How to measure the moisture content of concrete
Concrete is a cement composite material (calcium oxide) composed of coarse and fine aggregates bonded together. When mixed with water, cement powder undergoes a chemical reaction to combine aggregate materials into durable, stone like building materials. However, during hardening (solidification), this large amount of water still retains moisture in the porous concrete. In the following months, this moisture will slowly dissipate from the concrete until it eventually mixes with the moisture content in the air.
Measure the moisture content of concrete
When applying protective coatings or other flooring materials to concrete slabs, it is crucial to ensure that the humidity level inside the concrete has been reduced to an acceptable level. If not, the accumulated moisture on the coating or floor can cause discoloration, cupping, buckling, foaming, delamination, and/or mold growth. There are various methods for measuring the moisture content of concrete. Three common methods are to use non-destructive electronic instruments, anhydrous calcium chloride, or in situ relative humidity (RH) probes.
When applying protective coatings or other flooring materials to concrete slabs, it is crucial to ensure that the humidity level inside the concrete has been reduced to an acceptable level. If not, the accumulated moisture on the coating or floor can cause discoloration, cupping, buckling, foaming, delamination, and/or mold growth. There are various methods for measuring the moisture content of concrete. Three common methods are to use non-destructive electronic instruments, anhydrous calcium chloride, or in situ relative humidity (RH) probes.
Non destructive electronic instruments measure the electrical impedance of concrete, in conjunction with concrete. Because of their design, these meters can be affected by other slab conditions such as composition and presence of changes in concrete reinforcement materials. ASTM recommends that this concrete moisture meter be used for comparison rather than quantitative moisture content determination.
The anhydrous calcium chloride test involves measuring the weight of the salt and collecting moisture from the surface of the concrete due to the encapsulation area. However, there are clear doubts about the accuracy of this test:
There is no practical way to track national standards for these packages.
They measure moisture on the surface of concrete.
They are influenced by external conditions.
The new standard for measuring the concrete industry is the ASTM f2170 standard test method described in the in-situ relative humidity testing of concrete. It involves drilling holes into concrete and directly measuring the moisture content in the relative humidity slab using an electron probe.
