TABLE OF CONTENTS At its simplest, concrete is an artificial stone made of three ingredients: aggregate, cement, and water. The aggregate components, coarse and fine, are the meat and bones of concrete, giving it strength. Cement is the glue that solidifies the mixture, making concrete more than a pile of rubble. Water is required to hydrate ("activate") the cement particles and bind together all of the components. But, if the principle is so simple, why are there thousands of publications devoted to various aspects of concrete design and construction, and why have many dissertations been written about the minutest details of concrete's behavior?
The answer: Concrete is not a fully predictable material. Specifying certain mixture proportions and a level of workmanship does not guarantee the exact outcome. Concrete will invariably be a little stronger or weaker than anticipated, it may crack where it shouldn't, and, worst of all, it may not last as long as intended. When an existing concrete building is being renovated, its load-carrying capacity is uncertain, but can be determined by the investigative efforts described in Chap. 2. If the structure is found not to be strong enough for the proposed loading, it can be strengthened.
In this chapter we explore the history of concrete and design practices of the past, to give the reader an idea of what to expect in an old concrete structure. We then discuss some typical challenges involved in strengthening concrete buildings and describe the methods of upgrading various concrete...
