Claims:We Claim:

1. Granulated iron making slag (PGBS) based compacted constructional material like natural/river sand comprising
compacted and substantially free of porosity fine aggregates of granulated iron making slag(PGBS) having bulk density of at least 1350 kg/m3, preferably more than 1450Kg/m3.

2. Granulated iron making slag(PGBS) based compacted constructional material as claimed in claim 1 having sp. Gravity in the range of 2.6 to 2.75 preferably about 2.65 and water absorption in the range of 0.5 to 3.5 preferably about < 3%.

3. Granulated iron making slag (PGBS) based compacted constructional material as claimed in anyone of claims 1 to 2 comprising slag granules having blunted/round shaped particles in the size distribution conforming to IS 383 - Zone II.

4. Granulated iron making slag(PGBS) based compacted constructional material as claimed in anyone of claims 1 or 2 comprising said compacted and substantially free of porosity fine aggregates of granulated iron making slag(PGBS) in combination with anyone or more of natural/river sand, Crusher Dust and M-sand.

5. Granulated iron making slag(PGBS) based compacted constructional material as claimed in anyone of claims 1 to 3 comprising (I) totally of said compacted and substantially free of porosity fine aggregates of granulated iron making slag(PGBS) or (II) 50 to 75 % by wt. of said compacted and substantially free of porosity fine aggregates of granulated iron making slag(PGBS) and 25 to 50 % by wt. natural/river sand.

6. Granulated iron making slag(PGBS) based compacted constructional material as claimed in claim 5 suitable for concrete/mortar construction and providing cube strengths in M-40 grade concrete obtained thereof for (I) totally of said compacted and substantially free of porosity fine aggregates of granulated iron making slag(PGBS) in the range of 75 to 100 and for said (II) 50 to 75 % by wt. of said compacted and substantially free of porosity fine aggregates of granulated iron making slag(PGBS) and 25 to 50 % by wt. natural/river sand.

7. A process for the manufacture of granulated iron making slag(PGBS) based compacted constructional material as claimed in anyone of claims 1 to 6 comprising:

providing iron making slag and carrying out slag granulation process involving water jet/spray parameters to obtain slag granules having compact structure substantially free of porosity and improved bulk density with respect to the iron making slag; and

subjecting the thus obtained slag granules to abrasion process for desired blunted/round shape and structure of granules avoiding needle or flaky shape with sharp edges and obtaining therefrom the iron making slag(PGBS) based compacted constructional material like natural/river sand.

8. A process as claimed in claim 7 comprising
slag granulation process with controlled water jet/spray parameters to obtain slag granules having compact structure without porosity to achieve desired specific gravity and bulk density;

subjecting the thus obtained slag granules to abrasion process with controlled parameters in vertical shaft impactor to modify the shape and structure of granules to have rounded shape without breaking grains, avoiding needle or flaky shape with sharp edges; and

subjecting the shaped particles to screening to remove the particles above and below, the upper and lower size limits of the size distribution conforming to IS 383 - Zone II.

9. A process as claimed in anyone of claims 7 or 8 wherein said controlled water jet/spray parameters for slag granulation comprising water sprayed at a temperature < 50oC and at a minimum flow rate of 2500 m3/hr.

10. A process as claimed in anyone of claims 7 or 9 wherein said abrasion process with controlled parameters in vertical shaft impactor comprising feed rate of 0.8 – 1.1 T/min and rotor speed of 2500-2700 rpm resulting in tip velocity in the range of 30-45 m/s whereby the slag particles do not break and only change to rounded shape.

11. A process as claimed in anyone of claims 7 to 10 wherein said processing step of abrasion and screening, the bulk density of the slag is increased to 1500 kg/m3 and water absorption reduced from 8% to < 3%.
Dated this the 19th day of May, 2016
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)

, Description:FIELD OF THE INVENTION
The present invention relates to processed granulated iron making slag (PGBS) as fine aggregates and a process for converting granulated iron making slag(GBS) into fine aggregate to be used as 100% replacement of river sand for use in concrete, meeting the standard specifications for construction purpose. More particularly, the present invention is directed to provide a multistage process with selective parameters for converting granulated iron making slag(GBS) into fine aggregate for changing the structure and shape of the slag granules by subjecting to low temperature granulation, an abrasion process in a vertical shaft impactor and then screening, so that the low density and angular shaped slag particles are converted to high bulk density processed granulated slag particles(PGBS) of desired fineness/size distribution having rounded shape without breaking grains meeting the specifications for use in concrete as partial or total replacement of natural river sand. The performance of prepared concrete samples, replacing natural sand by processed granulated iron making slag (PGBS), indicates that it could be gainfully utilized up to 100 % as replacement of river sand as well as partial replacement with manufactured sand and river sand giving higher flexibility in construction.
BACKGROUND OF THE INVENTION
Granulated Iron making Slag (GBS) is a non-metallic product, consisting of glass containing silicates and alumino-silicates of lime and is a byproduct of the conversion processes. It contains about 0.5–0.8 % FeO, 35–42% CaO, 35–40% SiO2, 8–9% MgO, 8–15% Al2O3, 0.3–1.0% MnO and 0.7–1.5% S by weight. GBS is obtained by rapidly chilling (Quenching) of the molten slag at about 1500oC from the furnace by means of water and air. During the process of quenching, the molten slag undergoes accelerated cooling under controlled water flow condition and gets converted into glassy sand with 97% of the solid granulated slag particles less than 4 mm. Granulated iron making slags are available with steel industry for decades but were never accepted as a fine aggregated in construction activities till this developmental work. Several test have been carried out which confirms that granulated iron making slag is inert, non-toxic, free from traditional impurities (i.e., organic impurities, shells, clay) and is chemically similar to an aggregate. Though it looks like sand, granulated iron making slag (GBS) does not meet the physical property requirement of the aggregate specifications and when used in civil applications has resulted in lower strengths. There has been numerous published works on utilization of BF slag sand as replacement of river sand under various conditions and varying proportions in mortar and concrete. Most of the published literature recommends the usage of granulated BF slag as replacement of river sand in the range of 50 - 75 %. This difference is due to the variation in the quality of BF slag sand being used from different sources. Here, it is important to mention that the property requirement in granulated slags for use in cement and as aggregate is different. Slags to be used for cement making requires high glassy phase (>90%) whereas slags to be used as fine aggregate must have sufficient density (> 1400 kg/m3) or specific gravity (> 2.5). This is a standard property to meet the weight requirement in cubic meter of concrete. Most of the studies carried out in past have used the granulated slag with the density range of 0.95-1100 kg/m3 and this can be seen as the primary reason for reduction in strength with increasing proportions.

Comparison of GBS properties with river sand is shown in Table 1.

Table 1:
Properties River Sand GBS
Size IS 383 - Zone II (Fine) IS 383 - Zone I (Coarse)
Density, Kg/m3 1300 - 1600 1000-1100
Sp Gravity 2.6 - 2.8 2.3
Water Absorption 1 – 3 % 4 -6 %

A major drawback identified with the use of GBS in construction is the lower bulk density (1000 -1100 kg/m3) in comparison to that of river sand (1300-1600 kg/m3) which results in lower strength of concrete. Higher water absorption and lower specific gravity also contributed to it lower properties.

Moreover, Size distribution of conventional GBS particles showed that the particles are mostly in coarser zones of standard size distribution and lack finer component. When used in concrete, it lowers the compaction and reduces the strength. The coarser GBS particles have irregular shape and appear porous with sharp edges, whereas the finer GBS particles have needle or flaky shape with sharp edges. The glossy needle like particles renders the GBS difficult to handle with bare hands.

There has been thus a continuing need in the field of developing substitute aggregate from iron making slag for replacement of natural river sand to provide a process to convert GBS as fine aggregate as a having modified physical properties especially density, size distribution and shape as per standard for use in concrete to meet strength and other required properties in construction industry.

Present work is thus focused on identifying the reasons for reduced strengths of GBS and developing a processing technology for converting GBS into acceptable fine aggregate. Various tests conducted under this study have confirmed that GBS can be used as 100% replacement of natural sand in concrete mix design if slag density is increased to at least 1400 kg/m3.

OBJECTS OF THE INVENTION

The basic object of the present invention is directed to provide processed granulated iron making slag (PGBS) as fine aggregates as total or partial replacement of river sand and a process for converting granulated iron making slag(GBS) into construction grade fine aggregate for up to 100% replacement of river sand for mortar/concrete in civil construction.

A further object of the present invention is directed to a process for converting granulated iron making slag(GBS) into construction grade fine aggregate which will have bulk density of slag particles increased to at least 1350 kg/m3, specific gravity more than 2.5, and with reduced water absorption.

A still further object of the present invention is directed to a process for converting granulated iron making slag(GBS) into construction grade fine aggregate as replacement for river sand wherein the density, size distribution and shape of GBS is modified to meet applicable standards.

A still further object of the present invention is directed to a process for converting granulated iron making slag(GBS) into construction grade fine aggregate as replacement for river sand wherein highly porous structure of granulated slag(GBS) is improved for denser structure avoiding porosity resulting in improved density and more compact structure for desired bulk density and specific gravity by involving optimized granulation parameters.

A still further object of the present invention is directed to a process for converting granulated iron making slag (GBS) into construction grade fine aggregate as replacement for river sand wherein slag particles are subjected to selective abrasion process and screening step to meet the shape and size distribution requirement as per standards for ensuring desired strength level of mortar/concrete.

A still further object of the present invention is directed to a process for converting granulated iron making slag(GBS) into construction grade fine aggregate as replacement for river sand wherein flow characteristics of the mortars with processed granulated iron making slag (PGBS) are equally good or marginally better than the mortars with river sand, the compressive strength of mortars using PGBS is much higher than the strength of mortar with river sand, also the Flexure bond strength of masonry using mortars having PGBS as aggregate is higher when compared to masonry flexure bond strength with mortar using river sand.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to provide Granulated iron making slag (PGBS) based compacted constructional material like natural/river sand comprising
compacted and substantially free of porosity fine aggregates of granulated iron making slag(PGBS) having bulk density of at least 1350 kg/m3, preferably more than 1450Kg/m3.

A further aspect of the present invention is directed to said Granulated iron making slag (PGBS) based compacted constructional material having sp. Gravity in the range of 2.6 to 2.75 preferably about 2.65 and water absorption in the range of 0.5 to 3.5 preferably about < 3%.
A still further aspect of the present invention is directed to provide said Granulated iron making slag (PGBS) based compacted constructional material comprising slag granules having blunted/round shaped particles in the size distribution conforming to IS 383 - Zone II.

Another aspect of the present invention is directed to said Granulated iron making slag (PGBS) based compacted constructional material comprising said compacted and substantially free of porosity fine aggregates of granulated iron making slag (PGBS) in combination with anyone or more of natural/river sand, Crusher Dust and M-sand.

Yet another aspect of the present invention is directed to said Granulated iron making slag(PGBS) based compacted constructional material comprising (I) totally of said compacted and substantially free of porosity fine aggregates of granulated iron making slag (PGBS) or (II) 50 to 75 % by wt. of said compacted and substantially free of porosity fine aggregates of granulated iron making slag(PGBS) and 25 to 100 % by wt. natural/river sand.

A further aspect of the present invention is directed to said Granulated iron making slag(PGBS) based compacted constructional material suitable for concrete/mortar construction and providing cube strengths in M-40 grade concrete obtained thereof for (I) totally of said compacted and substantially free of porosity fine aggregates of granulated iron making slag(PGBS) in the range of 75 to 100 and for said (II) 50 to 75 % by wt. of said compacted and substantially free of porosity fine aggregates of granulated iron making slag(PGBS) and 25 to 50 % by wt. natural/river sand.

A still further aspect of the present invention is directed to a process for the manufacture of granulated iron making slag(PGBS) based compacted constructional material as described above comprising:

providing iron making slag and carrying out slag granulation process involving water jet/spray parameters to obtain slag granules having compact structure substantially free of porosity and improved bulk density with respect to the iron making slag; and

subjecting the thus obtained slag granules to abrasion process for desired blunted/round shape and structure of granules avoiding needle or flaky shape with sharp edges and obtaining therefrom the iron making slag(PGBS) based compacted constructional material like natural/river sand.

Another aspect of the present invention is directed to said process comprising
slag granulation process with controlled water jet/spray parameters to obtain slag granules having compact structure without porosity to achieve desired specific gravity and bulk density;

subjecting the thus obtained slag granules to abrasion process with controlled parameters in vertical shaft impactor to modify the shape and structure of granules to have rounded shape without breaking grains, avoiding needle or flaky shape with sharp edges; and

subjecting the shaped particles to screening to remove the particles above and below, the upper and lower size limits of the size distribution conforming to IS 383 - Zone II.

Yet another aspect of the present invention is directed to said process wherein said controlled water jet/spray parameters for slag granulation comprising water sprayed at a temperature < 50oC and at a minimum flow rate of 2500 m3/hr.
A further aspect of the present invention is directed to said process wherein said abrasion process with controlled parameters in vertical shaft impactor comprising feed rate of 0.8 – 1.1 T/min and rotor speed of 2500-2700 rpm resulting in tip velocity in the range of 30-45 m/s whereby the slag particles do not break and only change to rounded shape.
A still further aspect of the present invention is directed to said process wherein said processing step of abrasion and screening, the bulk density of the slag is increased to 1500 kg/m3 and water absorption reduced from 8% to < 3%.

The above and other objects and advantages of the present invention are described hereunder in greater details with reference to the following accompanying non limiting illustrative drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Figure 1: represents a comparison of particle morphology (a) River sand and (b) GBS.

Figure 2: represents graphically the effect of granulation water temperature on slag density.

Figure 3: micrograph showing the structure of low temperature water granulated slag.

Figure 4: represents effect of rotor velocity on particles in Vertical Shaft Impactor.

Figure 5: represents particles of river sand, GBS and PGBS.

Figure 6: illustrates graphically the comparative size distribution curves of the GBS, PGBS and River sand, with reference to IS 383 - Zone II- lower and upper limit.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS AND EXAMPLES

The present invention relates to fine aggregates of processed granulated iron making slag(PGBS) as total or partial replacement of river sand and a process for converting granulated iron making slag(GBS) into construction grade fine aggregate for up to 100% replacement of river sand for morter/concrete used in civil construction. It is an object of the present invention to provide a two step method to convert GBS into fine aggregate having the attributes comparable with river sand.

Accordingly, the first aspect of the invention resides in altering the slag granulation parameters as illustrated under example 1.

EXAMPLE 1:

Under this example how slag particle density is affected by altering the Slag Granulation parameters like water temperature, water pressure and water flow rate have been studied. Microscopic studies showed that lower density in slags is due to its vesicular structure with micro-pores present in the slag grains. The porous structure of GBS grains compared to river sand is shown in accompanying Figure 1. When the material solidifies under slow cooling conditions, escaping gases leave behind micro pores in the cooled mass. When formed under controlled rapid cooling, the slag tends to be hard and dense, making it especially suitable for use in all concrete applications. The applicants determined through experiments that density and specific gravity of granulated slags can be increased by optimizing granulation parameters such as water temperature and flow rate to produce slag sand similar to river sand. Based on this concept, several trials were conducted at iron making slag granulation system, with varying water temperature and flow rates. The granulated slag samples were collected and analyzed for specific gravity, bulk density and structure through microscopy. It was found that reducing the jet water temperature reduced the porosity in the slag granules. The highly porous structure of earlier granulation slag has improved to much denser structure resulting in improved density. Accompanying Figure 2 shows graphically the effect of slag granulation water temperature on slag particle density. It was found that under optimum conditions of granulation parameters, the bulk density of the slag can be increased to > 1350 kg/m3 as more compact structure can be developed in slag granules. Micrographs of the low temperature water spray granulated material shows lower porosity contributing to the increased density as shown in Figure 3. It was found that, for best results the jet water temperature has to be less than 50 oC and minimum water flow to be kept at 2500 m3/hr. Accordingly the process parameters were maintained to meet the optimized conditions.

However the shape and size distribution did not changed much and the issue of needle or flaky shape particles still existed and required further modifications. The shape and size distribution of slag particles was determined as per the following example 2.

EXAMPLE 2:
Under this example, the second aspect of the invention to determine the desired shape and size distribution of particles by modifying needle or flaky shape of the particles by subjecting it to customized shaping and screening process have been undertaken. The purpose was to increase the very finer portion of material (<300 microns) and to convert individual particles into rounded shape without breaking grains. This was also required to remove needle shaped materials. Increase in the finer fraction would have also helped in increasing the bulk density. It was envisaged that the slag particles should be subjected to abrasion process and not grinding to meet the shape and size requirement. As no customized equipment was available for abrasion process, it was decided to tune a vertical shaft impactor for achieving the desired function. Normally a vertical shaft impactor is used for crushing stones. In a shaft impactor, feed material drops through the feed tube onto the impeller table or enclosed rotor which, through centrifugal force, throws the material against stationary anvils made up of composite metal alloys. When the rock particles impact the anvils, it shatters along natural stress lines, creating a uniform, cubical product. This method of crushing is simple and economical to operate. A pilot scale vertical shaft impactor was brought and modified for studying the feasibility of achieving an abrasion function for slag particles. In an impactor, the particle projectile's velocity and impact force with which it hits the anvils decides whether the particle will get shaped, crushed or grinded. The velocity of the particles hitting the abrasive wall is known as tip velocity and measured in mps (meter/sec). Higher speed results in pulverizing and grinding as shown in Figure 4. Tip velocity which governs the size and shape of the processed slag particle generated is controlled by feed rate and rotor speed. It was found that by manipulating the rotor speeds the feed material can be subjected to only shaping. Series of experiments were conducted by varying these variables and at an optimized range of feed rate of 0.8 – 1.1 T/min and rotor speed of 2500-2700 rpm were found out. At these parameters, the resulting tip velocity is in the range of 30-45 mps where the slag particles do not break and only change the shape. These parameters require continuous fine tuning based on the input mean average size particle. The impactor processed slag granules were of rounded shape but the size distribution required some alteration. Hence, these shaped particles were subjected to screening to remove the particles above and below, the upper and lower size limits of the standard. After this second step of processing, the bulk density of the slag has further increased to 1500 kg/m3 and is close to the value of natural river sand. Water absorption reduced from 8% to < 3%. No needle shaped particles are left out in the final processed material.

Tests and Results

The physical characteristics of slag samples have greatly improved due to the processing methodology adopted. The particles shapes have improved. The particles had blunter edges as compared to needle or flaky shape with sharp edges in GBS. The processed granulated iron making slag (PGBS) was similar to 100% true river sand. Properties of GBS, PGBS and river sand are compared in Table 2. The shapes of the natural river sand and PGBS particles resemble closely. Comparison of particles of river sand, GBS and PGBS is shown in Figure 5. Size distribution of the processed granulated slag was also similar to river sand. PGBS matched the requirement of physical properties of fine aggregate to be used in concrete which is IS-383 Zone-II. Size gradation of PGBS is shown in Figure 6. In addition to properties the key advantage of slag sand over river sand is the absence of impurities like clay and silt.
Table 2:
Properties River Sand GBS PGBS
Size IS 383 - Zone II (Fine) IS 383 - Zone I (Coarse) IS 383 - Zone II
Density, Kg/m3 1300 - 1600 1000-1100 1500
Sp Gravity 2.6 - 2.8 2.3 2.65
Water Absorption 1 – 3 % 4 -6 % <3%

Table 3:
Fine Aggregate 7th day Strength, MPa (N/mm2) 28th day Strength, MPa (N/mm2)
100% Natural Sand 38-42 48-52
100% GBS 36.5 45.5
100% PGBS 42.9 53.3
50% PGBS + 50% NS 39 52
50% PGBS + 50% M - Sand 40.8 52.3
50% PGBS + 50% Crusher Dust 30.9 49.7

PGBS was then experimented for mortar and concrete cube testing, to check its strength when used with cement. The flow characteristics clearly indicate that the mortars with PGBS are equally good or marginally better than the mortars with river sand. The compressive strength of mortars using PGBS is much higher than the strength of mortar with river sand. Flexure bond strength of masonry using mortars having PGBS as aggregate is higher when compared to masonry flexure bond strength with mortar using river sand. It is possible to achieve good workability for the concrete using PGBS as fine aggregate. The results clearly show that with PGBS as fine aggregate it is possible arrive at mix proportion which yields desirable strength and slump, and meeting the IS 456 requirements. The slightly angular shape of some slag particles increases the amount of surface area for bonding with cement paste and reduces the high internal stress concentrations leading to higher strength values. The bond strength between the rebar and concrete with river sand and PGBS as fine aggregate was in similar range. Tests conducted at Applicant’s test facility have shown that processed granulated BF slag can be used 100 % individually and also in combination with Natural sand, Crusher Dust and M-sand. The strength values are shown in Table 3. This controlled granulation produced and impactor processed slag was finally matching the specifications of the fine aggregate standard. This innovative processing route developed for iron making slag has converted a waste into a commercial product.