CONSTRUCTION AND

QUALITY OF CONSTRUCTION

Compiled By: Prof. Dr. M. Shamim Z. Bosunia 19th June 2014

For an Engineer his works in profession, his knowledge in the technique of construction and his success in constructing a building is a thing of great pride for him. It is his professional religion and it is the self satisfaction aroused in him which enables him to apply his body and mind so diligently in the arduous and difficult task of the construction. This feeling of pride and the unspeakable satisfaction make his job pleasant and make him completely forgetful of the strains of his hard work and labor.

He is not only a builder of buildings but also ultimately is builder of the nation as well. The responsibility on him, however, junior/ young he might be, even as a Work Assistant, is very great indeed as a single brick in the foundation plays a vital role in the stability of the massive structure standing over the same.

It is to be borne in mind that the knowledge of affecting economy in a construction consistent with its strength and durability really makes a man an Engineer. It should therefore be a constant struggle by an Engineer to obtain the maximum amount of durability and strength with a minimum amount of expenditure. The question of durability and strength, however, should always have preference as the failure of structures means losing the entire economy.

Building engineering like all such branches in the technical field is a matter of strong commonsense and the application of the specialised methods and procedure in the various lines in the construction. The field engineers should therefore be very keenly alive to his own sense of examination and judgment and should rigidly follow the course of procedure and specification hereinafter described.

REINFORCING STEEL

Reinforcing steel is the most vital component of reinforced concrete structures. It is important that all design engineers, construction engineers, steel manufacturers and others who work with it understand its nuances and significances very clearly.

Feature of Steel & Concrete Bonding

The thermal expansion coefficients of the two materials, about 6.5 10-6 for steel vs. an average of 5.5 10-6 for concrete, are sufficiently close to forestall cracking and other undesirable effects of differential thermal deformations.

Feature of Steel & Concrete Bonding

While the corrosion resistance of bare steel is poor, the concrete that surrounds the steel reinforcement provides excellent corrosion protection, minimizing corrosion problems and corresponding maintenance costs. Durable concrete produces an environment of pH equal to +13.5 for the embedded reinforcements.

Typical Theoretical Stress-Strain Curves for Rebars

Typical Cross-Sections of MS, CTD & TMT Rebars

Note: MS : Mild Steel CTD : Cold Twisted Deformed TMT : Thermomechanicaly Treated

To summarize, attributes of reinforcements that are important for engineering of sound and durable RC structures are:

Bond with concrete Strength Ductility Resistance against corrosion

Important Attributes of Reinforcement

Ductility

Ductility of rebar is expressed as the ratio of ultimate deformation at collapse to deformation at yielding. The ductility of a mild steel rebar under the monotonic tensile loading is given by

Where , u and y are ductility factor, ultimate strain and yield strain of the rebar's respectively. This makes elongation a good indicator of ductility and is used as a parameter to characterize the rebar for ductility.

= u /y

Three grades of rebar; Grade415, Grade500 and Grade550 or their equivalent are taken for this exercise It is noted that there is only one grade of ASTM A706/A706M rebar available, which is Grade-420 recommended for earthquake resistant design. Australian/ New Zealand specification allows three categories of rebars of Grade-500: Class L (low ductility) 500L, Class N (normal ductility) 500N, and Class E (high ductility for earthquake prone region) 500E. Similar observation can be made on Euro code.

Grades of Rebars Used for Seismic Design

CONCRETE AND INGREDIENTS

Concretes versatility, durability and economy have made it the worlds most used construction material. The durability of concrete may be defined as the ability of concrete to resist weathering action, chemical attack, and abrasion while maintaining its desired engineering properties. The concrete ingredients, proportioning of those ingredients, interactions between the ingredients, and placing and curing practices determine the ultimate durability and life of the concrete.

Concrete For Durable Construction

Durable Concrete

Cross section of hardened concrete made with (Left) rounded siliceous gravel and (Right) crushed limestone. Cement-and-water paste completely coats each aggregate particle and fills all spaces between particles.

Section of Concrete

Schematic Representation of Manufacture and Hydration of Portland Cement

Development of Strength of Pure Compounds

Cement Standards and Type of Cement

ASTM (USA)

BDS EN (Bangladesh)

BS (UK)

EN (European)

BIS (Indian)

ISO (international)

Specification for Portland Cement Type I General Purpose Cement, OPC Type II Moderate heat/Moderate Sulphate

Resistance Type III High Early Strength Type IV Low Heat of Hydration Type V High Sulphate Resistance A Air -Entraining LA Low Alkali

ASTM C150

Bangladesh Government has adapted EN197-1:2000

standard as local cement standard in 2003 and has given its new standard as

BDS EN 197-1:2003

BDS EN 197-1:2003 (Composition)

naturalnatural

calcinedsiliceous calcareous

K S D b) P Q V W T L LL

CEM I Portland cement I 95-100 - - - - - - - - - 0-5

II/A-S 80-94 6-20 - - - - - - - - 0-5

II/B-S 65-79 21-35 - - - - - - - - 0-5

Portland-silica fume cement II/A-D 90-94 - 6-10 - - - - - - - 0-5

II/A-P 80-94 - - 6-20 - - - - - - 0-5

II/B-P 65-79 - - 21-35 - - - - - - 0-5

II/A-Q 80-94 - - - 6-20 - - - - - 0-5

II/B-Q 65-79 - - - 21-35 - - - - - 0-5

II/A-V 80-94 - - - - 6-20 - - - - 0-5

II/B-V 65-79 - - - - 21-35 - - - - 0-5

II/A-W 80-94 - - - - - 6-20 - - - 0-5

II/B-W 65-79 - - - - - 21-35 - - - 0-5

II/A-T 80-94 - - - - - - 6-20 - - 0-5

II/B-T 65-79 - - - - - - 21-35 - - 0-5

II/A-L 80-94 - - - - - - - 6-20 - 0-5

II/B-L 65-79 - - - - - - - 21-35 - 0-5

II/A-LL 80-94 - - - - - - - - 6-20 0-5

II/B-LL 65-79 - - - - - - - - 21-35 0-5

II/A-M 80-94 0-5

II/B-M 65-79 0-5

III/A 35-64 36-65 - - - - - - - - 0-5

III/B 20-34 66-80 - - - - - - - - 0-5

III/C 19-May 81-95 - - - - - - - - 0-5

IV/A 65-89 - - - - 0-5

IV/B 45-64 - - - - 0-5

V/A 40-64 18-30 - - - - - 0-5

V/B 20-39 31-50 - - - - - 0-5

a) The values in the table refer to the sum of the main and minor additional constituents.

b) The proportion of silica fume is limited to 10%.c) In Portland-composite cements CEM II/A-M and CEM II/B-M, in Pozzolanic cement CEM IV/A and CEM IV/B and in composite cements CEM V/A and CEM

V/B the main constituents other than clinker shall be declared by designation of the cement.

Fly ash

Main constituentsMinor

additional

constituents

a)

BF Slag Silica

Fume

Burnt.

Shale

Limestone Main

Types

Notation of the 27 products(type of

common cement)

Clinker Pozzolan

Portland-burnt shale cement

Portland limestone cement

Portland composite cement c)

CEM II

Portland slag cement

Portland pozzolana cement

Portland fly ash cement

6-20

21-35

CEM III Blast furnace cement

CEM V Composite cement c)

11-35

36-55

18-30

31-50

CEM IV Pozzolanic cement C)

Supplementary Cementitious Materials (SCMs)

Fly ash (Class C)

Fly ash (Class F)

Slag

Lime Stone

Silica fume

Calcined shale

Metakaolin (calcined clay)

CSH = Calcium Silicate Hydrate

Cement Hydration

Cement + Water CSH + Ca(OH)2

Pozzolanic Reaction of Fly Ash

Fly Ash + Ca(OH)2 + Water CSH

Pozzolanic Reaction (PCC)

Strength Development

Needed for two purposes: Chemical reaction with cement Workability

Only 1/3 of the water is needed for chemical reaction

Extra water remains in pores and holes Results in porosity Good for preventing plastic shrinkage cracking and

workability Bad for permeability, strength, durability.

Water

Durability is the ability of a Material or Structure to withstand its design service conditions for its design life without significant deterioration.

Durability

Potential durability of concrete is defined as the resistance of the cover concrete to the conduction of chlorides, sulphates, permeation of Oxygen and absorption of Water.

Durability Design Phylosophy

The Environment

Type and quality of constituent materials

Cement content and W/C ratio of concrete

Workmanship especially in compaction and curing

Cover to embedded steel

Shape and size of the member

Factors influencing Durability of concrete

Low permeability

Resistance to sulfate attack

Chloride attack on reinforcement

Resistance to Alkali Silica reaction

Low heat of hydration

High workability

Durable Concrete

Lower heat of hydration

High long term strength

High

chemical resistance

(sea water, chloride diffusion,

sulphate attack)

Low effective alkali content

Improved pump ability, compact ability

Performance of Composite Cement

Lower early strength

Improved fresh concrete properties

Performance of Composite Cement in Concrete

Low permeability, dense structure

Concrete

FINE AGGREGATE Sand must be cleaned, washed and of definite gradation. TEST for Sand: Fineness Modulus (FM) Salinity Bulking Testing for impurities For Good Concrete works FM must be 2.5 or above. CAUTION: Without sieve analysis tests mixing of coarse sand and fine sand must not be allowed. This is a very bad practice in out construction.

Surface area Calculation Example:

Agg. Size. (Say) 1X1X1 Cube Vol. = 1x1x1 = 1in3

Surface Area= 6 surface x1x1 =6 in2

Now if the 1x1x1 cube is cut into 8 pieces of x x Vol.=8x x x = 1in3

Surface Area=8x6x x =12in2

Which is Double of the 1X1X1 Cube. Hence, for smaller aggregates more cement to the extent of double amount is required.

Workability

Bleeding And Settlement

Bleeding is the development of a layer of water at the top or surface of freshly placed concrete. It is caused by sedimentation (settlement) of solid particles (cement and aggregate) and the simultaneous upward migration of water (Fig-5). Bleeding is helpful to control plastic shrinkage cracking. Excessive bleeding increases the water-cement ratio near the top surface; a weak top layer with poor durability may result. A water pocket or void can develop under a prematurely finished surface.

Bleed Water on Surface of Concrete Slab

Concrete of a Stiff Consistency (Low Slump)

Consolidation

The vibratory action permits use of a stiffer mixture containing a larger proportion of coarse and a smaller proportion of fine aggregate. The larger the maximum size aggregate in concrete with a well-graded aggregate, the less volume there is to fill with paste and the less aggregate surface area there is to coat with paste; thus less water and cement are needed. Concrete with an optimally graded aggregate will be easier to consolidate and place. Consolidation of coarser as well as stiffer mixtures results in improved quality and economy. On the other hand, poor consolidation can result in porous, weak concrete with poor durability.

Effect of Void in Concrete Due to Consolidation

Electro Micrograph showing Corrosion in Poor Concrete

Electro Micrograph showing NO Corrosion in Good Concrete

Corrosion in Concrete

Corrosion in Concrete

Hardened Concrete

Concrete strength increases with age as long as moisture and a favorable temperature are present for hydration of cement

Relationship of Strength Gain and Moist Curing

Typical Plastic Shrinkage Cracks

Plastic Shrinkage Crack

Damage Induced by Corrosion

Crack Due to Pressure of Rusting Reinforcements

Common problems due to corrosion

Delamination of Concrete Cover

Chemical Resistance

Portland cement concrete is resistant to most natural environments; however, concrete is sometimes exposed to substances that can attack and cause deterioration. Concrete in chemical manufacturing and storage facilities is especially prone to chemical attack. The effect of sulfates and chlorides is discussed above. Acids attack concrete by dissolving cement paste and calcareous aggregates.

Deterioration of Concrete Exposed to Seawater

COMPRESSIVE STRENGTH of CONCRETE is:

Specified in the Design

Measured by the Cylinder Test in which the :

i) 7 day strength = 65% of Specified Design Strength

ii) 28 day strength = Specified Design Strength

Cylinder Casting Requirements (ASTM designation:C31/C31M-03a)

Mold size CONSOLIDATION METHOD

TAMPING VIBRATION

Dia. x Ht.

in (mm)

Tamping Rod

(mm)

No. of

Layers

Rodding

Per Layer

No. of

Layers

Vibrator

insertions per

Layer

Approx

Depth of Layer

Dia. Length

4X8

(100x200) 10 300 2 25 2 1

One-half depth

of specimen

6X12

(150x300) 16 500 3 25 2 2

One-half depth

of specimen

4

8

6

12

FINE AGGREGATES:

Sylhet Sand of F.M 2.50

Local Sand of F.M 1.25

COARSE AGGREGATES:

20 mm (3/4 inch) down, well-graded stone chips used

12 mm (1/2 inch) down, well-graded stones chips used

20mm (3/4 inch) down, well-graded brick chips used

A mixture of 3/4 and 1/2 downgraded stone chips are used in most mixtures

3/4 downgraded brick chips are sometimes used in slabs

EXCEPTIONS are: i. Railing

ii. Dropwall Fins

For such Exceptions 12 mm (1/2 inch) down graded stone chips will be used.

POTABLE WATER is to be used in concrete mix

Potable water means water YOU CAN DRINK.

For CASTING, use WASA water supply

Water from any other source WILL NOT BE ALLOWED

Admixtures will be used:

As mentioned in the respective Drawings and Specs After approval by the Engineer

Examples of Admixtures used:

Water Proofing Admixture Plasticizer Jointing Admixture

SLUMP TEST is performed:

To check w/c of concrete and workability

During any type of casting

CURING TIME

Standard Curing Time: 28 days Use of SCMs might lengthen curing time

METHODS OF CURING:

Horizontal Surface by ponding of water Other Surfaces: by wrapping moist jute fabric and sprinkling water on them frequently with a hose

pipe

**Note: Date of Casting must be marked on Structure

to confirm curing period

Average Lap Length can be

Provided= Ld

Unless mentioned otherwise in drawings,

Ld can be selected from the following Charts:

For All Rebars:

Provide 90o STANDARD HOOKS (L-BENT)

if it is not specified in drawings

For beam bottom bar, lap should NOT be provided at middle third zone of the span

For beam top bar, lap may be provided at middle third zone of the span

Not more than 50% of the bars shall be spliced at one place

For slab bottom bar, lap should NOT be provided at middle third zone of the span.

Lap Splices are to be confined by hoops with maximum spacing or pitch of d/4, where d is the effective depth of

beam.

However, maximum spacing cannot exceed 100 mm.

All Beam and Slab Rebars should be extended into the support

upto Development Length

50 x Dia of Main Bar (min.)

For Footing, Column & Beam

in contact with Earth \ Water.

CLEAR COVER = 75 mm

Clear Distance between longitudinal bars shall not be less

than 1.5 times bar diameter, 1.5 times the size of coarse

aggregate nor 40mm.

1.5 db / 1.5* size of CA / 40mm

a)Free End of Slab incapable of Embedding

of Steel Bar in Beam / Wall

b) Others

Some inner Stirrups are provided to receive additional

Shear in Beam:

3 - LEG STIRRUP :

Some inner Stirrups are provided to receive additional

Shear in Beam:

4 - LEG STIRRUP :

At least 3 (three) Nos. Ties must be continued through

Beam-Column joint.

Bundle bar is the combination of 2 or more re-bars in

contact for acquiring more reinforcing area

Requirements for BUNDLE BAR:

Maximum re-bar can be bundled 4 Nos.

Bundle bars must enclosed with tie or stirrup of 12mm.

Bundle bars must terminate with at least 40db stagger except where the bundle Terminated. Where db is individual bar diameter.

Concrete cover is as per standard.

Development Length 48bdeq (both tension and compression) at Mid height of column.

- Any Loose Pocket found in Foundation Bed is to be

filled up with Compacted Sand of FM 2.5 min.

- Depth of Foundation as per Drawing.

Conceal Beam:

-Dont use any Conceal Beam in any Slab. -It does not have the effective function like standard beam.

If 25x25 column with 26 nos. 25mm bars are provided with fc =3.5ksi and fy=60ksi Pu=0.56[0.85x3.5x605 + 19.5x60] = 1663 k

For the same load 1663 k if a larger column of

27x27 is designed Then As required 14 in2.

COMPARISON:

Size: 25x25 Column 27x27 Column Area: Ag= 625 in2 Ag=729 in2

As= 19.5 in2 As= 14 in2

Comparing these two sections 15% Less cost is required for the larger

column of 27x27 . But the lateral stiffness of the larger column is improved by 36% against

the 25x25 column against Earthquake and Wind load.

Column Shuttering :

- All Columns shall be Cast at full height.

- For this Sufficient Support &

Tension must be provided to

ensure proper Alignment.

-Adequate Blocks must be Tied

carefully to ensure required

Clear Cover.

-No Kicker will be provided.

Kicker : No kicker will be provided for

Column, Retaining wall, Lift core , UGWR & OHWT

Shear Groove:

Shear Groove must be provided for

Column, Retaining wall, Lift core, UGWR & OHWT

OHWT Column:

Column height at OHWT will be up to Top slab of Reservoir.

Beam-Column Joint:

Top bar of Beam must be extended into Column

to a length

40db from column face at beam-column joint.

Casting: At least a clear gap of 3-days will be given

in between two consecutive layers of concrete casting

(column on footing/pile-cap, second layer of column on

first layer, etc.).

In case of slab, two consecutive segments of slab may

be cast with a gap of at least 2-days provided laborers

do not need to walk over the previous casting

Casting Duration:

12 working hours with same set of Labors.

Back Fill Adjacent to Retaining Wall : Use Sand of FM 2.5 @ 2' Width all around the Retaining Wall

Rest of the Area will be filled with Vity Sand.

Sanitary Holes : Keep Holes of all Outlets in Toilet & Kitchen before Casting Slab.

Put 12" Long same Rebar which are to be Cut in the Slab at

both sides.

Alignment of Column Main Bars : There must be at Least 2 Nos. of Ties in Column over Slab level

during Casting of the Slab to Ensure Alignment of Column Main

Bars.

For Any Construction the utmost importance

should be on the QUALITY of its products.

For this :

Quality of Materials must be ensured Quality of Construction must be strictly controlled