Concrete Training Manual  

 

 

 

                                      

 

 

 

 

Abdalla F. Sadi

Concrete Engineer

 

 

 

 

 

 

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Index:

 

 

Chapter (1) : Concrete components

 

[1] Cement

 

1.                  Cement production

2.                  Types of cement          

3.                  Testing The Cement

 

[2] Aggregates

 

1.                  Sources

2.                  Geological Classification

3.                  Size Of Aggregate

4.                  Shape And Texture Of Aggregate

5.                  Grading of Aggregate

6.                  Hardness Of Aggregate

7.                  Fineness Of Aggregates

8.                  Moisture condition of aggregates

9.                  Specific Gravity and unit weight

10.              Bulking of Sand

11.              Impurities In Aggregates

 

[3] Water

 

1.                  Impurities in water

2.                  Effects of the quality of water on concrete

 

 

Chapter (2) : Hardening of the cement paste

 

1.                  Hydration of cement

2.                  Components of the cement

3.                  Chemical reactions

4.                  Rate of hydration

5.                  Heat of hydration

6.                  Hydration stages

7.                  Setting of cement paste

8.                  Paste microstructure

9.                  Porosity

10.              Development of strength

11.              Curing

 

Chapter (3) : Concrete properties

 

1.                  Workability

2.                  Bleeding and segregation

3.                  Strength

4.                  Durability

 

 

 

Chapter (4) : Durability problems in concrete

 

1.                  Freezing and thawing:

2.                  Sulphate attack:

3.                  Alkali-aggregate reaction

4.                  Sea Water Attack

5.                  Carbonation

 

Chapter (5) : Concrete basic relation

 

1.                  Water

2.                  Aggregates

3.                  Air content

4.                  Temperature

5.                  Age

6.                  Cement

7.                  Other factors

 

Chapter (6) : Admixtures

 

1.                  Water reducers

2.                  Superplasticizers

3.                  Accelerators

4.                  Set-retarders

5.                  Air-entraining admixtures

6.                  Pozzolans

7.                  Silica Fume

 

Chapter (7) : Concrete mix design

 

1.                  Introduction

2.                  ACI Absolute method

3.                  The British method

 

Chapter (8) : Jordanian specifications

 

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 1 : concrete components

 

At a basic level, concrete consists of cement, aggregate, water and entrapped air.

 

Cement

 

Cement production:

 

Hydraulic cement is the cement that undergoes a chemical reaction with water and will set and harden in air or under water and does not undergo any changes due to exposure to water.

 

The major raw materials in manufacturing cement are:

 

1. Calcium: found in limestone, shale and marl.
2. Silica: found in sand, clay, shale and marl.
3. Alumina: found in clay, shale and slag
4. Iron oxides: found in iron ore, clay, and mill scale.

 

The production process:

 

1. Collecting the raw materials: while calcium source controls the location of the plant, silica is usually shipped to the plant.
2. Preparing the raw materials: grinded to a mixture of specified proportions.
3. The materials are fed to an inclined rotating klin from the higher edge while heat is blown from the lower edge.
4. The materials burn in the klin (1400-1600 C°), Forming new compounds (C3S, C2S, C3A, C4AF and others) that fuse as 3 - 3.5 mm balls called “Clinker”.
5. The clinker is cooled down and grinded to a fine powder.
6. Gypsum is added.

 

Portland cement is basically a mixture of:

C3S	3CaO.SiO2	Tricalcium silicate
C2S	2CaO.SiO2	Dicalcium silicate
C3A	3CaO.Al2O3	Tricalcium aluminate
C4AF	4CaO.Al2O3..Fe2O3	Tetracalcium aluminoferrite
CSH2	CaO.SiO2.H2O		Gypsum

 

 

 

 

 

 

 

 

                            Where: CaO = C    SiO2 = S    Al2O3 = A    Fe2O 3= F   H2O = H

 

The proportion of each component makes the difference from one type of Portland cement to another as each component has a different effect on the final property of the cement. The properties of these four major components can be controlled by:

 

1. Changing the proportion of the raw materials in the klin.
2. Changing the temperature in the klin
3. Changing the duration in the kiln
4. Adjusting the amount of the added gypsum.

 

 

 

In addition to the main components, other materials are also present in low quantities like MgO, TiO2, Mn2O3, K2O and Na2O. Two of them  (K2O and Na2O) are known as "The Alkalis" they react with some aggregate types causing disintegration of the concrete in addition to affecting the rate of the gain of strength of cement.

 

 

Types of cement:

 

Type I             : General purpose Portland cement

                        No exposure to sulphates in the soil or ground water.

 

Type II            : Modified Sulphate resistant Portland cement

                        Moderate Sulphate attack, this cement got a higher rate of hydration than type I.

 

Type III          : Early strength Portland cement

Used when there is a need for removing formwork earlier or early strength is required for further construction (higher CS content and higher fineness of cement).

 

Type IV          : Low heat of hydration Portland cement

This cement got a low heat of hydration (low content of C3S and C3A) but ultimate strength is not affected.

 

Type V            : High Sulphate resistant Portland cement

                        Used in Sever Sulphate attacks conditions , this cement got a low content of C3A

 

In addition to the five major types of Portland cement, a number of special purpose hydraulic cements are manufactured. Among these is white Portland cement. White Portland cement is identical to gray Portland cement except in color. During the manufacturing process, manufacturers select raw materials that contain only negligible amounts of iron and magnesium oxides, the substances that give gray cement its color. White cement is used whenever architectural considerations specify white or colored concrete or mortar.

 

For local Jordanian cement, by experience the cement content should be increased by 20 kg/m³ to maintain the same compressive strength.

 

Testing The Cement:

 

The compressive strength of cement is tested using a standard concrete mix or testing the cement paste in two methods:

 

BS

Cement: sand 1:3     standard one-size sand

Water content=10% mass of the dry materials

Cubes of 71 mm

Demolded after 24 hours and cured in water

Tested in a wet surface condition

 

ASTM

w/c = 0.485

Cement: sand 1:2.75 Ottawa sand

Demolded after 24 hours and cured in saturated lime water at 23C°

Aggregates

 

The large, solid coarse aggregate particles form the basic structural member of concrete. The voids between the large aggregate particles are filled by smaller fine aggregate particles, the voids between the smaller fine aggregate particles are filled by still smaller particles, and Finally, the voids between the finest grains are filled with cement while all the particles are bonded by the cement paste.

Aggregate occupy almost three quarters of the concrete volume. It increases the strength of concrete, reduces the shrinking tendencies of the cement, and is used as economical filler. Because aggregates fill up 60-80% of the concrete volume, their properties greatly influence the strength, durability, and the structural performance of concrete.

 

Sources:

 

        1. Natural and crushed      : River gravel and sand, crushed quarry rock.

        2. Manufactured               : Expanded shale, blast furnace slag.

        3. Recycled                      : Old concrete or asphalt pavement.

 

Geological Classification:

 

Natural aggregates result from the breakdown of large rock masses. Rocks can be of three basic types:

1. Igneous: produced from hardening of volcanic lava. This includes granite and basalt.
2. Sedimentary: form from he deposits of disintegrated existing rocks or inorganic remains of marine lives. This includes limestone, shale, chalk, chert, and sandstone.
3. Metamorphic rocks: form from the igneous or sedimentary rocks coming under heat and 

            pressure.  Like quartzite.

 

Size Of Aggregate:

 

Aggregate size is usually defined by the following two terms:

 

1. Nominal maximum size: the smallest sieve size that the percent passing for that sieve isn't less than 95%. (The smallest of all the sieves having a percent passing >=95%).

2. Maximum size: the smallest sieve size for which 100% of the sample passes through, usually one sieve size bigger than the nominal maximum size.

 

Aggregates can be categorized into two types with respect to size:

 

1. Coarse aggregates      : aggregate that have a minimum of 20 % retained on sieve #4.

2. Fine aggregates          : aggregate that is 100 % passing the 3/8” sieve with a minimum                                                    of 80% passing the #4 sieve.

                          

Local aggregates and sizes
Aggregate local name	Size	First sieve to be retained on
Jozeah	40 mm	1 ½ “
Fuliah	25 mm	1 “
Humsiah	20 mm	¾”
Adasiah	12 mm	½”
Sumsumiah	9.5 mm	3/8”
Sand (2)	4.75 mm	#4
Sand (3)	1.18 mm	#16

 

 

 

 

 

 

 

 

 

 

 

 

Slandered ASTM sieves
Sieve	Sieve	Aggregate Type
No.	Size
3"	75	Coarse
2.5"	63
2"	50
1.5"	37.5
1"	25
3/4"	19
1/2"	12.7
3/8"	9.5
#4	4.75
#8	2.36	Fine
#16	1.18
#30	0.6
#50	0.3
#100	0.15
#200	0.075	Silt
	< 0.02mm	Clay

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Shape And Texture Of Aggregates:

 

Particle shape classification BS 812
Rounded	Fully water worn or completely shaped by abrasion.
Irregular	Naturally irregular or partly shaped by abrasion with rounded edges.
Angular	Well-defined edges formed at the intersection of rough planner faces.
Flaky	Thickness smaller than the length and width.
Elongated	Length larger than the width and thickness.
Flaky and Elongated	Length larger than the width and the width larger than the thickness.

                                        

Local Available Aggregate Shapes
Rounded	From the desert, river and sea shores
Angular	Crushed rocks and crushed rounded gravel

 

 

The degree of packing of one sized aggregate depends on the shape and texture.

 

Flakiness/Elongation Index: percent of mass of flaky/elongated particles in a sample of aggregates.

 

Grading of Aggregate:

 

Concrete is made with aggregate particles covering a range of sizes up to a maximum size. The particle size distribution is called grading.

 

To achieve a well graded aggregate content. The total aggregate weight is divided over many aggregate piles each with a different grading and maximum size. This will ensure better packing and a minimum void.

 

Three different kinds of size distributions: continuously graded (well graded), gap-graded, and uniformly graded, are illustrated in the figure below.

 

- Well-graded aggregates are desirable for making concrete, as the space between larger particles is effectively filled by smaller particles to produce a well-packed structure.

 

- Gap grading is a kind of grading which lacks one or more intermediate size.

 

- Uniform grading; only a few sizes dominate the bulk material. With this grading, the   aggregate particles  are not effectively packed, and the resulting concrete will be more porous.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Hardness Of Aggregate:

 

Hardness, or resistant to wear is an important property of concrete and can be measured using the Los Angeles abrasion test. Which will judge the hardness of the aggregates by measuring the resulting amount of material less than 0.075 mm after the aggregate and steel balls are rotated 500 times in a cylinder.

 

Fineness Of Aggregates:

 

A factor relating to the fineness of the aggregates, useful in detecting slight variations in the aggregates supplies from the source, which will affect the workability of the concrete. The fineness modulus is usually calculated for the fine aggregates only since sand gradation has the largest effect on workability. The fineness modulus can be used to check the constancy of grading when relatively small change is expected; but it should not be used to compare the grading of aggregates from two different sources.

 

Fineness modulus = Sum of the cumulative percent retained on the sieves (excluding #200) 

                                   divided over 100.

 

The sieves used for determining the Fineness Modulus are the sieves that have a ratio of 1/2 in size. Those sieves are:

 ( #100 , #50 , #16 , #8 , #4 , 3/8" , 3/4" , 1 ½" ) and larger, increasing in a ratio of (2 : 1).

 

Note that when the percent retained for any lower sieve is zero, the cumulative percent retained should be entered as (100)

 

 

Fineness modulus	Description
2.3 – 2.59	Fine sand
2.6 – 2.89	Medium sand
2.9 – 3.10	Coarse sand

 

 

 

 

 

 

 

For blended types of aggregates:

 

FM blend = FM(A) * PA/100  +  FM(B) * PB/100 

 

FM: fineness modulus

A,B : aggregate A, aggregate B

PA,PB : percentage of A,B

 

Moisture condition of aggregates:

 

The moisture condition of aggregates refers to the presence of water in the pores and on the surface of the aggregates. There are four different moisture conditions:

 

1. Oven Dry (OD): This condition is achieved by keeping aggregates at a temperature of 110⁰C for a period of time long enough to reach a constant weight. Pores in the aggregates are dry.

 

2. Air Dry (AD): This condition is achieved by keeping the aggregates under room temperature and humidity. Pores inside the aggregates are partly filled with water.

 

3. Saturated Surface Dry (SSD): This condition is achieved by immersion the aggregates in water for 24 hours followed by drying of the surface with wet cloth. Pores in the aggregates are filled with water while the surface is dry.

 

4. Wet (W): The pores of the aggregate are filled with water and the surface of the aggregate is covered with a film of water. Achieved as in the SSD condition but without drying the surface.

 

 

Specific Gravity and unit weight:

 

Pores in an aggregate unit volume consist of voids between aggregate particles and voids in the aggregate particle itself (impermeable and capillary)

 

Specific Gravity also known as the “Relative density” is the ratio of mass (weight in air) of a unit volume of a material to the weight of the same volume filled with water.

 

The absolute specific gravity (ASG) (particle density): refers to the weight and volume of the solid part of the aggregate excluding all pores in and out the aggregates.

 

The bulk specific gravity (BSG): refers to the weight and volume of the solid materials and the voids in the aggregates with out the voids between the aggregate particles measured in OD and SSD conditions.

 

The apparent specific gravity (apparent particle density) : refers to the volume of the solid materials including the impermeable pores but not the capillary ones in the aggregates.

ASG > BSG (SSD) > BSG (OD)

Because the porosity of most rocks are low (1-2%) the values of all the specific gravities are in the range of  2.5 – 2.8

 

Unit weight (UW): the ratio of the aggregate weight to their volume considering the volume of the voids in and out the aggregates.

 

Bulking of Sand:

 

When the dried sand gets wetted, its volume will stay constant till it reaches 100% absorption. If  the moisture content increase after the 100% saturation, the volume of the sand will increase as the forces of surface tension push the particles away from each other. This will also decrease the unit weight of sand because the water is taking the place of sand grains in the unit weight and because water is lighter than sand the unit weight will decrease.

As the water content increase more and more, the thin film of water surrounding the particles thickens, the volume of the sand will decrease because of the lubrication effect that will help pack the sand particles closer.

Impurities In Aggregates:

 

There are four types of impurities in the aggregates that can lead to lowering the quality of the concrete:

 

1.      Organic impurities: these are the decaying products of vegetable matter found usually in sand and easily removed by washing. The presence of these organic materials will affect the hydration of the cement paste.

 

2.      Clay and fine materials: clay, silt and crushing dust found in aggregates as surface coating will affect the bond between the aggregate surface and the cement paste. Silt and crushing dust could also be present as loose materials increasing the water requirements of the concrete because of their large surface area.

 

3.      Salt: found in sand collected from sea or river shores can be removed by washing. may cause corrosion of steel reinforcement in concrete. In addition to absorbing moisture from the air which will form   white deposits on the surface.

 

4.      Soft particles: such as clay lumps, wood and coal will cause scaling of the surface and lack of durability.

 

 

Impure Substances	Effects on concrete
Organic impurities	Affects setting and hardening time and may cause deterioration
Materials finer than number 200 sieve	Affects bonding and increases water requirement
Coal, lignite, or other lightweight materials	Affect durability and may cause stains and pop outs
Soft particles	Affects durability
Friable particles	Affects workability and durability and may cause pop outs

 

 

Water       

 

The quality of water used in concrete is judged by the impurities in it and the effect it could have on the concrete.

 

In general, the water suitable for concrete should be fit for drinking provided that it doesn't contain a high concentration of sodium and potassium because of the danger of alkali-aggregate reactivity.

 

Impurities in water:

 

1. Suspended solids: high amounts of solid can increase the water demand, increase dry shrinkage, cause Efflorescence and affect air entraining.

 

2. Dissolved solids: dissolves salts can cause slower setting and hardening times and reduced strength.

 

3. Organic materials retard hydration and entrain excessive amount of air.

 

Effects of the quality of water on concrete:

 

Hardening of the concrete: water containing Humic or other organic acids also water with high alkaline content.

 

- Strength: water containing Algae tend to entrap air thus lowering the strength.

 

- Staining of the concrete surface: water with high chloride (salt) content like seawater.

 

- Corrosion of the steel reinforcement: water with high quantities of salts like seawater.

 

- Higher early strength with a lower long-term strength: water high in NaCl, MgCl2 and MgSO4 like

   seawater.

 

- Alkali-aggregate reactivity: water with a high concentration of sodium and potassium like some  

   tab water.