Abstract An innovative option to extend the service life of construction and building materials is the use of bio-healing agents. This study was focused on assessing the protection and consolidation effect of eco-friendly healing agents by analysing the water absorption of recycled concrete. A recycled concrete with 50% replacement of natural coarse aggregate by construction and demolition waste (CDW) aggregate and a similar recycled concrete in which, additionally, the Portland cement was replaced by recycled cement (with 25% ceramic waste) were biotreated by healing agents. These agents were obtained by using waste biomass of two different mixed microbial cultures from polyhydroxyalkanoates production processes. Results have shown that biotreatments decreased the water absorption significantly, more evident in concrete samples with both recycled cement and aggregates than on the other type of concrete. Resumen Una innovadora posibilidad planteada para prolongar la vida útil de los materiales de construcción y edificación es el uso de agentes bioreparadores. Este estudio se centró en la evaluación del efecto protector y consolidante de agentes reparadores y respetuosos con el medio ambiente mediante el análisis de la absorción de agua del hormigón reciclado. Un hormigón reciclado con sustitución del 50% de los áridos gruesos naturales por residuos de construcción y demolición (RCD) y un hormigón reciclado similar en el cual, además, se sustituyó el cemento convencional Portland por cemento reciclado (con 25% de residuo cerámico) fueron biotratados con agentes reparadores. Estos agentes se obtuvieron en el proceso de producción de polihidroxialcanoatos utilizando biomasa residual de dos cultivos microbianos mixtos diferentes. Los resultados mostraron que los biotratamientos disminuyen significativamente la absorción de agua del hormigón, siendo más eficaces en las muestras de hormigón que combinan cemento y árido reciclado que en el otro tipo de hormigón.authorsversionpublishe

Faria, Paulina

Freches, André Correia

Garcia-Gonzalez, Julia

Guerra-Romero, Manuel Ignacio

Juan-Valdes, Andres

Lemos, P. C.

Moran-del Pozo, Julia

Pereira, Maria Alice Santos

English

New University of Lisbon's Repository

  
1 
 
ECO-FRIENDLY HEALING AGENTS FOR RECYCLED 
CONCRETE 
Julia GARCÍA-GONZÁLEZ 
PhD. Researcher. Escuela de Ingeniería Agraria y Forestal, University of Leon.  
julia.garcia@unileon.es 
André FRECHES 
Researcher. LAQV-REQUIMTE, Dep. of Chemistry, Faculdade de Ciências e Tecnologia, 
Universidade NOVA de Lisboa. a.freches@campus.fct.unl.pt 
Paulo C. LEMOS 
Principal Investigator. LAQV-REQUIMTE, Dep. of Chemistry, Faculdade de Ciências e 
Tecnologia, Universidade NOVA de Lisboa. paulo.lemos@fct.unl.pt 
Alice S. PEREIRA 
Professor. UCIBIO-REQUIMTE, Dep. of Chemistry, Faculdade de Ciências e Tecnologia, 
Universidade NOVA de Lisboa. masp@fct.unl.pt 
Andrés JUAN-VALDÉS 
Professor. Escuela de Ingeniería Agraria y Forestal, University of Leon.    
andres.juan@unileon.es 
Julia Mª. MORÁN-DEL POZO 
Professor. Escuela de Ingeniería Agraria y Forestal, University of Leon.  
julia.moran@unileon.es 
M. Ignacio GUERRA-ROMERO 
Professor. Escuela de Ingeniería Agraria y Forestal, University of Leon.  
ignacio.guerra@unileon.es 
Paulina FARIA 
Professor. CERIS and Dep. Civil Engineering, Faculdade de Ciências e Tecnologia, 
Universidade NOVA de Lisboa. mpr@fct.unl.pt 
 
 
 
 
 
2 
ABSTRACT 
An innovative option to extend the service life of construction and building materials is the 
use of bio-healing agents. This study was focused on assessing the protection and 
consolidation effect of eco-friendly healing agents by analysing the water absorption of 
recycled concrete. A recycled concrete with 50% replacement of natural coarse aggregate by 
construction and demolition waste (CDW) aggregate and a similar recycled concrete in 
which, additionally, the Portland cement was replaced by recycled cement (with 25% ceramic 
waste) were biotreated by healing agents. These agents were obtained by using waste 
biomass of two different mixed microbial cultures from polyhydroxyalkanoates production 
processes. Results have shown that biotreatments decreased the water absorption 
significantly, more evident in concrete samples with both recycled cement and aggregates 
than on the other type of concrete. 
 
RESUMEN 
Una innovadora posibilidad planteada para prolongar la vida útil de los materiales de 
construcción y edificación es el uso de agentes bioreparadores. Este estudio se centró en la 
evaluación del efecto protector y consolidante de agentes reparadores y  respetuosos con el 
medio ambiente mediante el análisis de la absorción de agua del hormigón reciclado. Un 
hormigón reciclado con sustitución del 50% de los áridos gruesos naturales por residuos de 
construcción y demolición (RCD) y un hormigón reciclado similar en el cual, además, se 
sustituyó el cemento convencional Portland por cemento reciclado (con 25% de residuo 
cerámico) fueron biotratados con agentes reparadores. Estos agentes se obtuvieron en el 
proceso de producción de polihidroxialcanoatos utilizando biomasa residual de dos cultivos 
microbianos mixtos diferentes. Los resultados mostraron que los biotratamientos disminuyen 
significativamente la absorción de agua del hormigón, siendo más eficaces en las muestras 
de hormigón que combinan cemento y árido reciclado que en el otro tipo de hormigón. 
 
Keywords:  Surface healing, mixed microbial culture, biotreatment, water absorption, 
construction and demolition waste, recycled aggregate, recycled cement, ceramic waste. 
 
1. INTRODUCTION 
Repairing needs gradually increases with 
the increase of age of concrete 
structures. In some cases, it can be more 
economical to accept the need for repair 
at suitable intervals than to attempt to 
build a structure that will be maintenance-
free under severe conditions for a long 
period. In addition, in spite of the 
relatively good durability of concrete as 
construction material, there are large 
numbers of structures worldwide which 
deteriorate due to expected factors that 
generate cracks (overloading, fatigue 
effects, changes in use, natural disasters, 
etc.). Therefore, surface cracking in 
concrete structures is inevitable; however, 
some cracks shall be repaired to prevent 
further structural damages and save 
money by being proactive. Several 
studies have tested the surface healing 
effect of organic and inorganic treatments 
on cement-based materials [1-7], showing 
improvements on permeability, resistance 
to moisture diffusion and filling of surface 
  
3 
cracks and voids. This study searches for 
a suitable bioproduct compatible with the 
existing cementitious substrate and able 
to improve the concrete surface quality by 
biotreatment of incipient cracks and 
porous structure. External repairing 
decreases maintenance costs of aged 
concrete structures and increases 
sustainability in the construction industry, 
being important advantages of this 
technology. 
2. MATERIALS AND METHODS 
A recycled concrete with 50% 
replacement of natural coarse aggregate 
by CDW aggregate (RAC - recycled 
aggregate concrete) and a similar 
recycled concrete in which, additionally, 
the Portland cement was replaced by 
recycled cement (with 25% ceramic 
waste) (RACC - recycled aggregate and 
cement concrete) were prepared to 
assess the protection and consolidation 
effect of an eco-friendly healing 
biotreatment on water absorption. A 
commercially available Portland blended 
cement CEM III/A 42.5 N/SR was 
conformed to the Spanish [8-9] and 
European [10] standards. In RACC, this 
Portland cement was replacement by 
recycled cement with 25% waste ceramic 
fraction. Table 1 shows the chemical 
composition of both types of cement. 
 
Natural aggregates presented a siliceous 
nature and complied with the 
requirements of the EHE-08 [11] and EN 
12620+A1 [12]. Recycled mixed 
aggregates (RMA) were obtained through 
a mechanical treatment of CDW in a 
recycling plant located in the Autonomous 
Community of Madrid (Spain). The 
composition of the RMA, determined 
according to EN 933-11 [13], is presented 
in Table 2. 
 
Chemical composition (%) 
  CEM III/A 
42.5 N/SR 
Recycled 
cement 
Al2O3 7.59 7.32 
CaO 51.33 47.04 
Cl 0.02 0.04 
Fe2O3 2.04 3.06 
MgO 3.87 2.24 
P2O5 0.06 0.17 
K2O 0.60 1.70 
SiO2 25.08 29.35 
Na2O 0.14 0.41 
SrO 0.11 0.08 
SO3 2.54 2.45 
TiO2 0.39 0.31 
ZnO 0.04 0.03 
Cr2O3 0.01 0.01 
MnO 0.22 0.09 
LOI 3.930 2.66 
 Table 1: Chemical composition of Portland and 
recycled cement 
 
Component % 
(w/w) 
Unbound aggregates (natural 
aggregates without cement 
mortar attached) 
44.1 
Ceramics (bricks, tiles, stoneware 
and sanitary ware, …) 
33.6 
Concrete and mortar (natural 
aggregates with cement mortar 
attached) 
17.5 
Asphalt 0.4 
Glass 0.8 
Gypsum 3.5 
Other impurities (wood, paper, 
metals, plastic, …) 
0.1 
Table 2: Non-floating components of recycled 
aggregates 
 
4 
Physical and mechanical properties of 
RMA and natural aggregates such as D/d 
ratio [14], fines content [14], flakiness 
index [15], Los Angeles coefficient [16], 
were within the suitable parameters 
established by EHE-08 [11] for the 
concrete manufacture. Nevertheless, 
results obtained for RMA water 
absorption [17] showed a greater 
variation compared to the natural 
aggregates. The presence of attached 
mortar and ceramic materials in the 
recycled aggregates caused significant 
water absorption, higher than the one of 
the natural aggregates. The use of 
aggregates with high water absorption 
could result in a workability drawback. 
Consequently, the RMA were pre-
saturated: a technique that showed to be 
a suitable method to manufacture 
inexpensive recycled concrete with low 
strength requirements and maintain a 
suitable workability [18]. Table 3 shows 
the detailed composition of the different 
raw components used in the manufacture 
of the concretes (RAC and RACC, both 
have the same composition, only the kind 
of cement is changed). The w/c ratio and 
fck of both concretes is 0.5 and 25 MPa, 
respectively. 
Material Composition 
Water (l)  155 
Cement (kg) 313 
Sand 0/4 mm (kg) 97 
Sand 0/5 mm (kg) 442 
Gravel 4/10 mm (kg) 242 
Gravel 6/12 mm (kg) 81 
RMA 4/20 mm (kg) 323 
Table 3: Mix composition per cubic metre of 
concrete 
 
The test samples were cubes cut from 
concrete specimens that were molded, 
and had a cut surface with 50 mm x 50 
mm. 
 
The bioproducts used as healing agents 
were eco-friendly, being obtained by 
waste biomass from a microbial mixed 
culture (MMC) for polyhydroxyalkanoates 
production using pine wood bio-oil as 
substrate, on one hand, and crude 
glycerol (biodiesel by-product) on the 
other hand. MMC cell walls were 
disrupted by sonication (MMC-P_S and 
MMC-Gly_S) or not (MMC-P and MMC-
Gly). In addition, two different 
concentrations of each product were 
tested (* - 1 Vol. of biopolymer:2 Vol. of 
water – lower concentration; ** - 1 Vol. of 
biopolymer:1 Vol. of water – higher 
concentration). Table 4 shows the 
different treatments.  
 
Samples were treated with 2 mL of each 
bioproduct suspensions by using a 
pipette, covering the top surface. 
 
The effect of each bioproduct on surface 
treatment was evaluated and compared 
with untreated samples (control) and 
treated with the same volume of tap water 
(reference). For each biotreatment and 
concrete, three samples were tested. The 
test room conditions were 20±2°C and 
40±5% relative humidity (RH). Two days 
after the application, the healing capacity 
was assessed by water-drop absorption 
test performed in the test room. This test 
allows evaluating the permeability 
variation of the biotreated surfaces by 
monitoring the time required to absorb a 
water drop under open air conditions. The 
test was video recorded and the 
absorption time was then defined for each 
concrete, number of applications and 
treatment. 
  
5 
 
 
Treatment 
code 
Treatment definition 
Control Control 
H2O Reference with water 
MMC-Gly* MMC from glycerol 
without sonication, lower 
concentration 
MMC-Gly** MMC from glycerol 
without sonication, 
higher concentration 
MMC-Gly_S* MMC from glycerol with 
sonication, lower 
concentration 
MMC-Gly_S** MMC from glycerol with 
sonication, higher 
concentration 
MMC-P* MMC from pinewood 
biooil without sonication, 
lower concentration 
MMC-P** MMC from pinewood 
biooil without sonication, 
higher concentration 
MMC-P_S* MMC from pinewood 
biooil with sonication, 
lower concentration 
MMC-P_S** MMC from pinewood 
biooil with sonication, 
higher concentration 
Table 4:  Code and definition of treatments 
 
3. RESULTS AND DISCUSSION 
Figure 1 shows the time of water drop 
absorption for each biotreated concrete 
samples, the control (untreated) and the 
reference (with water application) 
samples. 
Results have shown that all biotreatments 
increase significantly the absorption time, 
improving the expected durability of the 
concrete surfaces. On the contrary, the 
reference concretes, with tap water, 
presented an increase in water drop 
permeability, being the absorption time 
shorter than in the control concrete in all 
cases. 
The water drop absorption test shows that 
the MMC treatments are noticeable more 
effective in concrete with recycled cement 
than with conventional cement. This 
demonstrates the importance of the type 
of construction material surface to treat. 
Further research is needed, but these 
results point an appropriate healing effect 
of eco-friendly biopolymer treatments, 
improving with the presence of recycled 
ceramic. Also it is shown that, in most of 
cases, the biopolymer concentration 
directly benefits the healing effect on the 
treated samples.  However, the sonication 
step apparently does not have influence 
over the water absorption of the 
concretes tested in this research, or even 
the water absorption resistance of the 
concrete samples decreases in 
comparison with the samples treated with 
the same bioproduct without sonication 
(MMC-P samples). 
Chandra et al. [2] tested the use of cactus 
extract on concrete samples surface, to 
improve the water absorption resistance, 
achieving an upgrade of 83%. Woo et al. 
[1], evaluating the barrier performance of 
silane/clay nanocomposites as a coating 
material on concrete structures under 
different accelerated weathering tests, 
obtained an increase of water resistance 
of 29-57%. The improvement observed in 
this study is clearly higher (578-7328%). 
Further studies will allow to justify this 
effect and if it will be durable. 
 
 
6 
Figure 1: Water drop absorption time on concrete samples 
 
5. CONCLUSION 
A single application of the biotreatments 
with bioproducts from a mixed microbial 
culture for polyhydroxyalkanoates 
production process increases significantly 
the water drop absorption time on both 
recycled aggregate concrete and recycled 
cement and aggregate concrete, 
producing a decrease of their permeability 
and demonstrating the biopolymer healing 
effect.  
The MMC treatments are noticeable more 
effective in concrete with recycled cement 
than with conventional cement, which 
means in this case that the presence of 
recycled ceramic in the concrete 
increases the healing effect of biopolymer 
treatments of treated surfaces. 
ACKNOWLEDGMENTS 
This work was supported by a STSM 
Grant from the COST Action CA15202. 
(http://www.sarcos.enq.cam.ac.uk) and 
the Project BIA2017-83526-R “Procesos 
de auto-sanado mediante bio-polímeros 
en hormigones y morteros reciclados”, 
funded by the Spanish Ministry of 
Science, Innovation and Universities. This 
work was also supported by the Associate 
Laboratory for Green Chemistry-LAQV 
0
500
1000
1500
2000
2500
3000
3500
RAC RACC
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7 
and Applied Molecular Biosciences Unit-
UCIBIO which are financed by national 
funds from FCT/MCTES 
(UID/QUI/50006/2013; 
UID/Multi/04378/2013) and co-financed 
by the ERDF under the PT2020 
Partnership Agreement (POCI-01-0145-
FEDER – 007265; POCI-01-0145-
FEDER-007728). 
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10.1061/(ASCE)0899-
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[4] B. Pigino, A. Leemann, E. 
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[5] S. Amidi, J. Wang, Surface 
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March 2016. DOI: 
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[7] J. Li, Z. Yi, Y. Xie, Progress of 
silane impregnating surface 
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120-125, January, 2012. 
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Reception Instruction (RC-16), 
2016. 
[9] UNE 80303-1 Cements with 
additional characteristics. Part 1: 
Sulphate resisting cements, 
Madrid, 2013. 
[10] EN 197-1 Cement. Part 1: 
Composition, specifications and 
conformity criteria for common 
cements, Brussels, 2011. 
[11] EHE-08 Code on Structural 
Concrete, Madrid, 2008. 
[12] EN 12620+A1 Aggregates for 
 
8 
concrete, Brussels, 2008. 
[13] EN 933-11 Tests for geometrical 
properties of aggregates - Part 11: 
Classification test for the 
constituents of coarse recycled 
aggregate, Brussels, 2009. 
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properties of aggregates - Part 1: 
Determination of particle size 
distribution - Sieving method, 
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properties of aggregates. Part 3: 
Determination of particle shape - 
Flakiness index, Brussels, 2012. 
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and physical properties of 
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of particle density and water 
absorption, Brussels, 2013. 
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Robles, A. Juan-Valdés, J.M. 
Morán-Del Pozo, M. I. Guerra-
Romero, Pre-saturation technique 
of the recycled aggregates: 
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drawback in the recycled concrete 
manufacture, Materials, vol. 7, pp. 
6224-6236, September 2014. DOI: 
10.3390/ma7096224 


Eco-friendly healing agents for recycled concrete

Repositório da Universidade Nova de Lisboa

  1  ECO-FRIENDLY HEALING AGENTS FOR RECYCLED CONCRETE Julia GARCÍA-GONZÁLEZ PhD. Researcher. Escuela de Ingeniería Agraria y Forestal, University of Leon.  julia.garcia@unileon.es André FRECHES Researcher. LAQV-REQUIMTE, Dep. of Chemistry, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa. a.freches@campus.fct.unl.pt Paulo C. LEMOS Principal Investigator. LAQV-REQUIMTE, Dep. of Chemistry, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa. paulo.lemos@fct.unl.pt Alice S. PEREIRA Professor. UCIBIO-REQUIMTE, Dep. of Chemistry, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa. masp@fct.unl.pt Andrés JUAN-VALDÉS Professor. Escuela de Ingeniería Agraria y Forestal, University of Leon.    andres.juan@unileon.es Julia Mª. MORÁN-DEL POZO Professor. Escuela de Ingeniería Agraria y Forestal, University of Leon.  julia.moran@unileon.es M. Ignacio GUERRA-ROMERO Professor. Escuela de Ingeniería Agraria y Forestal, University of Leon.  ignacio.guerra@unileon.es Paulina FARIA Professor. CERIS and Dep. Civil Engineering, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa. mpr@fct.unl.pt      2 ABSTRACT An innovative option to extend the service life of construction and building materials is the use of bio-healing agents. This study was focused on assessing the protection and consolidation effect of eco-friendly healing agents by analysing the water absorption of recycled concrete. A recycled concrete with 50% replacement of natural coarse aggregate by construction and demolition waste (CDW) aggregate and a similar recycled concrete in which, additionally, the Portland cement was replaced by recycled cement (with 25% ceramic waste) were biotreated by healing agents. These agents were obtained by using waste biomass of two different mixed microbial cultures from polyhydroxyalkanoates production processes. Results have shown that biotreatments decreased the water absorption significantly, more evident in concrete samples with both recycled cement and aggregates than on the other type of concrete.  RESUMEN Una innovadora posibilidad planteada para prolongar la vida útil de los materiales de construcción y edificación es el uso de agentes bioreparadores. Este estudio se centró en la evaluación del efecto protector y consolidante de agentes reparadores y  respetuosos con el medio ambiente mediante el análisis de la absorción de agua del hormigón reciclado. Un hormigón reciclado con sustitución del 50% de los áridos gruesos naturales por residuos de construcción y demolición (RCD) y un hormigón reciclado similar en el cual, además, se sustituyó el cemento convencional Portland por cemento reciclado (con 25% de residuo cerámico) fueron biotratados con agentes reparadores. Estos agentes se obtuvieron en el proceso de producción de polihidroxialcanoatos utilizando biomasa residual de dos cultivos microbianos mixtos diferentes. Los resultados mostraron que los biotratamientos disminuyen significativamente la absorción de agua del hormigón, siendo más eficaces en las muestras de hormigón que combinan cemento y árido reciclado que en el otro tipo de hormigón.  Keywords:  Surface healing, mixed microbial culture, biotreatment, water absorption, construction and demolition waste, recycled aggregate, recycled cement, ceramic waste.  1. INTRODUCTION Repairing needs gradually increases with the increase of age of concrete structures. In some cases, it can be more economical to accept the need for repair at suitable intervals than to attempt to build a structure that will be maintenance-free under severe conditions for a long period. In addition, in spite of the relatively good durability of concrete as construction material, there are large numbers of structures worldwide which deteriorate due to expected factors that generate cracks (overloading, fatigue effects, changes in use, natural disasters, etc.). Therefore, surface cracking in concrete structures is inevitable; however, some cracks shall be repaired to prevent further structural damages and save money by being proactive. Several studies have tested the surface healing effect of organic and inorganic treatments on cement-based materials [1-7], showing improvements on permeability, resistance to moisture diffusion and filling of surface   3 cracks and voids. This study searches for a suitable bioproduct compatible with the existing cementitious substrate and able to improve the concrete surface quality by biotreatment of incipient cracks and porous structure. External repairing decreases maintenance costs of aged concrete structures and increases sustainability in the construction industry, being important advantages of this technology. 2. MATERIALS AND METHODS A recycled concrete with 50% replacement of natural coarse aggregate by CDW aggregate (RAC - recycled aggregate concrete) and a similar recycled concrete in which, additionally, the Portland cement was replaced by recycled cement (with 25% ceramic waste) (RACC - recycled aggregate and cement concrete) were prepared to assess the protection and consolidation effect of an eco-friendly healing biotreatment on water absorption. A commercially available Portland blended cement CEM III/A 42.5 N/SR was conformed to the Spanish [8-9] and European [10] standards. In RACC, this Portland cement was replacement by recycled cement with 25% waste ceramic fraction. Table 1 shows the chemical composition of both types of cement.  Natural aggregates presented a siliceous nature and complied with the requirements of the EHE-08 [11] and EN 12620+A1 [12]. Recycled mixed aggregates (RMA) were obtained through a mechanical treatment of CDW in a recycling plant located in the Autonomous Community of Madrid (Spain). The composition of the RMA, determined according to EN 933-11 [13], is presented in Table 2.  Chemical composition (%)   CEM III/A 42.5 N/SR Recycled cement Al2O3 7.59 7.32 CaO 51.33 47.04 Cl 0.02 0.04 Fe2O3 2.04 3.06 MgO 3.87 2.24 P2O5 0.06 0.17 K2O 0.60 1.70 SiO2 25.08 29.35 Na2O 0.14 0.41 SrO 0.11 0.08 SO3 2.54 2.45 TiO2 0.39 0.31 ZnO 0.04 0.03 Cr2O3 0.01 0.01 MnO 0.22 0.09 LOI 3.930 2.66  Table 1: Chemical composition of Portland and recycled cement  Component % (w/w) Unbound aggregates (natural aggregates without cement mortar attached) 44.1 Ceramics (bricks, tiles, stoneware and sanitary ware, …) 33.6 Concrete and mortar (natural aggregates with cement mortar attached) 17.5 Asphalt 0.4 Glass 0.8 Gypsum 3.5 Other impurities (wood, paper, metals, plastic, …) 0.1 Table 2: Non-floating components of recycled aggregates  4 Physical and mechanical properties of RMA and natural aggregates such as D/d ratio [14], fines content [14], flakiness index [15], Los Angeles coefficient [16], were within the suitable parameters established by EHE-08 [11] for the concrete manufacture. Nevertheless, results obtained for RMA water absorption [17] showed a greater variation compared to the natural aggregates. The presence of attached mortar and ceramic materials in the recycled aggregates caused significant water absorption, higher than the one of the natural aggregates. The use of aggregates with high water absorption could result in a workability drawback. Consequently, the RMA were pre-saturated: a technique that showed to be a suitable method to manufacture inexpensive recycled concrete with low strength requirements and maintain a suitable workability [18]. Table 3 shows the detailed composition of the different raw components used in the manufacture of the concretes (RAC and RACC, both have the same composition, only the kind of cement is changed). The w/c ratio and fck of both concretes is 0.5 and 25 MPa, respectively. Material Composition Water (l)  155 Cement (kg) 313 Sand 0/4 mm (kg) 97 Sand 0/5 mm (kg) 442 Gravel 4/10 mm (kg) 242 Gravel 6/12 mm (kg) 81 RMA 4/20 mm (kg) 323 Table 3: Mix composition per cubic metre of concrete  The test samples were cubes cut from concrete specimens that were molded, and had a cut surface with 50 mm x 50 mm.  The bioproducts used as healing agents were eco-friendly, being obtained by waste biomass from a microbial mixed culture (MMC) for polyhydroxyalkanoates production using pine wood bio-oil as substrate, on one hand, and crude glycerol (biodiesel by-product) on the other hand. MMC cell walls were disrupted by sonication (MMC-P_S and MMC-Gly_S) or not (MMC-P and MMC-Gly). In addition, two different concentrations of each product were tested (* - 1 Vol. of biopolymer:2 Vol. of water – lower concentration; ** - 1 Vol. of biopolymer:1 Vol. of water – higher concentration). Table 4 shows the different treatments.   Samples were treated with 2 mL of each bioproduct suspensions by using a pipette, covering the top surface.  The effect of each bioproduct on surface treatment was evaluated and compared with untreated samples (control) and treated with the same volume of tap water (reference). For each biotreatment and concrete, three samples were tested. The test room conditions were 20±2°C and 40±5% relative humidity (RH). Two days after the application, the healing capacity was assessed by water-drop absorption test performed in the test room. This test allows evaluating the permeability variation of the biotreated surfaces by monitoring the time required to absorb a water drop under open air conditions. The test was video recorded and the absorption time was then defined for each concrete, number of applications and treatment.   5   Treatment code Treatment definition Control Control H2O Reference with water MMC-Gly* MMC from glycerol without sonication, lower concentration MMC-Gly** MMC from glycerol without sonication, higher concentration MMC-Gly_S* MMC from glycerol with sonication, lower concentration MMC-Gly_S** MMC from glycerol with sonication, higher concentration MMC-P* MMC from pinewood biooil without sonication, lower concentration MMC-P** MMC from pinewood biooil without sonication, higher concentration MMC-P_S* MMC from pinewood biooil with sonication, lower concentration MMC-P_S** MMC from pinewood biooil with sonication, higher concentration Table 4:  Code and definition of treatments  3. RESULTS AND DISCUSSION Figure 1 shows the time of water drop absorption for each biotreated concrete samples, the control (untreated) and the reference (with water application) samples. Results have shown that all biotreatments increase significantly the absorption time, improving the expected durability of the concrete surfaces. On the contrary, the reference concretes, with tap water, presented an increase in water drop permeability, being the absorption time shorter than in the control concrete in all cases. The water drop absorption test shows that the MMC treatments are noticeable more effective in concrete with recycled cement than with conventional cement. This demonstrates the importance of the type of construction material surface to treat. Further research is needed, but these results point an appropriate healing effect of eco-friendly biopolymer treatments, improving with the presence of recycled ceramic. Also it is shown that, in most of cases, the biopolymer concentration directly benefits the healing effect on the treated samples.  However, the sonication step apparently does not have influence over the water absorption of the concretes tested in this research, or even the water absorption resistance of the concrete samples decreases in comparison with the samples treated with the same bioproduct without sonication (MMC-P samples). Chandra et al. [2] tested the use of cactus extract on concrete samples surface, to improve the water absorption resistance, achieving an upgrade of 83%. Woo et al. [1], evaluating the barrier performance of silane/clay nanocomposites as a coating material on concrete structures under different accelerated weathering tests, obtained an increase of water resistance of 29-57%. The improvement observed in this study is clearly higher (578-7328%). Further studies will allow to justify this effect and if it will be durable.   6 Figure 1: Water drop absorption time on concrete samples  5. CONCLUSION A single application of the biotreatments with bioproducts from a mixed microbial culture for polyhydroxyalkanoates production process increases significantly the water drop absorption time on both recycled aggregate concrete and recycled cement and aggregate concrete, producing a decrease of their permeability and demonstrating the biopolymer healing effect.  The MMC treatments are noticeable more effective in concrete with recycled cement than with conventional cement, which means in this case that the presence of recycled ceramic in the concrete increases the healing effect of biopolymer treatments of treated surfaces. ACKNOWLEDGMENTS This work was supported by a STSM Grant from the COST Action CA15202. (http://www.sarcos.enq.cam.ac.uk) and the Project BIA2017-83526-R “Procesos de auto-sanado mediante bio-polímeros en hormigones y morteros reciclados”, funded by the Spanish Ministry of Science, Innovation and Universities. This work was also supported by the Associate Laboratory for Green Chemistry-LAQV 0500100015002000250030003500RAC RACCWater drop absorption time (s)   7 and Applied Molecular Biosciences Unit-UCIBIO which are financed by national funds from FCT/MCTES (UID/QUI/50006/2013; UID/Multi/04378/2013) and co-financed by the ERDF under the PT2020 Partnership Agreement (POCI-01-0145-FEDER – 007265; POCI-01-0145-FEDER-007728). REFERENCES [1] R. S. C. Woo, H. Zhu, M. M. K. Chow, C. K. Y. Leung, J. Kim, “Barrier performance of silane-clay nanocomposite coatings on concrete structure,” Compos Sci Technol, vol. 68, pp. 2828-2836, November 2008. DOI: 10.1016/j.compscitech.2007.10.028 [2] S. Chandra, L. Eklund, R. R. Villarreal, Use of cactus in mortars and concrete, Cem Concr Res, vol. 28, pp. 41-51, January, 1998. DOI: 10.1016/S0008-8846(97)00254-8 [3] C. K. Y. Leung, H. Zhu, J. Kim, R. S. C. Woo, Use of polymer/organoclay nanocomposite surface treatment as water/ion barrier for concrete, J Mater Civ Eng, vol. 20, pp. 484-492, July 2008. DOI: 10.1061/(ASCE)0899-1561(2008)20:7(484) [4] B. Pigino, A. Leemann, E. Franzoni, P. Lura, Ethyl silicate for surface treatment of concrete – Part II: characteristics and performance, Cement Concr Compos, vol. 34, pp. 313-321, March 2012. DOI:10.1016/j.cemconcomp.2011.11.021 [5] S. Amidi, J. Wang, Surface treatment of concrete bricks using calcium carbonate precipitation, Constr Build Mater, vol. 80, pp. 273-278, April 2015. DOI: 10.1016/j.conbuildmat.2015.02.001 [6] L. Jia, C. Shi, X. Pan, J. Zhang, L. Wu, Effects of inorganic surface treatment on water permeability of cement-based materials, Cement Concr Compos, vol. 67, pp. 85-92, March 2016. 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Part 3: Determination of particle shape - Flakiness index, Brussels, 2012. [16] EN 1097-2 Tests for mechanical and physical properties of aggregates - Part 2: Methods for the determination of resistance to fragmentation, Brussels, 2010. [17] EN 1097-6 Tests for mechanical and physical properties of aggregates - Part 6: Determination of particle density and water absorption, Brussels, 2013. [18] J. García-González, D. Rodríguez-Robles, A. Juan-Valdés, J.M. Morán-Del Pozo, M. I. Guerra-Romero, Pre-saturation technique of the recycled aggregates: solution to the water absorption drawback in the recycled concrete manufacture, Materials, vol. 7, pp. 6224-6236, September 2014. DOI: 10.3390/ma7096224 

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Eco-friendly healing agents for recycled concrete

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