Mette Rica Geiker

Shrinkage-Reducing Admixtures and Early-Age Desiccation in Cement Pastes and Mortars

Fundamental studies of the early-age desiccation of cement-based materials with and without a shrinkage-reducing admixture (SRA) have been performed. Studies have been conducted under both sealed and drying conditions. Physical measurements include mass loss, surface tension, X-ray absorption to map the drying profile, internal relative humidity (RH), and autogenous deformation. Interestingly, although the SRA accelerates the drying of bulk solutions, in cement paste with a water-to-cement (w/c) ratio of 0.35, it actually reduces the measured drying rate. Based on the accompanying X-ray absorption measurements and a simple three-dimensional microstructure model, an explanation for this observation is proposed. In sealed systems, at equivalent hydration times, the SRA maintains a greater internal RH and reduces the induced autogenous deformation. Thus, these admixtures should be beneficial to low w/c ratio concretes undergoing self-desiccation, in addition to their normal usage to reduce drying shrinkage.

CHLORIDE DIFFUSION IN PARTIALLY SATURATED CEMENTITIOUS MATERIAL

The paper proposes a combined application of composite theory and Powers’ model for microstructural development for the estimation of the diffusion coefficient as a function of the moisture content of a defect-free cementitious material. Measurements of chloride diffusion in mortar samples (440 kg/m 3 rapid-hardening Portland cement, w/c=0.5, maturity minimum 6 months) stored at 65% and 85% RH, as well as

The effect of measuring procedure on the apparent rheological properties of self-compacting concrete

Abstract Torque versus time during testing of the rheological properties of fresh concrete has been investigated. The testing was performed in a BML viscometer and on a self-compacting concrete (w/c=0.45, 70% rapid hardening Portland cement, 3% silica fume, 27% fly ash, third generation superplasticizer). The relaxation period needed to obtain steady-state flow may affect the rheological properties estimated and should be taken into account in the selection of measuring procedures. Nonsteady state is likely to cause an overestimation of the plastic viscosity and an underestimation of the yield value. Furthermore, lack of steady state may explain the apparent shear-thickening behaviour of self-compacting concrete reported elsewhere.

Chemical shrinkage of portland cement pastes

Chemical shrinkage of normal Portland cement pastes (0.4 ≤ w/c < 0.8) has been measured at 20°C and of pastes with w/c = 0.5 furthermore at 35, and 50°C by means of measuring the volume change of samples of cement paste during the hydration. A small increase in the chemical shrinkage at “infinite time” was found at increasing water-cement ratio. The influence of the temperature was found to be twofold: Increasing temperature caused an increasing rate of the development of chemical shrinkage and a decrease of the chemical shrinkage at “infinite time”. n nEarlier studies of chemical shrinkage of Portland cement paste are also reported.

A method for measuring the chloride threshold level required to initiate reinforcement corrosion in concrete

Information on the chloride threshold level that is necessary to initiate corrosion of steel reinforcement in concrete is required for service life calculations and performance testing of concrete. This paper proposes a method for determining the chloride threshold level causing the corrosion of steel in concrete. The method takes into account the need for accelerated chloride ingress and limitation of possible corrosion of steel parts not intended to act as anode.RésuméLe niveau de chlorures au-delà duquel la corrosion des armatures en acier est déclenchée dans le béton renforcé, est un paramètre dont la connaissance est nécessaire aussi bien lors de la conception, que des essais de performance du béton. Une méthode de détermination de ce seuil est proposée dans cet article. La méthode tient compte à la fois de laccélération induite du flux dions chlorure et des limitations liées à une possible corrosion de lacier.

Photogrammetric assessment of flexure induced cracking in reinforced concrete beams under service loads

ID Number (given by the scientific editors/organizers): ..............153

On the effect of laboratory conditioning and freeze/thaw exposure on moisture profiles in HPC

Abstract The effect of selected conditioning (drying and resaturation) and freeze/thaw exposure on the moisture profile in a two-powder concrete (equiv. w/c=0.39, 8% silica fume) has been investigated. For comparison, the effect of conditioning and freeze/thaw testing according to SS 13 72 44 (“Boras method”) on moisture profiles in a three-powder concrete and two plain concretes (w/c=0.45) was measured. The investigations were supplemented by determination of frost resistance and chloride profiles after freeze/thaw exposure, as well as petrographic analysis. The investigations indicate that the present methods of conditioning only have very limited effect on high-performance concretes (HPC).

Nanotechnologies for sustainable construction

Abstract: This chapter seeks to highlight key aspects and recent trends in the development and application of nanotechnology to facilitate sustainable construction, use and demolition of buildings and infrastructure structures, i.e. ‘nanoconstruction’. Nanotechnology is not a technology but a very diverse technological field that covers many application areas. The chapter therefore aims to provide a framework for addressing relevant issues of green nanoconstruction and to bring an overview and illustrative examples of current early developments.

Nanotechnologies for Climate Friendly Construction – Key Issues and Challenges

Expectations as to the climate potentials of nanotechnology are high, none the least related to the construction sector. This paper seeks to highlight key aspects in the early development and application of eco-innovative nanotech solutions in the construction sector, “nanoconstruction”. The paper provides a framework for addressing relevant issues of green nanoconstruction and takes stock of current challenges. Eco-innovative nanoconstruction has the potential to simultaneously enhance the competitiveness and climate potential of the construction sector and could become a key strategic factor for the sector ahead. However, the considerable lack of knowledge both on the eco-opportunities and risks of nanoconstruction and the industrial dynamics involved forms a serious barrier for pursuing nanoconstruction as a serious strategic target for business and policy.

Prediction of the Impact of Flow-Induced Inhomogeneities in Self-Compacting Concrete (SCC)

SCC is nowadays a worldwide used construction material. However, heterogeneities induced by casting may lead to variations of local properties and hence to a potential decrease of the structure’s load carrying capacity. The heterogeneities in SCC are primarily caused by static and dynamic segregation. The present paper reports property maps for a beam based on particle distributions at the end of casting derived from numerical flow simulations. A finite volume based numerical model is used to predict particle distributions at the end of casting, which are then converted into property maps using semi-empirical relations from the literature.