maxit floor Moisture Environment Concepts  
   
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Background
Risk Factors
Damage Processes
When tp Use Adhesives?
Drying
Drying Phases
Concrete Beams
Calcium Sulphate
Concrete with levelling
Single-side Drying
Optimal Drying
Humidity Measurement
Questions

Concrete with levelling

Concrete with Cement-based Levelling Material

maxit's levelling compounds meet functional criteria specified in terms of adhesion strength and resistance to rolling-wheel loads when applied to all types of concrete (normal and high-performance). In the case of newly cast concrete, the levelling material should be applied no earlier than 28 days after casting to allow for concrete shrinkage. The application of the levelling material increases the moisture content at the top of the concrete, but the material will not be affected at a deeper level where the RH is measured. These are the important considerations related to drying:
Normal concrete with levelling
  • A cement-based levelling compound can be applied at the earliest when the concrete achieves an RH of < 95% (CM < 5%) measured at the equivalent measurement depth. If the concrete structure is to be covered with a vapourtight surface material such as a PVC covering, it is often specified that an RH of 85% (CM < 3.5%) is required. Would it be better to apply levelling material at an early or a later stage in the process with regard to the total drying time? It is usually argued that the concrete structure should be allowed to dry for as long as possible, delaying levelling for the requisite drying time before installing the covering.
  • However Abrahamsson A and Tammo K, 2003 have investigated the drying of test specimens of 120mm thick concrete with different water/cement ratios and with a 10mm covering of levelling compound. Their results indicate that it makes relatively little difference to the drying out of the structure whether the levelling compound is applied at an early or late stage.
  • A possible explanation of these findings is that the higher water vapour resistivity resulting from the thicker construction with the levelling compound is compensated by the lower water vapour resistivity of the wetter material.
High-performance concrete with levelling compound
  • For high-performance concrete with a water/cement ratio of 0.35, Abrahamsson and Tammo's research indicates that a levelling compound has no significant effect on the drying of the concrete, probably because the concrete is so impermeable that moisture is unable to penetrate lower than the topmost surface layer.
  • The combination of high-performance concrete with early application of levelling compound is an optimal one. The method eliminates the need for thorough drying and the levelling compound protects against alkaline breakdown of adhesives and flooring materials (Alexandersson, LTH 2004).