racookpe1978
Nuclear
- Feb 1, 2007
- 5,969
Not a on-the-job question, but it relates to concrete wear-and-tear.
Assume a 30-year-old "nominal concrete" driveway, no rebar.
If I am pressure washing it to remove mildew and years of accumulated tree sap and gunk with a "Big Box" rented pressure washer rated at 2000 psi, will the washing force erode the concrete?
Question was asked by she-who-must-obeyed, and a neighbor. My answer was "no."
My reasoning was two fold:
A test area with the nozzle held 1/2 inch from the concrete for 20 seconds showed no erosion of the concrete nor any breaking out of the aggregate from the matrix. Aggregate was already visible at the top of the concrete: it was not "smooth" before testing. Normal nozzle position was 2-3 inches from the concrete being swept side-to-side with a constant but overlapping motion, so in one place for 20 seconds was far in excess of what was normally done. Figure an average total water impact area of 2-1/2 inches x 1/4 inch "fan" when it hit the concrete.
second was my assumption that a 2000 psi washer is putting out 2000 psi at the PD pump outlet. Down a 50 ft, 1/4 internal diameter hose, through hose and washer fittings, and then out the nozzle reduces the pressure even more.
Going out the nozzle itself spreads out the force over a bigger area, and so reduces the final pressure even more. But the water at the nozzle hole is much faster than than the slower water in the hose -> so is the impulse force more important than pressure?
Assume a 30-year-old "nominal concrete" driveway, no rebar.
If I am pressure washing it to remove mildew and years of accumulated tree sap and gunk with a "Big Box" rented pressure washer rated at 2000 psi, will the washing force erode the concrete?
Question was asked by she-who-must-obeyed, and a neighbor. My answer was "no."
My reasoning was two fold:
A test area with the nozzle held 1/2 inch from the concrete for 20 seconds showed no erosion of the concrete nor any breaking out of the aggregate from the matrix. Aggregate was already visible at the top of the concrete: it was not "smooth" before testing. Normal nozzle position was 2-3 inches from the concrete being swept side-to-side with a constant but overlapping motion, so in one place for 20 seconds was far in excess of what was normally done. Figure an average total water impact area of 2-1/2 inches x 1/4 inch "fan" when it hit the concrete.
second was my assumption that a 2000 psi washer is putting out 2000 psi at the PD pump outlet. Down a 50 ft, 1/4 internal diameter hose, through hose and washer fittings, and then out the nozzle reduces the pressure even more.
Going out the nozzle itself spreads out the force over a bigger area, and so reduces the final pressure even more. But the water at the nozzle hole is much faster than than the slower water in the hose -> so is the impulse force more important than pressure?