Bertil Persson

Hydration and Strength of High-Performance Concrete.

L’evolution a long terme de l’humidite relative interne, de la resistance et de l’hydratation ont ete etudiees sur huit betons en conservation etanche, a l’eau, pendant 28, 90 et 450 jours. Le rapport eau/ciment du beton oscillait entre 0,22 et 0,58. La moitie des betons contenaient 10% de fumee de silice. Les echantillons consistaient en disques de 1 metre de diametre et de 100 mm d’epaisseur. Les cotes plats de l’echantillon grand format etaient rendus etanche par de la resine plastique epoxydique. L’echantillon grand format simulait une colonne de 1 m de diametre. L’humidite relative interne etait mesuree par un ensemble de 144 tuyaux en plastique de 50, 150 ou 350 mm partant de l’arete circulaire du disque. La conservation etanche montrait une autodessication notable, tout particulierement lorsque la fumee de silice entrait dans la composition du beton. Meme en cas de conservation sous l’eau, l’humidite relative interne dans un beton ayant un rapport eau/ciment de 0,22, tombait a 0,8 au bout de 450 jours de conservation, a 50 mm de la surface de l’eau. Il s’averait que l’autodessication du beton etait fonction du temps et du rapport eau/ciment. Pour obtenir une resistance, un total de 648 trous etaient perces dans les disques. La resistance du beton s’accrut regulierement tout au long des 450 jours, independamment du type de conservation. L’evolution de la resistance etait aussi indepenante de la distance entre le bord durci du disque et les trous (50, 150 et 350 mm). La resistance etait affectee par le type de conservation uniquement pour un beton ayant un rapport eau/ciment eleve. Une autre equation indiquait que le ”quotient de rendement” entre la fumee de silice et la teneur en ciment, pour ce qui est de la resistance a la compression de 432 trous, oscillait de 1 a 8 en fonction de l’âge et du rapport eau/ciment du beton. En consequence, l’evolutionde la resistance s’avera plus lente pour des betons contenant de la fumee de silice que pour des betons sans fumee. Pourtant la resistance de betons avec la fumee de silice augmenta meme audela de 450 jours. Des rapports furent etablis entre une resistance a la compression et une resistance a la traction pour 648 echantillons. Au bout de 450 jours, la resistance a la traction etait plus faible par rapport a la resistance a la compression, en conservation a l’air et sous l’eau que par conservation etanche, cela etant du probablement a des autocontraintes creees par les differences d’humidite dans le beton.

Seven-year Study of the Effect of Silica Fume in Concrete.

Abstract An experimental and numerical study of the long-term interaction between silica fume and Portland cement in concrete subjected to air, water, or sealed curing is outlined. About 250 kg of eight qualities of each concrete were studied at four different ages each over a period of 7 years between 1989 and 1996. Parallel studies of strength, hydration, and internal relative humidity were performed. Half of the concretes contained silica fume. New and original results and analyses of the interaction between Portland cement and silica fume related to compressive strength, split tensile strength, hydration, and internal relative humidity are presented. The specimens are available for future measurements.

Experimental Studies on Shrinkage of High-Performance Concrete

This article outlines experimental and numerical studies on shrinkage of high-performance concrete (HPC). Carbonation shrinkage especially may introduce surface cracking in concrete, which affects the durability. In order to study shrinkage, cylinders of eight qualities of HPC were investigated. Parallel studies on autogenous shrinkage, drying shrinkage, hydration, internal relative humidity, and strength were carried out. Previous research in the field is summed up. Mechanisms of carbonation shrinkage by modeling correlations to the composition of the HPC and the physical properties are presented. The results indicate that carbonation shrinkage may be avoided by addition of silica fume. The project was carried out from 1992 through 1996.

Sulphate resistance of self-compacting concrete

This article outlines a laboratory study on sulphate resistance of self-compacting concrete (SCC). For this purpose, more than 40 cylinders of concrete were subjected to a solution with sodium sulphate, sea or distilled water during 900 days. Age at start of testing was either 28 or 90 days. Weight and internal fundamental frequency (IFF) were measured. Comparison was done with the corresponding properties of vibrated concrete (VC). When cured in a solution with sodium sulphate, the results show larger loss of mass of SCC than that of VC probably due to the limestone filler content in SCC. After curing in water, sea or distilled, no such weight difference between the curing types was observe. IFF did not decrease or differ between the two types of concrete, i.e. no internal deterioration took place due to thaumasite sulphate attack (TSA) during the 900 days of exposure. The project was carried out from 1999 to 2002.

Eight-Year Exploration of Shrinkage in High-Performance Concrete.

In this paper an experimental and analytical exploration on the effect of water-binder ratio (w/b), silica fume and age on autogenous, carbonation, drying and total shrinkage of High-Performance Concrete (HPC) is outlined. Eight types of HPC were studied. Carbonation, internal relative humidity (RH) and strength were studied on specimens from the same batch of HPC that was used in the studies of shrinkage. The results indicate fairly good correlation between carbonation, shrinkage, w/b and RH. The type and amount of silica fume affected shrinkage.

Quasi-Instantaneous and Long-Term Deformations of High Performance Concrete with Sealed Curing

Abstract This article outlines an experimental and numerical study on quasi-instantaneous and long-term deformations of high performance concrete subjected to sealed curing. For this purpose more than 100 cylinders and 400 cubes were made of eight concretes and studied in relation to creep and shrinkage, hydration, internal relative humidity, and compressive strength. One heat-cured concrete was studied at temperatures other than 20°C varying between −20°C and 60°C. Analyses were carried out of quasi-instantaneous deformation, short- and long-term basic creep, and autogenous shrinkage. Relationships were obtained between elastic modulus and creep compliance, and hydration, internal relative humidity, and compressive strength. New and original results are presented on relationships between autogenous shrinkage and internal relative humidity. Other results confirm and validate earlier findings of normal strength concrete regarding relationships between creep compliance, porosity, compressive strength, and maturity for high performance concrete. The project was carried out at Lund Institute of Technology between 1992 and 1996.

A NORDTEST Method for Verification of Self-desiccation in Concrete

Abstract This article outlines a new NORDTEST method for verification of self-desiccation in concrete. The method involves measurements of the internal relative humidity (RH) on pieces of concrete at age 1 month. The measured RH is then compared with the requirements according to the owner. The new NORDTEST method for self-desiccation permits requirements to be made of the self-desiccation of high-performance concrete (HPC) in accordance with present demands on strength. During the development of the test method, experimental studies were carried out on nine concretes with water/cement ratio (w/c) varying between 0.32 and 0.50. Half of the concretes contained 5% silica fume. The experiments showed a significant effect of cement type, silica fume, and w/c on the self-desiccation in concrete. The test method was also verified in the field, both when manufacturing the concrete and on site. The method was developed after cooperation between the Technical University of Denmark and Lund University. The experimental studies were performed at the Division of Building Materials, Lund Institute of Technology, Lund, Sweden in 1995–1999.