Video from my YouTube channel

Subscribe to My You tube channel

concrete workability

By -

 concrete workability is a property of concrete determining the ease of mixing, placing and compacting concrete with minimum loss of homogeneity.







Factors affecting workability 

  1. W/C: increasing of water-cement ratio will increase concrete workability but it will reduce the strength of the concrete mix. increasing water-cement ration will increase concrete permeability and this will reduce concrete strength and durability. on the other hand, using concrete with little water insufficient to interact with cement particle to cause hydration this will result in strength reduction. W/C usually ranges from 0.35-0.40.
  2. size of aggregate: Bigger size of aggregate means lesser surface area. as a result, the amount of water required for wetting the aggregate surface is lesser than the smaller size.and this will result in higher workability for the same water content.
  3. the shape of aggregate: aggregate with elongated flaky shapes will reduce the workability of concrete compared to round or cubical aggregate.
  4. Grading of aggregate: well-graded aggregate will enhance concrete mix workability. when the voids are reduced, extra paste will be available to give better lubricating effects.
  5. using of admixture: adding of admixture such as superplasticizers helps in increasing concrete mix workability and reduce W/C. 
Measuring concrete workability

concrete workability can be measured using one of these tests:
adding water to increase concrete workability at the field(for ready-mix concrete) is highly prohibited because it will increase concrete permeability and this will reduce strength and durability of concrete.

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

Bundled Bars

By -
Image
sometimes the required reinforcement bar will not fit for a given section of beam or girder, in this case, we resort to bundling a group of parallel bars, up to four bars can be bundled together,  ACI 7.6.6.2 stating that bundled bars should be enclosed within stirrups or ties, bundled bars should be tied, wired and fastened together to ensure remaining in position whether vertical or horizontal, ACI 7.6.6.3 stating that bars have diameter greater than 36 mm(#11) shall not be bundled in beams, the limitation of bundled bars size is for beam or girders in building, the small size of building members make it unpractical to bundle bars with size larger than 36mm(#11), in bridges the size of members are bigger and therefore it is allowed to bundle up to two bars with size greater than 36mm (#11). figure 1 showing bundle bar arrangements. figure 1 construction management: concrete construction bridge construction:How to become a bridge engineer when two or more ...
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

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

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

Driven piles

By -
Image
Driven piles have been used widely as a foundation for different structures. In this type of foundation. Piles are driven to soil mechanically using a hammer. There are enormous types of driven piles. construction management: concrete construction bridge construction:How to become a bridge engineer  Steel H Piles Section of H-pile consists of flange and web, as shown in figure no:1. They are driven using a high impact hammer, and the likelihood of pile damage is low. H-piles resists the loads through skin friction or end bearing or both. Since the displacement of soil is minimal, this type of piles can be driven into dense granular soil or stiff clay layers. Although some problem during driving may arise. Plugging is one of them. After driving the pile to a certain level. soils will adhere to pile web and between the flange creating a closed end. This will change the pile to displaced pile and complicate pile driving. H-piles should be protect...
Read more

Casing for piles

By -
Image
The casing is a thick steel tube. The casing used extensively in construction drilled piles. The casing used to guide the drilling rig to drill the pile hole in the correct location. Also, it can be used to stabilize and prevent the soil from collapse until the concreting of the pile is completed. Furthermore, the casing will be used to hang the steel cage until the concrete is poured. The used casing should be thick and strong enough to resist the imposed stresses during the installation and removal process for temporarily casing. The casing should be clean, smooth, free from encrusted concrete, or any damage that can affect the size and shape of the pile. Figure 1 The casing length will vary according to the purpose of use and the type of the soil. If supporting fluids are used to stabilize the soil, the casing will be used as a guide for the drilling rig. Therefore, the casing length will be short. If the casing is used to support the soil, the casing length should be s...
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

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