Self-Consolidating High Performance Concrete – SCC – Self-Compacting & Highly Flowable Concrete

Many laboratory experiments and field tests have shown that SCC pours do not generate full hydrostatic pressure at the bottom of the structure. Tests performed by Vanhove and Djelal (2002) showed a maximum pressure 64% of maximum hydrostatic pressure for a wall placed at 25 m/h from above and a maximum of 68% of maximum hydrostatic pressure for a wall placed at 19.5m/h by pumping from the bottom of the wall. In their study, the maximum pressure was not found at the bottom of the wall but at a height of 1.5m. Maximum hydrostatic pressure was determined using the overall height of the structure.

Testing has also been conducted in field installations. A 28-foot high wall was constructed in the structures lab at the University of Illinois at Urbana-Champaign. The wall was created with SCC material and filled in one continuous pour lasting about seven hours. It was found that only within the top four feet of placed concrete were pressures approaching full hydrostatic pressures recorded. The maximum pressure reached was 5.5 psi, which was only approximately 20% of the maximum hydrostatic pressure at the point of measurement. This wall was filled at a relatively slow rate, maximum of 5.5 ft/hr, due to the large dimensions of the structure (5 ft thick, 80 ft long and 28 ft high). The wall required 415 cubic yards of material. A companion test column was fabricated which involved filling a 10.5-ft tall column. The column was filled at a rate of 60 ft/hr and the highest pressure measured one foot from the bottom. The highest pressure recorded was 80% of hydrostatic pressure. The wall and column were filled using a concrete pump and the material had a target slump flow of 28 in. but varied during the day from 23.5 to 29 in. during the time of the pour and the density of the material was 151 lb/ft³.

Figure 1. Pressure exerted by SCC on formwork over time

A large reconstruction project in Peoria, Illinois involved the construction of many new retaining walls. The project is being constructed with SCC for the walls. Several of these walls were instrumented with pressure gages to study the development of pressure on the formwork. Figure 1 shows the results of one such wall. One sensor was placed 1.5 ft off the bottom of the wall and the second sensor was placed 6.5 ft off the bottom of the wall. The first hour of pouring was at a rate of 9 ft/hr, the second hour at 4.5 ft/hr and slower for the final hours. The bottom sensor reached a maximum pressure of 7 psi with where as hydrostatic pressure would have been 20 psi. Additionally, the highest pressure was reached long before the pour was finished. It is also important to note that at some point in the pour additional concrete in the wall did not cause the pressure to rise, as evident by the maximum pressure occurring just over an hour into the pour which lasted 4 hours.