Kurt Kielsgaard Hansen

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.

Preliminary Observations of Water Movement in Cement Pastes During Curing Using X-Ray Absorption

Abstract X-ray absorption and concurrent mass measurements are used in quantifying water movement in 4 to 5 mm thick cement paste specimens with their top surface exposed to drying. Experimental variables examined in this preliminary study include water-to-cement (w/c) ratio and open vs. capped samples. Layered specimens (e.g., 0.3 w/c ratio paste over 0.45 w/c ratio paste) are also examined to monitor the preferential water movement from less dense (higher w/c ratio) paste to denser paste due to capillary forces. For the open samples examined in this study, the initial drying is observed to occur uniformly throughout the thickness of the specimen, as opposed to proceeding as a sharp front progressing inward from the surface exposed to the external environment. In the layered specimens, the higher w/c ratio paste layer is seen to “dry out” first regardless of its location within the composite. The implications of these experimental observations for curing of concrete and application of repair materials are discussed.

Improved Suction Technique for the Characterization of Construction Materials

The suction technique is a method from soil science that is used for the study of moisture storage capacity in porous construction materials at high relative humidity levels (above approximately 93 %). The samples to be studied are placed in a pressurized container (an extractor) on a water saturated ceramic disk or membrane. The pressure corresponding to a certain relative humidity level is established and moisture is expelled from the samples until moisture equilibrium is reached. This paper presents two adjustments to this method and their applicability. The first adjustment is a new procedure for determining the equilibrium moisture content of samples during the experiment. The method (referred to as the balance method) is to simply keep track of all water entering and leaving the system and use these data to estimate the moisture content of the samples. The advantage of this approach is that the experiment does not need to be stopped and restarted for each relative humidity level tested. The main disadvantage of the method is that the estimation of the moisture content in the samples depends on a correct estimation of the moisture content of the ceramic disk. The second adjustment is the development of a pressure regulation system that keeps the pressure constant (±0.015 bar) within an extractor for weeks.

Seasonal Heat Storage in Underground Warm Water Stores (Construction and Testing of a 500 M3 Store)

The project contains the projection, the construction and the testing of the efficiency of a 500 m3 warm water store. The aims of the project are: gathering practical experience with the actual realization of the pilot plant; monitoring the overall behaviour of the storage system; verification and modification of the digital computer program.

Frost susceptibility of sub-base gravel used in Pearl-Chain Bridges: an experimental investigation

Abstract This study investigates frost susceptibility of sub-base gravel determined by the ASTM D5918-13 standard as a conservative estimate of the frost heave risk of fill in overfilled arch bridges, particularly in Pearl-Chain Bridges. Frost heave of granular materials has been of great research interest from the end of the 1920s until the present day. Most new literature relates to empirical results that are several decades old. This is also the case for Danish tender specifications according to which the frost susceptibility of a sub-base gravel is solely assessed from its fines content. However, no actual frost tests have been carried out to verify this assumption. In the present study, the frost susceptibility of four different Danish gravel materials is categorised from their heave rate. We test two Danish sub-base gravel materials, with particle size distributions of 0–8 mm and 0–31.5 mm, respectively, and also two modified sub-base gravel materials with increased and reduced fines contents. The fines content of the gravel materials is analysed by laser diffraction, and compared with two common frost susceptibility criteria, Casagrande’s and Schaible’s, and with Danish tender specifications. Even though the two sub-base gravel materials are expected to be frost safe, 0–31.5 mm sub-base gravel shows medium frost susceptibility, whereas 0–8 mm sub-base gravel shows negligible frost susceptibility. The gravel materials with increased and reduced fines content are categorised as having low to medium frost susceptibility and low frost susceptibility, respectively. The permeability of the gravel materials is determined, and the permeability coefficient of 0–31.5 mm sub-base gravel is five times greater than that of 0–8 mm sub-base gravel. The results suggest that the criterion used to classify the frost susceptibility of Danish sub-base gravel materials based solely on their fines content is insufficient, and that the permeability coefficient should also be considered.

Specimen or Core; In the Laboratory (Sides Available)

When also the sides, of a specimen or a core from a structure, are available during the moisture measurement procedure numerous techniques are applicable compared with when only the exposed surface is available.

Time Domain Reflectometry

Originally, the TDR measurement technique was developed to detect defects in telecommunication cables and electrical wires, Moffitt (1964). Within recent decades, TDR was also applied to determine and monitor volumetric moisture contents in particulate and porous media, in particular soil but lately also building materials such as building bricks, concrete, sandstone, etc., see e.g. Dobson et al. (1985), Topp et al. (1980), and Phillipson et al. (2008). TDR is in general based on the measurement of the propagation time of an electromagnetic signal along a wave guide also referred to as probe, usually there and back. In the low frequency range, i.e. <10 GHz, water possesses a considerably higher relative permittivity (e w ≈ 80) than mineral compounds (e s ≈ 4) or air (e a ≈ 1). From the measurement of the propagation time of an electromagnetic signal along a wave-guide, the mean relative permittivity, which is among others moisture dependent, of the investigated dielectric material is derived from the reflection picture. Subsequently, the volumetric water content can be determined directly from the mean relative permittivity applying suitable material functions, which relate mean relative permittivity and volumetric moisture content.

Monitoring, Remote Measurements

A special group of applications is “monitoring” where a series of moisture measurements are to be done in the same position at a number of occasions. This kind of application requires certain measures to overcome some special challenges when measurements are done during a longer period of time.

Self-Compacting Pervious Concrete Mix Design for Permeable Concrete Soakaway Rings

Permeable concrete soakaways store surface rainwater and let it seep slowly into the soil. This minimizes the risk of flooding, which is an increasingly larger problem because of climate change causing heavier and heavier rainfalls. In the present study, a self-compacting pervious concrete mix design is developed to use for permeable soakaway rings. A self-compacting mix design ensures a more uniform void distribution throughout the soakaway ring compared to the use of a conventional stiff pervious concrete mix design. The study is divided into two main parts: laboratory testing, in which the influence of the casting height on the void distribution is also considered, and full-scale casting of a 2.25-m-high pervious concrete soakaway ring. The overall conclusion is that a successful self-compacting pervious concrete mix design was developed by carefully balancing the use of a superplasticizer and stabilizer. Thereby, it was also possible to perform a successful full-scale casting.

The Effects of Moisture and Temperature Variations on the Long Term Durability of Polymer Concrete

The use of polymer concrete to precast products in construction presents normally many advantages compared to traditional concrete. Higher strength, lower permeability, shorter curing periods, better chemical resistances and a better durability is normally predicated, however this is a research field where published data are scarce. Durability and constantly high and good physical properties are some of the most important properties of the materials used in the building industry. Thermal durability, i.e. the ability of a material to retain its original physical-mechanical properties during and after exposure to different thermal conditions is very important. In this paper, an experimental study concerning the influence of temperature and moisture in cyclic conditions on the durability of polymer concrete based on an unsaturated polyester resin is described and the results are presented. The change of some physical-mechanical properties before, during and after exposure to different thermal conditions is measured. This study was initiated by an in-situ investigation on failures which have occurred on a number of steps on some heavily trafficked public outdoor stairs.