This study presents the effect of corrosion of prestressed concrete (PC) strands on the prestressing force and the reduction mechanism of the uniaxial force. A total of 14 strands was tested by combining a rigid frame testing machine with an electrified accelerated corrosion device. The specimens were divided into two groups having prestressing levels of 70% and 50% of tensile strength of PC strands. The expected degree of corrosion of the specimens, which was defined by the mass loss, was calculated from controlled electric current and time. A rigid frame testing machine was used to sustain the tensile force of the PC strands, and the prestressing force and deformation of the strand were continuously measured during the corrosion test. The test results indicate that the prestressing force decreases with the increase of corrosion. After the corrosion tests, tensile loading tests were carried out on the specimens that did not rupture during the corrosion test. It was found that corrosion led to the deterioration of the tensile properties of the PC strands, and the ultimate tensile capacity of the corroded PC strand was related to the fracture condition.
In the present paper, the effects of the thermal insulation layer on the temperature field of concrete board and further on the development of mechanical properties of the concrete are investigated by a temperature field model that takes cement hydration heat into account. In the modeling, factors that may influence the development of temperature in the board, including the thickness of the insulating polystyrene foam board, concrete strength, and casting seasons are considered. The effect of temperature rise on the mechanical properties of the concrete is evaluated through a model of degrees of cement hydration and compressive strength of concrete. The results show that the temperature inside the concrete board is greatly increased after placing a thermal insulation layer on the surface of the concrete after casting. More uniform temperature distribution along the slab thickness is observed compared to that without the thermal insulation layer. Temperature rise inside concrete board can greatly speed up cement hydration and the development of concrete strength. Curing with a reasonable thermal insulation layer allows the heat of cement hydration to be used effectively to increase the strength of concrete and to realize demoulding around 24 hours after casting.
Electro-deposition repairing concrete crack technique is of vital importance to prolong the service life of the concrete structure in the marine environment. In this paper, the repairing effect using seawater as an electrolyte was compared with ZnSO4 solutions, and the mechanism of electro-deposition repairing concrete cracks under seawater environments was investigated. Besides, various parameters such as electrode materials, electrode distances and current density were studied in seawater. The experimental results indicated that electro-deposition repair using seawater is highly effective compared to using ZnSO4 solutions. The Cl- removal efficiency can reach to 16.25% with titanium mesh as the anode and seawater as the electrolyte. The main crystal mineral composition using seawater is brucite, calcite and aragonite, and the percentages of Mg(OH)2, Ca(OH)2 and CaCO3 are approximately 68%, 7% and 23%, respectively. Rather than Na+, Mg2+ and Ca2+ in seawater were the primary ions promoting the repair of concrete cracks. When the seawater and titanium mode was used, the reaction products were the densest and the repairing effect was the best. Furthermore, when the titanium electrode distance was 0 mm and the current density was 0.25 to 0.5 A/m2, the electro-deposition repairing effect was the best. This paper presents a new method for the research of electro-deposition repairing concrete cracks in the submerged zone of marine environment.
The purpose of this research work was to study the effect of polyethylene glycol (PEG) and polypropylene glycol (PPG) as polyether polyols on the properties of mortar specimens. Electrochemical measurement was used to investigate the change in charge transfer resistance of mortar during the hydration of cement. The mechanical properties of the mortar specimens were studied by flexural and compressive strength tests. The results show that PPG helps to improve the mechanical properties of mortar specimens compared with PEG, and that the improvement is better for high molecular weight. The mechanism of the interaction between PEG and PPG molecules and C-S-H gel was examined by molecular dynamics simulations and density flooding theory calculations, and the effect of molecular weight of PEG and PPG on the interaction of surface of C-S-H gel is discussed.