Effect of Elastic Modulus of Capping Material on Measured Strength of High-Strength Concrete Cylinders.
Effect of Elastic Modulus of Capping Material on
Measured Strength of High-Strength Concrete Cylinders.
Vichit-Vadakan, W.; Carino, N. J.; Mullings, G. M.
Cement, Concrete, and Aggregates, Vol. 20, No. 2,
227-234, December 1998.
concretes; cap thickness; capping materials; compressive
strength; elastic moduli; high strength concrete;
modified cube strength; resonant frequency testing
Studies have shown that end conditions of concrete
cylinders tested in compression can have a significant
effect on the measured strength of the cylinders,
especially when high-strength concrete is used. The ASTM
standard for bonded caps has requirements for minimum
cube strength of the capping material and maximum cap
thickness. However, a study by researchers at the
National Ready Mixed Concrete Association (NRMCA) showed
that the 50 mm cube strength may not be very useful in
determining whether the capping material will perform
adequately when testing high-strength concrete. In the
study reported in this paper, the dynamic modulus of
elasticity and modified cube strength (ASTM C 116) of
various capping materials were evaluated as a function
of age. The results showed that each capping material
has a unique relationship between dynamic elastic
modulus and cube strength. The elastic modulus of
different capping materials can vary greatly at a given
cube strength. For example, at a modified cube strength
of 80 MPa, the elastic modulus of neat cement paste, at
30 GPa, was twice the elastic modulus of one sulfur
mortar, at only 15 GPa. The elastic modulus of the
capping materials was correlated with previously
reported cylinder strengths. In cases where the cylinder
strength was affected by the capping material, there is
evidence that the cylinder strength was related to the
modulus of elasticity and not to the cube strength of
the capping material.