Effect of carbonation on non-destructive strength and durability assessment of limestone based concrete

For the condition assessment and determination of residual bearing capacity of existing concrete structures, strength and durability related properties of the reinforced element are of high importance. Assessment of these properties can be performed by (i) destructive testing of drilled cores and testing the extracted samples in lab environment for compressive strength evaluation and determination of carbonation depth and (ii) indirect methods by using non-destructive techniques such as rebound hammer, ultrasonic pulse velocity tester, resistivity meter and air permeability meter. The experimental program is conducted on concrete slabs of different strength classes intended for various exposure classes according to EN206, based on a limestone aggregate matrix where different amounts of CEMI and CEMIII (260-340 kg) and alternating w/c-ratios (0.40-1.00) were used. The plates were tested at the age of 90 days and the test program was repeated at the age of 5.5 years, after exposing the elements in a sheltered outside environment to natural carbonation, in order to evaluate the effect of carbonation on the mechanical and durability related properties. Best fit correlations between the output of these different techniques were established by means of regression analysis. By using UPV and air permeability testing devices the strength and carbonation coefficient can be obtained non-destructively. Furthermore, the effect of age (i.e. carbonation) on the established correlation curves and predictive models is clearly noticeable.