Production and evaluation of exposed aggregate concrete surfaces using four different repair systems for road concrete with variation of surface retarders and their application rates as well as hardening accelerators and their addition rates

Duration: 01.02.2010 - 31.11.2011

In road construction practice, a high early strength of repair concrete is indispensable, because traffic areas should be reopened to traffic as quickly as possible. When replacing slabs, a minimum compressive strength of 20 N/mm² is required after 8h. Currently, dry concretes with special binder combinations or early high-strength flow concretes are used for textured surfaces. There are currently no ready-to-use repair concretes for exposed aggregate concrete construction. Therefore, basic laboratory tests are necessary to check, modify or develop new concretes for this application. A critical factor could be that despite the application of a surface retarder, these faster-hardening concretes develop their strength so quickly that the time window left for brushing becomes extremely narrow. The lower limit of the time window is determined by the fact that the coarse aggregates must already be sufficiently firmly bound in the non-retarded mortar matrix, the upper limit results from the fact that the retarded surface mortar can still be brushed out. This is to be optimised for different repair systems with different surface retarders and hardening accelerators.