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* Corresponding author: 550818454@qq.com
Study on the technology of strengthening concrete by
impregnation with modified sodium silicate compound
strengthening fluid
Yang Dishan1,*, Yan Tongyu1, Huang Xiaoyu1, Xiong Ying1, Lin Xi1, Zhou Hong2 and Shi Jianguang2
1National Grid Fujian Electric Power Co., Ltd. Institute of Economics and Technology, Fuzhou 350012, China
2School of Architecture and Civil Engineering, Xiamen University, Fujian 361005, China
Abstract. It is the key to the concrete repair and strengthening construction that the base concrete has a
certain quality and strength. Based on the strengthening mechanism of sodium silicate,the sodium silicate was
modified to develop a kind of compound strengthening liquid. Through the contrast test results of concrete
impregnation. The strength of C5 concrete before and after strengthening is increased by 42.5%, while the
strength of C10 concrete is increased by 21.4%, and the strength of C15 concrete is increased by 10%.
1 Introduction
It is very common and serious that the durability damage
of the outdoor concrete structure support in the coastal
substation, which causes the aging and deterioration of
concrete in different degrees[1,2]. There are four steps, base
treatment, interface treatment, repair treatment and
surface treatment in the repair process of durability
damage[3]. The treatment of concrete base includes
eliminating the defects such as floating slurry, weathering
and spalling, and chiseling base to meet the requirements
of certain roughness[4~7], so as to ensure that repair and
reinforcement materials and base concrete bond strength
enough to ensure that damage does not occur at the
interface. But it is difficult the concrete base treatment
construction as to cause dust and other environmental
problems, especially for the construction of the outdoor
concrete support of the substation. Therefore, it is
effective technical measures to reduce or avoid the
elimination, roughen and other concrete base if we can
reinforce the concrete base directly after surface cleaning,
improve the quality and strength of concrete base and
meet the bonding conditions between repair or
reinforcement materials. So, on the basis of summarizing
the research results of sodium silicate reinforced concrete,
the modified sodium silicate composite reinforced
concrete was developed in this paper. Through the
contrast test after concrete immersion, the reinforcement
effect of impregnation was studied.
2 Research status of sodium silicate
reinforced concrete technology
Sodium silicate solution state, generally colorless or
slightly colored transparent or translucent viscous liquid.
Molecular formula Na2O·mSiO2, molar ratio of silica
sand to alkali, i.e. the molar ratio of SiO2 to Na
2O,
determines the modulus M of sodium silicate. The
modulus not only reflects the composition of sodium
silicate, but also affects the physical and chemical
properties of sodium silicate. Therefore, different
modulus of sodium silicate has different uses[8]. Shi[9]
found that sodium silicate sodium silicate can hydrolyze
at room temperature, ionize the silica gel and dehydrate
and condense to form a network structure with Si-O-Si as
the framework. Fan[10] Using nano-silica soaking solution
soak, PVA solution strengthening, soaking in the sodium
silicate solution strengthening, sodium silicate solution
immersion as well as PVA solution soak four kinds of
strengthening methods for recycled aggregates for
strengthening experiment, found that modified PVA
solution and sodium silicate solution immersion of
recycled coarse aggregate has good effect, the PVA
solution concentration was 0.5%, concentration of sodium
silicate solution was 5% when modified effect is best,
recycled concrete 28-day strength increased by 7.2% and
23.7% respectively. In order to study the influence of
inorganic surface treating agent on the surface
performance and durability of airport pavement concrete,
Li[11] used sodium silicate with lithium silicate to form
composite sodium silicate inorganic surface treatment
agent, the inorganic surface treatment agent is coated on
the surface of concrete block. The test results showed that
the surface hardness of concrete reached 9.0 after 7 days.
E3S Web of Conferences 293, 02021 (2021) https://doi.org/10.1051/e3sconf/202129302021
GCEECE 2021
© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution
License 4.0 (http://creativecommons.org/licenses/by/4.0/).
3 Research and development of
modified sodium silicate composite
reinforcement solution and
experimental study on impregnating
reinforced concrete
3.1 Research and development of modified
sodium silicate composite reinforcement
solution
The modification methods of sodium silicate mainly
include enhancing the penetration ability of sodium
silicate, increasing the curing strength of sodium silicate,
and speeding up the curing time of sodium silicate. To
enhance the penetration ability of sodium silicate is to
reduce the viscosity of sodium silicate and make it easier
to penetrate into the concrete. The penetration of liquid in
concrete can be regarded as capillary water absorption,
and the penetration depth of solution in capillary can be
described by Equation (1).
tkt
r
x
2
cos (1)
Where, x is penetration depth; σ is surface tension; r is
pore radius; θ is the contact angle; η is viscosity; T is time;
K is the capillary coefficient or permeability coefficient.
It can be seen from Equation (1) that, under the same
conditions, the penetration depth of the solution in
concrete is determined by the contact angle and interfacial
energy of the solution, and the relationship between the
contact angle and interfacial energy can be expressed by
Young's Equation (2).
lg
cos
slsg
(2)
Where: γsg is solid-gas interface energy; γsl is the solid-
liquid interface energy; γlg is the liquid-gas interface
energy; θ is the solid-liquid contact angle.
According to Young's equation (2), the contact angle
is affected by the solid-liquid-gas interface energy, which
is determined by the liquid's surface tension. In order for
the liquid to be wetted at the solid interface, it is necessary
to reduce the surface tension of the liquid. The addition of
chemical surfactants can effectively reduce the surface
tension of the liquid, Li[12] pointed out that the surfactant
is a compound composed of two groups with different
properties: hydrophilic group and hydrophobic group.
Hydrophilic group is generally non-polar hydrocarbon
chains, while hydrophobic groups are generally polar
groups such as − OH, − COOH and − SO3. When the
surfactant is dissolved in water, its hydrophilic end will be
attracted into the water molecules, and its hydrophobic
end is repelled, so the molecules in the surfactant on the
surface of water orientation, resulting in water solution
surface tension greatly reduced, thereby greatly
improving the wetting ability of the solution.
In addition, the penetration depth can be increased by
reducing the viscosity of sodium silicate, and the viscosity
can be adjusted by changing the concentration of sodium
silicate. The influence of concentration and modulus on
the viscosity of sodium silicate is plotted by Zhu[13]. The
viscosity of sodium silicate increases linearly when it
exceeds the critical value. Since the modified sodium
silicate module used is 3.4 and the critical concentration
is 37%, 2.7 liters of water should be added for dilution per
liter of sodium silicate to minimize its viscosity while
maintaining the concentration of sodium silicate as much
as possible.
The curing strength of sodium silicate is generally
related to the curing conditions and additives in sodium
silicate. The addition of additives in sodium silicate can
also improve the curing strength and bonding strength of
sodium silicate. There are four curing ways of sodium
silicate including heating hardening, microwave
hardening, carbon dioxide hardening, alcohol and ester
hardening[14]. The mechanism of hardening of sodium
silicate by heating is mainly that the heating will
dehydrate the sodium silicate, which will have different
hardening processes at different temperatures. When the
temperature reaches more than 100 degrees, the Si-OH
bond in the sodium silicate will dehydrate and associate
with each other and form Si-O-Si bond, so the sodium
silicate will form a stable material with Si-O-Si chain
structure. Microwave hardening is the use of microwave
to accelerate the hardening of sodium silicate. The
temperature will rise rapidly after the sodium silicate
absorbs the energy of microwave. The silica molecules
and water molecules in the sodium silicate will oscillate
at a high speed at the same time. The colloidal particles
will accelerate the movement and under the influence of
heat, and quickly form a dense and small glass-like
network structure of colloidal particles. CO2 gas
hardening refers to the rapid hardening of sodium silicate
by blowing CO2. Under the action of CO2 gas, sodium
silicate can react with CO2 to form silica gel. At the same
time, CO2 has a good drying effect, which can quickly dry
sodium silicate. The water of silica gel is evaporated and
dehydrated to form solid SiO2, which is finally condensed
and hardened. The hardening of alcohols and esters
refers to the addition of organic esters can react with
sodium silicate, so that the modulus of sodium silicate
increases, and further dehydration of sodium silicate
occurs hardening. Studies have shown that adding
polyols in sodium silicate can improve the bonding
strength of sodium silicate after curing.
The mechanism is not exactly the same although the
four methods can make the sodium silicate hardening. The
compressive strength of sodium silicate obtained by
microwave hardening method is higher, while that
obtained by alcohol and esters hardening method has
better bonding property. Li[15] found that adding a small
amount of sodium tetraborate can improve the hardening
strength of sodium silicate, and the bond strength
increases with the increase of sodium tetraborate content.
Sodium tetraborate or borax, molecular formula
Na2B4O7∙10H2O is a very important boron mineral and
boron compound. It is usually a white powder containing
colorless crystals and soluble in water. Sodium tetraborate
presents a tetrahedral form because its structure formula
is similar with sodium silicate, both of them are
tetravalent boron atoms or silicon atoms connected with
three oxygen atoms. Therefore, adding sodium tetraborate
in sodium silicate can form a composite glass network
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E3S Web of Conferences 293, 02021 (2021) https://doi.org/10.1051/e3sconf/202129302021
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with sodium silicate and improve the integrity of the
network, so as to improve the curing strength of sodium
silicate.
It is necessary to control the dosage of curing agent
because sodium silicate penetrating into concrete takes a
certain time as well as adding curing agent can not make
sodium silicate solidify too fast so as to lose liquidity.
When sodium silicate is added to sodium silicate, it can
react with the hydrolysate of sodium silicate. The
hydrolysis reaction of sodium silicate is shown in
equation (3).
Na2SiO3+3H2O=2NaOH+Si(OH)4 (3)
The product Si(OH)4 is also called orthosilicate,
generally written as H4SiO4, but written as Si(OH)4 is
easier to understand. Adding sodium fluosilicate to
sodium silicate can react with NaOH, the hydrolyzed
product of sodium silicate. The reaction formula is shown
in Equation (4).
Na2SiF6+6NaOH=Na2SiO3+6NaF+3H2O (4)
By combining the two equations above, the total
equation can be obtained, as shown in Equation (5).
2Na2SiO3+Na2SiF6+6H2O=6NaF↓+3Si(OH)4 (5)
It can be concluded from the total reaction that after
adding NA2SiF6, it reacts with NaOH, thus accelerating
the hydrolysis of sodium silicate. Si in Na2SiO3 and
Na2SiF6 all generates the orthosilicate monomer Si(OH)4.
Si(OH)4 is an elastic colloid, and it is also the material that
finally plays a bonding role. Orthosilicate can be
dehydrated and condensed to form a network structure
material with Si-O-Si chain. The NaF generated by the
whole reaction is insoluble material, so if the sodium
silicate is solidified in the concrete, the NaF generated can
not only fill the gap after the solidification of sodium
silicate, but also fill the pores in the concrete, which is of
positive significance to enhance the curing strength of
sodium silicate and concrete strength. Therefore, the
addition of Na2SiF6 not only shortens the curing time of
sodium silicate, but also improves the curing strength of
sodium silicate.
Based on the control of sodium silicate concentration,
the selection of surfactants and additives, and the control
of curing agent dosage, the sodium silicate is modified to
improve its permeability and wetting ability, and improve
the curing strength, bond strength and concrete strength,
so as to achieve the purpose of providing concrete
durability and strength. The material preparation of
modified sodium silicate composite reinforcing solution
selected the sodium tetraborate product produced by
Tianjin Zhiyuan Chemical Reagent Co., Ltd. The
molecular formula is Na2B4O7∙10H2O, the molecular
weight is 381.38, and the purity is 99.5%. The molecular
formula of sodium dodecyl sulfate produced by Beijing
Jintong Letai Chemical Products Co., Ltd. is
C12H25SO3Na. Due to the negative charge of sulfonic acid
group-SO3 on the left side, it belongs to anionic surfactant.
The molecular formula of sodium fluorosilicate produced
by Pingxiang Baishi Chemical Reagent Co., Ltd. is
Na2SiF6 with purity of 99.0 %.
3.2 Manufacture of concrete test blocks and
impregnating reinforced concrete
The main materials of concrete test block are silicate
cement, water, coarse aggregate and fine aggregate. The
cement is P·O32.5 ordinary Portland cement, which meets
the national standard GB175-1999 <Portland cement,
ordinary Portland cement>. The flexural strength of 3 d
and 28 d is 4.0 MPa and 7.6 MPa, respectively. The
compressive strength of 3 d and 28 d is 18.8 MPa and 37.4
MPa, respectively. The fine aggregate used is
manufactured sand from Quanzhou, Fujian, and the
apparent density is 2680 kg/m3. According to the
requirements of GB/T 14684-2011 <Sand for
construction>, the percentage of sieve residue meets the
requirements. The coarse aggregate is gravel from
Fujian Xiamen, and the continuous gradation is 5~25 mm.
According to the requirements of GB/T 14685-2011<
Construction pebbles and gravels>, the cumulative
screening percentage of gravel aggregate meets the
standard requirements. Water is tap water. Three
concrete blocks with different mix proportions of C5, C10
and C15 were designed. According to< Selection table of
concrete sand ratio> in JGJ 55 - 2011 <Specification for
mix design of ordinary concrete>, the sand ratio was
determined to be 45%, and then the amount of coarse and
fine aggregate was determined by the absolute volume
method. Three kinds of concrete mix ratio see table 1.
Table1. Mix ratio of three kinds of concrete test blocks.
Concrete
label
Material dosage/(kg/m3)
cement water sand the stone
C5 156 195 915 1, 118
C10 207 195 894 1, 092
C15 256 195 875 1, 069
In order to make the modified sodium silicate
reinforcing liquid penetrate deep into the concrete as far
as possible, the concrete test block was infiltrated by
impregnation method. Three different strength concrete
test blocks were put into the impervious PE plastic bag,
and then the matched reinforcing liquid was added. The
opening was closed to ensure that the reinforcing liquid
was not evaporated, and the environment temperature was
20 °C and the relative humidity was 70% (figure 1).
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Figure 1. Concrete test mould, test block and impregnation method.
(a) test mould; (b) test block; (c) Impregnation method.
4 Properties of concrete reinforced by
modified sodium silicate composite
reinforcing solution
4.1 Compressive strength of concrete reinforced
with modified sodium silicate composite
reinforcement solution
It can be seen from the comparison of the compressive
strength of concrete reinforced by modified sodium
silicate composite reinforcing liquid (Fig. 2, Table 2) that
the strength of C5 grade concrete increases by 42.5%, that
of C10 grade concrete increases by 21.4%, and that of C15
grade concrete increases by 10%. Sodium silicate is the
liquid form of sodium silicate, which contains more
silicate, and free Ca after entering the concrete2+. In
addition, the three-dimensional mesh material with Si-O-
Si chain is generated when the modified sodium silicate
composite reinforcing liquid is solidified, so the
reinforcing effect is better.
4.7
8.4
14.2
6.7
10.2
15.7
C5 C10 C15
0
2
4
6
8
10
12
14
16
Compressive Strength (MPa)
Concrete Grade
Control Group
Modified Sodium Silicate
Reinforcing Method
Figure 2. Comparison of compressive strength of concrete
before and after reinforcement.
Table2. Compressive strength of concrete before and after reinforcement with modified sodium silicate composite reinforcement
solution.
group Concrete label Test block number /MPa Average/MPa
1 2 3
Modified sodium silicate
composite reinforcing
liquid before reinforcing
C5 4.8 4.8 4.6 4.7
C10 8.6 8.1 8.6 8.4
C15 14.7 13.8 14.0 14.2
Modified sodium silicate
composite reinforcing
liquid after reinforcing
C5 6.7 6.7 6.7 6.7
C10 10.4 10.4 10.0 10.2
C15 15.9 15.7 15.7 15.7
4.2 Microstructure of Modified Sodium silicate
Composite Reinforcement
The microstructure shown in the concrete after
reinforcement by modified sodium silicate composite
reinforcement solution can be divided into two categories.
The first category is the dense network structure formed
by the condensation of integral sodium silicate itself, such
as the left part of the scanning electron microscope after
10,000 times magnification ( Fig. 3 ). The second is the
C-S-H gel produced by the reaction of silicate in sodium
silicate with Ca(OH)2 in concrete. It can be seen that the
reinforcement mechanism of sodium silicate for concrete
substrate can be divided into two categories. The first is
its own condensation curing, and the second is the
reaction with calcium hydroxide that does not contribute
to the strength in concrete to generate calcium silicate
hydrate that plays a major role in the strength. From the
analysis of the reinforcement mechanism and curing
mechanism of modified sodium silicate composite
reinforcement solution, the reinforcement can be divided
into two aspects. The first aspect is the reaction of silicate
ions in sodium silicate and calcium ions in concrete to
generate calcium silicate. On the other hand, the self-
curing of sodium silicate forms a polymer with Si-O-Si
chain. Therefore, the modified sodium silicate
composite reinforcement solution improves the internal
microstructure of concrete and the reinforcement effect is
good.
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Figure 3. Microstructure of concrete reinforced by modified sodium silicate composite reinforcing solution.
(a) 10000-fold; (b)300-fold
5 Conclusion
The sodium silicate was modified by controlling the
concentration of sodium silicate, selecting surfactants and
additives, and controlling the dosage of curing agent. The
permeability and wetting ability were improved, and the
curing strength, bond strength and concrete strength were
improved. The modified sodium silicate composite
reinforcement solution was prepared by adding sodium
tetraborate, sodium dodecyl sulfate, sodium fluosilicate
and other materials. Through the comparative test of
concrete impregnation, it can be found that:
(1) Modified sodium silicate composite reinforcement
solution has a very significant reinforcement effect on
low-strength concrete. The strength of C5 concrete
before and after reinforcement increased by 42.5%, C10
concrete by 21.4%, and C15 concrete by 10%.
(2) It can be seen from the microstructure of the
reinforcement solution, it can be seen that the
reinforcement effect comes from the reaction of silicate
ions in sodium silicate and calcium ions in concrete to
form calcium silicate, and the glass itself is solidified to
form a polymer with Si-O-Si chain.
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