Lightweight Concrete for High Strength - Expanded Shale & Clay

Appendix B. Creep and Shrinkage
B.1 Creep of HPLC
While it is clear that HPLC can be produced with high strength lightweight concrete, its
creep characteristics have not been extensively or systematically investigated. Creep is typically
reduced in HPC but is typically greater in lightweight concrete. These competing effects make
creep in HPLC difficult to predict.
Moreover, some observations and recommendations presented in the literature are not
consistent. For instance, Berra and Ferrada (1990) concluded that specific creep in HPLC is
twice that of normal weight concrete of the same strength. On the other hand, Malhotra (1990)
gave values of creep of fly ash HPLC in the range 460 to 510 µε. These values are fairly close to
those obtained by Penttala and Rautamen (1990) for HPC, and they are significantly lower than
the values between 878 and 1,026 µε reported for HPC by Huo et al. (2001).
In a recent state-of-the-art report on high-strength, high-durability structural lightweight
concrete, Holm and Bremner (2000) remarked on the discrepancies found in the literature. They
contrasted the work of Rogers (1957) with the research done by Reichard (1964) and Shideler
(1957). In the former, creep of HSLC was found to be similar to that measured in companion
HSC while the last two found greater creep in “all lightweight” concrete (fine and coarse
lightweight aggregate), than in the normal weight concretes.
Leming (1990) compared the creep of three mixes: two 4,000-psi concrete with same mix
proportions, but with either lightweight or normal weight coarse aggregate. The third mix was
an 8,000-psi concrete with lightweight coarse aggregate. One-year creep was 1,095, 608, and 520
µε for the 4,000-psi lightweight, 4,000-psi normal weight concrete, and 8,000-psi lightweight
concrete, respectively. The result for the 8,000-psi lightweight concrete was 85% of the value
obtained for the 4,000-psi normal weight concrete.
There have been few research studies concerning creep of HPLC. However, conclusions
from different researchers are sometimes opposed which makes the estimate of creep in HPLC
extremely difficult. As a consequence, when HPLC is to be used in a certain project,
performance of a laboratory creep test for the specific mix is recommended in order to obtain
more accurate data for the design and prediction of creep in the project.
The two principle phases of HPLC: high performance matrix and lightweight aggregate
have several possible specific implications on creep in concrete. It is commonly assumed that
B-1