Investigation of Lightweight Concrete and Materials, East Los Angeles Comprehensive Health Center Building

摘要

The objective of this investigation was to determine the causes of the undulation problem (waffle pattern) that developed in the lightweight concrete floor slabs at the East Los Angeles Comprehensive Health Center and to determine the effect, if any, on the serviceability and the safety of the structure. Samples of portland cement and lightweight aggregate were examined using petrographic methods. Concrete cores obtained from the structure were tested for air content and unit weight. Simplified model tests and study of early concrete volume changes were carried out in the laboratory to simulate the construction conditions. In addition, two-dimensional thermal calculation for predicting concrete temperatures during construction was performed. Based on the results of these laboratory examinations and inspection of the construction photographs, it can be concluded that the undulations were not caused by a materials problem and should not have structural implications. It is believed that the waffle pattern was developed due to the movement of the upper reinforcing steel bars while the concrete was still unhardened. The waffle effect seen on the hardened lightweight concrete floor surfaces was largely residual due to incomplete removal during finishing operations. If indeed there was any movement after finishing of these surfaces, it was probably due to a combination of factors such as expansion due to aluminum contamination of aggregates, form settlement, and perhaps, other factors that could not be positively identified. (Author)