Method for repairing and restoring deteriorated cement-containing inorganic material

A method for repairing and restoring a deteriorated cement-containing inorganic material such as reinforced concrete by applying a solution of a water-soluble silicate compound to its surface to have it impregnated with said solution, and then topcoating said material with cement paste or/and mortar.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a method for repairing and restoring a 
deteriorated cement-containing inorganic material, typically reinforced 
concrete, according to which the repaired cement-containing inorganic 
material can be kept alkaline semipermanently. 
2. Description of Prior Art 
A reinforced concrete structure is a complex durable structure of cement 
concrete with reinforcements which are protected against rusting in a 
highly alkaline atmosphere in the concrete, but the concrete itself is 
carbonated by carbon dioxide in the air to cause rusting of the 
reinforcements over a long-time period. When the reinforcements are 
rusted, the covering concrete cracks due to the cubic expansion pressure, 
and oxygen and moisture enter from the cracks to promote rusting, thus 
causing scale-off of the covering concrete. As a result of the repetition 
of such an action, the reinforced concrete structure is badly impaired in 
its durability. Such a phenomenon may occur in short-time use if the 
structure is placed under certain environmental conditions. It is 
aggravated by fire or exposure to exhaust gas, and especially marine 
structures or structures located close to the seaside tend to suffer such 
damage early in use since the reinforcements of these structures are 
always exposed to a corrosive environment. 
This phenomenon is observed not only in reinforced concrete but also in 
other inorganic materials containing cement. These materials are hardened 
and petrified in long-time use under various conditions. These 
cement-containing inorganic materials are most suited for general 
structures and buildings because of their excellent rigidity and 
durability, but they suffer such damage and aging gradually or even 
rapidly (in short-time use) under certain conditions not only due to the 
carbonating actions (which are caused and/or promoted not only by carbon 
dioxide in the air but also by exhaust gas, fire, etc.) but also under the 
influences of other factors such as penetration of water (including 
seawater and water containing acids, alkalis, salts, etc.) and oils, wear, 
cavitation, alkali-aggregate reactions, etc. Further, in the case of 
cement concrete, it usually inevitably suffers from cracking due to 
shrinkage on drying and other types of structural cracking, and if cracks 
are formed in such concrete, its waterproofness is degraded to let 
weathering such as carbonation of concrete advance deep into the inside 
thereof. 
Thus, if such deterioration of quality or durability of a reinforced 
concrete structure or component inorganic material thereof, such as cement 
concrete is left unattended, the structure will turn into a dangerous 
state which may lead to a disaster. To avoid this, it is desirable to 
rebuild the structure, but due to the need to save material and energy in 
these years, repairing and restoring of the structure and its component 
material is now given serious consideration, and an advanced technique for 
such reparing and restoring of material is sought after in the field of 
civil engineering and construction, too. 
Hitherto, repairing of a reinforced concrete structure has been made by 
applying an anti-corrosive paint such as zinc-rich paint or an epoxy resin 
to the exposed reinforcements, or the damaged section has been tentatively 
repaired by injecting an epoxy resin or the like into the cracked portion 
of the concrete, since no effective alkalinity recovery method was 
available for the repairment of the carbonated portion of the concrete. 
However, zinc-rich paint is unable to protect the alkali in the concrete 
in a satisfactory way, while the epoxy resin has problems not only in 
workability and economy but also, more importantly, in durability since it 
is an organic compound. In the use of the epoxy resin for repair of marine 
structures, a case is reported where corrosion of the inside 
reinforcements started again in about one year after the repair work. 
Therefore, in view of the durability after the repair work, it is 
desirable to use an inorganic compound as the repairing material for the 
reinforced concrete structures. On the other hand, utilization of a 
special colloidal silica prepared by combining an alkali metal silicate 
and an ammonium silicate compound has been studied for preventing surface 
deterioration of inorganic material (Japanese Patent Publication No. 
19609/1978). However, although such a colloidal silica has excellent water 
and weather resistance, it is poor in its ability to recover alkalinity in 
the carbonated portion of the concrete because of a high molar ratio of 
SiO.sub.2 and a low alkalinity. Also, since such a colloidal silica is 
composed of colloidal particles, its penetrability into the inside of 
concrete is lower than that of watersoluble compounds. 
Surface reinforcement of the inorganic material by impregnation with a 
water-soluble silicate compound is also considered, but such a compound 
tends to be eluted to lose its effect in long-time use because of its poor 
water resistance after curing. Also, mere coating with cement paste alone 
or together with a high polymer dispersion or mere mortar grouting on the 
scaled-off portion of concrete is unsatisfactory for reinforcing the 
concrete body or for preventing corrosion of the reinforcements by 
recovery of alkalinity because of poor penetrability into the inside of 
the aged or deteriorated concrete. 
Thus, a means for realizing recovery of alkalinity in the inside carbonated 
portion of concrete and its surface reinforcement by impregnation with a 
water-soluble silicate compound and at the same time the development of a 
topcoat (with cement paste or mortar) for preventing elution of the 
water-soluble silicate compound have been keenly required. 
SUMMARY OF THE INVENTION 
Under these circumstances, the present invention was worked out with the 
object of providing an effective method for repairment and restoration of 
a deteriorated cement-containing inorganic material by applying a solution 
of water-soluble silicate compound to its surface to impregnate the 
material with said solution and then topcoating the surface of the 
impregnated inorganic material with cement paste or mortar, or coating 
mortar on cement paste, to thereby eliminate the defects of the prior art 
and to provide reinforcement and repair of the weakened layer of the 
cement-containing inorganic material and the prevention of advancement of 
deterioration of the material while also preventing corrosion of the 
reinforcements to improve the durability of said material by the 
synergistic effect of said silicate solution and topcoat. 
DETAILED DESCRIPTION OF THE INVENTION 
The repairing and restoring method for a deteriorated cement-containing 
inorganic material according to this invention will be described in detail 
below in accordance with the respective steps of the method. 
(1) Step of applying a solution of a water-soluble silicate compound to the 
surface of a cement-containing inorganic material to have the latter 
impregnated with said solution. 
This is the first step of the method of this invention in which a solution 
of a water-soluble silicate compound is applied to the surface of a 
cement-containing material such as concrete to have it impregnated with 
said solution. The water-soluble silicate compound used in this step is a 
silicate represented by the general formula: M.sub.2 O..sub.n SiO.sub.2 
(wherein M is Li, Na, K, Cs or an ammonium component, and n is an 
integer), alone or as a mixture with other substance(s). As the ammonium 
component, examples are primary amines such as methylamine and ethylamine, 
secondary amines such as dimethylamine and diisopropylamine, tertiary 
amimes such as trimethylamine and triethanolamine, quaternary ammoniums 
such as monomethyltriethanolammonium and tetraethanolammonium, and 
ammonia. The value of n is preferably around 1 to 5, but it is not 
specifically defined and may be suitably selected within the range that 
will not affect the water solubility and penetrability of the compound 
when it is actually used. An additive or additives such as a curing agent 
for improving water resistance of the silicate compound after curing by 
drying may be added in an amount which does not affect the workability and 
penetrability of the compound. If the silicate compound is to be used 
without any additive, it is recommended to use lithium silicate which has 
a relatively high water resistance. Though the concentration of the 
silicate compound solution used in this invention is not specifically 
defined, usually it is less than 30%. The thus prepared solution of a 
water-soluble silicate compound is infiltrated into the body of the 
deteriorated material such as concrete and then dried while maintaining 
the surrounding thereof in an alkaline state, whereby a hard ground is 
obtained. 
(2) Step of topcoating with cement paste. 
Topcoating with cement paste in this step is usually accomplished by spray 
coating or trowelling to a thickness less than several mm. The cement 
paste used for this topcoating has the following composition: 
(a) cement: 40-60 parts 
(b) aggregate smaller than 0.3 mm in size: 60-40 parts 
(c) anion-polymerized styrene/butadiene rubber (SBR-A) dispersion (solid 
content): 2-8 parts 
Usually Portland cement is used as the cement paste, but other types of 
cement may be used in some cases. The "SBR-A dispersion" is a 
styrene/butadiene copolymer dispersion obtained by copolymerizing styrene 
with butadiene by using an anionic surfactant as the emulsifier or 
polymerizing agent. Usually a dispersion with a styrene content (in the 
whole dispersion) of 40 to 65 % is used, but an especially good result is 
obtained when the styrene content is 50 to 65%. Mixing of this SBR-A 
dispersion can amazingly better adhesion of the coating to the body of the 
inorganic material such as concrete and can further improve the 
waterproofing properties and airtightness of the plastering in comparison 
with the case where an SBR-C dispersion obtained by using other 
polymerizing agents, such as a cationic surfactant, or other polymer 
dispersion is mixed, and thus the use of said SBR-A dispersion can provide 
cement paste which is capable of best attaining the object of this 
invention. 
If necessary, a commercially available anti-corrosive for reinforced 
concrete may be added to the cement paste. 
(3) Step of topcoating with mortar. 
This mortar coating is performed either immediately after the step (1) or 
after completion of the steps (1) and (2). 
This mortar coating is usually accomplished by spray coating or trowelling 
to a thickness of usually less than several mm. In case the worn-off 
portion of concrete is deep, this mortar coating may be applied for 
filling said portion. 
The mortar used in this step has the following composition: 
(a) cement: 20-40 parts 
(b) aggregate smaller than 1.2 mm in size: 80-60 parts 
(c) SBR-A dispersion (solid content): 2-8 parts 
The cement and SBR-A dispersion used as the mortar components are the same 
as those used in the cement paste described in step (2) above. 
This mortar is intended to improve the waterproofing properties and 
airtightness like the cement paste used in step (2). Since the mortar of 
the above composition is especially resistant to cracking, use of such 
mortar conducive to the attainment of the object of this invention. 
A conventional repair method for concrete or the like is usually finished 
by the application of the cement paste of step (2), but, the above mortar 
topcoating step in further added to drastically improve the weather 
resistance (durability) after the repair work. 
The deteriorated cement-containing inorganic material to be actually 
repaired may present various conditions such as: (a) merely cracks are 
formed in the concrete; (b) scale-off of the concrete has not reached the 
reinforcement but the carbonation has advanced close to the reinforcement; 
and (c) scale-off of the concrete has reached the reinforcement make it 
bare. In any of these cases, step (2) (application of cement paste) or (3) 
(application of mortar) or the combination of both steps (2) and (3) is 
performed after completion of step (1) (application of water-soluble 
silicate compound). The actual repair work is usually conducted in the 
following way: water-soluble lithium silicate is applied to penetrate into 
a portion to be repared, followed by coating with cement paste, and the 
cases where the worn-off portion is deep, the mortar is applied to fill up 
the gap, and then this portion is further topcoated with cement paste and 
mortar in that order to finish into a planar surface. 
Next, the results of measurement of (a) depth of carbonation, (b) water 
adsorption, (c) presence or absence or crack(s), (d) presence or absence 
of alkalinity in the reinforcement atmosphere mortar and (e) area of 
reinforcement rusting in the application of the cement paste and mortar 
according to this invention under the given conditions in comparison with 
the results obtained in the similar application of cement pastes 
containing polymer dispersions other than SBR-A and mortar are shown with 
the test methods used. 
TEST Methods 
(A) The compositions of the cement pastes and mortar used in the tests are 
shown in Table 1 (all the tables are at the end of the specification). 
In Table 1, the compositions of the respective specimens are shown by the 
parenthesized numerical figures. 
(a) Samples Nos. 101 to 109: these are specimens comprising a 1:3 mixture 
of Portland cement and aggregate smaller than 0.3 mm in diameter (standard 
sand mortar, for comparative test) to which, in addition to SBR-A used in 
this invention, an ethylene/vinyl acetate/vinyl chloride copolymer 
emulsion, an acrylic ester/styrene copolymer emulsion, an acrylic ester 
emulsion, an ethylene/vinyl acetate copolymer emulsion, SBR-C 
(cation-polymerized styrene/butadiene copolymer powder), VAc/Veova (vinyl 
acetate/vinyl versatate copolymer emulsion) and VAc/Veova/vinyl laurate 
(vinyl acetate/vinyl versatate/vinyl laurate copolymer powder) were added 
as additional polymer dispersions, each in an amount of 3.0% as solid 
matter, or no such polymer dispersion was added (nine specimens in all). 
(b) Sample Nos. 201 to 209: specimens comprising a 1:1 mixture of Portland 
cement and aggregate smaller than 0.3 mm in diameter (cement paste) to 
which the same polymer dispersions as specified in (a) above were added or 
no such dispersion was added (nine specimens in all). 
(c) Sample Nos. 301 to 309: specimens comprising a 1:2.33 mixture of 
Portland cement and aggregate smaller than 1.2 mm in diameter (mortar) to 
which the same polymer dispersions as specified in (a) above were added or 
no such dispersion was added (nine specimens in all). 
(B) Amount of water added to the specimens 
The amount of water added (including water in the polymer dispersion) 
required for attaining a slump value of 35.+-.5 in the slump test 
according to JIS A 1173 (Method of test for slump of polymer-modified 
mortar). 
(C) Depth of carbonation 
Phenolphthalein indicator was sprayed to the broken-out section and the 
non-reddened portion was measured. 
(D) Water absorption 
Water absorption was measured according to JIS A 6203 (Polymer dispersions 
for cement modifier) under drying conditions of 60.degree. C. and 48 
hours. 
(E) Standing under standard conditions (standard curing) 
Standing at 20.degree. C. and 90% RH for 2 days, then in water of 
20.degree. C. for 5 days, and at 20.degree. C. and 60% RH for 21 days. 
(F) Carbonization conditions 
Left to stand under 100% CO.sub.2 and 4 kg/cm.sup.2 after the above 
standard curing. 
(G) Drying-immersion repetition test 
The cycle of 2-day drying (standing) in the air at 60.degree. C. and 2-day 
immersion in 20.degree. C. water or in a 5% saline solution was repeated 
10 times. 
(H) Weight change 
Measured by as scale which can gauge up to 10 mg. 
(I) Presence or absence of cracks 
Determined by observing the 4.times.4.times.9 cm reinforced specimens with 
the eye. 
(J) Presence or absence of alkalinity in reinforcement atmosphere mortar 
Determined by using a phenolphthalein indicator. 
(K) Area of reinforcement rusting 
The rust was reproduced on a polyethylene sheet to draw up a developed plan 
and it was copied and analyzed by a video pattern analyzer. Test Results 
(a) Depth of carbonation (mm) 
The results of measurement of the depth of carbonation conducted under 
various (six different) conditions are shown in Table 2. Under any 
condition, the depth of carbonation observed when using the cement paste 
(Sample No. 206) and mortar (Sample No. 306) according to this invention 
was equal to or less than those observed when using other specimens, 
indicating an excellent airtightness of the coating according to this 
invention. 
(b) Water absorption (%) 
The test results are shown in Table 3. The cement paste and mortar used in 
this invention were both low in water absorption, indicating their 
excellent waterproofing properties. 
(c) Weight change 
The result of determination of weight change (%) under various (five 
different) conditions are shown in Table 4. 
The cement paste and mortar used in this invention were small in weight 
change, indicating little increase of weight by the rusting of the 
reinforcement. 
(d) Formation of cracks 
The results of visual observation of cracks under various (four different) 
conditions are shown in Table 5. In the table, + indicates presence of 
crack(s) and - indicates no formation of cracks. 
The cement paste and mortar used in this invention were resistant to cracks 
and excellent in durability. Especially, the mortar used in this invention 
resulted in no development of cracks under any condition. 
(e) Alkalinity of reinforcement atmosphere mortar 
The results of examination of alkalinity of reinforcement atmosphere mortar 
under various (four different) conditions are shown in Table 6. In the 
table, O indicates that the mortar was not carbonated, .DELTA. indicates 
that the mortar was partially carbonated, and X indicates that the mortar 
was carbonated. The cement paste and mortar used in this invention have a 
stronger ability to maintain the surrounding of the reinforcement alkaline 
than the other samples. 
(f) Area (%) of reinforcement rusting 
The results of measurement of the area of reinforcement rusting under 
various (four different) conditions are shown in Table 7. The cement paste 
and mortar used in this invention formed a smaller rusted area of 
reinforcement than the other preparations under any condition. 
The foregoing test results being judged as a whole, the mortar used in this 
invention gave the best result in each test and the cement paste according 
to this invention showed the next best result. 
Also, among the polymer dispersions tested, SBR-A showed the best result in 
almost all of the tests.