Lightweight Concrete for High Strength - Expanded Shale & Clay

Changes in moisture migration: the seepage theory views creep as a result of water
movement under stress from micropores to the larger capillary pores. If water migration is the
main factor in concrete creep, both the aggregate porosity (i.e., volume of pores, pore size, and
pore distribution) and the permeability of the cementitious matrix become important factors.
Several (ACI-213, 1999; Holm, 1995; Neville et al., 1983) have cited the importance of using
lightweight aggregate in a saturated condition while mixing. If the aggregate is not saturated, a
more rapid movement of water from the paste would be expected to lead to greater creep. On the
other hand, the moisture conditions given by the saturated lightweight aggregate could replace
the water lost under stress (seepage).
B.2 Shrinkage of HPLC
As occurs with creep of HPLC, there are only a few articles regarding shrinkage of
HPLC. Besides, they usually do not report autogenous and drying shrinkage separately, but as
overall shrinkage. Berra and Ferrada (1990) found that compared with HPC, HPLC had a lower
shrinkage rate, but a higher ultimate value. According the authors, the lower rate was caused by
the presence of water in the aggregate which delays drying. Holm and Bremner (1994) also
observed that HSLC mix lagged behind at early ages, but one-year shrinkage was approximately
14% higher than the HPC counterpart. Holm and Bremner (1994) measured a higher shrinkage
when they incorporated fly ash to the HSLC mix. Malhotra’s (1990) results, on the other hand,
showed that fly ash particles in the HPLC helped to reduce shrinkage after one year.
Leming (1990) reported one-year shrinkage of 4,000-psi and 8,000-psi lightweight
concretes, made with saturated expanded slate, of 390 and 310 µε, respectively while the
corresponding shrinkage of a 4,000-psi NWC was found to be 360 µε. Bilodeau et al. (1995)
investigated HSLC with 28-day compressive strength ranging from 7,250 to 10,000 psi and
found that the 450-day shrinkage was in the range 518 to 667 µε. Curcio et al. (1998) reported
that one-year and ultimate shrinkage of HPLC with Type III cement and fly ash was 450 and 500
µε, respectively.
Kohno et al. (1999) found out that autogenous shrinkage is reduced by the use of
lightweight fine aggregate. They concluded that this is because water lost by self-desiccation of
the cement paste is immediately replaced by moisture from lightweight aggregate. Aïtcin (1992)
reported values of shrinkage of HPLC as low as 70 and 260 µε, after a 28-day curing.
B-3