Due to the increasing use of rapid construction methods and the challenges of maintaining construction schedules, a growing demand exists for procedures that can assure quality of work without sacrificing the pace of construction. The quality control of construction materials specifically, the mechanical properties of concrete are among the most important concerns in today’s construction industry. In the present study, the correlation between fiberreinforced concrete’s compressive strength and dynamic modulus to its ultrasonic pulse velocity is investigated at early ages up to 7 days after mixing. An experimental program involving 189 FRC specimens were designed containing different types of structural fibers, fiber volume fractions, and watertocement ratios. Mathematical equations were developed to predict the earlyage compressive strength and dynamic modulus of four different types of fiberreinforced concrete based on ultrasonic pulse velocity. The predicted compressive strength and dynamic modulus from the proposed equations showed good agreement with the measured ones.
Debido al aumento del empleo de métodos rápidos de construcción y los desafíos de mantener los calendarios de construcción, ha aumentado la demanda de procedimientos que permitan asegurar la calidad del trabajo sin sacrificar el ritmo de producción. Dentro del control de calidad de los materiales de construcción, las propiedades mecánicas del hormigón se encuentran entre las preocupaciones más importantes. En este estudio se investiga la correlación entre la resistencia a la compresión y el módulo dinámico del hormigón reforzado con fibras, con la velocidad de pulso ultrasónico a edades tempranas hasta 7 días después del amasado. Para ello se diseñó un programa experimental que involucró 189 muestras de HRF que contenían diferentes tipos de fibras estructurales, fracciones de volumen de fibra y relaciones agua/cemento. Se desarrollaron ecuaciones matemáticas para predecir la resistencia a la compresión y el módulo dinámico a edades tempranas de cuatro tipos diferentes de hormigón reforzado con fibras, en función de la velocidad del pulso ultrasónico. Tanto la resistencia a la compresión como el módulo dinámico pronosticados a partir de las ecuaciones propuestas mostraron una buena correlación con las medidas experimentales llevadas a cabo.
To ensure the safety, longterm performance, and durability of concrete structures in an accelerated construction schedule, an understanding of concrete behavior and an evaluation of its mechanical properties at early ages plays an important role in the construction quality control and planning process. Concrete’s compressive strength and dynamic modulus at an early age dramatically impact its longterm efficiency, durability, and properties. Early age of concrete is typically defined as the first few hours or days after casting concrete, which is marked by the setting and hardening processes as hydration occurs. During this time, the fluid phase of fresh concrete transitions into the hardened state, resulting in the development of mechanical properties, heat release, and deformations due to the success of the hydration reactions. The mechanical properties of earlyage concrete develop at different rates, depending on mixture proportions, including the fiber content, watertocement (w/c) ratio, age, and curing conditions (
Concrete is a widely used construction material due to its high compressive strength, although it has a relatively low tensile strength when compared to other construction materials. Therefore, concrete is often reinforced with structural fibers to enhance its mechanical and physical properties. Fiberreinforced concrete (FRC) is classified into steel fiberreinforced concrete (SFRC), glass fiberreinforced concrete (GFRC), synthetic fiberreinforced concrete, and natural fiberreinforced concrete (
As an alternative to destructive testing, several studies exist in the literature containing empirical equations based on nondestructive test methods, such as the ultrasonic pulse velocity (UPV), to predict the compressive strength and dynamic modulus of concrete (
A number of research studies have investigated the relationship between UPV and the compressive strength and dynamic elastic modulus of plain concrete. However, as discussed, better estimation of these properties in terms of the ultrasonic pulse velocity measurement depends on numerous mixture parameters, such as fiber type and volume fraction, w/c ratio, temperature, coarse aggregate, shape, and cement type (
In the present study, FRC cylindrical specimens were cast, cured, and tested for compressive strength, dynamic modulus, and ultrasonic pulse velocity. The cement type and aggregate size remained constant, while the effect of change in fiber type, fiber volume fraction, watertocement ratio, and test age on the prediction of FRC compressive strength and dynamic modulus were investigated. Two sets of new empirical equations were proposed to predict the compressive strength and dynamic modulus of FRC based on UPV. The first set of equations predicted the compressive strength of earlyage steel, polypropylene, nylon, and glass FRC. The second set of equations predicted the dynamic modulus of earlyage steel, polypropylene, nylon, and glass FRC. The accuracy of these new equations was tested by measuring the coefficient of variation between the measured values and the predicted values from the proposed equations.
An experimental program was designed and conducted to establish a correlation between FRC’s earlyage UPV and its earlyage compressive strength and dynamic modulus. This program involved 189 specimens of 100 mm × 200 mm FRC cylinders with different mixture proportions. The UPV, dynamic modulus, and compressive strength were measured using an ultrasonic concrete tester, a resonance test gauge, and a compression test machine, respectively. The experimental program outline is shown in

Type I/II 

4.7625 mm (0.1875″) 

Nylon, polypropylene, steel, and glass 

0.5, 1.0, and 1.5 

0.40, 0.45, and 0.50 

Cylinder 100 mm × 200 mm (4″ × 8″) 

1, 3, 7, 28 

Compression test machine 

Ultrasonic concrete tester, resonance test gauge 

Compressive strength, dynamic modulus 
Portland cement type I/II was combined with gravel; sand; water; and nylon, polypropylene, steel, and glass fibers to produce four different types of FRC. The fiber properties are presented in
Stainless Steel  AR Glass  Virgin Nylon  Polypropylene  


1.18  0.014  0.038  1.52 

25.4  13  19  19 

7800  2700  1150  910 

1030  2000  300  410 

203  77  2.8  5.6 

1516  1121  225  160 

Nil  < 1%  3% by Weight  Nil 

High  High  High  Excellent 

High  High  High  High 
Reinforcing fibers are added to concrete at different dosages depending on the intended application and fiber type.
Fiber Addition Rates  Nylon  Polypropylene  Steel  Glass 

Plastic Shrinkage Cracking  0.6 kg/m^{3}  0.9 kg/m^{3}  1015 kg/m^{3}  0.30.6 kg/m^{3} 
Structural Performance      1580 kg/m^{3}  515 kg/m^{3} 
No.  Reference  Fiber Volume Fraction (Vf) Ranges  

Steel  Glass  Nylon  Polypropylene  
1  ( 
02%       
2  ( 
  05%     
3  ( 
02%       
4  ( 
  02.4%     
5  ( 
    01.5%   
6  ( 
01.5%       
7  ( 
      02% 
8  ( 
02%      02% 
Fiber Type  ID  Vf (%)  W/C  C (kg/m^{3})  CA (kg/m^{3})  FA (kg/m^{3})  W (kg/m^{3})  Fiber (kg/m^{3}) 

Plain Concrete  Mix 1  0.00  0.40  503.3  709.7  986.5  201.3  0.0 
Nylon  Mix 2  0.50  0.40  500.8  706.1  981.5  200.3  5.7 
Mix 3  0.75  0.40  499.5  704.3  979.1  199.8  8.5  
Mix 4  1.00  0.40  498.3  702.6  976.6  199.3  11.4  
Mix 5  0.75  0.45  487.3  687.1  955.0  219.3  8.5  
Mix 6  0.75  0.50  475.6  670.6  932.1  237.8  8.5  
Polypropylene  Mix 7  0.50  0.40  500.8  706.1  981.5  200.3  4.5 
Mix 8  0.75  0.40  499.5  704.3  979.1  199.8  6.8  
Mix 9  1.00  0.40  498.3  702.6  976.6  199.3  9.1  
Mix 10  0.75  0.45  487.3  687.1  955.0  219.3  6.8  
Mix 11  0.75  0.50  475.6  670.6  932.1  237.8  6.8  
Steel  Mix 12  0.50  0.40  500.8  706.1  981.5  200.3  39.0 
Mix 13  0.75  0.40  499.5  704.3  979.1  199.8  58.5  
Mix 14  1.00  0.40  498.3  702.6  976.6  199.3  78.0  
Mix 15  0.75  0.45  487.3  687.1  955.0  219.3  58.5  
Mix 16  0.75  0.50  475.6  670.6  932.1  237.8  58.5  
Glass  Mix 17  0.50  0.40  500.8  706.1  981.5  200.3  13.5 
Mix 18  0.75  0.40  499.5  704.3  979.1  199.8  20.2  
Mix 19  1.00  0.40  498.3  702.6  976.6  199.3  27.0  
Mix 20  0.75  0.45  487.3  687.1  955.0  219.3  20.2  
Mix 21  0.75  0.50  475.6  670.6  932.1  237.8  20.2 
Twentyone separate mixes (batches) were prepared and nine specimens per mix were produced, yielding a total of 189 specimens. These 189 specimens were categorized into five groups: the first group (Mix 1) had specimens with no fibers, the second group (Mixes 26) had specimens with nylon fibers, the third group (Mixes 711) had specimens with polypropylene fibers, the fourth group (Mixes 1216) had specimens with steel fibers, and the fifth group (Mixes 1721) had specimens with glass fibers. The concrete was mixed, placed, consolidated, and cured in accordance to ASTM C192 (
The ultrasonic pulse velocity of each specimen was determined according to ASTM C597 (
The dynamic modulus of each specimen was determined according to ASTM C215 (
The compressive strength of each of the 189 cylinders was tested according to ASTM C39 (
Some researchers have studied the development of ultrasonic pulse velocity of plain concrete over time and concluded that the rate of gain of UPV is high during early ages and then slows at later ages (
In the current study it was observed that Polypropylene fibers increase entrapped air voids at 1.0% or higher fiber volume fractions, that results in decreasing of the concrete workability and creating difficulties when compacting the mixes, which is in agreement with the observations in similar studies (
The gain in concrete compressive strength is rapid at an early age. This rapid early gain in strength is directly linked to the increase of the gel/space ratio of calcium silicate hydrate (
The gain in concrete elastic modulus is extremely rapid at an early age. This rapid early gain in strength is directly linked to the increase of the gel/space ratio of calcium silicate hydrate (
The relationship between UPV and compressive strength of concrete at the age of 28 days has been investigated extensively in previous works, while only a few studies have discussed the relationship between UPV and compressive strength of concrete at early ages. It has been observed that the relationship between concrete compressive strength and ultrasonic pulse velocity is better estimated by utilizing the exponential equation forms as shown in
Reference  Equation  Limitation 

( 
ƒ_{
c
} = 0.013 
Containing silica fume, superplasticizer, and steel fiber at 1, 2, and 3%. Age  28 days 
( 
ƒ_{
c
} = 0.016 
Containing silica fume, superplasticizer, and PVA fiber at 0.25, 0.5, and 0.75%. Age  28 days 
( 
ƒ_{
c
} = 0.15 
Containing recycled factory brick aggregate, calcium aluminate cement, silica fume, superplasticizer, and polyvinyl alcohol fibers at 0.5% fiber volume fraction. Age  7 to 63 days 
( 
ƒ_{
c
} = 33.27 
Highstrength concrete containing 0, 0.2, 0.4, and 0.6% of twisted bundle nonfibrillated, monofilament, and fibrillated polypropylene network plus silica fume. Age  7 to 63 days 
( 
ƒ_{
c
} = 0.00055 
Age  28 days CA = 1100 kg/m^{3} 
( 
ƒ_{
c
} = 0.0012 
Age of 3 hr and over Temperature 0° to 60°C 
( 
ƒ_{
c
} = 1.19 
Age  7 to 138 days Cubes 
( 
ƒ_{
c
} = 2.8 
Concrete slabs 
( 
ƒ_{
c
} = 2.016 
Concrete cubes 
( 
ƒ_{
c
} = (109.6 + 33 
Concrete cylinders 
( 
ƒ_{
c
} = 9.502 
Age  7 and 28 days Cubes M15 grade 
( 
ƒ_{
c
} = 2.701 
Age  7 and 28 days Cubes M20 grade 
( 
ƒ_{
c
} = 4.104 
Age  7 and 28 days Cubes M35 grade 
( 
ƒ_{
c
} = 8.4 * 10^{9}( 
Age  7 to 90 days 
Where ƒ_{
c
} is compressive strength in MPa and
The proposed
For G, P, and NFRC
For SFRC
Where ƒ_{
c
} is compressive strength (MPa),
For G, P, and NFRC
For SFRC
Where σ is fiber flexural strength (GPa), ɭ is fiber length,
For
The development trend of compressive strength and dynamic modulus and ultrasonic pulse velocity with hydration time was observed to be exponential at the early ages. Therefore, the prediction of FRC’s compressive strength and dynamic modulus at early ages based on ultrasonic pulse velocity is expressed using an exponential relationship which is well aligned with similar studies in the literature (
For G, P, and NFRC
For SFRC
Where
For G, P, and NFRC
For SFRC
Where σ is fiber flexural strength (GPa), ɭ is fiber length,
This paper investigates the correlation between the earlyage ultrasonic pulse velocity and the earlyage compressive strength and dynamic modulus of nylon, polypropylene, steel, and glass fiberreinforced concrete. The study was needed because the preliminary study conducted prior to this research revealed that the existing equations did not provide a good prediction of fiberreinforced concrete’s earlyage compressive strength and/or dynamic modulus based on UPV. The mixture parameters investigated included fiber volume fractions of 0.5% vol., 0.75% vol., and 1.00% vol., and watertocement ratios of 0.40, 0.45, and 0.50. The ultrasonic pulse velocity, compressive strength, and dynamic modulus were measured for the specimens using an ultrasonic concrete tester, compression test machine, and resonance test gauge, respectively. Two sets of equations were proposed to predict the earlyage compressive strength and dynamic modulus of FRC based on ultrasonic pulse velocity. The first set of equations predicted the 3day and 7day compressive strength of nylon, polypropylene, steel, and glass fiberreinforced concrete. The second set of equations predicted the 3day and 7day dynamic modulus of nylon, polypropylene, steel, and glass fiberreinforced concrete. The proposed equations can predict the earlyage compressive strength and dynamic modulus of multiple fiberreinforced concrete types, due to the incorporation of different fiber properties as variables in the equations. No other equations have been found in the literature capable of accurately predicting the earlyage compressive strength and dynamic modulus of multiple types of fiberreinforced concrete with different mixture parameters.
The accuracy of these new equations was tested by measuring the coefficient of variation between the measured values and the predicted values from the proposed equations. The coefficients of variation between the measured and predicted compressive strengths showed reasonable agreement with the measured values, and ranged from 6.4 to 14.6 percent. The coefficients of variation between the measured and predicted dynamic moduli also showed reasonable agreement with the measured dynamic moduli, and ranged from 3.3 to 9.2 percent. Based on these results, it appears that the proposed
Conceptualization: D. Castillo, S. Hedjazi. Data curation: D. Castillo. Formal analysis: D. Castillo, S. Hedjazi. Investigation: D. Castillo, S. Hedjazi. Methodology: S. Hedjazi. Project administration: S. Hedjazi. Resources: S. Hedjazi. Supervision: S. Hedjazi. Validation: D. Castillo, S. Hedjazi. Visualization: D. Castillo. Roles/Writing, original draft: D. Castillo. Writing, review & editing: S. Hedjazi.