CONSTRUCTION AND QUALITY OF CONSTRUCTION Compiled By: Prof. Dr. M. Shamim Z. Bosunia 19 th June’ 2014
Oct 03, 2015
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