Geert De Schutter

Hydration and temperature development of concrete made with blast-furnace slag cement.

In Europe, massive concrete elements often are made with blast-furnace slag cements. To better deal with the problem of early-age thermal cracking in these cases, a new hydration model for blast-furnace slag cements is developed, which is based on isothermal and adiabatic hydration tests. In the hydration model, the heat production rate is calculated as a function of the degree of hydration and the temperature. The accuracy of temperature simulations using this new hydration model is evaluated by tests on hardening massive concrete cylinders made with blast-furnace slag cement.

A Pore-Scale Study of Fracture Dynamics in Rock Using X-ray Micro-CT Under Ambient Freeze–Thaw Cycling

Freeze-thaw cycling stresses many environments which include porous media such as soil, rock and concrete. Climate change can expose new regions and subject others to a changing freeze-thaw frequency. Therefore, understanding and predicting the effect of freeze-thaw cycles is important in environmental science, the built environment and cultural heritage preservation. In this paper, we explore the possibilities of state-of-the-art micro-CT in studying the pore scale dynamics related to freezing and thawing. The experiments show the development of a fracture network in a porous limestone when cooling to -9.7 °C, at which an exothermal temperature peak is a proxy for ice crystallization. The dynamics of the fracture network are visualized with a time frame of 80 s. Theoretical assumptions predict that crystallization in these experiments occurs in pores of 6-20.1 nm under transient conditions. Here, the crystallization-induced stress exceeds rock strength when the local crystal fraction in the pores is 4.3%. The location of fractures is strongly related to preferential water uptake paths and rock texture, which are visually identified. Laboratory, continuous X-ray micro-CT scanning opens new perspectives for the pore-scale study of ice crystallization in porous media as well as for environmental processes related to freeze-thaw fracturing.

Applicability of degree of hydration concept and maturity method for thermo-visco-elastic behaviour of early age concrete

Whereas the degree of hydration concept and the maturity method are often treated as two competitive approaches for dealing with properties of early age concrete, it is shown in this contribution that both methods principally yield the same results and conclusions. Moreover, the applicability of both methods for the delayed mechanical behaviour of the early age concrete (basic creep and relaxation) is outlined as well. In this way, together with the well known applicability for strength and stiffness development, both methods now can be recognized as valid tools for modelling the total thermo-visco-elastic behaviour of early age concrete.

Final report of RILEM TC 205-DSC: durability of self-compacting concrete

Because of the different mix design in comparison with traditional concrete and the absence of vibration, different durability characteristics might be expected for self-compacting concrete. The state-of-the-art report, prepared by RILEM Technical Committee TC 205-DSC focuses on the Durability of SCC, by first gathering the available information concerning pore structure, air-void system and transport mechanisms. The available durability results are studied and summarised keeping in mind the fundamental mechanisms and driving forces. All relevant durability issues are considered, like carbonation, chloride penetration, frost resistance, ASR, sulphate attack, thaumasite formation, fire resistance, etc... It is not the intention to give a review on these durability aspects for concrete in general. The aim however is to point at the specifics related to the use of SCC, e.g. due to the addition of a large amount of limestone filler, etc... This paper summarizes the main conclusions of the State-of-the-Art Report.

Creep and shrinkage of self-compacting concrete.

Due to its advantages during placing, self-compacting concrete (SCC) seems to be a very promissing material for concrete construction. At this moment however, not much information is available concerning the fundamental background of the properties of the SCC. At the Magnel Laboratory for Concrete Research, an extended research programme is going on in order to more fundamentally understand the behaviour of this material. This research project includes the study of the fresh, hardening and hardened SCC, with due attention given to the time-dependent mechanical behaviour. In this contribution, results are reported concerning the creep and shrinkage of SCC. The measurements are carried out on sealed and unsealed specimens in order to be able to extract basic and drying creep and shrinkage. Different mix compositions are considered, studying different parameters, like cement type, filler type, c/p (cement to powder ratio). To study the deformations in more detail, the applicability of traditional creep and shrinkage models is investigated. Well-known models like the CEB-FIP Model Code 1990, the ACI-model and the model of de Larrard are evaluated. Some suggestions are made to include the influence of the addition of the fillers in the model of the Model Code.

Numerical Model for Chloride Penetration into Saturated Concrete

Chloride-induced corrosion is the most important durability issue in a reinforced-concrete structure. In this paper, the multispecies model was used to describe the chloride transport in saturated concrete. The model was solved by using the finite-difference method by inputting parameters such as porosity, density, chemical composition of pore solution, diffusion coefficient, and chloride-binding isotherm. A depth-dependent diffusion coefficient, instead of a fixed diffusion coefficient, was used in this model. The chloride-binding isotherm was directly obtained from the diffusion test. Finally, the numerical simulation results were validated with experimental results. It was found that the numerical simulation results were in good agreement with the experimental results.

Influence of cracks and crack width on penetration depth of chlorides in concrete

ABSTRACT Chloride induced reinforcement corrosion is the main durability problem for concrete structures in a marine environment. If the chlorides reach the reinforcement steel, the latter will depassivate and start to corrode in presence of air and water. Since the corrosion products have a larger volume than the initial products, concrete stresses are induced, leading to spalling and degradation of the concrete structures. If cracks are present in concrete, the penetration of chlorides is much faster than in uncracked concrete. In this way, the corrosion process is initiated earlier and the service life is decreasing drastically. In order to investigate the effect of cracks on the chloride penetration, a testing program was carried out. Firstly, a method was developed to create cracks in concrete. Afterwards, chloride penetration tests with the non-steady state migration test described in NT BUILD 492 were carried out. From the penetration profiles, the influence of the crack width on the maximum penetration depth and the extent of the crack influencing zone were investigated. This leads to the conclusion that for increasing crack width, the maximum penetration depth is increasing and that the extent of the crack influencing zone is depending on the crack width.

Mechanical properties of self-compacting concrete

The State-of-the-Art Report of RILEM Technical Committee 228-MPS on Mechanical properties of Self-Compacting Concrete (SCC) summarizes and extensive body of information related to mechanical properties and mechanical behaviour of SCC. Due attention is given to the fact that the composition of SCC varies significantly. A wide range of mechanical properties are considered, including compressive strength, stress-strain relationship, tensile and flexural strengths, modulus of elasticity, shear strength, effect of elevated temperature, such as fire spalling and residual properties after fire, in-situ properties, creep, shrinkage, bond properties, and structural behaviour. A chapter on fibre-reinforced SCC is included, as well as a chapter on specialty SCC, such as light-weight SCC, heavy-weight SCC, preplaced aggregate SCC, special fibre reinforced SCC, and underwater concrete.

Influence of Cracks on the Service Life of Concrete Structures in a Marine Environment

Chloride initiated reinforcement corrosion is the main durability problem for concrete structures in a marine environment. If the chlorides reach the reinforcement steel, it will depassivate and start to corrode in presence of air and water. Since the corrosion products have a larger volume than the initial products, concrete stresses are induced, leading to spalling and degradation of the concrete structures. If cracks, caused by early drying, thermal effects, shrinkage movements or overstress, are present in the concrete, the penetration of chlorides is much faster compared to uncracked concrete. In this way, the corrosion process is initiated earlier and the service life is decreasing drastically. In order to study the influence of existing cracks in concrete structures on the penetration of chlorides a test program was set up at the Magnel Laboratory for Concrete Research of Ghent University, Belgium in cooperation with the “Politehnica” University of Timisoara, Romania. The first part of the test program consists of concrete specimens with artificial cracks. The chloride penetration into the concrete was realised with a non-steady state migration test and modelled with the finite element method COSMOS/FFE Thermal software. Based on the experimental and numerical results, a crack influencing factor was determined. With this factor, the resulting service life of the cracked concrete construction is determined and compared with the original service life.

Bond Behaviour and Shear Capacity of Self-Compacting Concrete

In this paper the bond mechanism of steel reinforcement to concrete and the shear capacity are examined. Tests have been conducted on conventional vibrated concrete (CVC) and self-compacting concrete (SCC). The results from pull-out tests on 200 mm cube specimens show that for the same compressive strength the maximum bond stress for SCC is as high or higher than for CVC and this for all tested diameters (8, 12 or 16 mm). The bond stress increases with increasing bar diameter. The specimens were loaded at constant rate and during testing the slip of the bars and the applied load were recorded. The four-point loading tests point out a slightly decreased shear capacity of SCC in respect to CVC with the same compressive strength. The shear capacity decreases with increasing shear span-to-depth ratio a/d (2 to 3) for all the tested concrete types. During the testing the maximum applied load was recorded and the crack and failure mechanism were observed.