Abstract
According to two-stage (pre-placed aggregate) concrete technology, special grout is injected into forms or foundation trenches with aggregate, as backing, placed earlier. The fresh grout differs from the ordinary concrete mixture. Good quality two-stage grout can be prepared in high-speed mixers, for example an Ultramixer (3000 rpm). It is characterised by high fluidity, low sedimentation, good viscosity, intensive hydration and a notable increase in the cement particles’ surface. However, because of the unique and complex equipment involved, two-stage concrete technology is still underutilised. The aim of the investigation presented in this work is to design a mixture composition similar in features to Ultramixer grout. For this purpose, the new grout was prepared using a normal mixer (140 rpm) and some admixtures. The experimental tests were performed with different mix proportions. On the basis of the obtained results, an optimal composition has been proposed. A comparison of the new grout features with the properties of the grout produced by the Ultramixer has also been elaborated. The new grout design method can improve two-stage concrete technology. Some preliminary two-stage concrete tests are also presented.