Case studies on free drying shrinkage test sensitivity and on carbonation rate of mortar with photocatalytics

A number of recent studies have examined different methods for preventing concrete distresses and limiting structural failures in order to reduce construction repair costs. Common distresses are cracking, scaling, delamination, and spalling. The causes of these concrete distresses can be from a wide variety of mechanisms, two of which are shrinkage and carbonation, which will be investigated in separate case studies. A common influence on both shrinkage and carbonation is the environmental exposure effect. In one case study, shrinkage was investigated to find out the effects of different environmental conditions (specific relative humidity RH and temperatures) and specimen size (or surface area exposed to the environment). The free drying shrinkage based on ASTM C157 was measured for two mortar mixtures but with different storage conditions (ranging from 4.5% RH to 99.9% RH and 11.2 °C to 25.4 °C on average) from 12 hours to 56 days. Three to four replicates of these mortar samples in each storing environment were also tested at each sample size of 1” prisms (1”Ã-1” Ã-11.25”), 2” prisms (2”Ã-2” Ã-11.25”), and 3” prisms (3”Ã-3” Ã-11.25”). The results verified that high humidity reduces shrinkage. It was also found that 3” prisms (surface area to volume ratio of 1.51) reduce shrinkage sensitivity among any storage environment. In another case study, carbonation was investigated to find out if the rate and depth were influenced by the presence of a photocatalytic material TiO2. A plain mortar mixture was compared to the same mortar with the TiO2 sprayed on the sample surface, and compared to the same mortar with 1% cement replacement of TiO2 particles. All samples were exposed to the same outdoor environment for up to 100 days. A scanning electron microscope and energy dispersive spectroscopy was used to verify the interior TiO2 content in the mortar. Thermo-gravimetric analysis and mass spectrometry were used to determine the amount of carbonation from samples taken at different ages and different depths. Result indicated mortar containing photocatalytic materials either embedded or sprayed on the surface have more carbonation at later ages and at the surface.