Civil Engineering Materials (CGN 3501C) Exam 1

What percentage of concrete by volume is aggregate?

60-80%

Functions of aggregate in concrete

1. Economy- aggregate as space filler

2. Strength

3. Reduction in shrinkage and expansion

Desirable Characteristics of Aggregates

1. Hard, strong, and durable

2. Free of organic impurities

3. Low alkali reactivity with cement

4. Proper gradation- for good workability and packing of voids

What size of aggregates gives better packing (big vs small)?

It doesn't matter

Classifications of Aggregate

- By size (coarse vs fine)

- By source (natural vs artificial/synthetic)

- By type of rock (igneous, sedimentary, metamorphic)

What classifies a coarse vs fine aggregate?

- Coarse- particles retained on No. 4 sieve (4.75 mm/ 3/16 in)

- Fine- particles pass through No. 4 sieve

What are examples of natural mineral aggregates?

sand, gravel, crushed stone

What are examples of artificial or synthetic aggregates?

blast-furnace slag, expanded clay, expanded shale

Describe Intrusive Igneous and the type of aggregate it creates

- formed by the slow cooling beneath of the earth's surface

- characteristics: completely crystalline minerals, coarser grain.

- examples- granite, trap rock

Describe Extrusive Igneous and the type of aggregate it creates

- formed by more rapid cooling at or near the earth's surface

- characteristics: finer grain, minerals with smaller crystals or glassy structures.

- examples- basalt, perlite

Describe Sedimentary Rock

- formed from disintegration of other rocks and deposited as sediments

- examples- limestone, sandstone, shale

Describe Metamorphic and the type of aggregate it creates

- igneous or sedimentary rocks that have changed its structure due to heat and pressure

- usually harder and denser

- examples- marble, slate

How to predict the behavior of aggregates in service

- from past performance record- the best basis for prediction of performance

- from mineral composition; for example if the minerals are known to cause a alkali-silica reaction

- from results of tests- most common method

What is the LA Abrasion Test and when do you use each test?

- purpose- to determine hardness or resistance to abrasion of an aggregate.

- use ASTM C 131 for aggregates smaller than 37.5 mm (1.5 in)

- use ASTM C 535 for aggregates larger than 19.0 mm (3/4 in)

LA Abrasion Test Procedures

1. Run sieve analysis on test sample to determine weight retained on #12 sieve (1.7 mm or 0.067 in.). Place test sample in L.A. testing machine (rotating drum with metal balls inside); C131 -5,000 g sample, 6 to 12 metal balls (depending on aggregate size) or C535 -10,000 g sample, 12 metal balls

2.The L.A. machine is rotated at a speed of 30 to 33-rpm for 500 revs.

3. Run sieve analysis on test sample after the test.

4. L.A. loss is computed as: [(Change in weight retained on #12 sieve)/(Original Wt retained on #12 sieve)]X100

What should the results of LA loss be according to the FDOT?

less than 45%

What is the purpose of the Aggregate Soundness Test?

to measure resistance of an aggregate to weathering through cycles of soaking in sodium or magnesium sulfate and oven drying

Aggregate Soundness Test Procedures

1. Separate aggregate into different sizes by sieving. From each size fraction, weigh out a sample of specific amount to be tested.

2. Immerse each test sample in sodium sulfate or magnesium sulfate for 16 to 18 hours.(Sodium sulfate is more severe)

3. Dry test sample to constant weight in an oven at 110 C.

4.Repeat procedure (steps 2 & 3) for 5 or 10 cycles.

5.Determine % weight loss of each sample after test by sieving it through a specified sieve.

6.Calculate and report: % Soundness Loss = Weighted average of % weight loss after test

What should the results of Soundness loss be according to the FDOT?

should be less than 12%, for 5 cycles of Sodium Sulfate

What is the purpose of the Test For Potential Alkali Reactivity( Mortar Bar Method )?

to determine the potential alkali reactivity of an aggregate

Test For Potential Alkali Reactivity (Mortar Bar Method ) Procedures

1. Make bars of mortar 1 in x 1 in x 12 in (1 part cement to 2.25 parts of graded aggregate).

2. Measure the length of the bars after 24 hours in the molds, and store the bars at a constant temperature of 100 °F in sealed moist containers.

3. Measure length changes at 1, 2, 3, 6, 9 and 12 months.

4. If expansion is greater than 0.05% at 3 months or 0.10% in 6 months, the aggregate is considered to be alkali reactive.

According to the mortal bar method what expansion values make the aggregate considered reactive (at 3 and 6 months)?

.05% at 3 months or .10% at 6 months

What is the purpose of the organic impurities test (for sand)?

to determine the presence of injurious organic compounds in natural sands

Organic Impurities Test (For Sand ) Procedures

1.Mix the sand with a 3 % solution of Sodium Hydroxide and allow it to stand for 24 hours.

2.Compare the color of the liquid to a solution of Potassium Dichromate in Sulfuric Acid (light yellowish color).

3. If the color of the liquid is darker, organic impurities might be present, and further tests (such as ASTM C87) should be made before the sand can be approved for use.

Effect of Organic Impurities in Fine Aggregate on Strength of Mortar Procedure

1. Make 3 (2-inch) cube specimens of mortar with washed aggregate, and 3 specimens with unwashed aggregate with specified consistency and proportions.

2. Run compressive strength test at 7 days.

3. Calculate and report:

[(average strength of mortar with unwashed agg.)/(average strength of mortar with washed agg.)]X 100%

What should the strength ratio of the Effect of Organic Impurities in Fine Aggregate on Strength of Mortar be?

should be greater than 95%

What percent of materials can pass through a No. 200 sieve (for coarse and fine aggregates) and how is this done?

- 1% of coarse agg and 3-5% for fine agg

- determine % passing sieve by wet sieving and drying

- 2 methods: A only uses water, B uses water and a wetting agent

What is the purpose of the Lightweight Particles in Aggregate test?

to determine the percentage of lightweight particles in aggregates

Lightweight Particles in Aggregate Procedures

1. A heavy liquid with a specific gravity of 2.0 (typically a solution of zinc chloride) is used to separate coal and lignite. A heavy liquid with a spec. gravity of 2.4 (typically a solution of zinc bromide) is used to separate chert and shale.

2. The separated lightweight particles are washed, dried and weighed. Results are reported in %.

What are the typical max results of the lightweight particles in aggregate test (2 values)?

- .05-1% for coal and lignite

- 3-8% for chert and shale

Clay Lumps and Friable Particles in Agg. Test Procedures

1. Soak aggregate in water for 24 hours.

2. Roll and squeeze aggregate particles between thumb and forefinger to attempt to break them into smaller sizes.

3. Use wet sieving and oven drying to determine the weight of the particles broken down.

4. Report results in % by weight

What aggregate particle shape and surface texture is undesirable for concrete?

flat and elongated

Which creates a greater strength in concrete: crushed or noncrushed aggregates?

they are the same

- rough textured and angular agg give better bonding and therefore a greater strength in the water cement ratio

- rough and angular agg requires more water to produce the same workability

- these effects offset

Describe lightweight aggregates, give examples and when it is used

- bulk unit weight of less than 70 pcf

- examples- pumice (natural agg), expanded clays, expanded shale, expanded perlite

- used to produce structural lightweight concrete or nonstructural insulating concrete

What is the range for normal natural aggregate unit weight?

95 to 105 pcf

Describe heavyweight aggregates, give examples and when it is used

- bulk unit weight over 130 pcf

- examples- iron ore, titanium ore, steel punchings

- used to produce heavyweight concretes for use as nuclear radiation shields

Describe Blast-Furnace Slag

- waste product from the blast-furnace process for manufacturing of steel and iron

- bulk unit weight of 70 to 85 pcf

- used in making precast concrete products, such as masonry blocks, where high strength is not required

- sulfur content in slag may cause durability problem in concrete. FDOT specs limit sulfur content to a maximum of 1.5%

Can recycled concrete be used as aggregate?

yes

What are some of the consequences of using recycled concrete as aggregate?

- the strength and durability of the concrete produced are limited by those of the old concrete

- generally has a higher absorption, a lower specific gravity, and a lower strength than a normal natural aggregate

What is hydraulic cement and what is an example?

- hardens by reacting with water to form a water-resistant product

- the presence of air is not required for the hardening process

- example: Portland cement

What is nonhydraulic cement and what is an example?

- reacts with water to form a product which is not stable in water

- the hydration product may then react with air to form a water-resistant product

- example: Quick Lime

Describe the cement used by the Greeks and Romans

a blend of lime and pozzolanic materials to produce a hydraulic cement

Who created modern Portland cement and when?

Joseph Aspdin in 1824

Why is it called Portland Cement?

the concrete it produced resembled the color of the natural limestone quarried on the Isle of Portland, a peninsula in the English Channel

Describe the steps in the manufacture of portland cement by the dry process using a preheater

1. quarrying and blending of raw materials

2. proportioning and fine grinding of raw materials

3. kiln system- preheating; burning; cooling and clinker storage

4. finish grinding and shipping

What are examples of sources of lime (CaO) in Portland Cement?

calcite, limestone, marl, shale, aragonite

What are examples of sources of iron (Fe2O3) in Portland Cement?

clay, iron ore, mill scale

What are examples of sources of silica (SiO2) in Portland Cement?

clay, marl, sand, shale

What are examples of sources of alumina (Al2O3) in Portland Cement?

aluminum ore refuse, clay, fly ash, shale

What are the 4 main compounds of portland cement?

- tricalcium silicate (C3S)

- dicalcium silicate (C2S)

- tricalcium aluminate (C3A)

- tetracalcium aluminoferrite (C4AF)

- these 4 compounds make up over 90% of portland cement by weight

How much does a commercial bag of Portland cement weight in the US?

94 pounds

What are the typical particle size, specific gravity, and typical unit weight of portland cement?

- particle size- finer than no. 200 sieve (75 micrometers)

- typical specific gravity- 3.15

- typical unit weight- 94 pcf

Why is gypsum added to cement?

to slow down rate of aluminate hydration and thus, the rate of setting

Is the hydration of Portland cement endo or exothermic?

exothermic

Describe C3S, C2S, C3A, and C4AF in the hydration process

- C3S- Hydrates and hardens rapidly; Largely responsible for initial set and early strength

- C2S -Hydrates and hardens slowly; Contributes largely to strength increase beyond one week

- C3A-Hydrates rapidly and liberates a large amount of heat; Contributes slightly to the early strength; A cement with a high C3A content is more susceptible to sulfate attacks, which cause expansion and cracking

- C4AF-Contributes little to strength. However, its presence reduces the clinkering temperature in the production of cement, and thus helps to reduce cost

Describe Type I of Portland Cement

- For general use

- No limits are placed on any of the four principal compounds.

Describe Type II of Portland Cement

- Moderate sulfate resistance & moderate heat of hydration

- Specification limits the C3A content to a maximum of 8%

Describe Type III of Portland Cement

- High early strength

- C3A content is limited to a maximum of 15%

Describe Type IV of Portland Cement

- Low heat of hydration

- Maximum limits of 35% and 7% on C3S and C3A, respectively

- Minimum of 40% C2S

Describe Type V of Portland Cement

- High sulfate resistance

- Maximum limit of 5% on C3A

What are types IA, IIA, IIIA used for?

air-entraining

What is Pozzolan and give an example?

- siliceous or siliceous/aluminous materials which have little or no cementitious value alone but that react with lime and water to form a cementitious product which is stable in water; calcium silicate hydrate (CSH)

- examples- volcanic ash (pumicite) and fly ash

What are the characteristics of a pozzolanic reaction?

- Reaction is Slow

- It consumes calcium hydroxide instead of producing it

- The large capillary spaces are filled up by the reaction products, making the concrete less permeable and more durable

Describe granulated blast-furnace slag

- Blast-furnace slag is a nonmetallic waste product from the blast-furnace process in the manufacturing of iron and steel

- Granulated slag is a glassy product formed by rapid cooling of the molten blast-furnace slag; consists mainly of silicates and aluminosilicates of calcium

- Granulated blast-furnace slag is self-cementing. but when it hydrates by itself, the amount of cementitious products formed and the rate of formation are insufficient to give adequate strengths for structural applications.

- When used in combination with Portland cement, the hydration of the slag is accelerated in the presence of calcium hydroxide and gypsum. The calcium hydroxide is also consumed by the slag in a pozzolanic reaction.

Describe Portland blast-furnace slag cement (Types IS)

a blend of Portland cement with 25 to 70% by weight of granulated blast-furnace slag.

Describe Portland pozzolan cement (Type IP & P)

- blend of Portland cement with 15 to 40% fine pozzolan by weight

- type P has a lower early strength than type IP, and is used when high early strength is not required.

Which has higher early strength pozzolans and blast-furnace slags or normal concrete?

normal concrete

Which has higher heat of hydration pozzolans and blast-furnace slags or normal concrete?

normal concrete

Which has higher ultimate strength pozzolans and blast-furnace slags or normal concrete?

can be higher in pozzolans and blast-furnace slags

Which has a more rapid strength gain pozzolans and blast-furnace slags or normal concrete?

Portland blast-furnace slag cement has a more rapid strength gain than Portland pozzolan cement.

Is water resistance increased or decreased in the presence of pozzolans and blast furnace slags?

increased because calcium hydroxide is consumed

Is permeability increased or decreased in the presence of pozzolans and blast furnace slags?

decreased because more pores are filled by the products of pozzolanic reaction

Is sulfate resistance increased or decreased in the presence of pozzolans and blast furnace slags?

- increased because rate of sulfate attacks is dependent on calcium hydroxide and permeability

- type IS cement containing 60 to 70% slag is highly resistant to sulfate attack irrespective of C3A content of the Portland cement and the reactive alumina content of the slag

Is alkali-aggregate expansion increased or decreased in the presence of pozzolans and blast furnace slags?

decreased

How are white and colored cements different in properties from Portland cement?

They are similar to normal Portland cement

When is white cement used and how is the color achieved?

- used to produce architectural concrete where white color is desired

- color is achieved by reducing the iron concrete of the cement

How is the color in colored cement achieved?

by adding pigments to white cements or using clinkers having the corresponding colors

What is the purpose of the Loss of Ignition Test (ASTM C114 Section 16)?

to measure the level of pre-hydration of a cement

Describe the testing procedure for the Loss of Ignition Test (ASTM C114 Section 16) and what is the max loss for each type

1. A 1 g sample of cement is placed in a crucible and ignited in a muffled furnace at a temperature of 950 +/-50 °C until constant weight is reached

2. Calculate and report the % weight loss

3. The weight loss is assumed to represent the total moisture and CO2in the cement.

4. ASTM C150 limits the maximum Loss on Ignition at 3.0% for Types I, II, III and V and 2.5% for Type IV Portland cement

What does a high % loss on Ignition gives an indicate?

a high prehydration and carbonation, which may be caused by improper storage and handling of the cement.

What is the purpose of the test for fineness of cement?

to measure the fineness of a cement

How does fineness relate to the rate of hydration?

the greater the fineness, the more rapid the rate of hydration

What are two common tests for the fineness of cement test?

1. wagner turbidimeter

2. blaine air permeability test (gives higher numbers)

Describe the procedure for the test for the fineness of portland cement using a turbidimeter

1. A sample of cement is dispersed in a glass tank of kerosene

2. A beam of light is passed horizontally through the cement suspension (at given elevations on a stated time schedule)

3. A photoelectric cell on the other side of the glass tank is used to measure the intensity of light passing through the suspension at specified times

4. The photocell readings (in microA) at the specified times are used to compute the specific surface of the cement tested (in cm2/g or m2/kg).

Describe the procedure for the test for fineness of portland cement using an air permeability apparatus

1. A sample of cement is placed in a cylindrical permeability cell and compacted to a specific porosity

2. One end of the permeability cell is connected to a manometer tube

3. Air is allowed to flow through the column of compacted cement in the permeability cell under a decreasing pressure

4. The time it takes for a specific volume of air to flow through the column of cement is measured.

5. The same test is run on a standard sample with known specific surface in the calibration testing

6. If the test sample and the standard sample are tested at the same temperature and porosity, compute the specific surface of the test sample

What equation is used to compute the specific surface of the sample after the blaine permeability test?

S=[S1(sqrt(T))]/(sqrt(T1))

- S= specific surface of test sample

- S1= specific surface of standard sample

- T= measured flow time for test sample

- T1= measured flow time for standard sample

What is the most commonly used test for the test of soundness and what is soundness?

- Soundness of cement is the ability to retain its volume after setting without undue expansion

- The most commonly used test is ASTM C151 standard test for Autoclave Expansion of Portland Cement

Describe the procedure for Autoclave Expansion of Portland Cement (ASTM C151)

1. Prepare a cement paste of normal consistency and mold a square prism specimen 1 X 1 X 11.25 inch. The paste is fairly stiff . At this condition, a standard Vicat plunger (with a diameter of 10 mm and a weight of 300 g.) settles to a depth of 10 mm in 30 seconds.

2. Take the specimen out from the mold at 24 hours

3. Measure the length of the specimen with a length comparator before putting it in the autoclave

4. Increase pressure and temperature of autoclave gradually from ambient condition to 295 psi and 420 °F in 45 to 75 minutes. Hold at this condition for 3 hours

5. Reduce pressure gradually to ambient condition in 1.5 hours before taking the specimen out

6. Measure the length of the specimen

7. Calculate and report % length change.

- ASTM C150 specification for Portland cement limits the maximum autoclave expansion to 0.80%

What is the purpose of the test for time of setting?

The characterization of the time of setting of a cement is to determine the quality of a cement with regards to its rate of setting

What are the two commonly used tests for time of setting and what do they determine?

- the gillmore and vicat test

- both tests determine the initial setting time and final setting time of a cement

- the gillmore test produced higher values than the vicat test

Describe the procedure for time setting using a Gillmore Needle

1. Prepare a cement paste of normal consistency and mold a circular pat with flat top. Base Diameter: 3 inches. Top Diameter: 2 inches. Thickness: 0.5 inch

2. Gillmore needle for initial set: 1/4 lb.in weight and 1/12 inch in diameter; Initial set occurs when the cement paste pat can bear this needle without appreciable indentation

3. Gillmore needle for final set: 1 lb in weight and 1/24 inch in diameter; Final set occurs when the pat can bear this needle without appreciable indentation

4. Report initial and final setting times in minutes

Describe the procedure for time setting using a Vicat Needle

1. Prepare a cement paste of normal consistency and place the paste in a conical ring with an inside diameter of 70 mm at bottom and 60 mm at top, and a height of 40 mm.

2. The Vicat needle has a weight of 300 g and a diameter of 1 mm.

3. Determine the penetration of the Vicat needle into cement paste in 30 seconds, every 15 minutes.

4. Initial setting time is reached when the penetration in 30 seconds is 25 mm; Data can be interpolated to obtain this time.

5. Final setting time is reached when the needle does not sink visibly into the paste.

What is the purpose of the test for strength characterization and what is the standard test?

- purpose is to ensure the quality of a cement with regards to strength development

- standard test- compressive strength of hydraulic cement mortars

Describe the procedure for the Compressive Strength of Hydraulic Cement Mortars Test

1. Prepare a cement mortar (using one part of cement to 2.75 parts of graded standard sand, and a w/c of 0.485 for non-entraining cements) and mold 2 inch cube specimens.

2. Remove specimens from mold at 24 hours and immerse them in water saturated with lime (except those tested at 24 hours).

3. Test the mortar cubes for compressive strength at 24 hours, 3 days, 7 days and 28 days. Report compressive strengths.

What is the required compressive strength for Type I cement?

1800 psi at 3 days and 2800 psi and 7 days

What is the purpose of the test for heat of hydration and what test is typically used?

- This test measures the heat of hydration at 7 days and at 28 days, and reports the results in cal/g or kJ/kg.

- The heat of hydration can provide information for calculating temperature rises in mass concrete.

- Heat of Hydration of Hydraulic Cement (ASTM C 186)

Describe consistency

the ease of flow of the fresh concrete

Describe cohesiveness

water holding capacity (or resistance to bleeding) and the coarse-aggregate holding capacity (or resistance to segregation) of the fresh concrete.

True of False: ease of transportation and placement and resistance to bleeding and segregation are desirable characteristics of concrete

true

For each consistency (dry, stiff, medium, wet, sloppy) give its slump and what type of work it is used for

1. Dry- slump (in)= 0-1

2. Stiff- slump (in)=.5-2.5; work- dams, large foundations

3. Medium- slump (in)= 2-5.5; work- pavement, footings

4. Wet- slump (in)=5-8; work- thin slabs, columns

5. Sloppy- slump (in)= 7-10