Question 1 |

In cement concrete mix design, with the increase in water-cement ratio, which one of the following statements is TRUE?

Compressive strength decreases but workability
increase | |

Compressive strength increases but workability
decreases | |

Both compressive strength and workability
decrease | |

Both compressive strength and workability
increase |

Question 1 Explanation:

As the water-cement ratio increases, the porosity in the hardened concrete increases and hence the strength decreases.

Also, as water-cement ratio increases, ducts higher water availability, the workability increases.

Hence, correct answer is (A).

Also, as water-cement ratio increases, ducts higher water availability, the workability increases.

Hence, correct answer is (A).

Question 2 |

It is given that an aggregate mix has 260 grams of coarse aggregates and
240 grams of fine aggregates. The specific gravities of the coarse and fine
aggregates are 2.6 and 2.4, respectively. The bulk specific gravity of the mix is
2.3.

The percentage air voids in the mix is ____________. (round off to the nearest integer)

The percentage air voids in the mix is ____________. (round off to the nearest integer)

2 | |

4 | |

8 | |

16 |

Question 2 Explanation:

Given that,

Coarse aggregate = 260 gms

Fine aggregate = 240 gms

G_{CA}=2.6

G_{FA}=2.4

Bulk specific gravity G_m=2.3

Percentage air voids in the mix = ?

G_t (Theoretical specific gravity)

\begin{aligned} &=\frac{\Sigma W}{\Sigma \frac{W}{G}}\\ &=\frac{260+240}{\frac{260}{2.6}+\frac{240}{2.4}}\\ &=2.5 \end{aligned}

\begin{aligned} % \text{ air voids} (V_V)&=\frac{G_t-G_m}{G_t} \times 100\\ &=\frac{2.5-2.3}{2.3}\times 100\\ V_V&=8% \end{aligned}

Coarse aggregate = 260 gms

Fine aggregate = 240 gms

G_{CA}=2.6

G_{FA}=2.4

Bulk specific gravity G_m=2.3

Percentage air voids in the mix = ?

G_t (Theoretical specific gravity)

\begin{aligned} &=\frac{\Sigma W}{\Sigma \frac{W}{G}}\\ &=\frac{260+240}{\frac{260}{2.6}+\frac{240}{2.4}}\\ &=2.5 \end{aligned}

\begin{aligned} % \text{ air voids} (V_V)&=\frac{G_t-G_m}{G_t} \times 100\\ &=\frac{2.5-2.3}{2.3}\times 100\\ V_V&=8% \end{aligned}

Question 3 |

Match all the possible combinations between Column X (Cement compounds) and Column Y (Cement properties):

\begin{array}{|c|l|}\hline \text{Column X}&\text{Column Y} \\ \hline (i) C_3S & \text{(P) Early age strength} \\ \hline (ii) C_2S & \text{(Q) Later age strength}\\ \hline (iii) C_3A& \text{(R) Flash setting}\\ \hline & \text{(S) Highest heat of hydration}\\ \hline & \text{(T) Lowest heat of hydration}\\ \hline \end{array}

Which one of the following combinations is correct?

\begin{array}{|c|l|}\hline \text{Column X}&\text{Column Y} \\ \hline (i) C_3S & \text{(P) Early age strength} \\ \hline (ii) C_2S & \text{(Q) Later age strength}\\ \hline (iii) C_3A& \text{(R) Flash setting}\\ \hline & \text{(S) Highest heat of hydration}\\ \hline & \text{(T) Lowest heat of hydration}\\ \hline \end{array}

Which one of the following combinations is correct?

(i) - (P), (ii) - (Q) and (T), (iii) - (R) and (S) | |

(i) - (Q) and (T), (ii) - (P) and (S), (iii) - (R) | |

(i) - (P), (ii) - (Q) and (R), (iii) - (T) | |

(i) - (T), (ii) - (S), (iii) - (P) and (Q) |

Question 3 Explanation:

C_3S- Responsible for early age strength

C_2S - Responsible for later age strength and lowest heat of hydration

C_3A- Flash setting and highest heat of hydration

C_2S - Responsible for later age strength and lowest heat of hydration

C_3A- Flash setting and highest heat of hydration

Question 4 |

Which of the following equations is correct for the Pozzolanic reaction?

Ca(OH)_2 + Reactive Superplasticiser + H_2O \rightarrow C-S-H | |

Ca(OH)_2 + Reactive Silicon dioxide + H_2O \rightarrow C-S-H | |

Ca(OH)_2 + Reactive Sulphates + H_2O \rightarrow C-S-H | |

Ca(OH)_2 + Reactive Sulphur + H_2O \rightarrow C-S-H |

Question 4 Explanation:

Pozzolanic materials have no cementing properties itself but have the property of combining with lime to produce stable compound.

Pozzolana is considered as siliceous and aluminous materials and when added in cement it have SiO_2 and Al_2O_3 form.

So, pozzolanic reaction :

H_2O + Reactive slilica-di-oxide + H_2O \rightarrow C-S-H gel or tobermonite gel

Pozzolana is considered as siliceous and aluminous materials and when added in cement it have SiO_2 and Al_2O_3 form.

So, pozzolanic reaction :

H_2O + Reactive slilica-di-oxide + H_2O \rightarrow C-S-H gel or tobermonite gel

There are 4 questions to complete.