Chloride content and the pH value of the pore solution in the neighborhood of steel reinforcement are decisive parameters for initiation and rate of corrosion. The pore solution of cement mortar and hardened cement paste has been expressed from the pore space by high pressure in the investigation. The influence of the water-cement ratio, age, and addition of chloride to the fresh mix on chloride content in the pore solution has been determined by ion chromatography. At the same time the pH value of the pore solution has been determined. The dissolved chloride content decreases with increase in the water-cement ratio. The amount of bound chloride increases with time, but it decreases with decreasing content of dissolved chloride in the pore solution. A significant influence of carbonation on the dissolved chloride content of the pore solution has been observed. With complete carbonation, the dissolved chloride content in cement mortar and hardened cement paste increases by a factor between 2 and 12. The bound chloride decreases by 27%-54%. As expected, the pH value decreases from around 13.2 to as low as 8.0 due to carbonation. It can be concluded that carbonation not only lowers the pH value but liberates bound chloride. This is one obvious reason why the combined action of chloride penetration and carbonation accelerates steel corrosion and shortens the service life of reinforced concrete structures.
Water repellent treatment has been considered an e ective preventive method against water and aggressive ions penetration into concrete and consequently can improve the durability of concrete structures. In reality, many concrete structures are exposed to conditions with high risk of carbonation. In this contribution, one type of ordinary concrete had been prepared and surface impregnated by 400 g/m 2 silane cream and 100 g/m 2 and 400 g/m 2 silane gel. In addition, integral water repellent concrete was produced by adding 2% silane emulsion. en, the specimens were exposed to accelerated carbonation for 7, 28, and 72 days. e e ect of water repellent treatment on carbonation of concrete has been investigated. e results indicate that surface impregnation reduced carbonation depth of concrete under RH 70%, but integral water repellent concrete increased carbonation. Carbonation reaction started behind the hydrophobic layer in the surface-impregnated concrete.e coe cient of carbonation can be described better by a hyperbolic function of time. Treatment by 400 g/m 2 silane gel and silane cream showed better e ciency on reducing carbonation than usage of 100 g/m 2 . Coe cient of water capillary suction was decreased signi cantly by both surface impregnation and integral water repellent treatment. It is an e ective method to protect concrete from water penetration into the material.
A carbonation model of reinforced concrete structures subjected to mechanical load based on experimental work is proposed in the paper. Correspondingly, a series of reliability analysis and service life prediction is carried out and reasonable results are acquired. Besides the effect of concrete cover, it indicates that mechanical load impacts the reliability and service life of the reinforced concrete structures significantly through example calculation. In the case of concrete cover of 40mm, the service life is shortened nearly half under a tensile load of 60% while the service life is lengthened 30% under a compressive load of 30%. In service life design or long term performance assessment, more work should be done with the consideration of the mechanical load effect.
Concrete structures are generally designed on the assumption that they will require no maintenance during their service life. The experience with reinforced concrete structures in the severe marine environment shows that this assumption is not valid. Almost everywhere in the world it is possible to find coastal structures, even some relatively new ones, which contain cracked or spalled concrete usually involving corrosion of the reinforcement. For most concrete structures, the typical situation during operation of the structures is that maintenance and repairs are mostly reactive, and the need for taking appropriate measure is usually realized at a very advanced stage of deterioration. For chloride-induced corrosion, repairs at such a stage are both technically difficult and disproportionately expensive compared to carrying out regular condition assessments and preventive maintenance. Therefore, for all concrete structures where high safety, performance and service life are of special importance, regular condition assessment and preventive maintenance should be carried out including chloride profiles, potential mapping, local inspection, etc. For all concrete structures in chloride-containing environments, however, special procedures for monitoring and control of chloride penetration during operation of the structures are needed. The establishment of such procedures should always be an impartment and integral part of the durability design. In this paper, some procedures for the preventive maintenance are described and discussed in more detail.
The NiCo layers with various Ni/Co atomic ratio have been successfully electroless deposited on PZT layers by varying the bath composition. As the cobalt atomic ratio in the deposited layer increases from 17.2 to 54.8 wt%, the magnetostrictive coefficient decreases. The magnetoelectric effect depends strongly on the magnetostrictive properties of magnetostrictive phase. The magnetoelectric coefficient of NiCo/PZT/NiCo trilayers increases with Ni/Co atomic ratio of the deposited NiCo layers increasing from 45:55 to 83:17. A maximum ME voltage coefficient of αE,31 = 2.8 V ⋅ cm−1 ⋅ Oe−1 is obtained at a frequency of about 88 kHz, which makes these trilayers suitable for applications in actuators, transducers and sensors.
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