Hygro-mechanical model for concrete pavement with long-term drying analysis

Concrete pavements are subjected to the combination of moisture transport, heat transport and traffic loading. A hygro-mechanical 3D finite element model was created in OOFEM software in order to analyse the stress field and deformed shape from a long-term non-uniform drying. The model uses a staggered approach, solving moisture transfer weakly coupled with MPS viscoelastic model for ageing concrete creep and shrinkage. Moisture transport and mechanical sub-models are calibrated with lab experiments, long-term monitoring on D1 highway and data from 40 year old highway pavement. The slab geometry is 3.5×5.0×0.29 m, resting on elastic Winkler-Pasternak foundation. The validation covers autogenous and drying strain on the slab. The models predict drying-induced tensile stress up to 3.3 MPa, inducing additional loading on the slab, uncaptured by current design methods

THERMO-MECHANICAL MODEL FOR CONCRETE PAVEMENT

This paper describes a numerical thermo-mechanical model for concrete pavement, implemented in OOFEM software. The thermal part is a heat transfer problem with appropriate initial and boundary conditions (sun irradiation, radiation and convection), calibrated from experimental data. Heat release from cement hydration is also included, calibrated for commonly used cements to demonstrate the difference that can be achieved with the binder selection. The mechanical part of the problem is composed of a 3D elastic concrete slab, subsoil Winkler-Pasternak elements and 1D interface elements, allowing separation in tension. The Winkler-Pasternak constants C1 and C2 were firstly determined from TP170 document and refined later from static load tests on the highway. The model validates well temperature field, static load test and provide several useful insight such as feasible time for summer casting, stress/strain fields and slab separation from the base

Behavior of predried mature concrete beams subject to partial wetting and drying cycles

The presented research focuses on the behavior of predried concrete beams with 2.5 m span subjected to cycles of nonsymmetric wetting and drying. Wetting is induced by partially immersing the specimens in a water basin. The submerged portion of the specimens was relatively low (1/5 to 1/10 of their height) leading to a highly nonuniform and nonsymmetric distribution of eigenstrains due to concrete swelling. Unlike conventional experiments on the volume changes of concrete, the measured quantity is not the axial deformation but the vertical displacement instead. This paper presents the experimental data obtained within two wetting and drying cycles, running over 1 year

MUPIF WORKFLOW EDITOR AND AUTOMATIC CODE GENERATOR

Integrating applications or codes into MuPIF API Model enables easy integration of such APIs into any workflow representing complex multiphysical simulation. This concept of MuPIF also enables automatic code generation of the computational code for given workflow structure. This article describes a ’workflow generator’ tool for the code generation together with ’workflow editor’ graphical interface for interactive definition of the workflow structure and the inner data dependencies. The usage is explained on a thermo-mechanical simulation

Micromechanical Analysis of Cement Paste with Carbon Nanotubes

Carbon nanotubes (CNT) are an attractive reinforcement material for several composites, due to their inherently high strength and high modulus of elasticity. There are controversial results for cement paste with admixed CNT up to 500 µm in length. Some results show an increase in flexural or compressive strength, while others showing a decrease in the values. Our experiments produced results that showed a small increase in fracture energy and tensile strength. Micromechanical simulations on a CNT-reinforced cement paste 50×50 µm proved that CNT clustering is the crucial factor for an increasein fracture energy and for an improvement in tensile strength

COUPLED SIMULATION FOR FIRE-EXPOSED STRUCTURES USING CFD AND THERMO-MECHANICAL MODELS

Fire resistance of buildings is based on fire tests in furnaces with gas burners. However, the tests are very expensive and time consuming. This article presents a coupled simulation of an element loaded by a force and a fire loading. The simulation solves a weakly-coupled problem, consisting of fluid dynamics, heat transfer and mechanical model. The temperature field from the computational fluid dynamics simulation (CFD) creates Cauchy and radiative boundary conditions for the thermal model. Then, the temperature field from element is passed to the mechanical model, which induces thermal strain and modifies material parameters. The fluid dynamics is computed with Fire Dynamics Simulator and the thermo-mechanical task is solved in OOFEM. Both softwares are interconnected with MuPIF python library, which allows smooth data transfer across the different meshes, orchestrating simulations in particular codes, exporting results to the VTK formats and distributed computing

Steel elements with timber fire protection - experiment and numerical analysis

Steel structural elements are sensitive to elevated temperatures, while timber elements have good thermal insulation properties. Timber material can fulfill the role of fire protection of steel members. The effect of the protection is demonstrated on an experiment with three beams with different levels of the protection, placed into a horizontal furnace. The experimental task was also numerically analysed with standard computational approach given by the Eurocode [1, 2], which leads to an interesting comparison, as the calculation is supposed to provide higher temperatures and larger deformations compared to the experimental data

FIRE PROTECTION OF STEEL ELEMENTS USING LIGHTWEIGHT HYBRID CEMENT MORTAR

Material properties of steel structures are significantly reduced at high temperatures, so a fire protection has strong positive impact on the fire resistance of the structure. Fire resistance of steel elements can be increased using a layer of cement-based materials as a fire protection. Most of commonly used cement-based materials do not withstand high temperatures without noticeable reduction of mechanical properties. Hybrid cement showed some interesting properties in the way of resistance to high temperatures and adhesion to steel surfaces, thus its behavior during fire exposure should be investigated. One experimental analysis with numerical simulation is presented in this article. It examines thermal material properties of lightweight hybrid cement mortar with expanded perlite from a simple experiment with a lab gas burner

HYDRATION OF PLASMA-TREATED ALUMOSILICATE BINDERS

Plasma treatment offers several applications in material science. In this research, the potential of plasma treatment is explored on the hydration of hydrophilic CNT-enriched cement and hydrophilic fly ash. The evolution of the hydration heat and the compressive strength show that a hydrophilic surface slightly accelerates the early-age hydration kinetics, while the long-term properties remain unchanged

A WEAK ALKALI BOND IN (N, K)–A–S–H GELS: EVIDENCE FROM LEACHING AND MODELING

The alkali bond in (N, K)–A–S–H gels presents an up-to-date insufficiently resolved issue with significant consequences for efflorescence in alkali-activated materials. A series of experiments shows nearly all alkalis are leachable from alkaliactivated fly-ash and metakaolin in excessive amounts of deionized water. A diffusion-based model describes well the alkali leaching process. Negligible changes of the (N, K)–A–S–H gel nanostructure indicate that Na,K do not form the gel backbone and H3O+ is probably the easiest substitution for the leached alkalies. Small changes in the long-term compressive strength of leached specimens support this hypothesis