In this contribution, a computational framework for the analysis of tertiary concrete creep is presented, combining a discrete element framework with linear visco-elasticity and rate-dependency of crack opening. The well-established Lattice Discrete Particle Model (LDPM) serves as constitutive model. Aging visco-elasticity is implemented based on the Micro-Prestress-Solidification (MPS) theory, linking the mechanical response to the underlying physical and chemical processes of hydration, heat transfer and moisture transport through a multi-physics approach. The numerical framework is calibrated on literature data, which include tensile and compressive creep tests, and tests at various loading rates. Afterwards, the framework is validated on time-to-failure tests, both for flexure and compression. It is shown that the numerical framework is capable of predicting the time-dependent evolution of concrete creep deformations in the primary, secondary but also tertiary domains, including very accurate estimates of times to failure. Finally, a predictive numerical study on the time-to-failure response is presented for load levels that can not be experimentally tested, showing a deviation from the simple linear trend that is

Motivated by tunnel accidents in the recent past several investigations into the sustained load behavior of adhesive anchors have been initiated. Nevertheless, the reliable life-time prediction of bonded anchor systems based on a relatively short period of testing still represents an unsolved challenge due to the complex non-liner viscoelastic behaviour of concrete and adhesives alike. This contribution summarizes the results of a comprehensive experimental investigation and systematically carried out time-to-failure analysis performed on bonded anchors under sustained tensile load. Two different adhesive materials that find widespread application in the building industry were used, one epoxy and one vinylester based. Performed experiments include full material characterizations of concrete and the adhesives, bonded anchor pull-out tests at different loading rates, and time-to-failure sustained load tests. All anchor tests are performed in a confined configuration with close support. After a thorough review of available experimental data and analysis methods in the literature the experimental data is presented with the main goals to (i) derive a set of recommendations for efficient time to failure tests, and (ii) to provide guidance for the analysis of load versus time-to-failure test data. Finally, a new approach based on a sigmoid function is proposed and compared to the established regression models. The analyses indicate a better agreement with the physics of the problem and, thus, more reliable extrapolations.

In the last decades, fastening systems have become an essential part of the construction industry. Post-installed mechanical anchors are frequently used in concrete members to connect them with other load bearing structural members, or to attach appliances. Their performance is limited by the concrete related failure modes which are highly influenced by the concrete mix design. This paper aims at investigating the effect that different aggregates used in the concrete mix have on the capacity of an undercut anchor under tensile quasi-static loading. Three concrete batches were cast utilising three different aggregate types. For two concrete ages (28 and 70 days), anchor tensile capacity and concrete properties were obtained. Concrete compressive strength, fracture energy and elastic modulus are used to normalize and compare the undercut anchor concrete tensile capacity employing some of the most widely used prediction models. For a more insightful comparison, a statistical method that yields also scatter information is introduced. Finally, the height and shape of the concrete cones are compared by highly precise and objective photogrammetric means.

For decades, concrete plays an important role worldwide as a structural material. Construction planning and reliability assessment require a thorough insight of the effects that determine concrete lifetime evolution. This study shows the experimental characterization as well as the results of subsequent aging simulations utilizing and coupling a Hygro-thermo-chemical (HTC) model and the Lattice Discrete Particle Model (LDPM) with aging effects for concretes at various early ages. The HTC component of the computational framework allows taking into account any form of environmental curing conditions as well as known material constituents and predicts the level of concrete maturity. Mechanical response and damage are captured by the well-established LDPM, which is formulated in the framework of discrete meso-scale constitutive models. The chemo-mechanical coupling is accomplished by a set of aging functions that link the meso-scale material properties to an effective aging degree, accounting for cement hydration, silica fume reaction, polymerization, and temperature effects. After introducing the formulations the framework is applied to experimental data of 3 standard low and higher strength concretes. Investigated tests include two types of unconfined compression, Brazilian splitting, three-point-bending, and wedge splitting. Following the model calibration the framework is validated by purely predictive simulations of structural level experimental data obtained at different ages for the same concretes.

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