The Influence of Natural and Nano-additives on Early ...

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ScienceDirect Procedia Engineering 172 (2017) 127 – 134

Modern Building Materials, Structures and Techniques, MBMST 2016

The influence of natural and nano-additives on early strength of cement mortars Piotr Brzozowskia,*, Elzbieta Horszczaruka, Khrystyna Hrabiukb a

West Pomeranian University of Technology in Szczecin, Al. Piastow 50, 70-311 Szczecin, Poland b Lviv Polytechnic National University, 12 Bandera street, Lviv, 79013, Ukraine

Abstract The study attempts to evaluate the impact of six different additives, including natural additives and nano-additives, on the early one day strength of cement mortars. Furthermore the use of heating process to increase the strength development process of tested mortars was analyzed. Tests were performed in three series with different water/ binder ratio, the values were: 0.3, 0.4 and 0.5. The results confirmed, that the tested additives can be used to improve the early strength of the cement mortars. especially for w/b ratio 0.4. Furthermore, thermal treatment contributed significantly to the growth rate of the strength of the modified cement mortars. © Published by Elsevier Ltd. This © 2017 2016The TheAuthors. Authors. Published by Elsevier Ltd.is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of MBMST 2016. Peer-review under responsibility of the organizing committee of MBMST 2016 Keywords: additives; water/ binder ratio; nanomaterials; cement mortar; heat treating.

1. Introduction Concrete is one of the most versatile materials used in the construction industry. It can be made components or objects of almost any shape with it and its parameters can be adapted to individual needs. A large branch of construction industry is the concrete prefabrication. In order to significantly reduce the construction time of the building, all or some of the elements are delivered to the site and assembled there. Besides structural components, in the offer there are more and more finishing elements, with a certain texture or color [1].

* Corresponding author. Tel.: +48-914-494-074; fax: +48-914-494-369. E-mail address: [email protected]

1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of MBMST 2016

doi:10.1016/j.proeng.2017.02.034

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Piotr Brzozowski et al. / Procedia Engineering 172 (2017) 127 – 134

Methods of implementation of precast have not changed in recent years, but there are new materials that can significantly speed up the manufacturing process. One of the main directions of development of prefabrication process has always been to achieve higher strength of the concrete without a significant increase in costs, and to ensure the highest available productivity, which significantly affects the time it takes for the removal of the formwork from elements. As the main ways of improving the strength of the concrete can be mentioned: reduction of water/ binder ratio, the use of high grades cements of high early strength, appropriate compaction, the use of chemical additives and admixtures as well as thermal or pressure processes. The first chemical bond accelerators used, were chlorides of calcium or sodium and potassium carbonate. In the production process of precast concrete elements three basic strength can be marked out: x unmold strength - enables removal of the formwork of element without damaging it and its transport to the place of maturation; x storage strength - allows the elements to be set in piles or stacks. Usually it’s about 50% of the target 28 day strength; x assembly strength - allowing the transport of these components to site and their installation. Usually set between 70-100% of the target 28 day strength. The first one has the greatest impact on the rate of the production process. Early unmolding allows for faster re-use of forms, which affects the number of elements produced. It is important therefore to achieve as soon as possible the required unmold strength. To achieve this goal, in the precast factories there is very often an additional thermal treatment of elements used. The most commonly used methods include: x infusion in condition of the natural pressure - the impact of the steam at a temperature up to +100°C on molded concrete element; x electric heating - electricity is passed through a molded fresh concrete, resulting in heating it from inside; x heating with hot air or steam - the heating medium is distributed around the molds of maturing elements; x infrared radiation heating - infrared rays heat the concrete surface; x the use of hot mix - heated components of the concrete mix are used, generally aggregates. Whichever method is used, the heating process can be divided into four phases: initial maturation, raising the temperature, heating at a constant temperature, and the cooling. Initial maturation usually lasts from 1 to 8 hours, this is the necessary time to reach concrete strength, which will allow it to carry the internal stresses due to temperature changes. A heating and cooling rate depends on the heating medium and the size of the element. The recommended range is 20-30°C/h. Because of the maximum temperature and the time of its operation, the heating phase cycles can be divided into short - high temperature and short warm-up time, medium, or long - lower temperature acting for a long time [2]. The aim of this study was to determine the possibility of using natural and nano-additives to accelerate the process of maturation of concrete. It was decided that the tests will be carried out on cement mortars and the reference time for strength tests was established as 1 day after molding. 2. Characteristics of materials and research methodology 2.1. Base components For the preparation of mortars Portland cement CEM I 52,5R, which meets the requirements of EN 197-1, was used. Due to its characteristics it is dedicated in particular to the construction and precast, aged in natural conditions, increased or decreased temperature, required high early strength. As aggregate washed river sand of particle size 0-2 mm was used. It had a particle size similar to standard sand in accordance with EN 196-1. Three series of cement mortars with a variable water/ binder ratio were made, respectively: Series 1 – 0.5; Series 2 - 0.4 and Series 3 - 0.3. Mortars composition are presented in Table 1. Base mortars - without additives were labeled BC. Mortars were designated by giving the abbreviation of additive, and a number representing the amount of it in

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reference to the mass of the cement. For the preparation of mortars superplasticizer based on polycarboxylic ethers was used. The amount of it was selected in the way to be able to observe the effects of additives on the flowability for the individual w/b ratios. Table 1. Mixture proportions of mortars (g/dm3).

Mortar designation

Cement

Sand

Metakaolin

Zeolite

C-S-H suspension

Polymer dispersion

Microsilica suspension

Silica fume

Series 1 w/b = 0.5

Series 2 w/b = 0.4

Series 3 w/b = 0.3

Water

HRWR

Water

HRWR

Water

HRWR

BC

512

1535

-

-

-

-

-

-

256

-

205

5.1

154

10.2

MK5

486

1535

26

-

-

-

-

-

256

-

205

5.1

154

10.2

MK15

435

1535

77

-

-

-

-

-

256

-

205

5.1

154

10.2

ZEO5

486

1535

-

26

-

-

-

-

256

-

205

5.1

154

10.2

ZEO15

435

1535

-

77

-

-

-

-

256

-

205

5.1

154

10.2

CSH4

512

1535

-

-

20

-

-

-

256

-

205

5.1

154

10.2

PD2

512

1535

-

-

-

10

-

-

256

-

205

5.1

154

10.2

MS5

495

1535

-

-

-

-

26

-

238

2.5

205

8.7

127

30.5

SF5

460

1535

-

-

-

-

-

26

256

2.5

205

8.7

154

30.5

2.2. Natural additives For the research were selected natural additives such: metakaolin (MK), zeolite (ZEO), and the addition of the silica fume (SF). The amount of the additives used was 5 and 15% by weight of the cement for the two first and 5% for the silica fume. Natural zeolite was used, formed by grinding and drying the rock, while the metakaolin was obtained by calcination of kaolin. All additives used are pozzolanic. When calculating the water/ binder ratio (according to PN-EN 206) the coefficient k = 1.0 was set for metakaolin and zeolite, whereas for silica fume it was equal 2.0. Table 2. Consistency results. Flowability [mm] Mortar designation Series 1 Series 2 Series 3 w/b = 0.5 w/b = 0.4 w/b = 0.3 BC

130

125

120

MK5

143

157

113

MK15

133

139

123

ZEO5

122

144

116

ZEO15

130

167

122

CSH4

116

113

107

PD2

117

173

122

MS5

132

117

109

SF5

130

115

108

2.3. Nano-additives In order to accelerate the cement hydration process, an aqueous suspension containing crystallization spores of nanoparticles C-S-H was used. It was added in an amount of 4% by weight of cement – CSH. Hydrated calcium

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silicates are gel composed of strongly adhesive nanoparticles, whose task is to fill all the places between the grains of cement. It is the most important component of the final product - cement stone, and has a huge impact on the properties of concrete grout and the final product. In the normal conditions the formation of phase C-S-H occurs in the vicinity of the cement grains or on their surface layer. This process slows down the subsequent movement of the reactants and products of reaction, what makes the hydration difficult and takes much longer time. The introduction of admixture containing nanocrystals to the grout entails that the formation of the gel C-S-H occurs at a distance from the surface of the cement grains. As a result, minor amounts of calcium hydroxide is exuded, and thus, further hydration is not affected and may be performed in a comfortable environment. This results in increased amounts of formed C-S-H gel, which significantly affects the strength of the concrete. The effect of addition of nanoparticles phase C-S-H on the strength of concrete can be observed mainly in the early age [3]. This admixture, is successfully used in the production of prefabricated elements [4]. Another tested additive was an aqueous suspension of SiO2 - designation MS, which was used in the amount of 5% of weight of cement. Studies published in [5-7] show that the SiO2 nanoparticles have a positive effect on the hydration process and microstructure of cement paste. This contributes in an strength increase of mortars containing them. Very important is the way of adding nanoparticles to the mixture. Aqueous suspension allows for even distribution of them in the volume of paste [8]. Solids content of the suspension was 30%. To calculate the water/ binder ratio the coefficient k = 2.0 was used, as for silica fume. The last admixture used, was dispersion of styrene acrylic copolymer - PD, in an amount of 2% of weight of cement. Use of a polymer affects the hydration of cement by forming a polymer film between the binder. In addition, the chemical reactions between the polymer molecules and the aggregates increase the adhesion of the contact zone [9]. Use of a polymer increases the tightness, frost resistance, the tensile strength of concrete. Furthermore it decreases the value of shrinkage strain of concrete [10]. 2.4. Preparation of mortars and the heating process The mortar components were mixed according to EN 196-1. All liquid additives have been mixed with the water prior to its addition to the cement. While the powders were pre-mixed with cement. After mixing the consistency of mortars was measured. The method of flow table according to EN 1015-3 was used. Next the mortars were poured in the molds and compacted in two layers. For each mortar two forms containing 3 specimens of dimensions 40x40x160 mm were made. Half of the specimens were matured for 24 hours at the temperature of 20°C covered with PVC film. Other molds were placed in an oven and subjected to heat treatment. The initial maturation time was 2 hours. The speed of heating and cooling of mortars was 20°C/h. The maximum temperature of 70°C was maintained for a period of 10 hours. During the process molds were not protected from above against moisture loss, and the whole process took place in the dryer with the forced movement of air. Mortars after heating process are marked with the letter T. After 24 hours from preparation all test specimens were unmolded, weighed and tested. Determination of flexural strength and compressive strength in accordance with EN 196-1 were carried out. For each determination three specimens were used. 3. Results and discussion 3.1. Consistency The results of flow of the mortars for individual series are summarized in the Table 2. An increase of fluidity of fresh mortars containing zeolite and metakaolin was observed. Especially for a water/ binder ratio equal 0.4. The addition of nanoparticles of C-S-H resulted in a decrease in the flow in relative to the basic recipe. The polymer in the presence of superplasticizer caused the increase of the flow. Both in the case of the microsilica and silica fume to ensure adequate consistency the use of superplasticizer was needed. For smaller w/b the amount of it was increased significantly.


3.2. Density in natural state As expected, there was an increase in the density of most mortars with decreasing water/ binder ratio. It is connected with the better compaction of mortars. Due to the fact, that the molds in the oven during heating process were not protected against moisture loss, there was observed a weight loss of specimens subjected to heat treatment. The results of densities and the comparison of mortar subjected to thermal treatment with those matured in natural conditions are presented in the Tables 3-5. The smallest drying was achieved for specimens containing the microsilica. In most cases, with the decrease in w/b the water loss after heating was smaller. This may be the effect of better reaction of the components, and therefore less amount of free water in the mortar structure. Table 3. Test results of Series 1 mortars after one day of curing. Series 1 w/b = 0.5 Effects of heating process Mortar designation

Flexural Density strength [kg/dm3] [MPa]

Compressive strength [MPa]

BC BC T MK5 MK5 T MK15 MK15 T ZEO5 ZEO5 T ZEO15 ZEO15 T CSH4 CSH4 T PD2 PD2 T MS5 MS5 T SF5 SF5 T

2.25 2.19 2.20 2.17 2.26 2.18 2.25 2.14 2.24 2.11 2.19 2.15 2.12 2.07 2.22 2.17 2.15 2.07

21.00 23.77 17.98 22.68 19.46 24.18 19.84 23.23 13.73 20.51 19.49 22.76 14.40 19.64 19.74 25.83 13.87 18.37

4.08 4.52 3.72 3.90 4.12 4.87 3.79 4.23 3.24 3.53 4.37 5.08 4.60 4.72 5.34 5.76 3.82 4.74

Change in mass [%]

Change in flexural strength [%]

Change in compressive strength [%]

-2.5

10.8

13.2

-1.6

4.7

26.1

-3.6

18.1

24.3

-5.0

11.6

17.1

-6.0

8.9

49.4

-1.9

16.3

16.8

-2.2

2.5

36.4

-2.3

8.0

30.9

-3.8

24.2

32.4

Fig. 1. Relative strength in comparison with base mortar not affected by heating process, Series 1.

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Piotr Brzozowski et al. / Procedia Engineering 172 (2017) 127 – 134 Table 4. Test results of Series 2 mortars after one day of curing. Series 2 w/b = 0.4 Effects of heating process Mortar designation

Density [kg/dm3]

Flexural strength [MPa]


2.25 2.16 2.32 2.27 2.27 2.24 2.26 2.21 2.25 2.19 2.24 2.19 2.13 2.00 2.24 2.21 2.18 2.12

4.80 5.24 5.54 6.42 5.36 6.78 4.83 5.47 4.94 5.36 6.19 6.28 5.52 5.70 6.84 7.28 4.24 5.10


25.43 30.43 31.93 35.33 27.60 35.68 29.89 32.28 22.48 35.30 27.34 28.78 16.53 24.52 30.35 38.84 14.66 28.95

Change in mass [%]



-4.0

9.1

19.7

-2.4

16.0

10.7

-1.1

26.4

29.3

-2.1

13.4

8.0

-2.7

8.6

57.0

-2.4

1.5

5.3

-6.2

3.3

48.4

-1.3

6.4

28.0

-2.8

20.5

97.5


3.3. Flexural and compressive strength Figures 1-3 show the results of change in flexural strength and compressive strength of mortars tested in relative to the basic mortars not affected by heating process. For high water/ binder ratio - Series 1, after the application of each of the additive, a reduction in the early compressive strength was observed. Only after undergoing a heating process it was possible to achieve satisfactory results for the mortars MK15, CSH4 and MS5. Comparing the flexural strength, a significant increase was obtained in the case of mortars containing the suspension of C-S-H, polymer and microsilica.

Piotr Brzozowski et al. / Procedia Engineering 172 (2017) 127 – 134 Table 5. Test results of Series 3 mortars after one day of curing. Series 3 w/b = 0.3 Effects of heating process Mortar designation

Density [kg/dm3]

Flexural strength [MPa]



2.28 2.26 2.34 2.23 2.28 2.27 2.28 2.28 2.23 2.20 2.23 2.19 2.16 2.07 2.29 2.29 2.22 2.18

6.48 6.92 6.28 6.38 5.78 7.74 6.27 6.75 5.74 6.32 6.61 6.71 5.71 6.88 7.96 9.18 4.63 5.83

37.80 41.89 33.95 44.30 31.89 48.09 39.42 48.76 33.59 45.63 29.34 30.41 24.16 31.81 37.39 47.43 16.36 31.31

Change in mass [%]



-1.3

6.7

10.8

-4.5

1.7

30.5

-0.5

33.9

50.8

0.0

7.7

23.7

-1.0

10.0

35.9

-1.8

1.6

3.6

-4.2

20.4

31.6

-0.1

15.3

26.9

-1.8

25.9

91.4


The biggest strength increase because of modifying the mortars witch additives was obtained for a Series 2. Except mortars containing the polymer and silica fume, other additions in most significantly improved early strength. Heating process of all mortars witch metakaolin, 15% zeolite and microsilica increased compressive strength in comparison to the base mortar by about 40%. As in the case of Series 1, adding the polymer increased the flexural strength but reduced the compressive strength of mortars. In the Series 3 positive effect on the strength was observed for the zeolite content of 5%, and for the microsilica. After the heating, higher strengths, in addition to these two, had mortars MK5, MK15 and ZEO 15.

133

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In Tables 3-5 the percentage changes in flexural strength and compressive strength of mortars affected by heating process compared with those matured in natural conditions were summarized. In the case of cement mortars modified with polymer, microsilica and 15% of the zeolite and metakaolin, for all water/ binder ratios, there is significant increase in compressive strength when subjected to the heat treatment. For those mortars the increase in strength in the relative to the mortars matured at 20°C ranged from 24.3 to 57%. Heating had the greatest influence on the strength increase obtained for mortars containing silica fume. Almost double increase the compressive strength was obtained for the w/b = 0.4 and 0.3. However for mortars containing addition of nanoparticles of C-S-H no satisfactory improvement in their strength, after applying high temperature, was achieved. Comparing the impact of silica fume and microsilica on the properties of tested mortars, it was observed significant difference in the way they act. For microsilica growth of early strength in comparison to the base samples was obtained. While for the silica fume significant decrease of early strength of mortars was observed. This effects are consistent with the results of the study of cement pastes described in [11]. During the compressive strength tests, different destructions of specimens were observed. For low values of water/ binder ratio, mortars not affected by thermal process were destroyed mostly by sudden explosion of specimen. The destruction of the same mortars subjected to heating was slow, gradual. It may be caused by the formation of microcracks and micro-scratch during the process of heating of mortars. 4. Conclusions Based on the results presented in the paper, it can be concluded that by using the natural and nano-additives, in the composition of cement mortars, the early strength of mortars can be improved. However, the test showed different effects of additives at different values of water/ binder ratio. The best effect of additives were obtained for Series 2 (w/b = 0.4), where only 3 of 8 additives did not improve the strength of the mortar. On the other hand, in Series 1 (w/b = 0.5) there were no increase in the properties of the mortars. It has been observed in that the use of silica fume in mortars resulted in a deterioration of their early strength. In contrast, the addition of microsilica, in the form of aqueous suspension, had a positive effect on the parameters of tested mortars after one day of hardening. Heating process contributed significantly to the growth rate of the strength of the modified cement mortars. For all tested mortars there was observed an increase in compressive and tensile strength after the application of thermal treatment. The use of additives and the thermal process composed together significantly improved the strength parameters of mortars, in comparison to the base mortars. References [1] J. Jasiczak, Kierunki rozwoju prefabrykacji betonowej w Polsce, Materiały Budowlane 11 (2011) 4- 9 (in Polish). [2] J. Rubin, Obróbka termiczno-wilgotnościowa metoda vaporyzacji, BRUKBIZNES 5 (2012) 16-19 (in Polish). [3] P. Brzozowski, M. Szczotkowska, Wpływ nanokryształów CSH na wytrzymałość betonów cementowych stosowanych w budownictwie komunikacyjnym, Przegląd Budowlany 7-8 (2013) 43-46 (in Polish). [4] T. Puzak, H. Skalec, K. Grzesiak, Nanotechnologia w prefabrykacji betonowej, Reologia w technologii betonu (2010) 45–56 (in Polish). [5] Li H, Xiao HG, J. Yuan, J. Ou, Microstructure of cement mortar with nanoparticles, Composites: Part B 35 (2004) 185–189. [6] E. Horszczaruk, E. Mijowska, K.Cendrowski, S.Mijowska, P.Sikora, Effect of incorporation route on dispersion of mesoporous silica nanospheres in cement mortar, Construction and Building Materials 66 (2014) 418-421. [7] P. Sikora, E. Horszczaruk, T. Rucinska, The effect of nanosilica and titanium dioxide on the mechanical and self-cleaning properties of wasteglass cement mortar, Procedia Engineering 108 (2015) 146-153. [8] E. Horszczaruk, E. Mijowska, K. Cendrowski, P.Sikora, Influence of the new method of nanosilica addition on the mechanical properties of cement mortars, Cement, Wapno, Beton 5 (2014) 308-316. [9] Yoshihiko Ohama, Polymer-based admixtures, Cement and Concrete Composites 20(2–3) (1998) 189–212. [10] M. Gruszczynski, Zastosowanie nowoczesnych betonów specjalnych na przykładzie naprawy falochronu wyspowego w porcie Gdynia, Przegląd Budowlany 1 (2014) 17-23 (in Polish). [11] Ye Qing, Zhang Zenan, Kong Deyu, Chen Rongshen, Influence of nano-SiO2 addition on properties of hardened cement paste as compared with silica fume, Construction and Building Materials 21(3) (2007) 539-545.