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Principles of Prestressed Concrete Technology

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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...
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concrete workability

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Concrete workability refers to the ease with which concrete can be mixed, placed, and compacted while maintaining uniformity and homogeneity. Several factors influence concrete workability, including water-cement ratio, aggregate properties, and the use of admixtures. construction management: concrete construction bridge construction:How to become a bridge engineer Factors affecting workability  1. Water-Cement Ratio (W/C): Increasing the water-cement ratio improves workability but reduces the strength of the concrete mix. A higher W/C ratio also increases permeability, compromising durability and strength. Conversely, using too little water may result in incomplete cement hydration, leading to a loss of strength. The typical W/C ratio ranges from 0.35 to 0.40 . 2. Aggregate Size: Larger aggregates have a smaller total surface area, requiring less water for wetting, which improves workability at the same water conte...
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Caliper logging test

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Caliper log tools are used to measure the diameter of a pile shaft. This technique is not limited to pile foundation applications but can be utilized in various fields. A caliper logging test provides detailed measurements of the pile shaft diameter at different depths, making it essential for verifying the cross-section of the shaft. The size of a drilled shaft can vary, and in some cases, it may be smaller than the required dimensions. Additionally, due to differential pressure in the surrounding soil or rock layers, some pile shafts may develop an oval shape instead of a uniform circular cross-section . Figure 1 construction management: concrete construction bridge construction:How to become a bridge engineer
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Crosshole Sonic logging test

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Cross-Hole Sonic Logging (CSL) Test The Cross-Hole Sonic Logging (CSL) test is a more advanced method compared to conventional integrity testing. It is primarily used to assess the quality of concrete in deep foundations, particularly in cast-in-place piles. Principle of CSL Testing Prior to pile casting, access tubes are securely fixed inside the steel reinforcement cages. The CSL test evaluates potential defects in the pile concrete shaft by measuring: First Arrival Time (FAT): The time taken for the ultrasonic pulse to travel between the transmitter and receiver. Wave Energy: The strength of the received ultrasonic wave. The wave velocity is calculated using the formula: This calculated velocity is then compared to the expected velocity of sound waves in concrete. Lower wave speeds and weak energy signals indicate potential defects, such as voids, honeycombing, or inclusions within the concrete pile. construction management: concrete constructi...
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Pile integrity test(low strain impact integrity test)

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          Pile Integrity Test A Pile Integrity Test (PIT) is a non-destructive method used to assess the structural integrity of cast-in-place concrete piles. The test is typically conducted seven days after casting to ensure the concrete has gained sufficient strength. construction management: concrete construction bridge construction:How to become a bridge engineer Concept of the Test The principle of the test involves introducing a sound wave into the pile shaft and comparing the measured wave velocity with the standard wave velocity for concrete. Any deviation in wave velocity may indicate anomalies such as cracks, discontinuities, or material inconsistencies within the pile. PIT provides valuable information regarding: Pile cross-section continuity Discontinuities or voids in the pile shaft Pile length estimation Quality of concrete within the pile Advantages of the Pile Integrity Test PIT is widely used for conc...
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Binding wire for steel reinforcement

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  Binding wires are used to tie steel bars together. These wires are playing a significant role in maintaining the reinforcement stability and rigidity. Wires are used to tie the steel bars at intersections points. By tying the steel bars together, we ensure that the steel bars will not move from their locations during construction or during the time of concreting. In slabs, binding wires are used to tie longitudinal and transverse bars together. In columns, it is used to tie vertical bars with stirrups.   Figure 1 There are various types of binding wires such as  Black annealed baling wire, Stainless Steel Binding Wire, and PVC coated binding wires.  Black annealed baling wire used to tie black steel. The popular size for black wire ranges from 16 to 22 gauges. Stainless steel binding wires are used to bind stainless steel reinforcement. Stainless steel reinforcement is used in a harsh environment where the black steel gets rusted quickly. Therefore, stainless ...
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Pile cap

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Pile cap used to transfer the loads from superstructure to the piling. The pile cap is thick concrete mat rests on piles. It is part of the foundation and used to distribute the loads over the piles. Piles used when the soil bearing is not enough to carry loads of the structure. Figure 1  construction management: concrete construction bridge construction:How to become a bridge engineer Pile cap construction procedure Excavation around piles: After 7 days of the casting of the pile the concrete will gain approximately, 70% of it is compressive strength. The soil around piles will be removed to the required levels and dimension that allows construction of the pile cap. A step shall be made if the excavation is more than 1.5 m to prevent soil collapse. Figure 2 Pile head cutting: Concrete will be removed up to cut off level. If concrete under the cut off level is unsound. It shall be removed, and the pile will be repaired...
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stress-strain diagram for aluminium alloy and rubber

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figure no:1 showing the stress-strain diagram for aluminum alloy. we can notice from the stress-stress diagram that aluminum has a considerable ductility. despite the absence of explicit yield point as in structural steel . the initial portion of the stress-strain curve is linear with a recognizable proportional limit. the proportional limit for aluminum alloy ranges from 70 to 410 Mpa (10 to 60 Ksi). aluminum alloy undergoes large strain before failure. ultimate stress ranges from 140 to 550 Mpa (20 to 80 Ksi). construction management: concrete construction bridge construction:How to become a bridge engineer Figure-1 Yield stress for aluminum alloy can be determined by drawing offset line parrel to the linear portion of the stress-strain curve. the straight line offset by a standard strain such as 0.002. the intersection point with the stress-strain curve is the point of yield stress. figure no:2 illustrates the concept of offset method. yield stress acquire...
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Non-Working Pile Testing and Static Compression Load Test

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Purpose of Non-Working Piles Non-working piles are constructed at the beginning of the project to evaluate soil bearing capacity and determine the maximum settlement. These piles are loaded up to twice the working load. Based on the test results, the pile length may be adjusted. If the measured settlement exceeds the allowable limit, the pile length will be increased accordingly. construction management: concrete construction bridge construction:How to become a bridge engineer Static Compression Load Test The static compression load test provides insight into how the pile responds to loading. Settlement is measured at different load increments to determine the appropriate pile design length. The maximum applied load is typically twice the working load (2 × working load) or as specified by local standards. The following steps outline the testing procedure: A. Steel Cage Preparation The steel reinforcement cage is prepared in accordance with the approved shop drawings. ...
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Repairing of concrete bulging

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Improper designing and installation of formwork for a concrete member can result in concrete Bulging. During the placing and compacting of concrete, forms may deflect largely in the weak areas. The deflection of forms will cause concrete to expand at this location, and this known as concrete Bulging. Concrete Bulging will spoil the appearance of a concrete member. Therefore we should always ensure that the forms are appropriately installed, and it is sufficiently supported to resist the concrete during placing and compacting. Bulging should be repaired in case we couldn't avoid it. The solution of concrete Bulging, offset, or surface irregularities are surface grinding. However, excessive surface grinding can weaken the concrete.  Figure 1 If the bulging or surface irregularities are small, grinding of concrete surface will be sufficient to remove surface irregularities. If the Bulging of concrete is significant, then the concrete should be chipped, and the surface...
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Concrete repair-selecting the repair method

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Repairing concrete structure passes through various stages. Selecting the correct repair method will depend on completing the previous steps, such as determining the cause of concrete damage, evaluate the extent of the damage, and assess the need for repair. The completion of these steps will define the type of conditions the repair must resist, the available repair construction time period, and when repairs must be accomplished. The data collected from performing these steps will help in selecting which of the 15 standard methods is suitable and durable for repairing the damaged concrete structure. Figure 1 In general, the old concrete surface should be prepared before beginning with the repairing process. It is essential to remove all unsound concrete before applying the repairing. Improper preparing of damaged concrete structure will result in unsatisfactory repair with low durability. The first step in preparing the old concrete surface is the saw cutting of repairin...
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Bridge Diaphragm

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The main function of diaphragms is to provide a stiffening effect to deck slab in case bridge webs are not situated directly on top of bearings. Therefore, diaphragms may not be necessary in case bridge bearings are placed directly under the webs because loads in bridge decks can be directly transferred to the bearings.On the other hand, diaphragms also help to improve the load-sharing characteristics of bridges. Diaphragms also contribute to the provision of torsional restraint to the bridge deck. Diaphragm will be used also to resist stresses that occurs during the post-tensioning process. Post-tensioning hardware are casted inside the diaphragm. Figure 1 construction management: concrete construction bridge construction:How to become a bridge engineer Types of diaphragm: Diaphragm at the span end: this type of diaphragms will be located between two bridge spans or at the bridge abutments. Expansion joints will be used to connect bridge spans. This ...
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Prestressing stands debonding

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  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.  
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Chamfers for concrete structures

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In general, the edges of concrete members are chamfered. Usually during the process of installing forms for a structural member such as pile cap, a chamfer a PVC chamfer as shown in figure no:1 installed at the edges of the structural members. These chamfers will form smooth slanted edges, as shown in figure no:2. The size of chamfers can be 20x20mm or more as shown on the contract drawing. The PVC chamfer fixed to forms by nails. We should ensure that the PVC chamfer fixed in their correct locations, and we should ensure that the PVC chamfer is straight and not moving up or down. Checking the alignment and location of PVC chamfer is important, so the chamfered concrete edge will have a good appearance after the form’s removal.  Figure 1 Figure 2 Chamfering the concrete edges done for many reasons such as aesthetics, some suggesting that the chamfering of concrete edges done for safety to reduce the damage of objects due to impact with sharp concrete edges. Actually, ...
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Prestressing strand manufacturing

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  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...
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