Scientists from the Brunel University in London and Mutah University in Jordan have developed a new type of concrete capable of curing in extreme warm or cold weather.
Concrete curing is a process that becomes ineffective in hot and cold environments for different reasons. In particular, high temperatures cause weakening of the bonds between concrete's components (cement and aggregates) while low temperatures result in the occurrence of micro-cracking as the water of the mixture freezes.
However, according to the new study, recently published in Construction and Building Materials Journal, adding sodium acetate in the mixture improves the curing process in extreme temperatures increasing concrete's compressive strength and decreasing the amount of water that the mixture absorbs.
Taking into consideration the fact that most additives reduce the compressive strength of concrete, the new findings are remarkable. “Currently, most available protective additives in concrete reduce its compressive strength. Sodium acetate, on the other hand, has proven its ability to preserve and even increase the compressive strength of concrete under harsh weather conditions,” Dr. Seyed Ghaffar, co-author of the study and Assistant Professor at Brunel’s Department of Civil and Environmental Engineering, stated.
The team tested 72 concrete samples with different proportions of sodium acetate that were cured at freezing (-25°C) or hot (+60°C) temperatures for 7 or 28 days. Then, they evaluated their mechanical properties, microstructure, water absorption and the interaction mechanism of concrete and sodium acetate by conducting compressive strength tests, Scanning Electron Microscope (SEM) analysis, Initial Surface Absorption Tests (ISAT) and Fourier-transform Infrared Spectroscopy (FTIR) analyses, respectively.
The results of the experimental procedure showed a spectacular 64% increase in the specimens' compressive strength for those cured under 60°C when using 4% sodium acetate in the mixture. Moreover, water absorption decreased by almost 80% when just 2% sodium acetate is incorporated.
An unfavorable effect concerning an increase in water absorption when adding sodium acetate in a mixture with high water-to-cement ratio (0.46) was noticed.
Scientists' next goal is to evaluate the impact of sodium acetate on concrete's long term strength and durability.