Video from my YouTube channel

Subscribe to My You tube channel

Why is larger concrete cover normally used in marine concrete?

By -

The concrete cover is provided for all reinforced concrete structures. It is provided to protect the reinforcement from the surrounding environment. The concrete cover will protect the reinforcement from the carbonation process and the ingress of aggressive chemicals. The carbonation process will reduce the Ph of concrete. Reducing the ph level of concrete will result in the acceleration of the rate of steel corrosion. Therefore concrete cover is provided to protect the reinforcement from the carbonation process. Also, the concrete cover provided to protect the reinforcement from the ingress of an aggressive chemical such as chloride. The presence of chloride can result in the corrosion of reinforcement. Protecting reinforcement from corrosion is essential. The corrosion of reinforcement will occupy a larger volume, which exerts stress on concrete, and this will cause concrete to crack and spall. 
Figure 1



 The concrete cover should be increased for structures located in a marine environment. The marine environment is considered an aggressive environment, and it contains a higher amount of aggressive chemicals compared to other environments. Therefore concrete cover should be increased for structures that exposed to the marine environment. Usually, a minimum cover of 75 mm is used for the structure located in a marine environment. 

Comments

Post a Comment

Videos from My Youtube channel

Popular posts from this blog

Rebar Splicing and Overlapping — ACI 318-19 Requirements Explained

By -
Image
Reinforcement splicing or overlapping is a fundamental requirement in reinforced concrete structures. Because reinforcement bars (rebars) are manufactured in limited standard lengths—typically 12 m —it becomes necessary to splice or overlap them to achieve the required continuity in structural members. The main purpose of a splice is to ensure smooth stress transfer between adjacent bars through the surrounding concrete. The overlap length, commonly known as the splice length , must be long enough to safely transfer the tensile stresses from steel to concrete without causing bond failure. It is recommended to avoid splicing in high-stress zones such as areas of maximum moment, and to stagger the splices to prevent congestion and reduce stress concentration. The ACI 318-19 providing the following recommendatin and requirement for the lap splicing: 1. Splice Limitation by Bar Size Lap splicing is not permitted for reinforcement bars larger than 36 mm in diameter. 2. Non-Contact L...
Read more

Pile cap

By -
Image
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...
Read more

Binding wire for steel reinforcement

By -
Image
  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 ...
Read more

stress-strain diagram for aluminium alloy and rubber

By -
Image
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...
Read more

Repairing of concrete bulging

By -
Image
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...
Read more

Non-Working Pile Testing and Static Compression Load Test

By -
Image
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. ...
Read more

Bridge Diaphragm

By -
Image
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 ...
Read more

Cofferdam structures

By -
Image
  Cofferdams are temporary structures used as a barrier to keep out the water and soil during the construction of a permanent structure such as a foundation in a maritime environment. The loads imposed on cofferdams structure includes hydrostatic forces of the water and dynamic forces due to waves and currents. The construction of cofferdams is a tough job since it is usually constructed offshore and in severe weather conditions. Therefore, the tolerance of construction may deviate from the design due to construction conditions, and cofferdams elements may deform significantly during cofferdam construction.  Figure 1 For a typical cofferdam, the construction sequence will be as follow. The construction of the cofferdam will begin with the preparation of the cofferdam area. The soil and sediments will be removed, and the area will be leveled.  The temporary support piles will be driven, and temporary supporting frames will be erected on support piles.   Figure 2 Drive...
Read more

The reasons behind the trimming of pile head

By -
Image
In general, the bored piles are casted to a level higher than the required pile cut-off level. Pile cut-off level is usually similar or a little bit higher than the blinding level of a pile cap. the process of constructing a cast-in-situ pile involves the following steps: installation of the temporary casing to prevent the soil collapse during the drilling process and to guide the drilling rig. Drilling the pile to the required level and diameter. Installation of a reinforcement cage. Reinforcement cage vertical bars will be extended above the pile cut-off level to improve the bonding with the pile cap. The casting of concrete usually done with a tremie pipe. Tremie pipe will be lowered to the bottom of the pile, and then the concrete will be poured. Once the casting is completed, the temporary casing will be removed. It is a common practice to cast the concrete above the cut-off level. the concrete casted then removed for the following reasons: during the casting pro...
Read more

Prestressing stands debonding

By -
Image
  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.  
Read more