International Concrete Abstracts Portal

The use of high-strength concrete in precast factories is a common solution to attain larger spans and columns with a higher load bearing capacity. Taking into account the cost for transform the mold turnover in the precast line, it is economical to alter the concrete composition and the amount and size of reinforcement to attain the higher requirements. In collaboration with a precast factory, a test program was carried out to reveal the influence of concrete composition and curing temperature on material properties. The goal of the project was to predict the strength evolution of the material, using conventional maturity functions. Therefore, different concrete compositions were used, varying from concretes normally used on construction site, to high-strength concrete. Different curing temperatures were considered. The paper presents the evolution of the compressive strength in time, taking into account different parameters as well as the evaluation of existing maturity functions. Among others, the maturity functions of Plowman, of Kee, of Freiesleben -Hansen and Pedersen and of Carino are investigated. Especially the model, proposed by Carino predicted the strength evolution adequately.

One of the main problems of sustainable building is that the existing systems don’t lead to clean and direct reusable secondary building materials after demolition. In constructions in the Netherlands many different building materials are being used. When a building has reached its end of life, it will be demolished and it becomes demolition waste. Because a lot of different building materials will be mixed together during the demolition process, much effort must be taken before the Demolition and Construction Waste can be re-used. To solve this problem, two steps need to be taken. Firstly a building should be designed for recycling and secondly all buildings should be dismantled into elements or reduce to in clean secondary materials. The approach here is twofold. Firstly, research into the demolition/dismantling-process in order to find the bottlenecks in closing of the material cycle (at either element or material level). Secondly, as a spin-off of solving these problems, recommendations for future building-systems: design for recycling. This paper describes how certain demolition and dismantling techniques can be used in achieving the goals of sustainable design and construction.

The alkaline nature of concrete made from normal Portland cements provides a natural protection against corrosion of steel bars embedded as reinforcement. Presence of chloride in small quantities, depending on the Cl-/OH-ratio, tends to destroy this passivity of steel reinforcement even at a pH considerably above 11.5. The present paper compares numerical predictions, using Fick’s second law of diffusion, against concentration profile of water-soluble chloride obtained from the atmospheric, tidal and submerged zones of six 32 year-old marine piles extracted from a wharf in the Port of Singapore. Concentrations of water-soluble chloride at the level of steel reinforcement were compared with the loss in mass of the reinforcing bars. The concrete was sampled using the drill and suction method at locations spaced approximately lm along the entire length of the extracted piles. The results show that the numerical estimates were in good agreement with the actual values of water-soluble chloride concentrations obtained under Singapore conditions. Diffusion parameters calculated were within the expected range for the grade of concrete used, 30MPa cube strength. Locations where reinforcement corrosion were found corresponded to those that showed presence of water-soluble chloride in concentrations as low as 0.025% by mass of concrete occurring mainly in the atmospheric zone.

The effects of metakaolin and silica fume on the creep and shrinkage of concrete were investigated. Compared with the control concrete, the concrete containing the mineral admixtures had lower early age autogenous shrinkage measured from the time of initial set, but the long-term autogenous shrinkage measured from the age of 24 hours was increased. The total shrinkage (autogenous plus drying shrinkage) measured from 24 hours was reduced. Drying shrinkage was less than for the control concrete. The basic creep of sealed concrete and total creep of drying concrete were significantly reduced due to metakaolin and silica fume particularly at higher replacement levels.

achieve durable repairs, it is usually necessary to ensure adequate bond between the repair and the existing concrete substrate. Tensile bond tests are being increasingly used for quality control/quality assurance testing. However, there has been little standardization of test methods. Consequently, a total of 266 partial-depth cores in 77 experimental repairs were tested to evaluate the effect of material properties and environmental conditions on the bond between nine repair materials and a common concrete substrate. Three pull-off testing devices were used to determine bond strengths for each of the experimental repairs. In addition, the testing devices themselves were evaluated by analyzing the magnitude and relative precision of the pull-off strengths, modes of failure, and ease of use in an effort to identify a reliable and practical device for determining in situ tensile bond. The optimum depth of core drilling into the existing substrate was determined by comparing theoretical finite element analyses of failure stress and location with measured test results.