preliminary characterization of excavated soils...

2

PRELIMINARY CHARACTERIZATION OF EXCAVATED SOILS

COLLECTED AT A CDW LANDFILL OF SÃO PAULO CITY

Karen Kataguiri (1), Maria Eugenia Boscov (1), Cláudia Echevenguá Teixeira (2),

Sergio Cirelli Angulo (1)

(1) Escola Politécnica, Universidade de São Paulo, Brazil

(2) Institute for Technological Research of the State of São Paulo (IPT), Brazil

Abstract

A case study was conducted to characterize materials received in a construction and

demolition waste (CDW) landfill located in the Metropolitan Region of São Paulo. The study

consisted in: systematic collection of 35 samples of materials received in the landfill, random

selection of 8 among the 35 samples, sample mass reduction, preliminary visual classification

(predominantly soil or CDW) and basic geotechnical characterization. 38% of the samples can

be classified as excavated soil using particle size distribution and visual classification criteria,

whereas 62% of the samples were classified as mixtures of excavated soils and other CDW

types (especially cement based materials). Samples classified as mixtures soil-CDW were

divided in fractions of different grain size intervals and further analyzed by microscopy to

estimate the percentage of soil grains and cement based material. Results suggest that at least

49% of the material passing the 2 mm sieve could be recovered as soil; however, this fraction

of the samples (particles with diameter 2 mm) are not very significant compared to the bulk

sample: most of the material received is still a mixture of excavated soils and other CDW

mineral types. Therefore, the need of a proper segregation of these CDW types is necessary at

construction building sites, prior to final disposal, to ensure optimal recovery.

1. INTRODUCTION

Construction industry is responsible for generating more than 50% of the urban solid waste

mass in Brazil [1, 2]. Rocks, soils, ceramics, concrete, mortars, and other mineral-originated

materials account for about 90% of the mass of construction and demolition waste (CDW) in

this country [3].

According to previous authors study, in partnership with the Building Contractor Union of

the State of São Paulo (Sinduscon-SP), the volume of excavated soil during construction is on

average six times higher than other construction waste fractions. Densely urbanized areas in

continuous growth, as the Metropolitan Region of São Paulo (MRSP), require large

underground parking infrastructure, which tends to generate large amounts of surplus soils. In

European Countries, soil generation is about three to four times higher than that of the other

CDW components [4].

Even though representing a very significant fraction, little research has been conducted on

the soil fraction present in the CDW. Excavated soils are generally disposed of in inert waste

landfills, along with other CDWs. The practice of dumping soil in the few landfills for inert

waste available in MRSP reduces their lifetime. Most of this material could be reused on

3

earthworks and trenchworks, vegetation replacement, paving, among other geotechnical uses,

or even as raw material for industrial products [5, 6, 7, 8]. While CDW has been employed as

aggregate for concrete and pavement construction, recovery of the dumped soil and the finer

fractions of CDW for geotechnical purposes is still to be explored.

This work aims to characterize and to establish technical and environmental criteria for

reuse of excavated soils and finer fractions of CDW for geotechnical applications, based on

laboratory tests carried out with samples collected at an inert waste landfill located in the

MRSP.

2. METHODOLOGY

The study consisted of two steps: a) sampling – systematic collection of 35 samples at an

inert waste landfill during eight weeks and random selection of 8 from the 35 samples, b)

characterization – visual classification (soil or mixture soil-CDW), particle size distribution

analysis, and determination of consistency limits for the fraction with diameter equal or lower

than 0.42 mm.

2.1 Sampling

C&D waste was collected in an inert waste landfill located in the south region of MRSP.

The landfill covers 360,000 m² and it is designed to receive 2,000 tons per day of mineral

C&D waste (concrete, mortar, ceramic, soils). The landfill receives material from

the southern region and part of the western region of São Paulo, as well as from other

neighboring cities: Embu, Embu Guaçu, Itapecerica da Serra, Santo Andre, São Bernardo do

Campo etc.

35 representative samples were collected from random trucks containing excavated soils

and other C&D materials. The program consisted of three collections per week (on Mondays,

Wednesdays and Fridays) during eight weeks, filling up a 40-L barrel per day, half in the

morning and half in the afternoon. Samples were collected at the moment of the material

discharge from the truck, from the scattered conical pile, with assistance of a tractor loader in

order to perform the collection at different positions of the scattered pile, preferably in the

middle and on the sides so as to obtain a more representative sample [9].

Among the 35 collected samples, 8 samples were randomly selected for conducting the

tests. Samples collection and mass reduction procedures were judicious to ensure samples

representativeness for the tests, considering the heterogeneity of the materials received at the

landfill [9].

2.2 Characterization

The initial material mass collected in each sample (about 40kg) was reduced to the

necessary masses for the tests using the riffle sample splitter (Jones type).

Particle size distribution of the bulk sample and consistency limits (liquid limit, plastic

limit and plasticity index) for the fraction with diameter 0.42 mm were evaluated according

to Brazilian standards ABNT NBR 6457: 1986, ABNT NBR 6459: 1984, ABNT NBR 6508:

1984, ABNT NBR 7180: 1988 and ABNT NBR 7181: 1988 [10, 11, 12, 13, 14], which are

similar to correspondent ASTM standards. Visual observation of the samples was conducted

to classify the samples according to the predominant material: (1) excavated soils and (2)

other CDW types (cement based materials – concrete and mortar – and red ceramic), which

were supposed to be a mixture of CDW and soil.

The next step was to determine the size fraction where soil particles were predominant in

the mixtures of CDW and soil. The mixtures of CDW and soil were sieved to the following

4

particle size intervals: 2.0 to 1.2mm, 1.2 to 0.6mm, 0.6 to 0.4mm, 0.4 to 0.1 mm, and 0.1 to

0.075mm. A minimum representative mass was calculated for each particle size interval [9]

and the size fraction of each sample was reduced to this minimum representative mass using a

rotary sample splitter for fine particulates. The minimum representative samples of each

particle size interval were observed through a microscope equipped with a digital camera, and

objective zoom lenses up to 325x were used to obtain the corresponding images. In each

image, the grains were numbered and classified as cement based material (present in high

percentage in C&D waste – fig.1a) or soil (typical clay and silt material). The grains which

were not covered with or did not present flecks of cement paste were considered as soil

grains; however, this procedure has limitations, because ceramic particles (fig.1b) can be

visually similar to soil grains (fig.2a, 2b).

For grains with diameter larger than 2.0mm, it was possible to notice the main presence of

ceramic and cement materials by means of naked eye observation (fig.3).

Figure 1: (a) Cement and (b) ceramic based grains smaller than 0.6mm of C&D waste

observed in digital microscopy

Figure 2: Soil grains smaller than 1.2mm observed in digital microscopy

a b

B-5 B-12

B-19 B-22

B-4

5

Figure 3: B-4, B-5, B-12, B-19 and B-22 sample grains larger than 2.0mm, mainly constituted

of ceramic and cement materials

3. PRELIMINARY RESULTS AND DISCUSSION

Fig.4 presents the particle size distribution of CDW landfill samples. B-7, B-15 and B-23

samples presented gravel fraction ranging between 7.2% and 23.0%, and fine fraction

( 0.075 mm) ranging between 31.4% and 48.6%. Samples B-4, B-5, B-12, B-19 and B-22

were preliminary and visually classified as mixed soil-CDW samples, with gravel fraction

ranging between 34.2% and 59.9%, and the fine fraction ( 0.075 mm) ranging between 9.2%

and 23.9%.

Figure 4: Particle size distributions of selected mineral CDW landfills samples

Particle size distributions of B-7, B-15 and B-23 presented higher percentage of fines than

the others (B-4, B-5, B-12, B-19, and B-22), being, in accordance with visual observation,

mainly constituted of excavated soils (fig.5). The B-4, B-5, B-12, B-19 and B-22 samples

were composed of a mixture of soils and other CDW types (especially cement based

materials, the most predominant fraction in this kind of waste – fig.6). According to these

results, only 38% of the studied samples can be considered as almost pure excavated soils;

most of them are mixtures of excavated soils and other CDW types.

0

10

20

30

40

50

60

70

80

90

100

0.000 0.001 0.010 0.100 1.000 10.000 100.000

Cu

mu

lati

ve

pa

ssed

ma

teri

al

(% g

/g)

Grains diameter (mm)

SAMPLES GRANULOMETRY

B-4

B-5

B-7

B-12

B-15

B-19

B-22

B-23

Clay Silt Fine Sand Medium Coarse Sand Gravel

Sieves (mesh) 200 100 50 40 30 16 10 4

6

Figure 5: Preliminary visual classification of B-7, B-15, B-23 samples, mainly constituted of

excavated soils by visual observation

Figure 6: Preliminary visual classification of B-4, B-5, B-12, B-19, B-22 samples, constituted

of a mixture of excavated soils and other CDW (mainly cement based materials)

Table 1 presents consistency limits and plasticity indexes of the fraction with diameter

equal or smaller than 0.42mm. 2 of 3 samples (B-15 and B-23) mainly composed of

excavated soils presented this fraction ( 0.42 mm) with plasticity, B-15 showing plasticity

compatible with clay and B-23 with silt. 3 of 5 samples (B-4; B-12 and B-22) composed of a

mixture of excavated soils and other CDW types presented this fraction with some plasticity.

Samples were classified according to the Unified Soil Classification System [15] (Table 1).

Table 1: Consistency limits and plasticity indexes of mineral CDW landfill fraction

( 0.42 mm) samples

Sample Liquid

Limit (%)

Plastic

Limit (%)

Plasticity

Index (%) Unified Soil Classification System

B-4 29 21 8 No applicable (mixed material)

B-5 28 * * No applicable (mixed material)

B-7 27 * * Well-graded Sand (SW)


B-15 30 21 9 Clayey Sand (SC)

B-19 * * * No applicable (mixed material)


B-23 33 27 6 Silty Sand (SM)

B-7 B-15 B-23

B-19 B-22

B-12 B-4 B-5

7

(*) fine fraction with no plasticity

Table 2 summarizes the counting of cement and soil grains. The digital microscopy image

criteria to determine the presence of cement material could not be applied for grains smaller

than 0.4 mm due to the difficulty to differentiate the cement paste grains from some feldspar

minerals.

For B-4 and B-12 samples (mixed soil-CDW samples with fraction with diameter

0.42mm showing some plasticity), separation of excavated soils (silt, clay and sand) was

possible for particle size fraction smaller than 2 mm (fig.7 and fig.8). Excavated soil

separation according to particle sizes was not possible for the other mixed samples, confirmed

by Fig. 9, 10 and 11.

Table 2: Composition classification (soil and cement based grains, smaller than 2mm) of

different particle size fractions of the mixed samples by digital microscopy

Sample Preliminary Visual

Classification

Particle Size

(mm)

Cement Fraction

(%)

Soil Fraction

(%)

B-4 Excavated soils with

other CDW types

2.0 – 1.2 49 51

1.2 – 0.6 65 35

0.6 – 0.4 61 39


other CDW types

2.0 – 1.2 84 16

1.2 – 0.6 89 11

0.6 – 0.4 98 2


other CDW types

2.0 – 1.2 37 63

1.2 – 0.6 45 55

0.6 – 0.4 53 47


other CDW types

2.0 – 1.2 92 8

1.2 – 0.6 92 8

0.6 – 0.4 91 9


other CDW types

2.0 – 1.2 98 2

1.2 – 0.6 92 8

0.6 – 0.4 96 4

Figure 7: Digital microscopy image of B-4 sample for particle size ranging from (a) 2.0 to 1.2

mm (b) 1.2 to 0.6 mm, (c) 0.6 to 0.4 mm.

a b c

8

Figure 8: Digital microscopy image of B-12 sample for particle size ranging from (a) 2.0 to

1.2 mm, (b) 1.2 to 0.6 mm, (c) 0.6 to 0.4 mm.

Figure 9: Digital microscopy image of B-5 sample for particle size ranging from (a) 2.0 to 1.2

mm, (b) 1.2 to 0.6 mm, (c) 0.6 to 0.4 mm.


1.2 mm, (b) 1.2 to 0.6 mm, (c) 0.6 to 0.4 mm.


1.2 mm, (b) 1.2 to 0.6 mm, (c) 0.6 to 0.4 mm.

a b c

a b c

a b c

a b c

9

4. CONCLUSIONS

This study presents a preliminary characterization of samples collected at an inert waste

landfill located in the Metropolitan Region of São Paulo (MRSP). 38% of the studied samples

can be classified as excavated soils using particle size distribution and visual classification

criteria, whereas 62% of the samples were classified as mixtures of soils and other CDW

types (especially cement based materials).

Two from the three excavated soil samples presented fraction with diameter 0.42 mm

with some plasticity, what was also observed in three of the five samples constituted of a

mixture of excavated soils and other CDW types. The mixtures, on the other hand, had a low

percentage of this fraction. The visual classification in excavated soil or mixtures soil-CDW,

therefore, does not provide a consistent indication of the plasticity of the fines.

Digital microscopy was used to classify the composition of mixtures in soil grains or

cement based materials for different particle size intervals. Results suggest that it is possible

to obtain material with predominance of soil grains sieving the mixtures soil-CDW through a

2 mm mesh sieve, a recovery of at least 49% of soil was possible in this case. As this material

still contains a percentage of cement, geotechnical tests will be carried out to assess the

geotechnical properties of the recovered material.

Preliminary investigations in this study shows that, using visual and particle size

distributions criteria, a recovery of at least 49% of excavated soils in samples collected in the

investigated inert waste landfill is possible. However, most of the material received is still a

mixture of excavated soils and other CDW mineral types. Therefore, the need of a proper

segregation of different CDW types is necessary at the construction building sites, prior to

final disposal, to ensure optimal recovery.

ACKNOWLEDGEMENTS

We gratefully acknowledge Institute for Technological Research of the State of São Paulo

(IPT) for supporting “Programa Novos Talentos” fellowship, and Building Contractor Union

of the State of São Paulo (Sinduscon-SP) for the technical and financial support provided for

research about construction waste generation indicators. We also acknowledge IPT and

Intercement for providing mineral CDW landfill samples used in this characterization study.

REFERENCES

[1] Associação Brasileira de Limpeza Pública e Resíduos Especiais (Abrelpe), ‘Panorama dos resíduos sólidos

no Brasil 2012’, Abrelpe, 2012. Available at: <http://www.abrelpe.org.br/Panorama/panorama2012.pdf>.

Acess in: 18th may 2014.

[2] Secretaria do Meio Ambiente do Estado de São Paulo (SMA), Sindicato da Indústria da Construção do

Estado de São Paulo (Sinduscon-SP), ‘Resíduos da Construção Civil e o Estado de São Paulo’, São Paulo:

SMA/Sinduscon-SP, 2012, 85 p.

[3] Angulo, S.C., ‘Caracterização de Agregados de Resíduos de Construção e Demolição Reciclados e a

Influência de suas Características no Comportamento Mecânico dos Concretos’, Tese de Doutorado, Escola

Politécnica, Universidade de São Paulo, 2005, 149p.

[4] Monier, V., Hestin, M., Trarieux, M., Mimid, S., Domröse, L., Van Acoleyen, M., Hjerp, P. and Mudgal,

S., ‘Study on the management of construction and demolition waste in the E.U’, Final report for the

European Commission (DG Environment), 2011.

[5] Department for Environment Food and Rural Affairs (Defra), ‘Construction code of practice for the

sustainable use of soils on construction sites’, United Kingdom, 2009.

[6] Swiss Agency for the Environment, Forests and Landscape (Saefl), ‘Guideline: reuse of excavated soils’,

Swiss, 2002.

10

[7] Waste & Resources Action Programme (Wrap), ‘Recycling of excavated spoil from utility works within

local authority areas, and promoting the use of recycled materials through good practice in procurement’,

United Kingom, 2005.

[8] Waste & Resources Action Programme (Wrap), ‘Recycled and stabilised materials in trench reinstatement’,

United Kingom, 2007.

[9] Petersen, L., Minkkinen, P. and Esbensen, K.H., ‘Representative sampling for reliable data analysis: theory

of sampling’, Chemometrics and Intelligent Laboratory Systems. 77(1) (2005) 261-277.

[10] ABNT (Associação Brasileira de Normas Técnicas), NBR 6457: Amostras de solo - Preparação para

ensaios de compactação e ensaios de caracterização. Rio de Janeiro, 1986.

[11] _________, NBR 6459: Solo - Determinação do Limite de Liquidez – Método de Ensaio. Rio de Janeiro,

1984.

[12] _________, NBR 6508: Grãos de solos que passam na peneira de 4,8 mm - Determinação da massa

específica. Rio de Janeiro, 1984.

[13] _________, NBR 7180: Solo - Determinação do Limite de Plasticidade – Método de Ensaio. Rio de Janeiro,

1988.

[14] _________, NBR 7181: Solo - Análise granulométrica – Método de Ensaio. Rio de Janeiro, 1988.

[15] Standard, A.S.T.M., D2487: Standard practice for classification of soils for engineering purposes (Unified

Soil Classification System). West Conshohocken, 2011.

preliminary characterization of excavated soils...

Documents