Sunday, December 14, 2014

Surveying Property - Top 10 Most Popular Articles of 2014



Merry Christmas and Happy New Year to all of my readers!

Source: http://www.123greetings.com/
Another great year for my blog! This time last year I published 'The 10 Most Popular Articles of 2013'  which commented that; ‘I have now received in excess of 145,000 page views and have over 33,000 followers on Twitter!’ Twelve months on and I have now received in excess of 280,000 page views and have over 36,500 followers on Twitter! I would like to thank all of my regular readers and all of those who have taken the time to post comments on the blog over the year.  Also, thank you for the many kind comments and positive feedback that I have received throughout the year.  Although I cannot respond to every comment, I really appreciate the feedback and support shown for the blog articles.

As 2014 draws to a close, this will be the final posting of the year. I have plans for some new and exciting articles for 2015, the first of which will be published on Monday 5th January 2015. I will continue to publish a new article every week, so make sure that you bookmark the site to ensure you do not miss out!

I thought that it would be a good idea to publish the 'top ten' most viewed articles of 2014. You can view each article by clicking on the links below.  Please also feel free to forward a blog link to anyone you think may be interested.


I would welcome any comments (which can be posted below) relating to the content of the blog and whether you find it interesting, useful (or not!) and whether you have any suggestions for future postings.  


Surveying Property 2014 Greatest Hits – Top 10 Most Popular Articles:

1.  World’s Tallest Buildings of the near future – By 2020! – In Pictures

2.  Modern Methods of Construction - Insulated Concrete Formwork (ICF)

3.  10 Highest Bridges in the World in Pictures

4.  More Shocking Health & Safety Poor Practice Pictures! – Part 2

5.  Retaining Walls - Part 1 – Spectacular Collapses!

6.  Party Wall etc. Act 1996 – Much more than just Party Walls!

7.  Japanese Knotweed - Not a weed to ignore!

8.  Victorian Houses – Part 1 - Dwellings of character but not without their problems!

9.  Victorian Houses - Part 3 – Some typical defects

10. Concrete – Part 1 - Understanding the basics


Please feel free to share this article and other articles on this site with friends, family and colleagues who you think would be interested

Information/opinions posted on this site are the personal views of the author and should not be relied upon by any person or any third party without first seeking further professional advice. Also, please scroll down and read the copyright notice at the end of the blog.

Sunday, December 7, 2014

Negligence – Part 1 – An Introduction - Construction & Built Environment



As professional people our Clients pay for our services with the expectation that we will provide a high quality service and give good appropriate advice.  In the event that we do not meet this expectation and our Clients suffer some loss or ‘damage’, then they may attempt to recoup any losses through the courts

Source: http://www.claimsjournal.com/
Professional people should have a good understanding of the law and especially those areas of law which are relevant to their own particular field.  There are however some areas of law that are better know and understood than others. Law (in general terms) does not discriminate between specific professional roles and practices. Moreover it relates to the manner, conduct, attention to detail and professionalism in which we undertake our day to day professional duties. Yes, there will undoubtedly be ethical standards and codes of conduct to follow which may vary from profession to profession, however the underlying principles will be the same.  These ethical standards provide a level of protection however they will not make a professional immune from acting and becoming negligent.

As professional people our Clients pay for our services with the expectation that we will provide a high quality service and give good appropriate advice.  In the event that we do not meet this expectation and a loss or ‘damage’ is suffered, then our clients may attempt to recoup any losses through the courts.  A particular area of law where professional people can find themselves brought into question in this respect is the Tort of Negligence. For the remainder of the article I will refer to the role of the built environment professional however the principles of negligence are relevant to all professional roles. I will introduce negligence and consider how it is defined and how it is measured and in part 2 I will discuss the main ‘ingredients’ necessary to prove negligence.

Source: http://www.albanyworkerscomplawyer.com/
A quick internet search provides numerous definitions for negligence.  Yourdictionary.com states negligence as ‘failure to use a reasonable amount of care when such failure results in injury or damage to another’ and lectlaw.com provide; ‘the failure to use reasonable care. The doing of something which a reasonably prudent person would not do, or the failure to do something which a reasonably prudent person would do under like circumstances. A departure from what an ordinary reasonable member of the community would do in the same community’. These definitions are interesting because throughout you will notice the word ‘reasonable’ or the term ‘reasonably prudent person’.  In order to assess whether a person has acted negligently the courts will consider a person’s conduct and actions against how a reasonable person would act in the same circumstances. As a construction/built environment professional, this assessment will consider whether an experienced person taking reasonable care would not have made the same mistake, then the professional person may be liable in negligence. This is worth thinking about when carrying out our day to day duties and why it is so important to act with professionalism, vigilance and attention to detail at all times.  I wonder how many of those who have been found liable in negligence, with hindsight will wish they had paid closer attention to these things.

An important factor of negligence is that a defendant (the person accused of negligence), does not intend for the bad consequence to happen.  If intent could be proved (the courts refer to this as mens rea, which is a latin term meaning ‘a guilty mind’), then this would more than likely result in a criminal prosecution and not a civil action.  There are however circumstances where a person can face a criminal action and later also face a civil action from those who have suffered the consequences of a negligent act.  As an example let us think about a passenger injured in a motor vehicle collision.  Drivers do not generally get into their vehicles each day with an intention to injure, however road traffic collisions occur on a regular basis.  A driver who exceeds the speed limit may face a criminal prosecution under the Road Traffic Regulations Act 1984, which could lead to a fine or imprisonment depending upon the severity of the offence. In addition the driver may also face a civil action in negligence from the passenger who was injured in the collision (or anyone else who is injured in the incident). This interaction between criminal law and civil law (in our example, negligence) is also something that can occur with the construction/built environment professions and something that all working in the sector should be conscious of.

It is not necessary to search too far to find examples of where construction/built environment professionals have been found to be negligent. One such example is the case of Theodore Goddard v Fletcher King Services (1996). Fletcher King had overall responsibility for a commercial letting. Theodore Goddard (Solicitors), which drafted the lease, accidentally deleted the upwards-only rent review clause. A Surveyor at Fletcher King reviewed the draft lease but did not notice the error. The judge found that although the Solicitor had primary liability for the terms of the lease, the amendment to the clause was 'such a blunder' that an experienced Surveyor should have noticed the deletion. The Surveyor was ordered to contribute 20% of the loss. This decision has potentially wide-ranging consequences for professionals who work together on a transaction and have some input in one another’s drafting, a common relationship between construction/built environment professional and legal professional.

In Part 2 I will discuss negligence in more detail and consider the main ‘ingredients’ necessary to prove negligence and in particular ‘duty of care’ and how this relates to the construction/built environment professional.  I will also discuss the famous case of Donaghue v Stevenson (1932), and how the decision in this landmark case formed the modern tort of negligence as we know it today.

Please feel free to share this article and other articles on this site with friends, family and colleagues who you think would be interested


Information/opinions posted on this site are the personal views of the author and should not be relied upon by any person or any third party without first seeking further professional advice. Also, please scroll down and read the copyright notice at the end of the blog.

Sunday, November 30, 2014

Law of Contract – Part 2 - How a contract is formed - Construction & Built Environment



As long as all of the relevant elements are in place a verbal contract can become legally binding in just the same manner as a written contract. Of course trying to prove that a verbal contract exists is far more difficult that a written contract by the very nature of no written evidence

Source: http://howng050.articlealley.com/
Within the law of contract the term ‘legally binding’ is actually very significant as it means that a relationship has now been formed which brings with it obligations. The point at which a contract becomes ‘formed’ and legally binding is therefore crucial to understand so that those involved do not inadvertently bind themselves to obligations without realising.  You may think to yourself that anybody should be aware of whether they have entered into a contract or not, however if you do some research it will not take you long to discover that a vast amount of disputes relate to whether a contract exists or has been formed in the first place. So this begs the question, ‘at what point is a contract formed and becomes legally binding?’


Firstly, it is worth being aware that most contracts take a written form however it is also possible to form a contract verbally.  As long as all of the relevant 'ingredients' are in place (which will be discussed below) a verbal contract can become legally binding in just the same manner as a written contract. Of course trying to prove that a verbal contract exists is far more difficult that a written contract by the very nature of no written evidence.  You may have heard the term ‘a verbal contract is not worth the paper it is written on’, which really demonstrates the difficulty that will be encountered for anyone who wants to take any form of action on the basis of a verbal contract.  Other evidence such as recordings may be used however there is no substitute for a written contract in the event of a disagreement or a dispute (although written contracts can often be poorly drafted, resulting in disagreement in interpretation).   

In order to form a legally binding contract there are four elements necessary.  These are; Agreement (which consists of both an offer and an acceptance), Consideration (something of value, which is not necessarily financial), an Intention to create legal relations and a Legal capacity to make the contract.

Source: http://theodoreempsonlaw.com/
As detailed above the first ingredient ‘agreement’, requires both an offer and an acceptance, and unless both are in place then there obviously cannot be an agreement, and therefore no contract. There is now well established precedent for what constitutes an offer, how an offer is made, how the offer is communicated etc. In terms of what constitutes an offer it is worth briefly exploring the distinction between an offer and something referred to as ‘an invitation to treat’. If we take an item displayed in a shop window or goods displayed in a supermarket as an example, then at what point is an offer being made?  It clearly would be inappropriate if it were possible to create a binding contract by a shop keeper or a supermarket displaying goods.  The display of goods with a price ticket attached in a shop window or on a supermarket shelf is not an offer to sell but an invitation for customers ‘treat themselves’ or to make an offer to buy.  When the item is taken to the checkout and money is exchanged (this is consideration which is another of the ingredients required to form a binding contract), this then has all of the ingredients necessary and a binding contract is formed at this point.

There a number of examples which demonstrate the distinction between an offer and an invitation to treat within case law, none more so than Fisher v Bell (1961). This case relates to the display of a flick knife in a shop window.  The wording of  the Restriction  of  Offensive  Weapons  Act  1959,  section 1(1), stated: ‘it was illegal to manufacture, sell, hire, or offer for sale or hire, or lend  to  any other person, amongst other things, any knife which has a blade which opens automatically by hand pressure……..’ The shopkeeper argued that he was not offering the flick knife for sale by displaying it in his window, merely inviting people to treat themselves. The court found in favour of the shopkeeper who was therefore deemed not guilty of the offence. An Invitation to treat leaves both parties free to change their minds, so a shopkeeper can decide to refuse to sell to a customer who he does not want to (for example, somebody who is under age or drunk). Also, a customer who puts something into their basket has the option to put it back or change their mind before proceeding to the checkout

Think also about auctions.  At what point in an auction is an offer made?  The auctioneer’s call for bids is and invitation to treat, which is a call for offers.  Bids that are then made are offers which the auctioneer is at liberty to accept or reject at any time, before the hammer goes down.  Likewise, a bidder is at liberty to withdraw their offer at any time before the hammer goes down.  We do not see this happening very often because it is likely that most people are not aware of this, however, if you make a bid and for some reason change your mind you do not need to sit silently and hope and pray that somebody else puts in a higher bid.  As long as you communicate your withdrawal clearly so that this is heard by the auctioneer and acknowledged, before the hammer goes down then that will effectively withdraw your offer, Payne v Cave (1789) demonstrates this well. The point at which the auctioneer’s hammer goes down is the point at which a binding contract is made, because there is an offer (from the bidder), an acceptance (from the auctioneer) and consideration (the sum of money agreed). An auction transaction will general assume an intention to create legal relations and as long as both parties have a legal capacity to make the contract, then a binding contract is formed.

Law of contract is a well developed area of UK law which has evolved over many hundreds of years. Therefore, there is no shortage of case law to refer back to in respect of both the formation of contracts as well how a contract may be brought to an end.  There are also many books and other literature that are available on the subject which discuss contract law in great detail.  In such a short article I can only really scratch the surface of this area of law and provide an introduction to the subject however, it is well worth researching contract law in more detail to help develop a greater understanding.  I always tell my students that the most effective way of understanding the main principles of any area of law, in addition to reading the legislation and/or previous cases themselves, is to refer to the details and decisions of these previous cases.  Whereas some of the legal principles may seem at first to be rather complicated and confusing, they often become much clearer when the details of the case and the rationale for the decision are understood.

Please feel free to share this article and other articles on this site with friends, family and colleagues who you think would be interested


Information/opinions posted on this site are the personal views of the author and should not be relied upon by any person or any third party without first seeking further professional advice. Also, please scroll down and read the copyright notice at the end of the blog.

Sunday, November 23, 2014

Law of Contract – Part 1 - What constitutes a contract? - Construction & Built Environment



After entering into a contract it is no argument or defence to claim the terms are ‘unfair’ as under the doctrine of freedom of contract, there is no requirement for the terms to be so.  The lesson here is to be fully aware of the terms of your contract and your contractual obligations before signing the contract, which will actually mean reading it, including the small print!

Source: http://www.holcomb-law.com/
I am sure that many of us have previously entered into a contract without fully understanding the terms of what we have agreed or indeed the implications of being in a ‘legally binding’ contract.  This may be because we are so keen to get our hands on whatever it is want/need that we often do not read the details of the agreement and particularly the small print.   Typical examples may include mobile phone contracts, tenancy agreements or commercial leases or where we have purchased something such as a house or a car. In fact the term ‘exchange of contracts’ is generally well known by those buying and selling property, however contracts are also formed for purchases of items for much less value, even single low cost items that you may not realise.  The actual price or value of something does not influence whether a contract is formed, as long as there is an exchange of something of value, something known as consideration, which does not necessarily have to be money.  I will discuss this in more detail in next week’s article.

Source: http://www.arabianbusiness.com/
Construction contracts can be particularly complex and many disputes that occur revolve around an argument of whether there is a binding contract in place or not. Solicitors and their legal representative will expend an enormous amount of time looking at the conduct of the parties, reviewing correspondence between the parties, looking at the wording of a contract and reviewing decisions of previous cases to try to establish legal precedent, in order to prove or dis-prove that a contract actually exists.  As you would expect this can prove to be very expensive and proof of the existence of a contract will have very different implications for the plaintiff (the person or party who brings the action/case) and the defendant (the person or party whom the action is brought).

In order to understand the basic concepts of English contract law it is worth being aware that many of the principles were developed in the eighteenth and nineteenth centuries under the doctrine of ‘Freedom of Contract’. This means that parties to a contract can enter into whatever terms they want, without any interference, influence or input from the courts or the government, with the exception of illegality, fraud or other legal wrong. The terms that are agreed within a contract may sometimes appear to be more in favour of what party over the other however, as the parties are free to enter into whatever terms they want this will still result in a legally binding contract once agreed and signed.  Therefore, after entering into a contract it is no argument or defence to claim the terms are ‘unfair’ as under the doctrine of freedom of contract, there is no requirement for the terms to be so.  The lesson here is to be fully aware of the terms of your contract and your contractual obligations before signing the contract, which will actually mean reading it, including the small print!

Source: http://www.sutherlandsurveyors.co.uk/
Most contracts are made in writing and in fact there are many suites of standard forms of contract available for all types of construction related projects such as JCT, NEC, ICE, FIDIC and others.  These provide ‘off the shelf’ solutions for a whole range of different types of projects and procurement methods, and are regularly updated to reflect industry and legislation changes by the bodies that draft them.  Although they include their own standard clauses these can be amended or deleted or even have new clauses added, to suite the requirements of the parties.  As these types of contracts have evolved, in most cases over many years, they are now well established within the UK construction industry and clearly saves time and money in writing and preparing bespoke contracts from scratch.

Although standard forms of contract are used extensively in the UK construction industry, they are not always as easy as you would think to get agreed and signed. A number of years ago I was involved in large new build housing development where I was acting as Employers Agent for a large Housing Association, a Registered Social Landlord (RSL). Before I drafted the JCT Design and Build contracts I asked the RSL whether they had any specific contractual terms which they wanted amending, adding or deleting from the contract.  About a week later, I received a document in the post from them which had obviously been prepared by their solicitors which gave almost a clause by clause narrative of amendments that they required. As I started making the amendments I started to wonder why they had bothered with the use of a standard form of contract as the amount of changes they required was so comprehensive.  I persevered with the changes and then eventually sent the contracts and documentation to the Contractor for signature, at which point the fun really started! I can only imagine what the Contractor thought when they noticed all of the amendments and all I can tell you is that they were not impressed. As the Contractor objected to some of the amendments and wanted other terms re-worded and others removed, the contract negotiations became very protracted, in fact after a number of meetings and endless emails and telephone conversations, both parties signed the contracts, however this took over two months to achieve from when I first drafted the initial contracts.

Whatever the nature of a contractual relationship, be it a multi-million pound new build housing development as described above or even something much simpler, it is worth understanding the fundamental ingredients that are required to form a legally binding contract, which I will discuss in next week’s article.

Please feel free to share this article and other articles on this site with friends, family and colleagues who you think would be interested

Information/opinions posted on this site are the personal views of the author and should not be relied upon by any person or any third party without first seeking further professional advice. Also, please scroll down and read the copyright notice at the end of the blog.

Sunday, November 16, 2014

Concrete – Part 3 – Understanding the basics - Chloride Attack, Alkaline Silica Reaction, Sulphate Attack & Others



In last week’s article I considered carbonation and in the final part of this ‘mini-series’ I will focus on other concrete defects, such as Chloride Attack, Alkaline Silica Reaction and Sulphate Attack amongst other concrete defects

Source: http://theconstructor.org/
Over the last few weeks I have discussed the wide use of concrete as a construction material, considered its many positive attributes and also explained the vulnerability of concrete to certain defects.  In last week’s article I considered carbonation (Link) and in this final part of this ‘mini-series’ I will focus on other concrete defects.

Chloride Attack – Chloride finds its way into and through concrete in a similar process to carbonation, due to its porous nature. Chloride ions which are introduced into concrete from de-icing salts or are within or in close proximity to marine environments can attack concrete aggressively resulting in a faster rate of deterioration compared to carbonation.  When chloride passes through the concrete and eventually reaches any reinforcement, corrosion will occur. Salt is a mineral substance which consists primarily of sodium chloride.  When the sodium chloride is dissolved in water, which may be present in the pores of concrete, a versatile, highly corrosive and mobile solution is formed of sodium ions (Na+) and chloride ions (Cl-).  Once this solution comes into contact with any reinforcement it will attach the passive layer which protects it. The reinforcement will then corrode in the presence of air and water, resulting in corrosion.  This will result in cracking and spalling which will appear very similar to the effects of carbonation.

The consequence of chloride attack can be seen on the underside of road bridges and buildings and structures in close proximity to the coast. As discussed above, the impact of chloride attack will appear very similar to carbonation, so it will be necessary to not only consider the environment but also undertake testing to confirm the cause.


Source: Source: http://www.adfil.co.uk/
Alkaline Silica Reaction – A good explanation of alkaline silica reaction is defined by www.lmcc.com/ as ‘Alkali-silica reaction takes place between reactive siliceous minerals in certain aggregates and OH- (hydroxide ions) in the cement paste. Alkalis (Na+ and K+) from the cement, mixing water, or environment increase the concentration of OH- ions in the concrete. The OH- ions attack susceptible aggregate minerals. The damaged framework forms a gel that absorbs water from the surrounding concrete. The gel expands, generating pressures that can crack the concrete. The damage may not be visible to the naked eye for years after the concrete has been placed’

Alkaline silica reaction can usually be identified by random cracking on the surface of the concrete and in advanced cases, a gel like substance may be visible or possible spalling of the concrete. Cracking usually appears in areas with a regular supply of moisture, such as close to the watercourses and ground behind retaining walls etc. In order to confirm the presence of alkaline silica reaction it is necessary for core samples of the concrete to be taken and put under a microscope to establish their mineralogical and chemical characteristics, this is something referred to as petrographic testing.


Source: Source: http://www.delftcluster.nl/
Sulphate Attack – Again, the porous nature of concrete makes it vulnerable to sulphate attack in the same manner as previously discussed for other defects.  Water containing dissolved sulphates such as sodium sulphate, potassium sulphate or magnesium sulphate can penetrate into the concrete and as it progresses, the composition and microstructure of the concrete will be changed.  This can then result in cracking, expansion and loss of bond between the cement paste and the aggregate, which often results in a loss of strength of the concrete. 

Possible sources of sulphates include seawater, oxidation of sulphide minerals in clay (such as copper) adjacent to the concrete (this can produce sulphuric acid which reacts with the concrete), bacterial action in sewers (anaerobic bacteria produces sulphur dioxide which dissolves in water and then oxidizes to form sulphuric acid), In masonry, sulphates are present in bricks and can be released over a long period of time, causing sulphate attack of mortar.

In the UK sulphate attack is particularly common in ‘older’ solid concrete ground floors.  The use of fill material became very popular for residential solid concrete ground floor construction from the early 1940s. In the early post war years, waste materials such as burnt colliery shale, blast furnace slag and red ash were promoted by the government as appropriate materials to use for this purpose. However, it was later discovered that these types of fill materials contained high levels of sulphates which often resulted in significant problems and associated expensive remedial works to replace affected floors. Sulphates from these fill materials, with the presence of water, would attack the tri-calcium aluminate (one of the components of Portland Cement), within the concrete, which would result in lifting, expansion and cracking of the concrete floor slab.  This problem was significantly reduced with the use of appropriate fill that did not contain these high levels of sulphates, together with the introduction of damp proof membranes (to reduce water penetration) and insulation to improve thermal efficiency. Replacement of a solid ground floor with a new floor is the only practical way of dealing with sulphate attack, which as you can see from the image below can be very disruptive as well as expensive.


Source: Source: http://www.mybuilder.com/
Other concrete defects – There are a number of other concrete defects that may be identified including ‘honeycombing’ concrete which occurs where wet concrete has not had all of the air taken out of it due to poor workmanship and lack of quality control.  In order to remove any air within wet concrete a vibrating poker is put into the wet concrete which agitates the wet mix and ensures that air voids are removed before the concrete cures (hardens).  If care is not taken during the installation process, or the installation is rushed, voids or honeycombs will be visible in the concrete when the formwork is struck (removed), similar to that identified in the image below.


Source: http://www.concrete.org/
Source: Source: http://www.zimbio.com/
Plastic Shrinkage – small cracks appear in the surface of freshly laid wet concrete soon after it has been placed, while it is still wet or plastic. Plastic shrinkage cracking is highly likely to occur when high evaporation rates cause the concrete surface to dry out too quickly, before it has the opportunity to set.  This is particularly problematic when wet concrete is being laid in high temperatures and highly humidity.  In order to slow down or control the curing process, damp or wet hessian may be laid over the newly laid concrete which is repeatedly wet to allow the water within the concrete to evaporate out at a much more natural rate, which will significantly reduce the risk of plastic shrinkage occurring.


Source: Source: http://theconstructor.org/
Over the last few weeks I have discussed some of the common defects that occur in concrete however you may come across other issues relating to expansion joints or insufficient cover, which primarily relate to poor design or poor workmanship.  These articles can become very technical and sometimes quite complex, hopefully the information provided has introduced some of the defects and may motivate you to undertake more in depth research for some of the defects considered.

Please feel free to share this article and other articles on this site with friends, family and colleagues who you think would be interested


Information/opinions posted on this site are the personal views of the author and should not be relied upon by any person or any third party without first seeking further professional advice. Also, please scroll down and read the copyright notice at the end of the blog.

Sunday, November 9, 2014

Concrete – Part 2 - Understanding the basics – Carbonation



There are a number of different defects that will influence the durability and ultimately the structural integrity of a concrete component. Concrete defects are difficult to visually identify in their early stages and generally only become evident when staining, cracking or distortion, start to occur

Source: http://sussexropeaccess.co.uk/
The popularity of concrete as a construction material was discussed in last week’s article (Link) due to its many positive attributes, including; it’s strength in compression, it’s flexibility, as it can be poured into infinite shapes/forms and sizes, it can be applied in situ (on site in its wet form), or it can be cast in a factory and delivered site as a complete component (pre-fabricated), it has good fire resistant qualities and is very durable if constructed correctly and maintained well.  The imperfections in concrete were also introduced and in particular concrete’s weakness in tension, where steel reinforcement is introduced to address this deficiency. 

As also stated in last week’s article, when encapsulated in the very high alkaline environment of concrete, reinforced steel will passivate.  This means that the steel will be much less chemically active than it would normally be as the alkaline concrete is effectively protecting it.  A particular problem however is that concrete is porous allowing moisture and other contaminants to enter the concrete which can eventually lead to corrosion problems of the steel reinforcement.  This will then lead to associated degradation and spalling (pieces of concrete breaking and falling away), which can result in significant serious health & safety implications.

A number of years ago I can particularly remember undertaking an inspection of a large Secondary School in the West Midlands area.  One of the largest blocks within the school was a three storey 1970’s exposed concrete frame building with brick infill panels. As with many secondary schools around the UK much of the building stock was poorly maintained due to ongoing funding issues.  I noted severe horizontal cracking of the concrete in a number of locations at first and second storey level, to a point where large piece of concrete were hanging precariously over a walkway which was one of the main thoroughfares around the school.   Strangely, staff at the school seemed to be oblivious to the danger, possibly because the problem was not at ground level and therefore not obviously visible.  Needless to say, I spoke to the Head Teacher and contacted the Local Authority immediately and had the area cordoned off until emergency repairs had been carried out to make the area safe.  This emphasises how serious concrete defects can be if left untreated.

There are a number of different defects that will influence the durability and ultimately the structural integrity of a concrete component, similarly to the example discussed above. Concrete defects are difficult to visually identify in their early stages and generally only become evident when staining, cracking or distortion, start to occur.  It is therefore worth understanding some of the common defects which affect concrete, one of which is carbonation.

Carbonation – Newly installed untreated concrete especially where located externally is particularly vulnerable to carbonation.  Once concrete is exposed to the air, carbon dioxide which is present in the air in concentrations of approximately 0.3% by volume (www.answers.com) will dissolve in water which can be present within the pores of the concrete and will form a mildly carbolic acidic solution. This acidic solution reacts with the alkaline calcium hydroxide (which is one of the compounds in concrete) to form calcium carbonate. This results in a pH value drop from more than 12.5 to approximately 8.5, which significantly reduces the alkalinity of the concrete. The carbonation process progressively moves through the concrete, with the pH drop occurring through the concrete. When the carbonation reaches any reinforcing steel, the passive layer around the steel will deteriorate when the pH value falls below 10.5. The passive protection around the steel therefore disappears so that when the steel is now exposed to moisture and oxygen, it makes it vulnerable to corrosion. The image below (started at the top left hand corner), demonstrates the progress of carbonation through concrete.


Testing is necessary to confirm that carbonation is occurring, which is usually carried out by applying a phenolphthalein solution to the surface of a freshly fractured or freshly cut piece of concrete. When the solution is applied non-carbonated areas will turn red or purple while carbonated areas remain colourless. Phenolphthalein will change colour at a pH of 9.0 to 9.5. Non-carbonated concrete without any admixtures will achieve a pH value of 12.5 or slightly higher.  The image below shows that carbonation has occurred at the left hand side of the sample taken, whereas the right hand side remains un-carbonated.


I have made reference the pH scale throughout this article. It is therefore worthwhile adding the image below for completeness;
Source: http://alissasohlovechemistry.wikispaces.com/
In next week’s article I will discuss a number of other defects that can occur in concrete including chloride attack, alkaline silica reaction, sulphate attack amongst others.

Please feel free to share this article and other articles on this site with friends, family and colleagues who you think would be interested

Information/opinions posted on this site are the personal views of the author and should not be relied upon by any person or any third party without first seeking further professional advice. Also, please scroll down and read the copyright notice at the end of the blog.

Sunday, November 2, 2014

Concrete – Part 1 - Understanding the basics



If installed correctly, newly installed reinforced concrete should last for many years with a minimal amount of maintenance; however it can be vulnerable in certain locations/uses to a number of possible defects, especially where used externally 

Source: https://www.flickr.com
Concrete is an extremely popular material for construction and can be found in most parts of the World in one form or another.  In many countries, along with the use of steel, concrete is the primary material used for buildings/structures of all shapes and sizes, because of its many positive attributes. These include; being extremely strong in compression, which means that it can sustain large loads which are applied, before it will start to deteriorate or fail. It is extremely flexible as it can be poured into infinite shapes/forms and sizes, it can be applied in situ (on site in its wet form), or it can be cast in a  factory and delivered site as a complete component (pre-fabricated), it has very good fire resistant qualities and is durable if constructed correctly and maintained well.  A significant disadvantage however is that concrete is extremely weak in tension, which in basic terms means that it will break up very easily when forces are applied that try to push or pull it apart.

Compressive and Tensile forces - To understand compression and tension forces let us think about a spring as an example.  If an even ‘push’ force is applied to each end of the spring at the same time then the spring will compress and shorten.  This action is adding compressive forces into the spring.  When a load is applied to the top of a concrete component in a building then exactly the same forces are being introduced, however concrete has the ability to withstand high levels of compressive forces, particularly when certain mixes are used or when steel reinforcement is added. Tension or tensile forces are effectively the opposite of what is described for compression.  Using our spring again as an example, instead of applying an equal ‘push’ force at either end, let us now apply a ‘pull’ force. This will lengthen the spring and add tensile forces within it.  This is what will happen toward the bottom of a concrete beam.  Whereas the compressive forces applied at the top of a concrete beam will apply load in a downward direction and compress the beam, this can also result in tensile forces appearing near the bottom of the beam which will have a tendency to want to ‘pull apart’, as identified in the image below:


Source: http://www.concretecountertopinstitute.com/
Concrete’s weakness in tension is therefore mitigated by introducing steel reinforcement (which is strong in tension) at the position in the concrete which is weakest in tension, which is near the bottom of the beam.  The result is a complete component which is strong in both compression and tension and capable of withstanding extremely large loads/forces, which is ideal for building and construction.

If installed with the correct materials/mix and good workmanship, newly installed reinforced concrete should last for many years with a minimal amount of maintenance; however it can be vulnerable in certain locations/uses to a number of possible defects, especially where used externally.  Some of the more serious concrete defects are a result of deterioration of the concrete which results in the reinforcement being exposed and starting to corrode.  Concrete is a very alkaline material, typically 12.5 to 13 on the PH scale.  When encapsulated in the very high alkaline environment of concrete, reinforced steel will passivate.  This means that the steel will be much less chemically active than it would normally be as the alkaline concrete is effectively protecting it.  A particular problem however is that concrete is porous allowing moisture and other contaminants to enter the concrete which can eventually lead to corrosion problems of the steel reinforcement.  If corrosion to the reinforcing steel occurs this will result in the build-up of corrosion generating internal stresses and subsequent cracking and spalling (breaking and falling away) of the concrete. This is demonstrated in the image below.
As explained above, when first installed the reinforcement in the concrete does not corrode because the concrete provides a protective alkaline environment due to the presence of large quantities of calcium hydroxide which is produced as Portland Cement hydrates and cures (hardens). (Portland Cement is the most common form of cement used in concrete for general purposes, which is produced from firing a mixture of clay or shale, and limestone or chalk.  The clinker that is produced in the kiln, as a result of the firing process is ground to the fine light grey powder which most people will be familiar with). However, when moisture and other contaminants enter the concrete an environment for a range of different concrete defects is created.

Over the next two weeks I will consider a number of different concrete defects including Carbonation, Chloride Attack, Alkaline Silica Reaction and Sulphate Attack.  Specific concrete defects are difficult to identify from a purely visual inspection, however, armed with the information discussed above and a little knowledge of what to look for it is possible arrive at a reasonable prognosis, which can be later confirmed with sampling and testing of the concrete.

Concrete is a very dense/heavy material and when it starts to exhibit defects that can result in cracking and spalling it can be very serious from a structural perspective as well as a health & safety perspective. The images below provide some examples of what can happen when concrete starts to exhibit defects, some of which I will discuss in more detail next week.


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