Though there are significant differences between the uses of concrete in structures, it is certain that the properties of the concrete should match the task they are meant to perform. For instance, concrete which is intended to perform well in seismic regions should ideally be designed differently from typical concrete. This is a practice which is already in place in newer structures in seismic zones.
During earthquake reconnaissance, I feel it would be especially beneficial to note the differences between concrete mixed with seismic codes considered and those which do not consider seismic activity. To discuss the properties for which concrete is designed, it is necessary to stress that the materials used to make a concrete mix can vary distinctly from region to region, and the methods by which concrete is poured may be significantly different than the typical codes seen in the United States. These variances lead to differences in the quality of mix which can be produced.
To analyze the impact of concrete mix design during earthquake reconnaissance, it would be beneficial to become familiar with the typical ingredients of concrete structures in the area in order to assess the general quality of concrete. The type of aggregate used affects bond strength and therefore affects the overall strength and quality of the concrete. One should also note the general practices used for pouring concrete such as the use of vibrators, knowledge of ideal pouring time and conditions, and finishing methods.
It is noted in many of the reports from the 1999 Chi Chi earthquake that insufficient concrete pouring practices may have been a factor in some of the residential damage. Documentation of earthquake damage in undeveloped regions such as Haiti and Africa shows that poor aggregate used in concrete mixes caused low bond strength between the aggregate and cement and contributed to structural failure. Knowing the general quality of concrete beforehand would be helpful in determining if failure is due strictly to structural design failure or material weakness.
Setting aside the differences in regional aggregate and construction practices, the differences in concrete properties due to additional mix ingredients which cause a specific effect, can be examined. Tailoring a mix design for ideal seismic performance can include additives which create a greater resistance to tensile forces, a greater resistance to moment, or added ductility. These deviations from standard mix designs are specified in ACI codes as appropriate for seismic regions and should be considered when analyzing a concrete structure’s failure.
I feel that it is important to try to brand failures, especially cracking, as being a material failure or structural failure. This distinction would help to determine if the methods for creating a seismically optimized mix is sufficient for the structures it is used in. Determining specific ingredients in poured concrete will be difficult, but some options include visual inspection if getting close is not a hazard or researching building information after the fact. Newly engineered buildings should be focused on because these buildings would most likely have special concrete mix designs.
The concrete structures considered “new” would depend heavily on the region’s engineering development. During our earthquake reconnaissance, I would like to keep in mind not only the structural significance of failures in concrete structures, but also the material failures. This focus could contribute to the research that is currently being done on different additives in concrete mixtures to create concrete with specific properties. With this knowledge, we can optimize not only a structure’s geometry, but also its specific force resistant properties.