Curious Civil Engineer

Jacks are essential tools in prestressing operations and are used to apply tension to strands within tendons. There are two main types of jacks: A. Mono-Strand Jack A mono-strand jack is primarily used in building construction, where tendons typically consist of a small number of strands (usually 3 to 4). This type of jack is designed to stress each strand individually, ensuring precise control over the tensioning process. Since buildings generally have shorter tendons compared to bridges, stressing strands one by one is a practical and efficient approach in this context. construction management: concrete construction bridge construction:How to become a bridge engineer B. Multi strands jack:  In bridge construction, where tendons contain a significantly larger number of strands, using a mono-strand jack would be impractical. Stressing strands one by one in such cases would not only be time-consuming but also increase the risk of strand entrapment. Ther...

1. Anchorage Anchorage is a device used to secure prestressing steel and is installed at the edge of a concrete member or the prestressing end. There are two main types of anchorage: Dead-end anchorage : Embedded within the concrete, providing a fixed termination point for the prestressing tendons. Live-end anchorage : Positioned at the edge of the concrete member, where prestressing occurs. The jacking operation is done at the live end anchorage and the applied load is transferred to concrete members after the completion of tendon jacking. construction management: concrete construction bridge construction:How to become a bridge engineer Anchorage device consists of: anchorage device A. Bearing plate :  Typically round or rectangular, its primary function is to transfer the prestressing force from the tendons to the concrete. bearing plate and wedging plate B. Wedging plate:  This component holds the stra...

Pre-tensioning In pre-tensioning, the prestressing reinforcement (strands or bars) are tensioned before the casting of concrete. Once the concrete gains sufficient strength, the prestressing force is transferred from the tendons to the concrete. Stages of Pre-tensioning: Tendon Placement & Tensioning High-strength steel strands are stretched between two end abutments (bulkheads) within a prestressing bed. Concrete Casting Concrete is cast around the tensioned tendons and left to cure. Transfer of Prestress After the concrete attains the required strength, the tendons are cut loose from the abutments. The prestress is transferred to the concrete due to the bond between the tendons and the hardened concrete. Effects of Prestressing The concrete undergoes elastic shortening due to the prestressing force. If tendons are placed eccentrically, the member develops a camber (upward deflection). Post-tensioning In post-tensioning, concrete is cast first , and after it gain...

Prestressed concrete technology is widely used across the world due to its numerous advantages. The capacity of reinforced concrete members is inherently limited. When subjected to loads, reinforced concrete tends to crack, reducing the structure’s durability by allowing water and harmful substances to penetrate. To address this issue, prestressing is implemented to enhance the load-bearing capacity of concrete members. This is achieved by compressing the concrete using high-tensile cables, ensuring that any applied load must first counteract the pre-existing compression before exerting stress on the member itself. Prestressing can be categorized into two methods: Pre-tensioning: The cables are tensioned before casting the concrete. Post-tensioning: The cables are tensioned after the concrete has been cast and gained sufficient strength. This technique offers several benefits, including increased structural strength, enhanced durability, a higher span-to-d...

  Prestressing strands is high tensile strength steel. The tensile strength of prestressing strands can reach up to 1860 Mpa. the process of manufacturing prestressing steel differs significantly from the conventional reinforcement.  Figure 1 The process of manufacturing strands will begin by de-scaling the raw material (wire rod). The purpose of de-scaling is to remove the iron oxides (mill scale) from the surface of the wire rod. after removing the mill scale, the wire rod's surface is coated with a textured coating to enhance the adherence of lubricants to the raw material surface. The most commonly used coating is zinc phosphate.  Figure 2 The wire rod then passed through a series of dies. The process of reducing the wire rod diameter is known as cold-drawing. In this process, the wire rod is drawn through a die with the required diameter. To prevent the wearing of dies, the wire rod will be drawn through a lubricant box. the lubricant will coat the wire with a thin l...

  Prestressing bridge concrete beams contributes to resisting the tensile stresses caused by the traffic loads and the beam's weight. Stressing concrete has various benefits, such as increasing concrete members' capacity, reducing the concrete member section, and increasing the span lengths for structures such as bridges and buildings. However,  The stressing of bridge beam ends can result in unwanted cracks. Therefore AASHTO calling for debonding a specific portion of strands at the beam end to minimize the stresses and reduce cracks. Figure 1 Debonding is achieved by wrapping the strands at the end of the beam with plastic. Wrapping the strand with plastic wrapping will prevent the strands from bonding with concrete, thus avoid transferring unwanted stress to the beam end. As a result, the unwanted cracks will be prevented by reducing the stress levels at the end of the beam.  

 Ductility is an important property of steel reinforcement. Ductility is the ability of the material to undergo plastic deformation before failure. The ductility of reinforcement is related to the elongation property. The ductility of reinforcement ensures safer and durable structures. Material that undergoes little or no plastic deformation is known as a brittle material. Brittle reinforcement can cause sudden structure failure because it doesn't undergo any plastic deformation before failure.  Figure 1 The ductility factor for reinforcement can be computed using the following equation: µ=ϵu/ϵy where, µ is the ductility factor ϵu is the ultimate strain ϵy is the yield strain In figure no:1-a, we can see the stress-strain curve for mild steel. The mild steel has well-defined yield stress and strain, as shown in the stress-strain curve. The reinforcing bar can recover all the elongation if the applied stress is lesser than the yield stress. This portion of the curve is kno...

 Construction management: Road construction course This course is designed to expand your practical side of engineering knowledge. This course is concentrating on the construction of roads. Here you will learn how the road is constructed. The construction stages such as protection of existing services, clearing the area, future utilities, preparing the road subgrade, then placing different pavement layers such as sub-base, base course, and asphaltic courses. We will also discuss the types of asphaltic course and the common defects of asphaltic pavement, such as permanent deformation, fatigue cracking, and low-temperature cracking. Also, I will show a typical cross-section of road and road profiles and many other subjects. Enroll from here  Pile foundation design This course will discuss the design of pile foundations. We will learn the methods of calculating the pile bearing capacity. The bearing capacity for a pile consists of skin and end bearing resistance. Here you will un...

Rebound hammer is a non-destructive test used to examine the hardened concrete. The principle of the rebound test is based on the rebound of a plunger. The plunger of the rebound hammer is pressed against a concrete surface. The hammer mass will be pushed back and secured to a pin. The impact spring is attached to the hammer mass, so it will be extended with the hammer mass. Then the hammer mass is released.finally, the mass will rebound against the concrete surface, as shown in figure no:1. The surface hardness and compressive strength will be correlated with the rebound of the spring controlled mass.  Figure 1 Figure 2 A rebound hammer can be used to evaluate the compressive strength of a concrete member, quality of concrete, and uniformity of concrete. The approximate impact energy required for the rebound of the hammer for different applications is shown in table no:1. Table 1 The procedure of conducting the rebound test will begin by the calibra...

Acidic materials are the material with Ph lower than 7. material with Ph higher than 7 classified as basic material. Neutral material has a Ph of 7. concrete has a Ph higher than 7, so it is a basic material. Concrete structures that are constructed in the vicinity of the acidic environment, such as mines, will be vulnerable to damage. Drainage water from existing mines has a ph value of about 1. this low ph value will deteriorate and severely damage the concrete quickly. However, the exposure of concrete to a high ph-value of 5 to 6 will also damage the concrete but at a lower rate. Figure 1 Acidic material will react with concrete cement paste. The cement paste then transferred to calcium salt. The calcium slat will be washed out by the water, and the aggregates will be exposed. The acid damage is similar to abrasion damage, except the aggregates don't have the polished surface. The concrete is a basic material. Therefore it will neutralize the effects of acid at...

  Soundness test conducted in cement to verify that cement will not undergo a destructive expansion after setting. The expansion of restrained concrete members will result in severe tensile stresses that can result in cracking and spalling of casted concrete. The expansion could occur due to the reaction of free lime, magnesia, and calcium sulfate.   Free lime found in the clinker. Free lime inter-crystallized with other compounds, and it tends to expand during the hydration process. The expansion of free lime is more than calcium oxide. Magnesia reacting with water similarly as calcium oxide does. But the crystalline formed due to the reaction of magnesia is deleteriously reactive, so it is unsound. Calcium sulfate can cause destructive expansion. The reaction of calcium sulfate will produce calcium sulfoaluminate (ettringite), which can result in the harmful expansion of cement.  Figure 1 A soundness test will be conducted using La Chatelier's appar...

Sodium magnesium and calcium sulfates are salts that can react with hardened concrete and cause deterioration for concrete structures. Sodium magnesium and calcium sulfates react with hydrated lime and hydrated aluminate in cement. This reaction will produce calcium sulfate and calcium sulfoaluminate. The volume of these products is greater than the volume of the cement paste, which undergoes the reaction with sulfates salts. This reaction will cause a destructive volume change. The increase of existing concrete will generate stress, which may result in concrete cracking and spalling. The using of sulfate resistance cement is recommended where the sulfate concentration is high. Sulfate resistance cement or cement type V will resist the sulfate reaction. Type V cement has a low calcium aluminate content, which enables this cement type to provide a good resist the sulfate deterioration. Therefore it should be specified and used when it is recognized that concrete must be exposed to...

Cooling of concrete is very important to prevent the thermal cracks. The rapid concrete hydration will generate a high amount of heat. This heat will cause high tensile stresses higher than fresh concrete strength. Concrete in hot weather and mass concrete are susceptible   to thermal cracking. In general concrete, the temperature is reduced to prevent thermal cracking. In addition to thermal cracking, hot weather can increase the rate of slump loss and increase the rate of water evaporation. The reducing of concrete temperature can be done by covering the aggregates, storing the cement in a shaded area, and using ice to cool the water. Recently liquid nitrogen used to reduce the temperature of concrete. construction management: concrete construction bridge construction:How to become a bridge engineer The LN has a temperature of -196 C˚ (-320F˚). The LN used to cool the concrete directly on the concrete mixer. LN is stored in a special tank that can endure the ...

A slip of a strand can occur during the stressing process or while anchoring the tendon. The slip of a strand can occur due to rusted wedges and rusted wedge plate holes. The rust or dirt will prevent the wedges from firmly gripping the strands. Worn teeth of jack wedge can be another reason for strand slipping. Strands slippage can be prevented by using of well-maintained wedges, wedge plates, and jacks.  construction management: concrete construction bridge construction:How to become a bridge engineer Slippage of strands will be discovered from the marks made on strands tail for this purpose. If the slip is significant (more than 1 in (25mm)), the effects of strand slip should be considered. Slipped strand will have lower stress than other strands. This will reduce the overall force of the tendon. In order not to overstress other strands, the prestressing force should be reduced proportionally to account for the strand slip. For example, if one strand out of ten ...

High-performance concrete possesses better properties and strength than typical concrete. High-Performance concrete mixtures are highly durable, and they have high ultimate strength. HPC has been used in tunnels, bridges, and tall building structures. Also, in shotcrete repairs, parking garage, and agricultural applications. ACI defined high-performance concrete as a concrete meeting special combinations of performance and uniformity requirements that cannot always be achieved routinely using conventional constituents and normal mixing, placing, and curing practice.  Figure 1 High-performance concrete mixtures developed for a specific application. The characteristics of high-performance concrete are developed to suit the specific application. Some of the properties that may be required include: • High strength • High early strength • High modulus of elasticity • High abrasion resistance • High durability and long life in severe environments • Low permeability and ...