ACI Concrete Repair & Restoration 3

Question 1

Carbonation of concrete is most likely to cause:

Accepted Answer

A reduction in pH that can lead to corrosion of reinforcement

Answer

Carbonation lowers concrete pH from ~12.5 to below 9, destroying the passive oxide layer that protects steel reinforcement.

Question 2

When grinding concrete joints to restore load transfer in a slab, what is the primary goal?

Accepted Answer

Reducing differential vertical movement (faulting) between adjacent panels

Answer

Diamond grinding levels faulted joints to eliminate differential movement that causes rough riding surfaces and pavement damage.

Question 3

Hydrostatic pressure on a below-grade concrete wall is best countered by a repair that:

Accepted Answer

Applies a hydraulic cement plug from the negative (dry) side

Answer

Hydraulic cement can be applied from the interior (negative) side to stop active water infiltration against hydrostatic pressure.

Question 4

Spalling along the soffit of a concrete bridge deck is most commonly caused by:

Accepted Answer

Corrosion of reinforcing steel expanding and fracturing the cover concrete

Answer

Corrosion products occupy up to 6 times the volume of the original steel, creating expansive forces that spall the concrete cover.

Question 5

Prior to applying a thin-bonded overlay, a pull-off (tensile bond) test on the prepared substrate should yield at least:

Accepted Answer

200 psi

Answer

ACI 546 recommends a minimum substrate tensile strength of approximately 200 psi before placing bonded overlays.

(ACI) American Concrete Institute Concrete Finisher Practice Test