Acoustic Emission Analysis of Prestressed Concrete Structures

Abstract

Abstract. Corrosion is a substantial problem in numerous structures and in particular corrosion is very serious in reinforced and prestressed concrete and must, in certain applications, be given special consideration because failure may result in loss of life and high financial cost. Furthermore corrosion cannot only be considered a long term problem with many studies reporting failure of bridges and concrete pipes due to corrosion within a short period after they were constructed. The concrete pipes which transport water are examples of structures that have suffered from corrosion; for example, the pipes of The Great Man-Made River Project of Libya. Five pipe failures due to corrosion have occurred since their installation. The main reason for the damage is corrosion of prestressed wires in the pipes due to the attack of chloride ions from the surrounding soil. Detection of the corrosion in initial stages has been very important to avoid other failures and the interruption of water flow. Even though most non-destructive methods which are used in the project are able to detect wire breaks, they cannot detect the presence of corrosion. Hence in areas where no excavation has been completed, areas of serious damage can go undetected. Therefore, the major problem which faces engineers is to find the best way to detect the corrosion and prevent the pipes from deteriorating. This paper reports on the use of the Acoustic Emission (AE) technique to detect the early stages of corrosion prior to deterioration of concrete structures. IntroductionSeveral structures e.g. bridges, buildings, concrete pipes, strong tanks, dams, nuclear reactor protective shells, railway sleepers, piles and pressure vessels are made of prestressed concrete in which prestressing steel wires are put into a permanent state of tension to compensate for the inadequate tensile strength of the concrete. Tensile cracking in the concrete is minimised by ensuring that the concrete is in compression under normal working loads by prestressing the steel reinforcement. Generally prestressed steel is between four to five times stronger than mild steel. The main advantages of prestressed concrete structural materials are that they are stronger, lighter and "crack free" [1] and hence these materials offer cost benefits over other materials. Corrosion is a big problem in numerous structures. The cost due to corrosion is estimated in billions of dollars every year. Department of Transport in the UK evaluated that, the cost of recondition of concrete structures damaged by corrosion problems is £755 million a year [2]. The problem of corrosion in this type of structure must be given special consideration because failure may result in the worst scenario a loss of life but at a minimum a loss in finance. Most studies indicate the main reason of failure of bridges and concrete pipes is due to corrosion during the short period after they were constructed. The concrete provides the ideal environment to protect the steel wires which are

Experimental Investigation of Steel Corrosion in Concrete Structures by Acoustic Emission Analysis

“…Numerous researchers have devised methodologies for assessing the severity of damage and categorizing cracks using acoustic emission (AE) signal parameters. These methods have used information on the hits, amplitude, frequency, and wave energy [6] .…”

“…It demonstrated the capability of the AE method for detecting the initial stages of the corrosion process, even before significant damage to the concrete occurs. Moreover, it can gauge the extent of damage being inflicted on the concrete [13,14,15,16,22] .…”

“…By adjusting the bolts and nuts, each wire was subjected to a tensile force of 20 kN, which was monitored using strain gauges attached to the wires. [16,17,20] .…”

“…Finally, the mortar 200*200mm and 20 mm thickness was coated on the upper surface of the concrete. The mortar consists of one part cement to not more than three parts fine aggregate by weight [6,18,21] . The final construction is shown in Figure 3.…”