Bond Strength Comparison Between Normal Water Concreting and Sea-water Concreting

Introduction

Throughout the world there are so many living areas which are located on the coastal area and islands. So, the process of building construction work have the heavy trend to work with seawater, therefore making use of seawater is an interesting innovation. Most important aspect of reinforced cement concrete is the compressive strength then the bond strength between steel reinforcement bars and concrete. Also, the water cement ratio (w/c) plays a vital role in concrete structures exposed in coastal areas.Portland composite cement is one of the largest and newest used cement in concrete by today.

In the research Adnan, Herman Parung, M. W. Tjaronge, Rudy Djamaluddin aimed to study and utilize seawater in concrete works and the concrete property difference between normal water concrete and seawater concrete. The method used in the research in totally experiment based.

From the year of 2007 many of researchers have done so many studies on bond strength between steel and concrete, however there are very limited information on seawater concrete.

Bonding Strength

Bond strength is the ability of reinforcing steel and concrete covering it in resisting forces from the outside or other factors that can cause the detachment of bonding between reinforcing steel and concrete. Bonding strength between reinforcement bar and concrete can cause for :

the chemical adhesion between the reinforcement bar and surrounding concrete;
frictional forces caused by roughness between reinforcement bar and concrete;
bearing forces on the concrete from the bar deformations.

Hence the bonding strength between reinforcing steel with concrete can be calculated by

Where:

τmax: Bond strength of reinforcement steel in concrete (N/mm2 ),

Pmax: Maximum load (N),

D: Reinforcement steel diameter (mm),

l: Embedded length (mm).

Properties of Materials

Concrete is a heterogeneous mixture of homogeneous materials, namely cement, aggregate, and water. In general, concrete contains about 1-2% air content, cement paste (cement and water) around 25-40%, and aggregates (fine aggregate and coarse aggregate) around 60-75%, respectively.

* All tables and data are collected from the journal "Bond between Steel Reinforcement Bars and Seawater Concrete" by Adnan, Herman Parung, M. W. Tjaronge, Rudy Djamaluddin, Civil Engineering Journal Vol. 6, Special Issue "Emerging Materials in Civil Engineering", 2020

Research & Results

Compressive Strength Test

The compressive strength test were carried out in three cubes specimens of dimensions 150×150×150 mm. The specimens were tested with UTM. At water-cement ratio (w/c) of 0.55, the average compressive strength of normal concrete is 23.00 N/mm² , while seawater concrete has a average compressive strength of 21.56 N/mm² .

These results indicate that the compressive strength of seawater concrete is 6.26% lower than that of normal concrete.

Bonding Strength Test

In the test of bonding between concrete and reinforcement was carried out with reference to RILEM and ACI 408R-03. The specimen was placed on a flat plate of confinement cage and the reinforcement was subject to tensile loads. This method can cause compressive stress on the concrete on one side and tensile stress on the reinforcement on the other side. The selection of test specimens in that study was planned so that the stresses that occur can typify the stress conditions in reinforced concrete structures. Based on the above considerations, this study determined a cube-shaped specimen with dimensions of 150×150×150 mm employed in the pull out test. Deformed steel bar with a diameter of 16 mm was embedded 5 times of its diameter (the bonded section length was 80 mm). The pull-out load was gradually employed until attaining the ultimate bonding stress.

In the pull-out test of steel reinforcement in normal concrete with a water cement ratio (w/c) of 0.55, the test specimens were treated with water curing for 28 days without acceleration (normally there was no rust). Below mentioned curve shows the research mix design.

At water-cement ratio (w/c) of 0.55, the bonding strength of normal concrete is 11.15 N/mm² , while seawater concrete has a bonding strength of 10.66 N/mm² .

These results indicate that the bonding strength of seawater concrete is 4.34% lower than that of normal concrete.

Conclusion

From the experiments and analyzes in this study, we can conclude that the water cement ratio (w/c) affects the compressive strength of concrete and the bonding strength. The compressive strength of concrete and the bonding strength got effected due to the quality and chemical components of sea water. Based on the study of bonding strength of steel bar in normal concrete and the seawater concrete, the findings were made :

Normal and seawater concrete had compressive strength of 23.00 and 21.56 N/mm² , respectively.
Normal and seawater concrete had bonding strength of 11.15 and 10.66 N/mm² , respectively.

The results of the analysis show a less pronounced decrease in compressive strength of 6.26% against the compressive strength of normal concrete and f the bonding strength of sea water concrete showed a less pronounced decrease in bonding strength of 4.34% to the bonding strength of normal concrete. Failure of the bond strength test specimen does not occur due to leaking of reinforcement and breaking of the concrete cover. The crack width of sea water concrete against normal concrete with a water cement ratio of 0.55 w/c seawater concrete is 0.15 mm against normal concrete is 0.10 mm, the average difference is 0.05 mm.

References

"Bond between Steel Reinforcement Bars and Seawater Concrete" by Adnan, Herman Parung, M. W. Tjaronge, Rudy Djamaluddin, Civil Engineering Journal Vol. 6, Special Issue "Emerging Materials in Civil Engineering", 2020
ACI Committee, “Bond and Development of Straight Reinforcing Bars in Tension” (ACI 408R-03), American Concrete Institute, Farmington Hills, Mich., (2003)
Rilem/Ceb/Fip, Recommendation reinforcement steel for reinforced concrete. Revised edition of: RC 6 bond test for reinforcement steel; (2) Pull-out test, CEB News 73, Lausanne, Switzerland (1983)

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