What is the difference between engineering stress and true stress?

In biology, Stress is something that disrupts homeostasis of an organism. In engineering, Stress is an external force that pushes, pulls, twists, or otherwise puts force on something.
Engineering stress assumes that the area a force is acting upon remains constant, true stress takes into account the reduction in area caused by the force.

Will Water damage concrete?

As far as only concrete is concerned i.e. plain concrete, the effect of water seePAge is very little (depending upon the grade of concrete) whereas for RCC (reinforced cement concrete) water that seeps in corrodes the reinforcement and thus reduces the life of the structure. The defects that water seePAge induces in concrete are as follows:
a) induces capillary formation (due to the detiorating characteristics of water)
b) With this capillaries the concrete starts sPAlling out; i.e. the places where capillaries are formed, with even slight amount of stress that portion comes out and exposes the steel to the atmosphere
c) Concrete has a pH of about 12 -13. It also reduces the pH of the concrete when in salty water (or) when exposed to marshy areas.
d) Reduces the overall strength of concrete
e) Reduces durability
f) Reduces permeability to further water see Page
g) Results in ageing of structures

What does civil engineering mean?

They do many interesting things. Their job has to do a lot with design and construction. They can tell you what works and what will not for all sorts of situations.
There is a lot of mathematics involved along with many other disciplines. They have to have a good solid understanding of how the environment works and how nature interacts with man made. They are probably best known for designing bridges, interstates, skyscrapers, canals, and so forth.