The definition of concrete durability can be explained as the ability of a specimen to resist any form of weathering action, namely abrasion, chemical, physical, or any other process of deterioration. In other words, the durability of concrete can also be defined as the ability to last a long period of time without significant deterioration or failure.
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Types of weathering include mechanical, physical, and chemical weathering of concrete including the alkali-aggregate reaction of sulfate attack and chloride attack.
Different long-term testing methods have been used over the years and more research has been done to improve the existing methods to be more economical and environmental. Consideration has also gone into methods that reduce the time in which these tests can be completed and assessed.
The Importance Of Long-Term Durability Testing
It is important to test for the durability of concrete bonds because of the following reasons. Firstly, concrete testing will allow the designers to determine accurately the lifespan of a specific structure according to its specific needs or requirements. If a structure is intended to last a specific period of time, long-term concrete testing can reveal the combination that is required for it to last that long.
There can be economic and environmental benefits to this testing. Economically, constant rehabilitation and patching up of structures are very expensive. Hence, long-term testing can reveal the right combination of concrete mixtures for durable structures, thereby reducing the number of times for rehabilitation.
Environmentally, constant rehabilitation will require more use of natural resources such as sources of energy, gypsum, or steel to continuously rehabilitate worn-out structures. Continued rehabilitation increases the carbon footprint, which is not environmentally friendly.
Developments In Concrete Bond Materials
New studies have revealed that the addition of carbon fibers amounting to 0.35 vol(%) results in mortars that bond more aggressively compared to old mortars. The increased bonds result in an 89% increase in concrete strength.
Another recent development that has the potential to increase concrete bond strength is the addition of polymer to the concrete. It increases the strength of bonds and the fracture energy of the interface that lies between prefabricated unmodified concrete and polymer cement concrete.
The introduction of the addition of polymer and carbon to cement has the potential to revolutionize the construction business. Cement manufacturing industries would slightly need to modify the ways in which they produce their cement to produce high-quality concrete.
Large projects would need to source large amounts of raw polymer and carbon products. Ultimately, the production of stronger concrete will result in the building of much more durable buildings. This will lead to concrete that lasts longer and is more economical in the long run in that the need for rehabilitation will be reduced.
Limitations that can arise in this development could be due to sourcing the polymer in areas where the recycling of plastic material is non-existent or very little. Additional limitations when utilizing concrete polymer may be caused by, firstly it is very expensive as opposed to the ordinary Portland cement.
Secondly, polymer concrete requires highly skilled and precise working while mixing it. Therefore it may require expensive machinery or highly skilled labor, both of which can be expensive.
Further Reading: Calcium Carbonate Concrete: Building on Recycling
Different Methods Of Testing Concrete In The Construction Industry
The most common method for in-situ concrete testing used is cured cylinders. Samples are cast and cured according to ASTM C13 (American Society For Testing Materials). This method, however, does not mean it is the most accurate or even the fastest method, it is just the method most project managers use simply because that’s the way things have always been done. A few examples of concrete bond testing and their pros and cons are discussed below.
Round hammer or Schmidt hammer (ASTM C805).
This method is relatively easy to use and can be done on-site. The major disadvantage is that pre-calibration required for accurate readings can be very time-consuming.
Ultrasonic pulse velocity (ASTM C597).
The velocity of a pulse vibrational energy through a slab is determined in this technique. The smoothness at which this energy traverses through the slab provides the measurement regarding the concrete density, resistance to deformation or stress, and concrete elasticity. The data collected is used to determine the slab strength. A disadvantage of this method is that it is highly affected by the presence of reinforcement and presence of moisture in the concrete.
Pullout Test (ASTM C900).
This method is easy to use and can be done on both new and old construction. The major disadvantage is that the method involves the destruction of concrete during the testing process. This is both not economical as the damaged concrete costs money and it's not environmentally sustainable as wasted resources are required to create the concrete like energy.
Wireless Maturity sensors (ASTM C1074).
An advantage of this method is that data can be given every 15 minutes in real-time and therefore is a more accurate method to test for concrete strength. The major disadvantage of the method is that it is very time-consuming to calibrate and therefore not economical with respect to time.
It is important to choose the correct method to test for concrete strength according to scheduled deadlines, project budget as well as environmentally friendly methods.
Implications and Further Research
Further research will result in the production of greener concrete with greater strength and durability resulting in stronger and aesthetically pleasing buildings that will stand the taste of time.
The research will also reveal ways in which we can eventually do away with ordinary Portland cement.
In the long run, the use of polymer concrete will be more environmentally friendly in that it will promote the recycling of plastic which is more environmentally friendly. Polymer concrete studies reveal that it is a greener alternative to ordinary Portland cement as it has properties with a reduced carbon footprint.
The carbonation of concrete is also environmentally friendly in that not only can the concrete strength be highly increased, but the use of carbon dioxide can also help reduce the already increased carbon that exists in our atmosphere. This ultimately reduces global warming and climate change.
References And Further Reading
Harmuth, H., 1995. Investigation of the adherence and the fracture behaviour of polymer cement concrete. Cement and concrete research, 25(3), pp.497-502. https://www.sciencedirect.com/science/article/pii/000888469500038E
Standard Specification for Portland Cement (2021). Available at: https://www.astm.org/c0150_c0150m-21.html (Accessed: 30 November 2021).
Lee, J., Kim, J., Bakis, C. and Boothby, T., 2021. Durability assessment of FRP-concrete bond after sustained load for up to thirteen years. Composites Part B: Engineering, 224,. https://www.sciencedirect.com/science/article/pii/S1359836821005588
Valipour, M. and Khayat, K. (2020) "Debonding test method to evaluate bond strength between UHPC and concrete substrate", Materials and Structures, 53(1). doi: 10.1617/s11527-020-1446-6. https://www.researchgate.net/publication/339731892_Debonding_test_method_to_evaluate_bond_strength_between_UHPC_and_concrete_substrate