U.S. patent application number 13/689943 was filed with the patent office on 2014-06-05 for nano-sized composites containing polyvinyl pyrrolidone modified sodium silicates and method for making binders using same.
This patent application is currently assigned to UNITED ARAB EMIRATES UNIVERSITY. The applicant listed for this patent is ABU DHABI UNIVERSITY, UNITED ARAB EMIRATES UNIVERSITY. Invention is credited to Maisa Mabrouk El-Gamal, Abdel-Mohsen Onsy Mohamed.
Application Number | 20140155533 13/689943 |
Document ID | / |
Family ID | 50826051 |
Filed Date | 2014-06-05 |
United States Patent
Application |
20140155533 |
Kind Code |
A1 |
Mohamed; Abdel-Mohsen Onsy ;
et al. |
June 5, 2014 |
NANO-SIZED COMPOSITES CONTAINING POLYVINYL PYRROLIDONE MODIFIED
SODIUM SILICATES AND METHOD FOR MAKING BINDERS USING SAME
Abstract
This invention provides a method to form nano-sized dispersed
structure consisting of aqueous sodium silicate and polyvinyl
pyrrolidone (PVP) solutions, and a binder consisting of a
nano-sized dispersed structure and calcium chloride dihydrate
solution. The invention provides also a method to immobilize sand
dunes and wind-blown dust by using the binder.
Inventors: |
Mohamed; Abdel-Mohsen Onsy;
(Abu Dhabi, AE) ; El-Gamal; Maisa Mabrouk; (Al
Ain, AE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ABU DHABI UNIVERSITY
UNITED ARAB EMIRATES UNIVERSITY |
Abu Dhabi
Al-Ain |
|
AE
AE |
|
|
Assignee: |
UNITED ARAB EMIRATES
UNIVERSITY
Al-Ain
AE
ABU DHABI UNIVERSITY
Abu Dhabi
AE
|
Family ID: |
50826051 |
Appl. No.: |
13/689943 |
Filed: |
November 30, 2012 |
Current U.S.
Class: |
524/436 |
Current CPC
Class: |
C09D 139/06 20130101;
C08L 39/06 20130101; C09K 3/22 20130101 |
Class at
Publication: |
524/436 |
International
Class: |
C08L 39/06 20060101
C08L039/06; C08K 3/16 20060101 C08K003/16 |
Claims
1. A nano-sized dispersed binder to immobilize sand dunes and
wind-blown particles, said binder comprising: a polyvinyl
pyrrolidone (PVP) modified sodium silicate and a calcium chloride
dihydrate solution.
2. A nano-sized dispersed binder according to claim 1, in which a
nano-sized dispersion structure referred to as mixture A is
comprised of an aqueous sodium silicate solution designated as
compound ("a") and a PVP designated as compound ("b") is formed
into a binder referred to as mixture B and calcium chloride
dihydrate solution referred to as compound "c" are mixed
together.
3. A nano-sized dispersed binder according to claim 2, in which
said binder comprises from 10 to 70 vol. % of water diluted
compound "a", from about 1 to 5 wgt. % of compound "b", and from
about 0.5 to 1.5 wgt. % of compound "c".
4. A nano-sized dispersed binder according to claim 2, in which
compound "a" has SiO.sub.2 to Na.sub.2O weight ratios of 3.22:1 and
40% solids.
5. A nano-sized dispersed binder according to claim 2, in which
water diluted compound "a" concentration ranges from 10 to 70 vol.
% and exhibit desirable physico-chemical characteristics for pH
from about 11.79 to 11.96, viscosity from about 1.33 to 9.48
centipoise, and density from about 1.089 to 1.265 g/cm.sup.3.
6. A nano-sized dispersed binder according to claim 2, in which
compound "b" has molecular weight of 40,000, film density of 1.207
g/cm.sup.3 and nitrogen content ranging from 11.5 to 12.8%.
7. A nano-sized dispersed binder according to claim 2, in which
compound "b" concentration ranges from 1 to 5 wgt. % and exhibits a
physico-chemical characteristics for pH from about 5.83 to 4.49,
viscosity from about 1.48 to 3 centipoise, and density from about
0.988 to 1.006 g/cm.sup.3.
8. A nano-sized dispersed binder according to claim 2, in which
compound "c" exhibits a concentration ranging from about 0.5 to
1.33 wgt. %.
9. A nano-sized dispersed binder according to claim 2, in which
mixture B possesses a pH value from about 10 to 11.
10. A nano-sized dispersed binder according to claim 2, in which
mixture B temperature ranges from 25 to 60.degree. C. and about
40.degree. C.
11. A nano-sized dispersed binder according to claim 10, in which
the desired concentrations for compound "a" ranges between 13-66.67
vol. %, compound "b" ranges between 1 to 5 wgt. %, and compound "c"
ranges between 0.5 to 1.33 wgt. %.
12. A nano-sized dispersed binder according to claim 11, in which
the desired gelation time ranges from 17 to 60 minutes.
13. A nano-sized dispersed binder according to claim 11, in which
optimum gelling characteristics can be achieved when the ratio of
reagent weight (compound "b" plus compound "c") over compound "a"
volume is maintained between 0.04 to 0.12, and viscosities between
2 to 6 centipoise.
14. A nano-sized dispersed binder according to claim 11, in which a
weight of mixture B aqueous solution is about 15 to 25% of dry
weight of sand dunes.
15. A nano-sized dispersed binder according to claim 1, in which
upon curing the solidified material (mixture B plus sand dunes)
exhibits a desirable compressive strength ranging between 3.59 to
5.29 MPa.
16. A nano-sized dispersed binder according to claim 1, in which
upon curing the solidified material (mixture B plus sand dunes)
endures a maximum material loss of 1 wgt. % when exposed to wind
velocity of 14 m/s for 1 hour.
17. A nano-sized dispersed binder according to claim 1, in which
upon curing the solidified material (mixture B plus sand dunes)
maintains a hydraulic conductivity in the order of
1.0.times.10.sup.-7 m/s.
Description
FIELD OF THE INVENTION
[0001] This invention relates to nano-sized composites and methods
for making and using binders using the nano-sized composites and
more particularly to nano-sized composites containing polyvinyl
pyrrolidone modified sodium silicate and methods for making and
using the same. The invention also relates to a binder comprising a
nano-sized dispersion structure and a calcium chloride dihydrate
solution for immobilizing sand dunes and wind-blown dust by using a
binder.
BACKGROUND FOR THE INVENTION
[0002] Sand dune movements and dust storms are common in Arabian
Gulf countries. It occurs because of the existence of fine
particles on the surface of the top soils, which are poorly bonded
and susceptible to erosion by wind and rain. This invention
pertains to binder compositions useful for binding particulate
matter and sand dunes.
[0003] Soluble silicates have been used as binders for many years
and in many applications. It is a white powder or colorless
solution that is readily soluble in water, producing an alkaline
solution. As this alkaline solution is neutralized, colloidal
silica aggregates to form a gel. To control aggregation, gelation
time, and gel performance, grouting systems were developed over the
last 100 years. These systems include: (a) acid reactant
(phosphoric acid, sodium hydrogen sulfate, sodium phosphate, carbon
dioxide solution), (b) alkaline earth and aluminum salts (calcium
chloride, magnesium sulfate, magnesium chloride, aluminum sulfate),
(c) organic compounds (glyoxal, acetic ester, ethylene carbonate
formamide).
[0004] U.S. Pat. No. 1,827,238 to Joosten describes a process for
solidifying permeable rock, loosely spread masses, etc. in which
silicic acid is introduced into the mass followed by the
introduction of carbon dioxide thus integrating and solidifying the
treated mass.
[0005] U.S. Pat. No. 2,968,572 to Peeler, Jr. teaches a process of
soil treatment in which the soil is contacted with a single liquid
mixture comprising an aqueous alkali metal silicate, and amide,
such as formamide and a metal salt such as sodium aluminate thereby
forming a water-insoluble gel.
[0006] U.S. Pat. No. 4,043,830 to Suzuki discloses a process for
consolidation of poor quality soil by injecting hardeners
comprising, for example, a mixture of water and a gelling agent and
a water glass aqueous solution containing a gelling agent such as
ethylene glycol diacetate.
[0007] U.S. Pat. No. 4,056,937 to Suzuki teaches a soil
consolidation process in which a hardener comprising an aqueous
solution of water glass and an acidic reactant, such as phosphoric
acid, is injected into the soil thereby solidifying the treated
soil.
[0008] U.S. Pat. No. 4,416,694 to Stevenson et al. discloses
foundry sand compositions made from foundry sand, an aqueous sodium
silicate binder and an alkylene carbonate which are used to form
molds and/or cores in metal casting.
[0009] U.S. Pat. No. 4,642,196 to Yah teaches a method and
composition for controlling dust occurring in the production,
handling, transport and storing of coal which includes applying
such as by spraying an aqueous solution of a gelatinized
starch.
[0010] U.S. Pat. No. 4,983,218 to Mascioli discloses a composition
and method for hardening an alkali metal silicate solution using
blends of alkylenediols, polyoxyalkylene glycols or hydroxyalkyl
ethers. The hardened alkali metal silicate compositions are useful
as binders in the preparation of foundry molds or in other
applications requiring agglomeration of particulate matter.
[0011] U.S. Pat. No. 5,059,247 to Crawford et al. teaches a foundry
sand composition that is self-hardening after a working life of
about 10-20 minutes composed of foundry sand, a sodium silicate
binder and a specifically defined polyester polycarbonate
hardener.
[0012] U.S. Pat. No. 5,336,315 to Cuscurida et al. describes a
process for soil stabilization in which soil particles are treated
with an aqueous solution of an alkali metal silicate, and a
carbonate reactant or gelling agent selected from the group
consisting of an alkylene carbonate, such as ethylene carbonate, a
polyester polycarbonate and mixtures thereof.
[0013] However, problems such as homogeneity, volume changes, loss
of strength, and in-situ application still exist. Therefore, it is
the purpose of this invention to provide a method to form a
nano-sized dispersed structure comprising or consisting of aqueous
sodium silicate solution and polyvinyl pyrrolidone (PVP) which
controls aggregation and homogeneity, and a binder consisting of a
nano-dispersed structure and calcium chloride dihydrate solution
which controls system aggregation, homogeneity, gelling time, gel
performance, and strength development. The invention also provides
a method to immobilize sand dunes and wind-blown dust by using the
binder.
[0014] Nano-sized composites consisting of aqueous sodium silicate
solution and PVP, and reactant consisting of calcium chloride
dihydrate solution can be injected as separate solutions, or can be
premixed to form a single solution that is then injected. Treatment
of soft soils by deep mixing with binders is the most frequently
used method of ground improvement and is increasingly being used
internationally over the last decades. Success of any treatment
method is directly related to overall strength development which is
a direct function of binder composition, method of application,
substrate formation and composition in terms of particle-size
distribution, grain size, particle shape and moisture content, the
ability of the grout to adhere to particle surfaces, and curing
environment.
SUMMARY OF THE INVENTION
[0015] In essence, the present invention contemplates a nano-sized
composite (1-100 nm) for use as a binder to immobilize sand dunes
and wind-blown particles. The composite comprises and/or consists
of a polyvinyl pyrrolidone (PVP) modified sodium silicate and a
calcium chloride dihydrate solution. In a preferred embodiment of
the invention, the composition includes about 13 to about 66 volume
percent of an aqueous sodium silicate solution, from about 1 to
about 5 wgt. % of PVP solution and from about 0.5 to 1.5 wgt. % of
calcium chloride dihydrate solution.
[0016] A second embodiment of the invention contemplates a method
for immobilizing sand dunes and wind blowable particles by applying
a composite according to the first embodiment of the invention
therein as for example by injection and/or thereon as for example
by spraying.
[0017] The invention will now be described in connection with the
following figures.
DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a schematic view of a polyvinyl pyrrolidone
modified calcium silicate production system;
[0019] FIG. 2 shows scanning micrographs of solidified sand dunes
with sodium silicates and calcium chloride without an addition of
PVP;
[0020] FIG. 3 shows scanning micrographs of solidified sand dunes
with a PVP modified sodium silicates and calcium chloride; and,
[0021] FIG. 4 is a graphical illustration of the fourier transform
infrared spectroscopy (FTIR) of solidified sand dunes with (a)
sodium silicates and calcium chloride without addition of PVP, and
(b) with PVP modified sodium silicates and calcium chloride.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
[0022] This invention provides a binder to immobilize sand dunes
and wind-blown dust, or any other surface where safety of motor
vehicles and durability of an access road is of concern. In this
invention a nano-sized dispersed structure, referred to as mixture
A, comprising or consisting of an aqueous sodium silicate solution,
designated as compound A, and a polyvinyl pyrrolidone (PVP),
designated as compound B, is formed to control aggregation and
homogeneity. Also, a binder, referred to as mixture B, consisting
of a nano-dispersed structure (mixture A) and calcium chloride
dihydrate solution, designated as compound C, is formed to control
system aggregation, homogeneity, gelling time, gel performance, and
strength development. FIG. 1 shows an explanatory view of a
polyvinyl pyrrolidone modified calcium silicate production system
for the intended purpose of this invention.
[0023] The binder employed in this invention can be injected for
in-situ application as separate solutions (mixture A and then
compound C), or can be premixed to form a single solution (mixture
B) that is injected, as shown in FIG. 1. Sand dunes are then harden
and prevent dust from flying. It also prevents sand dunes and dust
piles from movement due to water seepage. In some cases the binder
may be sprayed onto or partially sprayed onto the surface to be
fixed.
[0024] Compound A shall consist essentially from about 13 to 66
volume percent of an aqueous sodium silicate solution and from 1 to
5 weight percent of PVP solution. Compound B shall consist
essentially from about 0.5 to 1.5 weight percent of calcium
chloride dihydrate solution.
[0025] Control of gelation time is important with respect to the
applicability of the invention. It is a function of the binder
composition, ratios of mixed components, and environmental
conditions. When sand dunes and gel are in contact, mechanical
properties of solidified materials increase suggesting a possible
reaction between both components. The main reaction involved during
the material solidification is electrostatic interactions between
negative charges on the PVP chain and positively charged silica
species.
[0026] The rate of gelation and the consistency of the resulting
binder are controlled by varying reactant concentration, sequence
of mixing and mixing temperature. Practically, PVP is reacting with
a sodium silicate solution to form a nano-sized dispersed colloidal
system which polymerizes further with calcium chloride to form a
gel which binds sand dune particles together and fills the
voids.
[0027] Variation of the reactant ratios has an influence on the
characteristics of the desired gel. The characteristics recognized
as being the most important ones are pH, density, viscosity and
gelling time. The optimum gelling time suggested in this invention
is between 15 and 60 minutes.
[0028] Increase of temperature may facilitate the mixing and
gelation reaction by decreasing the viscosity coefficient,
increasing the diffusion coefficient and enhancing the reaction
between system components. When gelling mixture is mixed with the
sand dunes, a hard gel is formed. The two possible reactions
contributed to gel formation are polymerization and/or
precipitation.
[0029] In this invention, the PVP has been utilized to modify
sodium silicate and form a nano-sized (1 to 100 nm) dispersed
structure because of its following advantages as a biocompatible
polymer material: [0030] 1. PVP lowers the pH of sodium silicate;
where, silica particles carry negative charges at high pH values.
As a result, there are strong electrostatic repulsion forces
between silica particles. These forces are high enough such that
silicate solutions do not gel at pH greater than 11. To induce
gelation, these electrostatic forces were reduced by addition of
PVP. [0031] 2. PVP exhibits the ability to interact with a variety
of surfaces by hydrogen or electrostatic bonding and resulting in
protective coatings and adhesive properties. [0032] 3. PVP
interacts with positively charged silicate species
electrostatically through negative charges on its chain. [0033] 4.
PVP reacts with silicates in solution to form a nano-sized
dispersed structure, which polymerizes further in the presence of
calcium chloride to form the gel that binds sand dunes particles
together. The gel forms an adhesive bond with the surrounding sand
particles. [0034] 5. PVP reduces the gelation time of sodium
silicates and contributes to strength development with sand dunes
via electrostatic bonding. [0035] 6. PVP prevents silica
precipitation and volume change of treated soil matrix because
without addition of PVP to a mixture of sodium silicate and
CaCl.sub.2, an immediate precipitation occurred and gel was not
formed causing soil shrinkage. [0036] 7. PVP forms an intermediate
nano-sized dispersed structure which increases the adhesion
property of the formed gel on addition of CaCl.sub.2 to the mixture
of sand dunes. The inter diffusion of PVP had been a key factor in
improving the adhesion property of the silicate. [0037] 8. PVP acts
as a smoother for both silicates and sand dune particles. [0038] 9.
PVP facilitates hydrogen bonding between the amide carbonyl groups
of PVP and surface hydroxyl groups of silicate leading to a dense
hybrid structure. [0039] 10. PVP contains bulky side groups
composed of a five membered ring amide which contribute to friction
development and reduction of volume of voids within the solidified
matrix leading to overall restriction and immobility of sand
particles. [0040] 11. Chemical binding of PVP exfoliates silicates
and forms linked silicate particle chains that, when incorporated
in binders, improve the post-failure properties of the solidified
sand dunes. [0041] 12. PVP silicate gel system provides an
economical and environmental binding material because of its
biological compatibility, low toxicity, effectively produced
without fumes, odor-free, fast and easy to apply film-forming and
adhesive characteristics, unusual complexing ability, relatively
inert behavior toward salts and acids, and its resistance to
thermal degradation in solution.
[0042] Fourier transform infrared spectroscopy (FTIR) which is a
technique used to obtain an infrared spectrum of absorption,
emission, photoconductivity or RAMAN scattering of a solid, liquid
or gas.
[0043] One of the key goals of binding substances is a purposeful
correction of the formation of nano-phases achieved through
modification of the substance at nano-level. Nano particles induce
additional atomic bonding and increase viscosity of the liquid
phase, which helps to bind gelling materials and aggregate grains
and improves resistance to segregation as well as increases the
workability of treated materials. To obtain better properties of
solidified materials at the macro-level, the formation of phases
has to be purposefully corrected and the properties of these
materials have to be investigated at micro-level because
nano-additives in binders act as additional catalysts that change
the direction and rate of physical and chemical processes. PVP
modified sodium silicates solution contains nano colloidal
particles.
[0044] When PVP is added to sodium silicate in the initial stage, a
nano-sized dispersed system is formed. Therefore formation of large
crystal hydrates in the initial stage of structure formation is
hindered and thus formation of amorphous hydration structures of
nano-particle size that accumulate higher energy shall be promoted
in addition. A binding system consisting of colloidal sodium
silicate solution and PVP suspension may be used for this
purpose.
[0045] As described earlier, in this invention, a silicate polymer
gel is formulated by adding sodium silicate solution to a mixture
of polyvinyl pyrrolidone (PVP) as acidic reactant agent and calcium
chloride dihydrate as gel time control agent. This mixture is
capable of cross-linking the silicate and form a gel network, which
is penetrable into a coherent and hard mass, and can be efficiently
used for sand dunes solidification.
[0046] Practically, PVP reacts with sodium silicate solution to
form a nano-sized dispersed colloidal solution which polymerizes
further in the presence of calcium chloride dihydrate to form a gel
which binds sand dune particles together and fills voids. The rate
of gelation reaction and the consistency of the resulting gel are
controlled by varying reactant concentration, sequence of mixing
and mixing temperature.
Example 1
Alteration of the Composition of Sodium Silicate
[0047] The three basic techniques to change the composition of
sodium silicate compound to meet final product specifications are
the alkali change, dilution and the introduction of additional
ingredients. The sodium silicate solution is a viscous Newtonian
fluid. Neutral sodium silicate solution QP from Sigma-Aldrich was
used; it has the following specification: weight ratio of silica
(SiO.sub.2) to sodium oxide (Na.sub.2O) of 3.22:1, 37.6% wt. active
and 62.4% H.sub.2O, viscosity of 180 cp, density of 1.37 g/cm.sup.3
at 23.degree. C. and pH of 12. Sodium silicate solution was diluted
with distilled water to prepare all gelling solutions.
[0048] Dilution reduces the product's viscosity and increases its
penetration into soil strata. The dilution rate should be adjusted
on the basis of soil hydraulic conductivity and the desired
strength of the solidified mass. For soils with hydraulic
conductivity of 10.sup.-4 cm/sec, binder viscosity should be less
than 2 cP. However, binders having higher viscosities of 5 cP and
10 cP are applicable for soils with hydraulic conductivities
greater than 10.sup.-3 cm/sec and 10.sup.-2 cm/sec,
respectively.
[0049] Table 1 shows the effect of dilutions on the viscosity,
density and pH of sodium silicate solutions. This variation is an
advantage because soil structure tends to vary from place to place
and so silicate solutions of different concentrations, viscosities
and speeds of gelling are required. The binding strength of sand
with sodium silicates increases with increasing viscosity, but the
infiltration rate decreases with increasing viscosity. As a result,
highly viscous sodium silicates solution is left at the sand
surface to form a thin layer of binding crust. On the other hand, a
too low viscosity leads to a higher infiltration rate, which may
prevent the formation of a crust with sufficiently high binding
strength. Hence, proper emulsion dilution of the hardener is very
important to successfully glue the sand particles.
TABLE-US-00001 TABLE 1 Effect of dilution on viscosity, density and
pH of sodium silicate solutions Sodium Silicate Water Viscosity
Density (Vol. %) (Vol. %) pH (cP) (g/cm.sup.3) 100 0 12.03 179.00
1.3748 80 20 11.98 49.92 1.3279 70 30 11.96 9.48 1.2653 60 40 11.93
4.78 1.2211 50 50 11.90 3.39 1.1698 40 60 11.87 2.38 1.1457 30 70
11.84 1.96 1.1253 10 90 11.79 1.33 1.0899
[0050] When sodium silicate is dissolved in water, different
silicate species tend to dominate at varying pH as described below
(Iler 1979, see reference near end of specification).
SiO.sub.2+2H.sub.2O.fwdarw.Si(OH).sub.4 (1)
Si(OH).sub.4+OH.sup.-.fwdarw.HSiO.sub.3.sup.-+2H.sub.2O (2)
2HSiO.sub.3.sup.-.fwdarw.Si.sub.2O.sub.5.sup.2-+H.sub.2O (3)
Si.sub.2O.sub.5.sup.2-+H.sub.2O.fwdarw.HSi.sub.2O.sub.5.sup.3-+H.sup.+
(4)
HSiO.sub.3.sup.-+OH.sup.-.fwdarw.SiO.sub.3.sup.2-+H.sub.2O (5)
[0051] At pH lower than 11, silica polymerizes and forms stable
nano-colloidal particles with diameter about 1 nm. The polymer
growth from monomer to tetramer can be expressed as monomer
(H.sub.4SiO.sub.4(aq)) addition as shown (Icopini et al. 2005, see
references near end of specification):
H.sub.4SiO.sub.4(aq)+H.sub.4SiO.sub.4(aq).fwdarw.H.sub.6Si.sub.2O.sub.7(-
aq)+H.sub.2O (6)
H.sub.6Si.sub.2O.sub.7(aq)+H.sub.4SiO.sub.4(aq).fwdarw.H.sub.8Si.sub.3O.-
sub.10(aq)+H.sub.2O (7)
H.sub.8Si.sub.3O.sub.10(aq)+H.sub.4SiO.sub.4(aq).fwdarw.H.sub.8Si.sub.4O-
.sub.12(aq)+2H.sub.2O (8)
[0052] As indicated by the additional water generated in Eq. 8, the
final product is assumed to condense as a cyclic tetramer. In the
initial stages of reaction, silica monomers combine to form small
oligomers, which in turn react with monomers, as described by Eqs.
7 and 8, to form larger oligomers (Perry et al., 2000). These
silica oligomers maximize the number of siloxane bonds (Si--O--Si)
and minimize the uncondensed Si--OH groups (Iler, 1979). This
condensation is thought to lead to the formation of ring structures
with 3 to 6 silicon atoms linked by siloxane bonds early in the
process (Perry et. al., 2000).
[0053] As per Eq. 8, the critical nucleus generated behaves
chemically in a fashion that is similar to bulk amorphous silica.
Unlike classical colloidal systems, silica colloids are stable near
their zero point of charge (Allen and Matijevic, 1969). This lack
of reactivity is attributed to the fact that H.sup.+ can
out-compete all other dissolved species (including silica) for
silica surface sites at low pH. As pH increases towards 7, the
decrease in the activity of H.sup.+ and the increase in
un-protonated Si--O-- groups on the colloidal surfaces naturally
lead to an increased sensitivity of polymerization to ionic
strength and silica concentration.
[0054] At higher than neutral pH there is a decreasing sensitivity
of polymerization rate to silica concentration (Icopini et al.
2005). This phenomenon could be related to the increasing
electrostatic repulsion between negatively charged particles at
high pH due to the de-protonation of silica species.
[0055] The solutions at near-neutral pH exhibited the most rapid
rates of [SiO.sub.2].sub.n.ltoreq.3 loss, and the behavior of the
silica reactive fraction in these rapid reactions is complicated by
their subsequent involvement in reactions that ultimately led to
the growth of silica nanoparticles and the precipitation of
silica.
[0056] In addition, it is known that basic sodium silicate solution
with pH 11-12 comprise a large number of polysilicate anions
(Si.sub.4O.sub.8(OH).sub.4). Two opposite processes occur when such
solutions are diluted and acidified, as in the case of this
invention. De-condensation occurs upon dilution giving monomeric
species [Si(OH).sub.4-x].sup.x-, whereas protonation favors
oxolation reactions between Si--OH silanol groups leading to the
formation of oligomers and the precipitation of SiO.sub.2. Two main
species are observed in diluted solutions around pH7, namely,
[SiO(OH).sub.3].sup.- and Si(OH).sub.4, silicic acid being the
predominant. The condensation is supposed to proceed via the
reaction of singly ionized species with silicic or polysilicic
acid, Scheme 1.
##STR00001##
Example 2
Polyvinyl Pyrrolidone (PVP) Properties
[0057] Polyvinyl pyrrolidone (PVP) is a water soluble nonionic
polymer; it has both hydrophilic and hydrophobic characters. It
provides a remarkable combination of properties that no other
molecule is yet able to have. PVP polymer is high polarity/proton
acceptor, compatible with a variety of resins and electrolytes,
soluble in water and polar solvents, hard, glossy, transparent,
oxygen permeable films which adhere to a variety of substrates,
adhesive and cohesive properties and cross linkable. PVP exhibits
the ability to interact with variety of surfaces by hydrogen or
electrostatic bonding, resulting in protective coatings and
adhesive applications.
[0058] PVP polymers are available in several viscosity grades,
ranging from low to high molecular weights. The PVP K-30 (Mw of
40,000) type was used. The pH of 5% aqueous solution is about 5,
specific gravity at 25.degree. C. is 1.062 g/cm.sup.3, film density
is 1.207 g/cm.sup.3, specific heat is 0.803 Cal/g/KC and nitrogen
content is 11.5-12.8%. The interaction of PVP with water has been
extensively studied. Table 2 shows that pH, density and viscosity
of PVP solutions are affected by changing of PVP polymer
concentrations.
TABLE-US-00002 TABLE 2 pH, density and viscosity of PVP solutions
PVP Viscosity Density (Wt. %) pH (cP) (g/cm.sup.3) 1 5.83 1.48
0.9876 2 5.59 1.77 0.9896 3 5.20 2.16 0.9936 4 4.90 2.53 0.9966 5
4.49 3.00 1.0062
[0059] Generally, it is believed that, polar carbonyl groups of PVP
are responsible for interaction with other polar compounds through
hydrogen bonding. Water molecule form hydrogen bond to the polar,
negatively charged pyrrolidone carbonyl oxygen because pyrrolidone,
a five-membered planar lactam, affords maximum .pi., .pi. orbital
overlap. The canonical resonance forms highlight the potential for
a partial negative charge to form on oxygen as shown in Scheme 2.
The partial charge on nitrogen is sterically shielded by the
polymer backbone and the surrounding pyrrolidonemethylenes. Because
of high dipole moment and polarity, PVP has a noticeable effect on
water structure.
##STR00002##
Example 3
Reaction of Sodium Silicate with Polyvinyl Pyrrolidone
[0060] Nano-sized dispersed colloidal suspension is formed when PVP
solution is added to sodium silicate solution. The interacting site
of PVP segment in solution is the negatively charged carbonyl group
in the resonance structure of the pyrene ring of PVP segment shown
in Schemes 2 and 3. Hydrogen bonding is assumed to be the
predominant mechanism for the adsorption of PVP on sodium silicate
surfaces. This may be due to the acid-base mechanism between the
rich hydroxyl groups available on the silicate surfaces and PVP
polymers carbonyl groups which are capable of forming hydrogen
bonds at the interface.
[0061] Hydrogen bonding plays significant role in the treatment
process. Particularly, it is strong type of polar interaction,
which occurs in molecules where hydrogen atoms are attached to
highly electronegative oxygen atoms. In such case, the hydrogen's
sole electron is drawn toward the electronegative atom leaving the
strongly charged hydrogen nucleus exposed. Hence, the exposed
positive nucleus exerts considerable attraction on electrons in
other molecules forming a protonic bridge, which is substantially
stronger than most other types of dipole interactions.
[0062] In addition, since the chain length of PVP is a key
parameter it is advocated that pyrrolidone might serve as
substrates for silica formation. Furthermore, silicic acid
monomers, which brought close enough by interaction with PVP, shall
favor oligomerization. Gelation then proceeds by further
condensation of monomers with these pre-condensed species (Scheme
3).
##STR00003##
Example 4
Gel Formulation
[0063] Gelatinous silicate product is obtained as a result of the
interaction between nano-sized dispersed colloidal system of sodium
silicate and PVP (mixture A), and calcium chloride dihydrate
(compound C).
[0064] In another application the desired concentration of calcium
chloride solution (compound C) shall be added to PVP (compound B)
to form a new material, designated as mixture C. Then mixture C is
added to sodium silicate solution (compound A) to instantly form
liquid binder (mixture B) which is function of system
temperature.
[0065] In both applications, PVP acts as acidic reactant agent and
calcium chloride acts as a gelation time controlling agent or as an
accelerator. Calcium chloride controls gelation time and imparts
permanence to the gel. These reagents produce very low
penetrability gels, which are suitable for permeation treatments of
soil mass.
[0066] Silicates react with soluble calcium chloride to produce
insoluble calcium silicates or calcium silicate gels. Excessive
amounts of calcium chloride may result in undesirable flocculation
or formation of local gelation, producing variations in both the
gel and setting times resulting in poorly grouted area.
[0067] Control of gelation time is important in regard to in-situ
application. It is a function of the binder components, ratios and
environmental conditions. Gelation time is defined as the interval
between initial mixing of the binder components and formation of
the gel.
[0068] When mixture B is injected and/or mixed with sand dunes and
hardens the mechanical properties of the solidified material
increased suggesting a possible reaction between various
components. As indicated previously, the main reaction involved
during the material solidification is electrostatic interactions
between negatively charged ions on the PVP chain and positively
charged silica species, which are promoted with decreasing particle
size. Practically, PVP reacts with silicate solution to form
colloidal solution which polymerizes further with calcium chloride
addition to form a gel that binds sand dunes particles together and
fills voids. The gel forms an adhesive bond with the surrounding
sand dunes. Scheme 4 shows the distribution of negatively charged
ions along the PVP chain which could bring silica oligomers close
enough for condensation to occur.
[0069] When the resultant binding material mixed with sand dunes a
strong gel is formed. The highest degrees of interaction are formed
by electrostatic interactions followed by hydrogen bonding. It is
one of the aims of this invention is to form convenient compounds
by means of hydrogen bonding between silicate as Lewis-acid and PVP
as Lewis-base functional groups. In polymer reactions, a physical
bond (hydrogen bond) is formed. In this invention, the process
involved in solidifying sand dunes is the formation of insoluble
PVP modified calcium silicate nano-sized particles (mixture B)
which interact with sand dunes via electrostatic interactions.
Finally, the binder will form lubricant around solid surface, fill
the voids, inhibit volume changes, and contribute to overall
strength development of the solidified soil mass.
##STR00004##
Example 5
Optimization of the Gelation Process
[0070] To optimize the gelation process, three sets of experiments
were conducted. In the first set, sodium silicate solution
(compound A) was diluted with distilled water to different
concentrations from 100 to 10% by volume at fixed concentrations of
PVP (compound B) and calcium chloride (compound C). In the second
set, PVP (compound B) was added at different concentrations from 1
to 5% at fixed concentrations of calcium chloride (compound C) and
sodium silicate (compound A). In the third set, calcium chloride
(compound C) was added at different concentrations from 0.3 to 2%
at fixed concentrations of PVP (compound B) and sodium silicate
(compound A). Generally, sodium silicate concentration used in soil
grouting is in the range of 10 to 70% by volume, depending on the
material being grouted and the desired result to be achieved. For
other systems, which utilized polymeric materials as grouting
agents, polymer concentration varies from 2 to 10%. Since
temperature has a major effect on reaction processes, pH, gelation
time, and strength development, prepared mixtures were tested at
25, 40 and 60.degree. C.
[0071] Gelation times were determined by adding dilute solutions of
the gel-forming reagent to sodium silicate solution, mixing well,
and allowing the mixture to stand in a 4-oz. bottle kept in a 25,
40 and 60.degree. C. until a gel is formed. The gelation criteria
adopted in this investigation are the loss of uniform fluid flow,
the appearance of breakage planes when the mixture is tilted, and
the adherence of solid gel to the glass wall.
a--pH Gel System Dependency
[0072] In the chemical reactions, pH is always used as an important
response at constant mixing time and temperature. As a result of
negative charges of silica particles at high pH values; there are
strong electrostatic repulsion forces between silica particles.
These forces are high enough such that silicate solutions do not
gel at pH greater than 11. To induce gelation, electrostatic forces
should be reduced which could be realized via two approaches. The
first is to decrease pH while, the second is to reduce the
dielectric constant of the aqueous medium by adding salts. The
strength of ionic interactions is therefore inversely proportional
to the distance between the charges and the dielectric constant of
the solvent, which varies from 2 in non-polar solvents like hexane
to 80 in highly polar solvents such as water. Ionic interactions
are weakened as the ionic strength of the solvent increases and the
charge is shielded by counter ions. Ionic interactions are affected
by the pH of the solution since pH determines the number of charged
residues.
[0073] The alteration of pH of the mixture was determined using a
Beckman pH meter within 2 minutes after mixing. In this invention,
PVP and CaCl.sub.2 solutions reacted with sodium silicate solutions
and the mixture was set for gelation at 25.degree. C. Assuming that
the gelation is due to a condensation reaction of this type, fast
gelling should occur near the pH of least ionization, where there
is a minimum of repulsion forces between similarly charged silicic
acids or hydroxides, or an equal number of positively and
negatively charged species containing silicon hydroxides.
[0074] The experimental condition summarized in Table 3 indicates
that; the pH of the prepared mixtures after 2 minutes was between
10.3 and 11.08. It is also shown that the pH is decreased gradually
when the ratio of PVP to sodium silicate is increased and the ratio
of calcium chloride to sodium silicate is increased.
TABLE-US-00003 TABLE 3 pH variations as function of blend
concentrations at constant temperature Blend pH/25.degree. C.
Sodium Silicate Water CaCl.sub.2 PVP vol. % vol. % wt % 1 wt % 3 wt
% 5 wt % 13.00 87.00 0.50 10.70 10.72 10.64 33.33 66.67 0.50 10.97
10.91 10.86 66.67 33.33 0.50 11.08 11.02 10.93 13.00 87.00 1.00
10.61 10.55 10.52 33.33 66.67 1.00 10.91 10.78 10.70 66.67 33.33
1.00 10.99 10.91 10.82 13.00 87.00 1.33 10.35 10.36 10.30 33.33
66.67 1.33 10.74 10.73 10.65 66.67 33.33 1.33 10.92 10.82 10.72
b--Gelation Time System Dependency
[0075] Variation of the reactant ratios has evidently an influence
on the characteristics of the desired gels. The characteristics
recognized as being the most important ones are pH, and gelling
time. The time required for the mixture of PVP, CaCl.sub.2 and
sodium silicate solutions to become gelled was investigated. The
optimum gelling time is between 15 and 60 minutes. It has been also
established that the gel characteristics have their optimum values
when ratios of reagent weight (PVP and calcium chloride) and
silicate volume is maintained between 0.04 and 0.12, and
viscosities between 2 to 6 centipoises, which is controlled during
experiment design.
[0076] Table 4 points out that gelation time is reduced when PVP
and calcium chloride concentrations are increased and when sodium
silicate is decreased as well. Calcium chloride reacts with sodium
silicate to form calcium silicate, which has very low solubility in
water. The gelation time is significantly decreased with the
addition of calcium chloride (0.5 to 1.5%), especially at the low
sodium silicate concentrations (13 vol. %). With the addition of
more than 2% of calcium chloride to the silicate mixture, an
immediate precipitation was observed and the gelling status
vanished. Therefore, addition of Ca.sup.+2 ions has a catalyst
effect on gelation of the silicate. Table 4 demonstrates that
gelation time was dropped with increase of both of PVP and calcium
chloride.
TABLE-US-00004 TABLE 4 Variations of gelation time with blend
composition and concentration at constant temperature of 25.degree.
C. Blend Gelation time (min)/25.degree. C. Sodium Silicate Water
CaCl.sub.2 PVP vol. % vol. % wt % 1 wt % 3 wt % 5 wt % 13.00 87.00
0.50 540 180 60 33.33 66.67 0.50 600 420 210 66.67 33.33 0.50 3600
2880 2400 13.00 87.00 1.00 100 90 40 33.33 66.67 1.00 140 120 60
66.67 33.33 1.00 1320 900 600 13.00 87.00 1.33 50 40 38 33.33 66.67
1.33 90 78 51 66.67 33.33 1.33 980 600 100
c--Temperature Gel System Dependency
[0077] To estimate temperature effect on gelation time of sodium
silicate, PVP and calcium chloride, gelation time was measured at
different mixing temperatures of 25.degree. C., 40.degree. C. and
60.degree. C. The results shown in Tables 5 and 6 revealed that,
the interaction effect and consequently gelation process are
accelerated with temperature increases. Heat development
contributes to temperature rise of the silicate mixture to a level
necessary for the accelerator (CaCl.sub.2) to react with PVP and
sodium silicate thus, enhancing the gelation process. At room
temperature (25.degree. C.), a significant increase in gelation
time was detected. However, when mixing temperatures were elevated
from 25 to 40 and 60.degree. C., substantial decrease in gelling
times is observed. The effect of sodium silicate, PVP and
CaCl.sub.2 concentrations on gelation time has similar trends for
all tested temperatures of 25, 40 and 60.degree. C. A further
temperature increase might benefit both mixing and gelation
reaction through decreasing viscosity, increasing diffusion, and
enhancing reaction between participating reactants. Therefore, it
is safe to state that temperature utilization has an added extra
advantage to the developed system in this invention.
TABLE-US-00005 TABLE 5 Variations of gelation time with blend
composition and concentration at constant temperature of 40.degree.
C. Blend Gelation time (min)/40.degree. C. Sodium Silicate Water
CaCl.sub.2 PVP vol. % vol. % wt % 1 wt % 3 wt % 5 wt % 13.00 87.00
0.50 55 30 20 33.33 66.67 0.50 95 53 32 66.67 33.33 0.50 120 60 55
13.00 87.00 1.00 29 17 16 33.33 66.67 1.00 60 35 29 66.67 33.33
1.00 80 60 51 13.00 87.00 1.33 19 16 14 33.33 66.67 1.33 22 25 22
66.67 33.33 1.33 45 40 26
TABLE-US-00006 TABLE 6 Variations of gelation time with blend
composition and concentration at constant temperature of 60.degree.
C. Blend Gelation time (min)/60.degree. C. Sodium Silicate Water
CaCl.sub.2 PVP vol. % vol. % wt % 1 wt % 3 wt % 5 wt % 13.00 87.00
0.50 19 17 15 33.33 66.67 0.50 22 21 16 66.67 33.33 0.50 40 33 20
13.00 87.00 1.00 17 15 13 33.33 66.67 1.00 16 17 15 66.67 33.33
1.00 22 19 18 13.00 87.00 1.33 16 14 12 33.33 66.67 1.33 15 16 13
66.67 33.33 1.33 18 17 14
Example 6
Solidification of Sand Dunes
[0078] a--Analysis of Sand Dunes
[0079] The properties of sand dunes to be solidified or treated
were determined following the procedures described by ASTM
standards. Sand dunes were collected from Al-Jimi area of Al Ain
district of the United Arab Emirates. Particle size distribution is
characterized by grain size ranging from 0.1 to 1 mm and soil
composition of 35% gravel, 43% sand, 18% silt, and 4% clay; it is
described as siltysand. Soil indexes such as uniformity coefficient
of 14.11 indicating large range in grain sizes, and curvature
coefficient of 0.88 representing well-graded soil, were determined
Maximum dry density of 1.79 Mg/m.sup.3 and optimum moisture content
of 12% by dry weight were calculated from compaction tests. To
determine other relevant soil properties, specimens were compacted
at maximum dry density and optimum moisture content. Hydraulic
conductivity, which is a measure of the ease by which water can
seep through the soil, is 3.0E-05 m/sec indicating the high
permeable nature of this soil. In addition, strength properties of
the soil revealed that the shear strength of soaked specimens
decreased by about 2.5 times from those of un-soaked ones due to
destruction of brittle bonds between particles, and salt
dissolution upon wetting.
[0080] Mineralogical composition reveals that the major
constituents are silica, calcite and plagioclase, and the minor
constituents are dolomite, feldspar and kaolinite. Analysis of soil
water extract indicates that soil is alkaline with pH 8.1 and
electrical conductivity of 1.18E-03 S. These measured values were
confirmed by types and amounts of soluble ions in solution (Na, K,
Mg, Ca, CaCO.sub.3, HCO.sub.3 and Cl with measured concentrations
of 140, 8.5, 34, 48, 520, 140 and 460 ppm, respectively).
b--Treatment of Sand Dunes
[0081] Sand dunes can be first treated with aqueous sodium silicate
solution (compound A), followed by addition of PVP (compound B) and
then calcium chloride solution (compound C), or, if desired, the
PVP and calcium chloride (mixture C) can be applied first followed
by the application of sodium silicate solution (compound A).
Alternatively, aqueous silicate solution (compound A) and PVP
(compound B) are mixed together to form mixture A; then salt
solution (compound C) is added to mixture A to form mixture B,
which in turn is added to the soil (FIG. 1). It is preferred that
mixture B is added to the soil within a period of about 1 to 5
minutes because it will start to gel within 15 to 60 minutes.
[0082] Gel-granular mixture was prepared taking into account the
fluidity and the homogeneity of the mixture. In the presence of
high amount of gel solution, treated samples display flocculation
and heterogeneity. In the same way, in presence of low amount of
gel solution, the binder will not be able to cover grain surfaces
completely and treatment technique might not be practicable. The
preferred amount of such mixtures, to be used, is between 10 to 60%
calculated by the weight of the dry soil. On the other hand, in
other applications, the preferred amount is between 15 to 25%.
However, in this example, an optimum gel mixture ratio of 20% was
used. The treated sand dunes were compacted in cube mold
(50.times.50.times.50 mm) by a load of 10 N, and then specimens
were placed in an oven at 40.degree. C. for 3-7 days for
curing.
c--Strength of Solidified Sand Dunes
[0083] The optimum gel mixture used for treatment of sand dunes
varies depending on the desired strength in short- and long-term
perspectives, for both dry and wet conditions. Strength and good
durability are also important factors in cases of varying soil
conditions. An unconfined compressive test was conducted to study
the improvement in the mechanical properties of sand dunes treated
with binder consisting of mixture B. Tests were conducted using an
MTS.RTM. machine equipped with universal testing software (Test
Works.RTM.) capable of numerical and graphical analysis of the test
data. All tests were conducted at constant cross head speed of
5.times.10.sup.-6 m/s.
[0084] The influence of mixture B composition (i.e., sodium
silicate, PVP and CaCl.sub.2 contents) on strength developments is
described in terms of general strength levels with intention to
determine the optimum mixture composition for all tested cases.
Table 7 shows the effects of different admixtures used in
solidifying sand dunes. There are clear variations in strength with
respect to different gelling mixture compositions and sand
dunes.
TABLE-US-00007 TABLE 7 Variations in strength with respect to
different gelling mixture compositions and sand dunes Compressive
strength Blend MPa/40.degree. C. Sodium Silicate Water CaCl.sub.2
PVP vol. % vol. % wt % 1 wt % 3 wt % 5 wt % 13.00 87.00 0.50 2.58
3.46 3.87 33.33 66.67 0.50 3.40 4.04 5.15 66.67 33.33 0.50 5.04
5.97 9.69 13.00 87.00 1.00 2.40 3.59 3.68 33.33 66.67 1.00 3.42
4.10 5.59 66.67 33.33 1.00 4.88 5.29 10.51 13.00 87.00 1.33 2.48
3.38 3.79 33.33 66.67 1.33 3.44 4.27 5.86 66.67 33.33 1.33 4.80
5.85 10/37
Example 7
Morphological and Structural Evaluation
[0085] a--Morphological Evaluation
[0086] Microstructure observation of solidified sand dunes was
examined using JSM-5600 JOEL microscope equipped with an energy
dispersive x-ray detector for chemical analysis. Sample fragments
were coated with 12 nm gold layer to improve SEM imaging. The SEM
analysis conditions were: voltage is 15 kV; working distance is 20
mm; void pressure is ultimate pressure system control with fully
automatic and the image mode is secondary electron. The focus of
this examination is to evaluate the mechanisms involved in sand
dunes solidification. In case of solidified sand with sodium
silicate and calcium chloride dihydrate (without PVP), silicate
ties sand particles which appeared as continuous films that bridge
all over sand particles (FIG. 2). Such binding mechanism of sand
surfaces is not preferred from practical and mechanical viewpoints
due to presence of large distances between sand particles. Upon
addition of PVP modified sodium silicate gelling mixture (mixture
B), microstructure improved as shown in FIG. 3 where
nano-particulate gels and small amount of gel resides, as
inter-particle ties, covered sand particles. It is attributed to
the reaction between PVP with sodium silicate to produce nano-sized
colloidal structure followed by gelatin films. PVP also acts as a
smoother for both sand and silicate particles.
[0087] In addition, formation of dense hybrid structure was
observed with particle sizes ranging from micrometers to nanometers
(200 nm) due to hydrogen bonding between amide group of PVP and
surface hydroxyl groups of silicate. At higher magnification, a
solidified particle size of less than 100 nm was observed.
[0088] PVP bulky side groups (carbonyl groups) also contribute to
material development with high friction property, and reduction of
voids volume of polymer and silicates, leading to mobility
restriction of sand particles within the solidified matrix. The
results also suggest that multi-molecular systems, rather than
single components, are responsible for nano-structure formation and
overall stable binding system.
b--Structure Elucidation
[0089] While the SEM images have shown that solidification of sand
dunes has been established, it was necessary to confirm interaction
mechanisms between sodium silicate, PVP and sand particles. FTIR
spectra provide information about intermolecular interaction
corresponding to stretching or bending vibrations of particular
bonds. The IR spectrum was recorded by using Nicolet FT-IR (Model
6700) system. The IR spectra of solidified sand dunes were taken as
powder samples mixed with a small amount of KBr powder to make the
IR pellet.
[0090] FIG. 4 shows FTIR spectrum of sand dunes solidified with PVP
modified sodium silicate (FIG. 4b) and without PVP modification
(FIG. 4a). FIG. 4a shows (a) OH vibration (vOH) of water molecules
at 3400 cm.sup.-1, (b) bending of water molecules (.delta.H.sub.2O)
at 1640 cm.sup.-1, (c) asymmetric stretching of Si--O--Si at
980-1200 cm.sup.-1, and (d) deformation of Si--OH at 870 cm.sup.-1.
FIG. 4b shows additional bands for (a) C.dbd.O absorption peak from
amide group of PVP at 1652 cm.sup.-1, (b) C--N group at 1287
cm.sup.-1, (c) C--H bending vibrations at 1420-1460 cm.sup.-1.
Hydrogen bonding between the amide carbonyl groups of PVP and
surface hydroxyl groups of silicate causes a shift in peak position
of O--H towards lower wave numbers with increased intensity and
peak broadening. The shift in peak positions depends on the
strength of the interactions.
Example 8
Durability Performance
[0091] a--Hydraulic Conductivity
[0092] Hydraulic conductivity tests were performed for: (a) sand
dunes, (b) sand dunes mixed with gelling mixture, and (c) dune sand
sprayed with gelling mixture. The obtained hydraulic conductivity
measurements were 3.0E-05, 1.32E-07, and 1.22E-07 m/s,
respectively. These results revealed a significant reduction in
hydraulic conductivity of the sand dunes solidified with gelling
mixture (mixture B). Mixing of sand dunes with gelling mixture led
to coverage of sand particles with gelling mixture and formation of
inter-particle ties as seen from SEM pictures. This in turn
contributed to the formation of dense structure with low hydraulic
conductivity. On the other hand, sprayed specimens exhibited a
slightly lower hydraulic conductivity in comparison with that
treated by the mixing method which could be attributed to film
formation on top surfaces of sprayed specimens.
b--Effect of Humidity
[0093] To evaluate the durability of treated samples, a wet-test
procedure (soaking test) was developed. Treated specimens, with
curing time of 7 days, were placed on its side in water with 12.5
mm height of water for a period of 30 minutes. Then, the specimen
was removed from the water and left in air for 5 minutes.
Afterwards the specimen was subjected to compressive strength test.
Table 8 shows percent strength reduction of treated sand dunes,
after partial soaking in water, in relation to sodium silicate and
PVP concentrations. It was observed that, at fixed concentration of
calcium chloride dihydrate of 1 wt. % and different PVP
concentrations of 1, 3 and 5 wt. %, samples show slight decrease in
strength when sodium silicate concentrations increased due to
increase of mixture viscosity and binding strength between
silicates and sand particles. In addition, increasing of PVP
concentration induces inner ties between particles, thus, limiting
particle movements and strength loss under wet condition.
Therefore, to limit strength reduction, it is recommended to use
high concentrations of sodium silicates and PVP.
TABLE-US-00008 TABLE 8 Strength reduction with various blend
composition after partial soaking in water Blend Strength reduction
(%) Sodium Silicate Water CaCl.sub.2 PVP vol. % vol. % wt % 1 wt %
3 wt % 5 wt % 13.00 87.00 1 20.83 19.22 15.76 33.33 66.67 1 10.82
9.76 6.80 66.67 33.33 1 6.15 5.51 1.54
c--Wind Erosion
[0094] A wind tunnel study was conducted to evaluate the
effectiveness of gelling mixtures in reducing the erosion potential
of the treated material. The study was conducted using Armfield
Wind Tunnel for scientific investigation and experiments. Trays
were filled with treated and untreated sand dunes specimens and
subjected to free stream wind speeds of 3, 7 and 14 m/s for
different time intervals. The trays were weighed again and the loss
of loose (eroded) material was calculated. Prevailing winds from a
constant direction are the most important climatic element for the
formation of sand dunes. Winds of velocity greater than 5.3 m/s can
transport sand dunes. Table 9 shows an increase of the cumulative
soil loss for untreated sand dunes with increasing of wind velocity
and time. For treated sand dunes, the loss was very small measuring
about 0.8% after 30 minutes at wind velocity of 14 m/s. Such
results would lead one to conclude that the nano-sized PVP modified
sodium silicate binder, formulated in this invention, is beneficial
for controlling sand dunes mobility in harsh wind environments.
TABLE-US-00009 TABLE 9 Percent by wt of loss (eroded) material at
different velocities (m/s) % by wt of loss (eroded) material at
different velocities (m/s) Untreated Sand Dunes Treated Sand Dunes
Time (min) 3 7 14 3 7 14 5 28.35 49.23 55.44 0.1277 0.3799 0.3232
10 39.58 67.71 76.23 0.1277 0.4433 0.3878 15 58.28 70.90 85.31
0.1916 0.5066 0.5817 20 65.13 74.48 99.29 0.1916 0.5066 0.6464 25
70.34 76.72 100 0.1916 0.5066 0.7110 30 73.56 77.74 100 0.1916
0.5066 0.8403 35 74.93 78.77 100 0.1916 0.5066 0.8403 40 76.57
79.98 100 0.1917 0.5066 0.8403 45 76.64 81.07 100 0.1919 0.5066
0.8403 50 78.83 81.52 100 0.1919 0.5066 0.8403 55 79.04 81.64 100
0.1919 0.5066 0.8403 60 80.13 81.84 100 0.1919 0.5066 0.8403
REFERENCES
[0095] Allen L. H. and Matijevic E. (1969) Stability of colloidal
silica. I. Effect of simple electrolytes. J. Colloid Interface Sci.
31, 287-296. [0096] Icopini, G. A., Brantley, S. L., and Heaney, P.
J. (2005) Kinetics of silica oligomerization and nanocolloid
formation as a function of pH and ionic strength at 25.degree. C.
Geochimica et CosmochimicaActa, Vol. 69, No. 2, pp. 293-303. [0097]
Her, R. K. (1979). Chemistry of Silica--Solubility, Polymerization,
Colloid and Surface Properties and Biochemistry. John Wiley &
Sons. [0098] Perry C. C. and Keeling-Tucker T. (2000)
Biosilicification: The role of the organic matrix in structure
control. J. Biol. Inorganic Chem. 5 (5), 537-550.
[0099] While the invention has been disclosed in connection with
its preferred embodiments it should be recognized that changes and
modifications may be made therein without departing from the scope
of the appended claims.
* * * * *