Correct Option: A

Aerated concrete is produced by introducing gas into a concrete, the amount is dependent upon the requirements for strength. One method to achieve this is by using powdered aluminium which reacts with the calcium hydroxide produced upon hydration of the cement to form the hydrogen gas that foams and doubles the volume of the raw mix creating gas bubbles. However, an increase in aluminium cont ent causes a decrease in the compressive and tensile strengths. It also produces a decrease in the modulus of elasticit y. When the aluminium content is increased, the density is decreased and the porosity is increased.