Proper moisture curing leads to formation of more C-S-H crystals (not expansive) in the pores of the hardened cement paste. Will it be harmful (cause cracking) to concrete?

Sulfate attack leads to the formation of more ettringite crystals (expansive/size grow) in the pores of the hardened cement paste. Will it be harmful (cause cracking) to concrete?

The use of sea sand with a high concentration of salt can lead to the degradation of reinforced concrete. What is the main reason?

What is the natural pH environment of concrete?

Cement hydration is a heat-releasing reaction. Which one of the following methods cannot prevent thermal cracking in mass concrete construction?