Podcast
Questions and Answers
What is the typical volume ratio of sand to hydraulic lime when mixed for mortar?
What is the typical volume ratio of sand to hydraulic lime when mixed for mortar?
- 1:2 (correct)
- 1:1
- 2:1
- 2:2
Which type of mortar is primarily used for plastering?
Which type of mortar is primarily used for plastering?
- Cement clay mortar
- Mud mortar
- Fat lime mortar (correct)
- Hydraulic lime mortar
What process is used to prepare lime if a large quantity is required?
What process is used to prepare lime if a large quantity is required?
- Grinding (correct)
- Maturing
- Wetting
- Curing
Which mortar has gained popularity over lime mortar due to availability in the market?
Which mortar has gained popularity over lime mortar due to availability in the market?
What is added to clay mortar to improve its quality?
What is added to clay mortar to improve its quality?
What is a characteristic of gauged mortar?
What is a characteristic of gauged mortar?
What type of materials can be added to mud mortar to prevent cracks?
What type of materials can be added to mud mortar to prevent cracks?
What is indicated by the usage of colored cement in mortars?
What is indicated by the usage of colored cement in mortars?
What is one of the primary roles of sand in mortar and concrete?
What is one of the primary roles of sand in mortar and concrete?
Which of the following is NOT a characteristic of good sand?
Which of the following is NOT a characteristic of good sand?
What is the recommended cement to sand proportion for plastering masonry works?
What is the recommended cement to sand proportion for plastering masonry works?
Why is it important to keep mortar wet during the curing process?
Why is it important to keep mortar wet during the curing process?
What happens to the cost of cementing materials when using sand in mortar?
What happens to the cost of cementing materials when using sand in mortar?
Which property of sand aids in the formation of silicates in cement?
Which property of sand aids in the formation of silicates in cement?
What is a disadvantage of using sand that contains salt?
What is a disadvantage of using sand that contains salt?
How does sand help with the adherence of the binding material?
How does sand help with the adherence of the binding material?
Which materials are typically used to create mortar?
Which materials are typically used to create mortar?
What is a primary characteristic of cement when mixed with water?
What is a primary characteristic of cement when mixed with water?
What appearance does mortar have when it is initially mixed?
What appearance does mortar have when it is initially mixed?
Which property describes cement mortar?
Which property describes cement mortar?
Why do engineers prefer using concrete hollow blocks (CHB) for interior walls?
Why do engineers prefer using concrete hollow blocks (CHB) for interior walls?
Which of the following is a common use of mortar in construction?
Which of the following is a common use of mortar in construction?
What is one of the key benefits of using masonry materials like CHB in construction?
What is one of the key benefits of using masonry materials like CHB in construction?
What is the defining property of mortar when it comes to its consistency?
What is the defining property of mortar when it comes to its consistency?
What is the primary purpose of determining the initial setting time of cement?
What is the primary purpose of determining the initial setting time of cement?
How much water is used in the setting time test based on the consistency test for 300 gm of cement?
How much water is used in the setting time test based on the consistency test for 300 gm of cement?
What does the final setting time measurement indicate?
What does the final setting time measurement indicate?
What is the effect of a prolonged setting period on the cement structure?
What is the effect of a prolonged setting period on the cement structure?
What is the role of the cross-section of the needle in the initial setting time test?
What is the role of the cross-section of the needle in the initial setting time test?
Which component of the Vicat apparatus is used to perform the tests for setting time?
Which component of the Vicat apparatus is used to perform the tests for setting time?
What is the approximate duration for final setting time of ordinary cement?
What is the approximate duration for final setting time of ordinary cement?
What should occur during the initial setting time test according to the procedure?
What should occur during the initial setting time test according to the procedure?
How does increased fineness of cement affect bleeding in concrete?
How does increased fineness of cement affect bleeding in concrete?
What risk is associated with cements that gain strength rapidly?
What risk is associated with cements that gain strength rapidly?
What is one consequence of increasing the fineness of cement?
What is one consequence of increasing the fineness of cement?
What is the main objective of conducting a fineness test for cement?
What is the main objective of conducting a fineness test for cement?
Which statement describes an effect of fine cement on hydration?
Which statement describes an effect of fine cement on hydration?
What is a consequence of increasing fineness in relation to dry shrinkage?
What is a consequence of increasing fineness in relation to dry shrinkage?
What effect does the fineness of cement have on the rate of strength gain?
What effect does the fineness of cement have on the rate of strength gain?
Why is it important to control the fineness of cement during grinding?
Why is it important to control the fineness of cement during grinding?
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Study Notes
Artificial Sand
- Artificial sand is a by-product of crushing stones
Sand in Mortar and Concrete
- Sand is used in mortar and concrete to:
- Subdivide and spread the binding material
- Fill in gaps between building blocks
- Increase the density of mortar
- Prevent shrinkage
- Facilitate carbon dioxide absorption
- Reduce the cost of cementing materials
- Contribute to the formation of silicates during hardening
Properties of Good Sand
- Chemically inert
- Free from organic or vegetable matter
- Free from salt
- Sharp, angular, and coarse grains
- Well-graded
- Hard
Cement Mortar
- Cement and sand are mixed dry
- Water is added gradually and mixed with shovels
- Common cement to sand proportions:
- Masonry works: 1:6 to 1:8
- Plastering masonry: 1:3 to 1:4
- Plastering concrete: 1:3
Curing
- Cement gains strength gradually through hydration
- Mortar needs to be kept wet until hydration is complete
- Hydraulic lime mixtures have a 2:1 ratio of sand to lime
- Lime is prepared by pounding (small quantities) or grinding (large quantities)
Lime Mortar
- Has good grinding properties
- Fat lime mortar is used for plastering
- Hydraulic lime mortar is used for masonry
- Historically cheaper and widely used, but cement mortar has largely replaced it
Mud Mortar
- Made from wet clay lumps that mature for 1-2 days
- Kneaded until the desired consistency is reached
- Fibrous materials, such as gobber, are added to prevent cracking
- Outer plaster is sprayed or painted with bitumen for durability
- Used for temporary sheds and cheap houses in rural areas
Special Mortars
- Cement Clay Mortar:
- Improves quality of clay mortar
- Clay to cement ratio is 1:1
- Economical and increases durability
- Gauged Mortar:
- Lime mortar with added cement
- Cement, lime, and sand proportions: 1:1:6, 1:2:9, and 1:3:12
- Must be used within 30 minutes after mixing
- Cheaper than cement mortar, with a quality between cement and lime mortar
- Decorative Mortar:
- Made with colored cement
- Used for aesthetic purposes
Fineness of Cement
- Indicates particle size and specific surface area
- Affects hydration rate and strength gain
- Can reduce bleeding but may increase the need for water, leading to shrinkage
- Measured using a fineness test
- Finer cement reacts faster with water, resulting in faster strength development and higher heat of hydration
Setting Time
- Initial Setting Time:
- Cement paste is prepared with water
- A needle is used to penetrate the paste
- Time is measured until the needle no longer penetrates 5 mm into the paste
- Final Setting Time:
- Cement paste is prepared
- A needle with an annular collar is used
- Time is measured until the needle makes an impression but the collar does not
- Typical initial setting time for ordinary cement is around 10 hours
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