The durability of concrete infrastructure is related to the properties of the
applied concrete and the effects of the aggressive external environment on
it. When concrete is directly exposed to soft water, the leaching of calcium
ions from hardened cement or cement-based pastes occurs, causing reduction
in strength and further deterioration of the concrete structure. This paper
presents the experimental results of soft water attack effects on phase
composition and compressive strength of blended cement pastes, when cement
is replaced with 0%, 10%, 20% and 30% of natural zeolite. In order to
simulate soft water attack in laboratory conditions, paste specimens were
exposed to leaching in deionised water up to 180 days. The evaluation of the
changes in phase composition (ettringite, portlandite, calcium silicate
hydrate gel) due to calcium ion leaching was made based on X-ray diffraction
analysis, Fourier transform infrared spectroscopy and paste compressive
strength tests. The presence of portlandite and ettringite after 180 days of
exposure to deionised water indicates that leaching did not influence the
stability of the hydration products in blended cement pastes. Moreover,
blended cement paste with 10% of natural zeolite had a higher compressive
strength than the reference one.