D. Van Gemert

CHEMICAL, MICROBIOLOGICAL AND IN SITU TEST METHODS FOR BIOGENIC SULFURIC ACID CORROSION OF CONCRETE

Abstract Biogenic sulfuric acid corrosion is often a problem in sewer environment: it can lead to a fast degradation of the concrete structures. Since the involvement of bacteria in the corrosion process was discovered, considerable microbiological research has been devoted to the understanding of the corrosive process. Mechanical engineers have focused on experiments comparing the resistance of several concrete mixes against biogenic sulfuric acid corrosion. Because of a lack of standardised methods, different test methods have been used, and various parameters have been modified to evaluate the resistance of the materials. The research done on sulfuric acid corrosion of concrete can roughly be divided in three groups: chemical tests, microbial simulation tests, and exposure tests in situ. In this article, an overview of the recent developments in the test methods for biogenic sulfuric acid corrosion and the obtained results are presented. Possible differences between biogenic sulfuric acid corrosion and chemical sulfuric acid corrosion are delineated.

Force transfer in epoxy bonded steel/concrete joints

Abstract External steel reinforcements are being used for restoring and repairing concrete structures. The external steel is glued to the concrete with an epoxy adhesive. The joints are usually loaded in pure shear or in bending shear. Experimental results of the stress distribution in the adhesive layer in laboratory test specimens are given and the testing machine, developed for these experiments, is also described. The ultimate load bearing capacity and the phenomena accompanying rupture of the connection are examined. From the experiments, design rules are drafted for the external reinforcements and their anchorage to the concrete.

Resistance to biogenic sulphuric acid corrosion of polymer-modified mortars

Abstract The use of polymer-modified mortar and concrete (PMM and PMC) is investigated to improve the durability of concrete sewer pipes. The aim of the research is to ameliorate the resistance of concrete to biogenic sulphuric acid attack through polymer modification. Prior to the durability tests, experimental research is carried out to reveal the influence of polymer modification on the physical and mechanical properties of mortar and concrete. The results of this research are presented in this paper. Due to the interaction of the cement hydrates and the polymer particles or film, an interpenetrating network originates in which the aggregates are embedded. The density, porosity and location of the polymer film depend on the type of polymer emulsion and on its minimum film-forming temperature (MFT). If air entrainment is restricted, an increased flexural strength is measured. Scanning electron microscope (SEM) analyses reveal the presence of polymer film and cement hydrates in the mortar. The polymer film causes a retardation of the cement hydration as well as a restriction of crystal growth.

Effect of mixing procedure on injectability of cementitious grouts

Injection grouts made of cement and mineral additives, such as lime and natural or artificial pozzolans, coagulate in suspension; the use of a superplasticizer is not sufficient to improve injectability when penetrability in very fine voids is required. The effect of two different mixing procedures, one with a mechanical and one with an ultrasonic mixer, has been studied. Ultrasonic mixing improves dispersion, especially when silica fume is added to the grout, and permits the use of a water content lower than that of high turbulence mixing for the achievement of the same penetrability of the grout.

Structural restoration of wooden beams by means of epoxy resin

The structural restoration of deteriorated beam ends by means of epoxy mortar is discussed. The results of a test programme are presented: determination of bond strength as a function of the degree of humidity of the wood; anchoring strength of glass-fibre reinforced polyester bars and steel bars, glued in wood or in epoxy mortar. A comparison is made between the results of these elementary tests, and the behaviour of restored full-size beams. The phenomena leading to rupture of the structural element are described, in order to define the direction of future research.

Structural repair of a reinforced concrete plate by epoxy bonded external reinforcement

Abstract The paper deals with the repair of a severely damaged reinforced concrete plate with epoxy bonded steel strips. The method consists of gluing steel elements to the concrete by means of epoxy glue. The paper describes the structural damage to the plate, and the procedure followed in handling the repair. Results of laboratory experiments related to the actual repair are given. Other possible applications for the repair technique are indicated.

Sustainable construction: challenges, contribution of polymers, research arena

Sustainable development is one of the leading civilization ideas. This term means such a development that satisfies the present needs without a limitation of the possibility of satisfying the needs in the future. Sustainable development in construction is particularly important, as this branch of the industry is consuming enormous amounts of mass and energy. A new research area has been created by this idea. The new fields of investigation are involved with material, energetic, and environmental conditions, but also with such topics as protection against noise and the methods of the evaluation of the efficiency of waste materials storage. Merging the worlds of cement concrete and concrete-polymer composites opens ways to synergetic effects that support sustainable material development. Implementation of the idea of sustainable development in the construction industry will be a source of scientific and engineering inspiration for many years to come. 1. Sustainable development – a challenge for civilisation The notion of sustainable development aspires to the role of a leading civilisational idea. Sustainable development “implies meeting the needs of the present without compromising the ability of future generations to meet their own needs” [UN, 1987]. The term is the most frequently found expression in forecasts and similar studies. It follows from philosophical premises and – in Poland – it is a constitutional prerequisite: ”The Republic of Poland shall safeguard the independence and integrity of its territory and ensure the freedoms and rights of persons and citizens, security of citizens, safeguarding of Poland‟s national heritage, and ensure the protection of the natural environment pursuant to the principles of sustainable development.” Therefore, sustainable development constitutes a principle that is to be followed by the Republic of Poland, in turn safeguarding fundamental values. In the Environmental Protection Laws, the definition of sustainable development is expanded further: such socio-economic development, in which – in order to equalise the opportunities to access the environment by individual communities or their members – both of contemporary generations and those still to come – a process of the integration of

Evolution in Modeling Microstructure Formation in Polymer-Cement Concrete

Hardened PCC material consists of two interpenetrating matrices of polymer phase and hydrated cement with random dispersion of the aggregates. Different models have been proposed to describe the built up of microstructure in this material, and to explain or even to design its characteristic properties. This paper deals with the evolution of the microstructure models with time, showing a growing understanding of the microstructure formation during hydration and hardening, as well as a better knowledge of the morphology and behavior of the polymer phase within the composite material. Better understanding of microstructure formation was supported by the development and improvement of SEM analysis technique, and further integration of the time scale in the models was enabled by ESEM analysis during hydration and hardening of fresh mixes. Enhancement of SEM resolution and magnification capabilities also enabled to study the effect of very low amounts of polymer on the microstructure. The paper deals with the physical mechanisms, described by the models, and shows the improvements added in the successive models, leading to an increased understanding of the synergies realized by the interaction and collaboration of polymers and hydraulic cement.

Triaxial testing of historic masonry, test set-up and first results

In 1998 the Reyntjens Laboratory acquired a big size triaxial cell testing device for the testing of heterogeneous materials. The goal of the triaxial test set-up is to gather information about the material behaviour under a multi-axial stress state. In that it simulates the confining pressure of the surrounding material. In 1998 and 1999 the test set-up was developed. Meanwhile the first test results on the triaxial behaviour of lime mortar and masonry have been acquired. In the case of masonry cores, special attention is paid to the resulting biaxial yield-criterion. as this is of major importance for an assessment of the structural safety of the masonry. The study on lime mortar aims at determining its deformability in the case of a triaxial compression state. Especially the influence of the pore structure is evaluated. The research goal is the better understanding of the mechanical behaviour of ancient masonry, seeking for scientific explanation about the relative high mechanical strength of masonry built up with lime mortar that is considered to be a weak material. The test set-up is illustrated, the first test results and the resulting biaxial yield criterion for masonry based on cores are presented. Triaxial tests on both hydrated and hydraulic lime mortars as well as the mutual influence between the triaxial behaviour of the mortar and its pore structure are studied and discussed.

Diffusion-Convection transport of salt solutions in cracked porous building materials Part 1: Parameters, model description and application to cracks

Diffusion-convection transport through differently oriented cracks is investigated in cell experiments. Testing two perpendicular directions of the cracks proves the existence of rotational convective flow in cell experiments. Despite the saturated condition and the equal water levels at both sides of the sample at the start of the test, the results can not be explained by a concentration dependent diffusion only. Additional convective transport takes place due to a difference of hydrostatic pressure in both cells. Based on these findings a 3D model is developed to simulate the measured transport through isolated cracks. Subsequently, it was possible to simulate transport through cracked ceramic brick, revealing dominant transport through the cracks, largely overpassing transport through the uncracked porous zones.