Lars-Olof Nilsson
LTH, Building Materials, Faculty Member
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Research Interests: Thermography and Infrared
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ABSTRACT The first model to predict chloride ingress into concrete was presented by Collepardi in 1970 in Italian. That model was used for some 20 years for the design of concrete structures before it was realised that the main parameter,... more
ABSTRACT The first model to predict chloride ingress into concrete was presented by Collepardi in 1970 in Italian. That model was used for some 20 years for the design of concrete structures before it was realised that the main parameter, the apparent chloride diffusion coefficient, is not a material property. Since then, the Collepardi model has been significantly improved and developed into more or less sophisticated probabilistic models. Today, we have numerous models for predicting chloride ingress, but all of them have serious limitations that restrict the present use for long-term predictions. The paper describes the history of developing chloride ingress models. An overview is given of the fundamental differences between various models, from those based on Fick's 2nd law and constant or time-dependent diffusion coefficients and surface chloride contents to those based on chloride transport equations with or without a multi-species approach. The three main limitations are shown to be the lack of understanding the time-dependency of the apparent chloride diffusion coefficients and the lack of good long-term data, the chloride content increase with time close to the exposed surface and the difficulties in quantifying the boundary conditions for sophisticated ingress models.
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Chloride ions have been identified as an important cause of the initiation and acceleration of the corrosion of the reinforcements within modern concrete structures. This book introduces a comprehensive mathematical model used to describe... more
Chloride ions have been identified as an important cause of the initiation and acceleration of the corrosion of the reinforcements within modern concrete structures. This book introduces a comprehensive mathematical model used to describe the mass transport behavior of ionic species in porous media. It takes account most of the major mass transport mechanisms that involved. They are the convection with pore solution, the diffusion in pore solution, the physical/chemical adsorption/desorption on/off the solid phase of porous media and the dynamic electrochemical interactions within the local electrical field generated. The developed mathematical model has subsequently been adopted to model the chloride ingress process in the concrete under saline environmental conditions for the purpose of the service life assessment and the chloride removal process of the concrete under electrochemical treatment for concrete rehabilitation. This mathematical model and numerical methods described in this book can also be used for other environmental problems and engineering applications, such as underground pollutant disperse and land contamination modelling.
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In this paper a modified two-dimensional Luikov model for evaluating the non-isothermal moisture migration in porous building materials was proposed. The coupled heat and moisture transfer problem was modeled. Vapor content and... more
In this paper a modified two-dimensional Luikov model for evaluating the non-isothermal moisture migration in porous building materials was proposed. The coupled heat and moisture transfer problem was modeled. Vapor content and temperature were chosen as the principal driving potentials. The coupled equations were solved by a numerical method, which consists of a finite difference technique with a fully implicit
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To determine the material characteristics important for the drying of concrete an extensive investigation was made where the influence of the composition of the concrete was studied. The result is that, in particular the w/c ratio, the... more
To determine the material characteristics important for the drying of concrete an extensive investigation was made where the influence of the composition of the concrete was studied. The result is that, in particular the w/c ratio, the natural percentage of air and the increase of air percentage, if any, are of very great importance. The result also shows that the drying time can be reduced by one half by increasing the percentage of air at a constant w/c ratio. /TRRL/
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Research Interests: Engineering and Moisture
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A new model for wetting and drying of wood end-grain – with implications for durability and service-life
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Chloride ingress profiles do almost always have a peak at some depth but most prediction models are missing this peak. Some prediction models, such as the fib model, simply “cut off” a slice of the concrete up to the peak in further... more
Chloride ingress profiles do almost always have a peak at some depth but most prediction models are missing this peak. Some prediction models, such as the fib model, simply “cut off” a slice of the concrete up to the peak in further predictions. Other prediction models use data only from the profiles beyond the peak but include the concrete up to the peak as if it has the same properties as the rest of the concrete. A physical model has been developed to quantify the local changes because of leaching and the consequences of these changes with time. The model uses Fick’s 1st law for chloride diffusion and linear chloride binding. The depth of leaching with time is modelled with a simple square-root equation. The consequences of leaching are assumed to be linear from the surface into the maximum depth of leaching. The consequences of leaching are modelled as depth-dependent changes of porosity, chloride binding and the diffusion coefficient in Fick’s first law.
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The principles of installation of probes to measure moisture in a certain position in a structure or specimen are shown in Fig. 23.1.
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Abstract The chapter is a brief description of carbonation and chloride initiated reinforcement corrosion with the mechanisms and simple models for the ingress processes and the critical threshold levels. The term “durability” is replaced... more
Abstract The chapter is a brief description of carbonation and chloride initiated reinforcement corrosion with the mechanisms and simple models for the ingress processes and the critical threshold levels. The term “durability” is replaced by quantification in terms of “service life” and how this is used in design is explained. How the exposure conditions are treated in American and European standards is shown.
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The pressure of the pore water in a porous material is a measure of the state of the water.
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In a lot of applications there is a need to measure the distribution of moisture in a material, i.e. the moisture content or the state of moisture, at a certain, defined position or a series of positions.
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Non-saturated ion diffusion properties of cementitios materials were evaluated in an experimental study. The chloride diffusion coefficient was calculated by using the NernstEinstein equation. To assess this, resistivity measurements has... more
Non-saturated ion diffusion properties of cementitios materials were evaluated in an experimental study. The chloride diffusion coefficient was calculated by using the NernstEinstein equation. To assess this, resistivity measurements has been performed on mortars with different binders (OPC, OPC with 5% silica fume, 40% slag and 70% slag, respectively) and different w/b ratios (0.38 and 0.53). These have been conditioned to eight climates with RH from 100% to 33% RH. The results from the measurements have been corrected for the conductivity of the pore solution at the different degrees of saturation. The results for the Portland cement binders within the range 100% to 59% RH are presented. They showed that the diffusion coefficient of the mortar with high w/b ratio was higher at high RH. At low RH, the opposite was found and the material with low w/b ratio has higher diffusive transport. By comparing these results with the desorption isotherm, it is shown that the diffusive transpor...
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Rapporten avser folja upp och utvardera de resultat som kom fran projektet CONMOD rorande fuktanalyser. I de sju rapporterna som har utgjort underlag for denna undersokning har star det generellt sett valdigt lite om fukt med tva... more
Rapporten avser folja upp och utvardera de resultat som kom fran projektet CONMOD rorande fuktanalyser. I de sju rapporterna som har utgjort underlag for denna undersokning har star det generellt sett valdigt lite om fukt med tva undantag. De tva rapporter dar det star mest om fukt och fuktmodellering, ar dels i bilaga A5.4, i rapporten ”Barseback NPP- Material testing project”, Materialanalyser av prover fran reaktorinneslutningen B1 och dels i rapporten ”Forandringsprocesser i reaktorinneslutningar”. I den har rapporten belyses vilka matningar som ar utforda och var pa reaktorinneslutningen dessa matningar ar utforda. Ett antal olika fuktanalysmetoder har tillampats, bland annat har relativ fuktighet matts i borrade mathal, pa uttagna provbitar fran borrkarnor, kapillar mattnadsgrad har matts pa provbitar, mangden kemiskt bundet vatten har bestamts genom kemiska analyser och fukttransportegenskaper har bestamts pa utsagade skivor fran borrkarnor.I rapporten Forandringsprocesser i ...
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After further laboratory and field studies we have now used the previous and new findings to create a model for CO₂-absorption of concrete structures. Some knowledge is still missing and some results are still not fully understood. In... more
After further laboratory and field studies we have now used the previous and new findings to create a model for CO₂-absorption of concrete structures. Some knowledge is still missing and some results are still not fully understood. In those cases we have done our best to base the model on reasonable assumptions, from what could be expected from some new literature that has been studied.
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Flooring materials and adhesives can be degraded by high pH moisture from e.g. concrete. One way to avoid this degradation, is to dry the concrete and the screed to a sufficient moisture state prior to application of the flooring... more
Flooring materials and adhesives can be degraded by high pH moisture from e.g. concrete. One way to avoid this degradation, is to dry the concrete and the screed to a sufficient moisture state prior to application of the flooring material. One way to evaluate the moisture state in the materials sensitive to high pH moisture is to calculate the redistribution of moisture in the flooring system from application and onwards. The calculations require substantial knowledge in both moisture related material properties and mass transport calculations in porous materials. The availability of more user-friendly calculations tools stresses the need for a common methodology for both performance and documentation of the calculations. Several input parameters are needed for the calculation, such as boundary conditions, initial moisture distribution and material properties. The most important material properties are the water vapor sorption isotherms (desorption, absorption and scanning) and mois...
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Traditional methods for measuring moisture transport properties of concrete are time-consuming, especially since thick specimens are required, and steady-state methods are preferred. Non-steady state methods may be an alternative but the... more
Traditional methods for measuring moisture transport properties of concrete are time-consuming, especially since thick specimens are required, and steady-state methods are preferred. Non-steady state methods may be an alternative but the conditioning to uniform initial conditions is extremely difficult. The tin can method is, however, a good alternative under certain conditions and for certain concretes. Concrete is poured into a tin can and sealed cured in this way for at least a month. The can is opened, and the concrete is dried in a constant climate. Weight changes are recorded for several weeks. From these weight changes, the initial RH at start of drying, the drying climate and the desorption isotherm, the moisture transport coefficient or the moisture diffusion resistance factor are derived. The paper describes the theory behind the method and the unique conditions available for certain concretes that makes the method applicable. Examples of measurements are shown for a numbe...