new geoecoprotective properties of the construction materials for underground infrastructure development

Underground construction ability to absorb water has been investigated using wastewater with heavy metal ions.. Introduction The main idea of the paper is the utilization of cement based

Procedia Engineering 165 ( 2016 ) 1771 – 1775

1877-7058 © 2016 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 scientific committee of the 15th International scientific conference “Underground Urbanisation as a

Prerequisite for Sustainable Development

doi: 10.1016/j.proeng.2016.11.921

ScienceDirect

15th International scientific conference “Underground Urbanisation as a Prerequisite for

Sustainable Development”

New Geoecoprotective Properties Of The Construction Materials

For Underground Infrastructure Development

a

Emperor Alexander I St Petersburg State Transport University (PGUPS), Moskovsky pr 9, St Petersburg, 190031, Russia

b

St Petersburg State Institute of Technological (Technical University), Moskovsky pr 26, St Petersburg, 190013, Russia

c

Mozhaisky Military Space Academy, Zhdanovskaya st 13, St Petersburg, 197198, Russia

d

Peter the Great St Petersburg Polytechnic University, Politekhnicheskaya st 29, Saint-Petersburg, 195251, Russia

Abstract

The point of the paper is to introduce new characteristics of the underground construction materials which are important for geoecoprotection of infrastructure in the sense of durability and wastewater resistance The main idea is using absorption ability

of underground constructions on the cement base It was shown that utilization of silica sol solution instead of water allows one

to improve more than 50% main properties of the concrete on the cement base Because of that the new technology of fabrication

of the underground constructions on the cement base has been suggested (silica sol absorption technology, SAT - technology) Underground construction ability to absorb water has been investigated using wastewater with heavy metal ions Such kind of water has been absorbed by construction and detoxication of wastewater was demonstrated due to formation of heavy metal ions silicates in pores and capillary of material

© 2016 The Authors Published by Elsevier Ltd

Peer-review under responsibility of the scientific committee of the 15th International scientific conference “Underground Urbanisation as a Prerequisite for Sustainable Development

Keywords: underground, geoecoprotection, cement, building constructions

* Corresponding author Tel.: +7-921-912-64-07

E-mail address: marina.gravit@mail.ru

© 2016 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 scientific committee of the 15th International scientific conference “Underground Urbanisation as a Prerequisite for Sustainable Development

1 Introduction

The main idea of the paper is the utilization of cement based construction materials’ ability to absorb silica sol and heavy metal ion solutions for the two objectives – strengthening of the constructions if we have nanosolution and detoxication of the wastewater if we have heavy metal ion solution Such kind of problems are being observed

in the paper [1], especially important is to take into account donor-acceptor properties of solid surface [2-11] Phenomenon of the water absorbtion is known well enough for the underground building and the reason of such kind of the phenomenon is pores and capillaries in the solid materials on the cement base But instead of underground water it is passible to use silica sol solution in the early time of structure hardening and heavy metal ion solution in the time of underground exploitation of the building construction Under such kind of conditions new calcium silicate hydrates are formed if it has been used silica sol or heavy metal ion hydrates if it has been used heavy metal ion solution

The construction strengthening takes place because of the formation of new hydrates of calcium silicate in the pores and capillaries, and the detoxication from heavy metal ions takes place because of heavy metal hydrates formation From thermodynamics point of view reactions between silica sol, heavy metal ions and construction material on the cement base are allowed because of the negative Gibbs energy, table 1 [12-23]

Table 1 Thermodynamics of the some underground building system on the cement base

*SiO2∙H2

O – silica sol

**Pb(II); Cd(II); Fe(III); Сu(II) – heavy metal ions

According to the table 1 it is possible to form new calcium silicate hydrates (№1, 2, 3) and it is possible to form heavy metal ion hydroxides (№4,5,6,7,8) Also helps very low solubility of heavy metal ion hydroxides, lower, than 10-15 [15] Because of the formation of new calcium silicate hydrates, the improvement of the construction properties is observed And because of formation of hydroxides of heavy metal ions, the detoxication of wastewater takes place (purification of water from heavy metal ions) The strengthening provides the durability of the underground construction and because of that it can be named as “geoecoprotective” one The detoxication of wastewater in underground space from heavy metal ions by means of underground constructions on the cement base is important for environment protection

2 Experiment

Samples of concrete on the cement base and different additives have been used Samples were sinked in the silica sol solutions of 1, 2, 3 and 30% concentrations Time for start of saturation – 1, 3, 5, 7 days from the start of concrete article hardening, saturation time – till the end of process (till achievement of constant weight) Then in 28 days age samples were tested according to the usual procedures [15]

It has been found, that the best concentration for start of the absorption was 1,5-3% silica sol, time for absorption – 2-3 days from the concrete hardening start Then properties of the best sample obtained as described above were compared with properties of reference sample (table 2)

The second part of research was the following Samples of concrete of different classes after 28 days of hardening were soaked in the solution with heavy metal ions with different concentrations Change of chemical composition of solutions after that was investigated It was found that used samples are able to absorb heavy metal ions from the solution and after that solution are purified from ions (Table 3), so detoxication of the solution from heavy metal ions was demonstrated

Ca(OH)2 + 2(SiO2·H2O)* = CaO·2SiO2·2H2O + H2O -169.14

2Ca(OH)2+SiO2∙H2O=2CaO∙SiO2∙1,17H2O+1,83H2O -95.32

5Ca(OH)2 + 6(SiO2·H2O) = 5CaO·6SiO2·5,5H2O + 5,5H2O -584.80

5CaO∙6SiO2∙5,5H2O + Pb2+

aq** + 2OH

-aq+ 5H2O(ж) → Pb(OH)2(т) + 5CaO∙6SiO2∙10,5H2O(т) -91.96 5CaO∙6SiO2∙5,5H2O + Cd2+ **+ 2OH

-aq+ 5H2O(ж) → Cd(OH)2(т) + 5CaO∙6SiO2∙10,5H2O(т) -91.42 5CaO∙6SiO2∙5,5H2O + Fe3+

aq **+ 3OH

-aq+ 5H2O(ж) → Fe(OH)3(т) + 5CaO∙6SiO2∙10,5H2O(т) -221.90 5CaO∙6SiO2∙5,5H2O + Ni2+ + 2OH

-aq+ 5H2O(ж) → Ni(OH)2(т) + 5CaO∙6SiO2∙10,5H2O(т) -108.54 5CaO∙6SiO2∙5,5H2O + Cu2+ **+ 2OH

-aq+ 5H2O(ж) → Cu(OH)2(т) + 5CaO∙6SiO2∙10,5H2O(т) -120.63

Table 2 Improvement of concrete properties after silica sol absorption, %

Compressive strength + 52

Water notpermentility + 23 Low-temperature resistance, cycles + 50

Table 3 Wastewater detoxication properties of concrete samples

Concrete class, B Absorbed heavy metal ions, g/ton

Cd(II) Pb(II) Cu(II)

According to the table 3, the level of the absorption of heavy metal ions is different It depends on class of concrete samples (strength)

3 Results and Discussion

New position in the paper is reactions in the pores and capillaries of the construction materials with silica sol solution and heavy metal ion containing solutions Technology of using of such kind of properties improvements using silica sol absorption is suitable for monolith concrete underground construction and silica sol strengthening is good enough as well for any kind of concrete articles

Table 4 Classification building constructions

Nature Absorbing solution

Reactions in pores and capillaries of the stone of the

stone

Gibbs energy,

Δ ʹͻͺͲ ǡ kJ

New phases of the reactions

Geoecoprotection due to

silicate

calcium

hydrates,

pH > 7

1 SiO2∙nH2O – silica sol;

2 Al(III) –solution;

3 Fe(III) – solution

1 Soling;

2 Al3+ + 6OH- = [AlO3]3- + 3H2O

3 Fe3+ + 6OH- = [FeO3]3- + 3H2O

Negative

1 Silicate calcium hydrates

2 Aluminate calcium hydrates

durability

silicate

calcium

hydrates,

pH > 7

4 Organic,

solution, for example,

acid phenylic

4 2C6H5OH + Ca(OH)2 = Ca(C6H5O)2 + 2H2O Negative 4 Phenate

decreasing of danger

silicate sulfat

hydrates,

pH = 7

5 Pb(II)-solution

ions

5 Pb2+ + CaSO4∙2H2O = PbSO4↓ + Ca2+ + 2H2O Negative

5 Sulphats with very low solubility

Detoxication of heavy metal ions

silicate aluminate

hydrates,

pH > 7

6 SiO2∙nH2O – silica

6 Alumosilicate hydrates durability

If wastewater has been polluted with heavy metal ions, the detoxication takes place It was confirmed by practice during exploitation of underground concrete blocks strengthened with silica sol technology and blocks have shown almost no water absorption Sol absorption technology (SAT) should be recommended for common concrete articles

for decrease of water absorption Also concrete blocks were investigated in the underground space in the presence of wastewater polluted with heavy metal ions The result of the test was the same as one for the concrete examples, decribed above So, it is possible to use silica sol solution technology for improvement of properties more than 50 percent and because of that new technology of fabrication of underground construction articles on the cement base is suggested (Sol absorption technology, SAT) In addition, construction articles on the cement base may be used for detoxication of wastewater from heavy metal ions In the table 4 is shown classification of the construction on the different cement According to the table 4 it is possible to achieve geoecoprotection for every time and reaction in the poros and capillaries have been named lithosynthesis In the table 5 is shown the derection of the improvement

of the geoecoprotective properties according to the thermodynamic parameters of the building construction

Table 5 Thermodynamic parameters of phases and geoecoprotective properties

4 Conclusions

1 Improvement of properties of cement based underground construction articles is achieved by absorption of silica sol solution

2 It was shown that suggested approach provides articles with new geoecoprotective property, namely ability

to purify wastewater from heavy metal ions

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