Sea water:
All option are correct
Understanding the Properties of Seawater
The question asks about the characteristics of seawater. Let's examine each statement provided in the options to understand the properties of seawater.
Seawater is a complex solution primarily composed of water and dissolved salts. These dissolved substances give it distinct physical and chemical properties compared to fresh water, especially concerning its interaction with materials like concrete and steel reinforcement used in construction.
Seawater Salinity Percentage
The first statement claims that seawater contains a salinity of about 3.5 percent. Salinity refers to the amount of salt dissolved in water. The average salinity of seawater globally is indeed around 35 parts per thousand (ppt), which translates to 3.5 percent. This value can vary slightly depending on factors like evaporation rates, freshwater inflow, and freezing/melting of ice.
Therefore, the statement that seawater has a salinity of about 3.5 percent is widely accepted and factually correct.
Corrosion of R.C.C. Reinforcement by Seawater
The second statement addresses the effect of seawater on the reinforcement of Reinforced Cement Concrete (R.C.C.). R.C.C. structures often use steel bars as reinforcement within the concrete matrix. Seawater contains chlorides, which are highly corrosive to steel. When chloride ions from seawater penetrate the concrete cover and reach the steel reinforcement, they break down the protective passive layer on the steel surface, leading to corrosion (rusting).
Corrosion causes the steel bars to expand, which can crack and spall the surrounding concrete, reducing the structural integrity and durability of the R.C.C. element. Structures exposed to marine environments or built using seawater are particularly susceptible to this type of damage.
Hence, the statement that seawater corrodes the reinforcement of R.C.C. is correct and is a major reason why fresh water is preferred for mixing concrete in most construction applications.
Seawater Effect on Cement Setting Time
The third statement discusses the effect of seawater on the setting time of cement. The salts present in seawater, primarily chlorides and sulfates, can influence the hydration process of cement. In many cases, the presence of certain salts, particularly chlorides, can act as accelerators, causing the cement paste to set faster than it would with fresh water.
While this acceleration might seem beneficial, it can also negatively affect the long-term strength development and durability of the concrete, especially when combined with the risk of reinforcement corrosion and potential sulfate attack.
Thus, the statement that seawater accelerates the setting time of cement is generally considered correct, although the degree of acceleration can vary depending on the specific cement composition and the salt concentration in the seawater.
Conclusion on Seawater Properties
Based on the analysis of each statement:
- Seawater salinity is approximately 3.5 percent. This is correct.
- Seawater contains chlorides which corrode steel reinforcement in R.C.C. This is correct.
- The salts in seawater can accelerate the setting time of cement. This is correct.
Since all three individual statements are correct properties of seawater, the option stating that "All option are correct" accurately reflects the characteristics described.
| Property | Seawater Characteristic | Correctness |
|---|---|---|
| Salinity | About 3.5 percent | Correct |
| Effect on R.C.C. reinforcement | Corrodes the reinforcement | Correct |
| Effect on cement setting time | Accelerates the setting time | Correct |
Revision Table: Seawater Properties Summary
| Seawater Property | Key Detail | Implication for Construction |
|---|---|---|
| High Salinity (approx. 3.5%) | Contains dissolved salts (Chlorides, Sulfates, etc.) | Affects hydration, promotes corrosion, potential sulfate attack |
| Corrosive to Steel | Presence of Chlorides | Damages R.C.C. reinforcement, reduces structural life |
| Affects Cement Setting | Salts act as accelerators | Can cause flash setting, alter strength gain |
Additional Information: Seawater Use in Construction
Due to the detrimental effects discussed above, especially the corrosion of steel reinforcement, the use of seawater for mixing concrete in reinforced concrete structures is generally prohibited by construction codes and standards (like IS 456 in India or ACI in the USA). Using fresh, potable water is standard practice for ensuring the durability and long-term performance of R.C.C.
In mass concrete structures (like gravity dams) or plain concrete structures where there is no steel reinforcement, the use of seawater might be considered in some cases, provided its effects on strength development and potential sulfate attack are carefully evaluated. However, even in such cases, fresh water is typically preferred whenever available.
The presence of salts in seawater can also lead to efflorescence (white salt deposits on the concrete surface) and reduce the overall durability of the concrete.
Important Questions from Introduction
In the following table, the left column contains the names of standard graph algorithms and the right column contains the time complexities of the algorithms. Here, n and m are number of vertices and edges, respectively. Match each algorithm with its time complexity.
List I List II Standard graph algorithms Time complexities A. Bellman‐Ford algorithm I. O(m*log n) B. Kruskal’s algorithm II. O(n 3) C. Floyd‐Warshall algorithm III. O(n*m) D. Topological sorting IV. O(n + m) Choose the correct answer from the options given below :
How many cards must be selected from a standard deck of 52 cards to guarantee that at least three hearts are present among them?
Match List 1 with List 2 and choose the correct answer from the code given below:
List I
(Graph Algorithm)
List II
(Time Complexity)
a) Dijkstra’s algorithm
i) Θ(E log E)
b) Kruskal’s algorithm
ii) Θ(V 3)
c) Floyd-Warshall algorithm
iii) Θ(V 2)
d) Topological sorting
iv) Θ(V + E)
Where V and E are the number of vertices and edges in graph respectively.
The solution of recurrence relation: T(n)=2T(sqrt(n)) + lg(n) is
Modulus of elasticity of concrete, E is calculated using:
