Environmental factors and physical properties of latex modified concrete (LMC)
are hypothesized to contribute to early age cracking in bridge deck overlays. Cracking
permits the ingress of moisture and aggressive solutions into the substrate and may
contribute to other subsequent distresses. Understanding the material properties and
mechanisms involved is necessary to minimize these distresses.
This research consisted of a two part study: first, the development of LMC
strength and fracture properties at ages ranging from 5 hours to 28 days was studied, and
secondly, the effects of the environment on LMC distresses were modelled.
Environmental conditions: temperature, solar energy, and wind speed were determined
from weather records. A fracture mechanics based model, the Fictitious Crack Model
(FCM), incorporating finite element analyses and superposition techniques was employed
with material properties from the first part of study on LMC performance. Different
bilinear strain softening diagrams were used to predict fracture performance at different
ages. The predictions agreed well with the test data. The impacts of temperature
differentials on crack development were studied. The shrinkage effect was also indirectly
incorporated through the temperature analysis.
The material properties study indicated significant changes in strength, deformability
and fracture properties, particularly during the early age. The developments differ slightly from
conventional concrete. Test results indicated a significant improvement in reducing and
bridging microcracks, especially in the prepeak-load region. Fracture toughness and
deformability increased significantly with time. Fracture energy varied from 2.3 to 133.1 N/m,
depending on age, and to some degree, on notch depth ratio.
In the second stage, the FCM provided a reasonable prediction for crack initiation
and propagation when only temperature effects are of concern. Age, surface conditions
and structural restraint strongly affect crack resistance of the overlays. Only slight effects
were observed from the overlay thickness in the study range (51-76 mm). Shallow preexisting
cracks possibly reduce the crack resistance of the overlay about 30 percent. A
prolonged moist cure for 48 hours after placing is suggested to reduce the risk of
cracking. With available environmental information, it is possible to develop guidelines for
appropriate environmental conditions for LMC bridge deck construction to minimize the
risk of early age cracking. / Graduation date: 1997
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/33993 |
| Date | 27 November 1996 |
| Creators | Sujjavanich, Suvimol |
| Contributors | Lundy, James R. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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