rise to geometric imperfections: the height variation of different masonry blocks ΔH and the roughness of the support area Δh. This paper studies the effect of ΔH on the structural response and the load bearing capacity of masonry walls by highlighting the load percolation. Furthermore, an algorithm was developed to define a stress multiplier coefficient respecting the imperfections ΔH. The algorithm allowed predicting 77% of the amplified stress compared to the FE analysis and showed that the geometric imperfections govern the load percolation in a wall as well as the cracking mode and the bearing capacity. [less ▲]

The Deformation Area Difference (DAD) method for condition assessment of reinforced structures

in Engineering Structures (2018), 155

The investigation and condition assessment of bridges have a very high priority in the construction industry today. Particularly, due to the fact that many bridge structures are getting old and partly ... [more ▼]

The investigation and condition assessment of bridges have a very high priority in the construction industry today. Particularly, due to the fact that many bridge structures are getting old and partly reach the end of their useful life, the control and condition assessment of bridge structures have become very important and essential. The present research work introduces an efficient new method for condition assessment called the Deformation Area Difference (DAD) Method. This new method represents an attractive alternative to visual inspection and long-term monitoring. In this paper, the new method with its theoretical background is presented and explained by means of a laboratory experiment and some additional theoretical calculation examples. The experimental investigations have been realised on a reinforced concrete beam, which has been gradually loaded until failure. For each load step, the stiffness reduction and the apparent cracking have been monitored. High-precision measurements such as close-range photogrammetry, digital levelling and displacement sensors have been used for the determination of the deflection curve. The DAD method has been applied to identify the area of the crack pattern of the laboratory experiment. Furthermore, the method is discussed with regard to the load level and the precision of the deformation measurements. On the basis of the laboratory experiment, the applicability of the DAD method for damage detection could be proven. Furthermore, the sensitivity of the method with regard to the damage degree, the static system, the damage position and the impact of temperature variation were analysed. [less ▲]

Render comprising honeycomb and cementitious or clay or geopolymer material

Patent (2018)

Phase field simulation of early-age fracture in cement-based materials

E-print/Working paper (2018)

Krümmungsbasierte Methode zur lokalen Schadensdetektion von Brückenkonstruktionen

Presentation (2017, September)

Infrastructural integrity: The Laboratory of Solid Structures at the University of Luxembourg details its methods of assessing structural integrity

in Science and Technology (2017)