Miguel Azenha

Continuous Stiffness Monitoring of Cemented Sand through Resonant Frequency

Mixture formulation and in-situ quality control of the stabilized soils often represent difficult and challenging tasks. The present paper addresses the possibility of using a variant to a recently developed non-destructive technique for continuous monitoring of stiffness of hardening materials as a supporting means to the above-mentioned tasks. The material to be tested is placed inside a polycarbonate mold placed in simply supported conditions. The technique is based on the continuous monitoring of the first resonant frequency of this composite beam, which evolves as a consequence of the hardening of the material, and can be correlated with its E-modulus. The usefulness and potential of this experimental methodology for mixture formulation and quality control of stabilized soils is shown through a series of tests conducted on laboratory since the instant of mixing until 7 days. The conducted tests include complementary methodologies of characterization such as E-modulus measured on specimens with strain instrumentation, as well as monitoring with recourse to bender-extender elements.

Numerical benchmark campaign of COST Action TU1404 – microstructural modelling

This paper presents the results of the numerical benchmark campaign on modelling of hydration and microstructure development of cementitious materials. This numerical benchmark was performed in the scope of COST Action TU1404 “Towards the next generation of standards for service life of cement-based materials and structures”. Seven modelling groups took part in the campaign applying different models for prediction of mechanical properties (elastic moduli or compressive strength) in cement pastes and mortars. The simulations were based on published experimental data. The experimental data (both input and results used for validation) were open to the participants. The purpose of the benchmark campaign was to identify the needs of different models in terms of input experimental data, verify predictive potential of the models and finally to provide reference cases for new models in the future. The results of the benchmark show that a relatively high scatter in the predictions can arise between different models, in particular at early ages (e.g. elastic Young’s modulus predicted at 1 d in the range 6-20 GPa), while it reduces at later age, providing relatively good agreement with experimental data. Even though the input data was based on a single experimental dataset, the large differences between the results of the different models were found to be caused by distinct assumed properties for the individual phases at the microstructural level, mainly because of the scatter in the nanoindentation-derived properties of the C-S-H phase.

Glycerol resulting from biodiesel production as an admixture for cement-based materials: an experimental study

Concrete admixtures are frequently expensive and may carry relevant ecological footprints, reason why there is a growing necessity and interest in finding cheaper and more sustainable alternatives. The present work focused on the evaluation of the potential benefits that might be harvested by adding a partially purified biodiesel by-product as an admixture to cement-based materials. An experimental programme was carried out on several mixes of cement paste and mortar, incorporating the by-product in the cementitious mix in the following mass fractions (as a function of cement content): 0.5, 1 and 3%. Several testing techniques have been deployed for characterising material properties of the tested cement pastes and mortars, namely: flowability, setting time, compressive strength, elastic modulus, shrinkage and permeability. The obtained results led to the main observation that biodiesel-derived glycerol can be used as an accelerating admixture with the optimum mass faction of 1%.

Continuous Monitoring of Concrete Mechanical Properties since an Early Age to Support Construction Phasing

FEDER funds through the Operational Program for Competitiveness Factors - COMPETE and National Funds through FCT - Portuguese Foundation for Science and Technology under the project ViscoDyn EXPL/ECM-EST/1323/2013, as well to the Research Unit ISISE

On-site Monitoring of Mass Concrete

On-site monitoring of mass concrete offers several benefits. It may comprise a wide range of objectives from (i) the maintaining of adequate temperature conditions for the evolution of the desired concrete properties and to (ii) the determination of thermal and mechanical parameters for verification of the calculation models and assumptions applied for crack assessment of the considered structure. Next to very general information on monitoring of mass concrete, this chapter presents different levels of measures with regard to the purpose and expected insights into each level, available instruments and least requirements on practical application, as well as possibilities for result verification. The chapter focuses on both established techniques with comprehensive experiences in many applications and comparably new techniques available on the market. Finally, the presented techniques and approaches were exemplified on three different application examples with regard to different measurement systems as well as types of structures.

Study of Early Age Stiffness Development in Lime–Cement Blended Mortars

Lime-cement blended mortars are frequently used in building conservation, as well as in new masonry constructions. Since mortar plays an important role in governing the non-linear behavior and global performance of masonry from the earliest moments of construction, this work intends to study the evolution of its elastic modulus from very early ages. The development of stiffness in blended mortars has been studied using a recently developed approach called EMM-ARM (Elasticity Modulus Monitoring through Ambient Response Method). The method is based on continuous modal identification of the first flexural resonant frequency of composite beams that contain the material to be tested. The evolution of resonant frequency identified during the experiment can be directly correlated with the Young’s modulus by using the dynamic equation of motion. The experimental program involves validation of the applicability of EMM-ARM in blended mortars by comparison with results from conventional static method of cyclic compression according to EN 12390-13. Three distinct blended mortars (with target workability of 175 mm) with 33%, 50% and 66.67% lime in binder and 1:3 binder aggregate ratio, by volume, have been studied. The evolution of Young’s modulus will permit discussion on interaction of binders involved in the mixes. Such a study will also make it possible to explore the consequences of the observed kinetics of stiffness evolution on the stress development within masonry structures since the early ages of application of the mortar interface.

An integrated framework for multi-criteria optimization of thin concrete shells at early design stages

Abstract Thin shells are crucially dependent on their shape in order to obtain proper structural performance. In this context, the optimal shape will guarantee performance and safety requirements, while minimizing the use of materials, as well as construction/maintenance costs. Thin shell design is a team-based, multidisciplinary, and iterative process, which requires a high level of interaction between the various parties involved, especially between the Architecture and Engineering teams. As a result of technological development, novel concepts and tools become available to support this process. On the one hand, concepts like Integrated Project Delivery (IPD) show the potential to have a high impact on multidisciplinary environments such as the one in question, supporting the early decision-making process with the availability of as much information as possible. On the other hand, optimization techniques and tools should be highlighted, as they fit the needs and requirements of both the shell shape definition process and the IPD concept. These can be used not only to support advanced design stages, but also to facilitate the initial formulation of shape during the early interactions between architect and structural engineer from an IPD point of view. This paper proposes a methodology aimed at enhancing the interactive and iterative process associated with the early stages of thin shell design, supported by an integrated framework. The latter is based on several tools, namely Rhinoceros 3D, Grasshopper, and Robot Structural Analysis. In order to achieve full integration of the support tools, a custom devised module was developed, so as to allow interoperability between Grasshopper and Robot Structural Analysis. The system resorts to various technologies targeted at improving the shell shape definition process, such as formfinding techniques, parametric and generative models, as well as shape optimization techniques that leverage on multi criteria evolutionary algorithms. The proposed framework is implemented in a set of fictitious scenarios, in which the best thin reinforced concrete shell structures are sought according to given design requirements. Results stemming from this implementation emphasize its interoperability, flexibility, and capability to promote interaction between the elements of the design team, ultimately outputting a set of diverse and creative shell shapes, and thus supporting the pre-design process.

Assessing Viscoelastic Properties of Concrete during its Early Ages through Forced Dynamic Excitation of Test Beams

This paper aims to demonstrate the feasibility of a recently proposed approach (termed VisCoDyn) to assess the viscoelastic behaviour of concrete from the earliest ages, by introducing a known dynamic excitation to a simply supported specimen. The method involves the continuous monitoring of the response of the tested sample in terms of amplitude (force and displacement), as well as the evaluation of the phase lag between the applied force and the response. The acquired data is then used to calculate the storage and loss moduli, according to procedures that are normally used in the context of material testing in polymer science. Indeed, the loss modulus is known to be relatable to the viscoelastic properties of materials.The paper presents the current state of development of the VisCoDyn test methodology together with several test results obtain in specimens that were tested during the first 24 hours of curing. Parallel testing with other techniques is also presented for reference.

Innovative method for the continuous monitoring of concrete viscoelastic properties since early ages: concept and pilot experiments

FEDER funds (COMPETE program) and by National Funds through FCT (Portuguese Foundation for Science and Technology) in the scope of the Research Project EXPL/ECM-EST/1323/2013

Elasticity modulus monitoring through an ambient vibration response method : application to cement-based pastes

The E-modulus of cement-based materials is a property that experiences a high rate of change at early ages, and its continuous monitoring since casting is fundamental to identify the phase transition from fluid to solid. This paper presents a study with a recently developed non-destructive method for continuous monitoring the E-modulus of cement-based materials since casting. Based on the evaluation of the first resonant frequency of a composite cantilever containing the material under testing, it is possible to detect the E-modulus growth, and also to identify the changes on its evolution due to modifications on the mix composition. Twenty one compositions are tested, encompassing cementitious pastes with five types of cement and five w/c ratios, as well as three different contents of limestone filler, fly ash, silica fume and metakaolin.