jun domingo correlation between concrete strength

8/8/2019 Jun Domingo Correlation Between Concrete Strength

http://slidepdf.com/reader/full/jun-domingo-correlation-between-concrete-strength 1/6

Correlation Between Concrete Strength and Combined Nondestructive

Tests for Concrete Using High-Early Strength Cement

1Razon Domingo

2Sohichi Hirose

1Assistant Professor, Dept of Civil Engineering, FEA-WEast Asia College

2Professor, Dept of Mechanical and Environmental Informatics, TIT

Abstract

Correlations among compressive strength, flexural strength and combined nondestructive

testing methods for different design mixes using high-early strength cement were established

to predict on-site strength of portland cement concrete (PCC) pavement. Concrete mix

designs of varying water-cement ratios were prepared using high-early strength cement and

specimens were prepared and tested for compressive strength and flexural strength atdifferent ages. Standard beam specimens were also prepared to determine the corresponding

pulse velocity and rebound number. Good correlations were established in predicting the

flexural strength of pavement from compressive strength, ultrasonic pulse velocity and

rebound number but a better correlation is established using a combined ultrasonic pulse

velocity and rebound number.

1. Introduction

There is an ever-increasing demand by the traveling public to open pavements earlier to

traffic and because of shortened construction schedule; the inspection force needs to make

quick decisions about construction quality. The usual method of quality acceptance during

pavement constructions are limited to measuring slump and air content and fabricating beamsto test flexural strength. In recent years, significant developments have occurred in concrete

testing and in establishing test procedures for nondestructive testing (NDT).

Flexural strength (sometimes called the modulus of rupture) is typically used in portlandcement concrete (PCC) mix design for pavements because it best simulates slab flexural

stresses as they are subjected to loading. Flexural strength results are sensitive to many

factors, including fabricating, curing, and loading of the beams [1, 2]. Beams are very heavy

and can be damaged when handled and transported from the jobsite to the lab. Allowing a

beam to dry will yield lower strengths. Beams must be cured in a standard manner, and tested

while wet. Meeting all these requirements on a jobsite is extremely difficult often resulting in

unreliable and generally low modulus of rupture values [2]. Because these factors lead to

high variability, the concrete industry is interested in using compressive strength rather than

flexural strength tests for field quality assurance. With pavements, where flexural strength is

the important design criterion, the relationship between compressive strength and flexural

strength can be determined through trial batching the proposed concrete mixes and

establishing the correlation between the two by testing, thus permitting an accurate estimation

of the flexural strength of the as-delivered concrete by testing cylinders for compressive

strength [1, 3].



The objective of this research is to contribute to the development of a pragmatic method for

the improved nondestructive determination of concrete strength in structures, particularly on

PCC pavements. Specifically, this study would like to determine the correlations of concrete

strengths with some NDT methods using high-early strength cement (Type III) compared to

normal cement.

Although there can be no direct measurement of the strength properties of structural concretefor the simple reason that strength determination involves destructive stresses, several

nondestructive methods of assessment have been developed [4].

Anderson and Seals [5] performed two different experiments to establish the potential for

using dynamic non-destructive test procedures to predict long-term compressive, tensile and

flexural strength based upon six different concrete mixtures. Rajagopalan et al. [6] reported a

correlation between ultrasonic pulse velocity and compressive strength of concrete for some

typical mixes. The study measured simultaneous measurements of pulse velocity and

compressive strength made on 150 mm cubes, at different ages from 1 day to 28 days,

indicates a linear relation between strength and velocity.

The ultrasonic pulse velocity method is a stress wave propagation method that involvesmeasuring the travel time, over a known path length, of a pulse of ultrasonic waves. The test

method for pulse velocity through concrete is described in ASTM C597 [7]. The pulses are

introduced into the concrete by a piezoelectric transducer and a similar transducer acts as

receiver to monitor the surface vibration caused by the arrival of the pulse. A timing circuit is

used to measure the time it takes for the pulse to travel from the transmitting to the receiving

transducers.

Then, the velocity is calculated using equation 1.

T LV = (1)

Where, V = pulse velocity (m/s), L = length (m), and, T = effective time (s), which is the

measured time minus the zero time correction. The zero time correction is equal to the travel

time between the transmitting and receiving transducers when they are pressed firmly

together.

The rebound hammer test is described in ASTM C805 [8]. The test is classified as a hardness

test and is based on the principle that the rebound of an elastic mass depends on the hardness

of the surface against which the mass impinges. The energy absorbed by the concrete is

related to its strength [9].

When variation in properties of concrete affect the test results, the use of one method alone

would not be sufficient to evaluate the required property. Therefore, the use of more than onemethod yields more reliable results. Of a number of purely nondestructive tests, the rebound

(Schmidt) hammer and the ultrasonic pulse velocity combinations are the most commonly

used. Attempts have been done to relate rebound number and ultrasonic pulse velocity to

concrete strength [10, 11, 12].

In the majority of cases, the need for in situ concrete strength evaluation arises as a result of

suspect of quality of concrete. By developing a prior correlation for a range of concrete

grades and types, having only the source of coarse aggregate and a broad age group in



common, it is possible to obtain good indication of the in situ strength of concrete, expressed

as the value of a test result of a standard compressive specimen [13].

2. Experimental Design

Three concrete batches with varying water-cement ratios were mixed in the laboratory. Thedifferent mix designs are shown in Table 1. The materials used in the mix design were from

the same sources and the cement used is a Type III cement or high-early strength cement. The

design slump would be limited from 25 mm to 75 mm and water-cement ratios should be

between the range of 0.40 – 0.50 as used for pavement applications. The coarse aggregate

used has a nominal maximum size of 19 mm while the fine aggregate has a fineness modulus

of 2.70.

Table 1: Concrete Mix Design for Different Batches (1.0 m3)

Mix Design 1 2 3

w/c 0.49 0.45 0.41

*Cement,kg.

388 422 463

C.A., kg. 1002 1002 1002

F.A., kg. 802 773 737

Water, kg. 190 190 190

* Type III (High-Early Strength Cement)

The properties of fresh concrete (slump, density, air content and temperature) were

determined for each mix design and cylindrical and beam specimens were cast for

determining the properties of hardened concrete. The compressive strength and flexural

strength of hardened concrete were determined using specimens tested at 1, 3, 7, and 14 days.Two specimens were tested and the results averaged for each strength test at each age. Direct

ultrasonic pulse velocity and rebound number were also determined using 150 x 150 x 500

mm beam specimens. The actual set-up for ultrasonic pulse velocity determination is shown

in Figure 1.

Figure 1: Actual Set-up for Ultrasonic Pulse Velocity Determination



The results of these tests were analyzed to determine the relationship among flexural strength,

compressive strength, ultrasonic pulse velocity (UPV) and rebound number (RN).

3. Results and Discussion

The results of tests for fresh concrete are summarized in Table 2. Concrete mixes with water-

cement ratios of 0.49 and 0.45 exceeded the design slump of 25 mm to 75 mm.

Table 2: Properties of Fresh Concrete

Mix

No.

W/C

Ratio

Slump

(mm)

Unit Weight

(kg/m3)

Temperature

(°C)

1 0.49 150 2,419 16

2 0.45 125 2,325 15

3 0.41 75 2,319 15

The results of tests for hardened concrete are summarized in Table 3. Compressive strength

ranged from 12.82 to 48.70 MPa (1,860 to 7,063 psi) while flexural strength ranged from

2.24 to 9.10 MPa (325 to 1,320 psi). Direct UPV ranged from 3,821.40 to 4,772.70 m/s. The

rebound number ranged from 19 to 45.

Table 3: Test Results for Hardened Concrete

Mix

No.

Age Compressive

Strength

(MPa)

Flexural

Strength (MPa)

Direct Pulse

Velocity

(m/s)

Rebound

Number

1 1 12.82 2.24 3,821.40 19

2 1 14.80 2.80 4,000.00 22

3 1 21.83 4.36 4,200.00 291 3 20.30 4.75 3,963.00 25

2 3 23.90 5.78 4,153.80 31

3 3 28.20 6.60 4,375.00 35

1 7 30.60 6.20 4,385.20 32

2 7 33.60 7.20 4,500.00 38

3 7 39.80 7.83 4,666.70 42

1 14 33.20 6.60 4,458.30 37

2 14 38.40 8.10 4,595.70 42

3 14 48.70 9.10 4,772.70 45

The required flexural strength of 4.1 MPa using third-point loading is attained after only 3

days for all concrete batches since high-early strength cement is used.

Multiple regression is used to analyze combined NDT methods to predict flexural strength for

pavements and the results show good correlations between flexural strength as the dependent

variable and combined UPV and rebound number as independent variables (R 2

= 0.96). The

flexural strength can be predicted from combined UPV and rebound number using equation

2.



11.01)Direct UPV3.865(-RN)2.509(StrengthFlexural += Log Log Log (2)

Although the purpose of this study focuses on flexural strength of concrete pavement, the

compressive strength can also be predicted from the combined ultrasonic pulse velocity and

rebound number using equation 3 with R 2

= 0.97.

6.097-)Direct UPV1.633(RN)1.056(StrengtheCompressiv Log Log Log += (3)

4. Conclusions

Test results for hardened concrete show good correlations of flexural strength with

compressive strength, rebound number and ultrasonic pulse velocity. A better correlation is

attained in predicting the flexural strength of beam specimens using multiple regression

analysis with combined ultrasonic pulse velocity and rebound number as independent

variables.

Although the study concerns more on flexural strength, it is interesting to note that good

correlations are also established for compressive strength relating to ultrasonic pulse velocity

and rebound number contrary to other past studies. Similar to predicting flexural strength, a

better correlation is attained in predicting compressive strength using multiple regression

analysis combining ultrasonic pulse velocity and rebound number.

It is recommended that the third-point loading test for flexure be used both in the design and

in acceptance scheme for concrete pavements in the actual construction. Furtherance of this

study is also recommended by validating results of ultrasonic pulse velocity and rebound

number in actual tests during pavement construction.

5. Acknowledgements

This research was supported by the Japan Society for the Promotion of Science (JSPS) Core

University Program on Environmental Engineering.

6. References

[1] Kosmatka, S. Compressive Versus Flexural Strength for Quality Control of Pavements.

Concrete Products, pp. 14-15 (March 1988).

[2] National Ready-Mixed Concrete Association. What, Why and How? Flexural Strength of

Concrete. Concrete in Practice 16. NRMCA, Silver Spring, Md. (1992).

[3] National Ready-Mixed Concrete Association. Compressive Strength and FlexuralStrength Correlation. Technical Information Letter 492. NRMCA, Silver Spring, Md.

(1992).

[4] Malhotra, V. M. Testing Hardened Concrete: Non-destructive Methods. American

Concrete Institute, Monograph No. 9, 1976.

[5] Anderson, D.A., Seals, R.K. Pulse Velocity as a Predictor of 28- and 90-Day Strength.

ACI Journal Proceedings 78 (1981) (9), pp. 116 – 122. [8]

jun domingo correlation between concrete strength

Documents