Synopsis:
This paper maps the advancement of anti-washout admixtures for the first time on the Indian subcontinent. The anti-washout admixture was called for to be used to construct a weir for the Srisailam Dam throughout the Krishna River in Andhra Pradesh, India.
The project called for 30000 cubic meters of concrete to be done underwater without the erection of a cofferdam, and the job expense was approximately around $5.6 million.
The professionals were SNC Javelin, Canada, and the contractors were Patel Engineering, India. Because there were no producers of anti-washout admixture in India, this was a significant advancement from Sunanda Global’s lab, including over 100 trials that finished regarding 90000 liters of the admixture being used in the job.
INTRODUCTION
In mega hydropower structures and for mass underwater concreting projects like the construction of weirs, concreting for dams, and erection of caissons, concrete placed underwater is inherently prone to cement washout, laitance, partition, chilly joints, and also water entrapment.
Consequently, concrete placed under water is required to remain natural. A high degree of cohesiveness enhances homogeneity and the undersea concrete’s strength by reducing cement washout.
The required degree of concrete communication depends on many variables, such as the thickness and arrangement of placements, flow distance, required in-place strength, and exposure to moving water during the sequence.
At the same time, it should have some one-of-a-kind workability qualities. The crucial workability demands are that the concrete move quickly, preserve excellent communication against washout and segregation, and have self-settling attributes (because it is not practical to consolidate concrete underwater using mechanical resonance).
Figure 1. The Kinetic States of concrete as it is placed underwater
Concrete put undersea usually undergo a vast array of kinetic states, i.e., concrete fails a tremie pipeline at a high rate, blends and drains the tremie pipeline at slower speeds, and finally consolidates under pseudo fixed conditions.
Undersea concrete needs to drain the tremie pipe quickly, load the placement area, and combine under its weight. It is reported that the workability of undersea concrete needs to be higher than 175mm depression which assists in self-debt consolidation under its very own resilient weight.
The workability of undersea concrete includes different needs, such as self-leveling and high anti-washout features.
Research shows that high in-place concrete quality is carefully about the means concrete flows underwater. Examinations expose that concrete typically streams undersea, complying with Pattern 1: Bulged circulation; Pattern 2: Layered circulation.
Figure 2. Bulged Flow
When concrete is very flowable and cohesive, it tends to move in a “bulged circulation pattern” where freshly positioned concrete pushes formerly placed concrete sidewards, forming a successive collection of lumps.
It has been found that bulged flow pattern tends to create concrete with a reasonably level, smooth leading surface area and excellent high quality in place.
Figure 3: Layered Flow
On the other hand, less flowable concrete flows in a “split pattern” were recently positioned concrete flows up-wards around the positioning pipeline and over the top of the previously placed concrete.
This layered flow pattern subjects much more concrete surfaces to water and is generally related to outstanding sloped and rugged leading surface areas with a large quantity of laitance.
Hence it was comprehended and developed that the mix percentages of undersea concrete needed to compromise its flowability and communication. Without admixtures, these two inversely associated properties might not be acquired because higher flowability results in less natural concrete and vice versa.
WEIR PROJECT AT SRISAILAM, HYDERABAD-INDIA
M/s Patel Design Ltd, Mumbai, are the pioneers in the hefty civil engineering building and construction considering that the 1950s, especially in hydropower structures, were awarded the task as complete professionals for building a weir project at SriSailam, Andhra Pradesh.
PROJECT DETAILS:
Project Title: Weir Project at Srisailam Dam, Andhra Pradesh
Clients: Andhra Pradesh Power Generation Company (APGENCO)
Clients Consultants: SNC Lavelin Limited, Canada
Contractors: Patel Engineering Limited, Hyderabad
Concreting for Weir: 30,000 cu.m. (39,244 c.y.)
Dredging quantity: 40,000 cu.m. (52, c.y.)325
Estimated Project Cost: Rs. 25 Crores (approx $5.6 million)
MIX DESIGN DETAILS OF UNDERWATER:
Desired Strength: M20 grade concrete
Slump requirements: 170 mm – 230 mm with admixtures
Anti-washout admixture specified for tremie concrete.
The efficiency of anti-washout admixtures shall be determined based on the USA Corps of Engineers specification CRD-C61–” Test approach for figuring out the resistance of newly blended concrete to rinsing in water,” issued on December 1 st, 1989.
The maximum washout shall be at most 8% cumulative mass loss.
The tremie concrete mix will minimize water, retarding, and anti-washout admixtures. 15% of the cementitious material shall consist of a natural pozzolan or fly ash. Conversely, 8-10% silica fume might be used rather than an all-natural pozzolan or fly ash.
NEW BEGINNING
M/s Patel Design, Mumbai, and the specialists tried to resource anti-washout admixtures in the Indian subcontinent. Many building chemical suppliers concluded that the admixture would require to be imported. In addition, the effectiveness and compatibility of such an admixture can be determined just after lab and site trials.
Additionally, sourcing the product from outside India implied a hold-up in purchasing material for the currently granted time-bound agreement. Finally, the economy began to break down due to the different products and import duties.
M/s Patel Design in January 2004, then approached one of the leading building chemicals manufacturing firms in Mumbai, India, with an ISO 9001:2008 accreditation for R & D to create and produce an anti-washout system for the very first time in the nation.
RESEARCH & DEVELOPMENT EFFORTS
On the worldwide scene, the growth of anti-washout admixtures for undersea concreting was a reasonably new development. Although initial work was well established in the early seventies, the conclusive job was reported in the early nineties.
The task was divided into two components:
I. Product development, mix design trials, and site testing from Jan 2004 to Apr 2004.
II. Placement of 30000 cu. m. (39,000 cm) of underwater concreting from May-June 2004.
The R & D department of the chosen firm is recognized by ISO 9001:2008 and has in-house abilities to create products. Following a considerable literature study, a speculative program was begun at the R&D laboratory.
For virtually two months, numerous experiments were conducted to ensure that the wanted needs of a downturn, anti-washout homes, and stamina after seven days, in addition to simultaneous compatibility with fly ash and concrete, were satisfied.
After more than 100 tests, the final formula was created and was satisfying regarding anti-washout properties, compatibility, and wanted advancement of the stamina of concrete. After this, various tests were carried out at the concrete lab of Jawaharlal Nehru – Technological University, Hyderabad (JNTU) in the existence of the company’s R & D engineers, and also engineers from Patel Design Ltd and concrete technologists from JNTU.
SUCCESSFUL TRIAL
| w/c Ratio | 0.45 |
| Cement | 7.980 Kg (17.60 lbs) |
| Fly Ash | 2.660 Kg (5.86 lbs) |
| C.A. – 40 mm (1.57 in.)
20 mm (0.80 in.) |
20 Kg (44.00 lbs)
10 Kg (22.00 lbs) |
| Sand | 9.580 Kg (21.12 lbs) |
| Dust (0-5) | 9.580 Kg (21.12 lbs) |
| Water | 4.880 l |
| Superplasticizer | 70 ml |
| Anti-Washout Admixture | 10 ml |
| Slump | 170 mm (6.70 in.) |
The primary purpose of this workout was to create a user-friendly product that can be easily handled on challenging sites on rugged terrains. The completed product was additionally tested for skin irritability after performing tests on human beings, and the outcomes of these trials were discovered adequately.
After an acceptable test arose from the JNTU and authorization from the consultants, around 10000 liters of anti-washout admixture and 78,000 liters of suitable superplasticizer were dispatched to the project site at Srisailam.
These customized materials were made and delivered to the project site at Srisailam in Andhra Pradesh at an average of 10,000 liters per day in 8 consignments.
QUALITY ASSURANCE
As per ISO standards, quality control at all stages was strictly followed. This included quality control of raw materials, procedure control, quality assurance of ended-up items, and quality control of product packaging.
After the actual research laboratory tests, numerous on-site tests were conducted to monitor and examine concrete actions after admixing the designed anti-washout admixture and suitable superplasticizer.
To keep an eye on the quality assurance at the site, a team of R&D scientists, concrete technologists, and amount property surveyors were released from the making firm in Mumbai to the website at Srisailam, Andhra Pradesh.
Figure 4: Project site of Srisailam Dam, Andhra Pradesh, India
CONCLUSIONS
One of the best difficulties challenging the concrete market in the 21st century is meeting the enormous demands of a rapidly industrializing and urbanizing world and the conservation of nationwide sources.
In the Indian context, that implies the preservation of limestone reserves (used for concrete production), using auxiliary ingredients (fly ash, GGBS, silica fume) to concrete, and executing logistics regarding decreasing the carbon footprint of all linked procedures.
The development of anti-washout admixtures has had a revolutionary effect on the efficiency and sustainability of sunken concrete. Undersea concrete can accomplish high flowability at a low water-cement proportion and preserve appropriate cohesion to withstand concrete washout, partition, and bleeding.
Successful underwater concreting using the anti-washout admixture and fly ash at Srisailam dam, Andhra Pradesh, played a significant role in conserving more than 7 million lots of concrete which otherwise would have rinsed (45% saving in direct concrete price).
The usage of more than 3 million tons of fly ash (resulted in 20% cost savings due to the substitution of cementitious products). The job was finished in 45 days, creating a total decrease in the carbon impact.
Largely this breakthrough in anti-washout technology for the first time in India has made the building of hydraulic structures lasting. Hydraulic frameworks are vital for making India self-adequate regarding hydropower tasks, irrigation projects, etc.
Using such anti-washout admixtures has opened up methods for numerous applications in the building market in India any place underwater concreting becomes needed, such as situations of seismic retrofit layout and building and construction of bridges, tremie concreting to attach precast concrete pile caps, undersea repair of stilling containers, concreting for caissons, concreting for jetties, weirs, dams, canals, etc.
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