Methods and practice of treating horizontal construction joints when constructing concrete dams abroad

Conclusions

• 1. Treatment of the surfaces of construction joints is an expensive operation whose performance requires additional work by the concrete-placing equipment, which to some extent adversely affects the rate of concreting.

• 2. In recent years the surfaces of construction joints at foreign hydroprojects in the majority of cases have been treated by high-pressure (280–420 kg/cm²) water-air jets. Comparatively recently special concrete-setting retarders began to be used on foreign construction projects, thanks to which the time during which the concrete surfaces can be treated effectively by water-air jets is increased.

• 3. The spreading and brushing of a thin layer of sand-cement mortar onto the surface of horizontal construction joints for a long time was standard practice abroad in preparing the joints before placing the concrete in the next blocks. Investigations conducted in recent years did not confirm the superiority of a joint with an underlying layer of mortar with respect to cohesion and density over a joint on which the sand-cement mortar was not placed. In connection with this many design organizations in a number of countries and particularly in the U.S.A. do not include the placement of an underlying layer in the concreting technical specifications. This saves cement (about 2%) and reduces labor costs for preparing the blocks for concreting and increases the efficiency of concrete plants and concrete-placing equipment.