Description:4. DESCRIPTION
FIELD OF THE INVENTION

The present invention relates to recycled aggregate concrete. Specifically, the present invention relates to performance of nano silica based recycled aggregate concrete exposed to elevated temperatures.

BACKGROUND OF THE INVENTION

Concrete is a composite material composed of aggregate bonded together with a fluid cement that cures over time. Concrete is the second-most-used substance in the world after water and is the most widely used building material. Concrete was the material that was continually damaged for several hours straight during fire accidents or fire explosions, according to the prior case studies. Due to dangerous accidents, concrete that had been exposed to high temperatures for hours had lost some of its qualities, had grown weak, and could no longer be used. A solution to this problem has been discovered to enhance the qualities of concrete when concrete is subjected to high temperatures. The major goal of the idea is to keep concrete original qualities after being exposed to extreme temperatures.

Massive amounts of concrete debris were produced as a result of population growth. The same situation applies to rivers, which are disappearing daily as a result of extraction and transportation for building.

Cléo Laneyrie, Anne-Lise Beaucour, Mark F. Green, Ronan L. Hebert, Béatrice Ledesert, Albert Noumowe in the research article titled “Influence of recycled coarse aggregates on normal and high performance concrete subjected to elevated temperatures” disclosed that recycled concrete aggregates (RCA) can be a promising solution for sustainable development. For buildings, the high temperature performance is critical to estimate fire resistance. Thus, this paper investigates RCA concretes after exposure to temperatures up to 750 °C by considering laboratory and industrial RCA, and normal and high performance concretes. Tests were conducted on cylindrical specimens to assess cracking, mass loss, porosity, and thermal and mechanical properties. The residual performances for the recycled concretes were generally similar to but slightly worse than those observed for the reference concretes. The presence of non-cementitious impurities accelerates the damage of concretes with temperature.

Thus, there is a need to develop nano silica based recycled aggregate concrete.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the disclosure in order to provide a basic understanding to the reader. This summary is not an extensive overview of the disclosure and it does not identify key or critical elements of the invention or delineate the scope of the invention. Its sole purpose is to present some concepts disclosed herein in a simplified form as a prelude to the more detailed description that is presented later.

One object of the invention is nano silica based recycled aggregate concrete exposed to elevated temperatures.

The goal of the initiative is to reduce the amount of concrete trash generated by building and demolition waste that is dumped in landfills and disturbs the environment.

According to one aspect of the invention, manufactured sand (M-sand) and recycled aggregate from the construction industry were used as building materials in the manufacturing of concrete. Fire incidents and abrupt explosions in industries primarily affected concrete structures of higher grades. Three varying proportions were taken such as 30%, 45% and 60% of natural aggregates replaced with recycled aggregate. Portland slag cement was used as binder material and Nano silica was taken as the addition to cement (1.5% by weight of cement). Four grades (M20, M25, M30 and M35) were listed as (M20 with 0% crushed aggregate), (M20 with 30% recycled aggregate), (M20 with 45% recycled aggregates), (M20 with 60% recycled aggregate) likewise for grades. In this, thermal properties of concrete made with recycled aggregates are studied when they are exposed to high temperature at 2000c, 4000c, 6000c at interval of 1hr,2hr,3hr and 4hr durations after 28 days and also compared results with control concrete(0% recycled aggregates). To improve the thermal properties of concrete, of recycled aggregates and Manufactured-sand & Portland slag cement + 1.5% of Nano-silica were used. By addition of 1.5% of Nano silica to binder material, it gives additional properties to concrete to reduce void ratio and still becomes denser and shows better performance when effected by temperature. By replacing the recycled aggregate by 30%, 45% and 60% to crushed aggregate. There is a remarkable enhance in the mechanical properties at longer period of slag based recycled aggregate concrete due to the high pozzolanic nature and its ability to fill the voids. The positive effects of slag in recycled aggregate concrete up to 45% replacements are (i) to provide dense packing and (ii) to reduce the porous nature of concrete. The durability properties show better results up to 60% replacement of natural aggregates with recycled aggregates, the enhanced strength could be due to formation of additional C-S-H gel and later reaction of slag with Nano silica. Concrete containing recycled aggregate up to roughly 45% is appropriate for applications where temperatures must not exceed 400°C. Beyond 600oC, deterioration was substantially more severe and temperature had a significant impact on the mechanical characteristics of concrete (such as compressive strength). By conducting the experiment using recycled aggregate with Nano silica, mechanical and thermal properties of concrete has improved at 45% replacement of natural aggregates with recycled aggregates in concrete can be useful for slabs, beams. M-sand and PSC cement had shown high performance in durability aspects.

The invention may also relate to any alternative methods or processes comprising any combination of the above or below features within the scope of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the present invention will become apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments, in conjunction with the accompanying drawings, wherein like reference numerals have been used to designate like elements, and wherein:

FIG. 1 illustrates casting of cubes according to one embodiment of the invention.

FIG. 2 illustrates cubes after curing according to one embodiment of the invention.

FIG. 3 illustrates temperature test setup according to one embodiment of the invention.

FIG. 4 illustrates testing of cubes according to one embodiment of the invention.

FIG. 5 illustrates compressive strength of recycled aggregate concrete after exposed to 200 0C according to one embodiment of the invention.

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present invention in any way.

DETAILED DESCRIPTION OF THE INVENTION

It is to be understood that the present disclosure is not limited in its application to the details of composition set forth in the following description. The present disclosure is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

The present invention relates to performance of nano silica based recycled aggregate concrete exposed to elevated temperatures.

According to one embodiment of the invention, recycled aggregate from concrete waste and M-sand from industrial waste are chosen and used as building materials for the manufacturing of concrete in order to solve these issues. The primary innovation is on M20, M25, M30 and M35, which was utilized for industrial structures, small-scale businesses, and chemical factories. By conducting the experiments, recycled aggregate can be used as a substitute building material for concrete production by including Nano technology, which can assist to improve the qualities of concrete.

A comparison study was made on thermal properties of concrete with and without recycled aggregates and Nano silica 1.5% by weight of cement. For all the above grades, thermal properties were initially increased and later when exposed to further high temperature there is a loss of strength was observed. Compared to 0%, 30% and 45% replacement have shown a better performance and 60% replacement showed marginal difference in strength properties when exposed to temperatures. It was concluded that, 45% replacement showed better performance in mechanical and thermal properties when compared to 60% replacement of recycled aggregates

Portland slag cement:
Portland slag cement (JSW) conforming to IS 455 (1989) was used.
Table1: Physical properties of Portland slag cement
S.No Properties VALUE
1 Specific Gravity 2.9
2 Fineness of cement by Sieving 2%
3 Normal consistency 31%

M sand:
M sand conforming to grading zone-II (IS: 383) is used for producing concrete.

Aggregates:
Crushed aggregate: Locally available coarse aggregates are taken for producing concrete conforming to Grading zone of Zone-II of IS383-1970, nominal maximum size of aggregate 20 mm and 10 mm.

Recycled Aggregates: Conforming to Grading zone of Zone-II of IS383-1970, nominal maximum size of aggregate 20 mm and 10 mm. Recycled aggregates are obtained from 15 years old RCC building.

Nano silica: Nano-SiO2 had the advantages of large specific surface area, strong surface adsorption, large surface energy, high chemical purity and good dispersion.

Table 2: Properties of Nano silica:

S.No Property Value
1 Notation of Nano silica gel XLP
2 Active nano content(%wt) 14-16
3 PH 9.3-9.6
4 Specific Gravity 1.08-1.11

Table 3: Mix Proportins
Mix ID Grade of concrete
M1RCA(0%) M20 with 0% crushed aggregate
M1RCA(30%) M20 with 30% recycled aggregate
M1RCA(45%) M20 with 45% recycled aggregates
M1RCA(60%) M20 with 60% recycled aggregate
M2RCA(0%) M25 with 0% crushed aggregate
M2RCA(30%) M25 with 30% recycled aggregate
M2RCA(45%) M25 with 45% recycled aggregates
M2RCA(60%) M25 with 60% recycled aggregate
M3RCA(0%) M30 with 0% crushed aggregate
M3RCA(30%) M30 with 30% recycled aggregate
M3RCA(45%) M30 with 45% recycled aggregates
M3RCA(60%) M30 with 60% recycled aggregate
M4RCA(0%) M35 with 0% crushed aggregate
M4RCA(30%) M35 with 30% recycled aggregate
M4RCA(45%) M35 with 45% recycled aggregates
M4RCA(60%) M35 with 60% recycled aggregate

According to one embodiment of the invention, to minimize the issue, experimental works are been carried. In this invention, four grades of concrete M20, M25, M30 and M35 are chosen which are widely using for industrial and small scale constructions. In order to satisfy the thermal properties of concrete, M-sand & PSC cement were used with recycled aggregates.

FIG. 1 illustrates casting of cubes according to one embodiment of the invention.

FIG. 2 illustrates cubes after curing according to one embodiment of the invention.

FIG. 3 illustrates temperature test setup according to one embodiment of the invention.

FIG. 4 illustrates testing of cubes according to one embodiment of the invention. According to one embodiment of the invention, duration of 1hr, 2hr, 3hr and 4hr intervals were chosen from practical point for temperature explosive study. Using the debris for concrete was found to help reduce the thermal effects on concrete. M30 and M35 grade concrete with Nano silica was reduced by only 15% after exposed to 4hours temperature. There is marginal beneficial effect of Nano silica on recycled slag based concrete performance when exposure to temperature. Cubes after exposure to 600? at 4hour, strength of loss taken place about 25- 27% without Nano silica. M30 and M35 grade concrete having Nano silica was reduced by only 12 to15% after exposure to 2 hours temperature and 4hours around 22%. There is no visible positive effect of Nano silica on recycled slag based concrete when exposure to temperature beyond 400?. Porosity and density are the two most noticeable physical characteristics of RAC that govern how it will behave shortly before being exposed to high temperatures. This characteristic has been determined to be caused by cement pastes and mortar sticking to the aggregates. In concrete, density decreases as the proportion of recycled aggregate increases, but porosity rises as the percentage of recycled aggregate increases. 200, 400, and 600? exposures. Beyond 600 ?, deterioration was substantially more severe and temperature had a significant impact on the mechanical characteristics of concrete (such compressive strength). The residual compressive strength were weak for the 2-hour exposure time in the case of a genuine fire, where temperatures may surpass 1000°C; concrete structures need extra attention in the repairing situation if not completely demolished. Concrete containing recycled aggregate up to roughly 45% RCA content is appropriate for applications where temperatures must not exceed 400°C.It can be used for refectory linings ,industrial and commercial buildings and also suitable for Pedestals for Electric transforms and Pre cast elements (E.g Sleepers, Poles).

Fig. 5 illustrates compressive strength of recycled aggregate concrete after exposed to 200 0C. After being exposed to a temperature of 200 ? for 28 days, the compressive strength of concrete was tested. Compressive strength of control concrete was compared to concrete subjected to elevated temperature at 200 ?. Initially at first two hours, the strength loss was below 5-6% and the specimens lost strength was 8-10% after exposed to 4 hours temperature. There is a significant positive effect on compressive strength of concrete with Nano silica. Concrete exposed to temperature up to 2 hours has more strength in RAC than control concrete.

Fig. 6 illustrates compressive strength of recycled aggregate concrete after exposed to 400 0C. After being exposed to a temperature of 400 ? for 28 days, the compressive strength of concrete was found. For all combinations, the strength decrease at one hour was about 8-9%. Specimens after elevated temperature exposure, strength of the concrete being 9 to 13%. Cubes after exposed to 400 ? at 4hours, strength lost by 19% without Nano silica. M30 and M35 grade concrete with Nano silica was reduced by only 15% after exposed to 4hours temperature. There is marginal beneficial effect of Nano silica on recycled slag based concrete performance when exposure to temperature.
Fig. 7 illustrates compressive strength of recycled aggregate concrete after exposed to 600 0C. After being exposed to a temperature of 600?for 28 days, control concrete compressive strength was compared to strength of cubes exposed to temperature. For all combinations, the strength decrease at one hour was about 9 - 10%. Cubes after exposure to 600 ? for 2hours, loss of strength taken place about 20-22% without Nano silica. Cubes after exposure to 600 ? at 4hour, strength of loss taken place about 25- 27% without Nano silica. M30 and M35 grade concrete having Nano silica was reduced by only 12 to15% after exposure to 2hours temperature and 4hours around 22%. There is no visible positive effect of Nano silica on recycled slag- based concrete when exposure to temperature beyond 400 ?. Porosity and density are the two most noticeable physical characteristics of RAC that govern how it will behave shortly before being exposed to high temperatures. This characteristic has been determined to be caused by cement pastes and mortar sticking to the aggregates. In concrete, density decreases as the proportion of recycled aggregate increases, but porosity rises as the percentage of recycled aggregate increases. 200, 400, and 600 ? exposures. Beyond 600 ?, deterioration was substantially more severe and temperature had a significant impact on the mechanical characteristics of concrete (such compressive strength). The residual compressive strength values for all mixes of recycled aggregate concrete were weak for the 2-hour exposure time in the case of a genuine fire, where temperatures may surpass 1000°C; concrete structures need extra attention in the repairing situation if not completely demolished. Concrete containing recycled aggregate up to roughly 45% RCA content is appropriate for applications where temperatures must not exceed 400°C.

It will be recognized that the above described subject matter may be embodied in other specific forms without departing from the scope or essential characteristics of the disclosure. Thus, it is understood that, the subject matter is not to be limited by the foregoing illustrative details, but it is rather to be defined by the appended claims.

While specific embodiments of the invention have been shown and described in detail to illustrate the novel and inventive features of the invention, it is understood that the invention may be embodied otherwise without departing from such principles.
, C , C , Claims:WE CLAIM

1. A nano silica based recycled aggregate concrete composition, the concrete composition comprising:
natural aggregates manufactured sand (M-sand) and recycled aggregate from the construction industry;
portland slag cement as binder material; and
nano silica is added to the cement at 1.5% by weight of cement;
characterized in that
30%, to 60% of natural aggregates are replaced with recycled aggregate.

2. The concrete composition as claimed in claim 1, wherein the concrete composition has better resistance to heat at elevated temperatures when compared to the ordinary concrete.