International Concrete Abstracts Portal

In Japan, it has been predicted that enormous quantities of demolished concrete will be produced in the future. Therefore, a great deal of research is being conducted to find ways to recycle this demolished concrete as concrete aggregate. However, because the characteristics of the original concrete are not well known in many cases, the results are also not clear. Moreover, the recycling of the cement in concrete is also necessary from the standpoint of resolving global environmental problems and achieving sustainable development . This paper describes the properties of the concrete made with recycled aggregates from the original concrete of known quality and the recycling of the cement in concrete as the approach that should be taken in the 2 1 st century.

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.

Experimental and analytical studies on High Strength Concrete (HSC) columns subjected to biaxial bending are presented. The experimental work consisted of testing of twelve HSC columns. The primary test variables were load eccentricities about both the axes and the longitudinal steel ratio. All the columns were loaded to failure. The analytical work comprised development of a computer-based numerical algorithm to predict the strength of columns. The numerical analysis calculated the strength of the column in uniaxial bending separately about both the axes and applied the Bresler’s reciprocal load formula to predict the strength of the column in biaxial bending. The analysis applies to all grades of concrete. Good correlation between the test and calculated results is observed.

Self-compacting concrete, recycled concrete as aggregate, calcium nitrate accelerators—these are just a few of the topics covered in the 47 papers included in ACI SP-200, Fifth CANMET/ACI International Conference on Recent Advances in Concrete Technology. You’ll be able to compare the structural performance of full-scale columns using ordinary and self-compacting concretes and with stirrup configurations representing differing degrees of confinement. You’ll also learn about a procedure that improves the quality of concrete made using aggregate produced from recycled concrete, and about experiments showing that, at 5 °C, calcium nitrate is a much more effective accelerator than calcium chloride. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP200

The paper presents a critical review of the relationship between ettringite formation and sulfate attack. Ettringite formation is associated with expansion. However, not necessarily any ettringite-related expansion is related to sulfate attack. Early ettringite formation (EEF) which occurs immediately (within hours) in a plastic fresh mixture does not produce any damaging expansion and is associated with the regulation of setting time of portland cement paste. Expansion after the hardening of cement paste can be advantageously used for development of chemical prestress in expansive cements. Delayed ettringite formation (DEF) occurs at late ages and the related heterogeneous expansion in a very rigid hardened concrete can produce cracking and spalling. Two different types of DEF are examined depending on the sulfate source: DEF caused by external sulfate attack (EM) or internal sulfate attack (ISA). ESA, related to the interaction of environmental sulfate can be precluded by the use of impermeable concrete. with the cement matrix, On the other hand, ISA occurs in a sulfate-free environment due to the interaction of internal sulfate (from cement or gypsum contamined aggregate) with calcium-aluminate hydrates of the cement paste. Two different mechanisms of DEF caused by ISA are examined. The first one is based on the thermal decomposition of ettringite in high-temperature cured concrete elements and the subsequent re-formation of ettringite at ambient temperature in a saturated atmosphere. According to the second mechanism ISA is based on a chain of three essential events (microcracking, late sulfate release, and exposure to water) and DEF could occur even at room temperature.