Concrete Basics Quiz

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Questions and Answers

Which type of cement is recommended when high early strength is desired?

Rapid Hardening Portland Cement (correct)

Ordinary Portland cement

Low Heat Portland Cement

Hydraulic Cement

What distinguishes reinforced concrete from plain concrete?

It includes properly embedded reinforcement. (correct)

It uses different types of aggregates.

It is used primarily for aesthetic purposes.

It has a lower water-cement ratio.

What materials comprise plain concrete?

Cement, sand, and gravel only

Cement, fine aggregates, coarse aggregates, and water (correct)

Cement, water, and steel reinforcement

Cement, water, and fibers

What is the main purpose of embedding reinforcement in concrete?

To enhance resistance to tensile forces Signup and view all the answers

Which mixture results in a solid mass referred to as plain concrete?

Cement, fine aggregates, coarse aggregates, and water Signup and view all the answers

What is one characteristic difference between plain concrete and other types of concrete?

Plain concrete lacks embedded reinforcement. Signup and view all the answers

How many void cells does a standard concrete hollow block have?

Four void cells Signup and view all the answers

In construction, which benefit does reinforced concrete provide compared to plain concrete?

Greater flexibility under load Signup and view all the answers

Which of the following is commonly used to maintain the integrity of a concrete structure?

Regular reinforcement inspections Signup and view all the answers

What is the main advantage of using the volume method for proportioning concrete?

It is more convenient in practice. Signup and view all the answers

What is the typical thickness range for load bearing concrete hollow blocks?

15 to 20 centimeters Signup and view all the answers

In the example given, what is the equivalent meter conversion for 21 inches?

.525 meter Signup and view all the answers

Which materials are typically required for laying concrete hollow blocks?

Cement and sand for block laying Signup and view all the answers

What factor is crucial for fresh concrete to be considered workable?

Ability to fill voids around reinforcements Signup and view all the answers

What is the equivalent length in meters for 7 inches as calculated in the example?

.175 meter Signup and view all the answers

What is the thickness range for non-bearing concrete hollow blocks?

7 to 10 centimeters Signup and view all the answers

Why is it recommended to use concrete hollow blocks with bigger cells in estimating?

To ensure more realistic results Signup and view all the answers

Which of the following statements best describes a Prescribed Mixture?

The engineer specifies the mixture proportions. Signup and view all the answers

What is the primary consideration in determining the water-cement content ratio for concrete mixing?

Strength and workability of the mixture Signup and view all the answers

Which mixture classification places the responsibility of establishing the proportions on the contractor?

Designed Mixture Signup and view all the answers

How are materials for concrete structures measured prior to the acceptance of SI measurement?

In pounds and gallons Signup and view all the answers

What is the expected outcome of having the proper water-cement ratio in concrete?

Enhanced strength and durability of concrete Signup and view all the answers

Which requirement is NOT part of the ACI requirements for concrete?

Hardened concrete must be visually appealing Signup and view all the answers

What unit is now fixed at 40 kilograms per bag for cement measurement?

94 pounds Signup and view all the answers

What is the net area for the CHB after accounting for the space occupied by the posts?

56.00 m Signup and view all the answers

How many concrete hollow blocks are needed for the wall based on the net area calculated?

1,820 pieces Signup and view all the answers

What is the height of one concrete hollow block used in calculations?

20 cm Signup and view all the answers

When calculating the number of blocks in Area B, what is the average height used in the formula?

34.50 cm Signup and view all the answers

What is the total area calculated from Areas A, B, and C?

71.40 sq.m. Signup and view all the answers

What is the first step in both methods of calculating the number of concrete hollow blocks?

Determine the area for each section Signup and view all the answers

Which factor must be verified before estimating the quantity of concrete hollow blocks?

The clear height of the wall Signup and view all the answers

What is the main purpose of Table 2-2 referenced in the text?

To simplify block calculation methods Signup and view all the answers

What is the area of the wall if its dimensions are 3.00 m by 4.00 m?

12 square meters Signup and view all the answers

Using the Area Method, how many bags of cement are required for an area of 12 square meters with a class 'B' mixture?

6.26 bags Signup and view all the answers

How many concrete hollow blocks (CHB) are needed for an area of 12 square meters using the Hundred Block Method?

150 pieces Signup and view all the answers

What is the net area for CHB if the total length for CHB after accounting for posts is 56.00 m and the height is 2.60 m?

145.60 square meters Signup and view all the answers

If you need to account for concrete posts taking up space, how is the total number of concrete hollow blocks calculated?

Subtract the space for posts from total area Signup and view all the answers

When using the Area Method, what is the necessary first step to estimate the materials for laying concrete hollow blocks?

Calculate the wall area Signup and view all the answers

In the calculations for concrete posts, what is the dimension of a single post mentioned?

25 x 25 cm Signup and view all the answers

What is the outcome of dividing 150 concrete hollow blocks by 100 when using the Hundred Block Method?

1.5 Signup and view all the answers

Study Notes

Concrete

Plain concrete is made from cement, fine aggregates, coarse aggregates, and water.
Reinforced concrete includes steel bars embedded within the concrete to increase its strength.
Types of concrete:
- Ordinary Portland cement
- Rapid Hardening Portland cement
- Economy
Water-cement ratio is the most important factor in determining strength, durability, and workability of concrete.
Workability refers to the ability of the concrete to fill voids and around reinforcements easily.
ACI (American Concrete Institute) Requirements for concrete:
- Fresh concrete must be workable.
- Hardened concrete must be strong enough for the design load.
- Hardened concrete must withstand expected conditions.
- Concrete should be produced economically.
Concrete mixtures can be either designed or prescribed.
- Designed mixture: Contractor determines the mixture proportion to achieve the required strength and workability specified in the plan.
- Prescribed mixture: Engineer specifies the mixture proportion, and the contractor provides the correctly mixed concrete.
Materials for concrete structures were traditionally estimated in cubic meters.
Metrication (SI) has changed the unit of measure for cement from 94 lbs/bag to 40 kg/bag.
Example of converting inches to meters:
- 7 inches = .175 meters
- 21 inches = .525 meters

Concrete Proportion

Concrete mixtures are proportioned by weight or volume.
The volume method is more common and uses cement bags, measuring boxes for sand and gravel.
Weight method is used in ready-mix plants or as specified in plans.

Masonry

Concrete Hollow Blocks (CHB)

CHB are classified as load-bearing or non-bearing.
- Load-bearing blocks are thicker (15-20 cm) and used to carry loads.
- Non-bearing blocks are thinner (7-10 cm) and used for walls, partitions, fences, etc.
Standard hollow blocks have three void cells and two half cells, totaling four cells.
Estimating materials for CHB masonry work includes:
- Concrete hollow blocks
- Cement and sand for block laying
- Cement, sand, and gravel filler for the hollow core
- Cement and fine sand for plastering
- Cement, sand, and gravel for foundation or footing.

Estimating CHB Quantity

Using direct counting method: count CHB individually for each area of the wall.
Using area method: calculate the area of each section of the wall and refer to a table showing blocks per square meter.
Hundred Block method: calculate the area and convert to square meters, then refer to a table showing materials needed per 100 blocks.

Estimating Mortar for Block Laying

Area method: calculate the area of the wall and refer to a table showing mortar materials per square meter.
Hundred block method: find the number of blocks, convert to units of 100, and refer to a table showing mortar needed per 100 blocks.

Illustrative Example

A fence is 3.50 meters high and 40 meters long, with 25 x 25 cm reinforced concrete posts spaced 4.00 meters apart. Class B mixture is used for the CHB.
The solution involves calculating the gross area of the fence, subtracting areas occupied by the posts, and calculating the total number of blocks required based on the area method.
The example also demonstrates how to calculate the quantity of cement and sand needed for mortar based on the Hundred Block method.

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Description

Test your knowledge on the fundamental aspects of concrete, including its composition, types, and essential properties. Explore the significance of the water-cement ratio and the ACI requirements that govern concrete production. This quiz is ideal for students and professionals in construction and civil engineering.