Bundesanstalt für Materialforschung und -prüfung

International Symposium (NDT-CE 2003)

Non-Destructive Testing in Civil Engineering 2003
Start > Contributions >Posters > Material: Print

Parameters That Influence The Results of Non-Destructive Test Methods for Concrete Strength

Ana Catarina Evangelista, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
Ibrahim Shehata, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
Lidia Shehata, Universidade Federal Fluminense, Rio de Janeiro, Brazil

ABSTRACT

The Non-destructive Test methods (NDT) have been used to evaluate the concrete strength in many countries, and experimental studies have investigated which method is more reliable and practical. The concrete strength is estimated using curves that correlate the NDT measurements with the compressive strength of concrete established by a laboratory testing program. Usually the parameters that affect these curves are the water/cement ratio, the aggregate type, the maximum aggregate size and the cement type of the concrete. This work presents a study on the influence of the mentioned parameters when the ultrasonic pulse velocity, probe penetration and rebound hammer methods are used.

Introduction

Control tests for the compressive strength at the age of 28 days are usually made in standard cylinders (or cubes) for evaluating the quality of the concrete used in the structures. However, the specimens are not truly representative of the concrete in the structure, which had different conditions of placing, compacting and curing. In the last decades some attempts have been made to develop non-destructive test methods for obtaining information about the strength and other properties of the concrete as it exists in the structure.

For an adequate use of the non-destructive tests, it is necessary to know the factors that influence the obtained measurements, and the correlation between the compressive strength and these measurements for the type of concrete under investigation. This work presents the results of a study on the influence of the type and maximum size of the coarse aggregate, and the type of cement on the correlation curves for concretes made with materials available in Rio de Janeiro having a 28 days compressive strength varying from 16 MPa to 53 MPa.

Experimental Programme

Materials, Mixes and Specimens
Four different types of coarse aggregates were used; three crushed natural aggregates and one lightweight artificial aggregate: gneiss with two different grading, trachyte, and expanded clay. Characteristics of these aggregates are given in table 1. The fine aggregate was natural sand with fineness modulus of 2.71 and specific gravity of 2.62 kg/m3. Normal or rapid hardening Portland cement and chemical admixture (from 0.5% to 0.8% of the cement mass) were used. The volumes of coarse aggregate and water were the same in all concretes, in each series of concretes (M1, M2, M3, M4, M5) the water/cement ratios were 0.65, 0.60, 0.55, 0.50, 0.45 and 0.40, and the slump varied from 80 mm to 120 mm. The concrete mixes proportions are in table 2.

Characteristics Gneiss Trachyte Gneiss Expanded Clay
Maximum size(mm)19199.519
Specific gravity(kg/dm3)2.722.652.701.28*
Fineness modulus6.856.965.596.99
Table 1: Coarse aggregates characteristics.

*Satured surface dry

Materials M1 M2 M3 M4 M5
Coarse aggregate (kg)Gneiss Dmax=19mmGneissDmax=9.5mmTrachyte Dmax=19mmGneiss Dmax=19mmExpanded Clay Dmax=19mm
1075107010501075505
Fine aggregate (kg)830 to 680830 to 680830 to 680830 to 680 830 to 680
Cement (kg)277 to 450277 to 450277 to 450277 to 450*277 to 450
Water(l)180180180180180
w/c 0.65 to 0.400.65 to 0.400.65 to 0.400.65 to 0.400.65 to 0.40
Table 2: Concrete mixes proportions.

* rapid hardening cement
Dmax maximum size

The compression and non-destructive tests of the concretes were carried out at the ages of 3, 7, 14, 28 and 90 days.

Cylindrical specimens (150 mm x 300 mm) were used for the compression, rebound hammer (Proceq-Digi Schimdt equipment) and ultrasonic pulse (Pundit Equipment - 54 kHz) tests; for the probe penetration (Walsyva gun) tests, the specimens were prismatic (200 mm x 200 mm x 600 mm).

The cylindrical specimens were cured in water up to 48 hours before the date of the test, in view of the influence of humidity on the rebound hammer measurements. The prismatic specimens were immersed in water until the date of the probe penetration tests.

Results

The expressions proposed by other authors for correlating the compressive strength (fc) with the measurements of pulse velocity (V), rebound hammer index (R) and probe exposed length (Lp) are presented in tables 3, 4 and 5, respectively. Table 5 includes only the authors that used the same kind of gun used in this work. These expressions have been based on the results of concretes with various types of materials and mix proportions and, because of this, they represent quite different correlation curves. This is shown in figures 1, 2 and 3.

In this study, the standard curve fitting procedure considered different types of correlation relationship: linear, power, exponential, logarithmic and polynomial.

The best fit for the correlations between fc and V were the exponential curves shown in figure 1. A statistic analysis showed that, from the varied factors, the ones that had more influence on the correlation between fc and V were the density of the coarse aggregate and the type of cement.

Fig 1: Comparison between curves that correlate fc with V.

For the correlation between fc and R, the best fit was given by the power curves seen in figure 2. It was verified that the factors that have a significant influence on these curves are also the density of the coarse aggregate and the type of cement.

Fig 2: Comparison between curves that correlate fc with R.

In figure 2 it can be observed that the curve proposed by the manufacturer of hammer (Proceq-Digi Schimdt) gives lower compressive strength than the ones obtained in this work, except for the case of lightweight concrete (M5) when R is greater than about 30. The curves calibrated for concretes with higher strength differ considerably from the others proposed.

Linear correlations between fc and Lp were obtained for the concretes with crushed rock aggregate. The probe penetration test, with the probe (55 mm length and 6.3 mm diameter) and gun power load used, was not suitable for the lightweight aggregate concretes, since in most cases full penetration of the probe occurred. It is seen in figure 3 that the correlation curve for the concrete with rapid hardening cement in noticeably different from the ones for the concretes with normal hardening cement.


Fig 3: Comparison between curves that correlate fc with Lp.

Analysis of the variance (ANOVA) at a 5 % significance level, considering the data of series M1 concretes as the reference, showed which of the varied parameters had significant influence on the values of fc, V, R and Lp. The results of this analysis are in table 6. It is worthwhile pointing out that the coarse aggregate volume, that could have relevant influence on the results, was the same for the analyzed concretes.

Conclusions

The analysis of this work showed that parameters that significantly influence the concrete strength may not influence the non-destructive test results in the same way and vice versa.

For the concretes studied, it would be possible to use the same correlation curves for the concretes with rock crushed coarse aggregates and normal hardening cement. Different curves, however, would be necessary for the concretes with rapid hardening cement and lightweight aggregate.

The correlation curves given by different authors show that reliable estimate of in-situ strength can only be obtained if the correlation between compressive strength and the non-destructive test measurement for the same kind of concrete is properly established.

Author Expression* fc (MPa) Specimen Type of aggregate Note
Ravindrajah et al (1988)fc = 0,060e1,44V15,0 to 75,0Cube 100mmgranite (Dmax=20mm) 
Almeida (1993)fc = 0,0133V5543
fc = 0,011V5654
40,1 to 120,3Cube 150mmgranite (Dmax=25mm) 1st and 2nd test series
Gonçalves** (1995)fc = 0,02V - 65,418,0 to 42,0Core70mmx70mm-28 days to 3 months
Qasrawi (2000) fc= 36,72V - 129,0776,0 to 42,0Cube 150mmVariableAir cure
Soshiroda and Voraputhaporn (1999)fc 28 = 44,52V1 - 126,83
fc 28 = 54,18V28 - 206,27
20,0 to 65,0Cube 150mm GravelV1 - 1 day V28 - 28 days
Phoon et al (1999)fc = 124,4V - 587,0 + e35,0 , 55,0 and 75,0Cube 150mmgranite (Dmax=20mm)28 days
Pascale et al** (2000)fc = 10-28V8.127230,0 to 150,0Cube 150mm limestone(Dmax=15mm) 
Elvery and Ibrahim(1976)fc = 0,012e2,27V±6,415,0 to 60,0Cube 100 mmgravel (Dmax=19mm) 
Teodoru (1988)fc = 0,0259e1,612V2,0 to 24,0--28 days
Yun et al (1988)fc = 0,329V - 10655,0 to 30,0Core150mmx300mmgravel (Dmax=25mm and Dmax=40mm) 
Table 3: Expressions of other authors for correlating fc with V.

* fc in MPa and V in km/s , ** fc in MPa and V in m/s

Author Expression* fc (MPa) Specimen Type of aggregate Note
Ravindrajah et al (1988)fc = 7,25e0,08R15,0 to 75,0Cube 100mmgranite (Dmax=20mm) 
Almeida (1993)fc = 1,0407R1,155
fc = 1,041R1,155
40,1 to 120,3Cube 150mmgranite (Dmax=25mm) 1st and 2nd test series
Gonçalves (1995)fc = 1,73R - 34,318,0 to 42,0Core70mmx70mm- 28 days to 3 months
Pascale et al (2000)fc = 0,000135R3,442430,0 to 150,0Cube 150mmLimestone(Dmax=15mm) 
Qasrawi (2000)fc = 1,353R - 17,3936,0 to 42,0Cube 150mmvariable 
Soshiroda and Voraputhaporn (1999)fc 28 = 161R3 - 137
fc 28 = 147R28 - 16,85
20,0 to 65,0Cube 150mm gravelR3 - 3 daysR28 -28days
Proceq-Digi Schimdtfc 7 = 1,4553R7 - 22,817
f14 -56 = 1,398R14-56 - 2017
25,1 to 33,1Cube 200mm gravel(Dmáx=32mm)7 days14 days to 56 days
Lima and Silva (2000)fc = 0,0501R1,842825,1 to 33,1Cylinder   
Table 4: Expressions of other authors for correlating fc with R.

*fc in MPa

Author Expression* fc (MPa) Specimen Type of aggregate
Vieira (1978)fc = -0,7294 Lp + 41,2317,0 to 38,5Cylinder-
Danielleto (1986)fc = 0,08Lp2 - 780Lp + 187,5314,8 to 53,1Cylindergneiss
Table 5: Expressions of other authors for correlating fc with Lp.

*fc in MPa and Lp in mm

Varied parameter fc V fc-V R fc - R Lp fc - Lp
Type of crushed rock aggregate   X    
Lightweight aggregateXXXXX*X
Dmax X   X 
Cement typeX XXXXX
Table 6: Varied parameters that had significant influence on the results of fc, V, R and Lp, and on the correlation curves, considering concrete series M1 as a reference.

* probe penetration test results not considered

References

  1. Almeida, I. R., "Emprego do esclerômetro e do ultra-som para efeito da avaliação qualitativa dos concretos de alto desempenho (Portuguese)", Professorship thesis, Universidade Federal Fluminense, Niterãi, Brasil, 1993, 124pp.
  2. Danielleto, C.C. , "Avaliação da resistência do concreto em estruturas prontas (Portuguese)", MSc thesis, Universidade Federal do Rio de Janeiro/COPPE, Rio de Janeiro, Brasil, 1986, 175 pp.
  3. Elvery, R.H. and Ibrahim, L.A.M., " Ultrasonic assessment of concrete strength at early ages", Magazine of Concrete Research, December, 1976, pp.181-190.
  4. Evangelista,.A.C., "Avaliação da resistência do concreto usando diferentes ensaios não destrutivos" (Portuguese), DSc thesis, Universidade Federal do Rio de Janeiro/COPPE, Rio de Janeiro, Brasil, 2002, 216 pp.
  5. Gonçalves, A. , 1995, "In situ concrete strength estimation. Simultaneous use of cores, rebound hammer and pulse velocity", International Symposium NDT in Civil Engineering, Germany, pp.977-984.
  6. Lima, F.B. e Silva M.F.B., "Correlação entre a resistência à compressão do concreto e a sua dureza superficial (Portuguese)", Proceedings, IV Congresso de Engenharia Civil, Ed. Interciência, Juiz de Fora , 2000, pp. 429-440.
  7. Pascale, G, et al.,2000, "Evaluation of actual compressive strength concrete by NDT", 15th World Conference on Non-Destructive Testing , Roma,10pp.
  8. Proceq - DigiSchmidt, equipment manual.
  9. Phoon, K.K., et al, "Development of statistical quality assurance criterion for concrete using ultrasonic pulse velocity method", ACI Material Journal, September-October, 1999, pp.568-573.
  10. Qasrawi, H. Y., "Concrete strength by combined nondestructive methods simply and reliably predicted". Cement and Concrete Research, May, 2000, pp.739-746.
  11. Ravindrajah et al, "Strength evaluation of recycled-aggregate concrete by in situ tests",Materials and Structures, 1988, V.21, pp.289-295.
  12. Soshiroda, T. and Voraputhaporn, K., "Recommended method for earlier inspection of concrete quality by non-destructive testing", Concrete durability and repair technology, September, Dundee, 1999, pp.27-36.
  13. Teodoru, G.V , "The use of simultaneos nondestructive tests to predicit the compressive strength of concrete", Nondestructive Testing, Special Publication SP-112, American Concrete Institute, Detroit, 1988, pp.137-152.
  14. Vieira, D.P., "Método Brasileiro de Penetração de Pinos", XIX Jornadas Sudamericanas de Engenharia Estrutural, Santiago, Chile,1978.
  15. Yun et al , "Comparative evaluation of nondestructive methods for in-place strength determination", Nondestructive Testing, Special Publication SP-112, American Concrete Institute, Detroit, 1988, pp.111-136.
STARTPublisher: DGfZPPrograming: NDT.net