Every drop of water stored in reservoirs, water treatment plants and behind dams is vital to the well-being of the population they serve and the local economy. This mission is even more crucial given that increasingly severe drought conditions have led to significant water loss. 

As for our country’s wastewater treatment systems, communities need to be secure, knowing that none of the sewage sludge held in these facilities makes it into local groundwater or nearby waterways. Likewise, we must be confident that contaminants do not enter the clean water stored in our water treatment facilities.  

Water containment structures all have one thing in common — they rely on concrete to keep water in its place, whether fresh or fetid. However, concrete shrinkage can lead to cracks, creating an opportunity for water to escape or contaminants to enter. 

BILL LEADS TO EXPANSION

The longtime recognition of the improvements needed in this country’s water storage systems led in part to the passage of the 2022 bipartisan infrastructure bill, which will help municipal utilities deliver clean, reliable drinking water and help build secure operations. 

The challenges for utilities are that new water and wastewater structures with shrinkage cracking can face difficulties passing the required leak test and may require other expensive remedial work. These additional operations increase the cost of construction and can also extend project timelines, leading to delays and reduced owner/taxpayer satisfaction. In addition, decades of crack repair and maintenance represent a significant cost burden to the owner and headaches from taking a structure out of service while being repaired. 

Ultimately, concrete cracking compromises the life cycle of the structure. For example, concrete that should have lasted 50 to 100 years forces the utility to perform replacement after only two to three decades. 

The costly cycle of shrinkage cracks, repair, maintenance and deterioration can be significantly improved using a magnesia-based admixture, which is an effective means of mitigating shrinkage cracks and curling. Reducing or eliminating shrinkage cracks means contractors complete projects on time while reducing repairs and extending the project lifecycle.  

Projects can incorporate magnesium-based admixtures into the concrete for all water and wastewater structures, including reservoirs, primary and secondary treatment, clarifiers, aeration tanks and digesters. PREVent-C, an admixture developed by Premier Magnesia, is one of the only shrinkage reducers that’s NSF-61 certified for use in potable water applications to make regulatory compliance more manageable. 

BUILT TO LAST 

In South Dakota, a major containment project controlled the problem of concrete cracking by adding magnesium oxide to the concrete as a shrinkage compensating admixture.  

Around a quarter million households depend on electric power generated by the earthen Fort Randall Dam in South Dakota’s southeast corner. The dam spans the Missouri River and encloses Lake Francis Case — the 11th largest reservoir in the U.S. Historic flooding caused it to overflow. 

Army Corps of Engineers inspections found that necessary repairs to the dam would include partial replacement of large portions of the spillway slab. They were already concerned about concrete shrinkage and subsequent cracks in the spillway. 

In addition, the Corps found that in most areas of the dam, they would need to install reinforced steel to handle temperature and shrinkage. This approach would require them to drill 130,000 dowels into surrounding concrete laboriously.   

For a more straightforward and effective solution, the Corps opted to use PREVent-C admixture at a 5% dosage rate and a macro polypropylene fiber at 5 pounds per yard in addition to other adjustments to their specialty concrete mix design. This approach significantly minimized early-stage concrete cracking for a more substantial spillway slab. 

CONTROLLING OVERFLOWS

In another instance, a Pennsylvania utility used a shrinkage compensating admixture in an expansion project aimed at reducing overflows.

Expanding the wet weather treatment capacity by enlarging existing plant facilities has been a cornerstone in the Allegheny County Sanitary Authority’s strategy for reducing sewer overflows over the past 25 years. This stormwater runoff has been one of metro Pittsburgh’s most intractable problems. 

ALCOSAN’s $2 billion Clean Water Plan includes building the new East Headworks facility as part of the current ALCOSAN Plant Expansion Program. The expanded plant will increase the facility’s wastewater treatment capacity from 250 mgd to 600 mgd. The contractor drilled over 1,900 auger cast piles into the bedrock to serve as the foundation for the East Headworks facility. 

The engineer for the project was looking for a way to enhance the performance of the concrete in service and reduce potential cracking due to shrinkage or restraint on the project during the design stage.  

As many of the structures contain wastewater and thus need to be watertight, the engineer specified Sika Control NS as a basis of design for the shrinkage-reducing compensating admixture for the concrete. Premier Magnesia produces Sika Control NS under a private label agreement for Sika. 

Using a magnesium-based admixture will enable these utilities to minimize cracks in the surface of concrete structures to maximize public investment and ensure the facilities meet the needs of their residents for centuries to come.

Jim Preskenis is the specialty concrete admixture manager for Sika Corporation.