Building Material Failures And Prevention Strategies: Efflorescence And Concrete Spalling Case Studies

Question:

This ‘Condition Report’ gives you a chance to apply what you have learned by identifying various construction materials, and questioning how they are used.

You need to identify – in real life instances where construction materials have failed and / or deteriorated prematurely… and excellent / appropriate use of construction material(s)

For materials that have failed and / or deteriorated, you then need to:

a.explain how and why this has happened 

b.suggest how this could have been avoided.

For excellent materials, you then need to justify why you consider them to be excellent

You need to prepare a condition report which illustrates and describes the above.

Contributing Factors to Building Defects and Failures

Defects and failures in construction industry are very common phenomena and usually result into loss of properties and lives (Tchamba & Bikoko, 2016). Some of the main contributing factors to building defects and failures include: inappropriate design, unqualified incompetent personnel, poor workmanship, inadequate supervision and inspection, use of substandard materials, inappropriate use of the structures and poor maintenance (Ahzahar, et al., 2011); (Kioko, 2014). One of the main reasons why contractors use substandard materials is so as to increase their profit margins (Ayodesji, 2011). The aim of this report is to analyze two scenarios where building materials deteriorated and failed and one scenario where building materials performed perfectly. For the failed building materials, explanation has been provided on why the materials failed suggestions made on how the failure could have been prevented or remediated. For the material that performed well, an explanation has been given to support the good performance. This information can be used by different stakeholders in construction industry to ensure that they choose and use the best materials when constructing buildings. Such defects and failures should always be prevented or managed because they have numerous effects on project delivery time and budget, and durability, functionality and safety of the building. The methodology used to complete this report involves identifying a building material that deteriorated and failed prematurely, examining how it failed, determining why it failed and recommending possible prevention or remediation strategies (for failed materials) and identifying a building material that performed perfectly, examining how it was used and why it performed properly (for the excellent material).

Overview 

A five storey office building in Melbourne has tiled stairs and floor that are showing signs of efflorescence. The building is reported to be 20 years old but was renovated two years ago. Previously, the stairs and floor were not tiled but made of concrete only. The efflorescence is mainly coming from the stairs’ tile joints and flowing down to the floor. This has stained the stairs and given it a white coloured substance. If this problem is not remediated, the efflorescence will continue flowing thus staining the stairs and the tiled floor. As a result, the look of the stairs and floor will become completely unpleasant and their structural integrity will also decline.

    

Figure 1: Examples of efflorescence on the stairs

Efflorescence is a very common problem in buildings and it can affect floors, walls, pavement, stairs or any other element that is made of concrete, bricks, stones, tiles, etc. It appears as a white deposit of water-soluble salts.

Efflorescence: Causes, Prevention and Remediation

 

Figure 2: Efflorescence on a masonry wall

       

Figure 3: Efflorescence on the building stairs

How this happened

For efflorescence to occur, there must be existence of the following three conditions: soluble salts must be present; adequate moisture must be present; and a path (hydrostatic or evaporation pressure) must be there to enable penetration or transportation of the soluble salts (Weintraub, 2017). The problem in this case occurred when salt from the concrete, Portland cement, grout or water present in the stairs dissolved with water and got transported to the surface through the grout joints. The dissolved salt then evaporated leaving behind efflorescence. The source of salt could have been the Portland cement or grout used to install the tiles or the concrete used during construction of the stairs.

Why this happened

Cement

All types of cement contain alkalis such as potassium and sodium that are soluble in water. The amount of alkalis is directly proportional to the likelihood of the cement causing efflorescence. The Portland cement used in the construction of this building had a significant amount of alkali hence causing the efflorescence.

Admixtures 

The admixture used in this case was lime. It was used as a plasticizer and also to improve the bond between the tiles and mortar. Lime is likely to have caused efflorescence in this building because of the acid used to clean the stairs. Occasionally, acid was used to clean stubborn stains on the tiled stairs and floors. The lime present reacted with the acid to produce calcium chloride (a salt). The calcium chloride dissolved in water and moved to the surface to form efflorescence (Worthington, 2016).

Sand

Even though sand is not soluble in water, it has a significant impact on water resistance of the surface. This is due to the size and distribution of sand particles. The sand can also be contaminated with other water-soluble substances such as cement thus causing efflorescence indirectly.

Poor workmanship 

Poor workmanship is another reason why efflorescence formed in the stairs. From the analysis of the problem, the tile installer seems to have installed the tiles on uneven mortar bed creating voids for water penetration. When the tiles are tapped, a hollow sounding noise could be heard. Through these channels, water can easily move beneath the tile surface and dissolve the salts present there. The dissolved salts then move to the surface through the same channels and evaporates leaving behind efflorescence.

Preventing Concrete Spalling: Importance of Quality Workmanship and Materials

Prevention

The best way of preventing efflorescence is by regulating the above mentioned conditions, which must be met for the problem to occur. This can be achieved through good quality workmanship, use of low alkali cement, use of washed and clean sand, use of clean salt-free water, use of exact amount of water when mixing concrete, mortar or grout, and use of dense grout. The problem in this scenario could have been prevented if the tile installer ensured that he used the correct type of mortar (mix design proportion), the mortar bed was even and the grout was correctly installed without leaving any voids. With this quality workmanship, there would be no room for water penetration beneath the tile mortar bed for efflorescence to form.

Another preventive measure is by installing a waterproof membrane below the mortar bed. This helps in preventing flow of salts from concrete slab to the tile mortar and lastly to the surface (Australian Institute of Waterproofing, 2017).

Remedial Rectification

The efflorescence could be removed by washing the surface using a hand or dry brush and mild detergent then rinsing with water. However, the washing method is not a cure but an ongoing solution. After washing, a suitable non-breathable sealer is properly applied on the surface and the grout joints. Last but not last, a good water repellant is applied on the surface of the tiles.

Overview

A residential building in one of the suburbs in Melbourne has signs of concrete cancer or spalling on the surface of one of its external walls. The building is about 50 years old and it is predominantly made of reinforced concrete and masonry. However, spalling was not found in any other part of the building other than the one discussed in this report.

 

Figure 4: Section of wall showing spalling

Concrete spalling is a very common problem in reinforced concrete structures. It occurs when reinforcing steel starts corroding and disintegrating, which results into loss of cross-sectional area and strength (Naimi & Celikag, 2010). Deposition of iron oxides also start occurring, causing extensive forces in the concrete. As a result of these forces, concrete surrounding the corroding reinforcement starts cracking and spalling. As the concrete cracks, it exposes the steel reinforcement making it even to rust more. This deteriorates the overall structural soundness and integrity of the building. Previously, concrete spalling was predominant in coastal regions where structures are exposed to salty water but the problem is now everywhere due to other factors causes it such as use of poor quality construction materials, poor workmanship and poor structural design. Today, concrete spalling is a problem of great concern all over Australia (Howe, 2015).

    

Figure 5: Images of concrete spalling

How this happened

The owner of the property had identified small cracks in the building one year ago but they were constantly increasing. From physical examination of the building, several issues could be identified. First, concrete cover seemed to be less than the recommended values. Second, the spalling concrete looked like the sand used was of poor quality. Third, small holes could be seen on the surface indicating that there was poor workmanship. Lastly, the owner said that the builder did not apply any water repellant on the wall surface. A combination of these factors created cracks in the concrete. The cracks created a path through which water penetrated and reached the steel reinforcement. It exposed the reinforcement to water thus causing to corrode. Continued corrosion deposited iron oxides that applied significant force on the concrete causing cracking and spalling.  

Why this happened

Concrete

Concrete is a composite construction material comprising of coarse and find aggregates, cement, water and admixtures. The cement acts as a binder that holds together all other materials. The strength of concrete depends on several factors include: quality of its ingredients, mix proportions, and method of mixing, pouring and compacting or vibrating, and duration of curing. Concrete has a high compressive strength and is usually combined with reinforcing materials with high tensile strength so as to increase the overall tensile and compressive strength of the structure. In reinforced concrete structures, the concrete is used to cover the reinforcement so as to protect the later against corrosion thus increasing the durability of the structure.

Steel reinforcement

As aforementioned, concrete has high compressive strength and low tensile strength. For this reason, steel reinforcement, which has high tensile strength, is usually placed in concrete so as to provide the required tensile strength to the structure. This enables the structure to adequately resist both tensile and compressive forces. Steel reinforcement performs very well in preventing cracking of concrete. The two materials, steel reinforcement and steel, are also very compatible with each other because their expansion and contraction rates with temperature changes are almost the same, which helps in reducing stress fractures.

Water repellant

One of the contributing factors to deterioration of concrete strength and durability is undesired water penetration (Zhu, et al., 2013). This can be prevented by use of suitable water repellants (Tkach, et al., 2015). The water repellants are particularly mandatory for use in structured built in coastal regions (Dai, et al., 2010), such as most parts along the Australian coast. These substances increase the durability of concrete structures (Zhang, et al., 2017). This waterproofing material is used by applying it on a recently constructed concrete surface. It creates a water barrier that makes it difficult for water to penetrate through concrete and reach the reinforcement (Concrete Construction Staff, 2016).

Prevention

Concrete spalling can be prevented by provision of adequate concrete cover (by following the recommended values in the AS 3600-2009 standards), use of good quality construction materials, hiring trained staff to ensure quality workmanship (such as proper mixing, pouring, vibrating, compacting and curing of concrete), sufficient supervision of concreting works, and use of a suitable water repellant sealer on concrete surfaces.

Remedial Rectification

This problem could have been remediated by following these steps: removing the spalled or cracked concrete to a depth that is enough to allow proper cleaning of the corroded steel reinforcement; applying appropriate priming materials on the cleaned steel reinforcement to prevent further corrosion; reinstating the removed concrete with high quality concrete and applying a suitable water repellant sealer.

Overview 

Glass is a very important building material in modern architecture (Corbusier, et al., 2012). The main component of this material is silica, which is combined with sodium potassium carbonate so as to lower its melting point. Its durability is also increased by adding lead oxide or lime. Manganese oxide is also added so as to neutralize the negative effects of undesired iron that is found in impure silica. The key properties of glass are that it: absorbs, transmits and refracts light; is an excellent electrical insulator; can take excellent polish; is brittle and strong; resistant to atmospheric conditions; resistant to chemicals; is resistant to scratches; is available in different colors; can be drawn, blown or pressed; can be made stronger than steel and lighter than cork; and is easy to clean. There are also different types of glass including common glass, soda-lime glass, potash lead glass, potash lime glass and special glass (The Constructor, 2012).

Modern architects are using glass to open up buildings to the external environment and at the same time protecting them from environmental elements (Lewis, 2011). The glass can be mirrored to reflect light, imprinted with sophisticated designs, frosted to diffuse light, or effervesced to playfully and purposely distort vision. This material is able to provide relief from intransigent, opaque materials and also infuse the façade of the building with fluidity in a unique manner that cannot be done by any other material (Allen, 2015).  

Material 

The glass used on Nigel Peck Centre for Learning and Leadership (NPCLL) building is a demonstration of an excellent building material because it adequately serves its intended function. The glass was used to open the building to its surrounding environment, thus exposing the learning process to the community and at the same time create physical and visual connection to other existing buildings on the campus, and adjacent gardens and park. The glass also allow natural light to enter the building during the day thus reducing energy consumption. Since glass is a bad heat conductor, it also reduces energy consumption by air condition system. Last but not least, the glass gives the building a decorative and stunning architectural view, both from the inside and outside. The glass panels are fixed in steel frames (John Wardle Architects, 2013).

  

Figure 6: External views of the glass building

Appropriate use of construction materials

The choice of glass in the building was appropriate because it enabled the architect to combine different colors and patterns of glass so as to achieve unique and stunning views. In the inside, laminated and toughened glass and reflective glass louvres were used making the interior look elegant and stylish. Smoothened glass panels were used on the outside of the building, still giving it a stylish and stunning look. Even though the building was completed over a decade ago, the glass is still in excellent condition.

 

Figure 7: Different glass patterns and colors

   

Figure 8: Stunning look of transparent glass panels

Conclusion/Recommendations

This report has analyzed two scenarios of deteriorated or failed building materials (efflorescence and concrete spalling) and one scenario of an excellent building material (glass). Various options have been given on how the deteriorated or failed materials can remediated. Prevention techniques for the failed materials have also been provided. For the material (glass) that performed exceptionally, no recommendations have been given because the material performed as intended. If the recommended remediation options are implemented, the two deteriorated materials can still perform well throughout the lifespan of the building. This report has demonstrated the importance of using good quality materials in building projects. Besides that, it is also important to ensure that there is good workmanship, adequate supervision and inspection, and that trained workers are hired and they use the right equipment and construction methods to complete construction works. In general, the quality of materials used has a significant impact on the overall strength, stability, safety, functionality and durability of the building thus they must be selected properly.

References

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