Concrete and Masonry Section 13 Unit 39

1. Concrete and MasonrySection 13Unit 39

2. Introduction • Most buildings have concrete and/or masonry components. • The ability to use concrete and masonry materials is an essential skill for construction and, repair and maintenance of buildings.

3. Concrete

4. Concrete • Concrete is “a mixture of stone aggregates, sand, Portland cement, and water that hardens as it dries.”* • Concrete does not dry, it goes through a chemical reaction called hydration. *Agricultural Mechanics, Herren

5. Concrete - cont. Concrete is truly a versatile building material. It can be formulated with very specific performance characteristics in mind and include lightweight, heavyweight, porous, fiber-reinforced, mass, high-performance and cellular concretes. Advantages • Fireproof • Insect & rodent proof • Decay resistant • Storm resistant • Wear resistant • Waterproof (water resistant) • Strong • Attractive • UV resistant • Doesn’t require expensive equipment. • Available locally • Low original and maintenance costs • Sanitary and easy to keep clean • Recyclable

6. Concrete - cont. • Disadvantages • Labor intensive • Requires moving a lot of weight • Requires forms • Dense material • Special skills required to place and finish

7. Seven (7) Characteristics of Concrete 2. Resists attack by water 1. Durable 3. Resists manures and most chemicals. 4. Fire resistant 5. Very strong in compression 6. Weak in tension 7. Resistant to freezing and thawing

8. Characteristic 1 Durability Def: The ability of concrete to resist weathering action, chemical attack and abrasion while maintaining its desired engineering properties. Concrete ingredients, their proportioning, interactions between them, placing and curing practices, and the service environment determine the ultimate durability and life of concrete.

9. Characteristic 2 Resists Attack by Water Two characteristics; watertightness and permeability. Watertightness: the ability of concrete to hold back or retain water without visible leakage. Permeability: the amount of water migration through concrete when the water is under pressure or the ability of concrete to resist penetration by water or other substances.

10. Characteristic 2 Resists Attack by Water -cont. The same properties of concrete that make it less permeable also make it more watertight. Low permeability concrete requires a low water-cement ratio. Moist curing also reduces permeability. Factors that affect permeability and water tightness include: Permeability of the paste Permeability and gradation of the aggregate Quality of the paste Quality of the paste--aggregate transition zone Relative proportion of paste to aggregate

11. Characteristic 3 Resists manures and most chemicals. Good quality concrete is resistant to the acids of manure. Concrete is very alkaline, pH is usually greater than 12.5. Resistance can be increased with surface treatments. Concrete is susceptible to deterioration by sulfates.

12. Characteristic 4 Fire Resistant Concrete provides the best fire resistance of any building material. It does not burn, it cannot be 'set on fire' like other materials in a building and it does not emit any toxic fumes, smoke or drip molten particles when exposed to fire. Concrete and its mineral constituents enjoy the highest fire resistance classification. The strength of concrete will deteriorate with high temperatures.

13. The compressive strength depends on: • The strength of the aggregate • Proportion of aggregate sizes • Type of Portland cement • Purity of water • Uniformity of mixture • Procedures used in placing, finishing and curing Characteristic 5 Strong in Compression

14. Compressive Strength Influenced by Water/cement Ratio

15. Characteristic 6 Concrete is weak in tension Does this table and picture show why steel reinforcement is use in concrete?

16. Characteristic 7 Concrete is resistant to freezing and thawing • The resistance decreases as the permeability increases. • When concrete spaces are 91% or more full of water, freezing will damage the concrete. • When water freezes to ice it occupies 9% more volume than that of water. • Air entrained concrete is less permeable. • Example of freezing damage:

17. Concrete Constituents

18. Concrete Constituents Concrete: a mixture of aggregate and Portland cement paste. Aggregate: usually sand, gravel and/or crushed stone. Paste: Portland cement and water Process: the paste binds the aggregates into a rocklike mass as the paste hardens because of the chemical reaction (hydration) of the Portland cement and water.

19. Proportion of Constituents • Basic concrete mix: • Air 6% • Portland cement 11% • Coarse aggregate 41% • Fine aggregate 26% • Water 16%

20. Admixtures “Admixtures are materials other than cement, aggregate and water that are added to concrete either before or during its mixing to alter its properties, such as workability, curing temperature range, set time or color.” (http://www.toolbase.org/) “Admixtures cannot compensate for bad practice and low quality materials.”

21. Admixtures - cont. Common admixtures • Retarding admixtures • Accelerating admixtures • Super plasticizers • Water reducing admixtures • Air-entraining admixtures • Addition of fiber to concrete makes it tough and fatigue resistant. Such type of admixtures are used extensively in important engineering projects. Additional admixtures • Bonding, • Shrinkage reduction, • Damp proofing and • Coloring.

22. Types of Cement Different types of Portland cement are manufactured to meet many different applications of concrete. Types I & IA are the most common.

23. Air Entrained Developed during the 1930’s Produced by using air-entraining cement or by using an air-entraining admixture. Recommended for nearly all concretes that are exposed to freezing and thawing, and deicing chemicals. Spalding is a characteristic of using concrete without air entrainment.

24. Properties of Air Entrainment Increased freeze-thaw resistance Increased deicer-scaling resistance Improved sulfate resistance Equivalent Strength Improved workability

25. Aggregate

26. Aggregate • Concrete should include at least two different sizes of aggregate--fine and coarse. • Fine = 1/4 inch or less (not to include fines) • Coarse = 1/4 to 2 inch • Standard practice is to crush stone and the use screens to separate the sizes. • The correct proportion of fine aggregate and coarse aggregate can then be mixed together. • Aggregate should be 60 to 80 % of the volume. (cheapest material). • Stream bank aggregate must be tested for excessive silt and clay. (page 557, Fig 39-2)

27. Aggregate-cont. Aggregate diameter must not exceed 1/3 of slabs that do not use rebar. Aggregate diameter must not exceed 1/5 of void in forms were rebar is used. The largest recommended aggregate size is 2 inches for most applications.

28. Purchasing Concrete

29. Purchasing Introduction • For large jobs in is common practice to have the concrete delivered to the site. • The cost of having concrete delivered is determined by: • Quantity • Mix • Minimum charge • Unload fee • Mileage fee

30. Purchasing Concrete - Quantity Needed • Quantity needed • Concrete is sold by the cubic yard (yd3). • To determine the quantity need calculate the volume in cubic inches (in3) or cubic feet (ft3) and convert to cubic yards (yd3 or just yd). • 27 ft3 = 1 yd • 46656 in3 = 1 yd • Common practice to add 5 to 10% for waste and volume errors.

31. Purchasing Concrete – Quantity - Example • Determine the yards of concrete that will be required to pour a driveway that is 26 feet wide, 120 feet long and 6 inches thick. • Solution: • Adding 10%.

32. Purchasing - Mix • Two factors which determine the ideal mix. • Environment • Intended use • Environmental factors • Soil phosphates • Freeze – thaw • De-icers • Use factors • Maximum Load • Vibration

33. Purchasing – Basic Mix

34. Purchasing – Slump • The inches of slump indicates the water-cement ratio and the quality of the concrete. Slump is determine through a slump test.

35. Slump - Test • A slump test is conducted using an Abram’s cone, slump cone. • A slump cone is 8 inches in diameter at the bottom, 4 inches in diameter at the top and 12 inches tall.

36. Slump Test – cont. • Steps: • Moisten cone • Place cone on moist, smooth non absorbent level surface that is larger the the lugs on the cone. • While standing on the lugs, fill the cone 1/3 and uniformly rod 25 times. • Fill the cone 2/3 full and rod the 25 times insuring the rod just penetrates the first layer. • Over fill the cone and rod 25 times • Strike off the excess with the rod. • Slowly lift the cone vertically and place on surface beside concrete. • Place rod across the top of the cone and the concrete and measure the distance from the bottom of the rod to the surface of the concrete. • This distance is the inches of slump.

37. Mixing Concrete

38. Introduction • Small jobs can be mixed at the site. • Concrete weights over 4,000 pounds per cubic yard. • Therefore, it is important to determine amount of concrete first, because even a small volume of concrete can require moving a lot of material. • Using Quikcrete is a popular option to reduce the work. For more information go to: http://www.nrmca.org/aboutconcrete/

39. Quikrete http://www.quikrete.com/OnTheJob/ProductSelector.asp

40. Mixing Concrete • Characteristics of good mix: • Each aggregate particle is covered with cement paste • Each aggregate particle is bound to others • Cement paste • Water--cement ratio must be exact proportions. • Water in aggregate must be accounted for and deducted from water added to mix. • Water--cement ratio must be adjusted for different service conditions.

41. Concrete Mixes • The proportions of water, Portland cement, fine aggregate and course aggregates are not the same for all concrete jobs. • When mixing concrete it is common to express the mix (receipt) as a proportion. For example: 1 = 1 ft3 (sack) of Portland cement 2 = 2 ft3 of fine aggregate 2-1/4 = 2.25 ft3 of coarse aggregate • The proportions can be used on a volume or weight basis

42. Proportions • The proportions must be changed to meet the service conditions.

43. Mixing--cont. • The amount of water in the aggregate must be included in the calculations. • Effect of water in aggregate. (Fig 39-3)

44. Water vs. strength

45. Effect of Adding Water • Adding 1 gal of water to 1 yd3 of concrete: • Increases slump 1 inch • Decrease compressive strength by 200 psi • Increases shrinkage by 10% • Increases permeability by up to 50%

46. Estimating Materials - By Volume • Determine the amount of materials that will be required to pour a concrete slab that measures 12 ft x 10 ft x 3 in. A 1-2.1/2-3.1/2 mix will be used. • Step one: determine the volume required. • Adding the 10% =

47. Estimating Materials - By Volume - cont. • Step two: determine the yield of one batch of the receipt. • Because the aggregate mixes together, the yield by volume will only be about 2/3’s of the total volume. • Step three: determine the number of batches required. • 33 cubic feet of concrete is required, each one sack batch will yield 4.62 cubic feet. • The number of batches =

48. Estimating Materials - By Volume - cont. • Step four: determine the Portland cement, fine aggregate and coarse aggregate.

49. Concrete Mixes--cont. • When concrete ingredients are measured using weight, density conversions must be used. • Portland cement = 94 lb/ft3 (100 lb/ft3 often used) • Fine aggregate = 100 lb/ft3 • Coarse aggregate = 110 lb/ft3

50. Estimating Materials - By Weight • Determine the amount of materials that will be required to pour a concrete slab that measures 18 ft x 12 ft x 4 in. A 1-2.-3.1/2 mix will be used. • Step one: determine the volume required. • Adding the 10% =