Controlling crack formation since early ages: contributions of COST Action TU1404 and research project IntegraCrete

The present contribution summarizes main activitiesand conclusions brought about by two funded projects: EU-funded COST Action TU1404 ‘Towards the next generation of standards for service life of cement-based materials and structures’ and Portugal-EU funded project IntegraCrete ‘A comprehensive multiphysics and multiscale approach to the combined effects of applied loads and thermal/shrinkage deformations in reinforced concrete structures’POCI-01-0145-FEDER-007633 (ISISE)and by UID/ECI/04708/2019-CONSTRUCT -Instituto de I&D em Estruturas e Construções, funded by national funds through the FCT/MCTES (PIDDAC). FCT and FEDER (COMPETE2020) are also acknowledged for the funding of the research Project IntegraCrete PTDC/ECM-EST/1056/2014 (POCI-01-0145-FEDER-016841). The financial support of COST Action TU1404 through its several networking instrument

Numerical study on restraints effects in massive foundation slabs

The aim of the presented study is to simulate the restrained stresses in early age massive foundation slabs. The character of self-induced stresses related to internal restraints resulting from inhomogeneous distribution of thermal-humidity fields as well as restraint stresses related to limitation of structure deformations freedom are described in the article. The combined thermal and both autogenous and drying shrinkage effects are considered. The presented numerical study on the above mentioned effects are conducted with the use of original numerical model. The distribution and the magnitude of stresses induced by hydration temperature and shrinkage are computed, both in heating and curing phase of concrete curing. The special attention is paid to the externally restraint stresses depending strongly on contact layer between the slab and subsoil. Finally, the total restraint stresses are computed for slabs with different thickness.info:eu-repo/semantics/publishedVersio

Numerical simulation of the structural behaviour of concrete since its early ages

Tese de doutoramento. Engenharia Civil. Faculdade de Engenharia. Universidade do Porto, School of Enegineering. University of Tokyo. 200

Monitoring and simulating humidity profiles in concrete elements during drying

Integrated approaches towards the measurement and simulation of the internal humidity of cement based materials, in which the same team accomplishes all the tasks are scarce in the literature. Furthermore, the measurement of humidity in cement-based materials is a subject that requires experience and significant care to obtain reliable data. In view of this reasoning, the research here reported pertains to an integrated approach that focuses in two main topics: (a) several issues regarding the experimental measurement of internal humidity in cement based materials through sleeved humidity probes, with test series devoted to each issue (namely the type of sensor, the existence of Gore Tex fabric to protect the sensor and the influence of the permanence time of probes within measuring sleeves); (b) an experimental program for humidity measurement in concrete specimens, followed by the simulation through the formulation forwarded in the MC1990/2010. The successful achievement of the measurements and simulations reported herein corroborate the validity of the adopted strategies and assumptionsFEDER funds through the Competitivity Factors Operational Programme - COMPETE and by national funds through FCT within the scope of the projects POCI-01-0145-FEDER-007633 and POCI-01-0145-FEDER-016841 (IntegraCrete - PTDC/ECM-EST/1056/2014). The PhD grant of the second author is also gratefully acknowledged (SFRH/BD/80682/2011

Bender-extender elements for characterization of cement paste at early ages

The embedment of bender-extender elements in cement-based materials for assessment of the early development of mechanical properties is a relatively unexplored field. This technique provides the opportunity of embedding piezoelectric elements (emitter and receiver) into the tested material at the fresh state, generate waves and assess the velocity of propagation. It has the interesting feature of allowing distinct frequencies of wave to be explored at the several stages of stiffening of the testing material, thus maximising signal intensity and facilitating the identification of velocities. This paper presents an exploratory application of bender- extender elements to cement paste specimens, in parallel with other established experimental techniques, such as the Vicat needle, ultrasound pulse velocity measurements (with external probes), measurement of E-modulus through cyclic compressive testing and continuous assessment of the E-modulus of the cement paste through EMM-ARM. The results are evaluated and discussed in an integrated manner and conclusions are drawn in regard to the potential of using bender-extender elements in cement-based materialsFEDER funds through the Competitivity Factors Operational Programme - COMPETE and by national funds through FCT – Foundation for Science and Technology within the scope of the projects POCI-01-0145-FEDER-007633 and POCI-01-0145-FEDER-016

A cost-effective method to measure delayed deformations of building materials

Characterization of deformation related properties like creep, moisture expansion, drying shrinkage, and others, usually require a high number of specimens and long-term tests. Traditional measuring methods, such as LVDTs or Strain Gauges, end up being expensive, considering the initial cost, the time they are allocated to the experimental campaign, and the required data acquisition systems. This research proposes an innovative cost-effective solution to measure strains on building material using microscope scale images. The main features of the method are: a) cost-effective, b) appropriate for long-term tests, c) possibility of using with high number of specimens, d) good precision (<3μm), and e) open source. The development is being described into two stages including methodological aspects and validation which are discussed in this work. The developed method is based on a sliding ruler that is connected to the specimen. The ruler has two parts (one fixed and one movable), and their relative movement, as consequence of the deformation, is monitored with indicators. Using a USB microscope to capture sequential images, it is possible to determine the evolution of the deformation using artificial vision algorithms. This methodology was validated with traditional measurement methods.This work was financed by European Union’s Horizon 2020 research and innovation programme through Marie Sklodowska-Curie project SUBLime [Grant Agreement no. 955986]. This work was partly financed by FCT / MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE), under reference UIDB / 04029/2020

Mechanical properties of lime–cement masonry mortars in their early ages

Lime–cement mortars are often used in restoration of existing buildings (especially twentieth century onward) as well as new constructions, in order to combine the individual strengths of either type of binder. Despite the knowledge that mortars have a significant impact on the non-linear mechanical behaviour of masonry from the earliest moments of construction, literature that systematically quantifies the impact of adding lime to cement mortars, or vice versa is scarce and scattered. This work is therefore focussed on bridging the research gap that exists in lime–cement masonry mortars with regard to their mechanical properties in the early ages (up to 7 days of curing). Five different mix compositions have been studied with 1:3 binder-aggregate ratio and 10% to 75% lime content in the binder, both by volume. Changes in properties like mechanical strength and stiffness along with ultrasound pulse velocity have been quantified, correlated and associated with change in quantity of lime in the binder (by volume) of the mortar. It was found that every 10% increase in the quantity of lime in the binder led to a 14% decrease in mechanical strength and a corresponding 12% decrease in stiffness, at 7 days of curing age. E-modulus was found to evolve faster than flexural strength, which in turn was found to evolve faster than compressive strength. Impact of curing temperature and the concept of activation energy has been addressed for the mix 1:1:6 (Cement:Lime:Sand).EuLA - European Lime Association; FCT Phd Scholarship of 1st author. Portuguese Foundation for Science and Technology (FCT) to the Research Project PTDC/ECM-EST/1056/2014 (POCI-01-0145-FEDER-016841), as well to the Research Unit ISISE (POCI-01-0145-FEDER-007633

Impact of moisture curing conditions on mechanical properties of lime-cement mortars in early ages

Blended lime-cement mortars, which are frequently used in masonry construction, mature as a result of two different phenomena, namely lime carbonation and cement hydration. At any given temperature, these two processes require different moisture conditions for optimal contribution to the mechanical performance of mortar. Since mortars have an impact on the non-linear behavior of masonry from the time of application, it is necessary to optimize their performance with regard to composition and curing conditions. It is expected that a suitable choice of mortar in conjunction with the unit will provide better performance of masonry by reducing risk of cracking and facilitating durability of masonry. This work aims at studying the impact of environmental relative humidity (RH) in the curing process of lime-cement mortars, focusing on their early age behavior. Two mixes with 25% and 67% lime in the binder (by volume), binder-aggregate ratio of 1:3 and target workability of 175±10 mm were chosen for the study. Mechanical properties like compressive strength, flexural strength, open porosity and density have been studied at 2, 4 and 7 days of curing age. Temperature was kept constant at 20°C while three distinct environmental humidity conditions were tested: sealed environment, 90% RH, and 60% RH. Results have been explored to understand how the evolution of basic mechanical properties changed as a function of curing RH. Curing in sealed conditions and 90% RH did not result in similar values of strength, in either of the two blended mixes. For the mix with 25% lime - 3C1L12S (25%), hardening appeared to be guided by cement hydration. For the mix with 67% lime - 1C2L9S (67%), curing in RH of 60% and 90% resulted in almost the same strength at day 7, demonstrating that lime carbonation may be important earlier than 7 daysEuLA - European Lime Association, FCT PhD Grant of 1st Author. European Lime Association for funding this project. Funding provided by the Portuguese Foundation for Science and Technology (FCT) to the Research Project PTDC/ECMEST/1056/2014 (POCI-01-0145-FEDER-016841), Research Unit ISISE (POCI-01-0145-FEDER-007633), and scholarship SFRH/BD/137358/201

Mechanical characterization of lime-cement mortars: E-modulus and fracture energy

In masonry constructions, the choice of mortar composition is usually guided by requirements of the final application, which could range from new constructions to conservation projects. Often, lime and cement are combined together, to overcome their individual shortcomings and consequently serve as a suitable binder in masonry mortars. Depending on their proportion in the mixture, it may be possible to obtain a desired range of characteristics in different mechanical properties like strength and stiffness. However, existing studies exploring this subject are scarce. Therefore, this work aims at adopting a systematic approach to studying the effect of different lime-cement ratios on the mechanical properties of masonry mortars, specifically targeting a discussion on E-modulus and fracture energy. Three distinct mixes with quantities of lime varying from 25% to 67% (by volume) have been studied. The benefits and trade-offs associated with substitution of different quantities of cement with lime in mortars, have been explored with regard to resistance to crack propagation.EuLA - European Lime Association. FCT PhD grant for the 1st author. European Lime Association for funding this project. Funding provided by the Portuguese Foundation for Science and Technology (FCT) to the Research Project PTDC/ECM-EST/1056/2014 (POCI-01-0145-FEDER-016841), as well to the Research Unit ISISE (POCI-01-0145-FEDER-007633

Numerical simulation of the structural behaviour of concrete tetrapods subject to imposed deformations and applied loads

Tetrapods for coastal protection are frequently used in break waters for dissipation of wave energy. During their service, these plain concrete elements usually exhibit degradation signs with frequent premature rupture of one or more of their legs when located in highly aggressive environments subjected to extreme wave action. These ruptures tend to decrease the efficiency of breakwaters as a whole, thus diminishing their capacity to absorb wave energy. The present paper aims to contribute to a better understanding of the stress levels that occur in this kind of mass concrete elements, taking into account imposed deformations (associated with heat of hydration) and applied loads. A thermo-mechanical numerical simulation tool (3D), based on the finite element method, is used for the assessment of heat of hydration induced stresses. After an initial discussion of the temperature development inside the tetrapod, the corresponding residual stresses are presented and discussed, and conclusions are withdrawn with regard to the available capacity of concrete to withstand further applied loads. Finally, the subsequent behaviour of the tetrapod is assessed and compared to alternative solutions with internal reinforcement of the tetrapod legs, such as reinforced concrete (using stainless steel), steel fibre reinforced concrete and reinforced concrete with FRP’s