International Concrete Abstracts Portal

The development of cement-based screeds unbound to their support is still limited because of the curling which occurs at the corners and perimeter of the screed. This phenomenon is mainly due to the moisture gradient that appears within the thickness of the screed: the upper surface dries and shrinks, while the lower one remains humid. One possible solution limiting this phenomenon is using calcium sulfoaluminate cement instead of normal portland cement. Experiments utilizing an original device show that the curling is three times lower when using calcium sulfoaluminate cement. Moreover, when polyol is added to the mixture (0.63% of the cementitious material content), curling is still reduced by 23%. Polyol reduces drying shrinkage by 40%, but does not affect the mass loss of the screed and the porous distribution. The results obtained show that polyol can be considered as an efficient shrinkage reducing admixture (SRA) for calcium sulfoaluminate-based mortar and concrete.

Recycling of demolished concrete is an effective method for reducing construction waste. Recycled fine aggregate includes a large quantity of hydrated cement paste. The cement paste influences qualities of recycled fine aggregate, and, in turn, the properties of concrete containing recycled fine aggregate. As a result, concrete containing recycled fine aggregate has lower strength and durability than concrete with natural aggregate. However, the manner in which the quality of recycled fine aggregate influences the properties of concrete remains unclear. When considering the use of recycled concrete for construction, the durability of concrete with recycled fine aggregate must be investigated. The purpose of this study is to determine the influence of the quality of recycled aggregate on the properties of concrete at W/C ranging from 0.25 to 0.7. The parameters investigated to evaluate durability are strength, pore volume, shrinkage, carbonation, and resistance to frost damage. The results show that water absorbed by the aggregate migrates to paste around particles of aggregate, and influences the volume of water and pores in paste. Therefore, when recycled fine aggregate with high water absorption is used in concrete, shrinkage and volume of gas permeating into concrete increase, and durability lowers.

This paper proposes a model of the mechanical behavior of corroded reinforced concrete members subjected to bending under service load. The model is based on the formulation of a macro-element to be used in finite element analysis, having a length equal to the distance between two consecutive flexural cracks and a cross-section equal to the member cross-section. The mechanical formulation is based on the concept of the transfer length necessary for the transmission of tensile load from the reinforcement to tensile concrete through bond. It is thus possible to take into account the effect of reinforcement corrosion on the bond between the steel and concrete by increasing the transfer length as a function of the intensity of corrosion. The variation of the transfer length with degree of corrosion is expressed using a scalar damage parameter. Experimental validation is performed on a 17-year-old beam kept in a chloride environment under its service load.

Most organic admixtures for mortar and concrete are based on mineral oil derivatives. Future generations will need natural replacements that can secure a sustainable development, the so-called bio-admixtures. This study focuses on influence of vegetable oils on long term water repellency and other durability aspects. Vegetable oils from sunflower, olives, soya beans, peanuts, linseeds, corn and rapeseeds were tested in 2002: Dosages were 0.0, 0.5 and 1.5% vegetable oil by cement weight. The flexural and compressive strength of 1:3 mortars with w/c = 0.50 at 1 and 28 days were then measured together with the capillary water absorption and water vapour diffusion. Thereafter the specimens were stored in room temperature at 93% relative humidity for three years before compressive strength, chloride intrusion, carbonation, capillary water absorption, monolayer capacity and chemically bound water on the mortar samples were measured to investigate long term durability of the samples and how the water repellency changes with time. This last program is reported in the present paper.

In this paper, the calcium chloride resistance of concrete containing a low dosage of an expansive additive was investigated in comparison to that of plain concrete. To evaluate the chloride resistance, the length of change and compressive strength, EPMA and SEM were used. In addition, comparisons with previous results on chloride resistance of concrete with ordinary expansive additive were also confirmed.