Concrete Spalling

Building defects are very common in residential, commercial and industrial buildings. The defects can occur in either old or new buildings (Bakri & Mydin, 2014). These defects have numerous safety, cost and durability implications. Presence of these defects can affect the normal functioning of the building because its occupants or visitors will be worried about their safety (Othma, et al., 2015) and some of the defects even affect the indoor environmental comfort. The defects are caused by a variety of factors including improper design, use of low quality materials, poor workmanship and environmental factors, among others. Understanding these defects is very essential in coming up with prevention or remedial measures. This report presents an analysis of two building defects. One of the defects is in a residential building while the other is in a commercial/industrial building. The buildings investigated are in Hong Kong. The analysis entails description of the defects, symptoms of the defects, data related to the defects, desirable testing of the defects, possible causes of the defects, implications and risks of the defects, and suitable remedial measures for the defects. Information contained in this report can be used to repair similar defects in buildings or prevent these defects from occurring in future building projects.

The two building defects analyzed in this report are concrete spalling and dampness. These are some of the commonest defects in different types and sizes of buildings in any part of the world.

This is a type of building defect where the concrete surface breaks away and can extend to and expose the reinforcing bars. The defect usually happens in reinforced concrete structures but can also occur in natural stone or brick. It can be seen in concrete floors, slabs, columns or walls. Occurrence of spalling is driven by moisture entering into the concrete structure. When moisture enters a concrete structure that is exposed to varying temperatures, the moisture starts solidifying and expanding. This creates internal pressure on the concrete surface’s top solidified layer. When this continues over time, the expanded water’s internal pressure together with the force that is produced by the freeze-thaw cycles causes the top layer of concrete surface to disintegrate leaving spalls. Spalling concrete usually looks like oval, square, round or irregular depressions that are created along concrete joints or surfaces. This defect is very common in regions with cold climates where freeze-thaw cycles occur frequently or where de-icing chemicals are usually applied on buildings.

Dampness

Dampness is unwanted moisture present in a building. The problem in characterized by building materials becoming damp to a level where they get damaged. This is a building defect that is mainly characterized by penetration of water into the affected area. It is a very serious defect that can not only cause structural damage of the building but also make the building inhabitable because of poor indoor conditions such as high humidity, bad smell and poor air quality. Dampness leads to physical, chemical and biological deterioration of building materials. This poses serious risks to building performance. Studies conducted in 2004 showed that approximately 20% of buildings in the U.S., Canada and different European countries had signs of dampness (Agyekum & Ayarkwa, 2014). The dampness usually rises from penetration of rainwater through the outside walls, intrusion of ground water through the crawl spaces and basements, indoor moisture sources, flooding, faulty rainwater guttering and condensation (Ahmed & Rahman, 2010). Dampness is a damaging defect for both old and new buildings hence there is need to find more information about it so as to understand how to prevent, manage or repair it when it occurs.

Concrete spalling

The symptoms of concrete spalling include discoloration, striated lines, a rough, pitted and flaky texture and appearance, slight rust stains that are present on the concrete surface, cracks and visible sights of corroded and rusted concrete reinforcement. These symptoms are followed by breakages of the concrete surface. If the problem is not remedied, the breakages will continue until the concrete starts disintegrating and falling off the surface. The damage will continue going deep until the reinforcing bars are exposed.

Dampness

Some of the symptoms of dampness are: visible mold and fungi growth, musty smells, excessive condensation on the affected surface, presence of pets in the building, building blemishes, damaged building materials, wood rot, wet patches on the building surface and sagging ceilings. These symptoms show that there is presence of excessive humidity in the building.

Concrete spalling

The building had different sizes and shapes of spalls. Some of them had circular, rectangular, square, oval and irregular shapes. Table 1 below shows the dimensions of some of the spalls identified in the building

Table 1: Sizes of spalls

The data in Table 1 above shows that the building has different sizes and shapes of concrete spalling defect. The defects are visible and therefore requires immediate remediation.

Table 2 below shows dampness data obtained from a building using a surface electrical moisture meter. The data was obtained at different intervals along the wall of the building.

Symptoms of the Defects

Table 2: Dampness measurements

The data in Table 2 above shows that moisture content was very high at the lower level of the wall and very low at the top of the wall. There was a gradual decline in moisture content readings at the top of the wall followed by a sudden drop. This data shows that dampness was high at the bottom of the wall and very low or zero at the higher level of the wall. This can be an indication of rising dampness. The most probable cause of this kind of dampness is penetration of ground water through the crawl spaces and basements. The water intrusion may be due to lack or poor quality damp proof membrane, poor workmanship or use of porous masonry or concrete.

Concrete spalling

The testing done so far is visual inspection. Another testing that may be needed to as to develop a more appropriate diagnosis for concrete palling include:

Borescope: the technique can be used to investigate the condition of reinforcement in the affected area so as to determine if it should be replaced or not.  

Rebound hammer: the test can help in determining the compressive strength of concrete at the affected area. This is useful in establish the extent of damage caused by the concrete spalling.

Metal detector: the test can be used to determine the concrete cover so as to establish if the reinforcement is adequately covered. This information is useful in establish the repair mixture that should be used in repairing the defect.

The main benefits of these tests are: they can be completed quickly, they can be done by one person, they are relatively easy to perform and they provide useful data that will help determine the most appropriate technique to repair the defect. On the other hand, there are also some constraints of the tests including: the necessary equipment must be acquired and may be expensive, and each test can only be conducted successfully by a qualified and experienced person (surveyor).

The following are some of the desirable tests that can help in determining the most appropriate diagnosis for dampness in a building:

Electrical moisture meters: this test involves putting an electrical moisture meter on the affected surface and taking moisture content readings at regular intervals. The readings can be used to draw a moisture profile that shows dampness at different levels. The main benefit of this test method is that it is easy and inexpensive to perform but its constraint is that the results obtained are less accurate.

Data Related to the Defects

Borescope test: it can be used to observe the condition of internal components at the affected area. The test provides useful information about the extent of damage that has been caused by dampness. The main benefits of this test are that it is non-destructive and quick to perform. However, the test has some constraints including the need for the specialized equipment, can only be performed by an experienced specialist and interpretation of results requires an experienced person.

Carbide test: this test is used to determine the amount of moisture present in the building element being investigated. It is performed by taking samples of plaster or brick dust, placing them in a pressure cylinder, adding calcium carbide in the cylinder and measuring the amount of acetylene gas produced from the reaction of calcium carbide and the sample dust. The main benefit of this test is that it provides more accurate results while its constraint is that it does not differentiate between capillary and hygroscopic moisture (Sharman, 2016).  

Concrete spalling

The likely causes of concrete spalling include the following: inadequate concrete cover; use of low quality concrete (incorrect concrete mix design); poor workmanship including improper handling, pouring, vibrating and curing of concrete (Weintraub, 2018); exposure to freeze-thaw cycles; presence of alkali silica or sodium chloride; and excessive fire exposure. In all these possible causes, spalling occurs when moisture penetrates through the concrete surface until it reaches the reinforcement. The moisture causes rusting and corrosion of the reinforcement, which expands thus occupying more volume. The rusting, corrosion and expansion of reinforcement creates pressure that causes the concrete to spall.

Causes of dampness in a building include: lack or use of poor quality damp proof membrane, use of porous or poor quality building materials such as bricks/stones and concrete, poor workmanship (such as improper laying of mortar joints and leaving holes or cavities in the walls like those used for erecting scaffold), use of plaster containing salt, defective window sills, improper building orientation, plumbing leaks, sewer backups, leaking roofs and climate condition. In general, dampness is caused by poor design, use of poor quality materials and bad workmanship or faulty construction.

Concrete spalling

Concrete spalling has numerous implications on the structural integrity and safety of buildings. If the defect is not remedied, it can cause the structural member (reinforcing bars) to lose its strength due to corrosion. The alkali-silica reactions also affect the strength of concrete. With time, the concrete and reinforcing bars in the affected areas will become loose and start falling off. This causes a significant reduction in the structural strength of the entire building. Therefore the overall implications and risks of concrete spalling are that it can cause structural members to collapse or even the entire building. This puts the safety of people using or accessing the building, including occupants and other visitors such as people involved in inspecting, repairing and maintaining the building) at high risk (Webster, 2016). In case of structural failure and collapse of the building, many people in and around the building can get injured or even lose lives.

Testing of the Defects

Another implication is that concrete spalling can reduce the value of the building and if the damage is extensive, the cost of repairing or maintaining the building will increase significantly. Leasing or selling a building with spalling concrete is also difficult because potential lessees or buyers will be concerned about the associated safety risks and high remedial costs.

Dampness

Some of the implications and risks of dampness in buildings are: disintegration and decay of materials such as stones, steel, bricks and timber; dry rot in timber elements; damage of decoration of wallpaper and timber; efflorescence; metal corrosion; timber warping and decay; floor covering deterioration; termite infestation; weakening and crumbling of plaster; paint flaking, blistering and bleaching; and short circuiting and electrical installations damage. The implication of all these is that the building becomes structurally damaged thus reducing its strength, stability and durability. This puts the safety of occupants at risk because the building can be damaged severely and collapse causing injuries or even deaths.    

Dampness is also a major health risks in buildings. Some of the health problems associated with this defect include asthma, cough, upper respiratory tract infections, wheeze, eczema, shortness of breath, allergic rhinitis and bronchitis. Therefore the general implications of dampness is that it deteriorates the structural integrity of the building thus reducing its lifespan and at the same time puts the occupants at the risk of developing health problems especially respiratory-related infections because dampness lowers indoor air quality (Kong, et al., 2018). Living in a building affected by dampness also causes mental health problems such as anxiety and depression because occupants are always worried of what may happen to the building any time (Agyekum, et al., 2013).

Concrete spalling

Repair of concrete spalling mainly depends on the damage severity. If the damage is too much, there may be need to replace the damaged reinforcing bars. The general remedial process of concrete spalling involves eight steps. The first step is cleaning the affected area so as to remove stains and dirt including bond breaker agents (a pressure washer can be used for cleaning). The second step is cutting a regular shaped section (square, rectangular, circular, etc.) of the affected area and removing loose concrete to a depth of about 4cm using chisel and hammer. The third step is cleaning the exposed reinforcing bars using a wire brush and applying two coats of protective coating or anti-rust paint on the rebars. The fourth step is applying a suitable bonding agent on the affected area so as to improve adhesion. The fifth step is applying a suitable repair material mixture depending on the size (length, width and depth) of repair. The repair can be surface repair for spalling when depth of spalling is less than one-third of concrete thickness and full depth restoration when depth of spalling is more than one-third of concrete thickness (Rodriguez, 2018). Application of repair material is done by preparing the mixture, roughening the affected area, applying an appropriate adhesion agent, and using the admixture to patch the area. The patching material can be epoxy or Portland cement-based material. The sixth step is finishing, which entails scraping off any excess material using a margin trowel and level the surface properly. The seventh step is curing the surface for several days so that the repair material can gain the desired strength. The eighth and last step is applying a waterproofing membrane or paint so as to prevent the spalling from re-occurring (Hamakareem, 2018).

Causes of the Defects

Concrete spalling can be also be prevented through provision of adequate concrete cover and careful and proper preparation, pouring, curing and finishing of concrete work. Also after the concrete has cured properly, a water-repellant sealer should be applied on the surface (Paul, 2014).  

There are temporary and permanent remedies for dampness. Temporary remedies include applying bituminous paint, waterproof solutions, cement wash, paraffin oil, and Sylvester’s process. Applying bituminous paint involves cleaning the affected surface, allowing it to dry then applying a uniform coat of hot bitumen. Alternatively, cold bituminous emulsions can also be used. Waterproof solutions painting involves cleaning the affected surface and then applying the prepared waterproofing solution. Cement wash application involves preparing a thin consistency of cement-water mixture together with adhesive gum as an admixture, cleaning the surface then applying one or more coats of the cement want on the surface. Paraffin painting involves cleaning the affected surface and then applying paraffin oil on it. Sylvester’s process is done by cleaning the affected surface, applying the first coat of alum and soap solution, allowing the coat to dry up, followed by applying a second coat of the solution.

Permanent remedies basically involves identifying the cause of dampness and taking appropriate actions that will eliminate the cause. For example, if the dampness is caused by a leaking roof, the remedial measure would be to repair the roof so that it stops leaking and then repairing the affected area using a suitable temporary remedy.

Prevention measures for dampness include: application of damp-proofing membrane or course such as mastic asphalt, bituminous felts, cement concrete and plastic sheets; damp proof or waterproof surface treatment; and integral treatment. Damp proof or waterproof surface treatment involves filling up the openings present in materials that are exposed to moisture through application of a water repellant agent over the surface. Examples of water repellant agents that can be used include barium hydroxide, potassium/sodium silicates, magnesium sulphate and zinc/aluminium sulphate. Integral treatment is where specific compounds are added to the mortar or concrete when they are being prepared. The compounds act as barriers to the penetration of moisture. Examples of compounds used are fuller’s earth, talc and chalk. In case the entire external wall is affected, a cavity wall can be constructed around the wall so as to shield the building by creating a cavity between the building and the wall to prevent moisture from reaching the building wall.

Implications and Risks of the Defects

Conclusion and Recommendations

Concrete spalling and cracks are both structural and aesthetic issues that should be prevented or remedied immediately they happen. The two defects are an eyesore and if left untreated, they can lead to extensive structural damage of the building. This puts the lives of occupants and those in neighbouring buildings at risk.

Some of the general factors contributing to concrete spalling and dampness include: poor design, use of poor quality building materials, poor workmanship, incompetent and inexperienced workers, poor project management, limited time and cost, unsuitable construction equipment, ineffective communication and collaboration among parties involved in the project, unfavorable weather conditions, and improper building maintenance, etc. (Ali & Wen, 2011). Therefore the best approach of preventing or eliminating building defects is to start by identifying their root or direct causes (Aljassmi & Han, 2013). Some of the approaches that can be used to prevent occurrence of concrete spalling and cracks include: proper design, strict supervision, hiring competent and experienced workers, proper project and manpower management, proper communication and collaboration among stakeholders involved, and proper building maintenance. Every stakeholder involved in the design, construction and maintenance of the building has a role to play in preventing these defects.

The two defects discussed in this report can have devastating effects on the building if they are not remedied on time. If any of them is detected, the building owner or manager should hire a surveyor to assess the defect so as to determine the extent of its damage and establish the best diagnosis. Both concrete spalling and cracks have structural strength, stability, safety and cost implications. If these defects are not remedied on time, they can cause structural failure leading to collapse of the whole building.

References

Agyekum, K. & Ayarkwa, J., 2014. Dampness in Walls of Residential Buildings: The Views of Building Construction Professionals in Ghana. Africa Development and Resources Research Institute (ADRRI) Journal, 7(7), pp. 19-36.

Agyekum, K., Ayarkwa, J., Koranteng, C. & Adinyira, E., 2013. An Overview of the Symptoms Associated with Dampness in Walls of Residential Buildings in Major Towns in Ghana. Civil and Environmental Research, 3(9), pp. 1-9.

Ahmed, A. & Rahman, A., 2010. Treatment of Salt Attack and Rising Damp in Heritage Buildings in Penang, Malaysia. Journal of Construction in Developing Countries, 15(1), pp. 93-113.

Ali, A. & Wen, K., 2011. Building Defects: Possible Solution for Poor Construction Workmanship. Journal of Building Performance Simulation, 2(1), pp. 59-69.

Aljassmi, H. & Han, S., 2013. Analysis of Causes of Construction Defects Using Fault Trees and Risk Importance Measures. Journal of Construction Engineering and Management, 139(7), pp. 870-880.

Bakri, N. & Mydin, M., 2014. General Building Defects: Causes, Symptoms and Remedial Work. European Journal of Techhnology and Design, 3(1), pp. 4-17.

Hamakareem, M., 2018. What is Spalling Concrete? Their Causes and Repair. [Online]  Available at: https://theconstructor.org/practical-guide/spalling-concrete-causes-repair/26027/  [Accessed 24 January 2019].

Kong, X., Sun, Y., Weschler, L. & Sundell, J., 2018. Dampness problems in Tianjin dwellings: A cross-sectional study of associations with building characteristics and lifestyles. Indoor and Built Environment, 28(1), pp. 132-144.

Othma, N., Jaafar, M., Harun, W. & Ibrahim, F., 2015. A Case Study on Moisture Problems and Building Defects. Procedia – Social and Behavioral Sciences, Volume 170, pp. 27-36.

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Rodriguez, J., 2018. Tips for Preventing and Repairing Spalled Concrete. [Online]  Available at: https://www.thebalancesmb.com/how-to-repair-spalled-concrete-844938 [Accessed 24 January 2019].

Sharman, J., 2016. The NBS guide to damp: causes, effects and measurement. [Online]  Available at: https://www.thenbs.com/knowledge/the-nbs-guide-to-damp-causes-effects-and-measurement [Accessed 25 January 2019].

University Estate, 2016. Professional Surveying Practice , Reading, UK: UEMU.

Webster, M., 2016. Impact of deterioration on the safety of concrete structures – what can designers do to minimise risk?. [Online]  Available at:  https://mpwrandr.co.uk/impact-of-deterioration-on-the-safety-of-concrete-structures-designers/ [Accessed 24 January 2019].

Weintraub, E., 2018. The Definition of Spalling and How to Identify It. [Online]  Available at: https://www.thebalance.com/what-is-spalling-1798631 [Accessed 24 January 2019].