Abstract:
To study the effect of brick chips as coarse aggregate on creep behavior of concrete, a
comprehensive testing program is conducted at Bangladesh University of Engineering &
Technology, Dhaka, Bangladesh. Concrete cylinder specimens having compressive strength of
17.2,24.0 and 27.5 MPa are prepared rrom both natural stone and crushed clay brick aggregate.
Mix design ratios are evaluated in a way so that volumetric content of coarse aggregate (both
brick and stone) remain approximately same for all concrete samples. Specimens are then
subjected to creep testing at 7th and 28th day after casting and creep strain data are recorded up
to 300 days. Results show that although strength and other environmental parameters remain
same, concrete made rrom crushed clay brick as coarse aggregate have higher creep strain than
that of concrete made from natural stone aggregate. This increase in creep strain ranges rrom
30% to as high as 45% for the 300 day loading history considered.
Additionally, in order to select an appropriate model to predict creep in brick aggregate concrete,
effectiveness of five widely used prediction models are examined. For this, predicted creep strain
rrom ACI 209, CEB-FIP 90, B3, GL 2000 and Euro code 2 models are compared with
experimental results. Using statistical analysis, it is established that prediction of creep by
GL2000 model is closest to the experimental result. A modification factor is then proposed
which may be incorporated so that prediction of creep strains by GL 2000 model for brick
aggregate concrete becomes more realistic.
Furthermore, a simple design oriented empirical model containing only two parameters has been
developed to predict creep behavior of concrete made of crushed clay bricks as coarse aggregate
for a stress/strength ratio of 0.35. For each concrete strength category, using the available test
result a hyperbolic equation is developed from their creep-time behavior. These equations are
then combined and modified according to statistical norms to finally obtain a generalized
equation. Comparison of creep strain obtained from this equation with that of experimental
values show that the proposed model can closely predict creep in brick aggregate made concrete.
