Concrete typically performs well in most construction situations even though, during construction or in service, it may be exposed to severe environments. Occasionally, however, an unsatisfactory condition is suspected or distress is actually observed and the owner, engineer or contractor must decide what to do next. Specialized testing services can be used to provide some or all of the needed information.
A careful look at a structure by an alert inspector can provide a lot of useful information which can't be easily gathered in any other way. Besides noting features such as the nature and extent of cracking, evidence of settlement and condition of exposed surfaces, the inspector can also check for conditions that may cause distress: poor drainage, expansive soils or exposure to aggressive chemicals, for example.
Surveys made to document the condition of structures will generally include visual examination but can also involve the use of specialized methods for measuring such features as floor flatness, corrosion activity and the presence of voids beneath slabs.
NONDESTRUCTIVE IN-PLACE TESTING
Nondestructive in-place testing can be used to obtain estimates of in-place strength; determine the uniformity in strength of in-place concrete; detect cracks, delaminations and similar discontinuities; estimate the thickness of a slab or wall; or locate rebar and estimate the depth of cover and bar size. Rebound, pullout and penetration devices are in common use as are some pulse velocity devices.
WHAT IS PETROGRAPHIC EXAMINATION?
From microscopic analysis and various chemical tests, a petrographer can determine the air content of hardened concrete, make an estimate of the cement content, find evidence of carbonation or other reactions and detect admixtures or contaminating substances that may have been present in the concrete. He may also make general observations about water-cement ratio, degree of cement hydration, early frost damage, excessive bleeding and similar phenomena.