$16~\rm N/mm^2$ flexural strength This question more relates to construction and architecture but I am sure it will not be the problem to ask and get a good answer here. 
If we have declared flexural strength of concrete of 16 N/mm2, what does that " visually" mean? Example, if that " piece of material"-concrete has 16 N/ mm2 flexural strength and is 1,6m long, 12 mm thick and 140 mm wide and we support it at ends, how much kilos I can put in the middle and not to break it and what kind of impact to make and not to brake it?
 A: First of all let me make a correction in your given value of flexural strength of concrete. The value of  $16 Mpa$ or $16 N/mm^2$ is about the compressive strength of a typical concrete cube with an edge of 15cm under clear compression. It's tensile strength is about 1/10 of its compressive strength ,so it's about $1.6 Mpa.$
Like concrete ,most materials fail under tensile stress before they fail under compressive strength , so the maximum tensile strength is equal to the flexural strength.
Now about your question, in an hypothetical situation that we can actually build a concrete 
beam of 20mm thickness:
Suppose  we have a beam of 1600mm length with simple supports in it's ends in which acts  a point load $P$ as follows:

So,  $σ=3PL/2bh^2 <=> P=(1.6*2*20^2*140)/(3*1600)=37.33N$ or approximately $3.80Kg.$
edit: Having a second look to your question and to my answer, i realized that you mentioned a thickness of  12mm and not 20mm as i calculated above. This is one typical value of cement board's thickness.
 A lot of people cannot distinguish the difference between concrete and cement  .
If that's the case ,then for your given values:
$ σ=3PL/2bh^2<=>P=(16∗2∗12^2∗140)/(3∗1600)=134.40N$ or approximately $13.70Kg.$ 
