"We have found shotcrete produces a better product with less labor and accompanying savings, " explained Danny Brahana, ABE principle engineer, "And I think choosing the shotcrete method was influential in getting this project."
The company's bid was accepted by general contractors Balfour Beatty Construction US with offices in Dallas and Washington DC.
"The soil conditions in the Piedmont physiographic province of Georgia are igneous rock 50 to 80 feet deep, "according to Brahana
, "Weathering has resulted in silty sands."
We feel shotcreting is easier and provides a better seal than form and pour, "according to Brahana
An eight man crew , a pump man, nozzle man, a worker to blow out shotcrete rebound, two hosemen and two finishers , conducts the shotcrete operation using a Schwing SP 750-15 all-hydraulic concrete pump.
The pump is capable of 50 yards per hour output and can apply 1100 psi on the concrete.
The Rock Valve-equipped SP 750-15 is powered by a liquid cooled Deutz 100 horsepower diesel engine.
"We have tried several other pumps and the additional horsepower of the Schwing
provides the right combination of volume without hose surge, " Brahana
The hose man fills the void with the 4,000 psi shotcrete to a depth of about nine inches in one pass creating a "soft U" between the piles.
The finishers screed it to within an inch of the front of the piles and then a finish coat is applied.
The finish or flash coat is shot at a 45-degree angle which causes most of the aggregate in the mix to ricochet off the wall leaving a paste that is hand trowelled.
The two-inch slump shotcrete mix has to be just right for, according to Brahana
, to allow sufficient build-up and smooth finishing.
It is treated with an accelerator in cold weather and a retarder in warmer temperatures.
"Pump ownership with the Schwing's
has been painless, " states Brahana
, "We use Schwing's
line pump manufacturing facility and factory store in nearby Marietta for accessories and service support.
We are looking forward to a bright future competing with shotcrete."