Performance of mortars with the Performance of mortars with the addition of septic tank sludge ash of septic tank sludge ash

(1)

Performance of mortars with the addition of septic tank sludge ash

Maria del Pilar Durante Ingunza

a,⇑

, Gladis Camarini

b

, Felipe Murilo Silva da Costa

a

Federal University of Rio Grande do Norte, Department of Civil Enginering, Campus Universitário, Lagoa Nova, CEP 59078-970 Natal, RN, Brazil

b

GEDRRIC, LMC, LARES, University of Campinas, Department of Architecture and Construction, School of Civil Engineering, Architecture and Urban Design, Cidade Universitária Zeferino Vaz, s/n, CP 6021, CEP 13083-970, Brazil

h i g h l i g h t s

Septic tank ash (SA) addition improved overall condition of mortar.

Better performance in both the fresh and hardened state.

Improvement the particle packing by SA filling action.

SA addition increases density and reduces consistency of mortar.

a r t i c l e

i n f o

Article history:

Received 10 January 2016

Received in revised form 19 October 2017 Accepted 14 November 2017

Available online 29 November 2017 Keywords:

Septic tank sludge ash Mortars

Portland cement Performance

a b s t r a c t

This paper studies the performance of mortars with the addition of septic tank sludge ash (SA). The sludge is a non-dangerous and non-inert residue. The cement-sand content is 1:3, in mass, commonly used for masonry in building construction. The percentages of sludge ash additions were 5, 10, 15, 20, 25 and 30% related to the cement mass. The results show that the addition of SA improves the general condition of the mortars, within the limits studied in this paper, providing better performance on both fresh and hard-ened states.

1. Introduction

The sewage sludge use as a byproduct in the construction industry has been discussed in researches in the last decades [1–7]. Mostly, sewage sludge ash has been utilized in mortars as mineral addition, such as fillers, in bricks and in ceramic floors [8–15].

Although the sludge is not the only waste produced in the sew-age treatment system, it is commonly considered as a great envi-ronmental concern, specially its final disposal, due to the chemical characteristics and high production[16].

Septic tank sludge or septage is a type of sewage sludge defined as a liquid or solid material removed from a septic tank that receives only domestic sewage [17]. Septic tank sys-tems are commonly utilized in rural areas but also in urban areas without basic sanitation systems. Although EPA regula-tions includes this type of waste to land applicaregula-tions [18] it have been studied more rarely as raw material in civil

con-struction; probably due to its low production rather than its properties.

In order to use the sewage sludge in construction, its calcination is necessary, having as the main purpose the elimination of water, organic matter and pathogenic micro-organisms. The calcination also brings the interaction of the sewage sludge ash with the com-pounds from cement hydration.

The properties of sewage sludge as raw material depend on its origin, type of treatment, calcination temperature and fineness. The relevant physical characteristics of sewage sludge are particle size and their morphology. Thus, the filler action of the SSA favors the performance of mortars[19]. The chemical composition is, in fact, a limiting factor to the SSA pozzolanic activities, mainly due to the silica content[7]. Further, a low to moderate pozzolanic activity of the SSA has been reported[14,20]and an increase of the mortar’s mechanical performance with the SSA addition [8,9,21].

The irregular morphology of the grains of the SSA particles seems to cause a decrease in mortar mechanical performance. This can be explained by the increase in the water/binder ratio due to the high specific surface of the SSA[19]. In this way, some studies

https://doi.org/10.1016/j.conbuildmat.2017.11.053

E-mail address:[email protected](M. del P. Durante Ingunza).

Contents lists available atScienceDirect

Construction and Building Materials

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c o n b u i l d m a t

(2)

same order of magnitude of the concentrations of leachaged chemicals.

This experimental work studied the performance of mortars with addition of septic tank sludge ash (SA) as a contribution to the sustainable management practices of domestic wastes. 2. Experimental procedures

2.1. Materials

The cement used in all experiments was the CP-IV-RS-32 (equivalent to ASTM IP - Portland Pozzolan Cement) habitually used in local construction.Tables 1 and 2show the chemical and physical cement properties, respectively.

The fine aggregate was a quartz sand (natural river sand) (Fig. 1).

The sludge used is a septic tank sludge treated in a system of stabilization ponds, classified as not inert and non-hazardous waste.

The septic tank sludge calcination temperature was 850°C, adopted due to the full elimination of humidity and organic matter [25].

The milling time was defined on the basis of published work by Pan et al.[8], in which 6 h of milling resulted in greater pozzolanic activity and greater compressive strength.

All tests and analyzes were performed with the ash in its final stage of processing, i.e., all the SA passing through the sieve 0.075 mm.

The particle size distribution (Fig. 2) indicates that the average diameter of the used SA is of 30.23mm. Much smaller than the sand (720

l

m) and greater than that of cement (which varies between 10 and 15

l

m), giving the ash a filler characteristic. This feature allows the filling of the voids in the mortar and improves the cement matrix.

Regarding the specific gravity, the SA presents intermediate val-ues between the cement and sand. As the SA has a higher specific gravity than the sand, it is expected that the densities in the fresh and hardened state of the produced mortars with it will not increase.

Observed by Scanning Electron Microscope (SEM), the SA mor-phology (Fig. 3) shows an irregular surface formed by angular par-ticles with low sphericity, whose grains have a diameter smaller than 100

l

m (Fig. 3a). With the larger particles, there is a number of very small particles having the same angular morphology, whose diameters are smaller than 2

l

m (Fig. 3b). There is still a conglomerate of ash particles, which will certainly have a positive influence on the filler effect improving the cement matrix.

Chemically, the septic tank ash is mainly composed of SiO2

(34.9%), Al2O3(26.6%) and smaller proportions of CaO (5.8%), SO3

(5.8%), Fe2O3(5.4%), P2O5(5.2%), MgO (3.5%). The sample presented

a loss on ignition of 10.22% (Table 3). Table 1

Chemical of cement CP-IV-32-RS.

Oxides Content (%) SiO2 27.27 Al2O3 7.04 Fe2O3 3.78 CaO 50.59 MgO 2.23 SO3 3.59 Na2O 0.64 K2O 1.15 CO2 1.48 CaO free 1.06 Insoluble Residue 14.28 LOI 3.56%

LOI – Loss on Ignition.

Compressive strength (Mpa)

3 days 21.0 7 days 26.8 28 days 34.2 (*) Brazilian Standard NBR 5736[24]. 0 10 20 30 40 50 60 70 80 90 100 110 0,075 0,15 0,3 0,6 1,18 2,38 4,75 6,3 9,5 Sieve Size (mm) % Percentage Passing

Fig. 1. Sieve analysis of the natural sand.

(3)

The SA showed a pozzolanic activity of 74%, very close to the one established by the Brazilian standard [26] and ASTM [27]. Geyer[13]obtained similar results.

2.2. Mixtures

The cement-sand proportion used is 1:3, in mass, based on the works of Monzó et al.[9]and Coutand et al.[19]. This type of mor-tar is widely used in construction, and suitable for use in structural

concrete block masonry, masonry of stones, and other masonry components.

The water/cement ratio was the same in all tests, based on the flow table test to reach the mortar consistency index of 260 ± 5 mm. This value was obtained after several attempts and resulted in 418.75 g of water, corresponding to the water/cement ratio of 0.67.

The percentages of SA addition were 5, 10, 15, 20, 25 and 30% related to the cement mass (Table 4).

2.3. Methods

2.3.1. Tests on the fresh mortar

On fresh state, mortar consistency was assessed using the flow table (Fig. 4). In addition, entrapped air, bulk density and water retentivity were undertaken.

2.3.2. Tests on the hardened mortar

In hardened state, mortar bulk density, capillary water absorp-tion (Fig. 5), tensile strength (Fig. 6a), compressive strength (Fig. 6b) and adhesion strength (Fig. 7) were undertaken.

2.4. Microstructure

The mortar microstructure was observed using Scanning Elec-tron Microscopy, with a SEM HitachiTM3000, in order to identify and analyze the pores inside the matrix and the interface matrix-aggregate.

The samples to perform the microscopy were mortars with 0% and 20% of SA at the age of 91 days to verify the occurrence of poz-zolanic reaction.

3. Results and discussion 3.1. Tests on the fresh state 3.1.1. Mortar consistency

The mortar consistency results (Fig. 8) show that the addition of SA causes reduction in consistency rates. This occurred due to the SA irregular morphology, which absorbed part of the mixing water, lowering the workability and changing significantly the consis-tency rate of the mortar[9].

The mortars with 25% and 30% of SA addition showed a consis-tency lower than 225 mm and they were discarded.

Fig. 3. SEM images of SA.

Table 3

Chemical analysis of the SA.

Oxides Content (%) SiO2 34.94 Al2O3 26.65 Fe2O3 5.40 CaO 5.78 SO3 5.78 K2O 0.74 MgO 3.51 P2O5 5.21 SrO 0.01 MnO 0.04 TiO2 1.20 ZnO 0.34 CuO 0.09 Cr2O3 0.03 ZrO2 0.03 PbO 0.01 NiO 0.01 L.O.I. 10.22

LOI: Loss on Ignition.

Table 4

Mortar mix design.

SA addition Cement (kg) Sand (kg) SA (kg) Water/cement ratio (kg/kg) 0 1 1 0 0.67 5 1 1 0.05 0.67 10 1 1 0.1 0.67 15 1 1 0.15 0.67 20 1 1 0.20 0.67 25 1 1 0.25 0.67 30 1 1 0.30 0.67

(4)

3.1.2. Entrapped air content

The addition of SA causes a reduction in entrapped air content that is proportional to the quantity of ash added. Therefore, there was a reduction of 8.7% for the addition of 20% of SA.

This may be due to the lower water/(cement + ash) ratio and the filler action, since less water results in less empty spaces and the ash fine grains fill the voids, reducing the air content of the mortar.

3.1.3. Bulk density

The addition of SA increased the bulk density (1.8% to 20% of SA). Carasek[28]states that the density varies inversely with the

entrapped air content. If there is a reduction of voids, there is an increase in density.

3.1.4. Water retention

The SA addition increased water retention (3.5% to 20% of SA addition) caused by the reduction of voids and by the fine particles and the shape of the SA.

The ash particles when mixed into the mortar decrease the cap-illary voids, as well as the nucleation sites, and there is a less per-colation of water through the capillary pores and an increase in water retention[29].

Consistency - flow table

Entrapped air and bulk density

Fig. 4. Tests performed on the fresh mortar.

Fig. 5. Capillary water absorption test.

(a) Tensile strength

(b) Compressive strength

(5)

Fig. 7. Pull-out test.

Fig. 8. Consistency rate of standard mortars with the addition of SA.

0.16 0.15 0.15 0.14 0.13

0.21

0.20

0.18

0.16

0.10 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.19 0.20 0.21 0.22 0.23 0.24 0.25 0 5 10 15 20

Water absorpon by capillarity 10 min (g/cm²)

Water absorpon by capillarity 90 min (g/cm²)

SSA Addition (%)

(6)

Water retention may have influence on drying shrinkage since the change of capillary pores increase the tightness of mortars low-ering the evaporation of water and their loss to the substrate[30]. 3.2. Tests on the hardened state

3.2.1. Bulk density

The bulk density increased 2.6% to 20% with the SA addition. The mortar bulk density had a similar performance as in the fresh state, but with lower values. This may occur due to the water evap-oration during the curing period, which leads to the decrease of the total weight of the mortar[28].

3.2.2. Capillary water absorption

Capillary water absorption results at 10 min and 90 min (Fig. 9) indicate that, for the two measurement periods, the addition of SA

decreased the water absorption. This may be due to the better packing of the composite with the addition of SA, as well as the fil-ler effect caused by fine particles of SA occupying the empty spaces.

The capillary coefficient remained unchanged for all addition levels. The mortars have a low capillary coefficient, which also means a low value of permeability, contributing to the increase in waterproofness and durability.

3.2.3. Compressive strength

The results at 28 and 91 days (Fig. 10) show that SA addition increases the compressive strength. The highest value was obtained at the mortar with 20% of SA. After 91 days, the compres-sive strength increased 39%.

The SA filler action provides the particle packing, reducing the space available for the water, and increasing the mortar density.

15.8

16.7

17.7

18.7

19.7

16.4

18.1

19.8

21.4

22.8

8.0 9.5 11.0 12.5 14.0 15.5 17.0 0 5 10 15 20

SSA Addition (%)

Fig. 10. Compressive Strength at days 28 and 91 of mortars.

4.6

5.2

5.7

5.9

4.8

5.6

6.2

6.5

6.4

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 0 5 10 15 20

Flexural strength at 28 days (Mpa)

Flexural strength at 91 days (Mpa)

SSA Addition (%)

(7)

In this way, there is an increase in compressive strength and durability.

3.2.4. Flexural strength

The flexural strength results at 28 and 91 days (Fig. 11) increased related to the reference mortar. The highest value was to the mortar with 15% of SA addition. At the age of 91 days, the increase was of 35%. This result corroborates the information about the filler action of the SA, which results in better particles packing. 3.2.5. Microstructure

The reference mortar has pores with larger diameters than 20% SA mortar, which justify the obtained results, showing that mor-tars with SA addition have less voids and are more compact, result-ing in better mechanical properties (Figs. 12and13).

Fig. 14shows the transition zone of the mortar with aggregate (1) and the hydrated products from the paste, such as Calcium Sil-icate Hydrate, C-S-H (2 and 3), and Calcium Hydroxide, CH (4). In theFig. 15the CH does not appear which contributes negatively to the chemical stability of the compound, probably due to the poz-zolanic reaction that transforms CH into C-S-H, improving mechan-ical properties and reducing voids, confirming the previous results of improved performance of the mortars with the addition of ash. 4. Conclusions

The purpose of this work was to study the performance of mor-tars with the addition of septic tank sludge ash (SA). With this experimental work the following conclusions can be drawn:

1. The ash from septic tank sludge is a heterogeneous material, predominantly crystalline. It has an intermediate density between cement and sand, angular particles with low spheric-ity. The SA cannot be classified as pozzolanic, although it has a pozzolanic activity rate very close to that required by the Brazilian Standards.

2. The SA addition reduces the consistency of the mortar due to its absorption capacity.

3. With the SA addition, the entrapped air content and the capil-lary water absorption decreased. The fine particles filling action provokes the improvement of the particle packing, reducing the existing voids and increasing the mortar density.

4. The microstructure revealed that SA mortar shows less pores than reference. It is due to a better particle packing and, proba-bly, an over time pozzolanic reaction, providing better closing of the pores by hydrated calcium silicates (C-S-H).

5. The SA addition improved the overall condition of the mortar, providing better performance in both the fresh and hardened state. The 20% SA addition can be considered, on the limits stud-ied in this work, more suitable, technically and sustainably. Fig. 12. SEM image of reference mortar.

Fig. 13. SEM image of mortar with 20% of SA.

Legend: aggregate (1) C-S-H (2 and 3), and CH (4)

Fig. 14. SEM image of reference mortar (amplified).

Legend: aggregate (1) C-S-H (2), ettringite (3)

Fig. 15. SEM image of mortar with 20% of SA addition (amplified).

(8)

[5]I.-J. Chiou, K.-S. Wang, C.-H. Chen, Y.-T. Lin, Lightweight aggregate made from sewage sludge and incinerated ash, Waste Manage. 26 (2006) 1453–1461. [6]C.R. Cheeseman, C.J. Sollars, S. McEntee, Properties, microstructure and

leaching of sintered sewage sludge ash, Resour. Conserv. Recycl. 40 (2003) 13–25.

[7]M. Cyr, M. Coutand, P. Clastres, Technological and environmental behavior of sewage sludge ash (SSA) in cement-based materials, Cem. Concr. Res. 37 (2007) 1278–1289.

[8]S.C. Pan, D.H. Tseng, C. Lee, Influence of the fineness of sewage sludge ash on the mortar properties, Cem. Concr. Res. 33 (11) (2003) 1749–1754. [9]J. Monzó, J. Payá, M.V. Borrachero, A. Córcoles, Use of sewage sludge ash (SSA) –

cement admixtures in mortars, Cem. Concr. Res. 26 (9) (1996) 1389–1398. [10] M.A. Tantawy, A.M. El-Roudi, E.M. Abdalla, M.A. Abdelzaher, Evaluation of the

Pozzolanic Activity of Sewage Sludge Ash, International Scholarly Research Network, ISRN Chemical Engineering, 2012 Article ID 487037.

[11] F. Baeza-Brotons, P. Garcés, J. Payá, J.M. Saval, Portland cement systems with addition of sewage sludge ash. Application in concretes for the manufacture of blocks, J. Cleaner Prod. (2014),https://doi.org/10.1016/j.jclepro.2014.06.072. [12]J.E. Alleman, N. Bernan, Construtive sludge management: Biobrick, J. Environ.

Eng. 110 (2) (1984) 301–311.

[13] A.L.B. Geyer, Study of use of sewage sludge ash as an addition in concrete, in: 3th. International Conference on High- Performance Concrete, 2002, Rio de Janeiro. High performance concrete, vol. 1, 2002, pp. 111–124.

[14] M.C. Fontes, R.D. Barbosa, J.P. Toledo, Gonçalves potentiality of sewage sludge ash as mineral additive in cement mortar and high performance concrete, in:

ash, Waste Manage. 28 (12) (2008) 2495–2502.

[21]J.I. Bhatty, K.J. Reid, Compressive strength of municipal sludge ash mortars, ACI Mater. J. 86 (4) (1989) 394–400.

[22]F.C. Chang, J.D. Lin, C.C. Tsai, K.S. Wang, Study on cement mortar and concrete made with sewage sludge ash, Water Sci. Technol. 62 (7) (2010) 1689. [23]J.A. Cusido, L.V. Cremades, M. González, Gaseous emissions from ceramics

manufactured with urban sewage sludge during firing processes, Waste Manage. 23 (2003) 273–280.

[24] ABNT, Brazilian Standard Test Methods. NBR 5736. Pozzolanic Portland cement-Specification, 2003, Rio de Janeiro.

[25] Metcalf, Eddy, Wstewater Engineering. Treatment. Disposal and Reuse, 3rd ed., McGraw-Hill publishing Company, New York, 1992.

[26] ABNT, Brazilian Standard Test Methods, NBR 12653. Pozzolans- Requirements, 2012. Rio de Janeiro.

[27] ASTM C618-15, Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete, ASTM International, West Conshohocken, PA, 2015,http://www.astm.org.

[28] H. Carasek, Argamassas, in: G.C. Isaia, Civil Construction Materials and Principles of Materials Science and Engineering. 1st ed., vol. 2, IBRACON, São Paulo, 2007, pp. 893–944.

[29] D.C.C. Dal Molin, Mineral additions, in: G.C. Isaia, Concreto: Ciência e Tecnologia, IBRACON, São Paulo, Ed, 2011, 1946 p (Cap 8).

[30] A.M.P. Carneiro, M.A. Cincotto, V.M. John, The unit mass of sand as an analytical parameter of mortars features, Ambiente Construído 1 (2) (2007) 37–44 (São Paulo Brazil).