2 While mixing a concrete mix with a watercement WC ratio of

2. While mixing a concrete mix with a water/cement (WC) ratio of 0.55, a student accidently poured in extra water into the mix. Discuss the possible effects on the workability and the outcome on tests performed on such concrete at 7-day and 28-day.

Solution

As extra water is poured by the student, water/cement ratio increases which means that more water content is present per unit volume of concrete and mix becomes more diluted. Due to more water in concrete, it is easy to mix, compact, place & level concrete which increases the workability of concrete. So as W/C ratio increases, workability of concrete increases.

As more water is present in concrete which is  susceptible to loose excess water called bleeding. Bleeding cause micro channels and passages created in concrete whih allows water to flow and creates micro cracks and weak zones. Due these cracks and weak zones, compressive strength at 7 & 28 days decreses. It not only decreases compressive strength but it also dereases flexure & tensile strength of concrete and increses porosity. So, as W/C increases strength at 7/28 days decreses and porosity increases which means that concrete is less durable as extrenal chemical can penetrate concrete.