Evaluation of Microcapsules Filled with Nano Magnesium Oxide for Self-Healing Concrete

Abstract

This study aims to investigate the effect of the addition of Nano MgO on the self-healing behavior of concrete. The Nano MgO wereadded to the concrete mixtures at ratios of (0.3, 0.4, 0.5, and 0.6) % by weight of cement, respectively. Then, the compressive strength, density, and water absorption were measured at ages (7, 14, and 28) days. The results showed that the best compressive strength, density, and lowest water absorption were obtained by mixing 0.4% MgO with the weight of cement. SEM and EDX were used to characterize the concrete samples. SEM examination of the concrete samples with 0.4% MgO by weight of cement showed a dense microstructure with no pores and the formation of CSH. Microcapsules containing cement with 0.4% Nano MgO were prepared using a fluidized bed coating process (Pelletization method). The microcapsules were then added to concrete with (7, 10, and 13) % of the cement's weight. Compressive strength, water absorption, density, flexural strength, and splitting tensile strength tests were performed to study concrete properties. According to the results, MgO microcapsules were used as a useful material for the self-healing cracking process. Fabrication of Microcapsules 1- Polystyrene was dissolved with toluene at a ratio of 1:10 using a magnetic stirrer for 30 minutes, 70 C°, at a speed of 80 rpm. 2- 100 gm of cement was mixed with 0.4 gm of Nano MgO using a hand mixer for 10 minutes. 3- To perform the pelletizing process (fluidized bed coating), the polyurethane material consisting of polystyrene with toluene was placed in the spray gun that was fixed in the device shown in Figure 1, and it was pumped at a pressure of 7-8 bar, and the air jet installed at the bottom of the device was operated to raise the mixture consisting of cement and nanomaterials that was pumped out. Using a fixed injection, pumping the polystyrene solution for 3 seconds to obtain the best powder coverage and forming microcapsules with a homogeneous powder core covered with polystyrene. 4- Extract the microcapsules collected at the top of the device. 5- Drying in a drying oven for two hours at a temperature of 60 C°. Casting and Curing of Test Specimens The superplasticizer has been added to the water and the mixture was mixed for 10 seconds, then the Nano MgO has been added and placed in a sonicator (Powersonic 410, Hwashin Technology Company, Korea) for 30 minutes. The mixture was then placed in a mixing bowl, and cement has been added gradually with continuous mixing using a homemade electrical mixer, sand was added to the mixture gradually, taking a mixing period of 4 minutes. Finally, microcapsules have been added gradually with continuous mixing for 2 minutes. The concrete mixture has been poured into three different types of molds into 9 samples for each test: cubic molds (50*50*50) mm3 for compressive strength test, cylindrical molds (150 mm length and 50mm diameter) for splitting tensile strength tests, and Prismatic molds (40*40*160) mm3 for flexural strength test, molds they have been prepared and oiled in advance. After completing the pouring process, a polyethylene cover has been placed to ensure that the mixing water did not evaporate for 24 hours. After that, the molds have been opened and the models have been placed in the treatment basins until the test time. Figure 3 show Mixing and casting. They also improved concrete compressive strength, water absorption, density, flexural strength, and splitting tensile strength. 10% weight was selected as the best addition that enhances the characteristics that may be used in construction.