So, there is this teacher who wants to test how an chemical compound acts in the velocity of drying in concrete. Basically, i want to measure continuously (it would be great if i could do it with an arduino) the humidity level in a block of concrete. What is the best option? To use a air humidity sensor (DHT22, for example) or an ground humidity sensor? Or any other better option? The main purpose here is to store every measure of humidity along approximately 12 ou 13 hours. Any ideas? Thanks!
If this is a test block (and not a part of a building), the easiest solution is to place it on a scale.
The scale will indicate the amount of water that has evaporated from the block. From this it is easy to calculate the moisture content, either by volume or by mass. There are also scales that output the weight through e.g. serial port, which you can then log.
Air or ground humidity sensors would probably give you values that are related to the concrete water content, but they would need multi-point calibration if you need accurate readings. For example, temperature would affect the air moisture readings a lot.
You can also think of the concrete as being similar to wood ( a porous, composite solid) and use a wood moisture meter. They come in a wide variety of styles, choose the one that suits your application. You might have to drill holes in the concrete to insert the moisture meters that have probes, so if you choose this method you will have to drill precise diameter holes so that the probes will be in intimate contact with the concrete.