Completed doctoral projects
Impregnation of concrete structures
Anders Selander, Material, has been doing a doctoral project at The Royal Institute of Technology since 2004 that is financed by Formas and CBI’s Members’ Association. Head supervisor is Johan Silfwerbrand and assistant supervisors are Jan Trägårdh and Mårten Janz. The purpose of the project is to increase the understanding of how different types of water repellent agent (WRA) function in concrete and how they affect the transport mechanisms. The project includes several major series of experiments in the laboratory, field measurements and model development. The results thus far show that the penetration depth of a given WRA is determined by three factors – the porosity and moisture level of the concrete at the relevant time of treatment, and how long the treatment lasts. The influence of these three factors has been quantified and presented in an equation for the most common products on the market. Studies of moisture transportation and moisture fixing have created new knowledge regarding which part of the pore system is influenced by impregnation. Anders presented a licentiate thesis in October 2006 and is set to defend the PhD thesis in early 2010.
Advanced concrete material
Carsten Vogt, Material, has been doing a doctoral project at The Royal Institute of Technology since 2004 that is financed through different R&D assignments and CBI’s Members’ Association. Head supervisor is Jonas Holmgren, the Royal Institute of Technology, and assistant supervisor is Björn Lagerblad. The project concerns ultrafine particles, fibres and silica in cement-based material. The purpose of the project is to better understand what the composition of concrete should be in order to achieve specific chemical or physical characteristics. The project includes substudies of ultrafine particles, silica, glass fibres and glass fibre reinforced shotcrete. The benefit of the project is the development of ultra-high-performing glass fibre reinforced shotcrete. Carsten intends to present a licentiate thesis during Autumn 2009.
Incentive for technology development within operation and maintenance of roads and railways
In March 2007, Torbjörn Stenbeck, defended a project financed by Banverket, SBUF (The Development Fund of the Swedish Construction Industry) and The Swedish Road Administration and that has been linked to The Royal Institute of Technology and Centre for Operation and Maintenance. Head supervisor was Johan Silfwerbrand and assistant supervisor Folke Snickars of The Royal Institute of Technology. The main aim was to examine the way in which technology development can be promoted within operation and maintenance. Between the licentiate and the doctorate exam, the effect of exposure to competition and results-orientated contracts has particularly been studied through literature studies, case studies and interviews. The doctoral thesis shows that exposure to competition in Sweden, but not in North America, has led to major economic benefits but that no increase in the rate of innovation could be observed. Banverket’s incentive contract for operation and maintenance is highlighted as a model. Success factors are shown to be well-defined contracts, quantifiable objectives and consistent deviations handling (both positive and negative).
Chloride transportation and reinforcement corrosion in the interface between old concrete and repair concrete
Pål Skoglund, did his licentiate exam in February 2007 at The Royal Institute of Technology on a project financed by SBUF (The Development Fund of the Swedish Construction Industry), Banverket, CBI’s Members’ Association and the Swedish Road Administration. Head supervisor was Jonas Holmgren of The Royal Institute of Technology, and assistant supervisors Johan Silfwerbrand and Jan Trägårdh. The purpose of the project was to study the interface between old concrete and repair concrete with emphasis on chloride transportation and reinforcement corrosion. The project included an interview study mainly with clients, the analysis of 13 year-old reinforced test specimens of two concretes and with infused chlorides and the analysis of samples taken from a bridge, a multi-storey car park and a stairway in Stockholm. The thesis shows that reinforcement corrosion is initiated in the transition zone between chloride-contaminated substrate concrete and initially chloride-free repair concrete. Chloride is transported from substrate concrete and into repair concrete.
Design of concrete pavements
Johan Söderqvist, defended his licentiate thesis in December 2006 at The Royal Institute of Technology. The project was part of the industrial research programme Road/Bridge/Tunnel and was financed by Cementa, The Royal Institute of Technology and Vinnova. Head supervisor was Johan Silfwerbrand and assistant supervisor Erik Simonsen of Cementa. The purpose of the project was to develop a new design method for Swedish concrete pavements. The project included an examination of modern, international design methods, fatigue experiments on concrete, cement-bound gravel (CG) and composite beams made of concrete and CG, measurements of thermal gradients in three different places in Sweden and the development of a draft for a new Swedish design method. The fatigue experiments show that today’s Swedish concrete criterion that was developed by compression and tension test specimens also applies (as indicated earlier) to flexure, that the valid fatigue criterion for CG is unreasonably strict, and that the combination of concrete and CG is a strong alternative. The proposed design method is based on the fact that the layers beneath the concrete pavement are treated in the same way and using the same computer program that The Swedish Road Administration uses for the layers beneath the asphalt, and that concrete is then treated using an American design program.
Form pressure and thixotrophy in self-compacting concrete (SCC)
Peter Billberg, Materials, defended his thesis in October 2006 at The Royal Institute of Technology within a project financed by the Swedish Consortium for Financing Basic Research in the Concrete Field, The Development Fund of the Swedish Construction Industry (SBUF) and The Swedish Road Administration. Head supervisor was Johan Silfwerbrand and assistant supervisor Jonas Holmgren of The Royal Institute of Technology. The ultimate purpose of the project was to create new knowledge for effective, resource-efficient andwork environment-friendly civil engineering structures by using self-compacting concrete (SCC). The ability to use SCC’s thixotrophy as an option to reduce the form pressure under hydrostatic pressure was identified as an important sub-objective. In the project, four hypotheses were formulated on the mechanisms behind the thixotrophy of concrete, the structure of fresh concrete in two parts (one reversible and one irreversible), the characterisation of the structure and the fact that the structure affects the form pressure. The methodology consisted of a comprehensive literature study, field experiments with measurements of form pressure in a 3 m-high wall, laboratory experiments to study the structure of micro mortars and concrete and simultaneous measurements of structure and form pressure in a pipe in the laboratory. The results include methodology to determine the thixotrophy of SCC and a demonstrated link between structure and form pressure. One problem that was identified in the project was that SCC’s characteristics are sensitive to small variations in the sub-materials as early as the fresh stage. Peter is therefore continuing work in a project called Variation Stable (Robust) SCC with the aim of ascertaining the reasons for this sensitivity and in the long run being able to create an SCC that tolerates greater sub-material variations and has more constant characteristics.
Rheology of concrete containing crushed aggregate
Mikael Westerholm, obtained his licentiate exam in February 2006 at Luleå University of Technology within a project financed by Agricola Research Center, MinBaS and the Swedish Consortium for Financing Basic Research in the Concrete Field. Head supervisor was Eric Forssberg of Luleå University of Technology and assistant supervisors Johan Silfwerbrand and Peter Billberg. The purpose of the project was to clarify the effect of crushed aggregate’s characteristics such as particle shape and fine material characteristics on the rheological characteristics in the concrete mortar phase. As well as the examination of literature, the study included three experimental sections, one on the interaction between superplasticiser and fine material, one on the link between particle shape, specific surface and mineral composition and the rheology of the fine grained cement, and the third on the effect of fine aggregate materials on the rheology of fresh cement. We have known for some time that the rheology of concrete is controlled by the rheology of the mortar. The results show that the more the particle form deviates from the spherical, the greater the plastic viscosity. The greater the quantity of and the more inferior the fine material, the greater the yield stress. The workability can be improved through washing (elimination of the finest material) and increasing the quantity of superplasticiser. Mikael is now continuing work on different projects concerning self-compacting concrete, sprayed concrete and concrete containing crushed aggregate.
Function characteristics of concrete roads
In December 2003, Malin Löfsjögård defended her thesis at The Royal Institute of Technology. The project was part of the Road/Bridge/Tunnel industrial research programme and was financed by Cementa, The Royal Institute of Technology and Vinnova. Head supervisor was Johan Silfwerbrand and assistant supervisors Örjan Petersson, currently at Strängbetong and Ronny Andersson of Cementa. The purpose of the project was to study, chart and analyse the link between functional characteristics of concrete roads (such as friction androlling resistance, resistance to wear and tear and tracking, fire resistance, evenness, noise and luminosity) and social factors ultimately described as the road maintenance body’s, the road user’s and society’s expenses. The project included comprehensive literature studies and special studies on the design of street lighting and sealants. The project resulted in a proposal for a concrete road optimisation model. Parts of the model were used to make economic comparisons between older and modern concrete roads. Perhaps the most practical benefit is the thesis’ proposal for an improved design method for street lighting for concrete roads in that it has already been used by the motorway on the E4 outside Uppsala.
Industrial by-products in concrete
Helena Moosberg-Bustnes defended her thesis in December 2003 at the Luleå University of Technology. The project was financed by MiMeR, MinFo, MinBaS, Cementa, CBI and the Research School at Rock and Mineral Technology at Luleå University of Technology. Head supervisor was Eric Forssberg of Luleå University of Technology and assistant supervisor Lotta Lind of SSAB Merox. The project concerned fine particle by-products from the mineral and metallurgic industry and filler in cement-based material. The hypothesis was that these materials could be used and the objective was to test the hypothesis. The project included comprehensive tests of rheological characteristics, heat development, sustainability development and shrinkage in pastes and mortar. The conclusion was that residual material cannot just be used but should be used in concrete production with economy and the environment in mind.