Batching methods for rapid-hardening concrete

In order to mix rapid-hardening concrete different methods and site organisations are possible. Due to the fact that rapid-hardening concrete has a defined open time and has to reach a certain strength within a certain time the duration of batching and transporting should be as short as possible. The shorter the transport, the higher the strength that can be developed in the remaining time (e.g. 90 to 120 min) until hand-back to the client for flight operation. The homogeneity of the concrete and the mixing capacity of the concrete plant is at its optimum when using a batch plant with a twin shaft mixer. However, most batch plants are not airside and can not be used for the production of a machine-laid concrete, since the transport of the concrete is too time consuming (e.g. 30 to 45 min). Therefore, it is important to have a batch plant airside when using a slipform paver.
Using a mobile mixing truck, rapid-hardening concrete can be mixed on site and on time. No transportation of the fresh concrete is required. The concrete is mixed in a volumetric mixer. This mixer ensures a homogeneous concrete mix. The main difference between a batch plant and a mobile mixing truck is output capacity. With a mobile mixing truck a maximum of 20 m3 per hour can be batched and placed. This is sufficient for single slabs. Batch plants have output capacities of up to 250 m3 per hour. This is a proper amount to efficiently feed a paver laying up to 1’000 m2 of rapid concrete within a single night shift.