By Ben du Preez
Hindle Mason Projects (HMP) repairs poor concrete construction workmanship which is on the rise in South Africa.
This is due to many reasons, including skills shortages. The result is many concrete structures that require large repairs very early on in their lifecycle. A well designed and constructed structure should last between 50 and 100 years. They usually only require major repairs much later in their lifecycle. However, this is only if they have been maintained correctly and issues identified and corrected early.
There have even been instances of buildings collapsing before they have been completed. A case in point is the Neo Victoria building in George that collapsed during construction, resulting in injuries and fatalities. According to Home – CBE Council for the Built Environment, there were many warning signs that were ignored during construction. These included holes and cracks around the column bases, undersized support columns and missing expansion joints. [https://www.sciencedirect.com/topics/engineering/expansion-joints].
This follows the collapse of the partly completed Tongaat Mall, resulting in deaths and injuries. The Department of labour.gov.za attributed this to the absence of oversight and management failures.
These are extreme examples, but it does point to a worrying trend in the South African construction industry. In some instances, it is impossible to correct poorly designed and built concrete structures.
HMP understands concrete repair
HMP understands concrete and, therefore, how to repair it. Worryingly, we are seeing more poorly designed and built structures.
Poor concreting practices have even been observed on government construction projects. A case in point is the many newly built reservoirs for municipal water supply. These reservoirs leak through cold-joint lifts. This is the weakest link in concrete water-retaining infrastructure and where reinforcing bar starts to corrode first.
Honeycombing at the bottom of reservoir walls adjacent to joints between form panels and at cold joints is a recurring problem.
Large areas of honeycombing that have been observed time and again are due to poor compaction practices. This is in addition to the incomplete placement of concrete in formwork.
The many vertical cold joints that have been observed are due to working in one direction on closed-circuit structures.
Concerningly, there has also been high incidences of inadequate concrete cover and grout loss between adjacent shutters. The latter is another cause of honeycombing. Meanwhile, grout losses are due to leaking formwork.
Water stops have also not been installed correctly across concrete joints. They become misaligned and are damaged when adjacent panels are cast.
Bearing pads, which transfer loads to the foundation and facilitate movement, have also been incorrectly designed and installed.
HMP’s repairs address quality problems
HMP’s repairs address concrete construction quality problems. This is not only to improve aesthetics but also to prolong the lifecycle of reinforced concrete structures. It is simply not feasible to demolish poorly designed and built concrete structures if they can be salvaged.
One the leading problems that we encounter with new builds is micro cracking due to concrete bleeding. This occurs when free water in the concrete mix settles on the surface of placed concrete mix. When this water evaporates, it creates voids in concrete weakening the bond between cement paste and aggregates. Good site practices will avoid this by ensuring the correct cement-to-water ratio. This research explains the importance and need for a better understanding of water control in concrete mixes: (PDF) Water Control Management of Concrete Mixes on Construction Sites in Africa.
Another problem is spalling due to the porous nature concrete. Exposed concrete must be treated to avoid water from entering the concrete matrix. Moisture will eventually migrate to the reinforcing bar and initiate corrosion. The rust cracks the concrete enabling more water to enter and accelerate deterioration. Corrosion protection using quality materials [https://stoncor.co.za/] is also never a once off procedure. It needs to be incorporated into the maintenance of infrastructure over its long lifecycle. This is considering that waterproofing coatings and membranes wear or fade over time.
Unlike micro cracking, spalling is much more onerous to repair. It entails removing loose and damaged concrete and then reinstating the element with quality repair mortars. To ensure proper bonding, the surface must be prepared correctly. It is necessary to repair the exposed and corroded reinforcing steel before the repair materials are applied. If this is not done correctly or at all, corrosion will continue, rendering the repairs worthless.
HMP also repairs cracked concrete
HMP also repairs cracked concrete using various methods. One such process entails cleaning the cracks, undercutting them to create a wider and then filling them. The materials used depends on the type of crack. These include epoxy injections, concrete patching compounds or specialised repair mortars. Refer to Injection Systems | Crack Injection Waterproofing and Concrete Repair | Reinforced Concrete Protection. This is in addition to Concrete Repair & Protection Products | a.b.e.® Saint-Gobain.
Cracks are also due to the formation of tensile or bending stresses. This is because the stress applied to the concrete is greater than its tensile strength. Inspecting the tensile strength of concrete to ensure it is fit-for-purpose would have otherwise avoided this. One such test entails applying uniaxial tension to moulded concrete block.
Therefore, in these instances, reinforcing the structure will be necessary. A fast, practical and cost-effective way of doing this by applying carbon-fibre reinforcement. Fiber Reinforced Polymer (FRP) Fabrics | Structural Strengthening provides more information about this specialist process which we deploy. This is in addition to a host of other tried-and-tested strengthening techniques.
HMP repairs concrete honeycombing
HMP also repairs concrete honeycombing due to poor concreting practices similar to that encountered on the abovementioned newly built reservoirs.
Honeycombing does not just reduce the compressive strength of concrete; it also increases its porosity. This makes it prone to ingress of various deleterious materials and gasses. Therefore, it must be addressed urgently.
Again, repairing honeycombing is a specialist process. It entails first removing loose material from the affected area and then cleaning and preparing the substrate. Depending on the size and depth of honeycombing, various repair methods will be deployed. These include patching with mortar, epoxy injection and non-shrink grouts. Refer to SikaGrout®-212 | Low Shrinkage General Purpose Grout, epidermix Crack Injection System | a.b.e.® and MAPEFILL GP | Mapei, respectively. For large areas, shotcrete may even be deployed. This entails projecting concrete at high velocity to a vertical or overhead surface. The application consolidates the concrete. The hardened properties of shotcrete are similar to that of conventional in-situ concrete.
Then there is delamination due to shortcuts being undertaken on construction sites. Delamination is the separation of the surface layer from concrete elements. It occurs when the concrete surface is sealed while the underlying concrete is still bleeding and releasing air.
Minor delamination can be repaired by bonding the separated layers with epoxy or polyurethane. However, extensive delamination requires a more thorough process. This includes removing the damaged concrete, treating any exposed steel reinforcement and resurfacing with a new layer.
HMP’s concrete repair expertise
HMP’s concrete repair expertise is underpinned by our deep knowledge of concrete.
Many of the mistakes that we encounter could have been avoided by a robust quality management system.
As is the case with our repair projects, quality management ensures that start-to-end tasks are performed accurately. This enables us to guarantee our workmanship for the maximum available term. Any shortcut from procurement of repair materials to close out may compromise the overall quality of the project.
In addition to the correct use of concrete, contractors must ensure that their concrete mixes are fit-for-purpose. This must be done during the different stages of concreting to ensure durability, resistance and bearing strength.
Learn more about HMP. www.hindlemason.co.za
Du Preez is Contracts Director of HMP
