International Concrete Abstracts Portal

ACI SP-204 encompasses a wide range of subjects, including a detailed summary of worldwide provisions for crack control in reinforced and prestressed concrete beams, two-way slabs, and circular tanks. It also covers the latest Euro Code provisions, including design examples, early-age thermal cracking, crack mitigation effects of shrinkage-reducing admixtures fibers, repair of cracks, cracking in water-retaining structures, and an overview of the cracking developed during the 1999 earthquake in Turkey. 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. SP204

A reconnaissance visit was conducted to Turkey shortly after the August 17, 1999 Earthquake to investigate the performance of concrete structures. The dominant form of construction in the area was reinforced concrete frames, infilled with masonry walls. Extensive cracking and damage was observed in most structures located in the disaster area. This paper presents an overview of the types of cracking that can be expected after a seismic activity, as well as those observed after the August 17, 1999 Earthquake in Turkey. Causes of seismic damage are discussed with examples. A brief review of the seismological aspects of the earthquake and the overall performance of reinforced concrete buildings are provided.

Cracking in concrete repair systems is one of the truly critical phenomena of repair pathology responsible for corrosion, deterioration and failure. The problem of repair cracking has become widespread not only with respect lo severe environments which are intensifying restrained volume change stresses but also with respect to repairs in relatively benign environments. Cracking accelerates the penetration of aggressive substances into the concrete and repair material from the exterior environment which in turn aggravates any one or a number of various mechanisms of deterioration. Moisture transport mechanism in the repaired structures is a tool for transferring an outer standard environment into an inner environment, and from one inner environment (existing substrate) into another (repair material). The crack resistance of concrete repair is bearing on three equally important elephants: (I) design details and specifications; (2) repair materials; (3) in-situ workmanship and quality control This study demonstrates that the properties of cementitious repair materials have to be engineered for dimensional compatibility with existing concrete to improve their resistance to cracking. How good should the cementitious composite material used for repair of existing concrete structures be? How good is good enough? The paper summarized the factors involved and approaches taken when selecting cementitous repair materials. Performance criteria is presented for the selection of dimensionally compatible repair materials and standard material data sheet protocol. The recommended approach can enable material quality improvement, more accurate service life prediction, and satisfactory performance of repaired concrete structures during their intended service life.

AC1 3 18-99 no longer refers to Z factors or crack width formulae as in previous editions of the code. Instead, AC1 318-99 correlates bar spacing with clear concrete cover, indicating that following these guidelines will reduce crack widths at the concrete surface. Field investigations have found leakage at certain type cracks which exhibit widths of .23mm (0.009”) or greater. Research and condition surveys completed by the author have found greater potential for concrete deterioration at cracks which extend to embedded reinforcement as compared with low slump, low water/cement ratio concrete having adequate cover over reinforcement. Current codes and standards present considerable variation with regard to recommended maximum crack widths to prevent leakage. Use of AC1 3 18-99 to design liquid or gas retaining structures could lead to designs that are not conservative, not durable and possibly unsafe, if preventing leakage is an important requirement for the particular facility.

Drying shrinkage cracking can adversely affect the aesthetics, durability, and serviceability of reinforced concrete structures, thereby negating some of the benefits provided by high-performance concretes. Developed years ago but relatively new to the construction industry, shrinkage-reducing admixtures (SRAs) have been shown to provide significant reductions in concrete drying shrinkage and subsequent cracking. The potential benefits that SRAs provide have resulted in increased use of these products in the past few years. In this paper, data from laboratory testing and field investigations of SRA-treated concrete mixtures and their use in a few projects where watertightness was desired are presented and discussed. The findings of visual inspections of the projects performed shortly after construction and after a year in service will also be presented. The information to be presented verify the drying shrinkage reduction characteristics of SRAs and show that these innovative admixtures can provide substantial benefits with regards to improving watertightness and overall serviceability of reinforced concrete structures.