| Abstract | A theoretical and experimental study was conducted to observe the effectiveness of chemically
prestressed ferrocement (CPFC) which combines chemical prestress (CP) and ferrocement (FC).
Chemical prestress is produced in concrete or mortar by larger, but not too much amount of expansive
additive compared to the amount for shrinkage-compensation, with proper restraints.
Chemically prestressed concrete or mortar has comparatively ductile and high potential to
control crack width and number of cracks. Ferrocement, which has better crack arresting mechanism
with smaller crack width and spacing consists of wire mesh and as the case, skeletal bars
which should act as restraints against chemical expansion. Ferrocement has a high possibility to
be developed by chemical prestress on crack resistance especially higher first cracking strength,
and less deflection. Therefore, this study is quite meaningful to see the synergistic effect by
chemical prestress and ferrocement - chemical prestress developes ferrocement more than its
potential.
Based on the concept, mainly two types of test were conducted, namely direct tensile test and
flexural test. For direct tensile test, two specimens of the fifteen sets (totally thirty specimens)
were tested with four varying parameters, (i) Type of wire mesh - welded wire mesh and
hexagonal wire mesh, (ii) number of wesh layers - two and four, (iii) amount of expansive
additive - five percent and ten percent replacement to binder weight, and (iv) age - three, five,
and twenty-eight days. In this program, ultimate tensile capacity, cracking load, cracking strain,
and deformation against applied load were mainly observed.
For flexural test, chemically prestressed ferrocement was applied as strengthening material attaching
bottom surface of reinforced concrete beam by installing U-shaped mechanical shear
connectors. One control beam (control) and seven strengthened beams were tested under two
monotonically increasing load at twenty-eight days after installing ferrocement. Varying parameters
were the same as those of direct tensile test except age. In this program, mid-span
deflection, first cracking moment, and ultimate moment capacity were mainly observed.
As a result, chemical prestress was installed into each specimen of ferrocement. CPFC increased
first cracking stress significantly compared to that of FC at both experiments with less deformation
and deflection - especially under direct tensile condition. However, CPFC does not increase
ultimate tensile strength regardless amount of expansive additive. Theoretical value could have
good agreement with the experimental value of ultimate tensile strength which dominated by
strength of reinforcements. CPFC beams which had full composite action between ferrocement
and concrete increased ultimate moment capacity to that of control beam and FC. Furthermore,
increase in the number of mesh layers increases strength and stiffness of the CPFC and showed
higher first cracking strength than that of two layers on both types of wire mesh. |