Civil Engineers Association: September 2014

Defects in Bulding Leakage - Causes of Water Leak in Building

Here Are Some Common Location of Leakage or Seepage and its Possible Causes

Water leakage or water seepage is one of the major causes of common building defects. If water leakage can be prevented, almost
80% building defects can be eliminated. The locations and causes of water leakage in building is given in the below chart.

what is bar bending schedule?

Bar bending schedule(bbs)

Bar bending schedule is the detail list of reinforcement bars which are to be fixed in the structure.

it is always prepared before start of actual execution of work.

Use of 33,43,53 grade cement

''if
we use any of 33,43,53 cement ,@28 days depending on grade of concrete
like m20 we wl get 20N/mm2 , but why we using 33,43 etc cements we can
use only one grade of cement na''

Grade of cement means its minimum compressive strength which will be achieved at 28 days. 33 grade means cement will achieve minimum 33 n/mm2 strength at 28 days, same for 43 and 53 grade.

what is tie beam?

Shorter columns takes more loads, if the height of column is more it tends to buckle.

and the ratio of height to widht should not be more than 14.

so to prevent buckling we need to provide the beam, this beams are called Tie Beam.

What is meaning of concrete grades example ; M30

When we design a concrete for particular targeted compressive strength to achieve it is termed as Mix Design of Concrete. There are many methods to do the design.

if we take example of M30 Grade concrete

M stands for Mix,

30 stands for the characteristic compressive strength in n/mm2.

Types of cement and its IS Code

Following are the type of cements

CONCRETE & CEMENT HISTORY

CONCRETE & CEMENT HISTORY

Oldest surviving concrete is found in Yugoslavia which was thought to be laid in 5600 BC.

The first major users were Egyptians around 2500 BC and Romans from 300 BC.
Romans mixed materials from “Pozzuoli” a pink sand with lime mortar and built their structures. This is nothing but volcanic ash and they produced the first “POZZOLANIC” Cement.

OPC –ORDINARY PORTLAND CEMENT

Mr. JOSEPH ASPDIN –21STOCT 1824 –THE PRODUCT RESEMBLE NATURAL ROCK IN PORTLAND-ENGLAND

In India –1902 (South India structural) –India cement industries -1904

Aggregate types and its use with example

Here are the types of aggregates and its use

Common mistakes by unskilled workmen.during volume batching of concrete

Common mistakes by unskilled workmen.

Workmen , especially if unskilled, may make mistake because of ignorance. Insist on the following.

Procedures for implementing improved practice for mix proportions in concrete

Procedures for implementing improved practice for mix proportions.

Enforce the specifications for mix proportions in a gradual and orderly way so that work is not slowed down. Follow the sequence given below.

Guidelines for Storage of Cement

IS 4082-1996 laid down the stipulation for storage of cement as follows:
The height of stack shall not be more than 10 bags to prevent the possibility of lumping up under pressure. The width of the stack shall be not more than four bags length or 3 metres.

Handling bulk cement in RMC and Project sites.

Handling bulk cement in RMC and Project sites.

In major projects and in RMC plants cement is received in bulkers as the consumption of cement is very high on a day to day basis. In such cases the following precautions need to be taken to ensure the quality of cement received before it is used in concrete production

Advantages of using fly ash in concrete

Advantages of using fly ash in concrete

In plastic state concrete:
1) Improved workability: Fly ash is spherical in shape it produces a paste with superior plasticity and reduces the amount of water needed in a mix.
2) Reduced Segregation: The improved cohesiveness of Fly ash concrete provides added body to plastic state concrete which resist segregation.

Storage and Handling of aggregate

Storage and Handling of aggregate
As per IS 4082 – Aggregates shall be stored at site on a hard dry and level patch of ground. If such a surface is not available, a platform of planks or old corrugated iron sheets, or a floor of bricks, or a thin layer of lean concrete shall be made so as to prevent contamination with clay, dust, vegetable and other foreign matter. Store sand and coarse aggregates of different size fractions in separate stock piles, on firm ground or platform.

Durability of concrete

A concrete which performs satisfactorily in the environment during its anticipated exposure condition in its service is said to be durable one. The materials and mix proportions specified and used should be such as to maintain its integrity and if applicable to protect embedded steel from corrosion.

Chlorides in concrete

Chlorides in concrete :
If chloride is present in concrete there is increased risk of corrosion of embedded steel. The higher the chlorides content or if the structure is exposed to warm moist conditions, the greater is the risk of corrosion. All the constituents may contain chloride and concrete may contaminated by chloride from environment. To minimize the change of deterioration of concrete from harmful chemical salts, the levels of such harmful salts in concrete coming from concrete making material like cement. aggregate, water and admixture, as well as by diffusion from the environment should be limited. The total acid soluble chloride content should be calculated from the mix proportion and the measured chloride content of each of the constituents. The total chloride content (as Cl ) in concrete at the time of placing shall be as given in table

Sulphates in concrete

Sulphates are present in most cement and in some aggregates, excessive amounts of water-soluble sulphate from these or other mix constituents can cause expansion and disruption of concrete. To prevent this the total water soluble sulphate content of the concrete mix expressed as SO3 , should not exceed 4 % by ,mass of cement in the mix . The sulphate content to be calculated as the total from the various constituents of the mix.

Alkali – aggregate reaction

Alkali – aggregate reaction

Some aggregates contain particular variety of silica which react with the alkali (Na2O and K2O ) of cement , producing expansive reaction which cause cracking and disruption of concrete. Such disruption occur when

Bulking of sand and its effect on yield of concrete

Bulking of sand

(i) The increase in volume of sand due to moisture content is called bulking. Fine sands bulk more than coarse sands. Fully saturated sand occupies the same volume as dry sand. So, an easy way of determining the bulking of sand is by finding the decrease in volume of the given sand when fully saturated .

How to do compaction of concrete

- Each layer of Fresh Concrete shall be thoroughly compacted by vibrators to the minimum practicable consolidated volume.

Advantages of Crushed Sand ( manufactured ) over River Sand

Advantages of crushed sand (manufactured sand) over River Sand are as follows.

Types of Admixtures used it concrete

Types of Admixtures used in concretes with there functions are as follows

AIR ENTRAINING

improves durability, workability, reduces bleeding, reduces freezing/thawing problems (e.g. special detergents)

EFFECTS OF SILICA FUME ON PROPERTIES OF FRESH CONCRETE

EFFECTS OF SILICA FUME ON PROPERTIES OF FRESH CONCRETE

Water demand The water demand of concrete containing silica fume increases with increasing amounts of silica fume .This increase is due primarily to the high surface area of the silica fume. In order to achieve a maximum improvement in strength and permeability, silica-fume concrete should generally be made with a water-reducing admixture, a high-range water-reducing admixture (HRWRA), or both. The dosage of the HRWRA will depend upon the amount of silica fume and the type of water reducer used

How to do Concrete during rain

Placing concrete during rain.

Prevention of cracks in Fresh Concrete - Plastic Cracks

Identifying Plastic cracks

Prevention of cracks in Fresh Concrete - Crazing / Hair cracks

Prevention of cracks in Fresh Concrete - Crazing / Hair cracks

Identification

a) Craze cracks are fine cracks appearing in the hexagonal or octagonal pattern on the surface of the concrete.
b) They may be seen to some extent on nearly all surfaces, but they are most prevalent on trowelled surfaces.

Defects in Concrete and its Causes - Honeycomb

Honeycomb is a condition of irregular voids due to failure of the mortar to effectively fill the spaces between coarse aggregate particles. Where bridging of the aggregate particles or stiffness of the mixture is a cause of honeycomb, vibration may assist in overcoming the bridging by increasing the flowability of the concrete.

How to Determine Dry density by Core cutter method

Dry density by Core cutter method

Ref : IS 2720 (part XXIX)

Purpose : To find out the dry density of compacted soil in field.

Defects in Concrete and its Causes - Bugholes (Air surface voids)

Bugholes on vertical faces are normally caused by air bubbles, but occasionally by water entrapped between the concrete mass and the form, especially in sticky or stiff concrete mixtures of low workability which may have an excessive sand and/or entrapped air content. Also, the use of vibrators of too large an amplitude or the lack of complete insertion of the vibrator head may result in increased air-void formation.

Minimizing surface defects in Concrete

To minimize the size and number of bugholes and other defects, arising out of the consolidation the following practices should be followed:

• Vibration period should be of sufficient duration
•Vibrator insertions should be properly spaced and overlapped and the vibrator removed slowly

Defects in Concrete and its Causes - Form-streaking

Form-streaking is caused by mortar leaking through form joints and may be aggravated by over vibration from vibrators that are too powerful, or by using forms that vibrate excessively during consolidation.

Special Type concrete - Light weight concrete

Light weight aggregates can be either natural like diatomite, pumice, scoria, volcanic cinders, etc, or manufactured like bloated clay, sintered fly ash or foamed blast furnace slag. Light weight aggregates are used in structural concrete and masonry blocks for reduction of the self weight of the structure. The other usages of light weight aggregate are for better thermal insulation and improved fire resistance.

Quality assurance at site

Quality Assurance:

- All those planned and systematic action necessary to provide adequate confidence that a product or service will satisfy the given requirements for quality.

-Evaluating the performance on a regular basis to provide confidence to the customer that the project will satisfy the quality standards.

why we do the curing to concrete

Need for curing

a) The primary aim of curing is to prevent the loss of moisture from fresh concrete due to evaporation and to maintain the immature concrete moist for a suitable time until the concrete has reached the strength and hardness desired.

Selection of Maximum size of aggregate for concrete

he nominal maximum size of coarse aggregate should be as large as possible within the limits specified but in no case greater than one-fourth of the maximum thickness of the member, provided that the concrete can be placed without difficulty so as to surround all reinforcement thoroughly and fill the corners of the form. For most work, 20 mm aggregate is suitable. Where there is no restriction to the flow of concrete into sections, 40 mm or larger size may be permitted. In concrete elements with thin sections, closely spaced reinforcement or less cover, consideration should be given to the use of 10mm nominal maximum size.
Plums above 160 mm and up to any reasonable size may be used in plain concrete work up to a maximum limit of 20 percent by volume of concrete when specifically permitted. The plums shall be distributed evenly and shall be not closer than 150mm from the surface.
For heavily reinforced concrete members as in the case of ribs of main beams, the nominal maximum size of the aggregate should usually be restricted to 5 mm less than the minimum clear distance between the main bars or 5 mm less than the minimum cover to the reinforcement which ever is less.

Why we use 150mm size cube for compressive strength testing.

Hi all civil engineer,

when i was in collage i wonder that all constructions site have the cube size of 150mm x 150mm x 150mm.

I checked in the IS code but in that also they never says that u use 150mm cubes, you can use any size cube for testing of compressive stregnth.

Civil4M

Civil4M