Combating Black Rust and a Dodgy Drain

As engineers, we are often challenged with some interesting defects we must provide a solution for.  During the investigation process, we tend to uncover some intriguing case studies, some of which we will share with you now! This month the spotlight is on our ongoing projects at Petersham and McMahons Point,  which produced stories of black rust and dodgy drainage systems.

Petersham 

During a recent bout of wet weather, it came to our attention that the current underground drainage system at this property was ineffective. This issue resulted from lack of maintenance and build-up of leaves, dirt or roots which are now blocking the drain and prohibiting it from diverting the water into the gutter.

Instead of diverting the water away from the property, the water is building up and spurting out through a joint in the downpipe. In other areas of the property, these ineffective pipes are allowing water to pool at the base of the building, water build up that has the potential to enter the building's foundation and cause cracking issues.

CCTV will be used to determine the cause of the blocked pipe and then a plumber will be engaged to undertake repairs. 

From a strata perspective, ongoing general maintenance works can avoid these types of issues and eliminate large repair costs in their tracks.

McMahons Point

Recently our engineers provided specialist design and remedial advice at a McMahons Point complex. Inspection of this complex revealed that the steel reinforcement in the building's concrete slabs was severely corroded. The building is approximately 50 years of age and magnesite has been used on all the concrete floor slabs.
 
Black rust was evident in the reinforcement which can be identified as a thin black layer of discoloured crust indicating a lack of oxygen or in some cases contact with chlorides.
 
Reinforcing steel is made of iron, which is known to be highly susceptible to corrosion – especially due to chloride contamination found in magnesite.  
 
The black rust,  identified by our engineers,  formed within the steel reinforcement where there was little or no exposure to oxygen and contact with corrosion accelerators such as sodium chloride (found in magnesite toppings).

A scratch test was performed to identify weak locations throughout the bar and uncover how deep the corrosion was. This test revealed that the rust was occurring quite badly within the steel bar however, the damage was not very deep.
 
To resolve this issue our engineers recommend identifying the weak spots within the steel reinforcement. If weak spots are identified, pieces of additional reinforcement should be welded into critical areas to stabilise the steel and combat the corrosion.
 
If you believe you have magnesite on your concrete floors, please call us for an assessment – before it’s too late!