Concrete solutions

HamidReza Hassanli, Ehsan Emamifard Naeeni and Mansoureh Hasanzadeh discuss their experiences with self-compacting concrete

Construction of marine structures, including quays, is regarded as an expensive, difficult and challenging task the world over.

In Iran, financial constraints and a need to extend the service life of marine structures require that Preventive Maintenance be undertaken at ports jetties to safeguard national resources. Indeed, Iran’s Ports and Maritime Organization (PMO) has given a high priority to the repair and maintenance of existing structures including quays in recent years.

During the recent repair process carried out for quays 4 and 5 in Bushehr Port, engineers combined traditional repair materials with alternative ones in the form of self-compacting concrete for the sections where conventional concrete could not be used, those being in the repair of piles and the slabs beneath the decks.

Prior to the work taking place, special tests were administered to ensure the proper application of the method. This marked the first time that self-compacting concrete had been used for berth repair in Iran’s ports. 

Before opting to use self-compacting concrete, the team working on the project identified the weaknesses of traditional methods while undertaken repairs and then opted for the most reliable solution suitable for the characteristics of Bushehr’s marine environment. The team also varied the ratio of granules to ascertain the best mixture. 

The number one priority was to enhance technical quality in order to support the necessary marine operations and safe berthing. As part of its investigation, the team examined different viscosities of concrete in the varied mixes, as well as the outcomes of increasing of the number of holes for air outlets and decreasing the shearing distance for bars.   

The repairs at were targeted at damaged sections of quays 4,5 and 6, where around 500 metres needed urgent repairs to boost their service quality. The worst damage was on quays 4 and 5 over a 350 metres span of concrete piles and concrete decks. The project scope consisted of: 

  • Repairing the concrete piles with self-compacting concrete;
  • Repairing the slabs below the decks with self-compacting concrete;
  • Repairing the deck forehead and surface with conventional concrete;
  • Repairing and fixing the fender system (including the support fenders, frontal fenders, frame and chains); and
  • Construction and installation of pre-cast car-stoppers with conventional concrete.

The findings

The experiences on the project team are summarised here: 

Self-compacting concrete: The high fluidity of self-compacting concrete obviates the need for vibrators for its compaction, enabling it to be used in complex shapes of formwork which may otherwise be impossible to cast, giving it a far superior surface than conventional concrete. The common tests for this concrete in its wet status include: V shape funnel, slump test, Slump flow test T50, and tests after placing such as: compressive strength, Pull-off strength and pull-out strength. 

Piles concrete placement: Having identified the damaged sections of the old concrete in the concrete quay piles, reinforcements and damaged bars were replaced or deoxidized and then formworks were placed around the damaged piles. Then self-compacting concrete was cast into the formworks through a 10 cm hole made on the surface of the deck (without demolishing it).

Concrete placement for the slabs under the decks: After marking the areas of damage and removing the damaged layers of old concrete in the slabs under the deck up to the reinforcements, the damaged steel bars were either replaced or deoxidized and then the formworks were placed under the deck by means of shear reinforcement rods placed between the old and new concrete at planned distances of 75 cm to increase shear strength of the joint sections of old and new concretes. Concrete casting was done through a 10 cm wide hole on the deck. It needs to be noted that holes of 2.5 cm diameter were drilled in the deck in order to let the air imprisoned between the self-compacting concrete and the old one to escape. 

Concrete placement evaluation – piles: The piles were controlled by quality control tests during placement operations (including a slump test, Slump Flow Test T50, and compressive strength test), in addition to pull-off tests. The results confirmed the proper implementation of self-compacting concrete in piles and also the high adhesion between the new and old concrete. Table 1 displays the mean values for self-compacting concrete characteristics used in piles.

Concrete placement evaluation – slabs under the deck: During implementation and after completion of the concrete placement operations for the slabs under the deck, they were tested by different quality control tests such as slump test, slump flow T50, compressive strength test and pull-off test. The results were in an acceptable standard range, however, the results of pull-off test indicated an unsatisfactory adhesion degree between the old and new concrete. Further analysis attributed this failure to the improper movement of the concrete in the formworks, imprisonment of air between old and new concrete and concrete shrinkage. Shotcrete concrete was used in some parts of the decks, however during the coring operations for the pull-off test and prior to the implementation of the pull force, the cores separated from the concrete joints, a problem which made the team totally abandon using shotcrete and instead focus on the use of self-compacting concrete. 

Seven suggestions

Based on its experiences, the team developed seven suggestions for the improvement of self-compacting concrete and on ensuring sufficient adhesion between old and new concrete. Their studies revealed that these modifications can have a considerable influence on the final outcome of a project: 

  1. The use of round river sands instead of granite sand;
  2. Change the proportion of admixtures (decreasing rock flour and increasing sand);
  3. Add a limited amount of additive materials to enhance adhesion between self-compacting concrete and old concrete
  4. Increase the height of concrete funnel (one metre);
  5. Increase concrete viscosity by replacing parts of cement with micro silica; 
  6. Increase the number of holes for air outlets;
  7. Decrease the distance of shearing bar rods from 0.75×0.75 to 0.35×0.35.

Applying the above guidelines led to the problem of concrete adhesion between the old and new concrete being resolved to an acceptable degree. Consequently, the result of the pull-off tests was satisfactory.

Through sharing their experiences at Bushehr Port, the project team hope to offer guidelines and solutions for ports facing a quay repairs and considering the use of self-compacting concrete. In conclusion, since shotcrete is particularly vulnerable in corrosive marine environments, self-compacting concrete can be used as a suitable alternative for it. Unlike shotcrete, self-compacting concrete is much stronger, has more adhesion, is less permeable, provides a longer service life and, hence, successfully passes pull-off tests. 

HamidReza Hassanli and Ehsan Emamifard Naeeni are with Sazeh Pardazi Iran Consulting Eng Co, based in Tehran, Iran. They can be contacted on Hassanli@sazehpardazi.com and Emami@sazehpardazi.com respectively.. Mansoureh Hasanzadeh is with Bushehr Ports & Maritime Organization (BPMO), Bushehr, Iran and can be contacted on mhasanzade@alumni.ut.ac.it.

Table 1. Piles self-compacting concrete characteristics

Pull-off (Mpa)

Compressive strength 28 days (kg/cm2)

T50 (s)

Slump flow (cm)

Specifications

Min 2.0

350

3 -7

5 ± 70

Standard Rate

2.5

439

3.8

70.4

Samples mean


Table 2. The characteristics of self-compacting concrete for slabs beneath the decks (before and after modification)

Pull-off (Mpa)

Compressive strength 28 days (kg/cm2)

T50 (s)

Slump flow

 (cm)

Specifications

Min 2.0

350

3-7

5 ± 70

Standard Rate

0.5

470

3.6

70.9

Samples mean

Before modification

2.05

445

3.2

74.0

Samples mean

After modification

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