In this investigation, the effect of simulated desert climate on moisture loss (as it is related to
drying shrinkage), ultrasonic pulse velocity (internal crack detector), absorption (durability index) and compressive
strength (mechanical properties pointer) were studied. Concrete mixes, having w/c ratios of 0.35, 0.45 and
0.55 and polypropylene fiber volumes of 0, 0.1, 0.2 and 0.3%, were prepared and subjected to one of three conditioning
regimes after 14 days of moist curing. The samples were either kept in laboratory air, placed in an oven
operating two daily temperature cycles between 75°C and room temperature or placed in a continuous heating oven
at the same temperature. It was found that heating adversely affected all studied properties of concrete. The moisture
loss and absorption were increased by a factor that ranged between 4.23–29.96 or 2.8–18.67, respectively.
The compressive strength was reduced by 3.16 to 33.82% compared to the samples kept in laboratory air. The
inclusion of fibers improved the performance of concrete mixes compared to the no fiber mixes subject to temperature,
to a certain degree. Fiber volumes 0.1–0.2% are recommended in these conditions depending on the
type of mix. The presence of polypropylene fibers interferes with the elastic waves traveling through concrete
and hence reduces the pulse velocity. Heating of fiber concrete seems to magnify this interference and therefore
ultrasonic pulse velocity readings could not be used as internal crack indicators in the current study." |
