Description:FIELD OF INVENTION:

The invention relates to preparing construction material which is typically coarse and fine aggregates required in preparing cement concrete like material.

PRIOR ART:

Typically, aggregates are obtained from natural resources such as granite and other rocks, especially the ones which are fine grained find their source enormously from natural riverbeds as fine aggregate (sand). Due to the enormous demand for these aggregates, natural resources are depleting faster leading to demand to find alternate mode of aggregates. The scarcity of river sand has also increased the burden on coarse aggregates. So typically, crushed granite is also replacing river sand in many construction activities and crushed rock fines (CRF) are being used currently in India. It is produced from hard granite stone by crushing. Hence there is an urgent need to avoid depletion of natural resources like aggregates, coarse aggregates are replaced by artificial aggregates.

OBJECTIVES OF INVENTION:

The invention relates to innovative green products to achieve environmental sustainability by conserving the natural resources. Next to water, concrete is the most widely used construction material across the globe, which requires huge amount of coarse and fine aggregates.

DESCRIPTION OF INVENTION:

In product as per invention innovative material called “Geopolymer Coarse Aggregates” (GPAgg), which replaces the Sintered fly ash coarse aggregate (SFA), it is a type of Low Density Aggregate (LDA) and in addition to that, GPAgg can be used as conventional coarse aggregates for a maximum grade of concrete up to M35. The GPAgg yields the required properties in cement concrete.

The GPAgg has been created by using the by-products from thermal and steel plants with an addition of lime powder. The by-products used are “Fly ash” and “GGBFS” (Ground granulated blast furnace slag) obtained from thermal and steel plants respectively. The combined proportion of fly ash and GGBFS along with lime powders are activated using a chemical activator to bind the above said ingredients with a minimum quantity of water to form slurry. The prepared slurry was poured into the moulds to form solid blocks similar to rock like mass. The cast specimen was kept at ambient temperature for required curing. The (GPAgg) specimen was cured for 7 days and made into the required sizes of coarse aggregates like 20mm and 10mm with the help of stone crusher.

The chemical reaction that takes place in this case is a “Polymerization process”, whereas the OPC Cement concrete reaction is called as “Hydration process” that is chemical reaction when the water is added to the dry cement the chemical reaction starts.

The GPAgg consist of the following mineral and chemical additives:

1. Fly ash - is a by-product obtained from burning coal in thermal power plants.
2. GGBFS - is a by-product of the iron-making process in steel plants.
3. Lime - is a colorless crystalline powder manufactured by treating calcium oxide (quicklime) with water.
4. Alkaline solution prepared using sodium hydroxide and sodium silicate.

The process diagram charts depict the material preparation to form solid GP fragment, which is shown below in items (a) (fig. 1) and the qualification testing are shown in item (b) (fig. 2).

Fig. 1 - Process diagram of GPAgg preparation:

Part no. Part names
11 Fly ash
12 GGBFS
13 Lime
14 Alkaline solution
15 Geopolymer slurry
16 Forming solid GP fragment
17 GPAgg

Fig. 2 - Tests performed on GPAgg.,

Part no. Part names
21 Specific gravity
22 Dry loose density
23 Water absorption
24 Flakiness & elongation index
25 AIV Test
26 ACV Test
27 LAAV

Physical properties of GPAgg. prepared as per invention

The physical properties of GPAgg had been tested in accordance with IS 2386 and its relevant parts for evaluation of aggregate.

a) Specific gravity: for measuring the solid density of GPAgg using glass pycnometer bottle, it is a measure of the aggregate for its densified solidification under the formation of LAVA in nature for a big mountain, in a similar manner the GPAgg is also developed like a LAVA (slurry) and made into a rock fragment shaped before making into the required sizes of coarse aggregates. The test result is tabulated in Table 1.

The specific gravity (solid density) of GPAgg is derived based on mass/volume concept.

b) Water absorption: for measuring the absorption capacity of GPAgg with a given period of time, in general the aggregate is completely soaked in water for 24 hours and measured the water absorption capacity of aggregates, (the difference between SSD - (Saturated surface dry condition) and the dry weight is calculated as absorption capacity of aggregates). It is an indication of measuring the porous / voids present in the aggregate. Based on the surface area of aggregates the water absorption capacity is defined, [so less the surface area and lesser the absorption of aggregates, if it is derived from a single source from the parent rock of natural stones. It is based on the formation of natural rock and its constituents]. In a similar manner the GPAgg also determined for its water absorption capacity and the test result is tabulated in Table 1.

c) Dry loose bulk density: the dry loose bulk density of aggregates is used in large scale production of concrete in a project site. The aggregates are received at concrete batching plants either by volume or by weight through the trucks. The concrete is produced in concrete batching plants by weighment basis for batching the ingredients for an intended mix. The dry loose bulk density value is used for reconciliation purposes of aggregates in an operating site, since the materials are received in volume and consumed by weight in plants, so it is used to convert the materials as received in volume and consumed in weight, it is used to convert the materials for stock availability. The test result is tabulated in Table 1.

d) Flakiness & elongation indices: the aggregates are not desirable to use in making the concrete for intended works when its shape and sizes are not in a defined manner. Hence, the aggregates crushed from a rock fragment using different types of crushing methods adopted to produce the coarse aggregates for concrete. The aggregate with flaky and elongated in shapes are not desirable for concrete woks, which leads to affects the fresh concrete property in terms of its workability and strength of hardened concrete. The desirable shape and sizes of aggregates are: the aggregates should be in Angular shaped after crushing through crushing units to make the concrete to achieve intended properties in fresh and hardened state. The test result is tabulated in Table 1. For betterment in understanding the aggregate shape and sizes the images are shown below for the flaky (thickness) and elongated (length) of the particles (fig. 3a to 3c).

Figure 3. a) Shows aggregates in flaky and elongated shapes not desirable for concrete.
b) GPAgg, non-flaky and elongated particles desirable for concrete.
c) Natural stone in an angular shaped which is highly preferrable for concrete.

Mechanical properties of GPAgg. prepared as per invention

 AIV – Aggregate Impact value
 ACV – Aggregate crushing value
 LAAV – Los Angeles abrasion value

a) Aggregate impact value (AIV): the coarse aggregate is subjected to the dynamic load (shock) to assess its resistance under a sudden drop of a known load or weight over on it. The AIV indicates to take a call on deciding the suitability of aggregate for concrete works. If the value of AIV is lower as low as possible, it is good quality of aggregate to make concrete. The test result is tabulated in Table 2.

b) Aggregate crushing value (ACV): the coarse aggregate is subjected to the static load to assess its resistance under the continues loading for a known load of 400kN in 10 minutes. The ACV indicates to take a call on deciding the suitability of aggregate for concrete works. If the value of ACV is lower as low as possible, it is good quality of aggregate to make concrete. The test result is tabulated in Table 2.

c) Los Angeles abrasion value (LAAV): the coarse aggregate is subjected to an abrasion action by placing a known fraction (20mm to 12.5mm & 12.5mm to 10mm) of GPAgg into the rotating drum, for developing abrasion action the steel balls of approximately 48 mm in diameter are used. The drum is rotated for 500 revolutions and then evaluated for their suitability under wear & tear of the particles. This property of aggregate is mandatory when to use the GPAgg in the roads & runways where there is a rubbing action is taken place when the surface layer actioned by vehicle movements. Whereas in our case the GPAgg is used for superstructure works. Lower the LAAV value as low as possible, it is a very good quality of aggregate. The test result is tabulated in Table 2.

Table 1 Physical properties of GPAgg. prepared as per invention

Table 2 Mechanical properties of GPAgg. prepared as per invention

The novel features on GPAgg prepared as per invention

a. GPAgg doesn’t require OPC cement

b. Identified by-products from thermal (fly ash) and steel plants (slag-GGBFS) as the fine powder materials to use in making the GPAgg as per invention.

c. The fly ash of very fine in particle size has been used and it is passing 90-95% through a 45-micron test sieve.

d. The fly ash used in the invention which has a CaO content of about 2.0% and SiO2 content of 50% by its mass.

e. The ratio of fly ash and slag is adopted at 45:55 respectively, for developing the GPAgg.

f. The slag has a CaO content of about 40% and SiO2 content of about 35% by its mass.

g. A commercial grade NaOH flakes (sodium hydroxide) with a purity of about 90% has used been in this invention.

h. Sodium silicate in liquid form has been used with a ratio of SiO2/Na2O = 2, which accelerates in the polymerization process along with NaOH with a defined ratio.

i. Preparation of “Alkaline solution” to activate the binding materials for a product of GPAgg invention.

j. NaOH with 8 molarity has been found to provide the expected results, and it is prepared (by adding 262 grams of NaOH flakes and 738 grams of water by mass to make 1 kg of solution) and used in the invention, since it has shown (8 molarity of NaOH) required flow property in fresh state for handling to form any shape, and poured in to a mould to make a solid sample of GPAgg fragment.

k. Alkaline solution is prepared using a part of NaOH with 8 molarity and 2 parts of sodium silicate by mass.

l. Sequence in preparing the alkaline solution adopted:

a. 1 part of NaOH with 8 molarity is poured into a container and waiting to reach ambient temperature.

b. 2 parts of sodium silicate are then added into NaOH solution and stirred well for 2 minutes and left the solution for 24 hours.

c. After 24 hours the alkaline solution is ready for use.

m. Sequence in preparing the GPAgg matrix is:

a. Mixture proportion of GPAgg matrix is, dry fly ash, GGBFS and little quantum of lime powder kept at 60:35:5 respectively by mass.

b. The fly ash is introduced in a container of known quantity, and then added the GGBFS, lime powder. The powders were mixed using a mechanical stirrer for a minute to get uniformity in the blends.

c. The prepared alkaline solution was introduced gradually into the powder at the same time with a low rpm the mechanical stirrer was used to make the slurry of GPAgg. The mixing was continued for another 5-10 minutes to form a uniformity in the slurry.

d. After making the slurry, a simple flow test was carried out to assess its flowable characteristic of the slurry using a flow table with a conical shaped slump cone, and the measured flow was 250mm in spread over the table without any drops (blows) through the mechanism.

e. After the flow table spread test, the slurry was poured into a container and levelled manually by shaking the container to remove any air bubbles that got into the product and left in the container for 24 hours to make a solid rock like a mass.

f. GPAgg doesn’t require any special curing like water, steam, and heating through hot air ovens. Just by placing the container in the ambient temperature and it gets fully hardened and left for next 7 days at ambient.

g. After 7 days, the slurry becomes hard like natural rock and made into the required sizes like 20mm and 10mm as coarse aggregates, which is required for the intended works to produce the concrete.

n. An invented GPAgg is satisfying the codal requirement of IS 9142 Part 2 – 2018 (Specification – Artificial lightweight aggregate for concrete; Part 2 Sintered fly ash coarse aggregate). For physical and mechanical properties of coarse aggregate.

o. The GPAgg were tested for its physical properties in accordance with the methods set in IS 2386 Part 3. The results are tabulated in Table 1.

p. The specific gravity (solid density) of GPAgg is 2.36, which shows that a stage is called as (weathered rock) formation of a naturally occurred rock.

q. The sintered fly ash coarse aggregate (SFA) specific gravity (solid density) is 1.79, whereas the GPAgg is higher (2.36) than the SFA, so it indicates that the GPAgg has better performance than SFA in terms of physical and mechanical properties.

r. The GPAgg has a water absorption capacity of about 14.21% by mass. Since the GPAgg has higher absorbing tendency and it can be used in making RCC-Reinforced cement concrete up to M35 grade.

The GPAgg were tested for its mechanical properties in accordance with the methods set in IS 2386 Part 4.

s. Concrete with incorporation of GPAgg has very low thermal conductivity (K - Value), when compared with conventional concrete made with conventional coarse aggregates.

t. The GPAgg satisfying the mechanical properties of coarse aggregate produced by Sintering the fly ash aggregates in lines of IS 9142 Part 2, and the results are tabulated in Table 2.

The process involves preparing a slurry with fly ash and slag preferably GGBFS along with sodium hydroxide and sodium silicate with minimum water and using polymerization process. This slurry is poured into moulds for conversion to solid block, and the cast mould is maintained at ambient temperature for curing for at least 7 days.

This solid block can be thereafter crushed into coarse aggregates of required sizes.

The method allows mass production of coarse aggregate for concrete. Due to the enormous demand of aggregates for the construction industry, the demand can be met by preparing a novel aggregates by this new alternate mode as disclosed in this invention. The disclosure of this invention covers environmental concerns also as dumping of fly ash leads to health hazard and is a menace to society. The utilization of waste materials like fly ash as by-products of artificial aggregates, addresses the disposal issue in this industrial waste along with concern for healthy environment. The invention serves two purposes. Protects environmental concern and eliminates natural resource depletion.

The invention has been described in detail above, but various embodiments and variations are possible beyond the preferred embodiments disclosed in this document. All such variations and modifications as obvious to the skilled person is within the scope of this invention.
, Claims:WE CLAIM:
1. A process of preparing a coarse aggregate comprising of: -
a. preparing a slurry of fly ash and slag along with sodium hydroxide and sodium silicate involving a chemical process called “Polymerization” and thereafter binding the above said ingredients and then cast moulding the slurry to form solid blocks which is then crushed into coarse aggregates of required sizes.
2. The process as claimed in claim 1, wherein the fly ash is of very fine in particle size and preferably passing 90-95% through a 45-micron test sieve,
3. The process as claimed in claim 1, wherein the fly ash has a CaO content in the range of 2.0% and SiO2 content in the range of 50% by its mass.
4. The process as claimed in claim 1, wherein the ratio of fly ash and slag is in the ratio of 45:55 respectively.
5. The process as claimed in claim 1, wherein the slag which has a CaO content in the range of 40% and SiO2 content in the range of 35% by its mass.
6. The process as claimed in claim 1, wherein the sodium hydroxide (NaOH) is a commercial grade sodium hydroxide flakes with a purity in the range of 90%.
7. The process as claimed in claim 1, wherein the sodium silicate is in liquid state.
8. The process as claimed in claim 1 and 7, wherein the ratio of SiO2/Na2O = 2 for accelerating the polymerization along with NaOH with a defined ratio.
9. The process as claimed in claim 8, wherein the alkaline solution is prepared with a defined ratio by using 1 part of NaOH with 8 molarity and 2 parts of sodium silicate by mass.
10. The process of preparing alkaline solution as claimed in claim 9 comprises of:
a. pouring 1 part of NaOH with 8 molarity into a container,
b. allowing the NaOH to reach ambient temperature, and
c. adding 2 parts of sodium silicate into NaOH solution under stirring for around 2 minutes and then allowing to cool, the prepared alkaline solution left at ambient temperature for around 24 hours.
11. The process as claimed in claim 1, wherein further comprises:
a. selecting the dry fly ash, GGBFS and lime powder in the ration 60:35:5 respectively by mass,
b. pouring fly ash into a container,
c. adding the GGBFS and lime powder into the container,
d. mechanically mixing by stirring the powder contents in the container,
e. adding prepared alkaline solution into the container under continuous mechanical stirring for around 5-10 minutes to form blended slurry,
f. transferring the prepared slurry into a container,
g. removing air bubbles and levelling manually by mechanical shaking the container,
h. allowing the container with slurry to cool down for 24 hours thereby slurry transforming into a solid rock like mass,
i. allowing the mass to be maintained at ambient temperature for 7 days thereby solid rock mass transforming further into hardened rock like, and
j. crushing the prepared rock into desired sizes such as 20mm, 10mm coarse aggregates, which is required for the intended works to produce concrete.