Cementitious Materials (cementitious + material)

Distribution by Scientific Domains
Engineering100%

Selected Abstracts

Experimental analysis of compaction of concrete and mortar

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 15 2001
Nicolas Burlion
Abstract Compaction of concrete is physically a collapse of the material porous microstructure. It produces plastic strains in the material and, at the same time, an increase of its bulk modulus. This paper presents two experimental techniques aimed at obtaining the hydrostatic response of concrete and mortar. The first one is a uniaxial confined compression test which is quite simple to implement and allows to reach hydrostatic pressures of about 600 MPa. The specimen size is large enough so that concrete with aggregate sizes up to 16 mm can be tested. The second one is a true hydrostatic test performed on smaller (mortar) specimens. Test results show that the hydrostatic response of the material is elasto-plastic with a stiffening effect on both the tangent and unloading bulk moduli. The magnitude of the irreversible volumetric strains depends on the initial porosity of the material. This porosity can be related in a first approximation to the water/cement ratio. A comparison of the hydrostatic responses obtained from the two testing techniques on the same material show that the hydrostatic response of cementitious materials cannot be uncoupled from the deviatoric response, as opposed to the standard assumption in constitutive relations for metal alloys. This feature should be taken into account in the development of constitutive relations for concrete subjected to high confinement pressures which are needed in the modelling of impact problems. Copyright © 2001 John Wiley & Sons, Ltd. [source]

A numerical model for the time-dependent cracking of cementitious materials

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 7 2001
G. P. A. G. van Zijl
Abstract A unified finite element formulation is presented for the analysis of the time-dependent cracking of cementitious materials. The rate-type constitutive law incorporates linear visco-elasticity and continuum plasticity. The former accounts for the bulk creep via a Maxwell chain, while the latter describes crack initiation and propagation via a softening, anisotropic Rankine yield criterion. The rate dependence of bond ruptures leading to fracture is accounted for by considering the viscosity of the cracking process. This contribution to the cracking resistance also regularises the localisation process. It is demonstrated how other important phenomena in cementitious materials, such as stress-dependent hygral and thermal shrinkage, can be incorporated into the computational framework. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Gekoppelter Wärme- und Stofftransport einschließlich der Korrosionsprozesse in porösen Baustoffen mit dem Simulationsprogramm AStra

BAUPHYSIK, Issue 3 2007
Rosa Maria Espinosa Dr.-Ing.
Zur Beschreibung von Wärme- und Feuchtetransportvorgängen gekoppelt mit Stofftransportprozessen in porösen Baustoffen ist ein Differentialgleichungssystem bestehend aus der Energieerhaltungsgleichung und den Massenerhaltungsgleichungen aller beteiligten Stoffe einschließlich des Wassers aufzulösen. Hierzu ist die Modellierung der stattfindenden Phasenumwandlungen der vorliegenden Stoffe und der chemischen Reaktionen der Porenlösung mit der Baustoffmatrix erforderlich. Zu unterscheiden sind dazu inerte, nicht reaktive Baustoffe und reaktionsfähige, zementgebundene Baustoffe. Für die numerische Simulation dieser Vorgänge bzw. die praktische Handhabbarkeit der Problemlösung wurde eine benutzerfreundliche Programmoberfläche AStra geschaffen, die neben dem eigentlichen Berechnungsmodul die benötigten Pre- und Postprocessing Möglichkeiten beinhaltet. Für die Berechnung des zeitlichen Verlaufs eines lösenden oder treibenden Angriffs auf zementgebundene Baustoffe wird durch eine in Abhängigkeit der beteiligten Spezies geeignete Vorauswahl von ablaufenden Reaktionen der Rechenaufwand für die Vorhersage von Nichtgleichgewichtszuständen optimiert und damit die Möglichkeit geschaffen zeitliche Abhängigkeiten mit vertretbarem Berechnungsaufwand zu beschreiben. Zusätzlich können mechanische Beanspruchungen als Folge von Kristallisationsvorgängen zumindest qualitativ vorhergesagt werden. Im Folgenden werden eine Übersicht der implementierten Berechnungsmodelle sowie drei Anwendungsbeispiele von AStra vorgestellt. Coupled heat and mass transfer simulation including corrosion in porous building materials with the program AStra. For the description of corrosion processes of porous building materials, it is necessary to solve a system of coupled (non-linear) differential equations, which consists of a conservation equation for the energy and one for the mass of each substance (including water and air), whose content may change within the simulated time period. Indeed, it must be distinguished between degradation of reactive and of inert materials. The computation program AStra simulates a coupled transport of heat, moisture, air and chemical substances in porous materials. AStra consists of a user interface for pre- and post-processing and a computation module (solver), which contains the necessary algorithms to solve the system of coupled differential equations. Mathematical models for phase changes of salts and for chemical reactions between substances, including the components of the material matrix in case of cementitious materials, were developed. Furthermore, the computational cost for the prediction of the corrosion of cementitious materials was optimized by means of an adequate pre-selection of chemical reactions. Thus, it is possible to simulate corrosion processes within justifiable simulation time. On the other hand, a simulation of the mechanical stress resulting from crystallization processes is possible. This paper presents some applications of the programs and a brief introduction into their theoretical basis. [source]