Concrete is one of the strongest and most durable of building materials. For example, a fortress built between 1860 and 1880 in the sea near Copenhagen, Denmark is reported to be in excellent condition despite the severe exposure. However, concrete can and does fail. It is estimated that each year about five percent of all concrete construction, worth around one billion dollars, is unsatisfactory. Deterioration of concrete is not inevitable. When it does occur it is often caused by failure to follow such approved basic concreting practices as proper placing, consolidation, finishing, and curing on the job site. Overlooking any of the requirements can cause failure in the overall construction. Found in the article are pictures which exhibit and explain why some concrete failed to meet quality standards.