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Reinforcing the concrete structures

Part III :Role of good quality rebars in improving the durability of civil constructions and their endurance to natural disasters

As stated in second Part of this series of report, ASTM A615/A615M has no provisions to control higher values of yield strength (YS), minimum tensile to yield strength ratio and  upper limit of tensile strength (TS). These properties of rebars are of utmost importance and that’s why American Concrete Institute (ACI) code, ASTM A706/A706M and most other international codes related to reinforced concrete design for earthquake / huricane prone zones specify a minimum and maximum YS and TS and also a minimum value for  TS/YS ratio for rebars which should be > 1.25.  At first sight these stringent control of strength parameters seem very perplexing. Why should be a cap at strengths? Is stronger material bad for building structures ? To answer these points we have to understand the role of rebars in concrete structures.

Most of the Caribbean regions are prone to seismic and hurricane activities and their occurrence of high to moderate intensities are very common. The energies generated by these natural calamities are transferred to the structures on the earth. The maximum effect of these energies is on civil structures. If not properly dissipated through a man made system, these structures may have catastrophic collapse of buildings and other structures causing tremendous loss of human lives and properties. Concrete structures possess very high strength in compression but practically have zero endurance to tensile stresses. The natural disasters such as earthquakes and hurricanes cause tensile stresses on structures where a simple concrete with cement, sand and gravels fail miserably. Steel reinforcement bars have good tensile as well as compressive strengths. This material when embedded in concrete substantially imparts tensile properties, namely yield strength, tensile strength and ductility to the erected structures. The yield strength of rebars which is defined as the maximum force per unit area before they start yielding due to the tensile force , is very important and useful in absorption and dissipation of forces caused by natural disasters. A major chunk of these forces transferred to the concrete structures is absorbed by steel rebars during its yielding. However, the yielding force needed to yield rebars should not be too high than the designed  strength. The excess YS of rebars  will prevent its yielding during the events of natural calamities and forces will be transferred to concrete causing their fragmentation in to big chunks and falling down. The tensile strength of rebars which is the maximum  required force before it completely breaks  in to pieces, is another very crucial and important parameter that safeguards the concrete structures in event of very high intensity of forces . A higher TS of rebars with their longer elongation properties is good mate for concrete. In view of these facts, ACI, ASTM and other standards prescribe a minimum TS/YS ratio of 1.25. If proper rebars are  embedded in concrete   structures the losses due to natural disasters can be minimized to a significant extent. Now most of the countries especially in Europe, Asia and North America   are following building codes designed incorporating the rebars to withstand / minimize the impact of natural disasters.

For more information, please contact us at  This email address is being protected from spambots. You need JavaScript enabled to view it.  or via telephone at 299-0210 ext 5687

Reinforcing the concrete structures

Part II: Current scenario on quality of reinforcement bars used in Caribbean region vis-à-vis international  

It is a well known fact that steel rebars are embedded in concrete structures to improve their modulus of elasticity and strength.   Steel bars with proper chemistry, microstructure and surface treatments impart significant improvement in the above properties of the concrete. During the last two decades a phenomenal change in quality of reinforcement bars has taken place. Let us examine whether our (Caribbean regions) changes are in tune with the rest of the world. 

Keeping in view the economical aspects, durability, endurance to natural calamities (earthquakes, tsunami, hurricanes etc) and concerns for the carbon emission, significant modifications are being suggested and implemented on standards and code of practices for different sectors. The construction sector is not an exception to this.  A survey on trend of use of reinforcement bars (rebars) in construction sectors of Caribbean countries indicates that in majority of the cases plain / deformed steel bars conforming to the ASTM 615A are being used.   The steel rebars conforming to this standard are suitable for use in least demanding applications. The Caribbean region is very prone to seismic and hurricanes activities and therefore needs special precautions during erection of their buildings, bridges and other structures. To cope up with these natural disasters, ASTM and many standards of other countries came out with specific standards for manufacture and applications of rebars in seismic prone areas. ASTM A706/A706M is the standard for rebars for use in seismic prone areas. Let us examine the difference between ASTM A615/A615M (currently being used in Caribbean regions) and ASTM A706/A706M (improved version on rebars) standards:

ASTM A615 / A615M (420 grade)   ASTM A706 / A706M (420 grade)

 Steel chemistry

%P (Maximum)  0.06

 Steel Chemistry % Maximum)

C=0.30; Mn =1.50; P= 0.035; S=0.045; Si=0.50

 

Mechanical properties        

                                              Min.

YS                                   =  420 MPa

TS                                   =   620 MPa

% Elongation                   =   9

Bend test requirements   =3.5d-5d

 

Mechanical properties

YS                       Min.                     Max.

                           420MPa              540 MPa

TS                      550 MPa                 -                    

% Elongation     10-14

Bend test requirements   =3d-4d

The above table shows that the chemistry and mechanical properties of rebars are more strictly controlled for A706 / A706M than A615/A615M. These properties greatly affect the weldability and endurance to seismic / hurricane activities.

The majority of the countries of the world have now switched over to rebars conforming to ASTM A706 /A706M for designing of their civil structures. This standard ensures improved endurance to natural disasters, improved weldability as well as improved resistance to corrosion and pitting. A controlled chemistry of steel can be achieved only when steels are produced by blast furnace route or by electric arc furnace method after controlled purification of the molten metal. These methods of production of steel rebars reduce the casting defects such as voids, inclusions and tramp elements namely sulfur, phosphorus etc . Survey indicates that the rebars rolled from the ingots produced from iron scraps and melted in induction furnaces are very common in application in Trinidad and Tobago. The cost of production of rebars, by this route, is considerably cheaper than the other methods and is available at lower prices. Unfortunately the rebars produced by induction furnace route have many defects such as nonstandard chemistry, inclusions, and voids etc and difficult to meet the standard specifications. The general public unaware of these facts go for low cost  rebars easily available in the market. Use of such rebars in columns, roof castings, bridges and foundations are big concerns for safety and durability.

Stay tuned for the next part of this series which will focus on the role of good quality rebars in improving the durability of civil constructions and their endurance to natural disasters.

For more information, please contact us at This email address is being protected from spambots. You need JavaScript enabled to view it. or via telephone at 299-0210 ext 5687

 

 

Reinforcing the concrete structures

Part I: How effective are our reinforcements?

What you need to know about steel rebars

Amongst the vast numbers of man-made invented composites, the reinforced concrete comprising of cement, water, sand, gravel and steel, perhaps is a composite material that had maximum impact in revolutionizing the quality of life of human being. After curing, the concrete attains appreciably high strength in compression but remains very poor in tension, flexure, shear and torsion. It was an accidental discovery when a French gardener named Joseph Monier in 1867 observed that a phenomenal improvement in durability and strength of his flower pots took place after iron nails were embedded in castings made by Portland cement, sand and water. This discovery led to a series of developments in designing of rebars to achieve stronger and longer lasting concrete structures. It was a long journey for the currently popular TMT steel rebars to reach to its optimum properties imparting improved life to concrete structures.  Now TMT rebars are used all over the world for erection of bridges, flyovers, high and low rising buildings, pavements, concrete roads, canals, dams etc. These rebars are produced by quenching and tempering the process having composite microstructure with ductile core area and harder outer rim. This dual structure imparts strength as well as ductility to TMT rebars. They are free from any distortion of crystals of steels and therefore are more resistant to corrosion with desired ratio of tensile and yield strengths. The absolute carbon content is also kept at lower side in such types of rebars which improves their weldability.

 

pic 1

Figure 1 : Cross section of TMT bars is composite microstructure. The core area is soft pearlite – ferrite and the outer rim is harder tempered martensite microstructure 

 

Unfortunately production process of TMT type of rebars needs special mills with very strict control of quenching and tempering parameters. This increases their cost of production. Many companies still produce rebars without quenching and tempering treatments and market them in many countries. It is not possible to differentiate between TMT and non TMT bars just by looking from naked eye.  The users unaware about the quality of such rebars use them in their construction work. As shown in the following figure 2, both TMT and normal bars (non TMT) have ribs and it is not possible for consumers to differentiate between them. It can be differentiated only after looking in to the rim formed on the cross section of rebars. TMT bars develop a circular rim around the cross section but non TMTs do not exhibit such a rim.

pic 2

Figure 2 : Digital photographs of CTD, TMT and non TMT bars

How to find out whether the rebars are TMT or non TMT

It is very simple. Cut a small piece of the bar. Grind its cross section area on emery paper to remove scratches. Dip the cross section in acidified solution of alcohol for 30 seconds (98% alcohol + 2% nitric acid). Remove the bar from the solution and let them get dried. If a circular ring appears along the periphery of its cross section, it is TMT bar. The photograph of cross section of TMT bar after testing is shown in the above figure 2.

Part II of this series of write up will describe the “Caribbean vis-à-vis international scenario on use of rebars for reinforcement of concrete structures” 

 

Gaining a Competitive Edge: Entrepreneurship and Sports

Business and sports share many common features. The familiar “born or made” debate resonates for both Olympians and entrepreneurs. There are also unyielding obstacles despite talent or skill: a 5ft tall player will not make the NBA Basketball team.

Undoubtedly, an Olympian’s mindset is very different from that of a casual afternoon jogger. Not only do they both want very different outcomes – winning an Olympic medal versus exercise or weight loss – but it is reflected in their mindsets which drive their decisions and actions. One is hungry for ultimate success and remains fixated, maybe even obsessed, on being the absolute best and continues to train and show up for practice, day-in, day-out, sore muscles be damned. The other can opt out of afternoon jogging without pangs of guilt, if the weather is not conducive or some other activity takes precedence.

So too, entrepreneurs differ from a casual hobbyist who may dabble in an occasional commercial transaction at a craft market. An entrepreneur’s mindset and motivators are very different from that of a “wantpreneur,” and allow passion and perseverance to persist.

In the spirit of the 2016 Rio Olympics, the lens of sports rebounds with metaphors and lessons which can be applied in gaining a competitive edge in entrepreneurship:

Quadrathlon

Like the 400 meter individual medley, a combination of four different swimming styles – butterfly, backstroke, breaststroke and freestyle – swum by one swimmer, a quadrathlon is an endurance multisport with four sports in one. It consists of swimming, kayaking, cycling and running and requires an insane amount of endurance, power, technique and skill to ably compete at a world class level. It also requires a combination of muscles stretched beyond the 100-meter dash or an Olympic marathon.

In business, start-up founders must be able to wear multiple hats and understand all aspects of the start-up’s operations for it to function smoothly. Even when competitors may be seemingly edging ahead from the pack, carefully managing pace for the long haul is crucial, one step at a time despite encroaching muscle fatigue.

Gymnastics

Practise, Practise, Practise and more Practise! At the 2012 Summer Olympics, Gabrielle (Gabby) Douglas scored a historic victory in becoming the first African American to win gold in the individual all-round event. She also won a team gold medal for the U.S. at the same Summer Olympic event. Her formal gymnastics training began at 6 years old and at age 16, with an insatiable hunger for success, Gabby went from underdog to Olympian. On the road to Rio Olympics, she has worked on a new vault and new beam and floor routines. Her muscles are stronger.

In business, you cannot build muscles if someone else does the workout. An entrepreneur begins to forge a competitive advantage through practise, sacrifice, hard knocks and hard work. At age 14, when Gabby moved away from her hometown and family to pursue training with a world-renowned Olympic trainer, she was aligning herself to be trained by among the best in her field. By staying fully committed to getting better and showing up on time, comfort zones expanded and mental barriers injecting self-doubt began to chip away. The strongest performers harness a clear stillness of mind despite the distraction and noise of the sport arena or business landscape.

4X100 Meter Relay Race

Relay is a team sport, and success in the 4 X 100 meter relay race balances proper techniques with strategy. It is as much a skill event (fine-tuned through practice drills) as a speed event (timing the exchange). A strong relay team will also have trained substitutes, to fill any spot in the relay should a runner be injured, and preferably one who is trained to receive the baton in the right hand, and one who is trained to receive it in the left.

The business of entrepreneurship is a team activity. Even if there is a single founder or two or three co-founders, a company’s net worth is also determined by the strength of its network, measured in dollars and sense (knowledge and skills). A team of advisors, mentors and employees are at the nucleus of a network of:

 Supply chain partners: to buffer against disruptions in the supply of raw materials

 Freelancers: to enable a business to provide on-demand services, ramping up or scaling down operations relatively quickly

 Specialists: to provide deep functional expertise in particular functions

 Generalists: to apply knowledge and aptitudes to a variety of different fields

Timing and team composition (network) are key differentiators in enabling a relatively decent product / service platform to outperform a competing product / service.

A bad choice of a co-founder or a member of your team may (and probably will) bury your business in a matter of months. Just like the 4 X 100 meter relay, despite best efforts, one member of a small team who does not pull his weight will drag down all others.

Entrepreneurs find solutions and implement them. In so doing, we help design a world of change. At CARIRI’s signature Business Hatchery Programme, we support and energize early-stage entrepreneurs to grow their business, through group training and customized individual business coaching. Our Business Hatchery Food and Beverage Programme (5 weeks duration) will launch on 3 September 2016.

For more information please contact 299-0209 ext 2661 or email This email address is being protected from spambots. You need JavaScript enabled to view it. . Apply online: http://www.cedcariri.com/index.php/hatchery#thehatchery

3 ways calibration can affect your profits in this “recession”

ONLY THAT WHICH IS MEASURED CAN BE IMPROVED

While our country seeks for ways to bear this economic downturn, companies will have to find efficient ways of maximizing profits while reducing expenses.  Transportation, industry, trade - everything our economic world revolves around is affected by measurement. A price is attributed to a quantity of goods when traded or used.

What measures that quantity? The answer is ‘some piece of equipment or instrument’. Is this equipment an array of impeccably flawless machines always correctly quantifying amounts? The answer is ‘No’.

Equipment and instruments need to be serviced, validated, calibrated and kept in check. Calibration is about quality control, proper measurement and knowing every detail about quantifying your product and service. Calibration is the key to stepping ahead of the competition and maintaining a good brand.

What is Calibration?

A calibration is an operation which establishes a relation between values indicated by a measuring instrument and a known measurement standard. The result of a calibration is uncertainty – the range in which you can expect your measurements to deviate.  A calibration should not be confused with adjustment of a measuring system, often mistakenly called “self-calibration”, nor with verification of calibration. A calibration is not just a mere comparison between a known and an unknown but a scientific calculation itself.

If instruments are not calibrated routinely they can ‘drift’ due to environmental effects such as temperature, pressure, dust, etc.  Thus its inaccuracy of measurement will increase over time and will become unreliable. Here are 3 ways in which calibration can affect your profits.

1) Inaccurate equipment – profit/losses, inefficiencies

In a production factory type environment, equipment which is not properly calibrated can lead to large energy and product losses. For example in a bottled water production facility, if a piece of equipment which fills water in bottles is overfilling the bottles, a few milliliters of water is going to be wasted each time a water bottle is filled, eventually adding up to liters and hundreds of gallons of water being wasted each day. Not only is this a loss in profit for the company, it’s also bad for the environment as most bottled water comes from naturally occurring spring water.  Proper measurement and calibration can ensure that water is filled to the correct level each time, leading to no wastage of water. Similarly in an environment where powdered milk is being packaged by weight, a lack of calibration can lead to the customer getting more milk per pack or less milk in some cases. This can lead to either the customer or the company losing money.  In like environments, similar problems can occur in product packaging and weighing. These problems can easily be controlled by routinely calibrating equipment to track drift. 

2)Quality assurance – accreditation


Once a company is producing reports to clients which contain measurements, the validity of those measurements presents a risk to the client. If that client cannot quantify how much error is associated with tests being done, they are unsure of how that affects a product or processes they control. For a company to become ISO certified and especially ‘ISO 9001:2015, Quality Management’, the standard requires that for all equipment to produce valid results, they must be routinely calibrated and verified. Specifically this is found in ISO 9001-Clause 7.6, control of monitoring and measuring equipment. This must also be done at regular intervals so that control can be established over results being produced.  If your company is moving toward ISO 9002:2015 accreditation then calibration of equipment will become key to minimizing risk to customers.

3)Metrology Act of Trinidad and Tobago

Proclaimed on the 1st of May 2015 this act defines the International System of Units (the SI Unit) to be the primary system of measurement in Trinidad and Tobago. It sets out the specific units that should be used when trading for example; the kilogram for measurement of mass and Kelvin for temperature.  It states the Bureau of Standards can appoint inspectors of Metrology for proper administration of the act. These inspectors will also have the power to request documents describing the accuracy of equipment being used for trade and also detain that measuring device or goods which he believes has violated that act (Act No. 18 of 2004, Page 349).  Though not fully enforced at this time, accurate and precise measurement backed by well maintained equipment for the purposes of trade will not only be best practice but enforced by law. The principle behind this act is for all trade to take place at a point where each party received the same value for money.

As companies strive to become more competitive, costs and quality of work will become increasingly important. It is only when a parameter is measured, can it be controlled and improved. Calibration of instruments helps track drift, minimize it and ensure the validity of results produced by any equipment or processes. Without accurate data you cannot have confidence in service.

For more information about calibration and how it can help you, contact us at This email address is being protected from spambots. You need JavaScript enabled to view it. or call us at 299-0210 ext 5048.  We are always willing and able to find the best possible solutions for your calibration needs. 

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