Concrete: reinforced

Concrete is the most widely produced material on earth. The use of cement, a key ingredient of concrete, by Egyptians dates back more than 3500 years. In the construction of the pyramids, an early form of mortar was used as a structural binding agent. The Roman Coliseum is a further example of a historic landmark utilizing cement mortar as a construction material. Worldwide consumption of concrete is close to 9 billion tons and is expected to rise even further. 

In order to understand corrosion damage in concrete, a basic tmder-standing of the nature of concrete as an engineering material is required. A brief summary follows for this purpose. It is important to 

The reaction of the cement and water to form the cement paste is actually a series of complex hydration reactions, producing a multiphase cement paste. One example of a specific hydration reaction is the following  

A further important feature of the hydration reactions of cement with water is that the resulting pore solution in concrete is highly alkaline [refer to Eq. (2.28) above]. In addition to calcium hydroxide, sodium and potassium hydroxide species are also formed, resulting in a pH of the aqueous phase in concrete that is typically between 12.5 and 13.6. Under such alkaline conditions, reinforcing steel tends to display completely passive behavior, as fundamentally predicted by the Pourbaix diagram for iron. In the absence of corrosive species penetrating into the concrete, ordinary carbon steel reinforcing thus displays excellent corrosion resistance. 

From the above discussion, the complex nature of concrete as a particulate-strengthened ceramic-matrix composite material and the difference between the terms concrete and cement should be apparent. The term mortar refers to a concrete mix without the addition of any coarse aggregate. 

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Nesvijski, E.G., Nogin, S.I. Acoustic Emission Technics for Nondestructive Evaluation of Stress of Concrete and Reinforced Concrete Structures and Materials. Third Conference on Nondestructive Evaluation of Civil Structures and Materials, Boulder, CO, 1996. Nesvijski, E. G. Failure Forecast and the Acoustic Emission Silence Effect in Concrete. ASNT s Spring Conference, Houston, TX, 1997. 

The ultrasonic tomograph A1230 was developed to visualize in case of one side access the internal reinforced concrete structure at the depth of 1 m. This device uses 36-elements matrix array. 

Radiographic image of 800 mm thick reinforced concrete wall with vertical and horizontal bars clearly visible, in this case some 150 mm from the concrete surface (film side). 

Based on the technology developed for using PVA fiber as a replacement for asbestos in cement products, Kuraray has been developing thick fibers for reinforcing concrete (42). Super-thick fibers with a thickness of 39 tex (350 den) (200 p.m in diameter) to 444 tex (4000 den) (660 p.m in diameter) are now available the 39 tex material is used for reinforcing various mortar-based cement products and the 444 tex material for reinforcing concrete in civil engineering works such as tuimels, roads, harbors, and bays. 

USSR SU 1,742,254 (June 23, 1992), S. T. Babaev and co-workers (to Scientific Research Institute of Concrete and Reinforced Concrete). 

Fig. 4. Integrated vault technology for low level waste disposal where A represents waste containers that are placed in concrete overpacks and sealed with grout B, closed modules covered with a multiple-layer earthen cover, to direct water away from modules, and short rooted vegetation for erosion control and C, overpacks placed in reinforced concrete modules which are closed with a reinforced concrete roof Courtesy of Chem-Nuclear Systems, Inc.

Type I (Normal). This is the general purpose Pordand cement used for all appHcations where special properties are not needed. Common appHcations include concretes for paving, building doors, roof decks, reinforced concrete buildings, pipes, tanks, bridges, and other precast concrete products. In 1989 Type I and Type II accounted for over 92% of the Pordand cement produced in U.S. plants. Exact data are not available that separate Type I and Type II Pordand cement, but it can be assumed that Type I production was much greater than Type II. 

ACI Committee 318, Building Code Requirementsfor Reinforced Concrete and Commentary, ACI 318-89/318R-89, American Concrete Institute, Detroit, Mich., 1989, 353 pp. 

Roads and Walkways The cost of roads and walkways in chemical plants is difficult to estimate, since these vaiy with type of construction and thickness of applied cover. Some typical unit costs for roads are as follows For 305-mm (12-in) gravel base covered with 76-mm (3-in) asphalt, the cost is 17.10 per square meter ( 14.30 per square yard) for a reinforced concrete slab with a 152-mm (6-in) subbase, the cost is from 28.40 to 35.10 per square meter ( 23.80 to 29.30 per square yard), depending on the thickness of concrete (for M S = 1000). 

Fig. 1.6. The reinforced concrete footbridge in Garret Hostel Lane. An inscription carved nearby reads This bridge was given in 1 960 by the Trusted family members of Trinity Hall. It was designed by Timothy Guy MORGAN an undergraduate of Jesus College who died in that year. ...

By far the lightest pressure vessel is that made of CFRR Aluminium alloy and pressure-vessel steel come next. Reinforced concrete or mild steel results in a very heavy vessel. 

The proper choice of material is now a quite different one. Reinforced concrete is now the best choice - that is why many water towers, and pressure vessels for nuclear reactors, are made of reinforced concrete. After that comes pressure-vessel steel - it offers the best compromise of both price and weight. CFRP is very expensive. 

There are less exotic ways of increasing the strength of cement and concrete. One is to impregnate it with a polymer, which fills the pores and increases the fracture toughness a little. Another is by fibre reinforcement (Chapter 25). Steel-reinforced concrete is a sort of fibre-reinforced composite the reinforcement carries tensile loads and, if prestressed, keeps the concrete in compression. Cement can be reinforced with fine steel wire, or with glass fibres. But these refinements, though simple, greatly increase the cost and mean that they are only viable in special applications. Plain Portland cement is probably the world s cheapest and most successful material. 

In the case of higher protection current densities and protection currents, interference can occur on nearby installations not covered by the protection. The danger of anodic interference must be investigated by making measurements and prevented by taking appropriate measures [7] (see Section 9.2). For the same reasons, anode systems should not be installed near steel-reinforced concrete foundations. 

The danger of corrosion is in general greater for pipelines in industrial installations than in long-distance pipelines because in most cases cell formation occurs with steel-reinforced concrete foundations (see Section 4.3). This danger of corrosion can be overcome by local cathodic protection in areas of distinct industrial installations. The method resembles that of local cathodic protection [1]. The protected area is not limited, i.e., the pipelines are not electrically isolated from continuing and branching pipelines. 

For efficient current distribution, steel-reinforced concrete walls should be provided at the wall entrance of pipes and at least 1 m around them and up to the soil surface with at least 2 mm thick electrically insulating layers of plastic or bitumen. This is also recommended if the pipelines are laid in soil parallel to steel-reinforced concrete foundations and the closest spacing is smaller than twice the pipe diameter or smaller than 0.5 m [2]. 

Fig. 12-5 Voltage cone AU and pipe/soil potentials at a wall entrance in a steel-reinforced concrete foundation.

Installations with Small Steel-Reinforced Concrete Foundations... 

Pumping or compressor stations are necessary for the transport of material in pipelines. These stations are usually electrically separated from the cathodically protected long-distance pipeline. The concrete foundations are much smaller than in power stations and refineries. Since the station piping is endangered by cell formation with the steel-reinforced concrete foundations, local cathodic protection is recommended. 

Structures or pits for water lines are mostly of steel-reinforced concrete. At the wall entrance, contact can easily arise between the pipeline and the reinforcement. In the immediate vicinity of the pit, insufficient lowering of the potential occurs despite the cathodic protection of the pipeline. Figure 12-7 shows that voltage cones caused by equalizing currents are present up to a few meters from the shaft. With protection current densities of 5 mA mr for the concrete surfaces, even for a small pit of 150 m surface area, 0.75 A is necessary. A larger distribution pit of 500 m requires 2.5 A. Such large protection currents can only be obtained with additional impressed current anodes which are installed in the immediate vicinity of the pipe entry into the concrete. The local cathodic protection is a necessary completion of the conventional protection of the pipeline, which would otherwise be lacking in the pit. 

Considerable stray currents can, of course, be caused by dc-driven cranes that load and unload ships where the rails act as the return conductor for the current. The rails run parallel to the harbor basin, quay walls of steel-reinforced concrete or steel piling walls. These can take up a large part of the stray current and conduct it further because of their small longitudinal resistance. Noticeable stray current inter-... 

Steel constructions and pipelines must either be electrically connected to the reinforcement of reinforced concrete structures or electrically separated. If they are connected, a current density of about 5 mA m should be applied to the external reinforcement and calculated on the total area of the concrete surface. 

Very often steel sheet pilings exist in conjunction with steel-reinforced concrete structures in harbors or locks. If cathodic protection is not necessary for the reinforced concrete structure, there is no hindrance to the ingress of the protection current due to the connection with the steel surfaces to be protected. The concrete surface has to be partly considered at the design stage. An example is the base of the ferry harbor at Puttgarden, which consists of reinforced concrete and is electrically connected to the uncoated steel sheet piling. 

Ferry harbor, Puttgarden None 8500 and ca. 5500 steel-reinforced concrete 160 PtTi 360 20 X 100 >10... 

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