Transferability of results from laboratory test procedures to determine the frost de-icer resistance of pre-fabricated paving products in practical conditions

Since February 2005, the frost de-icer resistance for concrete paving must be proven with the modified slab test. Despite the discrepancy observed between the test results and the practical performance of stones laid, many customers prefer the CDF procedure.

The aim of this research project was to create a secured assessment background for testing the frost de-icer resistance of earth-moist produced concrete paving stones. The proposals could possibly be developed for testing in realistic conditions. In addition, environmental conditions and joint condition changes of laid concrete paving stones were recorded (monitoring) and implemented in an accelerated laboratory simulation with concrete paving stone surfaces (frost chamber). The correlation between weathering behaviour of the concrete paving stones in the laboratory testing procedure and weathering behaviour of the concrete paving stone surfaces in the frost chamber was investigated. Furthermore, the influence of paste content in the core concrete on the bond strength between face and core concrete was examined to research the causes for detachment occurrences in more depth.

In the completed research project, based on previous results in freezing chamber tests on concrete paving stone surfaces under practical test conditions, it was shown that the transferability of the results from laboratory test methods to determine the freeze-thaw resistance of two-layer concrete paving stones improves the behaviour when installed, in addition to the facing concrete also the core concrete with the slab test (according to DIN EN 1338) is examined.

In the current test practice, the two laboratory test methods Slab-Test and CDF-Test for double-layer concrete paving stones only assess the freeze-thaw resistance of the pre-set. An assessment of the core concrete is not carried out with these two test methods usually.

Insufficient freeze-thaw resistance of the core concrete is therefore not recognized in conventional testing practice. A core concrete with a low freeze-thaw resistance can fail in use and lead, inter alia, to the occurrence of chipping of the facing concrete, as it is not longer able to sufficiently absorb the mechanical stress resulting from its use.

• Contracting authorities for building projects with concrete paving stones may require, in addition to the facing concrete test, the testing of the freeze-thaw resistance of the core concrete.
• Concrete paving stone manufacturers should also use a strong concrete mix with a appropriate cement content in the core concrete to ensure that its freeze-thaw resistance remains sufficiently high.
• The regulation DIN EN 1338 could additionally be determinded the test of the freeze-thaw resistance of the core concrete.