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Microorganism-based bioplasticizer for cementitious materials
Construction and Building Materials 60 (2014) 91–97
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Microorganism-based bioplasticizer for cementitious materials F. Martirena a,⇑, Y. Rodriguez-Rodriguez b, A. Callico c, R. Gonzalez a, Y. Diaz a, G. Bracho c, A. Alujas d, J.O. Guerra de Leon d, Y. Alvarado-Capó e a
CIDEM, Universidad Central ‘‘Marta Abreu’’ de las Villas, Santa Clara, Cuba Centro de Bioactivos Químicos, Universidad Central ‘‘Marta Abreu’’ de las Villas, Cuba c Instituto ‘‘Carlos J. Finlay’’, Habana, Cuba d Facultad de Química y Farmacia, Universidad Central ‘‘Marta Abreu’’ de las Villas, Cuba e Instituto de Biotecnología de las Plantas, Universidad Central ‘‘Marta Abreu’’ de las Villas, Cuba b
h i g h l i g h t s A microorganisms-based bioplasticizer (MEF) is presented as plasticizing admixture. MEF increases flowability of pastes and mortars at relatively high dosages. The presence of lactic acid at MEF seems to influence plasticizing properties. At high dosages MEF seems to influence cement hydration, and has a retarding effect. Rheology tests in pastes and mortar prove changes of plasticity and viscosity.
a r t i c l e
i n f o
Article history: Received 31 December 2013 Received in revised form 25 February 2014 Accepted 25 February 2014 Available online 22 March 2014 Keywords: Plasticizers Concrete Rheology Bio-products
a b s t r a c t A plasticizer resulting from mixed culture of microorganism with beneficial effect that co-exist in a liquid environment has been evaluated as potential admixture for cement. The bioplasticizer MEF (Microorganism-based bioplasticizer) contains fermentation products from liquid cultures of lactic bacteria, phototrophic bacteria and yeast of more than 80 different species. The material was tested in pastes and mortar using a rheology protocol, and compared with series made with one commercial superplasticizer (SP). Cement pastes were prepared with different dosage of MEF (4%, 6% and 8%). The experimental program included the evaluation of the plasticity index from the minicone test; viscosity through the Marsh cone, and setting time with the Vicat needle. Further, mortars with the same dosage were prepared and their rheology, water absorption and mechanical properties were assessed. Results indicate that MEF has plasticizing properties; however the effect is lower than commercial SPs. The main reasons appear to be the high dilution rate. Concentration through roto-evaporation brings about an increase in plasticizing properties. Separation by polar fractions shows that apparently the plasticizing principle is related to the presence of lactic acid. MEF seems to influence hydration of the aluminates, and in high dosages it may have some retarding effect. It has proven to contribute to decrease viscosity of cement pastes and no major differences in performance were found with commercial SPs. Tests carried out in mortars confirm the results obtained in pastes. Mortars made with MEF show similar mechanical properties than those of the reference. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Superplasticizers (SPs) can strongly influence concrete rheology: the admixture of a SP can improve flowability of concrete. Alternatively, at the same flowability requirement, the
⇑ Corresponding author. Tel.: +53 5 263 7716. E-mail address: [email protected] (F. Martirena). http://dx.doi.org/10.1016/j.conbuildmat.2014.02.063 0950-0618/Ó 2014 Elsevier Ltd. All rights reserved.
water/cement (w/c) ratio can be reduced to improve the strength and durability of concrete [1]. SPs currently used have different origins and properties. The first generation of SPs was lignosulfonate-based air-entraining water-reducing agents. It was followed by the second generation of SPs, which consisted of b-naphthalenesulfonate based products. The latest generation of SPs consists of polycarboxylate-based products, which are the main SPs in use today, with very complex molecules that yield spectacular properties. Most of these products
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come in a synthesized form [2], derived from the oil industry. If sustainability is sought, the industry must shift from the use of nonrenewable, oil dependent products that ultimately lead to depletion of natural resources, to the development of new renewable biomaterials, which are totally biodegradable, and can be replenished through natural processes. There are experiences of applications of this approach on several areas of industry and engineering [3]. The effect of SP is the dispersion of fine solid particles in concrete. When no SP is added, the solid particles would tend to form agglomerates, and particle agglomerates will form, retaining water inside. With the admixture of a SP the solid particles disperse and agglomeration would be reduced, thus allowing the solid particles to be more closely packed and the amount of excess water in concrete to be reduced. These effects would directly increase the flowability of the concrete in fresh state and the porosity in hardened state, which is strongly related to strength and durability [4]. The technology ‘‘Efficient Microorganism’’ (EM) was created by the Japanese Teuro Higa, University of the Ryukyus, Okinawa, Japan. EM consists of mixed cultures of naturally occurring microorganism that can be applied as inoculants to increase the microbial diversity of soils and plant. EM contains selected species of microorganism including predominant populations of lactic acid bacteria and yeasts and smaller numbers of photosynthetic bacteria, actinomycetes and other types of organisms. All of these are mutually compatible with one another and can coexist in liquid culture. The product has applications in agriculture and environmental control of bio-wastes [5]. Concrete with EM was first developed in Japan, with the aim of healing concrete cracks through the biological activity. The product EM-1Ò with applications in agriculture and environmental fields was used as cement admixture [6]. There are other reports of the use of bacteria to improve certain properties of concrete, among them concrete’s healing through microorganism [7,8]; use of microorganism to improve mortar strength [9]; and bio-concrete with enriched bacteria culture [10,11]. Although they reckoned that workability of concrete was improved through the admixture of microorganism, its effect as plasticizer is not conclusively assessed. There are other sources of biological additives for concrete such as wastes of antibiotic manufacturing, lignosulfates from wastes of the paper industry, and yeast fermentation waste (YFW). For instance, YFW has proven to be a polyfunctional hydrophilizing admixture which fluidizes concrete mixtures, mainly due to the action of melanoidine–humin complexes contained in YFW on the surface of cement particles, leading to decrease of flocculation of cement particles [12]. The effect of plasticizers can be assessed through rheological changes in cement pastes, mortars and concrete. Rheology is the logical tool to characterize and describe the flow-behavior, thickening, workability loss, stability and even compactability of a fresh cement based particle suspension such as cement paste, mortar and concrete [3,13]. The relationship between the shear stress s that is applied on a fluid element and its resulting shear rate c_ is named apparent viscosity g. Rheology of cement paste normally dictates rheology of mortar and concrete, thus evaluating rheological properties of cement paste could illustrate the performance of a given plasticizer. There are several empirical tests that can characterize the viscosity of cement paste; they can be applied at different levels, that is, cement paste, mortar and concrete [14,15]. This paper aims at evaluating the plasticizing properties of an EM-like product, whose plasticizing properties will be assessed in pastes and mortar. Comparisons of performance with commercial plasticizers will be included in the discussion of the results.
2. Materials The bioplasticizer used in this research, referred as IH Plus in previous communications [16] is designated as MEF in this paper. MEF is produced at Institute ‘‘Carlos J. Finlay’’ in Habana using an ad hoc technology based on previously described procedures [5,6]. MEF consist on fermentation products from sequential anaerobic culture of natural growing microorganism. The initial inoculums comprise a combination of different species of lactic bacillus, phototropic microorganism and yeast. These microorganism were cultivated in two fermentation steps in controlled conditions, starting from a solid state process followed by a large scale liquid fermentation. Solid and liquid culturing media contains molasses as main source of carbon but also include substrates derived from waste milk products. Manufacturing process showed to be consistent and is complete in around 15 days. The final product was submitted to strict quality control (QC) evaluation according to client specifications. QC tests carried out in one year old material show no major variation of main properties; the product expiry date is therefore considered as one year for this investigation. The product MEF was characterized in a similar way to a commercial SP. The amount of total solids was determined according to the Cuban standard NC-271-1:2003. Density of the final product was determined according to the Cuban standard NC-271-2:2003. pH was determined following the procedure stated in the Cuban standard NC-271-4:2003. One commercial SP, Mapefluid N-200 supplied by the Italian firm MAPEI, naphthalene based, was used as reference for comparison. Table 1 presents the results of the chemical characterization of the product, and the reference SPs. The density of the product MEF is lower than the commercial SP N-200. It is consistent with the lower amount of total solids found in the sample of MEF tested compared to the commercial SPs. It could indicate that the product has a higher degree of dilution. MEF is more acid than commercial SPs, something which could impact on the alkalinity of the pore solutions, especially when a high dosage of the product – due to a high dilution – is used, as described in [17]. This should be further studied. Further, the concentration of metals in MEF was assessed aided by Atomic Absorption Spectrometry (AAS), with a PG-990 Atomic Absorption Spectrophotometer. Hollow cathode lamps were used as a source. The main metals assessed were Na, K, Co, Fe, Mn, Zn, Ca, Mg, Cu and Ni. Table 2 presents the main results obtained. The high concentration of metals such as K, Mg, Na, Fe and Ca should be regarded in the discussion of results, especially as far as the influence of the product in hydration is concerned. Reducing sugars in MEF were also determined according to the Cuban Standard NC-712: 2009; final molasses — determination of total reducing molasses by the Lane–Eynon method at constant volume. The concentration of reducing sugars was 0.49%, relatively low for cement chemical admixtures. The cement used in the studies carried out in pastes, mortar and concrete was produced in Cienfuegos, Cuba, and it is classified as a type I cement (Cuban norm NC-54 205:80 classifies it as P-35). Physical and mechanical properties are described in Tables 3–5. Fine aggregates used were fine river sand, sourced from quarry Arimao in the south-center part of Cuba. Predominant mineralogical composition of this material is sediments from weathering of original volcanic materials. Fig. 1 shows the grain size distribution of the fine material. The sand is slightly coarser than the specifications; this could influence the properties of mortars, but it was used in all samples tested.
3. Experimental procedures The experimental program carried out consisted of the evaluation of the impact of MEF on the rheology of pastes and mortars. Pastes were prepared with MEF and N-200 as chemical admixtures with water to cement ratio kept at 0.45. MEF was added in the proportions 4%, 6% and 8%, of the weight of cement. The high dosage of EM-like admixtures is commonly found in the literature, where concentration as admixture in concrete normally ranges between (6% and 15%) of the weight of cement used in the mix, probably due to the dilution effect [9]. Water content in all MEF pastes was corrected in order to compensate the extra amount of liquid
Table 1 Values of picnometric density, total solids and pH of MEF and N-200.
Density (picnometer) g/ml % Total solids (TS) pH
MEF
N-200
1.01 2.32 3.40
1.20 40.00 6.48
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Fig. 1. Grain size distribution fine aggregate.
Table 2 Elemental composition of MEF. Elem.
Na+ (mg/L)
K+ (mg/L)
Fetotal (mg/L)
Mn2+ (mg/L)
Mg2+ (mg/L)
Cu2+ (mg/L)
Ni2+ (mg/L)
Co2+ (mg/L)
Zn2+ (mg/L)
Ca2+ (mg/L)
Ntotal (mg/L)
Ptotal (mg/L)
MEF
56.40
2890.13
45.44
6.97
107.11
1.13
0.79
0.54
1.80
45.12
57.40
6.09
Table 3 Physical–mechanical properties of the cement used. Properties
Value
Bulk weight Density Normal consistency Initial setting time Final setting time 7d Compressive strength 28d Compressive strength 7d Bending strength 28d Bending strength
1103 kg/m3 3.15 26% 13500 30 4500 24.3 MPa 39.6 MPa 4.3 MPa 6.9 MPa
Replicas of the pastes were prepared with microbial cell free MEF in order to assess if the presence of microbial cell had some influence in the plasticizing activity. The bacteria were removed by filtering the product through 0.45 lm membrane filters (Sartorius). The testing program in pastes consisted of: Minicone test: this test is used to measure the modification of plasticity of pastes by chemical admixtures. It has been accepted as a real but simple rheological tool that allows its user to access an intrinsic property of the tested material instead of measuring a test geometry and material density dependent slump value [18]. Testing was done according to the Cuban Standard NC 235:2012. Pastes with different concentrations of plasticizer and a water to cement ratio of 0.45 were prepared and stirred at 300 rpm in a plastic recipient, and then placed in a truncated cone with 19 mm upper diameter and 38 mm lower diameter and 57 mm height, following the sized stated at NC 235: 2012 and ASTM Test C 143. After the minicone mould is removed, the diameter of the slump of the paste is measured and the plasticity index is calculated as described below:
Table 4 Chemical composition of the cement. Oxide
CaO
SiO2
Al2O3
Fe2O3
Na2O
K2O
MgO
(%)
62.64
21.20
5.79
2.70
0.00
0.61
1.22
Table 5 Mineralogical phases in unhydrated cement. Phases
C3S
C2S
C3A
C4AF
Free CaO
(%)
41.5
29.5
10.8
8.2
1.5
caused by the high dosage of admixture. The commercial SP was tested at maximum and minimum dosages 0.5% and 1.5% of the weight of cement, as recommended by the manufacturer. Each series of pastes tested was replicated 3 times for statistical consistency.
Pl ¼
Ap Ao 100 Ao
where Ap is the projected area of the cone of paste made with plasticizer; Ao is projected area of the cone of paste made without plasticizer Consistency test: Pastes made with cement and the plasticizers were prepared and normal consistency was determined aided by the Vicat needle test (Cuban standard NC
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524-2007). Further, setting time was determined in all pastes, to assess the influence of MEF on the speed of hydration of cement. Flow test: The Marsh cone test was used to assess the flowability of cement pastes. The test method is described at Cuban standard NC-461: 2006 (similar to EN 445: 1995). It measures the time in which a certain volume of paste that fills the cone flows through a 10 mm nozzle. The test can also measure the loss of workability and the influence of temperature. The flow time can be directly linked to the material behavior, and rheological parameters such as yield stress and plastic viscosity for Bingham fluids can be predicted [15,19]. The cement paste had a fixed w/c, and the percentage of plasticizer added was determined based on the saturation point for the system water/ cement/admixture. Viscosity was determined by the Marsh cone. Two different plasticizers should have two different saturation points, provided the dosage is the same. It can, therefore be used to assess the impact of plasticizers in flowability of cement pastes. Heat of hydration of cement pastes modified with chemical admixtures. With the aim of assessing the influence of the plasticizers and their dosage in the hydration of cement, isothermal calorimetry was conducted on samples in order to measure the heat flow and cumulated heat released during hydration of paste samples, as a means of assessing the progress of cement hydration. A thermometric TAM AIR calorimeter was used. It allows up to 8 simultaneous measurements with a (60–600) mW range. Experiments were conducted at 30 °C to resemble Cuban environmental conditions
4. Discussion of results 4.1. Influence on plasticity of cement pastes Fig. 2 presents a comparison of the plasticity index of all series tested according to the testing protocol with the minicone. Although a plasticizing effect of the product MEF is clearly observed, it is significantly lower than the commercial SP used as reference, despite the higher dosage of admixture used in the series made with MEF. This could be explained through the dilution effect on the MEF product, compared to the commercial SP. Results presented in Table 1 prove that the ratio between total solids in MEF and N-200 ranges around 15 times, thus indicating a higher dilution rate. Fig. 3 presents the results of plasticity index measured in the minicone test with a MEF product that has been concentrated through roto-evaporation at the lab. The concentrated product, used at the same dosage, shows an increase of around 45% of the plasticity index, apparently caused by the concentration effect. The performance of the material, however, remains far from that of the commercial SP. MEF is a natural product, and accordingly, it contains a great variety of different compounds, many of which have not yet been identified. In order to get more clarity on its active compounds, MEF was fractioned using Soxhlet equipment, based on the polarity of the solvent, with the aim of determining which fraction has more influence on the plasticity index. The solvents utilized were: chloroform, ethyl acetate, n-butanol, ethanol and water.
The testing program in mortars consisted of: Consistency of standardized mortars prepared with the chemical admixtures tested. It was done according to the Cuban Standards NC-170: 2002. Mortars were made with cement, water and fine aggregate at fixed water to cement ratio of 0.5. Table 6 presents the mix proportion used for all mortars. The dosage of the chemical admixtures was kept similar to the tests performed in pastes. Water content was corrected in all MEF containing mortars to compensate the extra liquid caused by the high dosage of admixture. The fresh mortar was placed in the cone shaped mould in a shake table and the final slump diameter indicated the consistency of each mortar Compressive strength at 7 and 28 days. The dimensions of mortar prisms were 40 40 160 mm cast according to the Cuban Standard NC-173, 2002. The dosage of the chemical admixtures was kept similar to the tests performed in pastes. Water content was corrected in all MEF containing mortars to compensate the extra liquid caused by the high dosage of admixture. The prisms were immersed in water until 24 h before testing. All prism were tested for water absorption at 28 days, following the procedure of the Cuban Standard NC-171, 2002.
Fig. 2. Plasticity index for all pastes tested at the minicone.
Table 6 Mix proportions of the mortar series tested for consistency. Series
Cement (g)
Sand (g)
Water (ml)
0.5% (N 200) 1.5% (N 200) 4% (MEF) 6% (MEF) 8% (MEF)
450 450 450 450 450
1350 1350 1350 1350 1350
225 225 207.72 199.08 190.44
Fig. 3. Plasticity index of pastes made with original MEF and concentrated MEF (75% concentration).
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The value of the total solid (TS%) present in the MEF is set, 100 ml of bioproduct are taken and are then dried. The solid obtained was introduced into a porous cartridge which is placed in the Soxhlet equipment. It starts to extract with different solvents, from the least to the most polar by a time of 4 h in each extraction. Distilled water was added to each fraction to match the content of TS% with the initial MEF. The plasticizing properties of the resulting liquid were tested with the minicone protocol, as described above. The fractions obtained were identified as follows: F2 is a mixture of extracted compounds into Ethyl Acetate, it represents 21.68% of the total compounds; F3 is a mixture of extracted compounds into n-butanol, it represents 16.32% of the total compounds; F4 is a mixture of extracted compounds into ethanol, it represents 4.54% of the total compounds, and F5 is a mixture of extracted compounds into water, that is, 46.74% of total compounds with polarity similar to water. Fig. 4 presents the plasticity index of minicone tests where MEF has been separated in several polar fractions. The polar fraction identified as F5 corresponds to the mixture to the most polar compounds into the MEF product. They have similar solubility that water. For every concentration a significant increase in plasticity is observed for the F5 polar fraction, even at smaller dosages. It could indicate that the plasticizing effect has a strong link with the polarity of the compounds, most likely lactic acid. Lactic acid is found in concentrations of approximately 100 mg/ L. It is formed as one of the metabolites obtained from the fermentation of whey with lactic acid microorganism during the manufacture of the product MEF. Through the interaction with cement particles during cement hydration, lactic acid could be adsorbed on the surface of cement grains releasing lactates ions [20]. The negatively charged lactate ions repel each other and by doing this they push cement grains apart. The plasticizing effect of lactic acid in cementitious materials has been described before [21]. Fig. 5
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presents a scheme that illustrates the mechanisms for the electrostatic repulsion. This could likely explain the plasticizing properties observed in MEF. The impact of the presence of bacteria and other microorganism on the plasticity of cement pastes was also assessed. Fig. 6 presents the results of plasticity index of cement pastes made with normal MEF and MEF filtered to remove microorganism, as part of the minicone testing protocol. In every dosage of MEF used no significant differences in the plasticity index were found. For higher dosages (8% of the mass of cement), an increase in plasticity is observed; this could reinforce the theory of the compounds that negatively influence plasticity, which were likely removed during filtration. This test rules out the hypothesis stated in the literature that live bacteria are responsible for the plasticity effect of bioproducts [6,12,9]. Further, at the high alkaline pH of the pore solution, even at very early ages, it is very unlikely that bacteria can survive on the pore system after hardening. The active principle, therefore, is more related to what remains after the metabolism of bacteria.
4.2. Influence on viscosity of cement pastes Fig. 7 presents the results of the Marsh cone test performed in cement pastes made with various dosages of MEF, and a series with no plasticizer and the series with the commercial SP as reference for comparison. tv In cement pastes made with MEF drops significantly compared with pastes made with no SPs. The flow time is proportional to the viscosity and yield stress, thus indicating that a modification of the viscosity and the yield stress of the system takes place when MEF is used; the optimized dosage for the
Fig. 6. Plasticity index of cement pastes made with MEF with and without microbial cell.
Fig. 4. Plasticity index for polar fractions of MEF.
Fig. 5. Repulsion forces between lactate ion and cement grains.
Fig. 7. Flow time of cement pastes tested with the Marsh cone.
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Fig. 8. Water demand of cement pastes according to normal consistency test.
product evaluated appears to be 8% of the weight of cement. Concentration of MEF appears to have some effect on flow time, although it does not seem to influence optimized dosage. In the range of dosage evaluated, no significant differences are established between the commercial SP used as reference and MEF. The reference series with no admixture flows in twice the time of any of the other series tested. [19] Fig. 8 presents the results of normal consistency tests, where the capability of reducing water on the cement paste was measured based on the depth of penetration of the Vicat needle, which could indirectly indicate changes in rheological properties of the material. For 10 mm penetration depth, water reduction ranged from (20% to 25%) compared to the reference cement paste without admixture. No major differences were observed in water reduction in the pastes made with MEF and those made with commercial SPs. 4.3. Influence on hydration of cement pastes The influence of MEF on the hydration of cement was assessed aided by isothermal calorimetry studies performed in cement pastes. The heat of hydration for the pastes made with MEF at different concentrations (4%, 6% and 8% of the weight of cement) were measured and compared with those of the corresponding control cement pastes (OPC with no SPs) and paste containing 0.5% commercial SP N-200, as showed in Fig. 9.
Fig. 9. Rate of heat evolution as a means of measuring the influence of MEF on cement hydration.
Fig. 10. Setting time of cement pastes according to Vicat test.
It´s generally accepted that initial setting typically occurs at the beginning of the accelerating period, where C3S begins to hydrate rapidly [22]. By the end of this period, once maximum rate has been reached, final set has taken place and early hardening has started. Comparing the time ranging from the end of the dormant period and the beginning of the acceleration period for the control Portland cement pastes to those with the admixtures, it seems that all the admixtures retarded the cement hydration. For all chemical admixtures, an increase on the heat evolution occurs as a shoulder after the first 12 h. Associated to this intensification on the cement hydration, an increase on the cumulative heat could be observed after the first 24 h for all systems when compared to control paste. This effect could be related to an increase of the heat released during hydration of the C3A phase, usually associated with an increase on ettringite formation and a delay on its conversion to monosulphate [23]. For pastes containing MEF the increase in the size of this shoulder was roughly proportional to the admixture concentration. Same trend was observed for the retardation time, result which is in agreement with the setting times as determined by Vicat test presented in Fig. 10. The higher the dosage of MEF, the longer the final setting time. Thus, the impact of MEF on the cement hydration needs to be further investigated. The mechanism of retardation in cement paste depends on the type of admixtures. For polynaphthalene based superplasticizers, it is suggested that the retardation was mainly due to the adsorption of admixtures on nucleating hydrate particles and intercalation into hydrate phases already formed which inhibit the development of hydration products [24]. As MEF is the result of microbiological fermentation under anaerobic conditions, it contains a high volume of carboxylic acids such as lactic and acetic acid. Retardation effects have also been recognized for admixtures based on hydroxyl carboxylic acids at high concentrations [25]. However, because
Fig. 11. Slump diameter of mortars in shake table.
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5. Conclusions The bioplasticizer MEF has proven to have moderate plasticizing properties, which are apparently limited by a dilution effect caused by the excess of water in its formulation. Concentration of the product through roto-evaporation techniques yields a higher plasticizing effect. Separation of polar fractions has proven that the fraction with the highest polarity, identified for lactic acid, proves to be the most active one. The speed of flow in the Marsh cone shows a contribution of MEF to the decrease of viscosity in cement pastes, which could complement the plasticizing effect. MEF seems to have some sort of influence on the hydration of the aluminates in the cement. Further, for higher concentration MEF has also some retarding effect. Fig. 12. Compressive strength in mortars.
Fig. 13. Water absorption in mortars.
of its complex nature, further research is needed to unveil the nature of the MEF over cement hydration, as discussed in the literature [16]. 4.4. Studies in mortars Fig. 11 presents the results of the consistency tests in mortars cast with different dosages of MEF and the reference SP N-200. A reference mortar was cast with no plasticizer. The diameter of the mortar cone subjected to shake shows a great similarity for all MEF dosages to the one obtained for N-200. The best results are obtained for 6% MEF. The reference mortar cast with no plasticizer presents a much smaller diameter, which indicates a clear plasticizing effect of MEF, in this case, very similar to commercial SP N-200. Compressive strength of mortars at 7 and 28 days, presented in Fig. 12, does not show any major difference between all mortars tested, which is consistent to the fact that the same water to cement ratio was used for casting them. Fig. 13 presents the results of water absorption in all mortars. Mortars made with MEF, especially those at higher dosages (6, 8%) show lower water absorption, even compared with commercial SP N-200. This could indicate an improve microstructure development, probably due to a better hydration of the reaction products, which leads to a lower porosity and the decrease of connected pores.
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Microorganism-based bioplasticizer for cementitious materials F. Martirena a,⇑, Y. Rodriguez-Rodriguez b, A. Callico c, R. Gonzalez a, Y. Diaz a, G. Bracho c, A. Alujas d, J.O. Guerra de Leon d, Y. Alvarado-Capó e a
CIDEM, Universidad Central ‘‘Marta Abreu’’ de las Villas, Santa Clara, Cuba Centro de Bioactivos Químicos, Universidad Central ‘‘Marta Abreu’’ de las Villas, Cuba c Instituto ‘‘Carlos J. Finlay’’, Habana, Cuba d Facultad de Química y Farmacia, Universidad Central ‘‘Marta Abreu’’ de las Villas, Cuba e Instituto de Biotecnología de las Plantas, Universidad Central ‘‘Marta Abreu’’ de las Villas, Cuba b
h i g h l i g h t s A microorganisms-based bioplasticizer (MEF) is presented as plasticizing admixture. MEF increases flowability of pastes and mortars at relatively high dosages. The presence of lactic acid at MEF seems to influence plasticizing properties. At high dosages MEF seems to influence cement hydration, and has a retarding effect. Rheology tests in pastes and mortar prove changes of plasticity and viscosity.
a r t i c l e
i n f o
Article history: Received 31 December 2013 Received in revised form 25 February 2014 Accepted 25 February 2014 Available online 22 March 2014 Keywords: Plasticizers Concrete Rheology Bio-products
a b s t r a c t A plasticizer resulting from mixed culture of microorganism with beneficial effect that co-exist in a liquid environment has been evaluated as potential admixture for cement. The bioplasticizer MEF (Microorganism-based bioplasticizer) contains fermentation products from liquid cultures of lactic bacteria, phototrophic bacteria and yeast of more than 80 different species. The material was tested in pastes and mortar using a rheology protocol, and compared with series made with one commercial superplasticizer (SP). Cement pastes were prepared with different dosage of MEF (4%, 6% and 8%). The experimental program included the evaluation of the plasticity index from the minicone test; viscosity through the Marsh cone, and setting time with the Vicat needle. Further, mortars with the same dosage were prepared and their rheology, water absorption and mechanical properties were assessed. Results indicate that MEF has plasticizing properties; however the effect is lower than commercial SPs. The main reasons appear to be the high dilution rate. Concentration through roto-evaporation brings about an increase in plasticizing properties. Separation by polar fractions shows that apparently the plasticizing principle is related to the presence of lactic acid. MEF seems to influence hydration of the aluminates, and in high dosages it may have some retarding effect. It has proven to contribute to decrease viscosity of cement pastes and no major differences in performance were found with commercial SPs. Tests carried out in mortars confirm the results obtained in pastes. Mortars made with MEF show similar mechanical properties than those of the reference. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Superplasticizers (SPs) can strongly influence concrete rheology: the admixture of a SP can improve flowability of concrete. Alternatively, at the same flowability requirement, the
⇑ Corresponding author. Tel.: +53 5 263 7716. E-mail address: [email protected] (F. Martirena). http://dx.doi.org/10.1016/j.conbuildmat.2014.02.063 0950-0618/Ó 2014 Elsevier Ltd. All rights reserved.
water/cement (w/c) ratio can be reduced to improve the strength and durability of concrete [1]. SPs currently used have different origins and properties. The first generation of SPs was lignosulfonate-based air-entraining water-reducing agents. It was followed by the second generation of SPs, which consisted of b-naphthalenesulfonate based products. The latest generation of SPs consists of polycarboxylate-based products, which are the main SPs in use today, with very complex molecules that yield spectacular properties. Most of these products
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come in a synthesized form [2], derived from the oil industry. If sustainability is sought, the industry must shift from the use of nonrenewable, oil dependent products that ultimately lead to depletion of natural resources, to the development of new renewable biomaterials, which are totally biodegradable, and can be replenished through natural processes. There are experiences of applications of this approach on several areas of industry and engineering [3]. The effect of SP is the dispersion of fine solid particles in concrete. When no SP is added, the solid particles would tend to form agglomerates, and particle agglomerates will form, retaining water inside. With the admixture of a SP the solid particles disperse and agglomeration would be reduced, thus allowing the solid particles to be more closely packed and the amount of excess water in concrete to be reduced. These effects would directly increase the flowability of the concrete in fresh state and the porosity in hardened state, which is strongly related to strength and durability [4]. The technology ‘‘Efficient Microorganism’’ (EM) was created by the Japanese Teuro Higa, University of the Ryukyus, Okinawa, Japan. EM consists of mixed cultures of naturally occurring microorganism that can be applied as inoculants to increase the microbial diversity of soils and plant. EM contains selected species of microorganism including predominant populations of lactic acid bacteria and yeasts and smaller numbers of photosynthetic bacteria, actinomycetes and other types of organisms. All of these are mutually compatible with one another and can coexist in liquid culture. The product has applications in agriculture and environmental control of bio-wastes [5]. Concrete with EM was first developed in Japan, with the aim of healing concrete cracks through the biological activity. The product EM-1Ò with applications in agriculture and environmental fields was used as cement admixture [6]. There are other reports of the use of bacteria to improve certain properties of concrete, among them concrete’s healing through microorganism [7,8]; use of microorganism to improve mortar strength [9]; and bio-concrete with enriched bacteria culture [10,11]. Although they reckoned that workability of concrete was improved through the admixture of microorganism, its effect as plasticizer is not conclusively assessed. There are other sources of biological additives for concrete such as wastes of antibiotic manufacturing, lignosulfates from wastes of the paper industry, and yeast fermentation waste (YFW). For instance, YFW has proven to be a polyfunctional hydrophilizing admixture which fluidizes concrete mixtures, mainly due to the action of melanoidine–humin complexes contained in YFW on the surface of cement particles, leading to decrease of flocculation of cement particles [12]. The effect of plasticizers can be assessed through rheological changes in cement pastes, mortars and concrete. Rheology is the logical tool to characterize and describe the flow-behavior, thickening, workability loss, stability and even compactability of a fresh cement based particle suspension such as cement paste, mortar and concrete [3,13]. The relationship between the shear stress s that is applied on a fluid element and its resulting shear rate c_ is named apparent viscosity g. Rheology of cement paste normally dictates rheology of mortar and concrete, thus evaluating rheological properties of cement paste could illustrate the performance of a given plasticizer. There are several empirical tests that can characterize the viscosity of cement paste; they can be applied at different levels, that is, cement paste, mortar and concrete [14,15]. This paper aims at evaluating the plasticizing properties of an EM-like product, whose plasticizing properties will be assessed in pastes and mortar. Comparisons of performance with commercial plasticizers will be included in the discussion of the results.
2. Materials The bioplasticizer used in this research, referred as IH Plus in previous communications [16] is designated as MEF in this paper. MEF is produced at Institute ‘‘Carlos J. Finlay’’ in Habana using an ad hoc technology based on previously described procedures [5,6]. MEF consist on fermentation products from sequential anaerobic culture of natural growing microorganism. The initial inoculums comprise a combination of different species of lactic bacillus, phototropic microorganism and yeast. These microorganism were cultivated in two fermentation steps in controlled conditions, starting from a solid state process followed by a large scale liquid fermentation. Solid and liquid culturing media contains molasses as main source of carbon but also include substrates derived from waste milk products. Manufacturing process showed to be consistent and is complete in around 15 days. The final product was submitted to strict quality control (QC) evaluation according to client specifications. QC tests carried out in one year old material show no major variation of main properties; the product expiry date is therefore considered as one year for this investigation. The product MEF was characterized in a similar way to a commercial SP. The amount of total solids was determined according to the Cuban standard NC-271-1:2003. Density of the final product was determined according to the Cuban standard NC-271-2:2003. pH was determined following the procedure stated in the Cuban standard NC-271-4:2003. One commercial SP, Mapefluid N-200 supplied by the Italian firm MAPEI, naphthalene based, was used as reference for comparison. Table 1 presents the results of the chemical characterization of the product, and the reference SPs. The density of the product MEF is lower than the commercial SP N-200. It is consistent with the lower amount of total solids found in the sample of MEF tested compared to the commercial SPs. It could indicate that the product has a higher degree of dilution. MEF is more acid than commercial SPs, something which could impact on the alkalinity of the pore solutions, especially when a high dosage of the product – due to a high dilution – is used, as described in [17]. This should be further studied. Further, the concentration of metals in MEF was assessed aided by Atomic Absorption Spectrometry (AAS), with a PG-990 Atomic Absorption Spectrophotometer. Hollow cathode lamps were used as a source. The main metals assessed were Na, K, Co, Fe, Mn, Zn, Ca, Mg, Cu and Ni. Table 2 presents the main results obtained. The high concentration of metals such as K, Mg, Na, Fe and Ca should be regarded in the discussion of results, especially as far as the influence of the product in hydration is concerned. Reducing sugars in MEF were also determined according to the Cuban Standard NC-712: 2009; final molasses — determination of total reducing molasses by the Lane–Eynon method at constant volume. The concentration of reducing sugars was 0.49%, relatively low for cement chemical admixtures. The cement used in the studies carried out in pastes, mortar and concrete was produced in Cienfuegos, Cuba, and it is classified as a type I cement (Cuban norm NC-54 205:80 classifies it as P-35). Physical and mechanical properties are described in Tables 3–5. Fine aggregates used were fine river sand, sourced from quarry Arimao in the south-center part of Cuba. Predominant mineralogical composition of this material is sediments from weathering of original volcanic materials. Fig. 1 shows the grain size distribution of the fine material. The sand is slightly coarser than the specifications; this could influence the properties of mortars, but it was used in all samples tested.
3. Experimental procedures The experimental program carried out consisted of the evaluation of the impact of MEF on the rheology of pastes and mortars. Pastes were prepared with MEF and N-200 as chemical admixtures with water to cement ratio kept at 0.45. MEF was added in the proportions 4%, 6% and 8%, of the weight of cement. The high dosage of EM-like admixtures is commonly found in the literature, where concentration as admixture in concrete normally ranges between (6% and 15%) of the weight of cement used in the mix, probably due to the dilution effect [9]. Water content in all MEF pastes was corrected in order to compensate the extra amount of liquid
Table 1 Values of picnometric density, total solids and pH of MEF and N-200.
Density (picnometer) g/ml % Total solids (TS) pH
MEF
N-200
1.01 2.32 3.40
1.20 40.00 6.48
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Fig. 1. Grain size distribution fine aggregate.
Table 2 Elemental composition of MEF. Elem.
Na+ (mg/L)
K+ (mg/L)
Fetotal (mg/L)
Mn2+ (mg/L)
Mg2+ (mg/L)
Cu2+ (mg/L)
Ni2+ (mg/L)
Co2+ (mg/L)
Zn2+ (mg/L)
Ca2+ (mg/L)
Ntotal (mg/L)
Ptotal (mg/L)
MEF
56.40
2890.13
45.44
6.97
107.11
1.13
0.79
0.54
1.80
45.12
57.40
6.09
Table 3 Physical–mechanical properties of the cement used. Properties
Value
Bulk weight Density Normal consistency Initial setting time Final setting time 7d Compressive strength 28d Compressive strength 7d Bending strength 28d Bending strength
1103 kg/m3 3.15 26% 13500 30 4500 24.3 MPa 39.6 MPa 4.3 MPa 6.9 MPa
Replicas of the pastes were prepared with microbial cell free MEF in order to assess if the presence of microbial cell had some influence in the plasticizing activity. The bacteria were removed by filtering the product through 0.45 lm membrane filters (Sartorius). The testing program in pastes consisted of: Minicone test: this test is used to measure the modification of plasticity of pastes by chemical admixtures. It has been accepted as a real but simple rheological tool that allows its user to access an intrinsic property of the tested material instead of measuring a test geometry and material density dependent slump value [18]. Testing was done according to the Cuban Standard NC 235:2012. Pastes with different concentrations of plasticizer and a water to cement ratio of 0.45 were prepared and stirred at 300 rpm in a plastic recipient, and then placed in a truncated cone with 19 mm upper diameter and 38 mm lower diameter and 57 mm height, following the sized stated at NC 235: 2012 and ASTM Test C 143. After the minicone mould is removed, the diameter of the slump of the paste is measured and the plasticity index is calculated as described below:
Table 4 Chemical composition of the cement. Oxide
CaO
SiO2
Al2O3
Fe2O3
Na2O
K2O
MgO
(%)
62.64
21.20
5.79
2.70
0.00
0.61
1.22
Table 5 Mineralogical phases in unhydrated cement. Phases
C3S
C2S
C3A
C4AF
Free CaO
(%)
41.5
29.5
10.8
8.2
1.5
caused by the high dosage of admixture. The commercial SP was tested at maximum and minimum dosages 0.5% and 1.5% of the weight of cement, as recommended by the manufacturer. Each series of pastes tested was replicated 3 times for statistical consistency.
Pl ¼
Ap Ao 100 Ao
where Ap is the projected area of the cone of paste made with plasticizer; Ao is projected area of the cone of paste made without plasticizer Consistency test: Pastes made with cement and the plasticizers were prepared and normal consistency was determined aided by the Vicat needle test (Cuban standard NC
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524-2007). Further, setting time was determined in all pastes, to assess the influence of MEF on the speed of hydration of cement. Flow test: The Marsh cone test was used to assess the flowability of cement pastes. The test method is described at Cuban standard NC-461: 2006 (similar to EN 445: 1995). It measures the time in which a certain volume of paste that fills the cone flows through a 10 mm nozzle. The test can also measure the loss of workability and the influence of temperature. The flow time can be directly linked to the material behavior, and rheological parameters such as yield stress and plastic viscosity for Bingham fluids can be predicted [15,19]. The cement paste had a fixed w/c, and the percentage of plasticizer added was determined based on the saturation point for the system water/ cement/admixture. Viscosity was determined by the Marsh cone. Two different plasticizers should have two different saturation points, provided the dosage is the same. It can, therefore be used to assess the impact of plasticizers in flowability of cement pastes. Heat of hydration of cement pastes modified with chemical admixtures. With the aim of assessing the influence of the plasticizers and their dosage in the hydration of cement, isothermal calorimetry was conducted on samples in order to measure the heat flow and cumulated heat released during hydration of paste samples, as a means of assessing the progress of cement hydration. A thermometric TAM AIR calorimeter was used. It allows up to 8 simultaneous measurements with a (60–600) mW range. Experiments were conducted at 30 °C to resemble Cuban environmental conditions
4. Discussion of results 4.1. Influence on plasticity of cement pastes Fig. 2 presents a comparison of the plasticity index of all series tested according to the testing protocol with the minicone. Although a plasticizing effect of the product MEF is clearly observed, it is significantly lower than the commercial SP used as reference, despite the higher dosage of admixture used in the series made with MEF. This could be explained through the dilution effect on the MEF product, compared to the commercial SP. Results presented in Table 1 prove that the ratio between total solids in MEF and N-200 ranges around 15 times, thus indicating a higher dilution rate. Fig. 3 presents the results of plasticity index measured in the minicone test with a MEF product that has been concentrated through roto-evaporation at the lab. The concentrated product, used at the same dosage, shows an increase of around 45% of the plasticity index, apparently caused by the concentration effect. The performance of the material, however, remains far from that of the commercial SP. MEF is a natural product, and accordingly, it contains a great variety of different compounds, many of which have not yet been identified. In order to get more clarity on its active compounds, MEF was fractioned using Soxhlet equipment, based on the polarity of the solvent, with the aim of determining which fraction has more influence on the plasticity index. The solvents utilized were: chloroform, ethyl acetate, n-butanol, ethanol and water.
The testing program in mortars consisted of: Consistency of standardized mortars prepared with the chemical admixtures tested. It was done according to the Cuban Standards NC-170: 2002. Mortars were made with cement, water and fine aggregate at fixed water to cement ratio of 0.5. Table 6 presents the mix proportion used for all mortars. The dosage of the chemical admixtures was kept similar to the tests performed in pastes. Water content was corrected in all MEF containing mortars to compensate the extra liquid caused by the high dosage of admixture. The fresh mortar was placed in the cone shaped mould in a shake table and the final slump diameter indicated the consistency of each mortar Compressive strength at 7 and 28 days. The dimensions of mortar prisms were 40 40 160 mm cast according to the Cuban Standard NC-173, 2002. The dosage of the chemical admixtures was kept similar to the tests performed in pastes. Water content was corrected in all MEF containing mortars to compensate the extra liquid caused by the high dosage of admixture. The prisms were immersed in water until 24 h before testing. All prism were tested for water absorption at 28 days, following the procedure of the Cuban Standard NC-171, 2002.
Fig. 2. Plasticity index for all pastes tested at the minicone.
Table 6 Mix proportions of the mortar series tested for consistency. Series
Cement (g)
Sand (g)
Water (ml)
0.5% (N 200) 1.5% (N 200) 4% (MEF) 6% (MEF) 8% (MEF)
450 450 450 450 450
1350 1350 1350 1350 1350
225 225 207.72 199.08 190.44
Fig. 3. Plasticity index of pastes made with original MEF and concentrated MEF (75% concentration).
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The value of the total solid (TS%) present in the MEF is set, 100 ml of bioproduct are taken and are then dried. The solid obtained was introduced into a porous cartridge which is placed in the Soxhlet equipment. It starts to extract with different solvents, from the least to the most polar by a time of 4 h in each extraction. Distilled water was added to each fraction to match the content of TS% with the initial MEF. The plasticizing properties of the resulting liquid were tested with the minicone protocol, as described above. The fractions obtained were identified as follows: F2 is a mixture of extracted compounds into Ethyl Acetate, it represents 21.68% of the total compounds; F3 is a mixture of extracted compounds into n-butanol, it represents 16.32% of the total compounds; F4 is a mixture of extracted compounds into ethanol, it represents 4.54% of the total compounds, and F5 is a mixture of extracted compounds into water, that is, 46.74% of total compounds with polarity similar to water. Fig. 4 presents the plasticity index of minicone tests where MEF has been separated in several polar fractions. The polar fraction identified as F5 corresponds to the mixture to the most polar compounds into the MEF product. They have similar solubility that water. For every concentration a significant increase in plasticity is observed for the F5 polar fraction, even at smaller dosages. It could indicate that the plasticizing effect has a strong link with the polarity of the compounds, most likely lactic acid. Lactic acid is found in concentrations of approximately 100 mg/ L. It is formed as one of the metabolites obtained from the fermentation of whey with lactic acid microorganism during the manufacture of the product MEF. Through the interaction with cement particles during cement hydration, lactic acid could be adsorbed on the surface of cement grains releasing lactates ions [20]. The negatively charged lactate ions repel each other and by doing this they push cement grains apart. The plasticizing effect of lactic acid in cementitious materials has been described before [21]. Fig. 5
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presents a scheme that illustrates the mechanisms for the electrostatic repulsion. This could likely explain the plasticizing properties observed in MEF. The impact of the presence of bacteria and other microorganism on the plasticity of cement pastes was also assessed. Fig. 6 presents the results of plasticity index of cement pastes made with normal MEF and MEF filtered to remove microorganism, as part of the minicone testing protocol. In every dosage of MEF used no significant differences in the plasticity index were found. For higher dosages (8% of the mass of cement), an increase in plasticity is observed; this could reinforce the theory of the compounds that negatively influence plasticity, which were likely removed during filtration. This test rules out the hypothesis stated in the literature that live bacteria are responsible for the plasticity effect of bioproducts [6,12,9]. Further, at the high alkaline pH of the pore solution, even at very early ages, it is very unlikely that bacteria can survive on the pore system after hardening. The active principle, therefore, is more related to what remains after the metabolism of bacteria.
4.2. Influence on viscosity of cement pastes Fig. 7 presents the results of the Marsh cone test performed in cement pastes made with various dosages of MEF, and a series with no plasticizer and the series with the commercial SP as reference for comparison. tv In cement pastes made with MEF drops significantly compared with pastes made with no SPs. The flow time is proportional to the viscosity and yield stress, thus indicating that a modification of the viscosity and the yield stress of the system takes place when MEF is used; the optimized dosage for the
Fig. 6. Plasticity index of cement pastes made with MEF with and without microbial cell.
Fig. 4. Plasticity index for polar fractions of MEF.
Fig. 5. Repulsion forces between lactate ion and cement grains.
Fig. 7. Flow time of cement pastes tested with the Marsh cone.
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Fig. 8. Water demand of cement pastes according to normal consistency test.
product evaluated appears to be 8% of the weight of cement. Concentration of MEF appears to have some effect on flow time, although it does not seem to influence optimized dosage. In the range of dosage evaluated, no significant differences are established between the commercial SP used as reference and MEF. The reference series with no admixture flows in twice the time of any of the other series tested. [19] Fig. 8 presents the results of normal consistency tests, where the capability of reducing water on the cement paste was measured based on the depth of penetration of the Vicat needle, which could indirectly indicate changes in rheological properties of the material. For 10 mm penetration depth, water reduction ranged from (20% to 25%) compared to the reference cement paste without admixture. No major differences were observed in water reduction in the pastes made with MEF and those made with commercial SPs. 4.3. Influence on hydration of cement pastes The influence of MEF on the hydration of cement was assessed aided by isothermal calorimetry studies performed in cement pastes. The heat of hydration for the pastes made with MEF at different concentrations (4%, 6% and 8% of the weight of cement) were measured and compared with those of the corresponding control cement pastes (OPC with no SPs) and paste containing 0.5% commercial SP N-200, as showed in Fig. 9.
Fig. 9. Rate of heat evolution as a means of measuring the influence of MEF on cement hydration.
Fig. 10. Setting time of cement pastes according to Vicat test.
It´s generally accepted that initial setting typically occurs at the beginning of the accelerating period, where C3S begins to hydrate rapidly [22]. By the end of this period, once maximum rate has been reached, final set has taken place and early hardening has started. Comparing the time ranging from the end of the dormant period and the beginning of the acceleration period for the control Portland cement pastes to those with the admixtures, it seems that all the admixtures retarded the cement hydration. For all chemical admixtures, an increase on the heat evolution occurs as a shoulder after the first 12 h. Associated to this intensification on the cement hydration, an increase on the cumulative heat could be observed after the first 24 h for all systems when compared to control paste. This effect could be related to an increase of the heat released during hydration of the C3A phase, usually associated with an increase on ettringite formation and a delay on its conversion to monosulphate [23]. For pastes containing MEF the increase in the size of this shoulder was roughly proportional to the admixture concentration. Same trend was observed for the retardation time, result which is in agreement with the setting times as determined by Vicat test presented in Fig. 10. The higher the dosage of MEF, the longer the final setting time. Thus, the impact of MEF on the cement hydration needs to be further investigated. The mechanism of retardation in cement paste depends on the type of admixtures. For polynaphthalene based superplasticizers, it is suggested that the retardation was mainly due to the adsorption of admixtures on nucleating hydrate particles and intercalation into hydrate phases already formed which inhibit the development of hydration products [24]. As MEF is the result of microbiological fermentation under anaerobic conditions, it contains a high volume of carboxylic acids such as lactic and acetic acid. Retardation effects have also been recognized for admixtures based on hydroxyl carboxylic acids at high concentrations [25]. However, because
Fig. 11. Slump diameter of mortars in shake table.
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5. Conclusions The bioplasticizer MEF has proven to have moderate plasticizing properties, which are apparently limited by a dilution effect caused by the excess of water in its formulation. Concentration of the product through roto-evaporation techniques yields a higher plasticizing effect. Separation of polar fractions has proven that the fraction with the highest polarity, identified for lactic acid, proves to be the most active one. The speed of flow in the Marsh cone shows a contribution of MEF to the decrease of viscosity in cement pastes, which could complement the plasticizing effect. MEF seems to have some sort of influence on the hydration of the aluminates in the cement. Further, for higher concentration MEF has also some retarding effect. Fig. 12. Compressive strength in mortars.
Fig. 13. Water absorption in mortars.
of its complex nature, further research is needed to unveil the nature of the MEF over cement hydration, as discussed in the literature [16]. 4.4. Studies in mortars Fig. 11 presents the results of the consistency tests in mortars cast with different dosages of MEF and the reference SP N-200. A reference mortar was cast with no plasticizer. The diameter of the mortar cone subjected to shake shows a great similarity for all MEF dosages to the one obtained for N-200. The best results are obtained for 6% MEF. The reference mortar cast with no plasticizer presents a much smaller diameter, which indicates a clear plasticizing effect of MEF, in this case, very similar to commercial SP N-200. Compressive strength of mortars at 7 and 28 days, presented in Fig. 12, does not show any major difference between all mortars tested, which is consistent to the fact that the same water to cement ratio was used for casting them. Fig. 13 presents the results of water absorption in all mortars. Mortars made with MEF, especially those at higher dosages (6, 8%) show lower water absorption, even compared with commercial SP N-200. This could indicate an improve microstructure development, probably due to a better hydration of the reaction products, which leads to a lower porosity and the decrease of connected pores.
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