Roller Types Soil Compaction Equipments For Backfilling

Roller Types Soil Compaction Equipments For Backfilling

There are different types of rollers and other soil compaction equipments available. Use of these compacting machines depends on soil types and moisture conditions.

Following are different types of Compaction Equipments for different soil types:

The soil compaction equipments can be divided into two groups:

• Light soil compacting equipments
• Heavy soil compacting equipments

1. Light Soil Compacting Equipments:

These equipments are used for soil compacting of small areas only and where the compacting effort needed is less. Below are light equipments for soil compaction:

(i) Rammers:

Rammers are used for compacting small areas by providing impact load to the soil. This equipment is light and can be hand or machine operated. The base size of rammers can be 15cm x 15cm or 20cm x 20cm or more.

Rammers for soil compaction

For machine operated rammers, the usual weight varies from 30kg to 10 tonnes (6 lbs to 22000 lbs). These hammers with 2- 3 tonnes (4400 to 6600 lbs)weights are allowed to free fall from a height of 1m to 2m (3ft to 7ft) on the soil for the compaction of rock fragments.

Rammers are suitable for compacting cohesive soils as well as other soils. This machine in areas with difficulty in access.

(ii) Vibrating Plate Compactors:

Vibrating Plate Compactor

Vibrating plate compactors are used for compaction of coarse soils with 4 to 8% fines. These equipments are used for small areas. The usual weights of these machines vary from 100 kg to 2 tonne with plate areas between 0.16 m2 and 1.6 m2.

(iii) Vibro Tampers:

Vibro tampers is used for compaction of small areas in confined space. This machine is suitable for compaction of all types of soil by vibrations set up in a base plate through a spring activated by an engine driven reciprocating mechanism. They are usually manually guided and weigh between 50 and 100 kg (100 to 220 lbs).

2. Heavy Soil Compaction Equipments:

These compacting machines are used for large areas for use on different types of soils. The heavy compaction equipments are selected based on moisture content of soil and types of soil. Following are different types of these equipments:

I) Smooth Wheeled Rollers:

Smooth wheeled rollers are of two types:

• Static smooth wheeled rollers
• Vibrating smooth wheeled rollers

The most suitable soils for these roller type are well graded sand, gravel, crushed rock, asphalt etc. where crushing is required. These are used on soils which does not require great pressure for compaction. These rollers are generally used for finishing the upper surface of the soil. These roller are not used for compaction of uniform sands.

Smooth Wheeled Rollers

The performance of smooth wheeled rollers depend on load per cm width it transfers to the soil and diameter of the drum. The load per cm width is derived from the gross weight of the drum.

The smooth wheeled rollers consists of one large steel drum in front and two steel drums on the rear. The gross weight of these rollers is in the range of 8-10 tonnes (18000 to 22000 lbs). The other type of smooth wheel roller is called Tandem Roller, which weighs between 6-8 tonne (13000 to 18000 lbs).

The performance of these rollers can be increased by increasing the increasing the weight of the drum by ballasting the inside of drums with wet sand or water. Steel sections can also be used to increase the load of the drum by mounting on the steel frame attached with axle.

The desirable speed and number of passes for appropriate compaction of soil depends on the type of soil and varies from location to location. About 8 passes are adequate for compacting 20 cm layer. A speed of 3-6 kmph is considered appropriate for smooth wheel rollers.

Vibrating smooth wheeled rollers

In case of vibrating smooth wheeled rollers, the drums are made to vibrate by employing rotating or reciprocating mass.

These rollers are helpful from several considerations like:-

• Higher compaction level can be achieved with maximum work
• Compaction can be done up to greater depths
• Output is many times more than conventional rollers

Vibrating smooth wheeled rollers

Although these rollers are expensive but in the long term the cost becomes economical due to their higher outputs and improved performance. The latest work specifications for excavation recommends the use of vibratory rollers due to their advantage over static smooth wheeled rollers.

(ii) Sheep foot Roller:

Sheep foot rollers are used for compacting fine grained soils such as heavy clays and silty clays. Sheep foot rollers are used for compaction of soils in dams, embankments, subgrade layers in pavements and rail road construction projects.

Sheep foot rollers are of static and vibratory types. Vibratory types rollers are used for compaction of all fine grained soils and also soil with sand-gravel mixes. Generally this roller is used for compaction of subgrade layers in road and rail projects.

Sheep foot Roller Compacting Equipment

As seen in picture above, sheep foot rollers consist of steel drums on which projecting lugs are fixed and can apply a pressure upto 14kg/sqcm or more. Different types of lugs are namely spindle shaped with widened base, prismatic and clubfoot type.

The weight of drums can be increased as in the case of smooth wheeled rollers by ballasting with water, wet sand or by mounting steel sections.

The efficiency of sheep foot rollers compaction can be achieved when lugs are gradual walkout of the roller lugs with successive coverage. The efficiency is affected by the pressure on the foot and coverage of ground obtained per pass. For required pressure and coverage of ground, the parameters such as gross weight of the roller, the area of each foot, the number of lugs in contact with the ground at any time and total number of feet per drum are considered.

The compaction of soil is mainly due to foots penetrating and exerting pressure on the soil. The pressure is maximum when a foot is vertical.

(iii) Pneumatic Tyred Rollers:

Pneumatic tyred rollers are also called as rubber tyred rollers. These rollere are used for compaction of coarse grained soils with some fines. These rollers are least suitable for uniform coarse soils and rocks. Generally pneumatic tyred rollers are used in pavement subgrade works both earthwork and bituminous works.

Pneumatic Tyred Rollers

Pneumatic rollers have wheels on both axles. These wheels are staggered for compaction of soil layers with uniform pressure throughout the width of the roller.

The factors which affects the degree of compaction are tyre inflation pressure and the area of the contact. The latest rollers have an arrangement to inflate the tyre to the desired pressure automatically. The total weight of the roller can be increased from 11.0 tonne to 25.0 tonne or more by ballasting with steel sections or other means.

(iv) Grid Rollers:

Grid rollers are used for compaction of weathered rocks, well graded coarse soils. These rollers are not suitable for clayey soils, silty clays and uniform soils. The main use of these rollers are in subgrade and sub-base in road constructions.

Grid Rollers

As the name suggests, these rollers have a cylindrical heavy steel surface consisting of a network of steel bars forming a grid with squire holes. The weight of this roller can be increased by ballasting with concrete blocks.

Typical weights vary between 5.5 tonnes net and 15 tonnes ballasted. Grid rollers provide high contact pressure but little kneading action and are suitable for compacting most coarse grained soils.

(v) Pad Foot / Tamping Rollers:

These rollers are similar to sheep foot rollers with lugs of larger area than sheep foot rollers.

Pad Foot / Tamping Rollers

The static pad foot rollers also called tamping rollers have static weights in the range of 15 to 40 tonnes and their static linear drum loads are between 30 and 80 kg/cm. These rollers are more preferable than sheep foot roller due to their high production capacity, and they are replacing sheep foot rollers.

The degree of compaction achieved is more than sheep foot rollers. The density of soil achieved after compaction with this roller is more uniform.

These rollers operate at high speeds, and are capable to breaking large lumps. These rollers also consists of leveling blades to spread the material.

Pad foot or tamping rollers are best suitable for compacting cohesive soils.

Causes Of Design And Detailing Errors In Construction Industry

Design And Detailing Errors In Construction Industry

Common design and detailing errors in construction arises due to either inadequate structural design or due to lack of attention to relatively minor design details. These types of design errors are discussed below:

Inadequate Structural Design

Due to inadequate structural design the concrete is exposed to greater stress than it can handle or strain in concrete increases more than its strain capacity and fails.

The symptoms of such kind of failures due to inadequate structural design shows either spalling of concrete or cracking of concrete. Excessively high compressive stress due to inadequate structural design results in spalling of concrete. Also, high torsion or shear stresses results in spalling or cracking of concrete. High tensile stresses also results in cracking of concrete.

To identify the inadequate design as cause of the structural damage, the structure shall be inspected and locations of the damage should be compared to the types of stresses that should be present in the concrete. For rehabilitation projects, thorough petrographic analysis and strength testing of concrete from elements to be reused will be necessary.

Prevention: Inadequate structural design can be prevented by thorough and careful review of all design calculations. Any rehabilitation method that makes use of existing concrete structural members must be carefully reviewed.

Design-Detailing-Errors-In-Concrete-Construction

Poor Design Details:

Poor design details can cause localised concentration of high stresses in structural members even if the design is adequate to meet the requirements. These high stresses may lead to cracking of concrete that allows water or chemicals to pass through the concrete. Thus poor design detail may lead to seepage through the structural members.

Poor design detail may not lead to structural failure, but it can become the cause of deterioration of concrete. These problems can be prevented by a thorough and careful review of plans and specifications for the construction work.

Types of poor design detailing and their possible effects on structures are discussed below:

Abrupt Changes In Section: 

Abrupt changes in section may cause stress concentrations that may result in cracking. Typical examples would include the use of relatively thin sections rigidly tied into massive sections or patches and replacement concrete that are not uniform in plan dimensions.

Insufficient Reinforcement At Corners And Openings: 

Corners and openings also tend to cause stress concentrations that may cause cracking. In this case, the best prevention is to provide additional reinforcement in areas where stress concentrations are expected to occur.

Inadequate Provision For Deflection: 

Deflections in excess of those anticipated may result in loading of members or sections beyond the capacities for which they were designed. Typically, these loadings will be induced in walls or partitions, resulting in cracking.

Inadequate Provision For Drainage: 

Poor attention to the details of draining a structure may result in the ponding of water. This ponding may result in leakage or saturation of concrete. Leakage may result in damage to the interior of the structure or in staining and encrustations on the structure. Saturation may result in severely damaged concrete if the structure is in an area that is subjected to freezing and thawing.

Insufficient Travel In Expansion Joints: 

Inadequately designed expansion joints may result in spalling of concrete adjacent to the joints. The full range of possible temperature differentials that a concrete may be expected to experience should be taken into account in the specification for expansion joints. There is no single expansion joint that will work for all cases of temperature differential.

Incompatibility Of Materials: 

The use of materials with different properties (modulus of elasticity or coefficient of thermal expansion) adjacent to one another may result in cracking or spalling as the structure is loaded or as it is subjected to daily or annual temperature variations.

Neglect Of Creep Effect: 

Neglect of creep may have similar effects as described for inadequate provision for deflections. Additionally, neglect of creep in prestressed concrete members may lead to excessive prestress loss that in turn results in cracking as loads are applied.

Rigid Joints Between Precast Units: 

Designs utilizing precast elements must provide for movement between adjacent precast elements or between the precast elements and the supporting frame. Failure to provide for this movement can result in cracking or spalling.

Unanticipated Shear Stresses In Piers, Columns, or Abutments: 

If, through lack of maintenance, expansion bearing assembles are allowed to become frozen, horizontal loading may be transferred to the concrete elements supporting the bearings. The result will be cracking in the concrete, usually compounded by other problems which will be caused by the entry of water into the concrete.

Inadequate Joint Spacing In Slabs: 

This is one of the most frequent causes of cracking of slabs-on-grade.

Sealing Materials For Construction Joints In Concrete Works

Sealing Materials For Construction Joints In Concrete Works

There are three types of joints in concrete construction, viz. construction joint, expansion joint and contraction joints. Learn more about Joints in Concrete Structures.

Materials for joints in water retaining structures and water tight structures

• Materials for joints in water retaining structures and water tight structures for sewage and effluent treatment shall be resistant to aerobic and anaerobic microbiological attack and resistant to attack by petrol, diesel oil, dilute acids and alkalis.
• Materials for joints in water retaining structures for potable and fresh water shall comply with the requirements of BS 6920.

Joint filler

Joint filler shall be firm, compressible, single-thickness, non-rotting filler. Joint filler for joints in water retaining structures and watertight structures shall be non-absorbent.

Bitumen emulsion

Bitumen emulsion for joints in water retaining structures and watertight structures shall comply with BS 3416. Bitumen emulsion for surfaces against which potable or fresh water will be stored or conveyed shall comply with BS 3416, type II.

Joints in Concrete Structures

Joint sealant

• Joint sealant shall be a grade suited to the climatic conditions of Hong Kong and shall perform effectively over a temperature range of 0°C to 60°C. Joint sealant for exposed joints shall be grey.
• Joint sealant other than cold-applied bitumen rubber sealant shall be:
• A gun grade for horizontal joints 15 mm wide or less and for vertical and inclined joints,
• A pouring grade for horizontal joints wider than 15 mm.
• Polysulphide-based sealant shall be a cold-applied two-part sealant complying with BS 4254. Polysulphide-based sealant for expansion joints in water retaining structures and watertight structures shall have a transverse butt-joint movement range of at least 20%.
• Polyurethane-based sealant shall be a cold-applied two-part sealant complying with the performance requirements of BS 4254.
• Hot-applied bitumen rubber sealant shall comply with BS 2499, type N1.
• Cold-applied bitumen rubber sealant shall be of a proprietary type.
• Joint sealant for joints in water retaining structures and water tight structures shall be as stated in Table-1.
• Primers and caulking material for use with joint sealant shall be of a proprietary type recommended by the joint sealant manufacturer.
• Different types of joint sealant and primers that will be in contact shall be compatible.

Table-1: Joint sealant for water retaining structures and water tight structures

Structure for retaining / excluding	Type of joint	Type of joint sealant
Sewage	All joints	Polyurethane based
Other than sewage	Expansion joint	Polyurethane based or Polysulphide based
	Horizontal joints other than expansion joints	Hot applied bitumen rubber, Polysulphide based or polyurethane based
	Vertical and inclined joints other than expansion joints	Polysulphide based, polyurethane based or cold-applied bitumen rubber

Bond breaker tape

Bond breaker tape shall be of a proprietary type recommended by the joint sealant manufacturer and approved by the Engineer. The tape shall be a polyethylene film with adhesive applied on one side and shall be the full width of the groove.

Bearing strip for sliding joints

Bearing strip for sliding joints shall consist of two plastic strips of a proprietary type approved by the Engineer. The strips shall be resistant to all weather conditions and to chemicals to which the structure will be subjected without impairing the reaction, durability or function of the strips.

The strips shall be of a type that will not require maintenance after installation. The strips shall be capable of withstanding a vertical load of at least 300 kN/m2 and shall have a maximum coefficient of friction of 0.3 under a constant shearing force.

Waterstops or water stoppers

Waterstops, including intersections, reducers and junctions, shall be of a proprietary type approved by the Engineer. Waterstops shall be natural or synthetic rubber or extruded polyvinyl chloride and shall have the properties stated in Table-2.

Table-2: Properties of waterstops or waterstoppers

Property of water stops	Rubber waterstops	PVC waterstops
Density	1100 kg/m3(+/-5%)	1300 kg/m3(+/-5%)
Hardness	60 – 70 IRHD	70 – 90 IRHD
Tensile strength	>= 20 N/mm2	>= 13 N/mm2
Elongation at break point	>450%	>285%
Water absorption	> 5 % by mass after 48 hours immersion	>0.15% after 24 hours immersion
Softness number	-	42 – 52

While principles of concrete joints remains same, references may also be made to ACI 224.3R-95 Joints in Concrete Construction and IS:3414 – 1968 – Indian Standard Code of Practice for Design and Installation of Joints in Buildings (Reaffirmed in 2010).

Guide for RCC Slab Design and Detailing in Building Construction

Guide for RCC Slab Design and Detailing in Building Construction

RCC Slab design and detailing guidelines for depth of slab, loads on slab, reinforcement guide for one-way and two-way slabs have been tried to present here. Following are the RCC Slab Design and Detailing guidelines:

RCC Slab Design Guidelines:

a) Effective span of slab:

Effective span of slab shall be lesser of the two

1.  L = clear span + d (effective depth )

2.  L = Center to center distance between the support

b) Depth of slab:

The depth of slab depends on bending moment  and deflection  criterion.  the trail depth can be obtained using:

• Effective depth d= Span /((L/d)_Basic x modification factor)
• For obtaining modification factor, the percentage of steel for slab can be assumed from 0.2 to 0.5%.
• The effective depth d of two way slabs can also be  assumed using cl.24.1,IS 456 provided short span is 3.5 m and loading class is < 3 KN / m²

Type of support	Fe-250	Fe-415
Simply supported	L/35	L/28
Continuous support	L/40	L/32

Or, the following thumb rules can be used:

• One way slab, d = (L/22) to (L/28).
• Two way simply supported slab, d = (L/20) to (L/30)
• Two way restrained slab, d = (L/30) to (L/32)

c) Load on slab:

The load on slab comprises of Dead load, floor finish and live load. The loads are calculated per unit area (load/m²).

Dead load = D x 25 kN/m² ( Where D is thickness of slab in m)

Floor finish (Assumed as)= 1 to 2 kN/m²

Live load (Assumed as) = 3 to 5 kN/m² (depending on the occupancy of the building)

Concrete Slab

Detailing Requirements of RCC Slab as per IS456: 2000

a) Nominal Cover:

For Mild exposure – 20 mm

For Moderate exposure – 30 mm

However, if the diameter of bar do not exceed 12 mm, or cover may be reduced by 5 mm. Thus for main reinforcement up to 12 mm diameter bar and for mild exposure, the nominal cover is 15 mm.

b) Minimum reinforcement:

The reinforcement in either direction in slab shall not be less than

• 0.15% of the total cross sectional area for Fe-250 steel
• 0.12% of the total cross-sectional area for Fe-415 & Fe-500 steel.

c) Spacing of bars:

The maximum spacing of bars shall not exceed

• Main Steel – 3d or 300 mm whichever is smaller
• Distribution steel –5d or 450 mm whichever is smaller Where, ‘d’ is the effective depth of slab. Note: The minimum clear spacing of bars is not kept less than 75 mm (Preferably 100 mm) though code do not recommend any value.

d) Maximum diameter of bar:

The maximum diameter of bar in slab, shall not exceed D/8, where D is the total thickness of slab.

Analysis of Rates for Cement Mortar in Building Construction

Analysis of Rates for Cement Mortar in Building Construction

Rate analysis for cement mortar requires estimation of materials for cement mortar, i.e. quantity of cement and sand required for 1 m³ for various proportions, i.e., CM 1:2, 1:4, 1:6, 1:8 etc. So, let us first calculate quantity of cement and sand required for 1 m³ of cement mortar.

For 1 cu.m of wet cement mortar, 1.3 m³ of cement and sand is required, due to presence of voids in sand in dry state. So, cement and sand quantity is calculated for 1.3 m3 of cement mortar.

Cement Mortar

Estimation of Materials for Cement Mortar:

Steps for calculation of quantity of cement and sand for cement mortar:

Consider, we want to calculate quantity of cement and sand for CM 1:X, where, 1 is proportion of cement and X is proportion of sand. Then, quantity of cement shall be calculated as:

Quantity of cement = 

Above formula gives quantity in volume. To calculate the quantity of cement in number of bags, we have to divide it by volume of cement of one bags. The volume of one bag of cement is 0.0347 m³.

Therefore, number of bags of cement =

Quantity of sand =

For example, for a proportion of CM 1:4,

Quantity of cement in bags =  = 7.492 bags

Quantity of sand = = 1.04 m³ of sand.

Estimation of Labour and Tools for cement mortar:

For 1 m³ of cement mortar, semi-skilled labour is required for 0.27 days for mixing, unskilled labour for 0.26 for carrying of cement, sand and water. Hire charges for mechanical mixer is taken in lumpsum of can be taken as 0.27 days for mixing 1cum of mortar.

Rate Analysis of cement mortar:

Rate analysis of cement mortar requires the rate of cement and sand multiplied with their respective quantity. Cost of labour and tools and tackles for the cement mortar is also calculated. Cost of cement, sand, labour and tools depend on local availability and local rates.

When, quantity of cement, sand, labour and tools are multiplied by its rates, and a contractors profit of 10 - 20% is assumed, the total sum of the amount is taken as the cost of 1 m³ of cement mortar, which is shown in the file below.

Pile Foundations Requirements and Functions in the Construction Industry

Pile Foundations Requirements and Functions in the Construction Industry

Pile foundation is required when the soil bearing capacity is not sufficient for the structure to withstand. This is due to the soil condition or the order of bottom layers, type of loads on foundations, conditions at site and operational conditions.

Many factors prevent the selection of surface foundation as a suitable foundation such as the nature of soil and intensity of loads, we use the piles when the soil have low bearing capacity or in building in water like bridges and dams

A pile foundation consists of two components: Pile cap and single or group of piles. Piles transfers the loads from structures to the hard strata, rocks or soil with high bearing capacity. These are long and slender members whose length can be more than 15m.

Piles can be made from concrete, wood or steel depending on the requirements. These piles are then driven, drilled or jacked into the ground and connected to pile caps. Pile foundation are classified based on material of pile construction, type of soil, and load transmitting characteristic of piles.

The use of pile foundations as load carrying and load transferring systems has been for many years. Timber piles were used in early days, driven in to the ground by hand or holes were dug and filled with sand and stones. The use of steel pile started since 19th century and concrete piles since 20th century.

With the change in technology and industrial revolution, many advance systems have been devloped for pile driving from the invention of steam and diesel pile driving machines.

The use of pile foundations is increasing day by day due to non-availability of land for construction. Heavy multi-storyed building are being constructed, and load from these structures can not be directly transferred to ground due to low bearing capacity issue and stability issues of building during lateral load application. So, demand for use of pile foundations are increasing day by day. Due to this demand for piles, there have been many improvements in piles and pile driving technology and systems. Today there are many advanced techniques of pile installation.

Pile Foundation Functions

Function of Pile Foundation:

As other types of foundations, the purpose of pile foundations is:

• To transmit the buildings loads to the foundations and the ground soil layers whether these loads vertical or inclined
• To install loose cohesion less soil through displacement and vibration.
• To control the settlements; which can be accompanied by surface foundations.
• To increase the factor of safety for heavy loads buildings

The selection of type of pile foundation is based on site investigation report. Site investigation report suggests the need of pile foundation, type of pile foundation to be used, depth of pile foundation to be provided. The cost analysis of various options for use of pile foundation should be carried out before selection of pile foundation types.

Unless the ground condition is rocks, for heavy construction and multi-storied buildings, the bearing capacity of soil at shallow depth may not be satisfactory for the loads on the foundation. In such cases, pile foundation has to be provided. The number of piles in a pile groups required is calculate from the pile capacity of single pile and the loads on the foundation. Piles are a convenient method of foundation for works over water, such as jetties or bridge piers.

Need for a Construction Management Degree Program

Need for a Construction Management Degree Program

Construction management degree can be obtained from universities online, or distance education and as a full-time course. But what are your objectives for a construction management degree? Why do you want to pursue a degree in construction management? These questions need to be answered before you opt for this degree.

What is Construction Management?

Construction management is the study and practice of the managerial and technical aspects of construction projects to maintain the quality of construction, delivery timelines at a reasonable cost.

Need for a Construction Management Degree?

Construction industry is the largest industry in the world. Economy of world today depends on infrastructure development. Construction industry has the ability to provide economic growth around the world. Construction industry employs the largest number of people in the world.

According to Construction Management Association of America (CMAA) the responsibilities of a Construction Manager falls into the following 7 categories:

• Project Management Planning,
• Cost Management,
• Time Management,
• Quality Management,
• Contract Administration,
• Safety Management, and
• Construction Management Professional Practices

Construction management professional practices consists of following activities:

• Defining the responsibilities and management structure of the project management team,
• Organizing and leading by implementing project controls,
• Defining roles and responsibilities and developing communication protocols, and
• Identifying elements of project design and construction likely to give rise to disputes and claims.

Every construction project consists of a number of complicated activities. Due to these complications, most construction projects exhibits cost overruns, time extensions, low quality construction and conflicts. To overcome these in a construction project, a construction manager has to learn and posses qualities as mentioned in above 7 categories.

These skills of construction management can be obtained from a construction management degree courses. Although, a degree cannot make anyone a successful construction manager, the skills gained from construction management course has to be applied at practically in a construction projects and should be analyzed from time to time for effectiveness and should be learned from experienced construction professionals.

The management of construction project is challanging as the works involved are unique in every construction project, it involves many contractors, subcontractors and consultants, large number of materials, machinery and equipments are involved and besides all these the construction projects are constrained by time, quality and cost and it possesses high risk.

Need for Construction Management Degree

What are construction management degree courses available?

Construction management degree courses are available in three formats:

• Online degree
• Correspondence or distance education
• Full time classroom course

All the above degrees are offered as one-year, two-years and four-years bachelors degree and master degree.

Which degree should you opt for:

It depends on your current qualification and position. If you are working in a construction industry and located at a remote place, you may not infrastructure for online study, you can chose distance education mode as your choice. The online degree and distance education mode is best when you are working. You get work experience with construction management degree.

It is my personal thought that you opt for construction management after some experience in construction industry. You get exposed to all the activities carried out in construction, working style, management of construction activities, cost, time management etc. before you opt for a degree course. This exposure will enable you to learn the construction management skills quickly and effectively.

Advantages of Bar Bending Schedule in Rebar Works

Advantages of Bar Bending Schedule in Rebar Works

Bar bending schedule provides details of reinforcement cutting and bending length. Advantages of bar bending schedule when used along with reinforcement detailed drawing improves the quality of construction, cost and time saving for concrete construction works.

Following figure shows a typical bar bending schedule with bending and cutting length:

Typical Bar Bending Schedule - Advantages

Advantages of bar bending schedule in concrete construction are:

• When Bar bending schedule is available, cutting and bending of reinforcement can be done at factory and transported to site. This increases faster execution at site and reduces construction time and cost due to less requirement of workers for bar bending. Bar bending also avoids the wastage of steel reinforcement (5 to 10%) and thus saves project cost.
• Using bar bending schedule for when used for Fe500, it saves 10% more steel reinforcement compared to fe415.
• It improves the quality control at site as reinforcement is provided as per bar bending schedule which is prepared using the provisions of respective detailing standard codes.
• It provides the better estimation of reinforcement steel requirement for each and every structural member which can be used to compute overall reinforcement requirement for entire project.
• It provides better stock management for reinforcement. Steel requirement for next phase of construction can be estimated with accuracy and procurement can be done. This prevents stocking of extra steel reinforcement at site for longer time, preventing corrosion of reinforcement in case of coastal areas. It also prevents shortage of reinforcement for ongoing work by accurate estimation and thus concrete construction works can proceed smoothly.
• Bar bending schedule is very much useful during auditing of reinforcement and provides checks on theft and pilferage.
• Bar bending schedule can be used for reinforcement cutting, bending and making skeleton of structural member before it can be placed at the required position. Other activities such as excavation, PCC etc can proceed parallel with this activity. So, overall project activity management becomes easy and reduces time of construction. It becomes helpful in preventing any damages due to construction time overrun.
• It provides benchmarks for quantity and quality requirements for reinforcement and concrete works.
• Bar bending schedule provides the steel quantity requirement much accurately and thus provides an option to optimize the design in case of cost overrun.
• It becomes easy for site engineers to verify and approve the bar bending and cutting length during inspection before placement of concrete with the use of bar bending schedule and helps in better quality control.
• It enables easy and fast preparation of bills of construction works for clients and contractors.
• The quantity of reinforcement to be used is calculated using engineering formulas and standard codes, so there is no option for approximate estimation of steel reinforcement.
• With the use of bar bending schedule, mechanization of cutting and bending of reinforcement can be done, again reducing the cost and time of project and dependency on skilled labor requirement. It also improves the reliability on accuracy of bar cutting and bending.
• When mechanized bar cutting and bending is used, the cost of reinforced concrete work per unit reduces and helps in cost optimization of construction project.

There can even more advantages of bar bending schedule. 

How to Create Bar Bending Schedule using Microsoft Excel?

Bar Bending Schedule can be created using Microsoft Excel also, if you have good knowledge in Macros.  

Selection and Applications of Concrete Admixtures in Construction Field

Selection and Applications of Concrete Admixtures in Construction Field

Concrete admixtures are used to enhance the properties of concrete for applications in concrete works with special requirements. Concrete admixtures are used to modify the properties of concrete to achieve desired workability in case of low water cement ratio, and to enhance setting time of concrete for long distance transportation of concrete. So, it is of much importance for a civil site engineer to know about the properties of admixtures for better selection and application in concrete works.

Selection of Concrete Admixtures:

Concrete admixtures shall be selected carefully as per the specifications and shall be used as recommended by the manufacturer or by lab testing report. The quantity of admixtures to be used for specific application of admixtures are recommended by the manufacturers. For use in large construction projects, the quantity of the admixture to be used shall be obtained from tests reports for concrete mixed with admixtures at various percentage admixtures use. These tests are conducted to understand the behaviour of admixtures on the desired quality and strength of concrete at different quantity of admixtures used. Thus, the optimum quantity of admixtures can be selected for specific application based on results.

The selection of specific admixtures for use in concrete to alter properties of concrete should be selected carefully  as per requirement of concrete works. Concrete admixtures should be used judiciously according to specification and method of application to avoid adverse effect on concrete properties at fresh and hardened state.

After selecting the admixtures product, one should carefully choose the supplier with quality product, timely service and at competitive price. The admixture supplier should be with good history and should possess the staff with efficient and professional experience to guide on effective application/use of admixture in right way.

Concrete admixtures should be accepted with test certificate, manufacturing date and its chemical composition, should comply specifications given by the authorities.

Concrete Admixtures Selection and Applications

Applications of Concrete Admixtures:

The following chemical admixture commonly used for specific purpose and are explained in detail:

i) Accelerating Admxitures:

Admixtures which are used to speed up the initial set of concrete is called an accelerator. The advantage of these admixtures are either to increase the rate of hydration of cement or to shorten setting time results in early strength development, removal of shuttering, reduction of curing period and specially when concrete used in low temperature and marine construction.

The common accelerator is Calcium chloride and rarely Tri-ethanolamine, Carbonates, Silicates etc., used. However the use of Calcium chloride is not permitted in Pre-stressed concrete whereas in other concrete it is restricted to 1.5% by eight of cement content.

Mechanism: According to investigations, the essence of hardening intensification is CaCl2 as a catalyst acts on hydration of C S results in increase the rate of setting and strength development. It also established from the figure 1 that the CaCl2 accelerate the setting time considerably.

(ii) Retarding Admixtures:

The function of retarded is to delay or extend the setting time of cement paste in concrete. These are helpful for concrete that has to be transported to long distance in transit mixers and helpful in placing the concrete at high temperatures, specially used as grouting admixture and water reducers results in increase of strength and durability.

The commonly known retards are Calcium Ligno-sulphonates and Carbohydrates derivatives used in fraction of percent by weight of cement.

Mechanism: The mechanism of set retards is based on absorption. The large admixture anions and molecules are absorbed on the surface of cement particles, which hinders further reactions between cement and water i.e. retards setting. Later as a result of the reaction between the organic salts and C3A for cement, the former are removed from liquid phase of system, thus eliminating further retardation. The figure 2 shows the effect of retards on setting.

(iii) Water-Reducing Admixture (WRA) :

The water reducing admixture are group of products which posses concrete of a given workability as measured by slump or compaction factor at a lower water-cement ratio than the control concrete.

The commonly used admixtures are Ligno-sulphonates and hydrocarbolic acid salts.

Mechanism: The principal role on mechanism of water reductions and set retardation of admixtures are usually composed of long-chain organic molecules and that are hydrophobic (not wetting) at one end and hydrophilic (readily wet) at the other. Such molecules tend to become concentrated and form a film at the interface between two immiscible phases such as cement and water, and alter the physio-chemical forces acting at this interface. The presence of such admixture in a fresh concrete results in:

• a reduction of the interfacial tension.
• an increase in the electro kinetic potentials and
• protection sheath of water dipoles around each particles i.e. mobility of fresh mix becomes greater, partly because of reduction in inter-particle forces and partly because of water freed from the restraining influence of the highly flocculated system which is now available to lubricate the mixture. Hence less water is required to achieve given consistency.
• High range water-reducing agents (HRWA) : These are the second generation admixture and also called as Superplasticizers. These are synthetic chemical products made from organic sulphonates of type RSO3, where R is complex organic group of higher molecular weight produced under carefully controlled condition :

The commonly used superplasticizer are as follows :

• Sulphonated melamine formaldehyde condensate (S M F C)
• Sulphonated napthalene formaldehyde condensate (S N F C)
• Modified ligno-sulphonates and other sulphonic esters, acids etc.,

Mechanism: The H R W A consists off very large molecules normally anionic in nature, are thought to be absorbed on to the cement particles become negatively charged and subsequently dispersed in the water, similar to the action of WRA. However the H R W A produce a much higher degree of dispersion and do not lower the surface tension of water significantly. The figure 3 shows the mechanism of Superplasticizer with cement and water.

iv) Air Entraining Agent Admixtures :

These are generally used to improve workability, ease of placing, increased durability, better resistance to frost action and reduction in bleeding.

The common Air-Entraining agents are natural wood resins, neutralized vinsol resins, polyethelene oxide polymers and sulphonated compounds.

Mechanism: These are anionic, because the hydrocarbon structures contain negatively charged hydrophilic groups, such as COO, SO3 and OSO so that large anions are released in water. Conversely, if the hydrocarbon ion is positively charged, the compound is cation active or cationic. In other words, anionic surface active agents produce bubbles that are negatively charged, cationic charged cause bubbles to be positively charged, surface active agents of all classes can cause air entrainment in concrete, but their efficiency and characteristics of air-void system vary widely.

Applications of Steel Fiber Reinforced Concrete

Applications of Steel Fiber Reinforced Concrete

Steel fiber reinforced concrete provides superior resistance to cracking and crack propagation due to increased tensile strength in concrete structures.

Applications of Steel Fiber Reinforced Concrete:

It is known that plain cement concrete does not have good tensile properties to resist flexure in structural members. In case of concrete reinforcement steel, cracks still appear on the tension face due to bending. So, to prevent cracking of concrete, specially in the case of water retaining structures, or water transporting structures, it is advisable to design structural concrete as uncracked section. This results in heavy structural design with resulting in high cost.

Steel fiber reinforced concrete is a low cost solution for uncracked section design of concrete members. Use of steel fiber reinforcement in concrete enhances the ability of structural members to carry significant stresses. The use of fibers increases the toughness of concrete under any type of loads. Fibers in concrete has the ability absorb more energy.

As recommended by ACI Committee 544, steel fiber reinforced concrete is used as supplimentary material to prevent cracking, to improve resistance to impact or dynamic loading and to prevent material disintegration.

A guide to design of concrete structures with steel fiber reinforcement has also been published by American Concrete Institue.

The applications of Steel Fiber reinforced concrete are for so varied and so widespread, that it is difficult to categories them. Following are the common applications of steel fiber reinforced concrete constructions:

• Tunnel linings
• Manholes,
• Risers,
• Burial Vaults,
• Septic Tanks,
• Curbs,
• Pipes,
• Covers,
• Sleepers
• Roller compacted concrete with steel fibers

Steel Fiber Reinforced Concrete

Application of Steel Fiber Reinforced Concrete in other Structures:

A) Highway And Airfield Pavements:

• Repair of existing pavement.
• Reduction in pavement thickness.
• Increase in resistance to impact.
• Increase in transverse and longitudinal joint spacing
• Smooth riding surface.

B) Hydraulic Structures:

• Resistance to cavitations or erosion damage.
• Repair of spilling basin.

C) Fiber Shotcrete (FRS):

The inclusion of steel fibers in shotcrete improves many of the mechanical properties of the basic material viz the toughness, impact resistance, shear strength, flexural strength, and ductility factor.FRS has been used for

• Rock stabilization, tunnels, dams, mines.
• Bridges arches, dome structures, power-house
• Stabilization of slopes to prevent landslides repair of deteriorated concrete surface, water channel etc.

A seminar report on fiber reinforced concrete is available which provides more information and mix design of fiber reinforced concrete. The technology used for production, properties and structural use of fiber reinforced concrete is also explained.