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FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
&
THE PATENS RULES, 2003
PROVISIONAL SPECIFICATION
[See section 10, Rule 13]
AN IMPROVED CAPPING SYSTEM FOR TESTING CONCRETE AND ROCK CORES;
HINDUSTAN CONSTRUCTION COMPANY LTD., A COMPANY INCORPORATED UNDER THE COMPANIES ACT, 1956, WHOSE ADDRESS IS HINCON HOUSE, LBS MARG, VIKHROLI (WEST), MUMBAI 400 083, INDIA
THE FOLLOWING SPECIFICATION
DESCRIBES THE INVENTION.

Field of Invention
The invention relates to an improved capping system for testing concrete and rock cores. More particularly, the invention relates to a method and a device for capping concrete cores and cylinders.
Background of the Invention
Cores from concrete structure such as those taken from pavement and lining of tunnels, concrete cylinders prepared at the time of casting concrete and rock cores, are used to determine the compressive strength by applying load. Generally, cores extracted from structures, in their raw form have irregular ends, and hence are unsuitable for testing. In order to get accurate results, it is important that the loading faces are parallel to each other and perpendicular to the axis of the core or cylinder. In other words, capping is a process that applies an appropriate paste like material on the irregular surfaces to obtain a smooth and plane finish, ensuring appropriate geometry. To overcome the effects of uneven end surfaces of the specimens many methods, known in the prior art, are employed to cap the ends of cylinders and cores, such as:
1. Capping with cements & mortars (Bonded caps):
This method provides neat cement paste for capping a concrete cylinder and/or core through bonded caps. The capping is achieved through application of capping agents such as neat hydraulic cement paste, high alumina cement mortar, high strength gypsum cement paste, and sulphur mortar. However, one of the disadvantages of the described method is the requirement of an extended time period for the hardening of cement paste. As a result, care needs to be taken to ensure appropriate curing of the cement paste during the extended time period. Also, care should be taken for consistency and shrinkage of cement paste. In the case of using sulphur mortar capping, care is needed to minimize the risk of fire (due to the relatively low ignition point of sulphur) and control emission of gases such as oxides of sulphur.
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2. Cutting and grinding of ends:
In this method, no external material is applied on the cores to achieve the required geometry. Instead, the required geometry is obtained by appropriate cutting and machining of the core. One advantage of the method is the utilization of the cut and grinded cores for testing of very high strength concretes. Another advantage of the method is availability of the samples for immediate testing without any waiting period. However, the method suffers from certain disadvantages such as high cost of equipment. More particularly, the said high cost occurs predominantly from equipment such as that of concrete cutter and grinder, and the blades, which need to be periodically changed.
3. Packing of neoprene pads:
The method is also referred to as 'Unbonded' caps. One advantage of the method is the absence of a waiting period for obtaining the cap. Capped structures obtained through unbounded caps can be used up to strength of 85 Mpa (Mega pascals). However, the method is not useful for low strength concrete. Also, the process of capping concrete cores through this method is quite expensive. Further, there is a possibility of rupture of specimen during testing. The said rupture of the specimen may be violent and hence care should be taken for safety by providing testing machine equipped with protective case. The protective case provided is to avoid damage to testing machines, which occurs due to sudden release of energy stored in the pads.
4. New improved capping system
The capping system according to the present invention employs
a) solid materials comprising of:
- Ground Granulated Blast furnace Slag (GGBS) - Conforming to IS 12089 -
1987
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- Silica Fume - Conforming to IS 15388 - 2003
- Metakaoline - Conforming to IS 456 -2000
- Fly ash - Conforming to IS 3812 - 2003
- Standard Sand (Grade - 3) - Conforming to IS 650 -1991, and,
b) alkali solution that comprises of a suitable combination of solutions of sodium hydroxide and sodium silicate is utilized along with the solid materials described earlier. Depending on the requirements, commercial grade sodium hydroxide pellets are dissolved in water, and the resulting solution is mixed with commercial grade sodium silicate solution to obtain the required solution (to be mixed with the solid powder mixture made up from constituents given above).
Use of these materials as supplementary cementations materials (SCM) in concrete industry is well known and reported. SCMs are utilized as partial replacements of Ordinary Portland Cement, and are known to participate in the secondary hydration processes involving a reaction between the silica in blast furnace slag, etc. and the calcium hydroxide that is formed during primary hydration, during which a reaction occurs between the components of cement with water giving calcium hydroxide and other hydration products. Some methods in the prior art have also utilized SCMs in the preparation of geo-polymer concrete wherein the polymerization achieved refers to reaction of alumina silicates with the hydroxides, under the application of heat. The polymerization process does not involve the use of water or cement, which are both essential ingredients in a hydration reaction. Further hydration requires a long duration of curing but polymerization is completed rapidly giving high strengths very early.
Brief Description of Drawings of the present invention:
Figure 1 shows a schematic representation of the aligning and heating device developed and employed in the new capping system.
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Table 1 shows the results of the tests carried out using the present capping system. The results show a direct comparison of the strengths of the capping achieved by the proposed method to that obtained using sulphur capping.
Description of the invention:
An object of the present invention is to provide an improved system for capping concrete cores and cylinders. Another object of the present invention is to provide a method for that predominantly utilizes industrial waste products to obtain a capping paste that is employed as a capping agent in the capping of concrete cores and cylinders. A further object of the present invention is to provide an automated device for capping of the concrete core and cylinder to ensure a rapid and environment friendly capping that is uniform and perpendicular to the axis of the concrete core and cylinder.
The present invention provides an improved system for capping concrete cores and cylinders. More particularly, the present invention provides a method for obtaining a paste employed as a capping agent in the capping of concrete cores or cylinders. The present invention differs from the methods stated in the prior art in that the present invention advantageously utilizes SCM to obtain a capping paste employed for capping concrete cores and cylinders. The present invention also provides a device for effective application of the obtained paste to cap concrete cores and cylinders.
The process for obtaining the capping paste utilized in capping of the concrete cores and cylinders comprises of following steps such as:
i. Making of the capping paste.
ii. Application of capping paste on concrete face.
iii. Heating.
iv. Capping of the concrete core and/or cylinder.
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Each of the above mentioned steps shall be described in detail herein as exemplary steps for achieving the said capping paste and utilization of the capping paste to achieve capping of the concrete cores and cylinders.
Process Steps:
Making of the capping paste: This step comprises of obtaining a synergistic (?) mixture of constituent materials through a mixing procedure. The said constituent material comprises of:
a) A solid part comprising of substances such as flyash, ground granulated blast furnace slag, silica fume and metakaoline and
b) A liquid part comprising of a solution of sodium hydroxide and sodium silicate
In one embodiment of the present invention the said solid part comprises of a synergistic mixture of flyash in the range of 10 weight percent (wt %) to 30 weight percent (wt %), Ground granulated blast furnace slag in the range of 45 weight percent (wt %) to 70 weight percent (wt %), silica fume in the range of 10 weight percent (wt %) to 30 weight percent (wt %) and Metakaoline in the range of 1 weight percent (wt %) to 15 weight percent (wt %). Further, the said liquid part comprises of Sodium hydroxide (NaOH) solution prepared from Sodium hydroxide pellets to a strength in the range of 12 Molar concentration (M) to 20 Molar concentration (M) and commercially available solution of sodium silicate having hydration in the range 40 % weight/volume (w/v) to 60% weight/volume (w/v). The solutions of Sodium hydroxide and sodium silicate obtained as described herein are then mixed in a ratio in the range of 1:1.5 to 1:3.
In order to prepare the paste used for the capping, the solid and liquid parts are subjected to a mixing procedure. The said mixing procedure can be achieved by a manual mixing procedure such as obtaining a mortar paste through operation by hand. The said mixing procedure can also be achieved by an automated procedure such as utilization of an appropriate mortar mixer. In one embodiment of the present invention
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the liquid and solid parts are mixed in a ratio in the range of 0.30 weight/weight (w/w) to 0.65 weight/weight (w/w) to obtain a capping paste. The capping paste thus obtained by mixing the solid and liquid parts is then applied to the extracted concrete core and/or cylinder.
Application of capping paste on concrete face: The capping paste required for application to the surface of the concrete cores and/or cylinders is obtained by the synergistic mixing of the solid and liquid parts by the process described earlier herein. A sufficiently homogenous mass of the said capping paste is achieved by the described process for obtaining the capping paste. The homogeneity of the said capping paste is to achieve a uniform application of the capping paste to the surface of the extracted concrete core and/or cylinder. In order to ensure an uniform application of the paste to the surface of the extracted concrete core and/or cylinder, the extracted core and/or cylinder is subjected to a preparation step. The said preparation step comprises of a process of cleaning of the surface of the extracted concrete core and/or cylinder. The surface of the extracted concrete core and/or cylinder generally comprises of surface impurities such as loose particles, oil, grease. The presence of such impurities impedes the uniform application of the capping paste to the surface and proper adhesion between the concrete and the capping paste. It is desirable that the concrete surface should be thoroughly cleaned to ensure an irregular surface of the extracted concrete core and/or cylinder free from the surface impurities. It is known in the prior art to adopt a plurality of cleaning process to ensure the extracted surface of the concrete core and/or cylinder free from surface impurities. In one embodiment of the present invention the said cleaning step advantageously utilizes a wire brush to remove any loose particles and / or laitance. The cleaning step ensures that the extracted concrete core and/or cylinder have an irregular surface free from impurities. Further, tests are carried out to ensure that the surface of the extracted concrete core and/or cylinder is free from surface impurities. In one embodiment of the present invention, the tests are carried out using
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saturated surface dry core/cylinder specimens i.e. a state where the pores are saturated with water but no excess water is adhering to surface. The capping paste is then applied to the irregular surface of the extracted core and sufficiently pressed to ensure proper adhesion.
Heating: The efficient capping of the surface of the extracted concrete core and/or cylinder can be achieved by application of heat to the capping paste. The amount of heat applied to the capping paste generally depends on the properties and proportion of constituents of the capping paste and/or the strength of the capping required for conduction of tests on the extracted concrete core and/or cylinder. In one embodiment of the present invention, the said heating of the capping paste is achieved by subjecting the capping paste to a temperature range of 30° Centigrade(C) to 120°C. Further, the said temperature is maintained for a time duration of 30 seconds to 5 minutes to ensure uniform capping. The said heating and subsequent capping of the cement paste may be carried using a device shown in Figure 1, the essential features of which are described below.
Capping of the concrete core and/or cylinder: The present invention provides an automated device for capping of the concrete core or cylinder, to ensure a rapid and environment friendly capping that is uniform and perpendicular to the axis of the concrete core or cylinder.
The device comprises of the following parts:
i. Two plates labeled (1) and (2), held vertical to each other with plate 1 being
horizontal and plate 2 attached to platel in a perpendicular direction
ii. A third plate labeled (3) fixed at one end of the frame of the plates, and held
perpendicular to both plates (1) and (2).
iii. A Fourth plate (4) parallel to plate (3) wherein means are provided to slide on
Plate 1 as shown.
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iv. Heating coils provided on Plates (3) and (4) are utilized to apply heat to the
capping paste.
In a preferred embodiment of the present invention, a device as explained earlier herein is employed for capping of the concrete cores and/or cylinders. The concrete cylinder and/or core is positioned on the frame as shown in the figure, and is held in place using suitable clamps X and Y. The capping paste applied at both ends of the concrete cylinder or core. By appropriately sliding it, plate 4 is held tightly in contact with the cylinder using a suitable clamp (Z). Due to the plate forcing the cylinder or core into a tight contact the capping paste applied on the faces of the cylinder or core is squeezed out. Heaters provided in plates (3) and (4) are switched ON to attain the pre estimated temperature. The clamp Z is removed to release Plate (4) and the cylinder removed from the frame. The hardened paste sticking to the ends of the cylinder may be removed by suitable trimming prior to the application of load for testing the strength of the extracted concrete core and/or cylinder.
The strength of the capping obtained by the process described in detail earlier herein is determined by application of the load to the capped concrete core and/or cylinder. Table 1 shows a comparison of the results of the tests carried out using the present capping system (using sulphur) with those carried out using the proposed new capping system. The results show that the strength of the concrete observed in both cases are comparable. In no case was any failure in the capping material observed during testing.
The improved capping system for concrete cores and/or cylinders described in detail herein is further illustrated by an example as described below.
Example 1:
In a preferred embodiment of the present invention, the process for obtaining the capping paste utilized in capping of the concrete cores and cylinders comprises of following steps such as making of the capping paste which comprises of synergistic
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mixture of a solid part and a liquid part. The said solid part comprises of at least 20 weight percent (wt %) of flyash, 60 weight percent (wt %) Ground granulated blast furnace slag, 20 weight percent (wt %) of Silica fume and at least Weight percent (wt %) of Metakaoline. Further, the said liquid part comprises of Sodium hydroxide solution prepared from pellets to a strength of at least 16 M (Molar concentration) and commercially available solution of sodium silicate having at least 52% water. The obtained solutions of sodium hydroxide and sodium silicate are then mixed in a ratio of at least 1:2.5. In order to prepare the paste used for the capping, the liquid and solid components are subjected to a mixing procedure as described earlier in the ratio of at least 0.36 weight/weight (w/w).
The capping paste thus obtained is applied to the surface of the extracted concrete cylinder and/or core by ensuring that the surface is free from all impurities to achieve uniform capping. The applied capping paste is further subjected to a heating step wherein the concrete core and/or cylinder capped with the capping paste is subjected to a temperature of at least 50°C for a duration of at least one minute to obtain uniform capping. Further, the capping of the concrete core and/or cylinder described by the example herein may be achieved by a device as described in detail earlier herein.
An improved capping system for concrete cores and/or cylinders described in detail earlier and illustrated effectively by providing example has improved the efficiency of the testing of the concrete cores / cylinders and the cost effectiveness.. The present invention advantageously utilizes cost effective material to achieve an efficient and uniform capping perpendicular to the axis of the extracted concrete core and/or cylinder. Further, employment of the automated device to obtain the said capping ensures error free and efficient capping of the extracted concrete core and/or cylinder.
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Advantages:
The present invention provides an improved system for capping of concrete cores and cylinders. Embodiments of the present invention provide a method and device for capping concrete cores and cylinders. The features of embodiments of the present invention include but are not limited to
1. The present invention provides means for effective utilization of industrial waste
products such as blast furnace slag and fly ash to yield cement paste
2. The paste manufactured does not produce any toxic fumes, dust, etc., resulting in an
emission free product.
3. Rapid setting of the cap, with no waiting period.
4. Automation of the capping process through effective utilization of a device to ensure
ensuring planeness and perpendicularity of capping.
Dated this 1st day of August, 2007.


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