Relating the structural strength of concrete sewer pipes and material properties retrieved from core samples

Figures & data

Table 1. Characteristics of studied sewer pipes.

No.	Origin	Service life	Surface damage class (BAF)	BAF class description
P01	De Hamer factory	New	–
P08	The Hague	1924–2013	4	Missing aggregates or reinforcement outside the surface protrudes
P10	The Hague	1924–2013	4
P02	Breda	1952–2013	3	Aggregates that protrude beyond the surface or visible reinforcement
P06	Breda	1952–2013	3

Figure 1. Schematic diagram of the adopted experiment principle (left) and actual experimental set-up (right).

Figure 2. Test set-up used for four-point loading flexural tests.

Figure 3. Successive stages in the test of a sewer pipe (P02) from Municipality of The Hague during the experiment.

Figure 4. Force-displacement response for; (a,b) the 61-year-old sewer pipes - P02, P06; (c,d) the 89-year-old sewer pipes - P08, P10; (e) the new sewer pipe - P01. Legend: F_v – vertical force; F_h – horizontal force; δ_fv – front vertical displacement; δ_fh – front horizontal displacement; δ_bv – back vertical displacement; δ_bh – back horizontal displacement.

Figure 5. Boxplot for the carbonation depths at the inside for pipes P02, P06, P08 and P10; discriminating between crown, lateral and invert positions. On each box, the central mark is the median, the edges of the box are the 25th and 75th percentiles, the whiskers extend to the most extreme data points not considered outliers (approximately ± 2.7σ), and outliers are plotted individually.

Figure 6. Boxplot for the carbonation depths at the outside for pipes P02, P06, P08 and P10; discriminating between crown, lateral and invert regions. On each box, the central mark is the median, the edges of the box are the 25th and 75th percentiles, the whiskers extend to the most extreme data points not considered outliers (approximately ± 2.7σ), and outliers are plotted individually.

Figure 7. The four-pint flexural test force-deformation response for; (a) the new sewer pipe – P01; (b) the 60-year-old sewer pipe – P02; (c) the 90-year-old sewer pipe – P08.

Figure 8. Examples of the studied thin section under the fluorescence light (P02 and P06).

Figure 9. Examples of the studied thin sections under the polarised light with the highlighted ettringite (P06 and P02).

Figure 10. Relation between force at the first crack and carbonation depth at the inner wall of the pipes.

Figure 11. Relation between force at the first crack and the carbonation depth at the inside and outside wall of the pipes.

Figure 12. Relation between force at the first crack and the tensile splitting strength.

Figure 13. Relation between force at the first crack and the tensile bending strength.

Figure 14. Relation between force at the first crack and the compressive strength.

Figure 15. Relation between force at the first crack and the water absorption.

Figure 16. Relation between force at the first crack and the density of the concrete.

Figure 17. Relation between thickness of the remaining healthy material and force at the first crack.

Table 2. Relation between carbonation depth and bending tensile strength.

Sample	Upper (crown) region		Lower (invert) region
	Stressed from inside σf (N/mm^2)	Stressed from outside [cd (mm)]	Stressed from inside σf (N/mm^2)	Stressed from outside [cd (mm)]
P02	5.25 [6.10]	7.22 [3.28]	3.79 [6.18]	5.46 [3.86]
P06	6.41 [7.44]	6.82 [4.63]	5.20 [5.74]	4.30 [2.68]
P08	3.67 [2.38]	1.59 [15.45]	2.82 [8.77]	1.81 [10.33]
P10	4.36 [1.88]	1.97 [14.12]	3.48 [2.90]	2.15 [6.00]

Legend: σ_f – bending strength, cd – mean carbonation depth in the stressed region.

Table 3. Calculated sample size required for 95% reliability.

Pipe	Parameter	Initial estimate for the mean value	Initial estimate for the standard deviation	Sample size for the mean values. Based on Equation (2)
New	Remaining healthy material	67.3 mm	2.1 mm	1
	Density	2317.0 kg/m^2	11.5 kg/m^3	1
	Tensile splitting strength	6.34 N/mm^2	.86 N/mm^2	7
P02	Remaining healthy material	64.0 mm	5.4 mm	3
	Density	2339.0 kg/m^3	2846.0 kg/m^3	1
	Tensile splitting strength	5.44 N/mm^2	.90 N/mm^2	11
P06	Remaining healthy material	61.0 mm	3.4 mm	2
	Density	2318.0 kg/m^3	30.5 kg/m^3	1
	Tensile splitting strength	4.58 N/mm^2	.53 N/mm^2	6
P08	Remaining healthy material	40.3 mm	8.9 mm	19
	Density	2316.0 kg/m^3	43.3 kg/m^2	1
	Tensile splitting strength	3.50 N/mm^2	1.32 N/mm^2	55
P10	Remaining healthy material	44.3 mm	11.0 mm	24
	Density	2322.0 kg/m^3	41.0 kg/m^3	1
	Tensile splitting strength	3.85 N/mm^2	2.08 N/mm^2	112

Figure 18. Relation between relative confidence interval and sample size.