Video from my YouTube channel

Subscribe to My You tube channel

concrete workability

By -

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.






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 content.
3. Aggregate Shape:
    • Aggregates with elongated or flaky shapes reduce workability compared to rounded or cubical aggregates.
4. Aggregate Grading:
    • Well-graded aggregates improve workability by reducing voids in the mix, allowing excess paste to enhance lubrication.
5. Use of Admixtures:
    • Chemical admixtures, such as superplasticizers, increase workability while reducing the required W/C ratio, improving both flowability and strength.

Methods to Measure Concrete Workability

Concrete workability is typically assessed using the following tests:

Field Considerations

In ready-mix concrete, increasing workability by adding water on-site is strictly prohibited because it increases permeability, ultimately reducing both strength and durability. Instead, workability should be adjusted using proper mix design and admixtures.



Comments

Post a Comment

Videos from My Youtube channel

Popular posts from this blog

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

Example 1:Flexural stress calculation using transformed area method for rectangular beam with double layer of reinforcing bars

By -
Image
assume the section for beam shown in figure 1 cracked calculate the flexural stresses for the given load or moment using transformed area method. construction management: concrete construction bridge construction:How to become a bridge engineer Figure 1 first, we will calculate the transformed area of steel. the concrete below the neutral axis will not contribute to resisting of tension. figure 2 shows the section after transformation  As=6*1=6.0in2 Transformed area for first layer=As*n=2*8=16in2 Transformed area for second layer=As*n=4*8=32in2 figure 2 Neutral axis can be calculated by equalling moment of area from both parts as shown below  16*(18-x)+32*(21-x)=(x/2)*(14*x) 960-48x=7x^2 7x^2+48x-960=0 x=8.77 in moment of inertia for transformed area= =(14*8.77^3)/12+8.77*14*4.385^2+16*9.23^2+32*12.23^2=9297.20in4 =0.44835ft4 flexural stress for compression zone. y at extreme compression equal 8.77in=0.73ft fc...
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

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

Analysis of T Beams

By -
Image
Analysis of T beam is similar to rectangular beam. same equations will be used if 'a' is less than the depth of flange hf. "a" is the depth of compression block. if "a" is larger than hf. compression stress will be distribuated over flange and web. flange and web has different width. therefore the compressive force C=0.85*fc'*hf*bf+0.85*fc'*(a-hf)*bw as shown in figure 1. Figure 1 construction management: concrete construction bridge construction:How to become a bridge engineer the procedure of analyzing of T Beams Compute T=As*fy determining if a > or < hf by calculating AC=T/0.85*fc', if AC>Area of flange(hf*bf) then a is more than hf if a<hf As*fy=0.85*fc'*a*bf a=(As*fy)/(0.85*fc'*bf) if a>hf AC=AC by flange +AC by web AC by web=(AC-AC by flange) bw*(a-hf)=(AC-AC by flange) a=(AC-AC by flange)/(bw)+hf AC by flange=0.85*fc'*hf*bf for this case we need to de...
Read more

shear key

By -
Image
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...
Read more

Chamfers for concrete structures

By -
Image
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, ...
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

Impact of Hot Weather on Concrete and Necessary Precautions

By -
Image
Concrete placement should not be permitted if the ambient temperature exceeds 38°C to 40°C . hence, it is recommended to place concrete when temperature is less than 35°C . If the temperature reaches 35°C or more, special precautions must be taken, as hot weather accelerates water evaporation from the concrete. This rapid evaporation negatively affects the hydration process, leading to reduced concrete strength and durability. Adverse Effects of Hot Weather on Concrete Increased Shrinkage – high temperatures cause excessive moisture loss, leading to greater shrinkage in concrete. Higher Risk of Cracking – Rapid drying can induce thermal and plastic shrinkage cracks. Reduced Durability – Increased evaporation increase concrete porosity, compromising its long-term strength and resistance to environmental factors. construction management: concrete construction bridge construction:How to become a bridge engineer Special Measures to Mitigate Hot Weather Effects To minimize ...
Read more

wing wall arrangement and orientation for abutments

By -
Image
wing wall main function is to retain the embankment near abutment. the common slope is 2:1. greater than 2:1 is not allowed. figure no: shows a wing wall for the abutment. Figure 1  there is three arrangement for wing wall: wing wall parallel to abutment: easy to build. construction can be done in a short time. this type of wing wall will not disturb the existing embankment and utilities but it is not the most economical arrangement.   figure 2 construction management: concrete construction bridge construction:How to become a bridge engineer wing wall at an angle with abutments: this type is most economical among the three arrangement. Figure 3 wing wall perpendicular to abutment: in this arrangement. wing wall provides a continuous alignment with bridge deck which can be used to support parapets. this arrangement will disturb existing embankment and utilities adjacent to the structure. for curve bridge, this type o...
Read more