Utility of curing by pressure vessel to improve cementations mixtures

Over the last years, the method of autoclave steam curing was the most effective way to improve the mechanical properties of concrete. Since this mechanism required high energy for efficient curing, the method of compressed air curing was designed. This study is investigated the effect of compressed air technique on the properties of cement mortar. The use of compressed air curing technology in the curing of cement mortar (fresh) is done by placing the cement mortar specimens in the newly created machine specially designed for this purpose and then applied pressure gradually on the specimens until the desired pressure level. The specimens should be kept inside the vessel under pressure for certain periods until maturity. The concrete is final to be de-molded and then placed in water at laboratory temperature. Then the mechanical tests for the specimens are conducted at specific ages. The improvement in properties was observed, where there was the development in the density and compressive strength of hardened cement mortar. This development is attributed to the effect of pressure on the size of air voids within the specimens. The air pressure on the cement mortar in the fresh state (before final setting) causes a significant decrease in the size of the air voids inside the model and causes an increase in the compact of the specimens. Three waiting times were studied before putting the specimens inside the pressure vessel (Three, four and five hours), after casting cement mortar directly and the optimal age was selected for the treatment. Three durations were tested for applying the pressure on the specimens inside the vessel (24 hours, 96 hours and 168 hours). The specimens were then removed and kept in water for tolerate time (144 hours, 72 hours, 0 hours). After the completion of the mechanical tests and comparing the results with the reference mix, it was found that the best age to start treatment is 4 hours (where the age of 3 hours was difficult to control the models because it did not harden enough), and that the best duration of curing was 168 hours where gave an increase percentage of 87. 95% at the age of 7 days and an increase rate of 79.81% at the age of 28 days after shedding the value of pressure (0.5 MPa). The tests showed a clear increase in mechanical properties of cement mortar, which encourages the use of this new and low-cost technology in precast concrete plant.