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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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Working piles (cast in situ piles)

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Various Methods Used in Constructing Cast In-Situ Piles The general concept of cast in-situ pile construction remains the same across various methods, with minor differences. Bored pile diameters typically range from 600 mm to 3000 mm, with depths reaching up to 70 m. This provides designers with significant flexibility to customize foundation designs according to site conditions and optimize costs for an economical solution. construction management: concrete construction bridge construction:How to become a bridge engineer cast in-situ piles method of construction: Casing Installation The depth of casing varies based on site conditions and soil properties. In the presence of loose soil, the casing length should be increased. The use of bentonite can help prevent soil collapse, reducing the required casing length. The primary function of the casing is to prevent soil collapse in loose soil conditions or when soil-supporting liquids are absent. It also allows land s...
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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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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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Bar Bending schedule (BBS)

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 The bar  bending schedule is a table that contains the details of reinforcement for a specific structural member such as footing, column, slab, and others. The bar bending schedule will contain the bars' dimensions to be used, the shape of the bars, the size of bars, bar mark, number of bars, and the weight of bars. BBS will be used to determine the weight of reinforcement required for a specific structural member.  there are various advantages of bar bending schedule such as: estimating the quantity of reinforcement for each structural member. So we can estimate the amount of reinforcement required for a construction project.  BBS will help in reducing the losses of steel by procuring the precise quantity of different rebar diameter.  BBS will reduce the wastage of reinforcement by providing the engineers with the exact dimension and shape of rebars. Knowing the exact dimension and shape will reduce the time of cutting and bending rebars.  BBS will reduce...
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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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shear key

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The purpose of the shear key is to improve the bonding between concrete surfaces. The shear key is usually made at the construction joint location to enhance the adhesion between the old and new casted concrete. Construction joint is considered a weak point because the concrete is not casted at one time, in large structures where the concrete can not be casted for some members at one time, such as a slab. We usually divide the slab and cast it at many stages. The large quantities of concrete will make it impossible to cast the slab at one time. Therefore, the casting will be done in several stages. The location of the construction joint should be selected carefully. Construction joint shall be made at the location of minimum shear and moment.  The bonding between old and new concrete can be improved by roughening the old concrete and forming a shear key on the concrete surface while the concrete is still plastic. The shear key can be formed by pressing timber into the concrete surf...
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Flakiness Index and Elongation Index of Coarse Aggregates

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Flaky and elongated aggregates can adversely affect concrete. Flaky and elongated aggregates are difficult to compact. Therefore using flaky and elongated aggregates will reduce concrete workability, which required more amount of water to produce a workable mix. Increasing water content will reduce concrete strength and durability. Moreover, these aggregates are not robust, which leads to lowering concrete strength. Figure 1 construction management: concrete construction bridge construction:How to become a bridge engineer The Flakiness Index of aggregates is the percentage by weight of particles whose least dimension (thickness) is less than three- fifths (0.6times) of their mean dimension. This test does not apply to sizes smaller than 6.3mm. The Elongation index of an aggregate is the percentage by weight of particles whose greatest dimension (length) is greater than nine-fifths (1.8times) their mean dimension. Flakiness and elongation tests ar...
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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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Whitney Rectangular Stress Distribution(derivation of beam expressions)

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experimental tests confirm that the strain varies in proportion to a distance from the neutral axis in compression and tension zone within and near the ultimate stress. compression stress will vary linearly as long the maximum stress is less than 0.5fc'. once the stress exceeds 0.5fc' the distribution of compression stress will change from linear distribution to the shape shown in figure 1. compressive stress will vary from zero at the neutral axis to a maximum value at or near the extreme fiber. neutral axis location and stress variation will differ from a beam to another. this variation depends on several factors such as magnitude and history of post loading, shrinkage, creep and speed of loading. construction management: concrete construction bridge construction:How to become a bridge engineer Figure 1 for simplification whiteny replaced the curved stress block with a rectangular stress block as shown in the figure 2. compressive stress assumed to ...
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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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why do we stagger reinforcement overlapping?

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First, we should know that steel rebar comes in standard length such as 12m. using very long reinforcement is impractical because it will result in difficulties in handling reinforcement by steel fabricators. Also, longer rebar is heavier and difficult to lift and move. So for a long structure such as a slab, we require a reinforcement length that is more than the standard reinforcement. We can't use a single piece of rebar for a specific length for such a structure, so we use two or more steel rebars to cover the entire length of the structure. Figure no:1 The zone of overlapping between reinforcement will be considered as a weak zone. Therefore, it is a good practice to stagger the reinforcement overlapping. Staggering is done by overlapping the reinforcement at a different location. Staggering reinforcement overlapping will reduce the number of rebars overlapped at the same point, which will be beneficial in two ways. Firstly, it will reduce the discontinuity of rebar at the s...
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