The premise of this paper is that low water-to-cement ratio (w/c), higher strength concrete may undergo substantial volume changes, especially at early ages (<24 hours), and the prevention of these volume changes can lead to micro and macrocracking. A series of experiments were conducted using a non-contact laser measurement system to quantify fundamental volume changes in fresh pastes before, during, and after the time of set. The laser measurements showed a dramatic initial length reduction up to the time of set. After initial set the mortar begins to swell slightly. Soon after the time of final set the mortar once again exhibits substantial shrinkage. In addition to monitoring length change, passive acoustic emission testing was performed on ‘model aggregate’ systems. Results of the acoustic emission tests are used to describe the microcracking that started to occur at the aggregate interface. To better understand how stress development leads to microcracking, an analytical model is developed in which the aggregate is idealized as an incompressible inclusion and composite theory was used to assess the stress that developed as a result of the restraint. The influence of aggregate size and volume content will be discussed and theoretical predictions will be compared with experimental observations.
|Title of host publication||Celebrating Concrete|
|Publication status||Published - 2003|