Influence of demoulding oil on the rheological properties of fresh SCC

In concrete research centers, the determination of the rheological properties of concrete is becoming a daily business, easy to perform when the proper apparatus (and staff) are available. On the building site, rheometers are still absent, although some portable rheometers have been developed. Instead, the slump (flow) test is the only one performed to characterize the "workability" of the concrete. On the other hand, the rheological properties are very important on site, especially in case of self compacting concrete (SCC), in order to know whether the concrete can provide proper filling of the formwork, which pumping pressures will be needed, how long the concrete can wait before placement, ... The difference between laboratories and building sites is not only noticeable by the test equipment, there is also another mentality and way of thinking. In a laboratory, the scientist tries to eliminate every disturbing factor as much as possible. On site, workmen prefer to work more easily, and if necessary, they apply some "tools" to ease their jobs, sometimes not being aware of the negative consequences. Specifically in the domain of rheological characterization of concrete and its application, there is a large difference between lab and building site. In the lab, thorough cleaning of the testing materials is obtained by washing with water, but on site, as the water availability is restricted, releasing agents are applied so that the concrete does not stick to the equipment. Although these releasing agents are applied daily, very few scientific reports have been made on their influence on the rheological properties. This paper describes the influence of one type of demoulding oil on the rheological properties of SCC. No research has been performed on the causes of the differences between SCC with or without oil, so the only purpose of this paper is to show the resulting differences. Secondly, the results have been obtained in steady state, thixotropy and loss of workability have not been investigated explicitly