A field examination of the pavements was organized by Vernon Marks of Iowa DOT. Site visits to pavements of Iowa US 20, Iowa 175, I-35, US 218, and I-80 allowed examination and designating coring locations. Sites were selected from pavements exhibiting no apparent deterioration, those slightly affected, and pavements with relatively severe damage. In the following paragraphs, the observations are summarized. More detailed observations are given in the results of petrographic examinations of specific cores.
In some cases, onset of pavement deterioration was visible as a slight darkening of the concrete in the transverse joint region. The darkening may reflect accumulation of dirt and other road debris and moisture migration within fine-sized cracks along the joints. Additional degradation resulted in development of cracking along the transverse joint and road edge, and along cracks parallel to vibrator trails (Figure 1). The degradation would be characterized initially as "low" severity according to the Strategic Highway Research Program (SHRP) Distress Identification Manual  and "moderate" as the deterioration progresses. The most severely deteriorated regions exhibited pattern cracking over the entire slab, more substantial darkening at joints, cracking paralleling joints and the road edge, along with minor spalling of concrete adjacent to the joint. Map cracking oriented in the longitudinal direction of the pavement, interconnected by slightly finer cracks perpendicular to pavement direction became more prominent with the progression of deterioration (Figure 2). Damage observed during the field examination does not exceed the "moderate" rating, although some of the sections of US 20 considered to be the most severely affected, were paved with an asphalt overlay at the time of the site visit.
Longitudinal cracks with widths ranging from less than 1 mm to 2 mm wide are present along some vibrator trails. Vibrator trails exhibit a slightly different texture, probably related to lack of coarse aggregate as observed in regions where the pavement surface had been ground. Gress  noted that the tining penetrated deeper across the vibrator trails. The cracking paralleling the longitudinal cracks may also be classified as "low" to "moderate" (Figure 3).
There was no evidence of any permanent volume change, deflection, closing / opening of joints, or tilting and shearing of slabs. All roads had a tined surface reportedly cut after the concrete had set  and the condition of the tine grooves varied from cleanly cut to having a torn appearance. The exposed pavement surfaces appeared satisfactory, though some surfaces reportedly experienced difficulty in finishing during the paving operation. Iowa DOT noted many of the mixes were "harsh" and were difficult to place . Secondary deposits in the form of a white efflorescence (probably carbonated calcium hydroxide) were noted along US 20 on surfaces and in cracks within the spalling adjacent to the joints, but only in regions with the most severe deterioration.
Figure 1. Onset of pavement deterioration is visible as a slight darkening of the concrete in the transverse joint region (top, I-80) and in pavements with advanced deterioration, a tightly-closed pattern cracking (bottom, US 20). Some of these pavements also have vibrator trails.
Figure 2. Map cracking oriented in the longitudinal direction of the pavement, interconnected by slightly finer cracks perpendicular to pavement direction becomes more prominent with progression of deterioration (top). Advanced degradation shows cracking paralleling the transverse joint and road edge, and along cracks within vibrator trails. The degradation would be characterized initially as "low" severity according to the SHRP Distress Identification Manual  and "moderate" as the deterioration progresses.
Figure 3. Pavements exhibiting severe deterioration show significant pattern cracking (here accentuated by moisture along the crack), cracking along joints, spalling along joint edges and white efflorescence. Open joints and lack of displacement along pavements slabs provides evidence against permanent expansive processes such as alkali-aggregate reaction and sulfate attack.