Modelling of Strength Parameters of HVFAC Roads

Abstract

The Concrete industry across the world is facing a challenge due to the depletion of the natural minerals used in making OPC, and it has become necessary to search for other pozzolanic materials. In research, it is found that various industrial waste materials like Fly ash, Ground Granulated Blast Furnace Slag (GGBFS), Copper Slag have pozzolanic and cementitious properties. Fly Ash is one of the best materials to use in cement concrete works. Its usage has many advantages like, Concrete of better rheology, Enhanced strength and durability, Preservation of limestone reserves, and minimizing greenhouse gas emissions. High-Volume Fly Ash Concrete (HVFAC), due to above many advantages, came into existence, in which the use of fly ash has crossed more than 50% replacement of OPC (i.e., Cement: Fly ash is 50:50). Strength parameters (Compressive strength, Tensile strength, and Flexural strength) of the HVFAC play a very important role during the design, construction of the concrete members, mainly the rigid pavements. The aim of this project is to formulate Model equations for the strength parameters of the HVFAC for various water/binder ratios at different concrete ages. These models are helpful in finding out the unknown parameter by just substituting the known values in the model equations.

Introduction

A. Need of the Day

With increasing infrastructure demands, natural resources like limestone are depleting. The concrete industry faces challenges in meeting demand sustainably. As a solution, industrial waste materials such as Fly Ash, Ground Granulated Blast Furnace Slag (GGBFS), and Copper Slag are being explored for their pozzolanic and cementitious properties, reducing pollution and conserving natural resources.

B. Rigid Pavements

Rigid pavements, made from cement concrete (PCC/RCC/PSC), are widely used globally. They require large volumes of cement. Replacing cement with waste materials like Fly Ash is essential to maintain sustainability without compromising on quality. Rigid pavement structure includes:

• Surface course (strongest layer)

• Base/sub-base layers (less stiff, aid drainage and frost protection)

C. Fly Ash

Fly ash is a by-product of coal combustion, collected via Electrostatic Precipitators (ESP) in thermal power plants.

1. Availability:

• Coal-based power plants generate millions of tons of fly ash annually.

• Modern ESPs produce low-carbon, high-quality fly ash.

2. Classifications:

• ASTM C-618:

  • Class F: Low Calcium (<10%), pozzolanic.

  • Class C: High Calcium (>10%), cementitious and pozzolanic.

• IS:3812:

  • Grade-I & Grade-II: For use in cement, mortar, lime pozzolana, etc.

3. Standards for Use:

Permitted by IS:456, IS:3812, IRC:68; ACI-318 has lifted limits on fly ash usage.

4. Applications:

• PPC production

• Performance enhancer in OPC

• Cement replacement in concrete

• HVFA concrete

• RCC for dams/pavements

• Fly ash bricks and building products

D. Fly Ash Concrete

Originated from research by R.E. Davis (1937), fly ash reacts with lime in cement hydration to form additional cementitious compounds.

Benefits:

• Improved strength, workability, and durability

• Resistance to sulphate, ASR, and thermal cracking

• Lower costs and better surface finishes

• Eliminates plastering defects

E. High-Volume Fly Ash Concrete (HVFAC)

Fly ash is used at higher volumes (>50%) for sustainable, durable concrete.

Key Characteristics:

• ≥50% fly ash of total cementitious materials

• Low water (≤130 kg/m³) and cement (≤200 kg/m³) content

• Superplasticizers used for high strength mixes

• Air-entraining admixtures for freeze-thaw durability

Advantages over Normal Concrete:

• Enhanced workability, surface finish, and pumpability

• Superior strength gain over time (up to 90 days and beyond)

• Excellent durability and resistance to chemical attacks

• Better cost-efficiency and life-cycle performance

Real-World Applications:

• 7-story building in Halifax (Canada) with 55% fly ash

• Wisconsin (USA) uses 60% Class-F fly ash since 1989

• Sydney Olympic facilities, Crown Casino basement, Jonas Salk Institute

• Projects in India, including an HVFA nano-concrete slab in AP (2013)

F. Present Work

The research focuses on developing Mathematical Models to predict:

• Compressive Strength

• Tensile Strength

• Flexural Strength
  At various concrete ages and Water-Binder (w/b) ratios.

II. Literature Survey

A. Mathematical Modelling

A mathematical model simplifies a real-world process using variables and equations to aid:

• Scientific understanding

• Decision-making (tactical and strategic)

• Predictive analysis

Stages of Modelling:

1. Building

2. Studying

3. Testing

4. Use

B. Choosing Mathematical Equations

Models can be derived from:

• Literature

• Physics analogies

• Empirical data and curve-fitting

C. Regression Analysis

A statistical tool for modeling the relationship between variables:

• Dependent Variable (Response)

• Independent Variables (Predictors)

Key Terms:

• S (Standard Deviation): Spread of predicted vs. actual values

• R² (Coefficient of Determination): Model accuracy

• Fit (?): Predicted value

• Residual: Error between observed and predicted value

III. Pre-Project Phase

A. Materials Used

1. Cement: Ordinary Portland Cement (IS: 12269, IS: 4031)

2. Fly Ash: Class-C (ASTM-C-618), from Vijayawada power plant

3. Coarse Aggregate: 20 mm crushed granite (IS specifications)

4. Fine Aggregate: River sand (Zone-II), clean and graded

5. Water: Potable water

6. Superplasticizer: Endure Flowcon 04 (IS: 9103, ASTM-C-494)

B. Preparation of Test Specimens

• Mix Design: As per IS: 10262

• Casting & Mixing: In pan mixer (40 liters)

• Curing: 24 hours at room temp, then water curing

Specimen Sizes:

• Compressive: Cubes (150mm x 150mm x 150mm)

• Tensile: Cylinders (150mm Ø x 300mm)

• Flexural: Beams (150mm x 150mm x 700mm)

C. Strength Testing

Performed at 28, 90, 180, and 360 days:

• Compressive Strength: Per IS: 516

• Tensile Strength: Using split cylinder test (IS: 5816)

• Flexural Strength: Modulus of rupture calculated based on crack location (IS: 516)

IV. Experimental Data

Data includes strength values (compressive, tensile, flexural) at varying:

• Ages (28 to 360 days)

• Water-Binder (w/b) ratios
  Used for developing predictive mathematical models.

Conclusion

The formulated Model equations are reliable for use in rigid pavements and the concrete industry using the HVFAC. (as proved in Chapter VII).

References

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Copyright

Copyright © 2025 Raja Gopala Raju Veepuri. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.