This technical note is recapitulation of the work carried out by researchers round the globe on characterization of waste paper sludge based on physical, chemical and mineralogical properties, activation mechanisms, pozzolanic reactivity, reaction kinematics and durability; for its possible utilization in construction industry as supplementary cementitious material, mineral admixture, partial replacement of binders in concrete, raw material for clay brick manufacturing, production of ceramics, soil stabilization in road works, reduction in carbon-dioxide emission etc., in order to encash various socio-economic and environmental benefits.

1. A report on
“UTILIZATION OF WASTE PAPER SLUDGE IN CONSTRUCTION INDUSTRY”
In partial completion of course on
Recent Advances in Construction Materials (CEL768)
Submitted by
Sandeep Jain (2014CET2226)
Submitted to
Dr. Shashank Bishnoi
Department of Civil Engineering
Indian Institute of Technology (IIT), Delhi

2. 1. Synopsis
This technical note is recapitulation of the work carried out by researchers round the globe on
characterization of waste paper sludge based on physical, chemical and mineralogical properties,
activation mechanisms, pozzolanic reactivity, reaction kinematics and durability; for its possible
utilization in construction industry as supplementary cementitious material, mineral admixture,
partial replacement of binders in concrete, raw material for clay brick manufacturing, production
of ceramics, soil stabilization in road works, reduction in carbon-dioxide emission etc., in order
to encash various socio-economic and environmental benefits.
2. Introduction
Due to exponential growth of population in recent years, resulting in greater demand for
construction and thus increasing pressure on utilization natural resources causing their acute
shortage. Cement is one of the main materials used by construction industry in large volumes and
its production leads to significant emission of carbon-dioxide; production of one ton of cement
emits approximately one ton of carbon-dioxide. Various researches are being carried in order to
achieve some replacement of cement clinker with other industrial by-products having pozzolanic
properties and hydraulic activity as supplementary cementitious admixtures (Segui et al., 2012).
Some of the successfully tested and used industrial wastes are fly ash, ground granulated blast
furnace slag, silica fume, etc. which offers benefits like potential savings in natural resources and
energy, reduction in impact of CO2 emission, and re-use of wastes which otherwise would have
been used as landfill and might require a waste management program.
One such industrial by-product is waste paper sludge from the paper manufacturing. This is
also commonly known by the names like paper de-inking sludge (García et al., 2007),
wastepaper sludge ash (WSA) (Segui et al., 2012), and hypo-sludge (Pitroda et al., 2013). The
Fig.1 shows global paper production (region-wise) in the year 2013. Bajpai P. (2015) has
reported that about 300 kilograms of dry sludge is generated in manufacturing of one tonne of
paper, and this amount greatly varies within different regions, due to change in recycling rates.
García et al. (2007) suggests that recycling to manufacture new paper is only possible for three to
eight cycles, residual sludge obtained beyond which must be discarded. At present, this residual
sludge is generally deposited in landfills causing disposal and environmental pollution problem
or is incinerated for recovery of energy, and is also used by ceramic industry and as agriculture
compost.

3. Fig. 1. Global Paper Production 2013 (By Region) (Source: PPI)
Owing to such a high volume of waste and its potential for re-use, the construction industry
presents a large forefront in recycling and reusing of waste paper sludge; which shall not only
solve the waste management problem, but may also serve as new resource for construction
industry.
3. Background
Although many possible re-uses of waste paper sludge in construction industry are reported in
the literature, the foremost use of this by-product is reported as a supplementary cementitious
material for partial replacement of cement in concrete production. In this portion of the report, an
overview is provided on characterization of waste paper sludge, activation mechanisms,
pozzolanic reactivity, reaction kinetics and its effect on durability of concrete. An effort is also
made to dwell upon the other possible re-uses of waste paper sludge.
3.1. Characterization of waste paper sludge
As waste paper sludge produced at source has a high water content ranging from 40-70%, and
must be dried before processing to resolve handling, incineration and shipping issues. The
composition of waste paper sludge varies largely depending on the grade of paper, raw material,
processing technique, quantity and quality of recycled paper used. Segui et al. (2012) carried out
characterization of waste paper sludge based on physical, chemical and mineralogical properties
as generalized below.
3.1.1. Physical Properties
To be able to re-use waste paper sludge in any application, it becomes prudent to know its
various physical characteristics like specific gravity, and fineness, particle size distribution. The
specific gravity is determined by hydrostatic weighting in kerosene (non-reactive liquid) found to
be in the range of 2.5 to 3 g/cm3. Blaine fineness shows widely varying results from 3000 to

4. 6000 cm2/g. The particle size distribution can be determined by using wet sieving and highly
inconsistent and dependent on grinding. The color is light to medium gray and may vary as per
raw composition.
As per the SEM observations (Fig.2a) by Segui et al. (2012) and (Fig.2b) by García et al.
(2007), the particles of waste paper sludge are highly porous. Various other researchers have also
observed that the particle were porous and gets agglomerated. This porosity of waste paper
sludge could lead to the increased water and plasticizer demand causing workability issues if
used in concrete production.
Fig. 2a & 2b. SEM Observation for Waste Paper Sludge by Segui et al. (2012) and García et al. (2007) respectively
3.1.2. Chemical Composition
The chemical composition of waste paper sludge is compiled in Table 1 based on the finding
of literature review. Dry waste paper sludge is formed mainly of calcium oxide (CaO), silica
(SiO2), and alumina (Al2O3) constituting to about 40-50% of total, with other oxides constituting
even less than 2% of total, except magnesium oxide (MgO) with a content of 4%. Some traces of
chloride ions and other metals like zinc; copper; lead; barium and chromium may also be present
sometimes depending upon the industrial whitening method used. All the authors have reported
significant amount of loss on ignition (LOI). The chemical composition is found to be dependent
on the temperature and time of calcination.
3.1.3. Mineralogical Composition
XRD techniques are generally employed for characterization of mineralogical composition of
waste paper sludge. The mineralogical composition consists of 2 fractions as organic and

5. inorganic. Organic part is cellulose (C12H20O10), and inorganic part comprises mainly of
crystalline mineral compounds like calcite (CaCO3), kaolinite (Al2O3.2SiO2.2H2O), free lime
(CaO), quartz (SiO2) and talc (Mg3Si4O10(OH)2) (Frías et al., 2014) (Fig. 4). Gluth et al. (2013)
and Segui et al. (2012) also detected gehlenite (Ca2Al2SiO7) as main crystalline mineral phase
and presence of portlandite (Ca(OH)2) is confirmed by Gluth et al. (2013) (Fig. 5a and 5b).
Table 1: Chemical Composition of Waste Paper Sludge
Oxide (%) CaO SiO2 Al2O3 MgO Fe2O3 TiO2 Na2O SO3 K2O P2O5 LOI
Frías et al. (2014)
700˚C/2h
40.2 22.3 14.6 2.4 0.6 0.3 0.1 0.3 0.4 0.2 18.52
Gluth et al. (2013)
*
44.18 22.33 11.97 2.42 0.59 0.36 0.24 3.64 0.40 - 13.34
Segui et al. (2012)
850˚C
45.5 28.0 13.2 4.0 1.3 0.7 0.4 1.3 0.7 0.4 5.7
García et al. (2007)
700˚C/2h
47.1 13.9 8.3 1.6 0.5 0.3 0.2 - 0.3 0.2 26.7
* Temperature not given by author.
Fig. 3. Ternary diagram for Waste Paper Sludge (Segui et al., 2012)

6. Fig. 4. XRD patterns showing mineralogical composition Waste Paper Sludge at different calcination temperature
(Frías et al., 2014)
Fig. 5a. XRD patterns for un-hydrated Waste Paper Sludge. T: talc, CH: portlandite, Q: quartz, Cc: calcite, G: gehlenite,
C: lime, C3A: tricalcium aluminate, C2S: belite (Gluth et al., 2013)

7. Fig. 5b. XRD patterns for Waste Paper Sludge. α: calcium silicate, c: calcite, g: gehlenite, L: free lime, m: merwinite,
M: mayenite (Segui et al., 2012)
4. Utilization of Waste Paper Sludge in Concrete production
The foremost application of waste paper sludge in construction industry is in concrete
production; as a supplementary cementitious material, or as partial replacement of binder or as
hydraulic mineral admixture.
Outcomes of various research shows that waste paper sludge when calcined for two hours at
around 650-750ºC, facilitate the production of metakaolin; which is highly reactive in nature and
having pozzolanic properties.
García et al. (2007) studied the pozzolanic properties of paper sludge waste and carried out
experiments by comparing the pure OPC with blend of 90% OPC plus 10% waste paper sludge.
They concluded that at calcination temperature and time of 700ºC and 2 hour respectively,
organic matter disappear and waste paper sludge become active by transforming kaolinite into
metakaolinite. They compared their results at varying calcination temperature and time period
with commercially available metakaolin (Fig. 6). This calcined product exhibit high pozzolanic
reactivity. The results also shows significant increase in compressive strength by 10%
replacement as waste paper sludge (Fig. 7), accelerated initial setting period, reduction in SO3
percentage.

8. Waste paper sludge has also shown positive results as hydraulic binder. Segui et al. (2012) has
experimented on utilization of waste paper sludge as hydraulic binder by preparing a paste with
water with water to binder ratio of 0.5. The result shows satisfactory 28 days strength
development with hydration of waste paper sludge leading to setting and hardening of paste.
They have further concluded that first the lime gets hydrated to calcium hydroxide resulting in
favorable alkaline environment for other phases to react to form C-S-H gel. Although some
limitations are also highlighted like presence of metallic aluminium may lead to expansion, also
presence of free lime could result in unsoundness.
Fig. 6. Pozzolanic activity of calcined Waste Paper Sludge with commercial metakaolin (García et al., 2007)
Fig. 7. Comparison of Compressive Strength (García et al., 2007)
Gluth et al. (2013) carried out extensive research on reaction products and strength
development of waste paper sludge activated with water and alkalis (NaOH and KOH) and found
that monocarboaluminate (CO3-AFm) is the principle reaction production in both the cases.
Small amount of CSH is also detected. Strength gain and formation of monocarboaluminate is
rapid for waste paper sludge activated by alkalis for 1 day curing but slower thereafter. Whereas

9. for water activated waste paper sludge the compressive strength is found to be twice higher for
28 days of curing while flexural strength is almost the same (Fig. 8).
Fig. 8. Strength of Waste Paper Sludge mortars: (a) Compressive (b) Flexural (Gluth et al., 2013)
In the recent review paper published by Frías et al. (2014), efforts are made to utilize waste
paper sludge as an eco-friendly and economical viable supplementary cementitious material in
cement production. They also highlighted the influence of activation condition on pozzolanic
properties, dependency of reaction kinetics on time and content of waste paper sludge, and
durability of cement blended with waste paper sludge. Their results are in-line with the finding of
other researchers like with varying temperature and calcination time the mineralogical
composition varies (Fig. 4). They reported that waste paper sludge when activated by calcination,
exhibits comparatively high pozzolanic reactivity (Fig. 9) than silica fume (SF), metakaolin
(MK), and fly ash (FA). Their result for rheological properties of blended cements with activated
waste paper sludge shows a considerable reduction in workability primarily due to presence of
free lime and calcite content, confirming the increased plasticizer and water demand, more
intensely with increasing calcination temperature and time period. Also a significant reduction in
initial setting time is noticed for blended cement (Fig. 10). Efforts are also made to determine the
effects of blending of waste paper sludge on mechanical strength and an improvement is
recorded up to 20% addition of activated waste paper sludge (Fig. 11). Other than physical and
mechanical properties, they also carried out durability assessment against chemically aggressive
environment, and blends shows improved resistance. Freeze-thaw resistance is also found to be
highly improved by use of activated waste paper sludge with cement (Fig. 12).

10. Fig. 9. Pozzolanic reactivity of Waste Paper Sludge (Frías et al., 2014)
Fig. 10. Initial setting time variation for 10% blended cement (Frías et al., 2014)
Fig. 11. Relative Compressive strength vs. curing duration for paste containing 0%, 10%, and 20% Waste Paper Sludge
(Frías et al., 2014)

11. Fig. 12. Improved resistance to freeze-thaw cycles for blended cement with Waste Paper Sludge (Frías et al., 2014)
5. Utilization of Waste Paper Sludge in Structural Ceramic and Clay Brick production
Another feasible alternative for utilization of waste paper sludge is possible in production of
clay bricks or structural ceramic. In the recent analysis carried out by Cusidó et al. (2015),
confirmed that clay brick production with partial addition of waste paper sludge is a technically
feasible solution. They used binary mixture of clay and waste paper sludge under various
formulations to study the physical, chemical and mechanical properties of the new material. The
waste paper sludge used by them has almost similar properties as described above. The outcome
for the research shows improvement in the thermal and acoustical insulation of material, which
can be attributed to the porous structure of waste paper sludge due to high presence of organic
compound like cellulose and also to presence of free lime (CaO). Results of compressive
strength for various blends ranging from 0% to 25% replacement with an interval of 5%, exceeds
10MPa (recommended) mark with an average strength of 39Mpa but overall decrease in
mechanical strength. However this fragility can be compensated by increased ductility of new
product. The thermal conductivity of material decreased with increment in percentage
replacement with extreme reduction of 38%, although the study shows drastic increment (300%
increment) of water absorption in new product. The new product does not emit any inorganic and
volatile organic compounds (VOC) material and has similar quality as conventional product.
This study thus depicts and paves the way for future research work for utilization of waste paper
sludge in various other applications in construction industry and can significantly economize the
production of various construction materials.

12. 6. Conclusions
The paradigm of information reported hereunder regarding the utilization of waste paper
sludge by construction industry, shows a strong technical feasibility for its re-use especially in
production of concrete as supplementary cementitious material, mineral admixture, partial
replacement of cement, in ternary blends cements as activator, and also as raw material for clay
brick manufacturing, production of structural ceramics, soil stabilization in road works etc.
Based on the limited understanding of waste paper sludge, following sets of conclusion can be
drawn from the foregoing.
1. Based on the characterization by various researchers, waste paper sludge has highly varying
chemical and mineralogical composition, primarily contains calcium oxide (CaO), silica
(SiO2), and alumina (Al2O3) and presence of other mineral and metal oxides depends on raw
material, processing technique, grade of paper, quality and quantity of recycled paper used.
2. It has porous structure which can be attributed to presence of free lime and alumina. On one
hand this high porosity can be a worrying characteristic if waste paper sludge is used for
concrete production and might cause workability issues, increased water and plasticizer
demand, and on other hand could enable the utilization of waste paper sludge for soil
stabilization in road works and can drastically improve the thermal and acoustic insulation
when used in production of clay bricks. Hydrogen generated by reaction of metallic
aluminium causes expansion in cement based material. It also shows a higher loss on ignition
(LOI) value.
3. Researchers report that activation of waste paper sludge is highly dependent on activation
temperature and time period of activation. However once perfectly activated, it shows high
hydraulic and pozzolanic reactivity (both for water-activated and alkali-activated) fairly
comparable to commercially available metakaoline, and silica fume. Presence of portlandite is
also reported and successful use of such waste paper sludge is demonstrated for self-activation
and activator for other pozzolanic materials like GGBS in ternary blend cements.
4. Depending on the activation condition and quantum of replacement, waste paper sludge shows
dual behavior on compressive strength of concrete. However, a judicious use up to 10% to
20% has shown significant gain in compressive strength. Initial setting time is also found to
be accelerated with utilization of waste paper sludge and can be attributed to presence of
organic matters like cellulose.

13. 5. From the durability point of view, it show improved resistance to aggressive chemical
environment and resistance against freeze-thaw cycles has also increase significantly.
Finally, it can be concluded that the re-use of waste paper sludge can significantly economize
the production of various construction materials and shall mutually benefit both the paper and
construction industry. Its judicious use can facilitate both socio-economic and environmental
benefits by reducing pressure on degrading natural resources.
7. References
Bajpai, P. (2015) “Generation of Waste in Pulp and Paper Mills”, Springer International
Publishing Switzerland (2015) DOI 10.1007/978-3-319-11788-1_2
Cusidó, J.A.; Cremades, L.V.; Soriano, C.; Devant, M. (2015) “Incorporation of Paper Sludge in
Clay Brick Formulation: Ten years of Industrial Experience”, Applied Clay Science, Vol. 108
(2015) 191–198
Frías, M.; Rodríguez, O.; Sánchez de Rojas, M.I. (2014) “Paper Sludge, an Environmentally
Sound Alternative Source of MK-based Cementitious Materials. A review”, Construction and
Building Materials, Vol. 74 (2015) 37–48
Gluth, J.G.G.; Lehmann, C.; Rübner K.; Kühne H. (2013) “Reaction Products and Strength
Development of Wastepaper Sludge Ash and the Influence of Alkalis”, Cement & Concrete
Composites, Vol. 45 (2014) 82–88
Segui, P.; Aubert, J.E.; Husson, B.; Measson, M. (2012) “Characterization of Wastepaper Sludge
Ash for its Valorization as a Component of Hydraulic Binders”, Applied Clay Science, Vol.
57 (2012) 79–85
García, R.; Vigil de la Villa, R.; Vegas, I.; Frías, M.; Sánchez de Rojas, M.I. (2007) “The
Pozzolanic Properties of Paper Sludge Waste”, Construction and Building Materials, Vol. 22
(2008) 1484–1490