Concrete Spalling ( Cancer ) Repairs, Ashfield Civic Centre
Constructed in the 1970s, the Civic Centre in Ashfield had slowly been deteriorating over the past decade. The first signs of deterioration noticed by the buildings owners (Ashfield Council) was small bulges in the over hanging slab. Not long after peaces of masonry start to fall on to the pathway below . The speed at which the concrete spalling ( cancer ) had spread took many by surprise and a decision was made to remove loose masonry and repair as soon as possible.
As with many cases in concrete cancer the cause can be laid with the original contractor.
#1 In the first picture below you will notice the long piece of steel reinforcing running parallel with the slab on the second floor. The steel had been set 50mm back from the face and underside, within standard practice. As the steel is more than 50mm recessed from the face and underside water in theory should struggle to penetrate from the surface and cause corrosion of the steel reinforcing and the spalling that follows, collectively known as concrete cancer. However what the original installer never took into consideration was the water drip on the underside. The water drip was in excess of 20mm recessed, bringing the surface and steel to within 30mm and thus in range of penetrating water and salt damage.
#2 Rain water outlets in some areas had insufficient overhand. This had allowed water to run down the face of the concrete and penetrate the surface the causing steel reinforcing to corrode.
Expose the corroded steel and remove loose material. Treat steel and substrate with appropriate products and coatings. Install helical dowel pins and apply grouts to surface. Extend length of water outlets.